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Lockheed VZ-10 / XV-4A/B Hummingbird

Lockheed had studied theapplication of jet ejectors to aircraft since 1956, and in 1959 a joint Army/Navy program supported further studies by the company. Results were such that Lockheed made an unsolicited proposal to the Army for design and fabrication of two research ?ight test vehicles. The company received a US Army contract in July 1961 to build two Hummingbird aircraft. Lockheed's Model 330 was initially designated the VZ-10, but was redesignated XV-4A in 1962. Called the Hummingbird because it was designed to rise straight up, land straight down, hover, and dash ahead, the XV-4A was a two-engine jet developed by the Lockheed-Georgia Company. The Hummingbird had a boxy fuselage housing the ejectors and augmentors. Along each side of the aircraft, jet engines produced 3,300 lb thrust either for horizontal flight, or diverted into the augmentor ejectors for vertical take-off and landing. Power was supplied by two Pratt & Whitney IT-12A-3 tur-bo jets exhausting into a pair of diverter valves. These valves can be switched to direct the exhaust through the primary nozzles of the lift system, thence through the ejector chambers and out the bottom of the fuselage. For conventional flight the gas is allowed to ?ow aft through a tail pipe. The ejector and engines are cross ducted to afford safety and control in the event of an engine failure. The two engines fed interleaved ejectors in case of engine failure. Because of the flow characteristics of the ejector system, failure of one engine still leaft 60% lift available for descent. Pitch and yaw control in hover is provided by reaction nozzles using engine exhaust. Roll control is obtained by using bleed air from the engine compressors. In all cases, the controls meter the flow of gas as required so that the sum total of lift remains unchanged. Ejectors are used on these reaction controls to augment the flow in a manner similar to the mainlift system.

The augmentors were constructed of stainless steel and titanium, accounting for a significant portion of the 5,000 lb empty weight and the 7,200 lb gross weight. Actual vertical thrust after installation losses was about 7,500 lb for a 1.04 thrust-to-weight. This was only a 14% net augmentation. Design augmentation of the jet ejector was 1.4, but it was expected that a favorable ground effect would be experienced down to about 2.5 feet above the ground, the point at which the ejector exits remain when the landing gear is in the static position.

Wind tunnel tests were conducted on a 0.16-scale XV-4B model to determine its aerodynamic characteristics. Six cold air ejectors were used to simulate four direct-lift and two lift-cruise jet engines. Longitudinal and lateral-directional aerodynamic characteristics were investigated for various model configurations, forward speeds, and power conditions in the transition and cruise flight ranges. In addition to control-effectiveness studies, the effects of power variations for different lift-nozzle settings and the effects of height above the ground were investigated.

Wind tunnel tests of the XV-4A Hummingbird at NASA Ames 40 x 80 foot wind tunnel consisted of 41 runs and a total of 944 test points. Tests were conducted over a range of speeds in all phases of flight from hover through transition to conventional flight. Pitch and yaw runs, as well as control effectiveness runs in all three modes were made. Many of the pitch runs were made well into the so-called deep stall angle of attack range. Wind tunnel tests of a full-scale XV-4A airplane were made to determine aerodynamic characteristics, including its ejector system, ejector performance, longitudinal characteristics, lateral-directional stability and control, and control power about all three axes at various airspeeds and control settings through the transition flight regime.

A contract wassigned in lune 1961, and the first conventional ?ight was accomplished on 7 July 1962, followed by the first free hover on 24 May 1963. The first transition was not completed until 8 November 1963, and the first aircraft crashed on 10 June 1964, killing the pilot.

This machine achieved a thrust augmentation ratio of 1.24, considerablyless than what was anticipated. During the flight test program, the actual vertical thrust realized was only about 93 percent of that predicted, and consequently the aircraft, the XV-4A, had a marginal lift capability. This marginal lift capability severely limited the capability to conduct quantitative data gathering during the flight test program. The feasibility of the augmented jet ejector concept was demonstrated; however, this concept was not considered to be competitive with other concepts for attaining a VTOL capability.

In late 1966 Lockheed modified one of the XV-4As to a new XV-4B configuration, the major change being repalcement of the XV-4A's two 1361kg thrust engines by four each of 1368kg thrust. Testing began in August 1968, but when the aircraft was destroyed in an accident in early 1969 further development was abandoned.

In the following two decades the ejector technology received considerable attention on account of its application to vertical and short take-off and landing (V/STOL) aircraft. The immediate plausible application was to achieve V/STOL capability of a flying machine. A later industrial development was the Rockwell XFV-12A. A low thrust augmentationL ratio of only 1.1 was achieved by this aircraft. A total of four ejector-augmentor flight systems (XFV-12A, XV-4A, XC-8A and the JW-1) reached research prototype/demonstrator vehicles.

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Page last modified: 30-03-2012 18:45:15 ZULU