Powered lift

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Bell Boeing V-22 Osprey flown by the U.S. Marines
A Spanish EAV-8B Harrier II+

A powered lift aircraft

fixed-wing
aircraft in combat or other situations.

Some powered-lift aircraft, like the

United States Marines, use a tiltrotor or tiltwing. These are called a convertiplane. Others like the British Harrier jump jet use thrust vectoring
or other direct thrust techniques.

The first powered-lift ratings on a

Bell Helicopter, Boeing, and the United States Marine Corps.[1]

Definition

Powered lift and thrust forces of various aircraft

The term is an aircraft classification used by the International Civil Aviation Organization (ICAO) and the United States' FAA:

Powered-lift. A heavier-than-air aircraft capable of vertical take-off, vertical landing, and low-speed flight, which depends principally on engine-driven lift devices or engine thrust for the lift during these flight regimes and on non-rotating aerofoil(s) for lift during horizontal flight.

— ICAO Annex I, Chapter 1.1 Definitions

Convertiplane

Main article: convertiplane

A convertiplane uses rotor power for vertical takeoff and landing (VTOL) and converts to fixed-wing lift for normal flight.

In tiltrotor and tiltwing designs such as the

propeller in forward flight. Some designs have a ducted fan
design, in which the propeller is surrounded by a large ring-shaped duct to reduce tip losses.

Tiltrotor

An USAF CV-22 in flight

The powered rotors of a tiltrotor (sometimes called proprotor) are mounted on rotating shafts or nacelles at the end of a fixed wing, and used for both lift and propulsion. For vertical flight, the rotors are angled to provide thrust upwards, lifting the way a helicopter rotor does. As the aircraft gains speed, the rotors progressively rotate or tilt forward, with the rotors eventually becoming perpendicular to the fuselage of the aircraft, similar to a propeller. In this mode, the wing provides the lift and the rotor provides thrust. The wing's greater efficiency helps the tiltrotor achieve higher speeds than helicopters.

The Osprey by

Bell Helicopter and Boeing is a twin-engine tiltrotor design that has two turbine engines each driving three-blade rotors. The rotors function similar to a helicopter in vertical flight, and similar to an airplane in forward flight. It first flew on 19 March 1989. The AgustaWestland AW609
(formerly Bell/Agusta BA609) tiltrotor is civilian aircraft based on the V-22 Osprey. The aircraft can take off and land vertically with 2 crew and 9 passengers. The aircraft is expected to be certified in the mid-2020s.

Tiltwing

The tiltwing is similar to the tiltrotor, except that the rotor mountings are fixed to the wing and the whole assembly tilts between vertical and horizontal positions.

The Vertol VZ-2 was a research aircraft developed in the late 1950s. Unlike other tiltwing aircraft, Vertol designed the VZ-2 using rotors in place of propellers.[2] On 23 July 1958, the aircraft made its first full transition from vertical flight to horizontal flight. By the time the aircraft was retired in 1965, the VZ-2 had accomplished 450 flights, including 34 full transitions.

Rotor wing

A rotor wing aircraft has been attempted but is not in wide use. The Boeing X-50 Dragonfly had a two-bladed rotor driven by the engine for takeoff. In horizontal flight the rotor stopped to act like a wing. Fixed canard and tail surfaces provided lift during transition, and also stability and control in forward flight. Both examples of this aircraft were destroyed in crashes. The Sikorsky X-Wing had a four-bladed rotor utilizing compressed air to control lift over the surfaces while operating as a helicopter. At higher forward speeds, the rotor would be stopped to continue providing lift as tandem wings in an X configuration. The program was canceled before the aircraft had attempted any flights with the rotor system.

Tail-sitter

A Tail-sitter is an aircraft that rests on the ground pointing vertically upwards, so that it rests on its tail. It takes off and lands vertically, tail down. The whole aircraft then tilts forward horizontally for normal flight. No type has ever gone into production, although a number of experimental variants have been flown, using both proprotor and jet thrust. Some have achieved successful transition between flight modes, as the turboprop-powered Convair XFY Pogo did in November 1954.[3]

The

annular wing forming a duct around a lift rotor. The transition to forward flight has never been achieved, although the SNECMA Coléoptère
took off, hovered and landed vertically, solely on pure jet thrust.

The German

pitch
axis after takeoff and acceleration for forward flight. The design was never built beyond model wind tunnel testing.

Direct thrust

Vectored thrust

The

Lockheed F-35B Lightning II is proposed as the next military VSTOL/STOVL
design, to replace the Harrier.

Lift jets

A lift jet is a lightweight jet engine used to provide vertical thrust for VTOL operation, and is then shut down in forward flight. Some VTOL designs have used both vectored thrust from the main engine together with auxiliary lift jets.

Lift fans

A

F-35 Lightning II
entered into production.

Additional examples

See also

Wikimedia Commons has media related to VTOL aircraft.

Notes

  1. ^ "Osprey Pilots Receive First FAA Powered Lift Ratings", www.boeing.com, 21 August 1997. 1999 Archive
  2. ^ "VTOL Design Problems." Flight. periodical. 18 October 1957. Retrieved on 22 October 2009.
  3. ^ "Convair XFY." Flight, 12 November 1954, p. 696.

References

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