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Aviation History
1957
1957 - 0742.PDF
748 FLIGHT, 31 May 1957 The short undercarriage legs of the Jet Provost Mk 2 can absorb very high touch-down rates of descent. By contrast with earlier trainers, the rudder is not normally used for taxying. JET PROVOST in the Air . . . A METEOR PILOT'S REACTIONS By C. M. LAMBERT NOW that I have sampled the Jet Provost I can well understandhow the R.A.F. flying training authorities arrived at their very high opinion of the machine as a basic trainer. I have flowna number of light jet aircraft from the Vampire Trainer down to the Sipa 200 Minijet; but in none of them did I find exactly theJet Provost combination of real jet-aircraft handling characteristics with true simplicity and moderate performance. The main purposeof a turbojet basic trainer is, after all, to teach a pupil from the outset the essentials of jet aircraft handling while not exposinghim from the very first to the blistering performance he will later meet in his operational type. The Jet Provost provides exactly this quality; the take-off runis long enough in time (though not necessarily in distance) to reproduce quite faithfully the take-off of some much heaviermachine like a Meteor. There is nothing of the tail-lifting and swing-correcting interlude between "brakes off" and fully airbornewhich is so characteristic of small piston-engined aircraft. The undercarriage is operated by push-buttons; retraction and exten-sion are very fast and virtually free from trim changes or thumping and rumbling noises. Flap selection is by a small lever which hasa single gated intermediate position to give take-off setting, and needs neither fumbling nor watching. In fact, the quicker thelever is moved the better. The power-lever action is very good; there is just enoughfriction to keep the lever where it is put, so that it can be moved easily with a touch of the hand; and the range of movement doesnot at any time exceed comfortable arm displacement. An acceleration control on the ASV.8 Viper allows the pilot literallyto slam the power lever open from the 8,000 r.p.m. position, and the acceleration of the engine itself is quick and smooth. Raisingof take-off flap causes a very small, firm trim-change combined with an almost imperceptible sink. A rate of climb of some2,000ft/min can be maintained steadily to something over 10,000ft, starting the climb at about 170 kt and decreasing speed by1.5 kt each thousand feet. Visibility, even through the heavily framed piston-Provostcanopy at present fitted, is good in all directions, though there is some interference on the left from the heavy windscreen bridgestructure. In service, Jet Provost Mk 3s will, of course, have the fully transparent windscreen and a slightly re-worked canopy. After I had taken off I climbed to 7,000ft, levelled off, andretained climbing power in order to observe the acceleration. It was slow but steady, and a gentle progressive nose-up trim-changeaccompanied the build-up of speed. When I reached 220 kt I applied elevator trim and found it extremely sensitive. As theEditor has remarked, the whole trim-range is encompassed with about one revolution of the trim wheel, a large cut-out in the rimmaking the datum position instantly appreciable to both hand and eye. The elevators give a firm, smooth response, the forces in-creasing steadily as speed builds up and being very well matched with the Provost's response. A sensible pull produces 2g andtwice that figure requires a pull which is firm but not too heavy. The ailerons are light and extremely effective at all speeds,giving an excellent approximation of the characteristics of fully powered ailerons with spring feel. The prototype aircraft whichI flew had a disconcertingly sudden response on initial aileron application, but reworking of aileron shrouds and horn shape willcure this in production aircraft. There was also a noticeable change in lateral trim with speed (right wing down at higherspeeds, left wing down at lower speeds) which is a characteristic of the prototype hand-built wings. The aileron trim was low-geared, but effective in cancelling this difference at any speed. I found the rudder control responsive, but heavy despite a sizeableservo tab; and this is exactly as it should be in a jet aircraft, for the rudder is really used only in the circuit. The air brakes are without doubt the most effective I haveever found in any aircraft. At circuit speeds they produce good deceleration, but at about 220 kt they have an effect like stampingon the brake pedal of a well-equipped car. These brakes consist of a strip of about 5in chord extending under the wing immediatelyforward of the flaps and over almost the whole flap span. This is balanced by a strip of about 2in chord, but of approximately thesame span, which extends above the wing to spoil some lift and provide a compensating trim moment. Actuation is by a slidingswitch recessed in the end of the power lever. In a dive, the Jet Provost gains speed steadily but not so rapidlyas to bring a pupil pilot too quickly against the speed limitation (360 kt below 10,000ft, 0.7 Mach above). When the nose is pulledup the speed drops off steadily, but again not with undue rapidity. Having exercised the basic controls of the aircraft I launchedinto a series of aerobatics which culminated in a highly unsuccess- ful stall turn from which we flopped over on to our backs to theaccompaniment of muttered apologies and comments from myself and Hunting Percival test pilot S. B. Oliver. I had applied rudderrather too late, at about 120 kt; and when it became clear that I had no more yaw in hand I eased the Jet Provost on to its back withthe remaining elevator control in order to avoid a tail-slide. The aircraft took it like a gentleman and showed no tendency to spin.I carried out my aerobatics between 8,000 and 11,000ft, making rolls at 180 kt and loops and rolls-off-the-top starting at 220 kt.Many light aircraft have a strong tendency to drop their noses at the end of a roll, but the Jet Provost could be held well withmoderate top rudder. In a loop it did not leave one too long without sight of one horizon or the other. A certain amount ofright rudder was required over the top to keep the axis of the loop straight. I found no signs of buffeting and no changes in controlcharacteristics in any manoeuvre; neither did I lose much height, though I did not pause between manoeuvres. Before returning to the circuit to try some landings and take-offsI completed a couple of stalls in the fully "dirty" configuration. As the speed fell back, air brakes were exchanged for take-off flapat 135 kt, whereupon a slight trim-change was noticeable. At 125 kt I pressed the undercarriage-lowering button, selectedfull flap and, throttled back to about 7,000 r.p.m., held height and waited for the stall. The speed fell off without unseemly hasteand the nose came steadily up as I maintained height. The speed came past the 70 kt mark, the aircraft buffeted firmly for an instantand then the nose fell cleanly away. There was only a slight tendency to drop a wing, the nose went smartly down a short waybelow the horizon, and the release of stick pressure was sufficient to initiate recovery. Height-loss was very small. Trying the sameagain, with the same results, I noticed that a little rudder was needed in order to keep straight in the final few knots above thestall, which came fully at about 65 kt. We had by then used about half our fuel load. In the circuit I made two landings and an overshoot, and foundno difficulty at all. From take-off to the beginning of the final approach there was no need to use the elevator trim; and aboutone-third aft trim from the neutral point removed all residual forces caused by full flap, undercarriage and reduction in power.The air brakes are not normally used in conjunction with flap, but it is not dangerous to do so and Hunting Percival pilots have oftenpopped the air brakes out immediately before touch-down. Their effect at very low speed is in any case small. There are no pro-nounced attitudes during the approach, and aileron and elevator control remain precise throughout. The engine is generally leftat 8,500 r.p.m. until a safe touch-down is assured, the speed being progressively reduced from 95 to 85 kt the while. Engine responsewhen adjusting the glide-path angle is good. Application of full power for an overshoot a short way from touch-down caused verylittle trim-change and the climb could be started immediately. The very fast undercarriage retraction was a great asset in thissituation. Touch-down itself is extremely simple. It requires only a veryslight check, which can be accurately judged; and as soon as the mainwheels are on the ground the stick can be released to put thenosewheel down as well. The ride after that is directionally stable and comfortable. Having the characteristic lack of drag of a jet (Concluded on page 752)
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