Bell XV - 15 The Bell XV - 15 was an American tiltrotor VTOL aircraft . It was the second successful experimental tiltrotor aircraft and the first to demonstrate the concept ' s high speed performance relative to conventional helicopters . Development . Early VTOL rotor aircraft . The idea of building Vertical Take - Off and Landing aircraft using helicopter - like rotors at the wingtips originated in the 1930s . The first design resembling modern tiltrotors was patented by George Lehberger in May 1930 , but he did not further develop the concept . In World War II , a German prototype called the Focke - Achgelis FA - 269 was developed starting in 1942 , but it never flew . Two prototypes that made it to flight were the one - seat Transcendental Model 1 - G and two - seat Transcendental Model 2 , both powered by single reciprocating engines . Development started on the Model 1 - G in 1947 , and it flew in 1954 . The Model 1 - G flew until a crash in Chesapeake Bay on 20 July 1955 , destroying the prototype aircraft but not seriously injuring the pilot . The Transcendental 1 - G is the first tiltrotor aircraft to have flown , and it accomplished most of a helicopter - to - aircraft transition in flight to within 10 degrees of true horizontal aircraft flight . The Model 2 was developed and flew shortly afterward , but it did not fly much beyond hover tests . The US Air Force withdrew funding in favor of the Bell XV - 3 . The Bell XV - 3 was first flown in 1955 . Like its predecessors , the XV - 3 had the engines in the fuselage and drive shafts transferring power out to tilting wingtip rotor assemblies . Other rotor concepts , such as slowed rotors , stopped rotors , folding rotors , and variable - diameter rotors , were investigated for subsequent designs , but Bell engineers Ken Wernicke and Bob Lichten deemed them unfeasible compared to experience with the XV - 3 project . Technological advances . One of the major problems with the early tiltrotor aircraft designs was that the driveshafts carrying power from the fuselage out to the wingtip rotors , along with the gearbox and tilting mechanisms at the wingtips , had substantial loads placed upon them and were heavy . They were transferring large amounts of power and torque long distances for an aircraft power transmission system . The XV - 15 experimental aircraft introduced a major design concept advance : instead of engines in the fuselage , the XV - 15 moved the engines out to the rotating wingtip pods , directly coupled to the rotors . The normal path for power was directly from the engine into a speed - reduction gearbox and into the rotor / propeller without any long shafts involved . There was still a driveshaft along the wings for emergency use to transfer power to the opposite rotor in case of engine failure , but that shaft did not normally carry any power loads , making it lighter . The tilting engine concept introduced complexities in the design of the engines and engine pods to be able to shift from operating horizontally to operating vertically . Those problems were addressed fairly early in the XV - 15 program . In the late 1960s and early 1970s , NASA and other researchers worked extensively on theoretical and wind tunnel tests of various rotor pods . Two companies were involved in the research and proposing designs : Bell Helicopter and Boeing - Vertol . The focus was on tilt rotor pods , integration of the tilting rotors with the wings and fuselage of the aircraft , and studying the airflow as the rotors tilted . Tilt rotors with fixed rotors and with folding rotors were investigated . XV - 15 project . What was to become the XV - 15 program was launched in 1971 at NASA Ames Research Center . After preliminary work , a competition was held to award two $ 0 . 5 million research and development contracts for prototype designs . Companies that responded included Sikorsky Aircraft Corporation , Grumman Aircraft , Boeing - Vertol , and Bell Helicopter . R & D contracts were issued to Bell Helicopter and Boeing - Vertol on 20 October 1972 . The two companies ' design proposals were delivered on 22 January 1973 . Competing designs . Boeing proposed a design , Model 222 ( not to be confused with the later Bell 222 conventional helicopter ) , in which the engines were in fixed pods at the end of each wing , and a small , rotating pod with the rotor was slightly closer to the fuselage on the wing . This design simplified the engine design by keeping it horizontal at all times without having very long driveshafts to the tilting rotors . In the Bell design , Bell Model 301 , the whole wingtip pod rotated between horizontal and vertical , with the engine and rotor assembly fixed together within the pod . This simplified the power transmission , but it had more complicated requirements for the engine design and was probably slightly heavier than the Boeing proposal . After a review of both proposals , NASA selected the Bell 301 for further development , and a contract for further R & D was issued on 31 July 1973 . Extensive engineering and testing took the next four years to complete the development of the aircraft . The first of two Bell XV - 15s , tail number N702NA , first flew on 3 May 1977 . After minimal flight tests at the Bell test facility , the aircraft was moved to NASA Ames Research Center in Mountain View , California , where it was then mounted in the large Ames wind tunnel and tested extensively in various simulated flight environments . For the U . S . Department of Defense Joint - service Vertical take - off / landing Experimental ( JVX ) aircraft program , Bell Helicopter and Boeing Vertol teamed to submit a bid for an enlarged version of the XV - 15 in 1983 . The Bell Boeing team received a preliminary design contract that year , which lead to the V - 22 Osprey . Flight testing . Following wind tunnel and flight testing by Bell , the aircraft was then moved to NASA Dryden , which is at Edwards AFB in the California High Desert . The XV - 15 flight testing continued expanding its flight envelope . It was able to successfully operate in both helicopter and normal aircraft flight modes and smoothly transition between the two . Once the aircraft was considered sufficiently tested , it was returned to Ames for further testing . The XV - 15s were deemed sufficiently tested , and one aircraft was taken to the 1981 Paris Air Show for demonstration flights . The New York Times praised its performance . " And if ever there was a lovable plane , it is the Bell XV - 15 . . . The machine , the hit of the show , performed a series of maneuvers including bowing to the crowd . " Over the next year , Senator Goldwater , Navy Secretary Lehman , and other officials were offered guest co - piloting flights to promote tiltrotor technology for military development . The XV - 15s were a standard demonstration in the annual summer airshow at the co - located Moffett Field Naval Air Station for several years during the 1980s . Both XV - 15s were flown actively throughout the 1980s testing aerodynamics and tiltrotor applications for civilian and military aircraft types that might follow , including the V - 22 program . Further testing . The first XV - 15 prototype aircraft , N702NA , was transferred back to Bell for company development and demonstration use . On 20 August 1992 , the aircraft crashed while being flown by a guest test pilot . He was lifting off for a final hover when a bolt slipped out of the collective control system on one pylon , causing that rotor to go to full pitch . The aircraft rolled upside down out of control and crashed inverted . While significantly damaged , the aircraft was largely structurally intact and both the pilot and copilot escaped with only minor injuries from the crash . The cockpit of the aircraft was salvaged and converted for use as a flight simulator . The second XV - 15 prototype , N703NA , was used for tests to support the V - 22 Osprey military tiltrotor program and Bell / Agusta BA609 civilian medium tiltrotor transport aircraft . It continued in primarily NASA test operations until September 2003 . The shortest take - off distance was achieved with the nacelles at 75 degrees angle . After N703NA was retired from test operations , it was donated to the Smithsonian National Air and Space Museum in Washington , DC . The XV - 15 was flown cross - country from Fort Worth , Texas to the museum before being decommissioned for display . It is now on display at the Steven F . Udvar - Hazy Center at Washington Dulles International Airport .