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Aviation History
1932
1932 - 0818.PDF
FLIGHT, AUGUST 12, 1932 CORRESPONDENCE The Editor does not hold himself responsible for opinions expressed by correspondents. The names and addresses of the writers, not necessarily for publication, must in all cases accompany letters intended for insertion in these columns. When he comes to the Schneider machines we fear our correspondent has his facts slightly wrong. The wing area of the Supermarine was 145 sq. ft., and not 169 sq. ft., as in the " Gull." The ratio of wing area to 145 maximum horse-power of the S.6 was ^-^ = 0.06. The HIGH-SPEED FIGURE OF "GULL" [2803] I have from the very first been an admirer of the Percival " Gull," and nobody would want to dispute its clean layout, but I should like to be so bold as to contradict your statement that its high-speed figure of 27 is the highest known so far. It is certainly a good value, but there are aeroplanes which score even higher. Take the Lockheed machines, which I regard as the cleanest design anybody has produced yet. The " Orion " as used by the " Swissair " is supposed to do 225 m.p.h. with an engine of 580 b.h.p. and a total wing area of 275 sq. ft. This works out at nearly 37. Now there is the case of the Supermarine S.6B, which, you say, has a lower H.S.F. than the " Gull." Assuming the b.h.p. to be 2,300 and taking the maximum speed it is capable of as 407 m.p.h., and also assuming the " 6 " to have a lower aspect-ratio, but the same area, as the and B.H.P., 1453 Gull '' and " 6 " respectively: Tqjr and loU V» " Gull," their H.S.F.'s are proportional to these are for 4073 .or 1.25:1, which gives the Supermarine a value of 34.75, say 35. The assumption regarding wing area may not be cor rect ; if the area is larger, the H.S.F. will go up, but it can come down to 133 sq. ft. and bring the H.S.F. to 27, like the " Gull's." I am unfortunately without reference books of any kind, and am prepared to be found wrongly informed. There is also the small matter of landing speed. Having been brought up on the rule that wing loading and maxi mum lift coefficient determine landing speed, while high- or low-wing arrangement influence it only to some 3 m.p.h. and aerodynamical cleanness does not make any difference, I am rather at a loss with a figure like 42 m.p.h. The wing loading of the " Gull " is reasonable, but on the high side, and taking KLmax = 0.8 to allow for a high- lift section and an area of 180 sq. ft. to account for fuselage lift, we get: V - V— V n.8 r196 KL 'l96 o-y X X W Ai 11-3 52-5 M.P.H. W _ 2,050 180" / = V A = = 11.31bs /sq. ft.) Allowing for the odd 3 m.p.h., the job being of the low- wing type, the landing speed, looked upon with a very kindly eye indeed, is somewhere near 50 m.p.h. If it is not, I shall be very glad to be convinced of my mistake, but at present I cannot see where it conies in. This question of landing speed is a curious one indeed. Some time ago I made out a list of aeroplanes produced in various countries, and found that some manufacturers, mostly in the States, underestimate their stalling speed to the extent of 20 m.p.h. or so. The Vickers Intercepter lands on paper at 63 m.p.h., but works out by calculation at 75 m.p.h., and anybody who has seen it land has felt like saying unkind things about it. I trust Mr. Edgar Percival will not think that I am trying to be equally unkind about his machine, for I am of the opinion that it is very fine indeed. These notes were put down out of pure interest, and I hope someone will come along and clear them up. The Hague, J. VAN HATTUM. August 3, 1932. [Our correspondent appears to be perfectly justified in his claim that the Lockheed " Orion " has a higher value of the " High-speed Figure " than the Percival " Gull." The two machines are not, however, comparable in that the " Orion " has a retractable undercarriage. That this should result in a large increase in the value of 7^— is only natural. In a " clean " aeroplane the undercarriage drag is a large percentage of the total. Quite likely, if the " Gull " had a retractable undercarriage, its " High speed Figure " would be as good as that of the " Orion." 2,300 ratio j 47 QQQ ( at 407 m.p.h.) works out at about 459, and if that is multiplied by 0.06, the result is 27.5 approxi mately, and not 85 as calculated by our correspondent. We must plead guilty to using somewhat ambiguous lan guage in stating that the " High-speed Figure " of the " Gull " was " even slightly higher than that for the Schneider machines." What we really meant was that the minimum drag coefficient appeared to be slightly lower, since the higher the propeller efficiency the greater the drag coefficient. The Supermarine S.6 was, of course, designed for high speed purely and simply, and is known to have had a very high propeller efficiency. The " Gull," on the other hand, is designed for cruising, and is pre sumed to have its greatest propeller efficiency not at top speed, but at cruising speed, or possibly somewhere be tween the two speeds. Thus it is permissible to assume that it has a lower propeller efficiency at top speed than had the S.6. Actually there is so little difference in the " High-speed Figures " that the two types appear to be near enough identical in their minimum drag coefficients. On the subject of landing speed, we sympathise with Mr. van Hattum. We also have at times been puzzled by the low figures achieved. Our correspondent should, how ever, distinguish between the minimum speed at which a machine will stay in the air and the horizontal speed over the ground in landing. When an aeroplane is landing, it is, of course, sinking at a rate which will vary according to the " fineness " and the wing loading. In other words, according to the gliding angle and gliding speed. We know for a fact that in the Percival " Gull " the air speed indicator needle goes " right off the clock," as the saying is, when landed at its slowest. As the A.S.I. cannot be trusted absolutely at the lowest speed, it may be slightly in error, but the figure is certainly not far removed from 42 m.p.h.—ED.] RISKS OF CLOUD FLYING [2804] There usually is a considerable body of opinion which, despite official inquiries into fatal crashes, believes that it knows the real causes. There can be no question that it is necessary for aviation that accident causes must be fully investigated for the benefit of would-be survivors of flying, no less than for the quelling of unhealthy rumour. After the Meopham disaster, rumour and uninformed opinion were rife. Various " Puss Moth " crashes have also given rise to quite unfair bias and suspicion. In re spect of the most recent—that of Mr. Bossom—such sus picion will set like drying mud if a clear exposition is not made available to the interested public. It seems, there fore, in the public interest that one should put on paper a possible cause of such accidents, and couple it with a serious warning. I claim to have some considerable know ledge of cloud-flying, and, more particularly, of the be haviour of all sorts of pilots when they find themselves inside a cloud. In a large number of cases, any one pilot will probably retain adequate control of his aircraft in a cloud, but it is equally certain that in other cases the same pilot will lose control, either after disturbance or after a given time-lapse. Loss of control often goes unrecognised by the pilot, who probably compensates for a nose-down attitude by almost sub-consciously throttling back a little, keeping r.p.m. and air speed in proper proportion. Until he emerges from the cloud he may have no idea that things have got out of hand. When he does emerge, the ground is usually seen looming deceptively close, and maybe in an unexpected quarter. The next and instinctive reaction is to pull every thing hard back. This in itself may obviously set up very unfair loads, particularly if a large aileron couple is simul taneously applied to correct bank. You will note that, so far, the chain of events agrees precisely with eye-witness reports in the two cases I specifically mention above. What happens next depends on the structural abilities of the air- 762
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