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Aviation History
1963
1963 - 0476.PDF
454 FLIGHT Internationa 4 April 1% Jet Flap in the Air HUNTING H.126 MAKES ITS FIRST FLIGHT THE first flight of the Hunting H.126 jet-flap research aircraft took place from the RAE, Bedford, on March 26. At the controls was Mr S. B. Oliver, chief test pilot of the company which designed and built it: Hunting Aircraft Ltd, of Luton, a member of British Aircraft Corporation. The current test pro gramme is referred to again at the conclusion of the following description. The H.126 is a single-seater powered by a single Bristol Siddeley Orpheus turbojet. It was built to Ministry of Aviation specification ER.189D for the full-scale investigation of the jet-flap principle, which has been the subject of much research at the National Gas Turbine Establishment, the Royal Aircraft Establishment and in the aircraft industry for a number of years. One of the major benefits of the jet flap is that it will permit substantially lower take-off and landing speeds. The principle of the jet flap was propounded, and patented, in 1952 by the National Gas Turbine Establishment, at Pyestock, Hants. It is a technique whereby the power of jet engines installed for propulsion can also be used greatly to increase the wing lift at low speed. As described in this journal on September 30, 1955, the original concept involved the expulsion of the whole engine efflux in the form of a thin sheet discharged downwards from the trailing edge of the wing. Later research has shown that more dramatic increases in lift coefficient, up to a theoretical maximum of 2.4TT, can be achieved by using relatively cold air and blowing through several nozzles around a radiused trailing edge, the lowermost slit blowing forwards to push the rear stagnation point as far forward as possible. In the H.126 the system is of necessity somewhat crude, because in any technological advance as fundamental as the jet flap full- scale testing must proceed in manageable steps. Far more efficient schemes have been tested in tunnels at the NGTE (see Flight for June 3, 1960, for example), but the H.126 has an essentially con ventional aerofoil employing blown flaps and ailerons. Where it differs from all previous aircraft is that the blowing is done with hot gas direct from the jetpipe, issuing through eight "fishtails" along the trailing edge of the fixed part of each wing. These fishtails discharge the hot gas in the form of a thin sheet over the top of the mechanical flaps and ailerons. Each of the latter is of quite small chord, and it acts only as a deflector for the sheet of gas which follows its upper surface as it is lowered. With the mechanical flap down, the jet stream flowing over it retards the airflow under the wing and increases it over the wing, so—say BAC—"increasing the lift to several times that of a conventional wing." At the same time, the efflux produces propulsive thrust, whether the flaps are lowered or not. The H.126 aircraft is unconventional in many ways, and posed numerous aerodynamic, thermodynamic and structural problems. Among the latter were the ducting of hot gases, large changes of trim which occur with such a large variation in lift coefficient, and the inter-relation between control jets (described later) and the conventional elevator and rudder controls. The pilot's cockpil is situated above the engine compartment. It is unpressurized. but oxygen equipment is installed, and a Martin-Baker ejection seat is fitted. The aircraft has a fixed nosewheel undercarriage. In addition to operating the normal control surfaces, the pilot's control column and rudder pedals also operate jet nozzles in the tail of the aircraft, which control pitch and yaw (primarily at very low speed). Nozzles in the wing tip, to control roll, are operated by an autostabilizer. The variable-incidence tailplane is hinged about its rear spar, and is operated by a hydraulic p.f.c.u. at the front attachment. The elevators are linked to the tailplane so thai the effective camber of the tail unit varies directly with incidence. The ailerons, which can be drooped to give a full-span jet flap, are each driven by a p.f.c.u.; the rudder is not power operated. The Orpheus engine has a simple pitot intake, and is fitted with an air starting system. Its entire efflux is ducted through a right-angled cascade to a vertical distribution manifold known colloquially as "the dustbin."' From the top of this manifold three ducts on each side lead into the wing and thence to the eight fishtails which exhaust over the full span of the flaps and ailerons. One of the three main ducts in the wing also supplies the roll-jet nozzle at the wing tip. From the bottom of the "dustbin" an additional jetpipe is led aft and bifurcated through each side of the fuselage to provide thrust in addition to that from the fishtails in the wing. Provision is made for these two jet nozzles to have thrust spoilers, controllable by the pilot There is another duct from the distributor manifold to supply the pitch and yaw control nozzles at the tail, and also a further due supplying a pitch-trim nozzle. Ducting of the hot gases has necessitated careful insulation and heat-shield precautions, to enable normal light alloys to be used for the main structure except at a few critical points. Extensive « search was necessary to select materials and perfect constructional methods, not only for the hottest parts but also for items subject to hot gas on one side and ambient airflow on the other (such as the flaps and ailerons). The instrumentation includes temperature recording at many parts of the aircraft. Each mainplane is of two-spar construction, attached to the fuse lage by pin joints and supported at about two-thirds span by single strut. The wing and strut attachments are so designed that the wing can have two alternative dihedral angles (4° or 8°). EacB aileron is attached to the wing by five hinges, and cooling a;r passed through the aileron via slots in the leading and trailing edges. The flaps are similar in construction to the ailerons. Each aileron and each flap has its own operating jack, mounted beneath the wing in a fairing box. The fuselage is of conventional stressed-skin construction w» longitudinal members and vertical frames, the latter being reinfo ce« at such points as wings, undercarriage and engine mounting atucfr ments. The two-spar tailplane is pivoted at its rear spar. Four ele vator hinges are bolted to the rear spar, the two inboard fittngi carrying a torque tube which incorporates the elevator lever. 1
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