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Aviation History
1945
1945 - 2186.PDF
NOVEMBER IST, 1945 FLIGHT 487 CORRESPONDENCE machines, and the articles published in recent issues haveshown how valuable this saving is. The use of flight refuelling as a means of " assisted . take-off," howevei, still shows advantages over other methods. An aircraft designed foi, say, a take-off wing loading of50 lb./sq. ft., but with a stiengthened wing structure to allow refuelling in the air to bring the aircraft up to, say, 70 lb./sq. ft., can show far greater advantages over an aircraft which may have to take oft at a rate of acceleration uncomfortableto the passengers; and where any breakdown would be most calamitous. Moreover, additional propulsive methods meanadditional structure weight (for strengthening) not balanced by reduction in fuel load. 1 Developments during the war have not been towards im-proving the payload/gioss weight ratio. We were building machines to defeat our enemies, not to fly trade routes econo-mically . The war is over and we have to think hard and act quickly/ if we are to gain any standing in air traffic. We have been shown a system which can be put into operation now, and itis now that we need it. GRAD.R.Ae.S. Correcting Faulty Logic IN Flight, October 18th, you publish a letter by a Mr. Huntleyin which he gave as his opinion that "assisted take-off has now outdated flight refuelling." Not having been connectedwith aviation for as many years as this gentleman, I hardly like to venture a correction, but the logic of his statementappears to be so much at fault I cannot resist it. Surely high wing-loadings, with inadequately lengthed run-ways, are the only reason for the adoption of the principle of assisted take-off, but whether an aircraft has a wing loading of,say, 30 or 5o lb./sq. ft., the total weight of the aircraft still equals structure wt. + fuel wt. + pay-load ; and it is obviousthat if the fuel load (i.e., fuel load at any given time) is reduced by the aid of refuelling in the air en route, then pay-load can'correspondingly go up. Also, with refuelling you have no huge tanks which, for most of the distance, are doing nothing(except adding weight). It might also be mentioned that the structure does not haveto be stressed to withstand high wing-loadings and extra accelerating forces at take-off. The rate of climb and general performance is not impairedas in the case of a heavily loaded (power and wing) aircraft, also the risk at take-off is considerably reduced and Grannyneed not suffer that horrible " + g" feeling which the pas- senger of any aircraft must have if it is being accelerated fromrest to 150 m.p.h. in 1,000 yards or so. I should think that some consideration should also be givento the fact that the -ideal flight refuelled aircraft is a large medium-range type which could be used on the medium-lengthair routes (i.e., London-Paris-Stockholm, etc.) as well as the long-distance routes where it would operate with the aid of|f.R. This would eliminate the need for special aircraft for specificroutes which, I understand, is the bugbear of airway operators. APPRENTICE. "THE TUNE HAS CHANGED" A.T.C Officers' ExpensesY OUR correspondent "Another One of Many " (Flight, Octo-ber 18th) mentions three items in regard to A.T.C. officers which 1 also agree with : (1) They did their job after longhours at their own work or business; (2) Very little help from V.I.P.s; (3) Out-of-pocket expenses. Regarding item (3) I can verify that many officers were putto considerable expense in travelling to and from their H.Q. to carry on the good work, apart from the fact that they alsotook charge of parties of cadets visiting R.A.F. stations, private cty^raft factories, etc., where the expenses of cadets were paidfrom squadron funds, but the officer paid his own. They were also expected to contribute to squadron sports funds, and inone case were asked to provide the necessary funds for a free Christmas party for the squadron (and they duly paid up). Other items, such as running their cars (using basic ration),where, in many instances, the squadron was dispersed in two or three schools in the district for the convenience of cadetsliving there, travelling to these places through fog and over icy roads—conditions under which an ordinary person wouldbe safely indoors by a nice fire. One other item so far not mentioned is " uniform allow-ance." Originally ^15, later increased to £20, it did not by any means cover the initial outlay for an outfit. Tunicand slacks ^10 10s , cap (forage) £1 9s. 6d. (Heaven knows why), two shirts with collars at £1 4s. each, raincoat at £4 10s.,shoes and socks (black), gloves, etc., more than swallowed up the allowance. If a greatcoat was thought necessary (andit was during the winter months) the officer bought it out of his spare pocket money, from £10 10s. upwards; when agracious Air Ministry consented to officers wearing a peaked cap (off ceremonial duty) no mention of allowance was thoughtof, and once again the officer went down his pocket, to the tune, of at least £2 15s. All renewal of items of kit after the first purchase has to bemade by the officer (including coupons). Shirts, collars, ties, socks, and gloves do not last for ever, and wartime itemsincrease in price, and the quality of material is definitely poorer, so more expense is incurred, and is as cheerfully paid,just to keep up the prestige. One suit of uniform is supposed to last four years, and theraincoat five years, but I wonder how many officers have been allowed any renewal expenses for kit after 41 years ofreal hard wear. Perhaps a grateful Air Ministry will shortly realise it is timethey did something about it, and make a further grant (and coupons as well) or is that, too, beneath the notice, of the V.I.P.s? "ONE OF MANY." DEFLEX-REACTION PROPULSION Where the Argument Breaks Down T HOPE the following will help to clear up the fallacy perpe-trated by Mr. Umpleby in his article " Deflex - Reaction Propulsion " (Flight, September 13).Let gas flow along any plith through the aircraft at the rate of M lb. per sec, entering and leaving it with axial componentsof velocity V>, VR, respectively. Further let its velocity vary in any manner along thepath. Let the tangent to the path at a point P, wherethe velocity is v, make an angle 1/1 with the axial direc-tion. Let s be the distance along the path from A to P.The mass of gas in an element ds of the path is M — ds lb. v V2Its acceleration is — = P \>y Newton's Third Law the force exerted by this element: on the aircraftis F, = — ds . v — tangentially v as - - _. M, „# ' • • •and F, = — ds . v2 -- normally. 2 v ds :. The total axial thrust (poundals) vi -j- normally and v ~ tangentially -p- dBut - pB fB / \ 1 (Fl cos </> — F2 sin i/> = M I \ / J A •'A dv cos — v sin </> -3- j dsdsj dv= -3- cos di — v sin tA - - ds, r v ds F = M '. V COS i/r = M - V B AThis proves that no matter how the gas is deflected within the aircraft, the total axial thrust is precisely the same, andthus deflex-reaction propulsion is doomed to failure. The point at which Mr. Umpleby's argument breaks down isthe assumption that the reaction at entry to the compressor is zero. This is true only if the aircraft is stationary, since whenin motion, half the intake air moving with the velocity of the aircraft must be deflected through 180 degrees to enter the farside of the compressor, thus producing a negative thrust. In the stationary case he considers, the exit velocity is 1 620 ft.'sec. and the thrust is therefore —'•— = 50.6 1b. The discrepancy between, this and Mr. Umpleby's result of 69.37 'b.is due to an accumulation of errors in his calculations. For example, at exit from the compressor he states that angle c is49 degrees, whereas it is obviously 32J degrees. He has also given the gas a deflection in the turbine for which he has notincluded the corresponding negative thrust. P. J. HIGGINS.
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