February 23, 1965: Vertical/Short Takeoff and Landing Engineering Testing

  • Published
  • Air Force Flight Test Center

Due to an anticipated lack of trained vertical/short takeoff and landing engineering test pilots in the Air Force, V/STOL training was documented as a new task to the USAF Aerospace Research Pilot School. To that end, the school acquired four Bell OH-13E Sioux “bubbletop” helicopters for the new curriculum.

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.  Most V/STOL aircraft types were experiments or outright failures from the 1950s to 1970s. V/STOL aircraft types that have been produced in large numbers include the F-35B Lightning II, Harrier, Yak-38 Forger and V-22 Osprey.  A rolling takeoff, sometimes with a ramp (ski-jump), reduces the amount of thrust required to lift an aircraft from the ground (compared with vertical takeoff), and hence increases the payload and range that can be achieved for a given thrust. For instance, the Harrier is incapable of taking off vertically with full weapons and fuel load. Hence V/STOL aircraft generally use a runway if it is available. I.e. short takeoff and vertical landing (STOVL) or conventional takeoff and landing (CTOL) operation is preferred to VTOL operation.  V/STOL was developed to allow fast jets to be operated from clearings in forests, from very short runways, and from small aircraft carriers that would previously only have been able to carry helicopters.  The main advantage of V/STOL aircraft is closer basing to the enemy, which reduces response time and tanker support requirements. In the case of the Falklands War, it also permitted high-performance fighter air cover and ground attack without a large aircraft carrier equipped with aircraft catapult.

The Bell H-13 Sioux is a single-engine single-rotor light helicopter built by Bell Helicopter. Westland Aircraft manufactured the Sioux under license for the British military as the Sioux AH.1 and HT.2.  In 1947, the United States Army Air Forces (later the United States Air Force) ordered the improved Bell Model 47A. Most were designated YR-13 and three winterized versions were designated YR-13A. The United States Army first ordered Bell 47s in 1948 under the designation H-13. These would later receive the name Sioux.  Initially, the United States Navy procured several Bell 47s, designated HTL-1, between 1947 and 1958. The United States Coast Guard evaluated this model, and procured two HTL-1s for multi-mission support in the New York Harbor. The most common U.S. Navy version of the 47 was designated the HTL-4, and dispenses with the fabric covering on the tail boom. The U.S. Coast Guard procured three HTL-5s in 1952 (similar to the HTL-4 but powered by a Franklin O-335-5 engine) and used these until 1960. The Coast Guard procured two of Bell's Model 47G and designated them HUL-1G in 1959.  The H-13 was used as an observation helicopter early in the Vietnam War, before being replaced by the Hughes OH-6 Cayuse in 1966.  The Bell 47 was ordered by the British Army as the Sioux to meet specification H.240, with licensed production by Westland Helicopters. In order to comply with the terms of its license agreement with Sikorsky Aircraft, which prevented it building a U.S. competitor's aircraft, Westland licensed the Model 47 from Agusta, who had purchased a license from Bell.[4] the first contract was for 200 helicopters. The first 50 helicopters of the contract were built by Agusta at Gallarate in Italy followed by 150 built by Westland at Yeovil. The first Westland Sioux made its maiden flight on 9 March 1965.


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