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Aviation History
1954
1954 - 0153.PDF
FLIGHT, 15 January 1954 71 FOKKER S.14 IN THE AIR . . . 200 kt. With maximum cruising revs of 11,800 at 30,000ft, the Mach number is about 0.73 and the T.A.S. 280 kt. Maximum cruising speed at sea level is 422 kt. In the unlikely event of a power failure a gliding speed of 145 kt I.A.S. should be maintained; the glide angle is such that from 10,000ft in still air 17 miles can be covered. According to figures obtained during early tests of the S.14 Nene, levels at full throttle at 20,000ft and 30,000ft gave true Mach number readings of 0.77 and 0.76 respectively. Sonderman now suggested that I dive once or twice to experience the transonic characteristics. Frankly, I had no idea how to judge a 30 deg dive in this icy and hazy blue, nor was I sure how best to get into the dive, or what, if anything, to do about power setting. Illogically, it did not occur to me to wonder how to pull out of the dive, although I knew from the book that there is at present a "2g" limitation at over about Mach 0.8 and 4.5g between 0.75 and 0.8. On production versions of the Nene Trainer the torsional strength of the wing is to be increased to permit 4g up to Mach 0.86. The wing form remains unaltered. The thickness ratio is approximately 12 at the root, and, unexpectedly perhaps, increases to a maximum of over 14i per cent outboard. In the physiological sense, I was a little apprehensive at the idea of an unpressurized dive, though intrigued at the pros pect of experiencing compressibility effects. Previously, flying solo, I had taken a Vampire and a Saab J.21R to the onset of mild buffeting, and then hurriedly recovered. I had also felt the same early symptoms in a Meteor and in a Canberra. There was no purpose in hanging about, so I trimmed carefully for level cruise, built up something over Mach 0.7 on the level with 11,800 r.p.m. and then peeled over to port and, finding the rudder pretty solid, held the nose straight and dived at what must have been about 20 deg. The altimeter started to behave like a clock without its escapement and at an indicated Mach number of 0.78 die airframe began to shake gently from the back end, the probe on the nose wobbling in sympathy. This mild buffeting did not bring any trim-change that I could notice. The buffeting increased as speed built up, and at approximately Mach 0.8 I was told to operate the dive brakes and leave the elevators alone. The result was a very pronounced deceleration, a slight nose-up trim- change, and a gentle pull-out. The dive brakes have been tested with satisfactory results up to the limiting dive speed of 490 kt. The official time for full opening of the brakes is 1.5 sec and the nose-up trim change with free controls, normal e.g. (21 to 22 per cent M.A.C.) gives less dian 1.7 g, reducing at high Mach numbers. We climbed back, and this time I was to dive a little more steeply and feel more severe buffeting. Once again I peeled over to port at about 34,000ft and down we went. The altimeter needle began to whirl round, the cloud tops seemed to be approaching very fast, and again came the shaking. I wondered if the probe would eventually shake off. At something a little over Mach 0.8 I again operated the dive brakes and, as before, a gende recovery followed automatically. The final dive was to be an all-out effort, and I had now got a better idea of dive angle. The nose went well down, and after Mach 0.8 at around 28,000ft, descending at more than 10,000 ft/min, we were really getting cake-walk treatment. At the' point when the Mach needle was touching the red sector on the dial and showing 0.83 the right wing started to go down in spite of opposite aileron, and I felt that perhaps I had been shaken and compressed (as well as decompressed) enough. The indicated speed was 400-and-a-bit knots, which works out at 635 m.p.h. true or, in terms of Mach number, 0.831 indicated, which I was told was 0.85 after correction. Once again the dive brakes opened almost instantaneously, giving immediate recovery, and when the nose was pointing upwards again Sonderman told me to use the speed and pull round in a huge loop. With requests for guidance on how hard or otherwise to pull, I managed to complete the loop according to plan. On previous occasions, in other jet aircraft, I have usually either flicked out or stalled out on top. Jet loops seem so huge and slow to one who now usually flies light aircraft. The recommended speed is 300 kt. During all this performance I had completely ignored the Nene, which whirred on regardless at 11,800 r.p.m. We had been air borne for about 30 minutes, and still had plenty of fuel. Rolling in a machine of this sort is hardly to be regarded as an aerobatic manoeuvre any more. At almost any speed, but preferably at 320 kt, and with more or less use of aileron and no conscious use of the other controls, the S.14 will roll smoothly COCKPIT LAYOUT (II): Equipment and controls continued :— (69) Seat-position control, (70) Ejec tion-seat jettison control, (71) Safety pin and sear, (72) Cockpit-heating and ventilation control, (73) Wind screen-heating control, (74) Wind screen de-icing pump, (75) Rheostat for instrument-panel lighting, red and white, (76) Emergency oxygen con trols for pilot and co-pilot, (77) Ground/flight switch, (78) Radio volume, pilot and co-pilot, (79) Igni tion isolating switch, (80) Generator switch, (81) Gyro-compass corrector, (82) Wheel-door test, (83) Power- failure fuse, (84) Main fuse, (85) Hand fire-extinguisher, (86) Hood limit switch, (87) Oxygen economizer, (88) A.D.F. amplifier, (89) Engine air-intake ducts, (90) Cabin-heating pipe, (91) A.D.F. loop antenna, (92) Switch, hood fully open, (93) Hood lock, (94) Oxygen bottles, (95) Fire- extinguisher bottles, (96) Hood sliding rail attachment point, (97) Transmitter-receiver S.V.R.174, (98) Inverter S.V.R.174, (99) Anti-g suit selector valv 00) Anti-g valve.
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