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Aviation History
1964
1964 - 1778.PDF
FLIGHT International, II ]unt 1964 VISIT TO GEORGIA... 987 bleed-air injected into a augmenter tube running through the fin/ tailplane bullet fairing. The purpose of the augmenter here is simply to reduce the air temperature and provide a higher mass flow allowing use of less fine and sensitive blowing slits. A variable- incidence tailplane or a larger elevator could have solved the prob- lem, but BLC was considered to be the better solution. During the transition BLC is automatically selected through a mode-selector switch, which also arms the doors and divertor actuators and initiates hydraulic pressure to the stabilization system. Apart from controlling attitude, the pilot has only to operate the diverters when he decides to change to forward thrust, and select gear up, doors closed and compressor bleed off at appropriate stages. Height control is by throttle manipulation. Ground effect provides positive pressure beneath the aircraft; recirculation sets in only after some time at full power on the ground, its main effect being to warm the intake air and reduce engine power. To make the forward transition, the pilot first tilts the Hummingbird about 10° nose-down to accelerate by simple thrust-axis inclination. At between 75 and 80kt he rotates nose-up again to achieve sufficient lift from the wing to be able to flick one engine to rearward thrust. Once this is accomplished the aircraft accelerates very rapidly, and may be set into quite a steep climb. As soon as 115 to 120kt, thej minimum wing-borne speed, is reached, the other engine is switched and the duct doors may be closed. The landing transition is a similar process, though in a film I was shown the pilot made little attempt to declerate by raising the nose. The final loss of speed was therefore a protracted operation, though at this early stage in experience this is understandable. It is estimated that at present forward transition takes between 45 and 60sec and that some three minutes' thrust-assisted flight are involved in each full-cycle sortie. With so much installed thrust, a conventional take-off is a fairly breath-taking operation, and one which the test pilots have described as "very stimulating." Simple Cockpit The cockpit of the Hummingbird prototype is much what one would expect. The second seat-space is occupied by recording equipment, autopilot control panel and duplicated VHF and VOR radios, the last-named to assist test flying in the traffic-ridden local flying area and to ensure quick return to base with low fuel reserves. Instruments include a miniature artificial horizon, g-meter, instan- taneous v.s.i., angle of attack indicator, a.s.i. and altimeter. The flight-mode switch and engine-diverter switches are on the rear of the conventional throttle quadrant, and the BLC switch is on the stick. A Douglas A-4E (Skyhawk) rocket ejection seat modified for zero-zero performance is fitted. All three undercarriage legs have rubber-in- compression shock absorption, with an ingenious tapered central friction rod of the type first applied by the Mooneys to their Mite. By comparison with the Hummingbird, Ryan's XV-5A fan-in- wing prototype, now entering the flight-test stage, is a heavier aircraft and has, by virtue of the lift fans, a heavier and thicker wing. But its installed thrust is lower, and its thrust augmentation is greater. It is perhaps a pity that the small budget on which the Humming- bird has been produced has forced the designers to find ways of keeping everything so simple and cheap that some of the possible lessons may not have been learned. A slightly less fettered approach to stabilization might have taken the system a little further, for stabilization must be an essential part of any operational system. But that the project has been able to progress to this point, and that this should have been possible within a huge company with all the latter's overheads and similar disadvantages, is indeed a major achievement, and an encouragement to VTOL design in general. Indeed, Lockheed might never have embarked on the Hummingbird had they not proved to themselves that they could reasonably make a small aeroplane when they designed and tested what has now become the Macchi 60. This, too, was a Mooney design. Tof> to bottom: a Hummingbird forward transition showing the hover with >2i° nose-up attitude; forward tilt and undercarriage retracting; full forward tilt during attitude acceleration; and levelling off to obtain wmg- lift at 80kt before diverting one engine and accelerating to full wing-borne speed of !20kt
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