Talking Proud Archives --- Military

Bell XP-77 - Never had a prayer of making the grade

By Ed Marek, editor

January 19, 2018
Join Team Talking Proud


The Bell XP-77 was quite an engaging though confusing program. From where I sit, it grew out of two developments:

  • The AAF needed a light, high speed, altitude interceptor pursuit aircraft. The British Spitfire, Messerschmitt Bf-109 and then the Japanese Mitsubishi A6M Zero underscored why the AAF needed such an aircraft.
  • There was also a military worry that the country was going to run short of light metal alloys. So the Army asked for an aircraft made out of non-strategic materials.

Stephen Wilkinson, writing for Air & Space Magazine, June 2013 noted:

"In 1935, only weeks after Larry Bell founded the Bell Aircraft Corporation, he suggested to his new chief engineer (Bob Woods) that they build a lightweight wooden airplane and enter it in the Cleveland National Air Races to garner publicity. Bob Woods didn’t know much about air racing, but he quickly sketched a slick Thompson Trophy racer concept—which never did race."

So one might conclude then that the idea of using non-strategic materials such as wood hit a positive nerve with Larry Bell.

Wilkinson also remarked:

"Bell Aircraft’s chief engineer, Robert Woods, was a whiz at coming up with boundary-busting ideas (he led the team that built the X-1), but when it came to turning his proposals into products, he was less adept. There’s no better example than his concept for an interceptor, the Bell XP-77."

Researching the evolution of this project requires a very nimble student. Requirements and approaches varied wildly. I’m not sure how everyone could keep up with the changing specifications. I fear I’ll put you through a bit of a wringer as we proceed.

Bell Aircraft people met with the AAF at Wright Field on October 30, 1941. They brought a proposal with them that would produce a compact, single-seat, single-engine fighter constructed largely of wood. Bell called the developmental aircraft the “Tri-4,” and later the “D-6.”

The Bell team had begun work in early 1941 to build a fighter called the Tri-4, which stood for an informal USAAF requirement for "400 hp, 4,000 lbs, 400 mph."

One can get easily lost in the research attempting to nail down the fighter's mission.

As far as I can tell, General Hap Arnold, shown here, wanted an aircraft able to carry one 325-pound depth charge for hunting enemy submarines or one 300-pound bomb for ground attack.

That does not jive with the next description of the mission.

Wilkinson described the mission like this:

"The XP-77 was to have just one job—point defense: protect a single installation, like a base or command center from the bombers coming to attack it. The job required a rapid climb to high altitude, where the interceptor would shoot down bombers from behind."

JapaneseMitsubishiZero MesserschmittBf 109

It also does not sync with reports that said the AAF was very concerned it did not have a fighter that could dogfight with the Japanese Mitsubishi A6M "Zero" (left) and the German Messerschmitt Bf 109 (right). US fighters at the time were fairly heavy, not highly maneuverable, and required powerful engines to get the speeds they were able to get. So I have seen its mission described as a "light weight" interceptor.

You can see the notable differences in mission descriptions, though I acknowledge I have not seen official documents.


Bell’s first request was to get information on the Ranger engine that was to be used. Here’s where it’s tough to understand what engine would be used. Ranger had a series of V-770 engines with a host of variants. The photo shows the V-770-7 engine in a mockup of the XP-77.


This is a closer look. Fundamentally it had a two-piece aluminum allow crankcase, steel barreled cylinders with aluminum alloy fins and aluminum alloy heads. It was an inverted V-12-type inline air-cooled engine, the only such American engine to reach production. In the end, very few AAF aircraft used these engines.

In any event, the standard V-770-6 engine emerged as the one to use. However, only six were available and they would not have a supercharger. The V-770-9 with a supercharger was at least 1.5 years away. With the standard engine, the expectation was that the aircraft could achieve desired results up to 12,000 ft. That apparently was acceptable. The project got the go-ahead on June 10, 1942.


The new aircraft with the V-770-9 supercharged engine was to achieve 410 mph at 27,000 ft using 500 hp. Its gross weight was to be 3,700 lbs., it would carry a 20 mm cannon firing through the propeller hub and two .50 cal synchronized nose guns. This is a graphic that shows the cannon protruding from the propeller hub. I have not found a photo of the aircraft that shows this, which makes me wonder. I have seen drawings o the aircraft design proposal and the gun through the propeller hub is on it. I suspect it never made it to the prototypes.

In any event, the V-770-9 supercharged engine was not available, so the idea was to go ahead with the V-770-6 engine without supercharger for six aircraft and see what happens.

Bell submitted two proposals, one for an aircraft part wood and par metal, another for an all wood construction. The AAF engineers liked the part wood, part metal design but that would cause a delay since Bell had already worked out the all wood version. So the all-wood version was selected.

The aircraft was built from plywood constructed from Sitka spruce. This species is light, soft and relatively strong and flexible, often used for housing and shipbuilding. It is used to this day for experimental aircraft. In October 1941 the National Advisory Committee for Aeronautics (NACA) issued Report Nr. 354, “
Aircraft Woods: Their Properties, Selection and Characteristics.” It is quite technical. For those of you who might like to dig into it, I commend it to you as it looks quite thorough.

Issues arose about gross weight. The design gross weight was now at 3,600 lbs. which was going to make the aircraft unfavorable for this mission. A decision was made to reduce the gross weight to 3,000 lbs. by eliminating a group of requirements in order to salvage performance. However, several design improvements were added.


Bell produced a mock-up for the XP-77 and the AAF reviewed it on September 22, 1942. The AAF said it was “very satisfactory” but then recommended 54 changes. This photo shows a XP-77 mockup at the Langley wind tunnel.

In January 1943 Mr. Omer L. Woodson, Vice President and Assistant General Manager, Bell Aircraft, informed the Army the first aircraft would not be available until May 1,1943, and that the balance would follow at a rate of about three per month. That was a four-month setback. Bell asked for a new schedule with the first aircraft ready by July 31, 1943 followed closely by the next five.

However, Bell also informed the Army that costs were going to rise to a point 365 percent higher than the original cost estimate. This caused turbulence within the Army’s procurement offices, so bad that one general officer suggested cancelling the contract. However, the Army allowed the increased funds.

On May 26, 1943 the Wright Field Engineering Division recommended the contract be terminated. Its people felt Bell had taken on more experimental development than it could handle. They opined the P-63A and P-59A programs would suffer. There was cause for this concern.

The Wright Field leadership felt it was worthwhile to go ahead with two aircraft vice six if for no other reason than to see what an all-wood aircraft would cost. However, Lt. General W.S. Knudsen, shown here Director of Production, War Department, asked Wright to explain why the program should not be cancelled. The authorities at Wright explained they intended to reduce to two aircraft.

As a result, part of the contract was cancelled, Bell was advised of the new two aircraft approach on December 20, 1943. Bell’s schedule was to deliver the first aircraft by January 31, 1944, and the second on March 1, 1944. Bell could not meet this schedule, and said the first aircraft would now be available by the end of February 1943. It then said that date would actually be March 5, with the second aircraft coming available on April 6. Then the expectation was the first aircraft would be delivered on March 6, but on March 7 Bell informed Wright there was a landing gear issue that required a new electrical system.


The net result was the first flight occurred on April 1,1944. The pilot reported the aircraft handled well.

Tests were then moved to Eglin. The highest speeds attained were 361 mph at 5,000 ft instead of 346 mph; the rate of climb was 2900 ft. per minute vice 3050 in the specification. The gross weight had climbed to 3857 lbs instead of holding at 3,700 lbs. And, of course, it was using the Ranger engine without supercharger.

The AAF canceled the program.

I have detailed reports on all the issues that arose during the development of XP-77. There were many. I’d like to conclude the discussion of the XP-77 by summarizing the issues faced by Bell. Remember, the company and the AAF were in uncharted territory shooting for an all-wood aircraft designed to be an interceptor.

  • Bell admitted it lacked experience in use of wood, plastic and magnesium alloys and that it would have to subcontract out to experts in these areas. Bell also said the Ranger engines were posing cooling problems.
  • Bell lacked experience with some of the subcontractors.
  • Subcontractors failed to meet delivery dates
  • Bell unable to commit enough people to the project because of higher priority projects
  • The Ranger V-770-9 high altitude engine was delayed, causing Bell to have to use the V-770-7 which could not provide the needed performance
  • Bell was overburdened with engineering development
  • Bell said the AAF glider program had placed a great deal of pressure on the woodworking industry. Furthermore Bell had to spend considerable training time with subcontractors to assure they met AAF standards.
  • Subcontracting required more engineering and a higher degree of completeness of the drawings.
  • Subcontractors had to be switched out for the wings. Problems were found in the gluing of the wing panels and were barely acceptable
  • During fight testing, the aircraft experienced unacceptable vibrations
  • The manual landing gear retraction system had to be replaced by an electrical system.
  • Overhead, tools and direct materials caused cost overruns, the latter two of which were attributed to the many unknowns connected with producing the first successfully constructed molded plywood fighter aircraft
  • Bell ran into a lot of problems constructing the fuselage and other plywood parts of the aircraft
  • The pilot of the second aircraft attempted an Immelmann maneuver and the aircraft fell into an inverted spin. The pilot was able to recover but shortly thereafter the aircraft went into another spin. The pilot couldn’t recover, bailed out and the aircraft crashed, a total loss.
  • There were significant cost overuns.