Bell XP - 77 The Bell XP - 77 development was initiated by the United States Army Air Forces during World War II to produce a simplified ' lightweight ' fighter aircraft using so - called " non - strategic " materials . Despite being innovative , the diminutive prototype proved tricky to handle and the project was canceled when the XP - 77 did not deliver its projected performance . Design and development . The Tri - 4 ( Company designations , later changed to D - 6 ) project with the Bell Aircraft Corporation was initiated in October 1941 . Originally a design study for the to meet the USAAF specifications for a " very light " interceptor , the XP - 77 was intended to be a small , light fighter much in the mold of the 1930s Thompson Trophy air racers . On 16 May 1942 , the USAAF recommended the construction and testing of 25 XP - 77s . The aircraft featured a single - engine , low - wing monoplane with mainly wood construction , equipped with tricycle landing gear , a Bell trademark that bestowed good ground handling . A sleek bubble canopy also provided all - round visibility ( except forward due to the extended nose ) ; a key requirement for a fighter . While originally conceived using an air - cooled 500 hp Ranger XV - 770 - 9 12 - cylinder engine with a supercharger , the prototypes were delivered with the non - supercharged XV - 770 - 7 engine due to engine development delays . With the anticipated delivery time of the original engine delayed for one and half years , Bell proposed that seven XP - 77s be built using the seven XV - 770 - 7 engines then available . The planned armament was one Hispano 20 mm cannon firing through the propeller hub ( much like the larger calibre 37 mm " moteur - canon " of the SPAD S . XII ) and two 0 . 5 inch Browning machine guns , with the option of either a 300 lb bomb or 325 lb depth charge with the deletion of the cannon armament . The mock - up inspection on 21 – 22 September 1942 produced some concerns from both the manufacturer and the USAAF inspection team . Weight had crept up beyond 3 , 700 lb design limit but delays in the program were experienced when the company resorted to sub - contracting the wooden construction while the ongoing production at the Bell facilities did not allow for the XP - 77 to take priority for research and development . Bell asked and received permission to reduce the production run of aircraft to two prototypes . Operational history . Testing . The XP - 77 project continued to suffer numerous delays , many related to correction of the excess weight issues . A change in subcontractor for the wing assembly also caused headaches as the first subcontractor refused to release necessary parts . Concerns over structural integrity relating to the glue and its binding properties were also difficult to resolve . With the anticipation that contract costs would soon be exceeded , and no hope that the supercharged engine would become available , the USAAF would only continue the project as an experiment to evaluate the use of wooden construction and materials in combat aircraft . The first XP - 77 flew 1 April 1944 at Wright Field but the flight tests revealed vibration problems due to directly mounting the engine to the airframe , without vibration isolation . The long nose and rear - mounted cockpit also inhibited visibility relative to operational aircraft of the time . The XP - 77 proved to be difficult to fly and despite flying without guns or armor , it did not come up to the expected performance estimates mainly because it was woefully underpowered . Further trials were conducted at the USAAF Proving Ground at Eglin Field with the second aircraft , which was destroyed when it entered an inverted spin while attempting an Immelmann , and the pilot bailed out . The development was terminated in December 1944 .