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McDonnell XV-1

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XV-1
Role Convertiplane
Manufacturer McDonnell Aircraft
First flight 14 July 1954
Number built 2

TheMcDonnell XV-1is an experimentalConvertiplanedeveloped byMcDonnell Aircraftfor a joint research program between theUnited States Air Forceand theUnited States Armyto explore technologies to develop anaircraftthat could take off and land like ahelicopterbut fly at faster airspeeds, similar to a conventionalairplane.The XV-1 would reach a speed of 200 mph (320 km/h; 170 kn), faster than any previous rotorcraft, but the program was terminated due to the tip-jet noise and complexity of the technology which gave only a modest gain in performance.

Development[edit]

In 1951, the Air Force announced a competition to develop a compound helicopter, an aircraft that could take off and land vertically, like a helicopter, but could cruise at higher airspeeds than conventional helicopters.[1]The joint research program was being conducted by the Air Force'sResearch and Development Commandand the Army'sTransportation Corps.[2]Bell Aircraftsubmitted the design for theXV-3,Sikorsky Aircraftsubmitted theS-57,a retracting rotor design, and McDonnell submitted a design modified from its Model M-28 design.[3]

On 20 June 1951, the Air Force and Army signed a Letter of Intent with McDonnell to award a contract to develop an aircraft based on their design.[4]McDonnell benefited from previous design work on the Model M-28 and had a completemockupready for inspection by the Army and Air Force by November 1951. McDonnell was given approval to begin fabrication of what was then designated the XL-25 ( "L" for Liaison). As the aircraft was being constructed the designation was changed to XH-35. Finally, the aircraft became the first vehicle in theconvertiplaneseries as the XV-1.[2]

The basic airframe came from an early post-World War II commercial airplane program[which?]for a four-place airplane in theBonanzaandNavionclass.[5]McDonnell enlistedKurt Hohenemser[6]andFriedrich von Doblhoff,the Austrian helicopter designer of theWNF 342,to provide technical direction in developing the tip-jet driven rotor system.[4]After 22 months of fabrication, the first aircraft (serial 53-4016) was ready for flight testing by early 1954.[2]

Design[edit]

Built mostly from aluminum, the XV-1 fuselage consisted of a streamlined tube mounted on skid landing gear, with a rear-mounted engine and a pusher propeller. It also had tapered stub wings mounted high on the fuselage. In turn, twin tailbooms and twin vertical surfaces, interconnected by a horizontal stabilizer elevator, were mounted to the wings. A three-bladed main rotor powered by blade tip pressure jets was mounted on top of the fuselage, above the wing roots.[1]

The convertiplane featured a singleContinental-builtR-975radial piston engine that powered twin air compressors. These forced high-pressure air through piping in the rotor blades to a combustion chamber on each of the three rotor tips, where a burner ignited fuel for increased thrust, which drove the rotors around and allowed the aircraft to fly like a conventional helicopter.[7] For horizontal flight, the engine was disconnected from the compressors and drove the two-bladed pusher propeller instead. During forward flight the wing provided 80% of the lift with the remainder generated by the main rotor autorotating at about 50% of normal rpm.[2][8]When in hover mode, the rotor turned at 410 RPM butslowed to180 RPM for high-speed flight above 125 knots (144 mph; 232 km/h).[9]

The cabin was covered almost entirely with Plexiglas windows providing visibility in all directions except directly underneath the aircraft. The cockpit consisted of tandem pilot and copilot stations, or the aircraft could accommodate a pilot and three passengers, or a pilot and two stretchers.[1]

Operational history[edit]

The two XV-1s

The XV-1 began tethered hovering flight tests on 11 February 1954, withtest pilotJohn R. Noll. The tether had lead weights intended to keep the aircraft inground effectuntil issues with the rotor'stip-jet propulsionsystem were solved. On 14 July 1954, the lead weights were removed and the XV-1 conducted its first free hovering flight.[1]As flight testing continued, McDonnell completed the second machine (s/n 53-4017).

The second aircraft was modified from the original XV-1 in an attempt to reduceparasitic dragduring high-speed forward flight. To achieve this end, the rotor pylon was reduced and the undercarriage was streamlined as well as strengthened.[4]The second XV-1 also featured two small tail rotors mounted on the outboard side at the end of each tailboom. These were a result of the hover test flights by Noll who remarked on the lack of yaw authority when using rudders only. The original XV-1 would later be modified with the tail rotors.[1]

By the spring of 1955, the second XV-1 was ready to join the flight program.[2]On 29 April 1955, the XV-1 made its first transition from vertical to horizontal flight, and on 10 October 1955, the second XV-1 became the first rotorcraft to exceed 200 mph (320 km/h; 170 kn), nearly 45 mph (72 km/h; 39 kn) faster than the helicopter speed record at the time.[1]The XV-1 achieved a mu (the ratio of airspeed to rotor tip speed)[10]of 0.95.[11]

After three years and nearly 600 hours between the two aircraft, the XV-1 contract was canceled in 1957.[4]Ultimately, it was determined that the XV-1's convertiplane configuration was too complex for the small advantages gained over conventional helicopters. The piston engine could not produce enough power to optimize the design advantages. Technological advances in conventional helicopter rotor design and engines in the following years would eventually negate the XV-1's performance margin.[1][3]The noise level was 116dBin the cockpit, but even higher for ground personnel who described the tip jet noise as "extremely irritating" and the noise level was still 90 dB1⁄2mile (0.80 km) away.[12]McDonnell would try to capitalize on the tip-jet rotor technology with a small crane helicopter design, designated Model 120 and first flown on 13 November 1957.[13]

Surviving aircraft[edit]

The Army retained 53-4016, which was transferred to theUnited States Army Aviation MuseumatFort Novosel,Alabama. 53-4017, the record-setting, second prototype, was donated by the Army to theSmithsonian Institution'sNational Air and Space Museum,Washington, D.C., in 1964.[2]

Specifications (XV-1)[edit]

Data fromHarding[2]

General characteristics

  • Crew:One (pilot)
  • Capacity:two passengers, or twolitters
  • Length:50 ft 5 in (15.37 m)
  • Wingspan:26 ft 0 in (7.92 m)
  • Empty weight:4,277 lb (1,940 kg)
  • Gross weight:5,505 lb (2,497 kg)
  • Powerplant:1 ×Continental R-975-19radial piston engine,525 hp (391 kW)
  • Main rotor diameter:31 ft (9.4 m)

Performance

  • Maximum speed:203 mph (327 km/h, 176 kn)
  • Cruise speed:138 mph (222 km/h, 120 kn)
  • Range:593 mi (954 km, 515 nmi)
  • Service ceiling:19,800 ft (6,000 m)
  • Rate of climb:1,300 ft/min (6.6 m/s)

See also[edit]

Aircraft of comparable role, configuration, and era

References[edit]

Notes[edit]

  1. ^abcdefg(Connor & Lee, 2001)
  2. ^abcdefg(Harding, 1997)
  3. ^ab(Markman, 2000)
  4. ^abcd(Francillon, 1997)
  5. ^(GlobalSecurity.org)
  6. ^Harris 2003, page 27
  7. ^"McDonnell XV-1 Convertiplane | National Air and Space Museum".airandspace.si.edu.Archived fromthe originalon 21 June 2019.
  8. ^Watkinson, John (2004).The Art of the Helicopter.Elsevier Butterworth-Heinemann. p. 355.ISBN07506-5715-4.
  9. ^Harris 2003, page 14
  10. ^What is the Mu-1 barrier?Flight Global,12 July 2005. Accessed: 18 January 2011.
  11. ^Anderson, Rod.The CarterCopter and its legacyIssue 83,Contact Magazine,30 March 2006. Accessed: 11 December 2010.
  12. ^Harris 2003, page 26
  13. ^(Donald, 1997)

Bibliography[edit]

External links[edit]

Wikimedia Commons has media related toMcDonnell XV-1.
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