The Bell XP-77 was a flawed American attempt to make a fighter plane made entirely out of alternative materials in the face of massive wartime resource shortages.
Its multiyear developmental cycle was nothing short of a fiasco, only serving to remind designers why the aeronautical industry had moved away from wood in favor of lightweight metal. Apart from its comical appearance, the Bell XP-77 had no redeeming qualities and was quickly retired soon after its maiden voyage.
Nowadays, it’s regarded as one of the most expensive mistakes of the Second World War.
During the course of the Second World War an increasing demand for military equipment created huge shortages of resources. Among the most scarce were strategic materials such as metals ands other alloys crucial in the production of aircraft, which compelled manufacturers to switch them with non-strategic materials from 1941.
As a result several experimental aircraft, such as the all-wood twin-engine Beechcraft AT-10 trainer, began to appear as ersatz replacements.
In 1941 at Wright Field, United States Army Air Force (USAAF) and Bell Aircraft Corporation officials discussed the possibility that the same approach could also be applied to other types of planes. On October 30th, the USAF would formally request Bell’s Chief Designer Robert J.Woods to design a fighter made from alternative materials that could meet the ‘4-4-4 combination’ of 400 horsepower, 4,000 pounds, and 400 miles per hour.
Six months later Wood submitted preliminary schematics for the Tri-4 which he envisioned would be made almost entirely out of wood with the exception of the laminate skin, which would be fashioned with metal. The Tri-4 was also made intentionally small so that it could excel in dogfights. The result of this was the awarding of a contract to Bell in April 1942 which called for the development of a light-weight fighter.
In May American General Hap Arnold would make the first order of 25 Tri-4 fighters. Here Arnold would also request further changes to the design, specifying that the Tri-4 should be equipped with a shackle for carrying a small bomb or a depth charge so it could participate in a ground attack role. As a result, the original 20 mm cannon was replaced with a bombing arrangement.
Given the designation P-77, Bell would base the layout off an earlier design known as the P-39 Model 3, first conceived in 1936, which had attempted to address the same problem, albeit in less desperate circumstances.
Following the inspection of a full-scale mock-up between September 21st and 22nd of 1942 USAAF requested that Bell make no less than 54 changes. Here it was also decided that the single-stage supercharged XV-770-6 engine was to be installed on the initial prototypes due to the unavailability of the two-stage supercharged XV-770-9. As such, six XV-770-6 units originally built for the US Navy were offered up.
Consequently, contract No.AC-30864 was issued on October 10th 1942 requiring the assembly of six XP-77-BE prototypes, two airframes for static testing, another full-scale mock-up, and a single one-ninth scale model to be used for wind tunnel evaluations. Clocking up a total cost of $698,761.88, Bell was also contractually obliged to deliver the first airplane within six months of the agreement.
On the other hand, with Bell Corporation also committed to the production of the P-39 and the development of the new P-59 and P-63 fighters during this period, the P-77 program was the subject of multiple delays. In addition to this, setbacks would cause the total cost of the program to skyrocket to a staggering $2,548,540.46 – almost quadruple the original figure.
This was mainly because it soon became apparent that the XP-77 would be seriously overweight if developers stuck to the 4,000 pound weight goal, resulting in an expensive program to reduce it to 3,000 pounds.
However total expenditure would soon plummet as raw materials once again became more abundant throughout 1943. As such, in August a decision was made to drastically cut down the program.
By December 20th 1943, the USAAF’s order had been reduced to just two prototypes, expected to be delivered on the revised dates of January 31st 1944 and March 1st 1944 respectively. With the project seemingly going nowhere, the planned supercharged XV-770-9 engines were also dropped and the XV-770-6s were kept.
On the other hand, with the news that subcontractor Vidal Research Corporation were unable to deliver the wings on time, a fresh round of delays occurred. With the first wing panel arriving considerably later on February 3rd 1944, the delivery date for the first prototype was pushed back to March 5th.
Difficulties with the undercarriage retraction system postponed it for a further month, with flight trials reorganized for April. Nevertheless that spring, two XP-77 prototypes with serial numbers 43-34915 and 43-34916 were ready to fly.
Successively known as the Tri-4, Design D-6, and Model 32, the Bell XP-77 was a low-wing monoplane made almost entirely from resin-bonded laminated Sitka wood and stressed skin that had an empty weight of 1,296 kilograms, a maximum weight of 1,829 kilograms, a length of 6.98 meters, and a height of 2.49 meters.
Its wings, which were 8.39 meters in span and 9.29 square meters in area, were of cantilever single spar design and had an aspect ratio of 7.56 as well as a NACA 65 low-drag laminar flow profile with a dihedral of 5 degrees. Underneath, the XP-77 landed with the assistance of an electrically-operated nose wheel undercarriage.
Its all-wood fuselage housed a fuel receptacle that had a maximum volume of 52 US gallons, and provision was made for a 32 US gallon auxiliary belly tank. These fed a 520 horsepower Ranger XV-770-6 twelve-cylinder air-cooled inline engine that drove an Aeroproducts two-bladed propellor that was 9 foot and 6 inches in diameter. Overall, the XP-77 had a top speed of 531 kilometers per hour and a service ceiling of 30,000 feet that it could climb to at a rate of 3,600 feet per minute, while its maximum combat range was 885 kilometers.
The Bell’s planned armament consisted of a single 20 mm cannon that fired through the propellor hub and dual 0.50 inch machine-guns situated in the forward fuselage. Later on, at the behest of General Arnold, the cannon was scrapped to make room for a 300 pound bomb or 325 pound depth charge.
On April 1st after an 8 month delay the Bell XP-77 piloted by Jack Woolams took to the skies for the first time with an uneventful 25 minute flight. Achieving a speed of only 531 kph (329 mph) and an altitude of 4,000 feet, the initial performance results were underwhelming.
The Bell was also criticized for having a take-off distance that was far too long, while test pilots complained that it produced unpleasant vibrations at certain speeds, which were doubtlessly made worse by the absence of engine-support vibration dampening mounts.
The fact that the V-770 was mounted on a rigid engine bearer and that the ailerons fluttered at higher speeds also contributed to the unwelcome buzzing.
Nevertheless, it was next transported to Wright Field on May 2nd 1944 where, during a battery of flutter and vibration tests, the nose gear collapsed and the plane skidded along the runway after the pilot attempted a hard landing.
Repairs were completed by July 22nd 1944, after which both models were ferried to Eglin Field for operational testing in late July and early August. During evaluations the XP-77 was discovered to have good handling characteristics but sub-par performance. With a top speed of 531 kilometers per hour, the Bell was a notably slower than conventionally built USAAF heavy fighters and its climb rate was too inferior for it to be classed as an interceptor.
The V-770 engines proved extremely unreliable, a trend that was replicated elsewhere since at around the same time this underpowered propulsion system had also been fitted onto the Navy’s Curtiss Seamew floatplane. During a 300 mile trip to central California, one Seamew pilot would have to ground his craft three times as a result of engine failures and was later forced to parachute out after the V-770 unexpectedly exploded mid-flight. As such, the future of this engine did not look bright.
The XP-77’s poor showing was compounded by a major accident on October 2nd 1944 involving the second prototype which crashed after entering an inverted spin that forced the pilot to bale out. These factors would ultimately lead to the program’s cancellation in December 1944.
Read More X-47A – The Flying Dorito
In the postwar years the XP-77 would make appearances at various airshows but would ultimately end up as a gate guard at an air base entrance where, after a long period of deterioration, it was destroyed.
- Crew: 1
- Length: 6.97 m (23 ft 10 in)
- Wingspan: 8.38 m (28 ft 6 in)
- Height: 2.50 m (8 ft 2 in)
- Max takeoff weight: 1,827 kg (4,000 lbs)
- Powerplant: 1 x Ranger XV-770-7 petrol V12, 520 hp
- Maximum speed: 330 mph (531 km/h)
- Range: 550 miles (885 km)
- Service ceiling: 9,175 m (30,100 ft)