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Aviation History
1943
1943 - 1106.PDF
448 Notes from a Test Pilot's Diary—5 FLIGHT APRIL 29TH, 1943 Aileron Control Differences Between Fabric and ISAetal-covered Surfaces : Importance of Manufacturing to Small Tolerances : Terminal- velocity Dives the Real Test By " WITNESS " GOOD ailerons do more than any other control tomake a pilot feel at home in an aircraft. A heavyrudder and elevators which tend to be over- balanced for small movements are easily forgotten, even in a fighter, if the ailerons feel " right." The view used to be taken that heaviness of aileron control in a bomber did not matter, provided that stability was good, and a steady course could be maintained without the need for frequent corrections by the pilot. But this war, in which four-engined bombers are expected to dive at 400 m.p.h. and be capable of violent evasive action during the pull- out, has changed our ideas in this respect. Series-production of every type of machine of which 1 have ever had experience indicates that, whilst it may be easy enough to build a prototype with good aileron control, manufacture in quantity produces entirely new problems. No other control surface is so sensitive to small discrepancies in profile, gap and fit of shroud. With the general tendency to change from the fabric- covered aileron, in which the tension of the fabric could not be guaranteed to be reproduced at a constant value, to the metal-covered type, we had reason to hope that much of our trouble would vanish. But metal-skinning has not turned out to give such an exact similarity of surface that fairly big aerodynamic differences are not discernible amongst metal-covered ailerons. At the same time, it must be acknowledged that the metal covering does generally give a stiffer aileron, and one with lighter handling characteristics, than fabric. Obviously, if it were practicable to manufacture to suffi- ciently small tolerances, metal-covered wings and ailerons could be produced with such accuracy that-the test pilot would never have to call for an aileron change. As things are, the test pilot must set his own standard of what, for the particular type of machine he tests, may be passed in the way of snatch or overbalance, and at \Vhat stage the ailerons are so heavy as to be an embarrassment in manoeuvre. T.V. Dive Test The only test which proves the ailerons throughout the speed range is the dive to the limiting speed of the air- craft. In extreme cases of overbalance, the ailerons may snatch so badly on the climb or during a full-throttle level flight that a dive is out of the question. Also, if a machine is trimming extremely one-wing-low, it may be impracticable to attempt a dive. But in ordinary cir- cumstances the dive will be the real test of whether the ailerons are satisfactory or call for adjustments. The ailerons should be worked throughout their full travel as the aircraft is allowed to accelerate gradually up to its maximum. This needs considerable strength on some types, and there was one fighter with fabric-covered sur- faces which often required both hands. Incidentally, with fabric one can sometimes improve a snatching ten- dency by carrying out several dives, due to the stretch- ing of the fabric with reapplied load. . When checking the lateral trim, whether in the dive or in any other-condition of flight, the need for prevent- ing yaw seems obvious, but it is sometimes overlooked. Quite apart from the fact that yaw in the dive produces excessive side loads on the tail unit, I have come across more than one instance of a test pilot being bewildered because he found that, for no apparent reason, a machine which had trimmed satisfactorily on one flight seemed to have become left-wing-low the next time he flew it. A careful investigation of how he had flown the machine revealed that on the second flight he had not noticed whether the sideslip hand of the turn-and- bank indicator had been central. When it had been explained that by flying with yaw one could automatic- ally make a machine one-wing-low, he soon proved :o his own satisfaction that by trimming his rudder to eliminate skid, he could get the machine to fly level without lateral pressure on the stick. Curing Overbalance The causes of overbalance and heaviness will vary to some extent according to the particular type. On one machine it may be permissible to thicken the trailing- edges of the ailerons by doping the same length of cord above and below on both sides, in order to cure snatch. On another the normal method is to increase slightly the down-droop of the ailerons, which will tend to hold the aileron-noses up into the wing and so reduce the effectiveness of the balance. Aerodynamic heaviness can only be cured, short of changing ailerons, by giving the ailerons a small amount of negative droop, or by closing up the gap if the design makes this possible. Sometimes it is difficult to differentiate between mechanical stiffness and aerodynamic heaviness. Just because the ailerons arc- free to move on the ground, it does not follow that excessive mechanical loads will not be felt when the wing Ilexes, as flex it must, under the loads imposed by the dive and pull-out. It is, therefore, always worth while checking the run of the controls, ten- sioning and possible causes of fouling before assuming that the aileron surfaces are the root-cause of heaviness. MASTER PILOT'S TICKET FOR CAPT. LORAINE CAPT. A. C. LORAINE, of British Overseas Airways Cor-poration Atlantic services, has been awarded the Air Ministry Master Pilot's Certificate No. 1 of Series 2, valid for land and marine aircraft. Master Pilot's Certificate No. 1 of Series i was awarded to Dipt, L. A. Walters, now Flying Establishcnent Officer of the Corporation, on February 15th, 1934- The principal difference between Series 1 and 2 is that a 1st Class Air Navigator's Licence must be held to qualify for the latter. Capt. Loraine was previously awarded No. 19 of Series 1 on July 10th, 1936, valid for landplanes. Capt. Loraine was second in command of the flying-boat? on which the Prime Minister made three crossings of the Atlantic. It will also be recalled that Capt. Loraine made a dramatic flight, without radio or weather reports, to West Africa after the fd 11 of France, and the entry of Italy in the war had resulted in the closing of the Mediterranean to civil aircraft.
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