Talking Proud Archives --- Military

Bell X-1: The wonder of "competing ideas"

"The race to break the sound barrier"

December 1, 2017

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This section will address the development of the Bell X-1. It is the aircraft for which Bell is best known. A group of sub-sections to this X-1 report on Bell Aircraft and some of its research and production aircraft will be published as well. Each of these merits their own individual in-depth reports but I lack the resources to accomplish that. So I will provide introductory reports about them.

You will know a subsection has been published if you see a link set up. As you go through some of these, you'll see what a tough business this was. Larry Bell was not enamored with producing fighters. He saw little future in it for Bell.

Bell Aircraft Corp.
Bell YFM-1 Airacuda
Bell XP-39 Airacobra
Bell P-76 Airaconda
Bell XFL Airabonita
Bell XP-77
Bell P-63 Kingcobra
B-29 Superfortress
Bell P-59A Airacomet
Bell XP-83
Others may follow

Bell X-1: The wonder of "competing ideas"

"The race to break the sound barrier"


On November 15, 1987, the Buffalo Evening News published a story by Mike Vogel entitled, “Boom Town.” He wrote:

“Forty years ago, Buffalo (New York) was at the center of the gutsiest experiment in aviation history: the race to break the sound barrier.”

Vogel went on to quote from a report signed by Capt. Charles “Chuck” E. Yaeger, USAF that said this:

“The needle of the Machmeter fluctuated at this reading momentarily, then passed off the scale. Assuming that the off-scale reading remained linear, it is estimated 1.05 Mach was attained at this time.”

Yaeger was slightly off. Analysis showed he and his aircraft, the Bell X-1A “Glamorous Glennis,” hit Mach 1.07, about 700 mph, at more than 42,000 ft. above the dry California lake beds. This occurred on October 14, 1947. Yaeger and his aircraft were the first to break the sound barrier, once thought by some to be an impenetrable wall for manned flight. The term "Mach" is used to reflect the ratio of the speed of a body, in this case an aircraft, to the speed of sound. Mach 1.0 is used to define the speed of sound.

The evolution of the Bell X-1 was part science, part engineering, part urgent technologic challenges, and part intense advocacy of competing ideas. I'll try to address all these relative to the Bell X-1's evolution. Going beyond the speed of sound in a manned aircraft presented many unknowns. There was a good deal of science. Engineers were able to apply this science to achieve that goal. But, there were many uncertainties along the way. There was a lot that was not absolute. As a result, many very smart people developed multiple and often conflicting ideas on the course that ought to be taken. Some how, it all came together and Yaeger flew"Glamorous Glennis" faster than the speed of sound.

Whenever new technologies and advanced technology systems begin to bubble up to the surface, there often is a scramble among brilliant people to advance their ideas about the course that ought to be taken. As a result, many competing ideas come to the fore and people will shoot off in multiple directions to advocate their approach. The debates about these competing ideas can become fierce. There is usually a lot at stake. There was a lot at stake here.

I should confess up front that this notion of "competing ideas" did not originate with me. I "borrowed" it from James R. Hansen, NASA History Office, in his
Chapter 10 of Engineer in Charge, A History of the Langley Aeronautical Laboratory, 1917-1958. He noted that once support developed for a high-speed research aircraft in 1944, several distinguished people "had competing ideas for the requirements of a high-speed research aircraft."

From the time the Wight Brothers developed the first practical fixed-wing aircraft, the field of aerodynamics and the development of new and better aircraft accelerated at breakneck speed. Aircraft emerged in WWI and WWII that were faster, more nimble, and more lethal. Up until WWII, the were all propeller driven. But during WWII the turbojet and rocket emerged to power aircraft and missiles. They were new technologies to the world of aeronautics, especially military aeronautics. The Germans and British led the pack in applying the turbojet to manned aircraft, and the Germans led the pack in applying the rocket to missiles such as the V-1 and V-2 used to attack Britain. The Americans lagged far behind.

That the Americans were so far behind during WWII was sobering. Then Major General Henry "Hap" Arnold, chief of the Army Air Force (AAF), shown here as a lieutenant general, was astonished in 1941 when he visited Britain and saw they were on the cusp of fielding a turbojet aircraft, and little did he know that the Germans were ahead of the British. He immediately returned home and set the wheels in motion for the US Army Air Force (USAAF) to get one on the runway and do so in a hurry. It was WWII, and only 1941. America's and Europe's future were at stake.

It's important to recognize that during the 1930s and 40s, aircraft were in the subsonic range, traveling slower than the speed of sound. In his book,
Probing the Sky, by Curtis Peebles points out:

P51MustanginNACAfullscale windtunnel
P-51 Mustang in NACA full scale wind tunnel, WWII

"With aircraft flying near the speed of sound, the old rules of subsonic aerodynamics no longer applied and the old tool of aeronautical research, the wind tunnel, no longer worked. Consequently, engineers lacked the means to determine if their designs would withstand actual flight conditions … The body of knowledge for the supersonic era was effectively recast and made anew … Creating the new era, with its own rules and tools, took place against the dynamic of the Cold War, forcing and feeding the need for ever-higher performance."

As frequently seems to be the case, however, during the 1930s at least two men, John Stack of the National Advisory Committee for Aeronautics (NACA), the predecessor of the National Aeronautics and Space Agency, NASA, and Major Ezra Kotcher, of the AAF Air Materiel Command (AMC) stand out in the development of the X-1. Each was already contemplating breaking the speed of sound in a manned aircraft. Each had different visions, each had different ideas, and those visions and ideas competed against each other throughout the development of the X-1. This competition is fascinating, and instructive. And their competition will be a highlight of this story.


There is a lot of history that goes with the X-1 achievement, more than I had imagined. A lot of that history has been documented by many learned people. I have found several histories of the Bell X-1 particularly useful and I will draw from them throughout:

W.G. Williams, writing "
Machbuster - A Test Pilot Recalls The Early Days Of Supersonic Flying, Where You Either Broke The Sound Barrier Or It Broke You!," said this:

"The sole purpose (of Government contracts for airplanes) was to explore and document the unknown. Some were designed to just go fast … As these new research aircraft came out they caught the public's imagination. Airpower had achieved a new importance when the dawn of the nuclear age ended World War II. Now these research programs promised to keep America on the leading edge of technology … The whole concept was exciting … The first major hurdle for these aircraft was to exceed the speed of sound and return to a safe landing."

That's what the Bell X-1 and its pilot did. They exceeded the speed of sound and returned to a safe landing. Follow-on flights would go even faster than this first record breaking flight. Enabling that to happen was no small or easy undertaking. Indeed Yaeger's historic flight was on the
50th flight of the X-1, the first flight having occurred on January 19, 1946, some 22 months earlier. I sold mention that John W. "Jack" Russell was Yaeger's crew chief.

What is the speed of sound?

We should get some basic understanding of what the sound barrier meant in the early 1940s, and earlier. It had for some time been a bone of contention; that is, there were competing ideas.

Dr. John D. Anderson, Jr., best known as the Curator of Aerodynamics at the National Air and Space Museum at the Smithsonian Institution, participated in writing the the National Aeronautics and Space Agency (NASA) series, “From Engineering Science to Big Science,” published I believe in 1998. He wrote Chapter 3, “Research in Supersonic Flight and the Breaking of the Sound Barrier."

Anderson said:

“The speed of sound is one of the most important quantities in aerodynamics; it is the dividing line between subsonic flight (speeds less than that of sound) and supersonic flight (speeds greater than that of sound).”

That sounds trite these day. But back then, that dividing line was huge. Anderson has presented some detailed science if you are interested. I commend
Anderson's paper to you.

As a broad statement, scientists knew there was such a thing as the speed of sound for many centuries. Artillery and bullets when fired demonstrated that to them. Both could and did break the speed of sound on a regular basis. In other words, you'll be hit by the bullet before you here the sound of the muzzle blast!

Francis Bacon broached the subject in the 16th century. It was largely a mathematical challenge.

Sir Isaac Newton in the 17th century researched the subject and computed the speed of sound at 979 ft. per second. As might be expected, there was no consensus agreement and a lot of doubt. Anderson said artillery tests had shown the speed of sound to be about 1,140 ft. per second. It turned out Newton had assumed that air temperature inside a sound wave was constant. That was a mistake.

Air temperature is very important to the matter of the speed of sound. For example, as the temperature decreases, the speed of sound decreases. That means the speed of sound for aircraft flying at higher altitudes is lower than if it were to be measured at sea level.

Pierre Simon Marquis de Laplace, a French scientist, determined Newton’s figure was too slow. He believed in 1802 that he found an error in Newton’s calculations. Others were also working hard at the time to figure all this out, and there was considerable debate, often heated debate. Laplace himself kept changing his own calculations. His focus had to do with the specific heat of air and associated pressure. By the 1830s it appeared that Laplace’s final work could not be discounted. Laplace concluded that the speed of sound was 345.35 meters per second, or roughly 1133.04 ft. per second.

If you are not a scientist or mathematician, and look up the speed of sound, you’ll find yourself immersed in a ton of technical details. The bottom line is “it depends” on air temperature. In glossing over all this, it appears the consensus is the speed of sound is 1,125 ft./second at sea level in dry air at a temperature of 68 degrees Fahrenheit. That works out to be about 768 mph. For those of us not so well educated, that’s called Mach 1. But remember, go to higher altitudes where the temperature is lower, then the speed of sound will be lower. Go to twice the speed of sound and you'll use the phrase Mach 2, etc.

Defining the speed of sound was an issue in the 20th century as well.

For example, on October 12, 1943, a large group of distinguished aerodynamics experts met at NACA. Aerodynamic experts were well aware of German rocketry, jet propulsion, and high speed aircraft design. No one really knew where the Germans were at the time, which created pressure in the US to move ahead since the US and its Allies were at war with Germany.

The first question they had to deal with was to come to some agreement regarding what the speed of sound was.

Multiple studies of the impact of air temperature were at the center of discussions. At the time the conclusion was the speed of sound was 1116.2 ft. per second, or about 761 mph. The end result was agreement at 1117 ft. per second. They simply agreed to round the number off. That figure was slightly slower than Laplace's computations.

Everyone understood there were variables affecting the speed of sound. I think, in order to move forward on high speed aircraft design and development, they needed to hone in on a number, at this very early point, so they could get started.

High speed problem: "Disturbing performance anomalies"

I'll refer to Dr. Richard Hallion many times throughout this report. Dr. Hallion, at the time the Air Force Historian, wrote a paper “The Air Force and the Supersonic Breakthrough” published in 1997 as part of the Technology and the Air Force: A Retrospective Assessment. In that paper, he refers to the high performance fighters of the 1930s and those flown in WWII as responsible for "the birth of supersonic flight." Hallion is the author and editor of numerous books relating to aerospace technology and military operations, as well as articles and essays for a variety of professional journals.

During the 1930s and WWII newer and faster aircraft came off drawing boards to production and operation at whirlwind speeds. With that a huge aerodynamic challenge emerged. Hallion commented:

“(At higher speeds) the accelerated airflow around the aircraft generated a series of disturbing performance anomalies including Shockwave formation, abrupt drag rise, a marked reduction in lift, an abrupt reduction in propeller efficiency, pronounced airframe buffet, occasional flutter of flight control surfaces, and unsettling control characteristics.” He also noted “the exact magnitude was not precisely understood” and said many aircraft were lost as a result.

Mike Vogel, reporting “Boom Town” published by the Buffalo Evening News on November 15, 1987 noted:

“Pilots forced by combat into power dives reported severe buffeting at speeds beyond 500 mph; controls often reversed, wings cracked, pilots were slammed around in the cockpit. If the speed wasn’t too high and the buffeting too severe, the flier might pull out with his skin intact; otherwise, his plane broke up and he bored a hole in the countryside.”


Stephen Dowling wrote, "The Spitfires that nearly broke the sound barrier," published by BBC. He wrote the British began high speed trials of the Spitfire in late 1943, with Squadron Leader J R Tobin (shown here), an American with the RAF, taking his Mark XI Spitfire such as shown above into a 45 degree dive. Dowling said the aircraft "reached a top speed of 606 mph, or Mach 0.89 … It was the fastest speed a Spitfire had ever flown – or at least the fastest that a pilot had lived to tell the tale. But a far more dramatic flight was soon to take place."

In April 1944, Squadron Leader Anthony F. Martindale put the exact same Mark XI Spitfire into a dive. This time, the reduction gear designed to limit its speed failed. The propeller ripped off and the diving aircraft reached more than 620 mph, Mach .92, as it plunged toward ground. Dowling commented:

"Martindale was saved by simple physics. With the heavy propellers wrenched off, the aircraft was now tail heavy and this change in the center of gravity forced it to climb up from the dive at great speed. Martindale was knocked unconscious from the climb, and woke to find his aircraft flying at 40,000 ft. Somehow he managed to glide the aircraft back to base, and emerged unscathed. The stress of the plane's dive had bent the wings."

One more interesting phenomenon occurred with the higher-speed fighters. Dowling said:

"Planes like the Spitfire had another big problem: the propeller itself. Older aircraft had a propeller that was directly connected to the engine; more power meant the propellers would spin faster and faster. Even with the plane traveling under 300 mph, the air traveling over these fast-spinning blades could reach supersonic speeds. The shock waves formed from this air traveling so fast over the propeller blades then added drag, buffeting and noise."

In effect, the propeller blades were like wings. By drag aerodynamicists mean the aircraft's motion through the air is being opposed.
Dr. Hallion spoke about this in a PBS interview:

"In the 1920s, a great number of researchers started looking at the problems of flow around propellers, because propeller tips were beginning to approach the speed of sound as the propeller rotated. A propeller is, after all, a rotating wing. And the connection was made in the minds of researchers that if a propeller encounters disturbing flow conditions at high speeds, then obviously at high speeds the wing of an airplane would as well."

Dr. John Anderson agrees:

"Ironically, the first inklings of compressibility problems occurred during the age of the strut-and-wire biplanes, with flight velocities about as far away from the speed of sound as you can get. It had to do with an airplane part, namely the propeller. Although typical flight speeds of World War I airplanes were less than 125 miles per hour, the tip speeds of propellers, because of their combined rotational and translational motion through the air, were quite large, sometimes exceeding the speed of sound."

The cause of the problem: Compressibility

Returning to Dr. Hallion:

"High performance fighters, propeller driven, jet propelled, and rocket propelled in the late 1930s and on through the Second World War” encounter a “generalized ‘compressibility crisis’” especially when an aircraft dove at speeds exceeding Mach 0.7.

Hallion talks in terms of a compressibility crisis because the aerodynamic affect can cause pilots to lose control of their aircraft. He said the technical challenge was not so much propulsion, but rather "what actually happens to an airplane as it approaches closer and closer and hopefully eventually passes through the speed of sound. The flow conditions around the airplane change completely."

I'm going to avoid going into technical details on compressibility. There is plenty of outstanding work available on the internet if you wish to pursue the topic. Compressibility is only an issue when an aircraft approaches the speed of sound. At lower speeds, air is viewed as “incompressible.” That is, its density remains about the same all around the aircraft. Since aircraft were all flying well below the speed of sound, most thought air to be incompressible. As knowledge of air being compressible emerged, many were surprised.

john-stack eastman-n-jacobs

John Stack (left), along with his boss Eastman Jacobs (right) of NACA did pioneering work on compressibility and found that at higher speeds, the closer one gets to Mach, the air flow does not remain about the same. In fact the air flow separates, one part beneath the wing, the other above the wing. They found the air flow becomes compressible on top the wing as one approaches Mach. That is, it squeezes or presses. In turn that creates added pressure on the wing.

From the web site
How things fly produced by the Smithsonian National Air and Space Museum:

"Air acts much differently at supersonic speeds than it does at subsonic speeds.


"When an airplane travels less than the speed of sound, the air ahead of it actually begins to flow out of the way before the plane reaches it. The pressure waves created by the airplane passing through the air end up being smooth and gradual.

"But as an airplane reaches the speed of sound … the airplane plows through the air, creating a shock wave. As air flows through the shock wave, its pressure, density, and temperature all increase—sharply and abruptly …The airflow behind the shock wave breaks up into a turbulent wake, increasing drag."

As a reminder, "drag" is an aerodynamic force that opposes an aircraft's motion through the air.

Dr. Hallion has said:

"The problem was that aircraft of the late 1930s into the 1940s were relatively high-drag designs. As a result, when dived to Mach = 0.7+, the airflow over their wings would accelerate to supersonic values. You thus had a paradox--a plane like a P-38 or P-47 or P-51 diving at Mach 0.75, but having accelerated flow over its wings of perhaps Mach 1.25. The wing would develop a standing shockwave, and behind it would be turbulent, distorted flow that would beat the tail to death. As well, the shock-induced airflow changes would greatly distort flight loads and controllability."

Anderson noted:


"The general aeronautics community was suddenly awakened to the realities of the unknown flight regime in November 1941, when Lockheed test pilot Ralph Virden could not pull the new, high-performance P-38 out of a high-speed dive, and crashed … The P-38 exceeded its critical Mach number in an operational dive, and penetrated well into the regime of the compressibility burble at its terminal dive speed … The problem encountered by Virden, and many other P-38 pilots at that time, was that beyond a certain speed in a dive, the elevator controls suddenly felt as if they were locked. And to make things worse, the tail suddenly produced more lift, pulling the P-38 into an even steeper dive. This was called the 'tuck under' problem."

Hallion reported something that turned out to be very curious at the time. Something happened between Mach 0.75 and Mach 1.25 in the wind tunnel testing. Below 0.75 there were no shock waves experienced, and above 1.25 he said “shock waves … did not interfere with reliable tunnel measurements.” So something happened between 0.75 and 1.25. It was important to know what happened, because an aircraft would have to travel through that environment to break the speed of sound.

Hallion said, "Wind tunnels were then of little use between Mach 0.75 and Mach 1.25 … As a result, we opted for piloted research airplanes, instrumented to use the sky as a laboratory, the first two of which were the Bell XS-1 and the Douglas D-558." The XS-1 was the original designation, standing for "Experimental Supersonic." In June 1948, that name was changed to the X-1. The D-558 was a Navy research aircraft that was developed because of that advocacy to stay transonic.

Anderson was a bit more direct. He wrote, "When a model was mounted in the flow, the flow field in the test section essentially broke down, and any aerodynamic measurements were worthless … In order to learn about the aerodynamics of transonic flight, the only recourse appeared to be a real airplane that would fly in that regime."

I’ll leave the subject there.

In the 1930s, the world was approaching WWII and in the 1940s was immersed in it. Concomitant with that was the development of jet propulsion, which would move aircraft even faster. There was competition between countries. As several were at war with each other, the competition was seen as vital. And scientists and engineers were coming face to face with this compressibility question.

The Germans and British


It’s hard to say exactly when the “bubbling up” of aircraft technologies occurred, but the 1930s and especially the 1940s are good places to start with WWII and the advent of the turbojet. Germany and Britain were the clear leaders, in that order. The US was way behind. The war provided considerable impetus to get closer to uncertainties surrounding high-performance fighters.

Wikipedia provides a list of firsts:


Frank Whittle of Great Britain, shown here, and, arguably, Hans von Ohain of Germany were the first to invent the turbojet, done in the 1930s.

heinkel-he-178 heinkel-hes-3b-1

The first turbojet to fly was the German Heinkel He 178 prototype on August 27, 1939, powered by the Heinkel HeS 3B, designed by Hans von Ohain. Only two prototypes were built. The German Luftwaffe was not interested.


The Italian Caproni Campini N.1 motor jet prototype flew on August 27, 1940. Themotorjet was designed by Secondo Campini. Its engine's compressor was driven by a conventional reciprocating engine. The aircraft did not become operational, but two prototypes were built.

GlosterE.28:39 Whittle_Jet_Engine_W2-700

The British experimental Gloster E.28/39 first flew on May 15, 1941. The photo shows test pilot Gary Sayers taking her up on her first flight. This was the first British jet-engined aircraft to fly and the third successful jet behind the He 178 and Caproni Campini. Two prototypes were built for testing. The Whittle W.2/700 engine was employed. The British were virtually step by step with the Germans. The Gloster Meteor, enabled by the Gloster E.28/39 evolution, flew in 1943 and commenced combat operations on July 27, 1944, two days after the German Me 262 flew combat.

Messerschmitt_Me_262A JunkersJumo004-BEngine

The first operational jet fighter was the German Messerschmitt Me 262 “Schwalbe” (Swallow). She was powered by two Jumo 004 engines. The aircraft first flew under jet power in 1942. She became operational on July 25, 1944. Her pilots claimed 542 kills of Allied aircraft suffering only 100 combat losses.

XP59A P-59-Airacomet-engine

Bell Aircraft developed the P-59A Airacomet. She was powered by an American version of the Whittte W.1 engine, later named the General Electric J31. She first flew in October 1942, she did go into production, but did not fare well and was cancelled.

As a reminder, the Bell X-1 was a rocket, and we are only at the beginning of the turbojet stage for manned aircraft. But the way technology was developing in those days, the move to rockets and the sound barrier happened quickly.


As an example, the Germans developed a rocket powered fighter aircraft that flew its first flight in September 1941. The Germans scored again, fielding the first rocket-powered fighter aircraft, and the first operational combat aircraft to use swept wings. She was the Messerschmitt Me 163 "Komet." The Me 163B, such as shown here, commenced small scale combat operations in spring 1944, and entered service with the Luftwaffe on July 28, 1944. Combat operations continued through the end of the war in May 1945. She achieved nine kills but 14 aircraft were, in large part because the Allies figured out when she was running out of fuel and then suddenly attacked them. Note the small propeller on the nose! It was there to work as a windmill generator for electrical power in flight.


The Me 163 employed the Walter HWK 109-509A liquid-fuel rocket engine producing 3,800 lbs. thrust capable of speeds up to 596 mph. The Aces Flying High web site said "The Me 163 used the highly volatile propellants of T-Stoff oxidizer (hydrogen peroxide) and C-Stoff (methanol-hydrazine) to create rocket fuel. The Walter rocket motor basically created propulsion through controlling the explosion that arose when the two types of fuel came into contact with each other."

The aircraft was built to fly from German airfields against attacking high altitude bombers. The strategy was to fly up through the clouds, get above the bombers, then dive to attack and glide to land on a landing skid. It had only seven minutes rocket power fuel.

Overall the aircraft was very dangerous to fly.

Let's switch back to Whittle.

Britain's Frank Whittle is often called the "Father of the Jet." He was the first to build and run a turbojet for aeronautical use. He was in the Royal Air Force (RAF) and ultimately became a pilot, and was said to be a bit of a daredevil. He was sent to the Air Ministry research laboratory, which was working on a turbine to drive a propeller. But Whittle had an idea that said enormous propulsive power could be produced by hot gas exiting an engine. He took his idea to his boss, A.A. Griffith, who dismissed it as foolish and based on faulty calculations. Nonetheless, he applied for a patent which was granted in 1932. The specifications were published worldwide.

Unfortunately, he had to tend to his RAF flying duties and his patent expired in 1935. Even though still in the RAF, he formed a company known as Power Jets in 1936. But then he was confronted by the Germans. Hans von Ohain, shown here, was a physics and aerodynamics student at the University of Göttingen and developed a "near-jet" engine, though it was not quite there. Richard Pohl of the university's Physics Institute liked the idea and took it to his friend Ernst Heinkel. Heinkel got von Ohain to brief his engineers and they also liked it.

Now a competition began between Whittle and Heinkel, shown here, the former not well financed, without any government support, and still committed to the RAF, the latter very well financed, with the resources of a major industrial concern, supported by engineers and scientists who could work the problem full time.

Whittle found a British company willing to assemble a prototype, and on April 12, 1937 he ran up the engine and it produced incredible power, though his colleagues scattered as flames erupted out of the tail pipe. In the meantime, Heinkel adjusted von Ohain's design and built the HeS2 turbojet engine which powered the V1 rocket, but did little to advance the turbojet for an aircraft. While Heinkel had been watching Whittle, he did not know of Whittle's success five months earlier. Oddly, the
Luftwaffe was not interested in Heinkel's engine, but now the RAF was interested in Whittle's. He developed the W1 and then the W2 engines.

General Arnold arranged for Whittle's engineering drawings and some Power Jet engineers to visit the US to help American engineers get going. I'll come back to this in a few moments, as this technology transfer upset the British but there was nothing the Brits could do.

The Germans and Americans


While the US was behind in turbojet technology, the US was a large, resourceful country and it led the Allies to victory in WWII. Germany lost WW II and its aeronautical industry virtually came to a standstill.


I won't throw you into a lot of history here. But as WWII came to a close, the Allies were up in the air regarding what to do about post-war Germany. The Second Quebec Conference of September 12 - 16, 1944, codenamed "Octagon," was held at the Château Frontenac in Quebec. It was the 11th meeting between FDR and Churchill. Stalin was not there, tending to the Germans instead.

The war in the minds of the Allies was effectively coming to a victorious end. All Allied forces were moving to squeeze the German military machine, such as it was at this time, back into Germany all the way to Berlin. But remember, the conference was held in September 1944 and the war went on until May 1945.

FDR had insisted the purpose of this Quebec conference was to discuss military matters, but there is cause to believe that he was not all that sincere. Something was in the wind because US Secretary of the Treasury Henry Morgenthau, Jr., shown here, attended. He was known to be keenly interested in what to do about Germany after the war, a purely political matter. He was known to favor dismemberment of Germany, feeling the only way to stop German aggression was to dismantle its industrial base. Furthermore, he was FDR's neighbor and good friend.

Indeed postwar planning had been well underway for some time. But the problem was there was no plan. The need for a plan was growing exponentially. That was in part due to the fact that there were tensions among the Allies and the Allied military forces who were now moving into Germany.

Morgenthau's friend, Dr. Harry Dexter White, shown here, was an economist and a principal adviser on monetary matters, one who would play a leading role in setting up the postwar economic order. He had developed a plan for Germany. For our purposes, however, White and his staff focused on postwar treatment of Germany. The end result in summer 1944 was what was known as the Morgenthau Plan, this a year before Germany surrendered. The Morgenthau Plan was a dismemberment plan.


In essence, it de-industrialized Germany. It broke it into two non-industrial, independent states, the northern and southern German states. These would be relegated to pastoral pursuits. A third zone would be created that would be an international zone, occupying much of the territory of industrialized Germany. The plan read in part:

"It should be the aim of the Allied Forces to accomplish the complete demilitarization of Germany in the shortest possible period of time after surrender. This means disarming the German Army and people, the total destruction of the whole German armament industry, and the removal or destruction of other key industries which are the bases of military strength … (The Ruhr area) should not only be stripped of all presently existing industries but so weakened and controlled that it cannot in the foreseeable future became an industrial area."


The is a photo of the blast furnaces of the Kloeckner works in Haps, one of the largest producers of iron and steel in the Ruhr, photographed before 1939. It gives you an idea of the heavy industry in the Ruhr area.

The Morgenthau Plan was not implemented, but this is an example of the American mindset the would go forward. In the end, Germany was divided into four zones of occupation with Berlin then divided similarly. But demilitarization of Germany remained very important.


At war’s end, the US had access to German research and development documents, the actual technologies and products that had been developed, and in some cases used operationally. Here you see a V2 Rocket that was being built by the Germans in a large underground factory, this one at Klein Bodungen. US forces are there examining it.


This is another V2 at Mittelbau Dora.


This is a photo showing the intricacies of the V2 rocket engine.

I show you these to demonstrate the Germans were very far ahead of everyone else. The Germans first launched a V-2 against Paris in September 1944, then one against the Hague and another against London. Launch sites were set up in the Netherlands. Some 3,172 were launched against targets in Belgium, Britain, France, France, The Netherlands and even at Remagen in Germany. In London alone 2,754 people were killed and 6,523 injured. Viewed as an average, two people were killed in London per launch, but one strike killed 160 and injured 108. An attack against Antwerp killed 1,736 and injured 4,500. On balance, the V-2 was destructive but not accurate. Nonetheless, the age of rocket powered missiles had arrived.

Not only did the US have access to German research and development, American engineers and scientists had access to the Germans who worked the problem during the war. This is a most interesting subject.


For example, German Major General Dornberger came to the US and became a Bell Aircraft vice president for engineering. He and many others came to the US by means of “Operation Paperclip.” Paperclip was a secret program in which more than 1,600 German scientists, engineers, and technicians were recruited in post-Nazi Germany and, along with their families, were taken to the U.S. for government employment at the end of World War II. The program was designed to transfer German rocket technology to the US. This photo shows the Werhner von Braun rocket team, about 118 strong, at Ft. Bliss, Texas, on the outskirts of El Paso.

von Braun was a German (later American) aerospace engineer and space architect credited with inventing the V-2 rocket for Germany and the Saturn 1 rocket and Saturn IB and Saturn V space vehicles. The Saturn I rocket was used for the US Apollo 8 moon orbit in 1969. He had worked in Germany with Dornberger and knew him well.

This transfer of brains, drawings, documents and product put the US aerospace community on a lightning track to develop and field new systems that, among other things, would lead to the jet fighters of today, ICBMs, and the Apollo landing on the moon.

The Germans and the Soviets


The Germans had designed a rocket-powered swept-wing vehicle called the DFS 346. It was intended for an air launch from the Dornier Do 217. The objective was Mach 2.6 and it would employ the Walter 509B/C twin-chamber rocket engine. The intent was to fly it over enemy territory for reconnaissance purposes, re-ignite the engines and return to home base. A prototype was under construction but the Soviet Army arrived. The Soviets took it and German engineers such as Hans Rössing and several from the Heinkel aerospace company and formed a Soviet-German experimental design bureau called OKB-2, located at Podberezhye north of Moscow and east of St. Petersburg.

In their book
Energiya-Buran: The Soviet Space Shuttle, Bart Hendriks and Bert Vis said Rössing led the team and by 1948 had a glider version called the 346-P which was flown. Interestingly it was air launched by a US B-29 after it had been confiscated by the Soviets when it made an emergency landing in Vladivostok. The 346-P flew carrying a rocket mock-up engine in 1949, again in drop tests. Development proceeded on the first rocket-propelled aircraft called 346-3. It accomplished three powered flights in 1951. The aircraft achieved 559 mph. The program experienced engine problems and there were man aerodynamic concerns. The program was dropped and the German engineers were sent back to the Democratic Republic of Germany (DDR), known then as East Germany.

The Soviets pressed on but found little military value and little future in rocket aircraft. According to the authors, no Russian pilot ever flew faster than the speed of sound in a rocket-propelled aircraft. The Soviets focused on rockets for missiles.

The British and Americans


The British-American connection is quite different but captivating.

HopkinsHarry HarrimanAverill

FDR sent Harry Hopkins (left), the Secretary of Commerce, and financier Averell Harriman (right) to Britain in March 1941 to plan for US involvement in WWII. Hopkins and Henry Stimson, Secretary of War, urged FDR to send Major General Hap Arnold to join the group. FDR had several issues with Arnold largely because Arnold was publicly advocating creation of the US Air Force as a separate service from the USAAF, and because Arnold had opposed providing American military aircraft to the British.

Nonetheless, FDR agreed and Arnold left the US on April 9, 1941. Arnold’s job was to find ways the USAAF might help Britain in the war. He toured factories, Royal Air Force (RAF) facilities, and met with leading British military officers and King George VI. Throughout he was envious of the RAF being an independent military service.

On his return to the US in May 1941, Arnold briefed FDR on his findings. FDR would say it was the best briefing he had heard regarding the state of Britain.

In his book
Hap Arnold: The General Who Invented the US Air Force, Bill Yenne said:

“On his visit to Britain, Arnold was shown Frank Whittle’s jet engine and had seen the jet-propelled Gloster E.28/39 during taxi tests. Under a cloak of secrecy, Lord Beaverbrook had even given him the blueprints for this remarkable innovation.”

Then Yenne said:

“According to his (Arnold’s) memoirs, ‘I called Mr. Larrry Bell, of the Bell Aircraft Company, and Mr. D.R. Schoulz (Shoults), of the General Electric Company, to a conference in my office.’”

Arnold then told General Electric to press on with its engine and enable Bell to build the plane. What Arnold wanted was a US jet aircraft. The effort was to be handled in secrecy.


As a result, Bell got a contract in October 1941 to build the XP-59 Airacomet using the General Electric J31 engine, which was an adaptation of the Whittle W.1. The aircraft flew in 1942. It was the first American turbojet aircraft to fly. Arnold received his third star to lieutenant general in February 1942.

MeteorEE210:Gto US

One of these aircraft, the third YP-59A (S/n: 42-22611) was supplied to the RAF in exchange for the first production Gloster Meteor I, EE210/G. This photo shows the Meteor EE210/G sent to the US by the RAF for testing. It was the first production Meteor Mk 1, and flew for the USAAF on April 15, 1944. The RAF GLoster Meteor was the only Allied jet fighter to achieve combat operations in WWII. The Meteor F variant achieved 600 mph or Mach 0.82 at 10,000 ft.

British pilots were not happy with the exchange. They found the P-59 aircraft compared very unfavorably with the jets they were already flying. Bell built 50 but they never saw combat, but instead were used for jet training, and by 1950 found to be no longer airworthy.


In June 1943, the USAAF told Lockheed to design a fighter around the De Havilland built Halford H.1B turbojet engine, developed in England, in response to Germany's Messerschmitt Me 262 jet fighter. A small team led by Kelly Johnson designed and built the XP-80 in 143 days. She was called the "Shooting Star" and in a test achieved a speed of 624 mph, a record at the time. Renamed the F-80, she was America's first operational jet fighter, and saw extensive service in the Korean War

By now the British Air Ministry had visions of breaking the sound barrier. It issued a contract in October 1943 to Miles Aircraft Co. to produce an experimental jet research aircraft capable of 1,000 mph and able to reach 36,000 ft. in 1.5 minutes.


Frank Whittle, the British jet engine designer who invented the turbojet engine and to whom I introduced you earlier, told the Air Ministry he could build the engine to do the job. Dennis Bancroft, shown here, a design engineer, was Whittle’s chief aerodynamicist. Miles Aircraft built the Miles M.52 turbojet-powered aircraft. The graphic is an artist's impression of the M52. At the time, bullets were the only thing known to fly faster than the speed of sound. So the aircraft was fashioned after the bullet.

The government cancelled the contract in 1946 because of budget constraints. WWII had emptied the country's treasury. One result was the British shared the design and research with Bell Aircraft. Bell’s people applied it to the Bell X-1. Miles Aircraft went bankrupt. Providing so much design and research data to the US made many Britains very angry. There was to be an agreement where the US promised to provide its own research and test data back to the British, and give the British access to the X-1. Bancroft maintained that never happened, that it was a one way street.

The major discovery in the US, however, was with the tailplane. The British employed a moving tailplane to overcome the compressibility challenges. Once the Americans saw that, the US classified the X-1 project Top Secret and closed it off to the British. The moving tailplane was a huge contribution to the Bell X-1, though some argue that US engineers had done significant research in this area already. I'll discuss it more later — the British call it a tailplane; these days we call it the horizontal stabilizer. Americans call the moving tailplane the movable horizontal stabilizer.

Bancroft said they could have had the M52 in the air breaking the sound barrier in 1946, 1947 at the latest. In 1948 the British dropped an unmanned rocket powered scale model of the M52 from a mother ship. It quickly broke the sound barrier. But it was only a model and had no pilot.

Eric Brown, a Royal Navy and M52 test pilot, said:

“Frankly I do not think they (Bell) could have gone supersonic so early without the data we passed on.”

Both Bancroft and Brown were very bitter about sending all their work to Bell. One Brit wrote on a blog
Secular Café:

“The Bell X-1 always annoys the tits out of me. The whole design was nicked (stolen) from Miles.”

That particular blog is interesting. I think you might enjoy reading it.

The British notwithstanding, Bell Aircraft participated in the explosion in aeronautical technology. It was among the US companies that earned the distinguished reputation of being a “Flight Pioneer.” While one can understand the British ire, the reality was the Americans had already started building a rocket-powered supersonic design of their own, though they did run into problems, several of which were solved having access to German and British documents and engineers. Many of the Americans would simply say the British confirmed their own thoughts on multiple subjects.

However you view it, the Germans and British contributed a great deal to the American X-1 program and several other programs that would become vital. I should stress, however, the American engineers and scientists were not just sitting there twiddling their thumbs. Though I will say Arnold's job on his visit to Britain was to help the British. What really happened is the British put the Americans in the driver's seat in developing aeronautical technology, and I will add the Germans put the US in the ballistic missile and space exploration business..

I'll now start getting into the nitty-gritty of the Bell X-1 development and the competition of ideas that ensued.



The National Advisory Committee for Aeronautics (NACA) and the Army Air Corps (AAC)/Army Air Forces (AAF) had a long history but during the 1930s and 1940s each saw an enormous amount of organizational change. I'll present a top-level view of where they were when the Bell X-1 program developed.

NACA was a US federal agency tasked to undertake, promote, and institutionalize aeronautical research. NACA had four facilities:

  • Ames Aeronautical Laboratory in Moffett Field, California
  • Aircraft Engine Research Laboratory in Cleveland, Ohio
  • Langley Memorial Aeronautical Laboratory in Hampton, Virginia
  • Muroc Flight Test Unit in Edwards, California

NACA was a civilian organization. It was mainly a research and development (R&D) outfit. By the 1930s its Langley organization had a Full-Scale Wind Tunnel, a Variable-Density Tunnel and Propeller Research Tunnel. NACA depended heavily on accumulating, digesting and analyzing test data using these wind tunnels. NACA made fundamental aeronautic breakthroughs in the way aircraft were built, tested and designed. In October 1958 NACA became the National Aeronautics and Space Administration (NASA). NACA was a top-flight outfit.


At the risk of oversimplifying a very complex issue, at this point in time I think of NACA as a wind tunnel outfit. I do not mean to say that is a bad thing; it is a good thing. The wind tunnel enabled multiple kinds of experiments during which a massive amount of data could be collected and later analyzed. Aeronautical development needs this type of effort. This is a photo of a model of the Bell X-1 in one of Langley's wind tunnels prior to the Yaeger flight.


The wind tunnels had grown to be quite large enterprises. This photo shows a NACA 16 ft. wind tunnel at Ames Aeronautical Laboratory. NACA's engineers, led by John Stack, about whom we shall talk a lot throughout this report, had started exploring high-speed wind tunnels in the early 1930s. The Laboratory developed special facilities and acquired some of the first supersonic aerodynamic data and specialized flow visualization equipment. That enabled the engineers to visualize shock waves emanating from aircraft at supersonic speeds.

NACA felt it to be its duty to provide the military services and industry with the very best research.

The Army Air Forces (AAF) succeeded the Army Air Corps (AAC) in June 1941 as a way to seek some separation between the ground and the air forces of the Army. The USAF would succeed it as its own military service separate from the Army in September 1947, just a month before the historic X-1 flight.

The AAF was a military command. Its people and equipment were at war against Germany and Japan. The Air Materiel Command (AMC) was a subordinate command to the AAF with its headquarters at Wright-Patterson Field in Dayton, Ohio. It had an Engineering Department that studied and designed aircraft bound for production, a Materiel Division which did R&D, procurement, supply and maintenance, and other entities that did maintenance and provided technical services. AMC as a military organization was most interested in R&D projects that could be taken to procurement and manufacture of product.

I have mentioned General Arnnold's visit to Britain several times where he was awed when he learned the Whittle jet engine would soon power an aircraft. Arnold set the stage for conflict between NACA and AAF. Dr. Hallion wrote:

“In April 1941, after seeing the rapid progress of British gas turbine research, Hap Arnold returned to the United States determined never to let the AAC develop a dependency on such outside organizations as the NACA for its future capabilities. The Arnold trip to England marked the birth of his interest in creating within the service its own scientific forecasting and research capabilities. This led in time to his strong reliance on Theodore von Kármán … who directed the Guggenheim Laboratory at the California Institute of Technology.”

Arnold's position on NACA was important to the development of the X-1. Kármán also played a role.

From where I sit, NACA was a research outfit mainly interested in gathering and analyzing data while the AAF’s AMC wanted to move ideas from research into production. Under Arnold's leadership, the USA was destined to be the world's very best and most advanced. The objective was to achieve air supremacy. But the US had a long slog ahead to achieve that.

The official description of the relationship between NACA and the AAF was that the Bell X-1, original designation XS-1, was a joint NACA-AAF project. That is true, but there was strong tension between the two.

Stack (NACA) vs. Kotcher (AAF), the competition of goals

I need to introduce you to two men who would be at the center of X-1 development, and at the center of NACA-AAF tensions.

John Stack of NACA. NASA has said:

"John Stack is internationally regarded by aerospace historians as one of the world’s most important aeronautical engineers with superlative technical expertise, leadership qualities and demonstrated management capabilities for critical national programs."

He was a graduate of MIT in aeronautical engineering. NASA went on to say:

"He soon developed an interest in the unexplored region of high-speed wind tunnels in the early 1930s and participated in the development of special facilities and acquisition of the first supersonic aerodynamic data and specialized flow visualization equipment which permitted researchers to visualize shock waves emanating from aircraft at supersonic speeds. By 1939 he had already become a noted specialist and was put in charge of all the high-speed wind tunnels at Langley and in1942 he became chief of a new Compressibility Research Division which focused on high-speed flight. In 1947 he was promoted to Assistant Director of the Langley Laboratory. Stack was a major driving force behind the conception and development of the Bell X-1 research airplane."


In 1933 and 1934, Stack envisioned developing an experimental aircraft to conduct research on compressibility. The Journal of Aeronautical Studies published a drawing of what such an aircraft might look like. Today one might say how unremarkable that drawing is. But back then, it was remarkable. It looks much like the X-1 that was developed in the 1940s. At the time Stack felt a propeller aircraft driven by a 2300 hp Rolls Royce jet engine could get the aircraft up to 566 mph. NACA did not do much with the idea.

Major Ezra Kotcher, USAAF. NASA has said, "(Ezra Kotcher) earned a B.S. from the University of California and an M.S. from the University of Michigan. In 1942, Kotcher joined the Air Force as a military officer and became a senior aeronautic engineer at Air Materiel Command. Four years later, he became the first director of the U.S. Air Force Institute of Technology (AFIT)." This photo shows him in 1950 when he was the first Director AFIT. He remained there until 1951 and was instrumental in getting the X-1 program off the ground. Dr. Richard Hallion has said he was an "unsung Army engineer" and is seen by others as having done pioneering work that led to the first supersonic airplane, the Bell X-1. Hallion said "Kotcher's boldness was remarkable." I'll underscore that point several times as press on.

In 1939, Kotcher too had suggested a transonic research aircraft be developed using either a gas turbine or rocket propulsion system. He prepared a paper entitled, "Future Aeronautical Research and Development Problems." General Arnold did not buy off on the idea, though this was before Arnold got wind of what the Germans and British were doing. Hansen remarked, "Like most revolutionary ideas it was premature." War was imminent. And the rigors of work associated with WWII put the idea on Kotcher's and AAF's back burner.

V1Rocket v2

So the idea of building an American aircraft to challenge the sound barrier fell on deaf ears for a few years. James R. Hansen wrote, NASA History Office, Engineer in Charge, A History of the Langley Aeronautical Laboratory, 1917-1958. In his Chapter 10, “Defining the Research Airplane,” Hansen said:

"In the spring of 1944, the American assault on the sound barrier (began).”

I recommend Hansen's paper to you, as well as
Chapter 9. I will be drawing from it quite a bit. He has some terrific history in there. If you get really enthusiastic, you might wish to go through the entire paper, twelve chapters long.

The "American assault on the sound barrier" began because it was clear military aircraft were getting faster and faster, the Germans had developed and employed the V-1 rocket (left) against London in June 1944, and V-2 rocket (right) against Western Europe in September 1944. The V-2 was the world's first ballistic missile. But the driving problem was that US and British propeller-driven fighters in a dive were experiencing all kinds of control and structural problems as their aircraft approached and perhaps even broke through the sound barrier.


The Germans placed the first operational jet fighter into combat in August 1944, the Messerschmitt Me 262 such as shown here.

All these German weapons introductions were made shortly after the Allied landings in Normandy in June 1944. While the Germans were back peddling in their war efforts on the ground, the new technologies threatened the Allied advances. The war was far from over, as we know only too well with the Battle of the Bulge in late 1944 to early 1945.

By 1944 Theodore von Kármán was the unofficial scientific advisor to General Arnold. I mentioned earlier that General Arnold came to rely on Kármán a great deal once he returned from Britain, aghast at what the British were doing, endnote knowing what the Germans were up to.

In 1941, Kármán, an American research engineer, helped establish the Aerojet General Corp., the first American manufacturer of liquid- and solid-propellant rocket engines. Kármán had done a great deal of work in aeronautics. General Carroll had asked Kármán if it were possible to build an aircraft that would go Mach 1.5. Kármán’s response was to the affirmative. But he suggested employing a very new technology known as the ramjet. But ramjet technology was too new to be accepted.

Nonetheless, Kármán’s affirmative assessment was a motivator.

The "American assault on the sound barrier" was in part driven by the perceived need to catch up to the Germans. And as one would expect, the assault started with a big meeting of interested parties. The meeting was held on March 15, 1944. NACA convened this series of meetings with the Navy and AAF to explore developing such an aircraft, but with a turbojet rather than a liquid-fuel rocket.

The meeting was chaired by Colonel Carl Greene, AAF AMC, and Capt. Walter Diehl (shown here) of the Navy's Bureau of Aeronautics, both of whom represented their services at NACA Langley.

In his book The Bird is on the Wing: Aerodynamics and the Progress of the American Airplane, Hansen wrote:

“Representatives from the various organizations expressed strong disagreements with one another about what type of airplane was needed, what its purpose should be, how best to go about developing it, what organization should be responsible for what. According to Stack and other NACA representatives at the meeting, the
raison d'être of a transonic airplane was to collect data at speeds approaching Mach 1."

The army representatives said what was needed was a bolder approach, using a turbojet or even a rocket if necessary that would blast past Mach 1 in as short a time as possible, hopefully before the war ended.

Erik Conway, in his book
High Speed Dreams: NASA and the Technopolitics of Supersonic Transportation, wrote:

"Stack began campaigning for such a craft in 1944, starting with Ezra Kotcher of the US Army Air Force's Materiel Command (which is responsible for aircraft purchasing), arguing that the Army Air Forces should explore the possibilities of such an aircraft themselves. Kotcher agreed with Stack, and at Wright Field in Dayton, Ohio, where the agency housed its research organizations, he and his AAF researchers began a 'Mach .999' study. The study's primary purpose was to evaluate propulsion options for the aircraft."

I'll address the propulsion issue later in more detail, but fundamentally Stack was looking at a turbojet and Kotcher a rocket.

According to Hansen both Stack and Kotcher agreed on some basics. They both believed the speed of sound did not present an impenetrable wall for manned aircraft. They both knew that using wind tunnels to simulate transonic flows was not enough. Only full-scale flight tests would prove manned aircraft could go faster than the speed of sound. Stack wanted to build a “flying laboratory,” and so did Kotcher. That meant they needed a research plane exclusive to the task. I do want to emphasize that both NACA and the AAF saw the plane as one that would be a research plane, not an aircraft to go into mass production. Beyond that, their visions separated.

Their visions conflicted:

Stack’s vision:
  • Small turbojet
  • Take off from the ground under its own power
  • Achieve maximum speed of Mach 1. However, the main goal was to fly safely at high subsonic speeds
  • Start tests at the low end of the compressibility regime, and ramp up on later flights to approach or break the sound barrier.

Kotcher’s vision:

  • A turbojet would not do the job. A rocket was required.
  • The objective was to break the sound barrier and fly through it and past it.
  • The research aircraft would have to be dropped from a mother ship in order to save on fuel. It would not be designed to takeoff from the ground, only land on it.

Each man built a group of advocates around him, advocates who were also decision-makers. Stack’s group was within NACA, and he involved all three NACA laboratories. Kotcher’s group was largely within the AAF, though Kotcher did involve some civilian experts from California Institute of Technology, Caltech, and he also went to industry, Bell included.

Right off the bat, at least two major competing visions for the aircraft were quite visible:

  • Research and approach the sound barrier (NACA) vs. research to break the sound barrier (AAF)
  • Turbojet (NACA) vs rocket (AAF)
  • Ground launch (NACA) vs. air launch (AAF)

I'll add one more competing idea, this at a leadership level in the two organizations. NACA saw itself as the honcho in town for this kind of thing, though it was not really a production outfit. General Arnold said he would not depend on organizations such as NACA to dictate his air force's future capabilities, and the AAF had ties to many production outfits and the ability to obtain funding for them.

Frankly, the battle was on!

I'll now grapple a bit with some relevant politics. I highlight references for some of it, I tell you where I am speculating. To me, it's all very riveting.

Let's start with a key memo.

According to Hansen’s book, on March 29, 1944, Major General John Carroll, AAF, chief of experimental engineering at AMC, sent a memo to Major General Oliver Echols, AAF, shown here, assistant chief of staff for the Air Staff for materiel, maintenance and distribution, that “laid out the most advanced AAF thinking. There is no doubt Ezra Kotcher wrote (the memo) for (General) Carroll.” Bureaucratically, Carroll's memo went upstairs to the AAF staff at the Pentagon.

According to Hansen, the five page memo, “Study of High Performance Jet Propelled Fighter Type Aircraft” of March 29, 1944, requested approval for Wright Field's engineers "to proceed with a 'purely experimental airplane' that could, in so far as possible, support the NACA research efforts." It did not say "comply with NACA," but said support the NACA research efforts in so far as possible. Wright Field received approval from the AAF to go head on April 15, 1944.

I will mix in my speculation for a moment.

In my view, Kotcher slipped a carrot in the memo signed by General Carroll. The memo mentioned Douglas Aircraft Corp. was enthusiastic to go supersonic. Hansen noted, “Earlier in 1944, Douglas had informed Wright Field (AMC) engineers of its interest in submitting a proposal for an airplane that would not only break the sound barrier but also achieve a top speed of fifteen hundred miles per hour, or Mach 2.” To my knowledge, AMC, notably Kotcher, did not bite at the Douglas offer.

At the very least, that notification of the Douglas offer signaled, "The train is leaving the station. We'd better get going and get on."

But I'll get a little more political than that.

Kotcher knew he had a “big gun” on his side. I mentioned earlier that General Arnold had set the stage for conflict between NACA and AAF after returning from Britain in 1941. Arnold did not want NACA tying his hands regarding future capabilities. Conway put it this way:

"This opened a rift between the NACA and Wright Field."

In line with General Arnold's desire to keep NACA at arm's length, General Carroll's memo said, "As yet no consideration has been given as to the manner or degree of participation of other governmental agencies in carrying out this program." Everyone knew that meant NACA which had a vision far different from that of the AAF.

I believe Kotcher could read the tea leaves, that he had his mind already decided, and perhaps the minds of his bosses as well. He led the AAF down a path toward a rocket powered aircraft that would use a mothership to drop it. Technologically, he felt that was the only way to go. He knew all along Stack wanted a turbojet that would be ground launched. And he knew the NACA and Navy, specifically Stack and Capt. Walter Diehl, USN, were in lock-step. Hansen commented it was clear to all hands the two services were going to develop an experimental aircraft "separately." I will add Kotcher also knew Douglas Aircraft had developed several combat aircraft for the Navy.

My guess is Kotcher knew Stack was stubborn as a mule, and was sure Stack would run to the Navy as soon as the AAF made its move to the rocket. Stack would seek the Navy's support to develop an experimental aircraft following Stack's vision. By dropping the Douglas Aircraft offer in the Carroll memo, Kotcher was effectively telling his bosses not only was the train leaving the station, but this would be AAF vs Navy/NACA, a most appealing competition. Indeed when Kotcher informed Stack in summer 1944 of the AAF's decision, that is exactly what Stack did. He went to the Navy to develop a competitor to what would be the Bell XS-1.

Conway also said this:

"(The rift between the NACA and Wright Field) was relatively easily resolved in December 1944. Since the Air Force was paying for the aircraft, its leaders chose to follow Wright's recommendation and buy a rocket plane. The AAF chose the Bell Aircraft Company to build the 'XS-1', as it was designated, at Bell's plant in Buffalo, New York.

"Stack was not the sort to give up early, and having been rebuffed by the Air Force, he turned to friends at the Navy Bureau of Aeronautics for support."

In this case, money talked. NACA lacked the resources to develop a research aircraft on its own. Such an aircraft would have to be sponsored by the military services and produced by private industry. And as Hansen suggested, each service would go its own way. And that is what happened.

I've gotten a little ahead of myself. I'll talk more about this Douglas effort later as it would compete with the Bell X-1. It was a Navy effort employing a turbojet following the NACA vision pretty much to the letter, though the Navy did want to develop a combat aircraft out of the undertaking and NACA was not all that interested in that.

Airframe design: a revolution is needed

The matter of airframe design is also a fascinating one. The debate seems to have started when discussing the question of jet propulsion. We need to note here that jet propulsion was fairly new to the Americans. The Bell P-59A Airacomet was the country's first jet propelled manned aircraft and it flew for the first time in October 1942. Furthermore, the engine was an adaptation of the British Whittle W.1. The Germans and British were far ahead. The Americans were playing catch-up.

The type of engine would drive the airframe design, turbojet or rocket. A turbojet would obtain its oxygen from ingesting the air, compressing it, and kicking it out. The rocket would carry its oxygen with it and did not need the features to ingest it from the outside.

On December 18, 1943, NACA, met in Washington to take a look at Britain’s jet propulsion experiments. A NASA Aeronautics Series book, Probing the Sky, by Curtis Peebles with contributions from Dr. Richard P. Hallion, wrote that William A. Durand, the chairman of the NACA Special Committee on Jet Propulsion, shown here, asked this million-dollar question at the meeting:

“What should the United States do with the turbojet propulsion technology being developed?”

Peebles noted that a dominant issue “was not the propulsion experimentation itself, but the loss of aircraft in high-speed dives,” to wit, the matter of compressibility.

I mentioned this as an issue earlier. Eastman N. Jacobs, an engineer at Langley’s airflow research branch concluded:

“The development of the jet power units themselves had progressed beyond the development of suitable airplanes to employ them.”

Peebles highlighted Jacobs' warning to the US aviation community:

“The revolutionary turbojet engine had to be matched with an equally revolutionary airframe design.”

Peebles put it this way:

“The United States was making the same mistake that the British had made, namely, applying a revolutionary engine to a conventional airframe.”

Peebles also noted that Robert W. Wolf of Bell Aircraft, a designer of the X-59's (first US turbojet) airframe and propulsion system "suggested that a high speed, jet powered research aircraft be designed … He knew more powerful engines were under development that would allow aircraft to reach transonic speed in level flight." Wolf suggested such an aircraft be designed. He wrote a letter to George W. Lewis, Director of Aeronautical Research for NACA (shown here) and suggested that available turbojets could propel an aircraft to speeds in level flight above Mach. The aircraft would have to be very versatile with regard to control surfaces and wings. Lewis responded it was giving such a project "our very serious concern."

I will get to the airframe design more specifically in a while. I wanted to highlight that all hands saw some revolutionary needed to be done. There was a consensus that such an aircraft should be developed. From where I sit, however, a few tough and defining decisions had to be made first:

  • Nail down the mission objective
  • Type of propulsion system
  • Airframe design, with a focus on the type of wings and control surfaces

Nail down the mission objective: transonic or supersonic?

This section was tough to assemble. I'll tell you why:

I alluded to this point earlier. Whenever new technologies and advanced technology systems begin to bubble up to the surface, there often is a scramble among very smart people to advance their ideas about the course that ought to be taken. As a result, many competing ideas come to the fore and people will shoot off in multiple directions to advocate their approach. The debates about these competing ideas can become fierce.

Shooting off in multiple directions with competing ideas certainly was the case with the Bell X-1.

I have outlined in broad terms the two major competing visions for the new research aircraft. A "vision" alone would not build the aircraft. A decision was needed that defined the mission objective. Too often Americans give too little thought to the mission.

The mission objective for this "flying laboratory" was argued right from the beginning. At the risk of oversimplifying the debate, I'll pit John Stack of NACA's Langley Research Center against Major Ezra Kotcher of AAF's AMC once again; that is, a civilian research organization against a military research and procurement organization.

Let's start with Stack, shown here. Recall his vision was for a ground launched turbojet propelled high speed aircraft which would approach but not necessarily break the sound barrier. In other words, his interest was in developing a transonic research aircraft. By definition transonic means approach the speed of sound only. He wanted to explore the "sonic frontier." He was very open about his position: he wanted to collect data for further research.

John Stack insisted the aircraft employ a turbojet. His position with rockets was they were unsafe. Hansen noted Stack had been campaigning privately for NACA to obtain military support for a turbojet powered aircraft to do high-speed research. He had even gone to Colonel Greene and Jean Roche at AMC's liaison office at Langley to persuade them to support a transonic research aircraft.

Hansen said Stack highlighted the words of Langley’s chief test pilot, Melvin Gough, shown here:

“No NACA pilot will ever be permitted to fly an airplane powered by a damned firecracker!"

Stack also held that a majority of Langley pilots opposed even the idea of a transonic aircraft. Hansen wrote:

“They (Langley pilots) had felt that they were being asked to risk their lives because wind tunnel personnel were unable to do the necessary work on the ground. Now pilots were going to be asked not only to sit in the cockpit of a radically new airplane, atop a heavy load of explosive fuels, but also to rely on only a rocket to keep them aloft! No pilot in his right mind would want to fly this plane.”

Stack further felt a rocket powered aircraft could not meet research needs because it would not be aloft long enough to collect the needed data. Rockets ate a lot of fuel quickly, as you'll see with the X-1. This need to collect data was a centerpiece of Stack's approach. Stack wanted to get aerodynamic data at high subsonic speeds that he could not get in the wind tunnel. That was why he proposed a "flying laboratory" in the first place.

In early 1944, the AAF undertook two separate studies to grapple with this sound barrier question:

  • The Development Engineering Branch of the Materiel Division at AAF Headquarters decided to study aircraft aerodynamics at speeds ranging between 600 and 650 mph, which were short of the agreed upon speed of sound. So that was at the Pentagon level.
  • Kotcher in turn asked the Design Branch of the Wright Field Aircraft Laboratory to compare the General Electric (GE) TG-180 turbojet with 4,000 lb. thrust to an Aerojet rocket engine with 6,000 lb. thrust. This would be a major point of the sound barrier debate: turbojet vs. rocket. I don’t think anyone seriously thought a propeller drive aircraft could do the job.

Recall that by this time, 1944, Theodore von Kármán was the unofficial scientific advisor to General Arnold. And, in 1941, Kármán, an American research engineer, helped establish the Aerojet General Corp. which produced rockets. Also recall General Carroll of AMC had asked Kármán if it were possible to build an aircraft that would go Mach 1.5. and Kármán responded to the affirmative.

You've got to love this Ezra Kotcher, and there's more to come after this next note. While those two studies were underway, Kotcher began his own study, which he designated the "Mach 0.999" study, cleverly using Mach 0.999 just short of Mach so as not to scare the brass too fast. Hansen described the study using the phrase "surreptitiously designated 'Mach .999,'", meaning keep the notion of going faster than Mach secret because it might not or would not be approved.

There is no doubt, however, Kotcher was committed to breaking the sound barrier and was convinced a turbojet could not power the aircraft through it. In his mind only a rocket could do that. It turned out he had read the tea leaves correctly. The Army was looking forward to using this "flying laboratory" as a window to developing fighter aircraft that would travel beyond Mach 1. Recall early on the idea was to build a research aircraft only and not something that would lead to a new fighter aircraft. General Arnold told Kármán in November 1944 to report on what he saw as the future of aviation. Arnold told him:

"Supersonic speed (was a) requirement.”

Kotcher had a friend in court to be sure.

I'll get just a bit ahead of myself again and say, in response to Arnold's direction, Kármán prepared two reports, published in mid-1945 and toward the end of 1945. One was entitled “Where we stand” and the other “Toward new horizons.”

Dr. Hallion, in a paper I mentioned previously, said the second report “confidently predicted a future for the Air Force built around supersonic manned and pilotless aircraft and missiles, atomic weapons and atomic energy, operations over global ranges, the ability to fly and navigate with greater precision and safety, the ability to attack in all-weather conditions with devastating force and greater accuracy, and the ability to defeat and counter enemy efforts to defend against aerial attack.”

That all translates to achieve air supremacy and keep it. Like Arnold, the project had caused Kármán to look forward, way forward. I can imagine the attitude. It might be like my wife's grandmother use to say: Research? Tish-tosh.

So while NACA was doing its thing, General Arnold had quietly set the tone for what the Army was going to do, Kármán was studying the problem committed to a supersonic Air Force, and Kotcher was wheeling and dealing not only to get the Army's approval to take this first bold step, but to set Bell Aircraft in motion to get the design going for real. Let's look at this latter point.

Now please remember, there was a lot of activity going on simultaneously, but we have not yet nailed a down a firm NACA-AAF decision on the mission objective. This was, after all, to be a joint NACA-AAF project.

In spring 1944 Kotcher was in the final throes of completing his "Mach 0.999" study.


Dr. Hallion's paper "Supersonic Revolution," tipped me to an exciting matter of teamsmanship. Kotcher's “Mach 0.999” study was done "in conjunction with Sergeant Alex Tremulis, shown here. He was an AAF NCO and wold become an automotive stylist who would go on to create the legendary postwar Tucker (Torpedo, as shown above)."

A short pause. The Tremulis story is an interesting one on its own. The website
Coachbuilt is the place to go to read about him in-depth. Coachbuilt said this about him:

"WWII was causing men to be called for the draft, so on July 23, 1941 he reported for duty at Fort Sheridan, Illinois. He was then assigned to the Air School at Chanute Field, Illinois. He brought his art portfolio with him and showed it to Lt. Colonel Myron A. Sine, USAAC Area Air Officer. Sine quickly concluded Tremulis needed to go to Wright Field where all the AAC design work was done. He then had to visit the personnel officer, Lt. Colonel O.L. Rogers. Rogers was summarily impressed with the portfolio and seven weeks later Tremulis reported to the AAC AMC, Engineering Division at Wright Field. He was assigned to the art department where he could create renderings of proposed aircraft.

"His talents as a first-rate illustrator came in handy while serving in the United States Army Air Corps during the Second World War, where, according to Lt. Col. C.E. Reichert, chief of the design branch at the Wright Field Aircraft Lab, Tremulis 'Put life into dull three-view drawings [which] helped to sell many an airplane design to the nation's top military chieftains.'

"Designer Audrey Moore Hodges praised him stating:

'Alex was just so far ahead. He was an absolute genius, and he could keep you spellbound for hours with his ideas.'

"Design historian Penny Sparke recalled:

'His fertile imagination was clearly geared to space-age images, and it aligned him with much of the thinking in post-war car design.”


Kotcher got hold of Tremulis and worked him into his Mach .999 study. Kotcher asked him to develop a design concept for a supersonic rocket powered aircraft. The study contained the sketch shown here, which was done by Tremulis. It is remarkable how closely this sketch resembles the X-1A. Indeed the Mach .999 study inspired the Bell X-1.

Dr. Hallion then further underscored what a clever guy the AAF had in Kotcher. Not only did he wiggle the way forward to get General Arnold and others to commit to a supersonic aircraft, he "just happened" to meet with Bell Aircraft chief engineer Robert Woods, shown here.

"In late November 1944, Kotcher used Tremulis’ seductive drawing to persuade Bell chief engineer Robert Woods to accept the challenge of building the world’s first supersonic airplane, launching Bell and the Army Air Forces on the path to the XS-1."

John Anderson and Richard Passman reported that Robert Woods, the chief of engineering at Bell Aircraft, "dropped by (Kotcher's office) for a casual visit and expressed a general interest in transonic developments." Kotcher and Woods had a meeting of the minds and, as Hallion said, Kotcher got Woods to commit Bell to the project, which by this time was AMC had designated MX-524.

So Woods "dropped by" Kotcher's office on November 30, 1944. While Kotcher worked hard to convince Woods to accept the challenge, Kotcher already had received the approval of the Army in mid-November to design and acquire what came to be known as the XS-1. Not only design such a plane, but power it with a rocket engine and attempt as early-on as possible to fly supersonically. According to Anderson, it was clear right then that the AAF's vision was going to be quite different from that of NACA.

The AAF without doubt was on the path to develop a special research aircraft employing a rocket engine with a goal of exceeding the speed of sound. However, Kotcher was very careful not to lay those objectives on everyone's lap too visibly, or they might start to tremble. I'll highlight two examples:

As mentioned earlier, Robert Woods of Bell Aircraft "just happened to drop by" Kotcher's office in November 1944. This meeting occurred a month before NACA was to host a set of meetings on the subject. Kotcher showed the Tremulis sketch to Woods. AMC had received a go-ahead from the AAF on April 15, 1944 and Kotcher obtained a project designation, MX-524 at about that time. It's now November 1944 and Kotcher is working to bring Bell Aircraft on-board, knowing full well he had all the AAF approvals he needed to get started. But again, not wanting to scare anyone away from his project, Kotcher old Woods the new aircraft would not initially be required to exceed Mach 0.8. Kotcher knew the objective was to break the sound barrier.

Second, let's look at the MX-524 designation. Andreas Parsch produced a listing of "
Designations of US Air Force Projects." He said, "The MX tables were generated from a list of MX project designators compiled from declassified USAF records by George Cully. Cully was a retired USAF officer and independent research professional" who had served in multiple important Air Force historical office positions. The MX-524 is listed as a "Rocket-powered transonic research aircraft." The listing also says it was replaced by MX-653 which is listed as "Transonic research aircraft (XS-1/X-1); continuation of MX-524."

So on the surface transonic was the name of the game. But rocket-powered was in the plan. Kotcher was not necessarily lying. The Bell XS-1 did not go faster than the speed of sound until its 50th flight, so it did take a while. Much like Stack had intended, the AAF and Bell tip-toed up to the sound barrier and then Yaeger blasted through it.

Having committed Bell to the project, Woods returned to Buffalo and immediately formed a design team: Bell chief engineer Robert Stanley, shown here, project manager Robert Frost, Benson Hamlin later replaced by project engineer Stanley Smith, and others. Robert Stanley was an aeronautical engineering graduate of the California Institute of technology and was a pilot of the P-59 jet fighter, America's first turbojet fighter. This photo shows Stanley in the P-29A cockpit.

Dexter Rosen wrote a letter to Air & Space/Smithsonian on October 11, 1993 challenging its report crediting Robert Woods as the designer of the X-1.

Rosen said Benson Hamlin, shown here, conducted the preliminary design working with a small cadre of engineering specialists. Rosen said they finished the project in 90 days. Rosen also implies there were serious differences in design philosophy between Woods and Hamiln, causing Robert Stanley to reassign Woods to other duties. Rosen wrote:

"Ben Hamlin and his group were solely responsible for defining all the design parameters which subsequently were incorporated in the detail design resulting in the historic X-1 airplane."

However, Leslie V. Beukema, also wrote
Air & Space to take issue with Rosen's views. Beukema said he was a design engineer in Bell's aerodynamics department and was assigned to work with Benson and his group. He commented:

"I must take issue with Dexter Rosen on the role Robert J. Woods played in the design of the X-1 … Woods worked closely with us during the entire preliminary design phase. Hamlin did the theoretical work while I made all the design layout drawings, as well as the three-view general arrangement drawing. This defined the overall geometry and placement of all major components and was in basic agreement with Woods' design concept sketches. Upon completion go the preliminary design phase, Woods proceeded to other projects but continued to give his input to the production design team."

Then, toward the end of December 1944, the Army went to Bell to negotiate procurement of a rocket-powered aircraft that would break the sound barrier. The project retained Kotcher’s MX-524 research designation. Stanley’s team at Bell began development of the “Experimental Sonic-1” aircraft, labeled the XS-1. It's interesting to see how Bell seems to have skirted whether it would be transonic or supersonic by giving the program that title.

It is at about this point that one might conclude the mission objective of the "flying laboratory" had been nailed down: rocket powered aircraft listed as transonic with a strong undercurrent of supersonic.

At about the same time Kotcher and Bell were doing their thing, John Stack was was in hot pursuit of an alternative, one that would be turbojet powered and be transonic.

Hansen wrote that Kotcher told Stack in summer 1944 the Army was going to go with the rocket engine. As I reported earlier, Stack immediately went to the Navy. He saw the AAF was calling the shots, in large part because the AAF was paying for the MX-524 project. But Stack remained convinced the AAF would not get many flights from a rocket powered aircraft. Stack and his team already had a design for a turbojet.

According to Hansen, the Navy had not done much aircraft research. However, the Navy was after a high-speed combat fighter. For his part, Stack stuck to his guns. He believed research work needed to use the turbojet and approach very high speeds but not break the sound barrier. In turn he felt that would provide the data that could be used to determine how best to break the sound barrier.

George W. Lewis, Director of Aeronautical Research for NACA (shown here) was good friends with Capt. Walter Diehl, USN, who served with the USN’s Bureau of Aeronautics (BuAer). Both men helped Stack detail Lewis' chief engineer, Milton Davidson, to work with the Bureau’s aviation design research branch to develop specifications for a transonic research aircraft.

In September 1944 Abraham Wyatt of BuAer proposed the navy procure a high-speed research aircraft. It would use a turbojet, take off from the ground and land under its own power, and would supply sorely needed research data. It would not exceed the speed of sound. The design closely matched what Stack's team had developed. The Navy tasked the project to Douglas Aircraft and told its people their design would have to achieve NACA's complete approval.

David L. Boslaugh, Captain., USN (Ret.) wrote a paper,
"First-Hand: The D-558-I Skystreak Project - Chapter 4 of the Experimental Research Airplanes and the Sound Barrier." There would be three phases:

Phase 1 was named the "Skystreak." It had these objectives:


  • "It would use the most powerful gas turbine jet engine available, which at the time was the General Electric TG-180
  • "The project would use the maximum capacity of the TG-180; that would in theory propel it up to a speed of Mach 1.
  • "The craft would operate (take-off) from the ground.
  • "It would carry 500 pounds of flight instrumentation."A Skystreak D-558-I aircraft in flight is shown here. The contract was let to Douglas in June 1945. Three aircraft were built, each one flew, totaling 228 flights all together. A second batch of three aircraft was ordered but canceled.


The D-558 “Phase 2” evolved to become the D-558-2 “Skyrocket." It was a Navy-NACA project. It had a hybrid jet/rocket propulsion system, was swept winged, and was dropped from a mother aircraft. It was the first US aircraft to exceed Mach 2, or twice the speed of sound. The "Skyrocket" first flew on February 4, 1948 and flew to Mach 2.005 on November 20, 1953. It flew its final flight in 1956. It had completed 21 contractor flights.

There was a Phase 3 which was to adapt the resulting aircraft to be a combat aircraft. This never materialized.


As an aside, the follow-on to the Bell X-1, the Bell X-2 "Starbuster," looks very much like the Skyrocket. It was a USAF-NACA project. The X-2 set an altitude record of 126,200 ft. and a speed record of of Mach 3.2 at 65,000 ft. However, this latter flight, piloted by Milburn "Mel" Apt went into a spin when he tried a banking turn still above Mach 3. The aircraft spun out of control, he ejected, the aircraft crashed, and Apt was killed. "Starbuster" flew its first flight on November 18, 1955.

I'm going to stop here and answer the question I posed earlier, which was to get a decision on the mission objective: transonic or supersonic.

My short answer is build two aircraft, one transonic, one supersonic. Or, as I might like to say: Punt.

Hansen described the resulting situation for the "flying laboratory" as follows:

"Thus by early 1945 the development of two different transonic research airplanes was under way in the United States: the rocket-powered XS-1, being built by Bell under Army Air Forces sponsorship, and the turbojet-powered D-558 being built by Douglas under Navy sponsorship. Though researchers at Langley would actively assist in the development and flight-testing of both airplanes, they would have reason to prefer helping with the D-558. It was most like the research airplane they wanted."

My purpose is to focus on the Bell X-1. I written a short appendix which highlights a few notes on the NACA-Navy D-558 effort.

Bell X-1 propulsion system

Hansen wrote, "On March 10, 1945 the AAF notified NACA it was awarding Bell a contract to develop a rocket powered research airplane." So that was that.


There was a group called the American Interplanetary Society (AIS) that formed in April 1930. The society's members were mostly science fiction writers. Science fiction was huge in the US at that time, giving young people a chance to dream about what could be. Four men, Lowell Lawrence, George Edward Pendray, Hugh Pierce, and engineer John Shesta, were members of the group. These men began designing rocket engines as part of this society. The photo shows AIS's first successful launch of the AIS #2 Rocket on Staten Island on May 14, 1933.

This group incorporated under Lovell Lawrence (shown here) as Reaction Motors, Inc. (RMI) in 1938. It was the first commercial rocket company in the US. It pursued contracts with the Navy and got its first contract to build rocket engines with the Navy in 1942. .

I noted earlier according to Hansen, the Navy had not done much aircraft research, though it was after a high-speed combat fighter. I'll interject here, however, that the Navy was interested in rockets. But it interest, in the main, was in rockets for space. The National Academy of Sciences and Department of the Navy did a study regarding the "
Navy's needs in space for providing future capabilities," published in 2005. That study said, in part, "The Navy, more than any other Service, embarked on a systematic program of investment in and support of basic research in its own in-house laboratories, in universities, in university-associated contract research centers, and in selected industrial research centers … Almost all of the modern space-based capabilities available to the DOD and the Navy are traceable to early investments in basic research made by the Navy and other DOD Services in the decades after the war."

A Princeton student, James Hart Wyld, shown here, had developed a two-pound self-cooled rocket that provided 90 lbs. of thrust back in 1938 and the Navy contracted RMI with Wyld as its research director to build more rocket engines, mainly for Jet Assisted Takeoff (JATO). By 1942 RMI was producing an engine with 1,000 lbs. thrust and by 1943 the company told the Navy it could produce 3,400 lbs. of thrust. The New Mexico Museum of Space History has said, "(Wyld's) concept of a regeneratively cooled liquid engine formed the basis for all modern liquid-propellant rocket motors." Simply said, the walls of the combustion chamber and the nozzle of a liquid rocket engine must be cooled. Regenerative cooling means one or both propellants are circulated as coolants around the outer surface of the wall to be cooled.

The Army contracted RMI in 1945 to develop a rocket engine for the first "X" series of experimental planes. Fundamentally the X-1 used four of Wyld's engines, each providing 1,500 lbs. of thrust totaling 6,000 lbs. of static thrust. Static thrust means the thrust developed by an airplane engine that is at rest with respect to the earth and the surrounding air.


The X-1 used RMI's four-chamber XLR-11 rocket engine, shown above. It was the first US rocket engine developed specifically for use in an aircraft. I want to show another photo of the engine.


I'm showing this photo to give you a sense for the size of the engine. Given that it powered the Bell X-1 to go faster than the speed of sound, it is rather small. In fact, it was compact. You'll see where it was located at the rear of the aircraft in a graphic on a moment, and you'll see it had to be small to fit.


Used in aircraft such as the XF-91 "Thunderceptor," it was so compact it could be mounted under the jet's tailpipe. The engine was employed to attain fast climb and high-speed interception. The XF-91 was a heavily modified version of the F-84 "Thunderstreak" which was highly successful in the Korean War.

Military Factory has said:

"The chief propulsion system for the X-1 became the XLR-11 liquid-fueled rocket engine (by Reaction Motors, Incorporated) which featured a four-chamber arrangement. As a rocket, the system would provide for only a short window of consistent thrust until its fast-burning fuel was used up. It was during this window that the all-important flight data would be collected for later assessment. The multi-chamber approach allowed the pilot to vary thrust through 1,500 lb thrust increments. The engine was buried within the stout, rounded fuselage (said to mimic the shape of a 0.50 caliber cartridge) of the X-1."

I'd like to piggy-back off the idea of burying the engine within the stout, rounded fuselage. This diagram shows the placement of the XR-11 engine. I'll show you the full schematic of where components were placed in the entire fuselage later when I discuss the fuselage. I will say here there are two propellant tanks tied to the engine, the liquid oxygen tank just forward of the wing, and the ethyl alcohol tank just to the rear of the wings. And of course, all that had to be linked to the engine and timed to fuel the engine correctly. The pilot also was tied to the engine, firing each of the four as determined by the pilot up after being dropped from a B-29 bomber (sometimes a B-50 bomber was used as well).


Chalmers "Slick" Goodlin, an American who joined the Royal Canadian Air Force (RCAF) during WWII and then became a Bell test pilot, found the XLR-11 engine to be some cause for cogitation. He said:

“Well, I first operated the rocket engine in a special test cell at the Bell facility at Niagara Falls. And I must say that it was a very unnerving experience because the rocket engine made such an ungodly noise and shook the whole building to its foundations. And that was the most worrying thing about the entire X-1 program was the rocket engine. I wasn't worried about the air frame, but the rocket engine with its volatile fuels, which were liquid oxygen and ethyl alcohol, gave one some concern … (My greatest concern was) that we would have an explosion in the rocket engine.”

Goodlin noted the airframe design obstructed the pilot's ability to see behind him. When he flipped the ignition switch, he might not know whether the engine started properly or whether his aircraft was on fire. He would have a chase plane and the pilots would call him and see if all was okay. And they did that frequently.


I'd like to borrow a transcript presented at and some other pilot remarks to emphasize this visibility issue and the flight process. This comes from a flight Yaeger took on December 12, 1947. Jack Ridley and Major Arthur Murray were flying F-86s such as shown here, Ridley low chase, Murray high chase. Major Harold Russell was flying the B-29:

DeYoreo: Roger, we’re all clear to drop at any time.
B-29 Pilot: Okay, I’m building up speed, 32,000 feet now, 210 miles an hour. Charlie, when I kick you out, you will probably be about approximately 10 miles north of Victorville on a heading of 280 [degrees].
Yeager: Okay. Boy, make sure it’s a minute when you drop me. It’s about 30 seconds from now, I reckon.
B-29 Pilot: Okay. You give me the word for the countdown.
Yeager: Okay, start your countdown slowly.
B-29 Pilot: Okay, starting countdown starting from 5 down to zero. 5 – 4 – 3 – 2 – 1 Okay, drop her Danny.
Co-Pilot: Drop.
Yeager: Firing (Chamber) 4.
Chase (Ridley): No light, just fuel.
Yeager: Is it on now?
Chase (Ridley): Yes.
Yeager: Fired #2.
Bell Truck: What cylinders are on, Chuck?
Yeager: #3 coming on now. Start.
Yeager: Cylinder seconds on 250 right now.
Yeager: Cylinder seconds back to 97 right now.
Bell Truck: We have your time, Chuck.
Yeager: Okay.
Yeager: Push over.
Bell Truck: 20 seconds.
Chase (Ridley): Got him in sight, Kit?
Chase (Murray): No, he’s going out of sight – too small.

Yaeger has remarked, "After drop, clear of the B-29 you'd fire off one, two or three or four chambers of the rocket motor. They were not throttle-able. You could just select the chambers either on or off, and you ran it until it ran out of fuel. And then you dead sticked into, into Roger's Dry Lake."

Slick Goodlin addressed it this way:

"So then when the drop took place, one would sort of count to ten and hit the rocket engine control. And we had four positions on the rocket engine for each rocket chamber. And to fire up one rocket. And of course the first time I did it, it was like being hit in the back with a lead boot. And the aircraft accelerated very, very rapidly. And of course as one increased the thrust by adding more rocket positions—actuating more rocket positions—well, the aircraft could go very fast indeed, and quickly leave behind the B-29 and the chase plane. And of course the first time I did that, why shortly after I accelerated, the fire warning light came on. And that caused the adrenaline to flow. And so I immediately shut off the rocket motor and called Dick Frost on the radio, who was flying the chase plane, and asked him if he could see any fire—that my fire warning light had come on. And of course he was way behind me and said he couldn't see any evidence of fire. But after I had slowed down, why he could pull up behind me and he could still see no evidence of fire, but my fire warning light was still on. So I dumped the rest of the fuel and went back to the landing area and set the airplane down. And sure enough we had sustained a rather serious fire in the engine compartment."

Bell X-1 wing design: straight or swept, and how thick?

A lot of work, thinking and debate went into designing the wings. Swept wings were disregarded.

First, the AAF specified straight wings. Peebles said that was because the AAF had planned its future jets using straight wings. In the 1940s, most airplanes had straight wings. De E. Beeler of NACA said, "The straight wing, we advocated that basically because of flight tests we did with a World War II fighter."

Robert T. Jones of the Langley Research Center threw a fly in the ointment. He labored through many scientific papers and his own mathematical calculations and concluded that a V-shaped or swept wing would “minimize compressibility effects.” He told John Crowley, the chief of research at Langley about his analysis and asked permission to run some tests. Crowley approved. Dr. Hallion wrote:

"In the fall of 1944, Robert T. Jones, a gifted aerodynamicist at the Langley laboratory, had independently postulated the concept of the sharply angled delta and swept wing as a means of delaying and minimizing transonic and supersonic drag, basing his work on earlier aircraft and missile design concepts by Michael Gluhareff and Roger Griswold, and the theories of émigré NACA aerodynamicist Max Munk. Like Munk’s ideas, Jones’ work stirred great controversy until, in the late spring of 1945, American researchers sifting through the rubble of the Third Reich’s aeronautical laboratories discovered the tremendous investment German engineers had made in swept-wing and delta aircraft and missiles."

However, Dr. Theodore Theodorsen, head of the Physical Research Division, blew a gasket. He was highly critical of Jones’ work, according to Peebles, calling it “hocus-pocus” and “a snare and a delusion.” He suppressed Jones’ papers from publication. NACA agreed with him, saying he had no experimental proof to justify his conclusions.

The tests Jones requested went ahead and concluded Jones was correct. The swept wing was the way to go. Henry Reid, Langley’s engineer-in-charge, went ahead and distributed the paper. In the mean time, as engineers began to go through German documents they found the Germans had done a lot of work on swept wing aircraft. Indeed NACA lagged far behind. This revelation angered the military.


Actually, Lt. John William Dunne, an Irishman in the British Army and an aeronautical engineer built a swept-wing airplane that first appeared in 1907, shown above as the D-5. It flew successful test flights on March 11, 1910. The aircraft showed remarkable stability and performed exceedingly well. The aircraft was produced by Short Brothers. The magazine Flight said this in its June 18, 1910 edition:

"There is no doubt that this flight marks an important period in the development of the aeroplane, and although the outcome of it can only be vaguely surmised, this in no way detracts from its present importance, and should increase, rather than otherwise, the amount of interest in the machine itself.”

But despite the science behind the aircraft and its test flights, the notion of swept wings did not gain popularity. By WWII, straight wings were seen as "ideal."


The Germans began to look at swept wing design as early as 1935. Dr. Adolf Busemann was a German aerodynamics pioneer. He presented a paper in 1935 that showed the benefits of swept wing design, incredibly in the supersonic and transonic regions. Their aeronautical engineers proved swept wings were useful and they were employed on the Messerschmitt Me 262, as shown here. Busemann moved to the US in 1947 and worked for NACA's Langley Research Center.


George S. Shairer was on Dr. von Kármán's team that visited Germany in May 1945. He found the Germans had been experimenting with all kinds of wing designs, swept forward, swept back, and aircraft with no tails. Shairer was aware of R.T. Jones' work on the swept wing. Having seen models of swept-wing aircraft in Germany, Shairer wired home and said: "Stop the (B-47) bomber design." The design was changed. The fist XB-47 would roll-out in 1947, shown here in flight.

The XS-1 design program began in late 1944 and had been moving along with its straight wing design. General Alden Crawford, chief of the Research and Engineering Division in the Office of the Assistant Chief of Staff for Materiel at Air Force headquarters, asked why the swept-wing theory had not been addressed during earlier design reviews. As it turned out, NACA people had informed the AAF about Jones’ swept-wing theory, but as I indicated earlier, had decided not to rock the boat of its future jet planning and stuck with the straight wings. Peebles said NACA went along with this decision because it did not want to overload development of the research aircraft with another unproven design concept.

The next item had to do with how thick the wings ought to be.

Hansen reported that Langley designers wanted a “thin wing section to minimize buffeting, loss of lift, and control problems that the experimental aircraft could probably experience at supercritical speeds.” The objective of thin wings was to dissipate or scatter the shock waves at these very high speeds.

However Hansen said the Langley engineers were vexed over this approach.They were worried the most about a “shock stall” once the aircraft achieved between 0.75 and 0.09 Mach. John Stack was in the thick of the debate. Stack and his group wanted thick wings. He agreed the thinner wing would obtain high speeds, but he argued that the thicker wings would get them as far into the supercritical region as possible. Further, he felt thicker wings would provide greater lift on landing and would provide needed strength in what he saw as an uncertain area.

Hansen opined that Stack was simply trying to do what he had always wanted to do, and get the aircraft into areas short of Mach that “aerodynamicists were most interested in studying and correlating with tunnel results,” to wit, use thicker wings.

Stack would now come up against Robert R. Gilruth, shown here, an engineer from the University of Minnesota who was in charge of Langley’s flight research section. Gilruth was certain thick wings would create problems. He felt thin wings would make the aircraft safer and had the highest probability of breaking the sound barrier.

Fundamentally the disagreement centered on whether to keep the aircraft just below Mach or go ahead and push it through Mach. We have seen this as a top issue throughout the development of the X-1. Floyd Thompson, Langley's chief of research, had 20 years under his belt in NACA flight testing. He was the one who would have to decide. Thompson concluded Gilruth was right: a thin wing it would be.


By this time in our story, you know John Stack well enough to know he would not give up. He pushed for two sets of wings, one eight percent thick and the other ten percent. The thickness is described as a percentage by dividing the thickness from the bottom to the top of the wing at its greatest point by the “chord line,” which is the distance from the leading edge to the trailing edge. That gives you a percentage.

NACA advised Bell to build two sets of wings, one at eight percent and one at ten percent. Bell complied with the advice. It built the first XS-1 with the thin wing. Hansen remarked that Gilruth's decision was one that would quietly advocate breaking the sound barrier as an objective. That of course had not been a NACA-Stack objective. The other point of interest is the argument was an intra-NACA one more than involving anyone else. Bell simply accepted the advice but, as an AAF project, was sure to make the first aircraft with the thinner wing to give the highest probability of breaking the sound barrier, which was the AAF objective all along.

So, here we are again: debate transonic vs. supersonic, build two aircraft; debate thin wing vs. thick wing, bold both!

Bell delivered X-1-1 (serial 46-062) to the AAF in December 1945. It had the a wing with eight percent thickness. Jack Woolams took it on the first glide flight at Pinecastle. The AAF sent it to Muroc in October 1946. Slick Goodlin took this one up on its first glide flight at Muroc on October 11, 1946.

The X-1-2 (serial 46-063) had a 10 percent ratio wing. The AAF had agreed to lend X-1-2 to NACA. The two agreed the former would employ X-1-1 to attempt to go faster than the speed of sound as soon as possible and then NACA would then use the X-1-2 with its thicker wing on transonic flights. Conway remarked, "The Air Force wanted the XS-1 to achieve supersonic speeds quickly, so that it could be used as a prototype for a supersonic combat plane." You might recall early in the discussions all hands agreed the "flying laboratory" was to be purely a research aircraft and not be used as a follow-on or prototype for a combat aircraft.

NASA's Armstrong Fact Sheet edited by Yvonne Gibbs said "Bell had proven the airworthiness of both aircraft up to speeds of Mach 0.8."

Conway wrote further, "The NACA wanted a longer duration, more systematic test program to collect data for comparison with wind tunnel data and to inform later designs."

X-1-1 was the one that would first break the sound barrier.

As an aside, a third X-1 in the series was produced but the AAF decided to cancel the contact. NACA picked up the contract. This aircraft exploded on the ground burning the pilot. He did survive though his recovery took a very long time.

Let's now move over to the horizontal tail wing in the rear of the aircraft, known to the Brits as the "tailplane."


XS-1 tail #6062 was the one to break the sound barrier. I've focused your attention with the yellow arrow to show that the tail-wing used was a "moving tailplane" as the British would say, or a movable horizontal stabilizer as many Americans say.

Arguably this was the most important design feature of the Bell X-1. Originally, the horizontal stabilizer was designed to be adjusted before flight and remain in a fixed position. That design was changed to the moving tailplane. This would allow the pilot to adjust the pitch of the tailplane using an electric motor. One author said:

"General Chuck Yeager has often credited the success of the X-1 with the pilot adjustable variable pitch horizontal stabilizer. It was years before other nations' design teams were able to duplicate this concept."

Ray Puffer, an USAF Historian, said:

“American scientists put the need for a moving tailplane in the X-1 specification but this feature put in there wasn’t particularly designed with that (speed of sound) in mind. It was just happy use of a facility that was already there.”

One unnamed source differs from that view:

"The specification supplied to Bell specified that the XS-1 be equipped with a movable horizontal stabilizer to provide pitch (nose up or down) control when shock waves made the elevators ineffective and spelled out also the rate of movement (one degree/second)."

The moving tailplane was not a new idea. Recall our earlier discussion of the British Miles M52 and Dennis Bancroft, its design engineer. Bancroft said a moving tailplane was absolutely essential to supersonic airplanes. Also recall how all the M52 data was transferred to the Americans, much to Bancroft's dismay.

I have seen reports that say Bell designers did design the tailplane to be moving, but they did so as a ground adjustable device not to be employed during flight. Jack Ridley, a chase plane pilot for the X-1 program shown here, convinced Yaeger he could use it during flight.

Chuck Yeager commented after his record flight that the X-1’s movable tailplane was kept classified for many years because it was so important to high speed flight. He mentioned that it was necessary to control the aircraft. He said:

"Obviously the reason we kept it classified was to keep the rest of the world from finding out about a flying tail that's necessary to control the airplane through the speed of sound."

Yaeger commented further on the tailplane after his record-setting flight:

"ln anticipation of the decrease in elevator effectiveness at speeds above .93 Mach, longitudinal control by means of the stabilizer was tried during the climb at .83, .88, and .92 Mach. The stabilizer was moved in increments of 1/4 - 1/3 degree and proved to be very effective; also, no change in effectiveness was noticed at the different speeds."

He would later say that a faster trim motor was installed to make it easier to adjust the tailplane.


Yaeger said it made the F-86 jet fighter that saw combat in Korea achieve a 10:1 kill ratio against the MiG-15. He noted the F-86, which was subsonic, could achieve supersonic speeds in a dive because of the tailplane.

Al Blackburn, a former North American test pilot, wrote a book,
Aces Wild: The Race for Mach 1. Air and Space Magazine took an excerpt and published it, "Did an XP-86 beat Yaeger to the punch?" I commend the excerpt to you; it's a fun read and gives you some insight into the test pilot breed. I summarize it briefly. Remember, the F-86 was a turbojet while the X-1 was a rocket. Both used the moving tailplane.


The photo above shows the first XP-86, serial PU597 which rolled out in August 1947. During 1947 test flights of this XP-86 one pilot, North American pilot George Welch, shown here on the side, always in an orange helmet, wondered what would happen at 35,000 if he "pushed the nose over into a 25- to 30-degree dive. What then?" Larry Greene, a leader in the aerodynamics section of North American's advance design group, responded, "By 30,000 ft. you're supersonic." So Welch asked about the risk, and Greene said he didn't know, but he guessed not very great. Welch said, "My guess is virtually zero." So Welch took his XP-86 up and put her in a dive followed by a bunch of maneuvers on October 1, 1947 and the belief was he went faster than sound. The problem was it was anecdotal, based on what Welch told his wife and some people hearing "ba-booms" in the sky when he was flying. The test pilots all hung out at the same bars, and effectively a competition developed as to who would for sure break the sound barrier first, the XP-86 or the X-1. The X-1 won the battle officially. Al Blackburn finished the article with this: "For the truly dedicated, it’s not so hard to say 'Leave the laurels to those who need and want them most, we have a job to do,' then laugh all the way to Pancho’s (Barnes’ Fly Inn) to needle the old gal about betting on the wrong contender."

So that was a bit of fun. As a final note on the tailplane, Hansen wrote, "The NACA's most important singular contribution involved the design of the plane's tail section … Stack and Gilruth instead that Bell make an all-moving horizontal surface; that is, make the entire horizontal stabilizer adjustable for the pilot in flight." They also argued the horizontal stabilizer could not be the same thickness as the wing!


Airframe design: The fuselage

Chalmers "Slick" Goodlin, a Bell test pilot who flew the X-1, said:

“I guess one could say that the X-1 was a bullet with wings on it. It was a very small aircraft.”

Recall the British M.52 was also designed to look like a bullet, even though it was a turbojet.


Bell designers examined a .50 caliber bullet flying at supersonic speed. It was quite stable. So they decided that was a good model to use. Actually munitions research on this phenomenon had begun many, many decades earlier. This was known as the Ogival Shape: having a curved, pointed shape.


There was no bubble canopy. The pilot could not see to his rear. De E. Beeler, a NACA aeronautical engineer, said that the pilot "had this high slope, aerodynamically it was perfect, but (the pilot) was stuck behind that. I addressed that earlier.


De E. Beeler also commented on the X-1's door. Beeler said:

"And the next thing is well, how does he get out? Well, by this door. And no seat ejection. And then if he climbs out successfully, and there is a wing right behind him that could make hamburger out of him, and if that didn't do it, it (the pilot) would take up and hit into the tail. So that was kind of a joking type of thing. But aerodynamically, particularly if it was going to be rocket-powered, it looked the most aerodynamically clean configuration I think that we could come up with."

Slick Goodlin put it this way:

"As a matter of fact I was unhappy about the X-1 from the escape potential because it was very badly designed from that standpoint. The entrance hatch was on the side directly in front of a very sharp wing. And I felt that if one had to bail out of the airplane in an emergency, if one didn't hit the wing, one would hit the horizontal tail surface, and therefore I thought it was a very dangerous airplane."


The smooth bullet-like contours were designed to enable the aircraft to slip through the air more easily. As a result, the fuselage was jam-packed. This graphic is a little hard to read. The aircraft carried:

  • Two propellant tanks, the liquid oxygen tank just forward of the wing, and the ethyl alcohol tank just aft of the wings.
  • Twelve nitrogen spheres for fuel and cabin pressurization: one in front of the pilot, nine behind the pilot forward of the wings, two more aft
  • Pressurized cockpit
  • Three pressure regulators
  • A retractable landing gear
  • Elements of the wing that went through the fuselage
  • A 6,000-pound-thrust rocket engine in the rear.
  • There was also some 500 lbs. of special instrumentation jammed inside over the wing elements going though the fuselage.


This is another view, again to give you a sense for how everything was really "full to the gunwales."

I'll note here that two-thirds of the gross weight of the aircraft was in fuel.

All that said, don't forget Eastman N. Jacobs, an engineer at Langley’s airflow research branch concluded early on:

“The development of the jet power units themselves had progressed beyond the development of suitable airplanes to employ them … The revolutionary turbojet engine had to be matched with an equally revolutionary airframe design.”

And that's what was delivered.

Launching the aircraft for flight: ground or air launch

Recall I said earlier that Stack's vision was for the flying laboratory to be ground launched, while Kotcher's vision was for an air launch. Hansen reported Stack sent a memorandum to Langley's chief of research saying "that everyone had agreed at the initiation of the project that five items were the basic requirements of the research airplane," one item of which was to take-off, fly, and land. Stack further reminded the chief that the "basic purpose of all this work" was to obtain actual flight compressibility data that could not be obtained in the wind tunnel.

Hansen further said that at a design review held on March 15, 1945, five days after the AAF notified NACA it intended to award the rocket powered research airplane to Bell, "Bell seemed to be planning for the XS-1 to take-off from the ground rather than to be launched from the air." Indeed Bell's top program design engineer
Bob Woods did prefer a ground launch because that would make the research aircraft more relevant to future aircraft, and was especially hopeful that Bell could obtain follow-on contracts for a number of aircraft to be rocket-propelled armed interceptors. He also felt there would be a five-minute burn time after a ground take-off which ought to be enough to attain maximum speed. Kotcher all along had planned for an air launch. However, according to John Anderson, the AAF had agreed to a ground launch.


Two months after that conference Bell changed the XS-1 to go with an air launch from a B-29 bomber. Benson Hamlin, the project engineer for the X1 program at the time, was responsible for the air launching techniques.

Substantial modifications had to be made to the B-29. Peter Davies describes many of them in his book,
Bell-X-1 on page 29. Bell engineers decided in favor of an air launch in order to save the fuel for the actual flight and therefore give it a fighting chance to go faster than sound. The AAF specified climbing up to Mach 1.2 supersonic cruising speed. Bell engineers knew that a new rocket fuel pump would not be ready in time, so they would have to design for pressurized fuel tanks, which already would reduce the aircraft's maximum thrust by about three minutes, from 5.4 to 2.6 minutes. Having to take off from the ground would take up even more fuel and would negate chances of breaking the sound barrier.

Buried in Stack's objection was the knowledge that the XS-1 would not be able to take-off from Langley with a rocket engine and therefore NACA would lose control if dropped from an AAF mother-ship from some air base.


Relevant to this, Hansen reported that both the AAF and NACA had agreed to conduct a series of unpowered glide tests. One of the objectives would be to find out if there were any peculiarities in the air drop scenario. The AAF selected Pinecastle Field (shown here in 1947) in central Florida near Orlando for the glide tests. NACA had insisted on using Langley, but lost that debate.

Since the field was near Orlando, NACA felt use of Pinecastle would help assess whether the rocket powered plane could be operated from conventional flying fields like Langley, near population centers. The project was secret. Though it was close to Orlando, the field itself offered a remote location for secrecy purposes. It also had a 10,000 ft. runway.

David Boslaugh, Capt., USN (Ret.), writing, "
First-Hand:The X-1 Project - Chapter 3 of the Experimental Research Airplanes and the Sound Barrier," said that Jack Woolams took the first glide test on January 25, 1946, dropped from 27,000 ft. by a B-29. Overall the flight went well. However, he had visibility problems landing at Pinecastle because of the streamlined canopy and landed short and to one side of the runway on the grass shoulder.


The AAF then became concerned about frequent clouds over Florida and spotting the aircraft, so in March 1946 decided to move to Muroc Army Air Field (shown here) in the Mojave Desert where there was a six-by-12 mile dry lake bed and plenty of good flying weather. The photo shows the field in 1946. I believe the NACA Flight Test Unit and the two X-1s were housed in the larger hangar shown by the yellow arrow. The runway extending out into the dry lake bed is at the top of the photo.

While the Pinecastle tests proved use of the B-29 airdrop would work, it cancelled out any NACA plans to use Langley. A conventional airfield was not workable. The net result was that air launch was going to be the only way to go.
According to NASA, there was only one ground launch of the X-1, on January 15, 1949. Yaeger was the pilot, reached over 23,000 ft., his fuel was exhausted, and he glided back for a landing. That occurred about 15 months after Yaeger broke the sound barrier from an air launch.

Yaeger has said the pilots had only about 2.5 minutes of fuel at full thrust.

In sum, NACA would not get a research aircraft that launched from the ground, and it would not be able to test the flights from the airfield at Langley, meaning it would have less control over the tests. I'll also mention that the AAF took control of the flight test program from the contractor on July 27, 1947. NACA would get control later, after the sound barrier was broken.

Let's take a look at what had to be done to prepare for a B-29 air launch. The
Smithsonian has a silent film on-line showing the steps to upload, drop, fly, land, and store the aircraft. There is also an excellent 17 minute film produced by the AAF AMC that shows you the step by step procedure. I've found some photos to help explain, some good resolution photos, some less perfect video grabs. I commend both those websites to you.


A crew employs a tug to tow the X-1 from the hangar to a fueling area.


A maintenance man uploads the liquid oxygen, 300 gallons.


A tank trailer is brought over that contains a 65-35 mixture of alcohol and water by volume respectively. Some 295 gallons are uploaded. The propellant for the rocket engine consisted of the combination of alcohol and liquid oxygen.


The aircraft is then loaded with high pressure nitrogen gas.


The men then tow the aircraft to a spot away from the fueling area for an engine run-up. They anchor the aircraft and operate the cylinders to check the functioning of the ignitor, propellant valves, and the complete motor unit. Here it looks like two cylinders are running. They did not always fire up all four.


Next, the men tow the aircraft to a loading pit. Before being placed in the loading pit, the pilot, in this case Yaeger, checks the aircraft engine tubes and moves around the control surfaces.


Once done outside the aircraft, the pilot goes into the cockpit to check out the controls, once again Yaeger.


The pilot will also briefly check the instruments.


This is another look at the cockpit through the door. It's close quarters.


With the pilot's checks complete, the men tow the aircraft to the subsurface loading dock, also known as the "loading pit." They lower the X-1 into place using cables, very carefully. They lower it backward so the aircraft faces forward.


Once in the loading pit, the maintenance crews check her out yet again.


Now they tow the B-29 to bring her over to the loading pit and place it on top of the X-1.

B29movedintopositionover X1

Special care must be taken as the B-29 is towed over the aircraft because the clearances are very tight. The B-29 mothership has been modified for this mission. The bomb-bay doors have been removed, along with the tunnel connecting the forward and rear pressurized compartments. I commend Peter Davies book, Bell-X-1, page 29 to get some details. The modifications were substantial. However, I will pass on, "Fitting the air-launch carriage suspension devices added 60 lb. to the XS-1."


Fabric straps fore and aft are connected to the cable by the standard bomb hoist. The hoist raises the X-1 so that the men can connect the aircraft to the bomb shackle. Davies' book also details how this was done on page 30, Bell-X-1.


Recall the X-1 went through an engine run-up. So now the B-29 with the X-1 strapped below is taken over to the fuel station to be refueled. The procedure shown to you before the engine run-up is repeated. This fueling operation takes about an hour.

B29withX1prepares fortakeoff

The B-29 is then towed clear of the fueling station, the B-29 crew boards along with the X-1 pilot, engines are started and the B-29 moves into position for take-off. Note the clearance between the bottom of the X-1 and the ground is slim at best. No bumpy rides allowed! Also keep in mind the X-1 pilot rides with the B-29 crew until everyone is ready for him to climb into the X-1.

Bell-X1 under B-29 Launcher

The B-29 takes off with the X-1 under her belly. An FP-80 propeller-driven aircraft is used as a chase plane and for photographing the aircraft in flight. The first captive flight was accomplished on January 10, 1946, I believe from Bell's plant runway. The "stork and baby" then flew to PInecastle on January 18. The first captive flight was flown from Pinecastle on January 21, 1946. The first air-drop glide flight was done on January 25, with the X-1 flown by Jack Woolams of Bell.


When the time is right, the pilot, Yaeger, boards an elevator that takes him down from the B-29 and allows him to get into the X-1. Once in, a crewmember boards the elevator and takes the door down to the pilot. The door is put in place, but the pilot must secure it from inside.


While in the air the X-1 pilot jettisons some fuel.


Once all hands are ready, the B-29 crew drops the X-1 and she's in the air. Next step is to fire up a chamber for propulsion. The pilot then ascends to the appointed altitude, fires up more rocket engine chambers, and takes her for a ride. Each mission would have a prescribed set of objectives. On the 50th flight, October 14, 1947, Yaeger and his X-1 exceeded the speed of sound achieving Mach 1.06 at 43,000 ft. He turned on all four cylinders for maximum power. Most of the X-1 air launches were over Victorville, California, southeast of Muroc.


The engines burned off all their fuel, and Yaeger glided the X-1 to a safe landing back at Muroc Field.

Second generation X-1s

I'll briefly mention that Bell produced a second generation of X-1s, and NASA has posted a fact sheet. The fuselage was 4.5 feet longer, the cockpit was redesigned to allow the pilot to enter from the top, and the aircraft got a new low-pressure turbo pump which eliminated the heavy liquid oxygen and alcohol tanks. That increased the aircraft's calculated performance to Mach 2.7 at 70,000 ft.

One X-1D was damaged after landing, and another, dropped by a B-50, had to be jettisoned because of a fuel leak. It was destroyed on impact. The pilot, Lt. Colonel Frank Everest, USAF managed to climb into the B-50 before he X-1 was jettisoned. The wreckage of the latter aircraft is shown here.

Joseph Cannon was the pilot for a second X-1D. Earlier Cannon had flown the X-1A, prior to Yaeger's record breaking flight. While he was checking the aircraft before a test flight on November 9, 1951, the volatile rocket fuel ignited, destroying the bomber and the X-1 and seriously injuring Cannon. He said, "It took me about a to recover."

Yaeger flew a X-1A on December 12, 1953 and he achieved Mach 2.44 at 74,200 ft. However, the aircraft rolled to the left, Yaeger tried to correct with right aileron and rudder, but the aircraft rolled to the right and started to tumble out of control. Peebles said it tumbled over 50,000 ft. Yaeger was knocked unconscious but came to at 29,000 ft. in an inverted spin. He was able to recover and land at Edwards AFB, California. Another flight on August 26, 1954 reached 90,400 ft. altitude but also experienced some instability issues though not as severe as what Yaeger encountered.

The Yaeger flight was later analyzed to be the result of "inertial coupling." Wikipedia has said "This happens when the inertia of the heavier fuselage overpowers the aerodynamic stabilizing forces of the wing and empennage." Empennage is an arrangement of stabilizing surfaces at the tail of the aircraft. Coupling was not known until high speed aircraft emerged.

As an aside, Yaeger said, "If I'd had (an ejection seat) you wouldn't still see me in this thing."

Between 1954 and early 1957 four more aircraft were destroyed by explosions. The program was terminated in January 1957.

The test pilots and their X-1s: Reacting to aircraft system failures

Up until now, we have discussed a lot of science. Let's now take a look at the realities associated with flight testing the Bell X-1. Mark Wade of Encyclopedia Astronautica has assembled a short brief on each Bell XS-1 test flight. It listed 155 test flights that began on January 19, 1946 and extended through October 23, 1951. X-1A, B, and E test flights were flown through November 6, 1958. The initial record-breaking flight was test flight nr. 50 on October 14, 1947.

As I went through the list, I was struck by the real world problems and challenges experienced by the test pilots. I'd like to give you some examples: multiple nose wheel collapses on landing, nose wheel failure to extend before landing, drop in chamber pressure, rocket cylinders failed to fire, engine shutdowns requiring fuel jettison and glide returns, small engine fires and shutdown, rocket fire and engine shutdown, partial engine malfunction due to faulty engine ignition plug, engine chamber explosion causing rudder to jam, lost cockpit pressurization, engine cutout after two ignition attempts resulting in fuel jettison and glide flight. And of course there were many flights with only minor deficiencies.

Chuck Yaeger, in his autobiography, noted that every flight made in the first X-1 over a three month period had to be terminated prematurely because of fires in the rocket engine compartment. He said there were seven or eight such fires in a row that no one could figure out,

Test pilot memoir - Bob Champine, NACA

Early on, I mentioned W.G. Williams, writing "Machbuster - A Test Pilot Recalls The Early Days Of Supersonic Flying,, Where You Either Broke The Sound Barrier Or It Broke You!" He reported on the memoirs of NACA pilot Bob Champine, shown here standing next to a Douglas Skystreak D-558-I. Williams highlighted this:

"Most of what has been written about these exotic flying machines primarily covers the cold, statistical facts of how often they flew, what speeds were reached on what dates, what types of engine they had, their length and span and other similar types of technical minutiae. Relatively little has been reported about what it was like to climb into one of these weird birds and try to fly them."

Champine flew both the X-1, D-558-I and D558-II (swept wing) for NACA starting in December 1947. He had a degree in aeronautical engineering from the University of Minnesota and wanted to fly instead of becoming a NACA engineer. He flew a variety of aircraft until his first opportunity to fly the X-1 on November 23, 1948. He took some familiarization flights and then took his X-1 through the sound barrier. Champine's memoir is as follows:

"My reaction was that it was a piece of cake. There was no problem; it was very easy to do. I was told that when I got to Mach 1, I should operate the controls through their full deflections. That meant I was to move the controls to full nose up, full nose down, full right roll, full left roll and to kick the rudders just to satisfy myself that the shock waves at Mach 1 left some control but that they were relatively weak at that speed. Since other guys had done it before me, I didn't worry too much and it was pretty much like they said it would be.

"It's true that there was a little tiny bit of buffeting and a little tiny bit of wing dropping, or rocking laterally as I went through the speed of sound, but it was quite controllable. Although at Mach l the controls were not very responsive, as soon as you got through Mach 1, good control response returned because then the wing was all in supersonic flow; the shock wave was attached to the leading edge and the controls were in nice flow again, whereas when you were going through the speed of sound, the shock waves danced on the control surfaces and caused the loss of control. Being in a P-51 in a steep dive with the controls shaking would be of far more concern to me than being in the X-1.

"The first subsonic flights in the X-1 were just one thrill after another. Just dropping out of the bomb bay was a big thrill the first few times...a tremendous thrill...and it was scary. After you did it three or four times, though, and went back to the office and sat down and thought about it, you realized that it was a real cool way of getting airborne with a heavy and dangerous load of fuel. With an airdrop, you were able to start at around 25,000 feet and you didn't have to go through the takeoff and low-altitude climb-out where, if you had a problem, you couldn't do anything about it. But, with an airdrop, if you had a problem after you launched, you could jettison the fuel and glide down to the lake bed. We became very ho-hum about it. It was very routine.

"We did not consider it very dangerous at all. In fact, my salary reflects that. I was out there flying those things on a salary of $2,600 a year and my lifestyle was very austere. I lived in a barracks and it was difficult for me to own an automobile. These barracks were very much like World War II soldiers' quarters; I think that Chuck Yeager may have complained about those living conditions in his book.

"The flights were considered just routine. It was a very ho-hum, eight hours a day kind of operation...for the pilots, anyway. However, you have to realize that in the California desert the wind picks up around noon and so we had to come in early in the morning to do our flying. As a result, the crew preparing the X-1 usually started loading L-O-X (liquid oxygen) and alcohol around midnight. It was a very slow thing because they had to cool down the aircraft like they do on the shuttle today. The loading of the fuels took a long time and the instrumentation guys came in really early to check out all the instrumentation to make sure everything worked and to install fresh batteries and film. Once the fueling started, only essential personnel were allowed next to the airplane, because if the L-O-X and the alcohol got together, there was an immediate explosion. Alcohol spillage of any kind was a dangerous situation.

"Once the aircraft was available for the pilot to go on board, it was very matter of fact, a 'Let's go fly today!' kind of operation. After I had been flying out there for about six months, I got a two step raise so I guess I was doing my job. I didn't ask for the raise; I was just delighted to be one of the flyers. I was like a kid with a new toy.

"The pilot actually entered the X-1 from the B-29 and we usually did that about 5,000 feet above the ground. That altitude had been chosen because, if you screwed up the works, from there you could get released from the B-29, jettison your fuel and still make a landing.

"Visibility through the canopy was very bad, but it was an increment better than looking over the nose of a P-51 on landing, and it was considered to be acceptable for those days. I thought it was even a little bit better than in an F4U Corsair. When you were at low speeds and high angles of attack coming around for a carrier landing in the Corsairs that I'd been flying, you simply couldn't see over the nose and had to look over the side. The X-1 was flown the same way.

"However, when you were making an approach in the X-1, the dive angle was relatively steep because 220-250 miles per hour was the normal glide speed and the nose was down quite a bit. It had a good glide, though. It went a long ways, but when you flared and raised the nose for the actual touchdown, you couldn't see.

"The X-1 was very, very maneuverable. The only place it was deficient was from Mach .95 to 1.01, the transonic range where the controls were not very effective. At high subsonic speeds it was an excellent plane. I can remember Chuck Yeager doing slow rolls in it during his glides.

"When the X-1 was being carried to launch altitude by the B-29, there was always an intercom to communicate with the B-29 crew. When you got into the X-1 and put on your helmet and oxygen mask and got all settled, you would report that you had done so to the aircraft commander in the B-29. The radio communication was a part of the procedures that covered the safety aspects of everything.

"On one memorable flight, we were climbing to launch altitude, around 25,000 feet and, suddenly, I couldn't communicate any more. I had lost all contact with the bomber. I checked all my connections and they did the same thing at the other end, but we couldn't find the problem.

"Since we were very close to the drop altitude, I took my knee pad card and turned it over and wrote on it: 'Secure the drop!' Now, I'd been in the Navy and to a Navy man, to 'secure' meant to stop doing something. I held this up and showed it to the men, forgetting that it was an Air Force crew. The crew chief assumed that 'secure' meant that, even though I couldn't talk, I was all set up to drop.

“As I sat in the X-1, I could see that the guys were getting ready to drop me. Well, I’m holding this card up and hollering at them and making noises as though I really don't want to go and all of a sudden I heard this little ‘pop’ as the bomb shackle broke loose and I was flying. Man, I wasn’t ready to go anyplace and they’re saying, ‘So long, Bob! Have a good trip.’”

“On that flight, it took some extra time but I did get everything set and I was able to run the rocket engines, do the flight card and make a successful flight out of it without talking to anybody. I still don't know why the radio didn’t work.”

“Later, as a result of that incident, I insisted that we install wiring for a light system. A red and green light appeared on the flight deck controlled from the cockpit of the X-1. If the aircraft commander had a red light, he needed to check before dropping the plane; if the light was green, he knew the test pilot was ready.”

“At every little speed increment, we had to operate the controls to measure the rolling velocities, pitching velocities and yawing angles at each of these Mach numbers.”

“Keep in mind that when you ran the engine to maintain fairly high speeds, you didn't have much fuel. With one rocket chamber firing, the fuel usually would run out in ten minutes. If you fired three chambers, you could barely get through Mach 1 and you were out of fuel in about four minutes. With all the chambers firing, the flight was really short. After 13 flights in the X-1, I had only logged 1.2 hours! You had to accelerate, stabilize on your Mach number, do your maneuvers and, by then, you were out of fuel. You'd have to glide down, land, refuel, come back up again and do the same thing at a slightly higher speed. We made those flights repetitively to measure the flying qualities that could be found at the different Mach numbers.

Appendix: The D-588-I "Skystreak."


The specification required using one General Electric (Allison) J35-A-11 turbojet of 5,000 lb. static thrust. It was to attain a maximum speed of 650 mph at sea level. It was a more conservative approach than the X-1. The website said, "It was intended from the beginning to be a research-minded, data collecting platform." Three of six planned Skystreaks flew 229 times from 1947 to 1953.

National Museum of the USAF has written: "Originally developed by the General Electric Co., the J35 was the USAF's first axial-flow (straight-through airflow) compressor engine. Late in 1947 complete responsibility for the production of the engine was transferred to the Allison Division of General Motors. More than 14,000 J35s had been built by the time production ended in 1955."


Commander Turner F. Caldwell, USN (right) set a world's speed record on August 30, 1947 flying four passes averaging 640.663 mph. Major Marion Carl, USMC (left) on August 25, 1947 beat that record averaging 650.796 mph. I do not believe the "Skystreak" flew faster than those speeds throughout the duration of flight tests. Some instability was detected as it approached the speed of sound.