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Aviation History
1950
1950 - 0430.PDF
Flight " photograph. cockpit. 288 FLIGHT, 2 March 1950 The simple, comfortable and well-ar HERMES IV In the Air . . . the distance from the engines. Several of the fairings and fittings—blinds, window frames and so on, of very light construction—set up a irritating buzzing, but that sort of thing can usually be remedied quite easily. The units of the air-conditioning system, located in the main coat com- partment (port rear), which produce whistling noises, are in process of being boxed in. Plenty of heat was available as soon as we had taken off, and by the time 15,000ft had been reached, the whole air- craft was warm and comfortable, with cabin altitude indi- cated as 1,000ft and differential pressure at 5^ lb/sq in. The windows are large enough to give most of the outside passengers a good view. - All this time our flight observer had been logging details of climb, checking rates with his stop watch, noting the trimmer positions and manipulating cabin-pressure controls in order to check their full and correct functioning. Next came some levels at E.C.B. (economical cruising boost, 38in, 2,400 r.p.m.). The altimeter indicated 16,000ft, the outside air temperature was —10 deg C, and the I.A.S. was 191 kt. This is equivalent to a T.A.S. of about 245 kt. For some time after this I had an opportunity to fly around as I wished while some miscellaneous airscrew- feathering tests were carried out. The airscrews are four- bladed de Havilland Hydromatics, 13ft in diameter. They are equipped for revers-pitch braking and have de-icing overshoes. One of the tests (to investigate the effect of a small mod.) was to feather No. 4 engine, the port outer, and see if, after a long period at high altitude, it would unfeather again. After a little hesitation it did. During the freezing process I circled around on three engines at 22,500ft and confirmed the impression that, for an aircraft of this size, and considering that there is no form of power assistance, the Hermes' controls are light and effective— •more so than on any comparable aircraft which I have handled. The rudder is unexpectedly effective at low cruis- ing speeds, and it is possible, without undue exertion and without the need for trimming, to hold the aircraft straight for some minutes when two engines are " out" on one side. The effect of feathering or unfeathering a single inboard engine is scarcely noticeable on the controls. The trimmers, conveniently placed near to their indica- tors on the central pedestal, are sensitive and seldom require more than a few degrees of movement, even ia asymmetric conditions. It always seems to me a somewhat drastic action volun- tarily to stall an aircraft of the size of the Hermes, although it happens to all of them during tests. The stall of the Hermes is certainly not alarming, and the aircraft protests at the indignity. The stall is officially described as '' not clearly defined." First there is a little shuddering and buffeting, and this is followed by more of the same thing, but with increased severity. If one continues to haul back on the control, one receives a pretty rough ride, but there is only a gentle sink without wing drop to mark the stall. Recovery is rapid when the backward pressure is released, although it seemed to me that the buffeting momentarily increased as the speed started to rise, presumably because the elevator remained briefly in disturbed air. With '' Everything up'' and a weight of about 69,000 Ib the stall speed indicated was 98 kt. With wheels down and 80 deg of flap, the stall was very similar in feel, but the speed was only 82 kt. The height was about 12,000ft. Later I tried stalling on a 30 deg banked turn. Again there was plenty of warning from buffeting, no tendency to drop the wing further, and immediate recovery. The indicated speed was between 105 and 110 kt and some aileron control remained all the time. During most of the period spent at 22,000ft and over. No. 4 Hercules was feathered and tie air speed remained at about i3okt I.A.S. with the other three engines still at E.C.B. This is remarkably good three-engine performance. I then handed the controls back to F/L. Broomfield for a time while he checked various maxima. Normally 262 kt I.A.S. is the highest speed allowed. We made a short burst at 280 kt and found everything very smooth and satisfactory. Other tests included timing wheels and flaps up and down at the limiting speeds for operation (flaps, 187 kt, 40 deg; 161 kt, 80 deg; wheels 187 kt). Other items on the check list included brake pressure build-up and timing of feathering and unfeathering of all four airscrews. Before returning to base I asked for a demonstration of the Smith's electric autopilot, the controls and indicators of which were situated beside my right knee when seated in the captain's seat. The power switches were already on and the instrument had had the necessary 45 seconds to warm up. This was indicated by the small amber lamp. Having trimmed the aircraft correctly, engagement simply entailed depressing the green button provided, and the air- craft was then under full automatic control. This was indicated by the extinction of the amber lamp and the illu- mination of a green one. The lamps are provided with a night dimmer. The pilot's control for the autopilot is a fairly large, hori- zontal, knurled knob. For climb (up to 2odeg), or dive (to 40 deg) it is pushed forward or backward in the normal sense. For bank, which is limited to 45 degrees in either direction, the rim of the knob is rotated. The autopilot is also provided with an elevator-trim indicator situated beside the control knob. Immediate disengagement occurs when the diminutive switch on the main aircraft control wheel is depressed. After this it was decided that we had covered enough ground for one flight, and so we headed for base. The test pilot lowered the wheels and flaps, throttled right back, and demonstrated a somewhat unconventional rapid descent. The actual landing which is described in these notes. This aircraft and several others are now ready for
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