Powered lift

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Powered lift or powered-lift refers to a type of aircraft that can take off and land vertically and functions differently from a rotorcraft in horizontal flight.

The term is particularly used by the United States Federal Aviation Administration for classification purposes. Powered-lift is one of the seven categories of aircraft designated by the Federal Aviation Administration; the other six being Airplane, Rotorcraft, Glider, Lighter-Than-Air, Powered parachute, and Weight-shift control.

Powered-lift means a heavier-than-air aircraft capable of vertical takeoff, vertical landing, and low speed flight that depends principally on engine-driven lift devices or engine thrust for lift during these flight regimes and on nonrotating airfoil(s) for lift during horizontal flight.

— FAA[1]

The first powered-lift ratings to be issued by the FAA on a civilian pilot certificate were on 21 August 1997, to pilots of Bell Helicopter and Boeing, and of the United States Marine Corps.[2]

Convertiplane[edit]

Main article: Convertiplane

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

In tiltrotor and tiltwing designs such as the Bell Boeing V-22 Osprey, the rotor swings forward to act as a propeller in forward flight. Some designs have a ducted rotor design, in which the rotor is surrounded by a large ring-shaped duct to reduce tip losses.

Tiltrotor[edit]

An USAF CV-22 in flight
Powered lift and thrust forces of various aircraft
Main article: Tiltrotor

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 Bell Boeing V-22 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 2017.

Tiltwing[edit]

Main article: 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.[3] 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[edit]

Main article: Rotor wing

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 ended their lives 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[edit]

Main article: Tail-sitter

A Tail-sitter is an aircraft that rests on the ground pointing vertically upwards, so that it rests on its tail and takes off and lands vertically. 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.

The coleopter type has an 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.

The German Focke-Wulf Fw Triebflügel was a design studied during the Second World War. It used pulse jets to power a rotor that rotated about the fuselage axis behind the cockpit. Similar to a coleopter fixed-wing aircraft, the Triebflügel was intended to take off and land on its tail, rotating on the pitch axis after takeoff and acceleration for forward flight. The design was never been built beyond model wind tunnel testing.

Vectored thrust[edit]

Main article: vectored thrust

The Harrier Jump Jet covers a series of a military VSTOL jet aircraft. It is capable of vertical/short takeoff and landing (V/STOL) and is the only truly successful design of this type from the many that arose in the 1960s. These aircraft are capable of operating from small spaces, such as fields, roads, and aviation-capable ships. The F-35 Lightning II version B is proposed as the next military VSTOL in order to replace the Harrier.

Lift jets[edit]

Main article: Lift jet

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[edit]

Main article: Lift fan

Lift fan is an aircraft configuration in which lifting fans are located in large holes in an otherwise conventional fixed wing or fuselage. It is used for V/STOL operation.

The aircraft takes off using the fans to provide lift, then transitions to fixed-wing lift in forward flight. Several experimental craft have been flown, but only the F-35 Lightning II entered into production.

Helicopter-airship compound[edit]

Piasecki Helicopter developed the Piasecki PA-97 Helistat using the rotor systems from four obsolete helicopters and a surplus Navy blimp, in order to provide a capability to lift heavier loads than a single helicopter could provide. The aircraft suffered a fatal accident during a test flight. In 2008, Boeing and SkyHook International resurrected the concept and announced a proposed design of the SkyHook JHL-40.

Examples[edit]

See also[edit]

Notes[edit]

  1. ^ Federal Aviation Regulations Part 1 www.faa.gov
  2. ^ "Osprey Pilots Receive First FAA Powered Lift Ratings", www.boeing.com, 21 August 1997. 1999 Archive
  3. ^ "VTOL Design Problems." Flight. periodical. 18 October 1957. Retrieved on 22 October 2009.

References[edit]