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Aviation History
1943
1943 - 1815.PDF
JULY 15TH. 10.43 FLIGHT CORRESPONDENCE The Editor does n<> hold Inmseti responsible, foi iht tww± i-x pulsed by cormspotulcnts. The names and addressee o/ the wnte.'s, noi necessarily lot publication, must in all rases accompany letters. \ REVERSIBLE-riTCII AIKSCXEW To Shorten the Landing Ran A WHILE ago you reicrred to authoritative figures provingthat such airscrews would be nowhere nearly efficient.enough to cluck the speed of a dive bomber. These one must accept. " K. V. P.'s" letter in your July 1st issue mentions anotheruse, however—one, indeed, which seems to me to be important beyond dispute—namely, the employment of "negativethrust " to shorten the landing run. At slow speeds aeiodynamic considerations scarcely enterthe discussion, and it seems lair, to judge purely train experi- ence, to assume that the deceleration caused by two engines"going backwards," full-bore, should be oi the same order as the acceleration produced by the same engines in startingfrom rest. As with modern tricycle undercarriages, the landing runpresents tar greater problems of space and time than the take- off run, it steins reasonable to press for the introduction ofreversible-pitrh airscrews solely loi this purpose, legarding any power of deceleration in flight which they might be lound toprovide as a pure bit of "buckshee" good luck. " DRIVER." BOMBER ARMAMENT Changes Interfere with Production I SHOULD like to reply to Mr. A. T. Ilenshaw's letter pub-lished in your July 1st issue, which deals mainly with bomber armament.First, he presses the need for heavier-calibre guns to be installed in our heavy bombers, and then contradicts himseltby saying that such installation would affect the present heavy bomb load, which he admits is of supreme importance. Secondly, it must be borne in mind that 0.303 cal. in./gunshave been our standard armament in this war, and production of these, together with, ammunition and turrets for them, isnow in full swing, "the very fact that the nose armament of , the Halifax has been reduced indicates that experience has^taught us to consider defensive armament after speed, bomb load, and range. Therefore, it seems that the need lor heavier-calibre guns is not sufficiently urgent to warrant the delay which would inevitably result from the change-over in pro-duction. As to why the Americans bomb from high levels, it is pre-sumably to minimise the danger from anti-aircraft fire, fighters being deajt with very effectively by the thirteen m./guns whichare carried. It should be remembered that the Lancaster attack on Le Creusot was made over weakly defended territory,and also had that invaluable element of surprise. If the .enemy were prepared for such attacks he would soon devise somethingto prevent them. A balloon barrage, for instance, would have a disastrous effect on scores of heavy bombers flying at lowaltitude and in close formation as the Fortresses do when attacking. I think that there is little doubt that the Americans &r&lt;;using "heavies" as profitably as it is possible to do in daylight. C. C. CO WEN (D/S Att. 154 Sqdn. A.T.C.). A Matter of Primary Function RECENTLY in your Correspondence page there has beensomewhat of a controversy regarding the merits of the 0.5m'. and 0.303m. machine-guns, and 1 feel I must put in aword for the armament of British bombers. Most of your correspondents apparently lose sight oi theiact that they are talking about bombers and forget that the bomber's chief weapon for ollenre lies in its bomb load, andnot in the number of guns it carries, so that a better argument is to compare the 2|-ton bomb load of the Fortress with the8-ton load of the Lancaster (on short range, of course) rather than compare the Lancaster's 0:303m. guns with the 0.5111. ofthe Fortress. And please do not forget when the Air Ministry talk about8,000-lb. bombs that they are almost twice the weight of a single Fortress's total bomb load. But to get back to thequestion of machine-guns. The armament of a heavy bomber is (or should be) purelydefensive, as a bomber's job is to bomb and not shoot down enemy fighters, however desiiable that may be. If Fortresses attempted night raids into the heart of theRuhr they would not be in a position to fly in protective forma tion, and their 0.5m. machine guns would be no use againrtthe 30,000 anti-aircraft guns which the Geimans claim help to defend the Ruhr. I would like to add that the Air Ministry and British air-craft industry know what they are doing. Two examples of this which can be referred to here are: — 1. When a good many people were clamouring loi a lankbuster" we had one which is the best weapon in the woild lor the job—I lie Hurricane lh>. 2. When >a number of persons were saying that, howevergood the heavy bomber was, we wanted a high-speed day bomber again, we already had the best weapon in the worldfor the job—the D.H. Mosquito. So, as •& word of advice to any persons who think we lasbehind in the air, I would say that the British censor is very strict. V. REDMAN (488 Squadron A.T.C.). SAILPLANE EFFICIENCY Pendulum and Weathercock Problems The Pendulum and Weathercock were flying hand in hand, P Each chortling long and loudly as they wiggled to and fro. "Do you think," cried they with n\ee, ' we'll ever make the land? ' " I doubt it," moaned Hie pilot, " I'm much too ill to know. ' —J. U VVM R. J. R. BROWN is most refreshingly naive with hiswea I hei cocking sailplane and pendulum tail plane— rather reminiscent of a duck! One suspects he has not flownor has missed the significance of the various parts of an air- craft with which one is familiar. Whilst conceding the rudder to be replaceable by moderntheory, the elevators are not, which brings us right back to the mysteries of aerofoils and lift. Lilt produced by any aerofoilsection worthy of the name is a lunction of the angle of attack or inclination of that section to the airstream and to the rela-tive speed of that air flowing around the section. For each value of speed v and angle a theie will be a different set oltwisting moments about the centre of pressure CP. When resolved, these moments will have to be in equilibrium,otherwise the wing and consequently the aircraft will porpoise. The tailplane has the happy purpo«e of damping out thislongitudinal "hunting" within small limits, and the con- trollable elevators take care of the bigger bumps and gusts.Let me say here that this is net halt what actijally happens, and is only serving to make my point. Elevators are not onlyhandy things to have around the craft, but are absolutely essential, and they must be under accurate and light controlwith plenty of " feel "—-ask any pilot ! How, let Mr. Lawson ask Himself, is he going to control asailplane to claw a few more feel ol altitude against a jealous gravity aud no b.h.p, to Imlp, without an elevator i Stillworse—how will he land ? ' Flying-on'' technique, maybe, shows promise with brakesand a deal of space, but 1 cannot think of anything more irritat- ing during a landing approach than a jammed or flappingelevator control, to omit the fearsome thought of a pendulum- controlled surface working its malicious will with the horizon. All the same, such an approach would be fhe sight ol acentury—viewed from a distance ! Sorry, Mr. Lawson, but you did ask for it! J. D. WALSH (A.F.R Ae.S.). Gas Turbines and Jet Propulsion for Aircraft By G. GEOFFREY SMITH, M.B.E. A second edition of the above booklet s now available frcm ' Flight" publishing offices. The new work consists often chapters and includes many '/lustrations. Price 3/6 plus 3d. post
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