Lift fan is an aircraft configuration in which lifting fans are located in large holes in an otherwise conventional fixed wing [1] 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.
A number of experimental aircraft were evaluated in the USA during the late 1950s and throughout much of the 1960s.
The Republic Aviation AP-100 was a prototype VTOL 6x General Electric J85 Turbojet engined nuclear capable strike fighter concept designed by Alexander Kartveli that had 3x ducted fans in the centre of its fuselage and tail as a possible contender for the TFX Program. [2] [3] [4]
The Avro Canada Avrocar, commissioned by the USA, was intended to be a technology demonstrator for a supersonic VTOL aircraft. It featured a single central fan in a circular flying wing, with engine thrust directed rearwards for forward flight. It underwent trials between 1958 and 1961 but, due to its unstable "flying saucer" aerodynamics and lower than expected thrust, never flew out of ground effect. The Verticraft Verticar of 1961 was a similar single-fan, directed-thrust, all-wing (or lifting body) aircraft, of conventional but very low-aspect-ratio wing planform. It failed to fly. A tandem-fan version was proposed but never built. [5] By contrast the Ryan XV-5 Vertifan of 1964 was an otherwise conventional delta-wing jet. It had a large fan in each wing and a third, smaller fan in the nose to provide balance in pitch. It was more successful, with one of the two prototypes flying until 1971.
The Vanguard C2 and C2D Omniplane had two fans side by side, with one in each wing. It underwent tethered trials between 1959 and 1962 but never flew untethered. In the late 1960s NASA conducted wind tunnel experiments on a series of larger aircraft designs using different numbers of fans in the wings. [6]
Beginning with a one-sixth scale model in 1962, Paul Moller has been experimenting with the flying saucer configuration ever since. All have had a central cockpit but have varied between a single lift fan surrounding the cockpit, twin fans behind the cockpit or, more recently, eight individual fans distributed around it. Some examples such as the XM-2 of 1965 have been able to hover within ground effect. The artificially stabilised M200X was re-engined in 1989 and can fly out of ground effect, but has not entered production. [7]
Several projects were announced in 2010 and 2011. The Ray passenger aircraft had four fans arranged approximately in a square, similarly to a quadrotor, with a small fan in front of a larger one behind it in each wing. [8] [9] [10] The Lockheed Martin VARIOUS was a multi-role military UAV with twin fans side by side, one in each wing. [11] [12] The Northrop MUVR ship-to-shore resupply aircraft similarly had a fan in each wing. [13] Unlike these the Anglo-Italian AgustaWestland Project Zero hybrid tiltrotor/lift-fan unmanned technology demonstrator was actually built and flew successfully in 2011. It has side by side twin fans which can rotate into a vertical plane to act as propellers in forward flight, while still located within the wing structure.
The F-35 Lightning II uses the Rolls-Royce LiftSystem, in which 29,000 hp [14] [15] [16] is diverted forward through a driveshaft from the engine's low-pressure (LP) turbine via a clutch [17] and bevel-gearbox to a vertically mounted, contra-rotating lift fan located forward of the main engine.
Israeli enterprise Urban Aeronautics is developing a wingless drone that uses a pair of lift fans to ensure lift by ground effect and another pair of fans for forward flight. [18]
| Type | Country | Date | Role | Status | Description |
|---|---|---|---|---|---|
| AgustaWestland Project Zero | Italy/United Kingdom | 2011 | Experimental | Prototype | 2 tiltrotor–fans; hybrid tiltrotor–fan in-wing unmanned technology demonstrator |
| Avro Canada VZ-9 Avrocar | Canada | 1958 | Experimental | Prototype | 1 central fan in circular flying saucer wing; 2 flown; trials 1958–61, never flew out of ground effect |
| Grumman Future Air Attack Vehicle (FAAV) | USA | 1993 | Fighter | Project | 2 fans in wings |
| Hawker Siddeley HS 138 | United Kingdom | 1969 | Strike fighter | Project | 4 fans in wings |
| Hawker Siddeley P.1017 | United Kingdom | 1962 | Fighter | Project | 2 fans in nose, 2? in tail sections |
| Lockheed Martin F-35 Lightning II | USA | Fighter | In service | 1 fan, F-35B variant only | |
| Lockheed Martin VARIOUS | USA | 2010 | Project | 2 fans; multi-role UAV [11] [12] | |
| Moller M200X Volantor | USA | 1989 | Experimental | Prototype | 8 fans in circular flying saucer wing |
| NASA wind tunnel test models | USA | 1967 | Transport | Project | Various designs [6] |
| Northrop Grumman MUVR | USA | 2011 | Project | 2 fans; ship-to-shore resupply aircraft [13] | |
| Pegasus VBJ | South Africa | 2019 | Business jet | Project | Fans in cranked dihedral wing, and at rear for thrust; 1/8-scale model flown, prototype due in 2020 [19] |
| Ray | 2010 | Project | 4 unequal-size fans [8] [9] [10] | ||
| Republic AP-100 | USA | 1957 | Strike fighter | Project | 3 fans in fuselage centre |
| Ryan XV-5 Vertifan | USA | 1964 | Experimental | Prototype | 3 fans unequal-size; 2 craft built, 1 flew until 1971 |
| Tactical Robotics Cormorant | Israel | Experimental | Prototype | UAV | |
| Vanguard Omniplane: C2, C2D | 1959 | Experimental | Prototype | 2 fans; tethered trials 1959–62 | |
| Verticraft Verticar | USA | 1961 | Experimental | Project | 1 fan in flying wing lifting body; 1 prototype, failed to fly [5] |
An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or the dynamic lift of an airfoil, or, in a few cases, direct downward thrust from its engines. Common examples of aircraft include airplanes, helicopters, airships, gliders, paramotors, and hot air balloons.
A short take-off and vertical landing aircraft is a fixed-wing aircraft that is able to take off from a short runway and land vertically. The formal NATO definition is:
A Short Take-Off and Vertical Landing aircraft is a fixed-wing aircraft capable of clearing a 15 m obstacle within 450 m of commencing take-off run, and capable of landing vertically.
A vertical take-off and landing (VTOL) aircraft is one that can take off and land vertically without relying on a runway. This classification can include a variety of types of aircraft including helicopters as well as thrust-vectoring fixed-wing aircraft and other hybrid aircraft with powered rotors such as cyclogyros/cyclocopters and gyrodynes.
For fixed-wing aircraft, ground effect is the reduced aerodynamic drag that an aircraft's wings generate when they are close to a fixed surface. During takeoff, ground effect can cause the aircraft to "float" while below the recommended climb speed. The pilot can then fly just above the runway while the aircraft accelerates in ground effect until a safe climb speed is reached.
The Harrier, informally referred to as the Harrier jump jet, is a family of jet-powered attack aircraft capable of vertical/short takeoff and landing operations (V/STOL). Named after a bird of prey, it was originally developed by British manufacturer Hawker Siddeley in the 1960s. The Harrier emerged as the only truly successful V/STOL design of the many attempted during that era. It was conceived to operate from improvised bases, such as car parks or forest clearings, without requiring large and vulnerable air bases. Later, the design was adapted for use from aircraft carriers.
A vertical and/or short take-off and landing (V/STOL) aircraft is an airplane able to take-off or land vertically or on short runways. Vertical takeoff and landing (VTOL) aircraft are a subset of V/STOL craft that do not require runways at all. Generally, a V/STOL aircraft needs to be able to hover. Helicopters are not considered under the V/STOL classification as the classification is only used for aeroplanes, aircraft that achieve lift (force) in forward flight by planing the air, thereby achieving speed and fuel efficiency that is typically greater than the capability of helicopters.
The Lockheed Martin X-35 is a concept demonstrator aircraft (CDA) developed by Lockheed Martin for the Joint Strike Fighter program. The X-35 was declared the winner over the competing Boeing X-32 and a developed, armed version went on to enter production in the early 21st century as the F-35 Lightning II.
Thrust vectoring, also known as thrust vector control (TVC), is the ability of an aircraft, rocket or other vehicle to manipulate the direction of the thrust from its engine(s) or motor(s) to control the attitude or angular velocity of the vehicle.
A tiltwing aircraft features a wing that is horizontal for conventional forward flight and rotates up for vertical takeoff and landing. It is similar to the tiltrotor design where only the propeller and engine rotate. Tiltwing aircraft are typically fully capable of VTOL operations.
A tail-sitter, or tailsitter, is a type of VTOL aircraft that takes off and lands on its tail, then tilts horizontally for forward flight.
A lift jet is a lightweight jet engine installed only for upward thrust.
The Ryan XV-5 Vertifan was a jet-powered V/STOL experimental aircraft in the 1960s. The United States Army commissioned the Ryan VZ-11-RY in 1961, along with the Lockheed VZ-10 Hummingbird. It successfully proved the concept of ducted lift fans, but the project was cancelled after multiple fatal crashes unrelated to the lift system.
The Lockheed XV-4 Hummingbird was a U.S. Army project to demonstrate the feasibility of using VTOL for a surveillance aircraft carrying target-acquisition and sensory equipment. It was designed and built by the Lockheed Corporation in the 1960s, one of many attempts to produce a V/STOL vertical take off/landing jet. Both prototype aircraft were destroyed in accidents.
A rotorcraft or rotary-wing aircraft is a heavier-than-air aircraft with rotary wings or rotor blades, which generate lift by rotating around a vertical mast. Several rotor blades mounted on a single mast are referred to as a rotor. The International Civil Aviation Organization (ICAO) defines a rotorcraft as "supported in flight by the reactions of the air on one or more rotors".
The Short SC.1 was the first British fixed-wing vertical take-off and landing (VTOL) jet aircraft. It was developed by Short Brothers. It was powered by an arrangement of five Rolls-Royce RB.108 turbojets, four of which were used for vertical flight and one for conventional horizontal flight. The SC.1 had the distinction of being the first British fixed-wing VTOL aircraft and the first one to transition between vertical and horizontal flight modes; it was also the first VTOL-capable aircraft with a fly-by-wire control system.
A powered lift aircraft takes off and lands vertically under engine power but uses a fixed wing for horizontal flight. Like helicopters, these aircraft do not need a long runway to take off and land, but they have a speed and performance similar to standard fixed-wing aircraft in combat or other situations.
The Rolls-Royce LiftSystem, together with the F135 engine, is an aircraft propulsion system designed for use in the STOVL variant of the F-35 Lightning II. The complete system, known as the Integrated Lift Fan Propulsion System (ILFPS), was awarded the Collier Trophy in 2001.
Aircraft can have different ways to take off and land. Conventional airplanes accelerate along the ground until sufficient lift is generated for takeoff, and reverse the process to land. Some airplanes can take off at low speed, this being a short takeoff. Some aircraft such as helicopters and Harrier jump jets can take off and land vertically. Rockets also usually take off vertically, but some designs can land horizontally.
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