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Aviation History
1944
1944 - 0828.PDF
432 FLIGHT APRIL 20TH, 1944 CORRESPONDENCE craft in question would have to be a turret fighter in order to knock down the Bombers' as they passed. I can only quote to Mr. Leach the two outstanding examples of the consequences of compromise, namely the Skua, prob ably one of the finest dive-bombing aircraft ever built, but barred from the top class by the inclusion in the specifications of reconnaissance and air combat requirements which so over loaded the aircraft that it became too slow for the proper execution of its initial function ; and then the Fulmar, designed with all the ingenuity and ability of Fairey aviation, but doomed as a fighter from the outset because the specification included a second seat for an observer and additional weight of gear that excluded high performance. Since, for the last four years, every brain in the country has been devoted to the1 recognised and essential need for squeezing not only'ioo per cent., but IOI per cent,, out of each aircraft in its own class, I fear Mr. I. M. Leach has not quite got the right answer. Should he care to go up in combat in his 85 per cent, aircraft I will be delighted to offer him a trip in a rather elderly Fulmar over Focke Wulf 190 country, which would undoubtedly convince him of the error of his ways. "NAVIATOR." J SORTING OUT THE SNAGS Ask a Test Pilot JUDGING from the letter published in Flight of March 30, either Mr. Blackburn has had very little experience of modem aircraft, or he has been extraordinarily lucky. If he asks any production, maintenance unit, or acceptance test pilot he will learn that, of aircraft which are handed over as being theoretically serviceable after ground check, 50 per cent, (as a minimum) are snagged for one or more troubles of the type mentioned by "Indicator." To quote only four examples, an undercarriage which, with its indicators, works perfectly on a ground rig, very often fails under airflow pressure; a directional gyro, picked and tested on the bench, will topple or precess when subjected to bumps 01 small amount of G; an airscrew may constant-speed on ground run, but may hunt badly in the air; and an r.p.m. indicator, though perfectly steady on the ground, will leap all over the place when subjected to flying vibrations. Further more, this sort of trouble can regularly crop up on aircraft which may have been tested and passed a week before, and which have been duly inspected before flight. I have no doubt that manufacturers would be happy to employ Mr. Blackburn at any figure if he could guarantee even an 80 per cent, freedom from retests for troubles which should, in his opinion, be discovered on the ground. "TEST PILOT." ROUND-THE-CLOCK BOMBING Change Hardly Worth While IN your issue of March 23rd, R. L. Gladwell has put forward a case for using part of the U.S. Bomber Force on night raids. Below is a precis of some arguments put forward in '' Target: Germany" by the Commanding General, Ejghth Bomber Command, "to those who favoured switching the American bombers completely to night operations '': (i) Day bombing permits destruction of small targets that could not be found, seen or hit at night, (ii) Day bombing is more economical, as a smaller force can destroy a given target, (iii) Enemy defences are kept on the alert 24 hours a day. (iv) U.S. crews are not equipped or trained in night bomb ing technique. Switching them over would involve a long training period at a time when delay is unthink able, (v) The number of enemy fighters destroyed by day can hardly fail to have an effect on the morale of Nazi pilots, (vi) At night the heavy defensive armament of the American "heavies" would be so much more dead weight. I have no doubt, myself, that greater accuracy can be achieved in daylight bombing, although it is true, as R. L. Gladwell points out, that night precision bombing has been greatly facilitated by the use of target indicators. Admittedly, not all the arguments enumerated above are sufficient to condemn a switch of part of the U.S. bombing potential to night raids. But providing the weight of the daylight offensive does not grow out of proportion to the night attacks of the R.A.F., the administrative difficulties involved would make even a partial "switch" hardly worth while. L. W. SAYER, Sgt./A.TX. THE DUCTED RADIATOR Why Negative Drag is Produced SQN. LDR. BROTHERTON, in his letter printed in Flight, April 6th, questions the truth of the statement made by a previous correspondent that the force on a Townend ring is directed forward. Not only have I actually seen this to be the case in a true-to-scale model, but the fact has a perfectly sound theoretical reason. In the model the ring was suspended by threads in its actual position and an air blast turned on. It was seen that the ring really moves forward against the air blast. POSITION WITHOUT AIR FLOW AIR FLOW From theoretical grounds the result can be easily understood. The Townend ring, like the slat of a slotted wing, produces a slot between itself and the engine. In this slot the air flow possesses a direction different from that which it possesses before passing through the ring—i.e., direction changes from AB to BC. * Considering the flow along BC, it is seen that by suitably shaping the ring the total air reaction acting on it will be in the direction OR (just as the air forces acting on the slat in the automatic slot move it out against, apparently, the air flow). By resolving the air reaction represented by OR into two components—one along the line AB and the other perpen dicular to it—it is clear that the component OP, instead of being a drag component, is a negative drag component—i.e., is actually helping the ring move forward, and if the latter is loose it will really move. The other component, QO, would be balanced by an equal and opposite component on the dia metrically opposite section of the ring, so it does not enter into the question. It might seem as though we are getting something for nothing (and so violating the Second Law of Thermodynamics), but, of course, we are not. It is merely a case of diverting more of the original energy of the airscrew into forward thrust and less being wasted in creating unwanted turbulence or drag. R. SHOHAM, B.Sc. New Edition. ^ GAS TURBINES AND JET PROPULSION for Aircraft By G. GEOFFREY SMITH, M.B.E. fa THIRD and enlarged edition of this "FLIGHT" book with illustrated descriptions and comments upon the varying forms of steam and gas turbine-compressor units, is now on the press, and will be available shortly. Fifteen chapters and many new drawings are included. In this latest edition the original chapters have been retained with modifications and additions. The joint official announcement of the R.A.F. and U.S.A.A.F. has made it possible to extend due credit to the inventive genius and pioneer work of British technicians who developed gas turbine units to a practical stage for aircraft. There is a foreword by Sir Geoffrey de Havilland. Orders for this third edition, which is priced at 6/- or 6/4 by post, wi" be executed in rotation, and should be addressed to-— Flight Publishing Co. Ltd., Dorset House, Stamford Street, London, St-'-
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