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Aviation History
1945
1945 - 1077.PDF
MAY 31ST, 1945 FLIGHT 591 CORRESPONDENCE 77r Editor does not hold himself responsible fot the views expressed by correspondents. The namss and addresses of (hi wrt'ert, not necessarily for publication, must in all cases accompany letters SPEED RANGE Trickery Near the Stall IN Flight, April 26th, on the editorial page, under the heading'' Stalling,'' you mention that when flying was in its in- fancy the speed range of aircraft was very small; to quote from your paragraph: " In fact, while the Gnome rotary engine was the popular type, one could hardly talk of speed range because the engine had no throttle." That is right up to a point; certainly this was the case with the Monosoupape. You will recall that in 1913 an astonished world was presented with the Sopwith Tabloid, which had a maximum speed of 92 m.p.h., and, as far as I can remember, a minimum speed of 34 m.p.h. This machine was engined with an 80 h.p. Gnome engine, not of Monosoupape type, but an earlier variation with inlet valves TB its pistons. *»^ draw your attention to this because your statement hardly seems to be consistent with facts as they were in 1913. I think also the original Avro 504 with a similar type of engine had a speed range very nearly as wide as that of the Sopwith Tabloid. R. C. McLEOD. [We perfectly remember the little Sopwith 'tabloid flown by the late Harry Hawker. We also recall the various versions of Gnome rotary engines, from the original 50 h.p. through the 70 h.p. and 80 h.p. to the Monosoupape. The point we wished to make was that one could hardly talk of speed range, since it was very nearly impossible to maintain level flight near the lower end of the speed scale so long as power control merely consisted of a "blip switch." We are quite aware that some of the early machines had quite a range between top speed and the lowest speed at which they could be touched-down after a glide approach, although it used to be said of one type of biplane famous at Hendon in the early days that it '' flew at 40 m.p.h. and landed at 50 m.p.h."—ED.] JETS AND TURBINES A Question of Propulsion Efficiency I FEEL 1 must reply to Mr. A. Stone's criticisms (Flight, May10th) of my letter (Flight, April 26th) in which I en- deavoured to explain what seemed to me to be the answers to some questions on jet propulsion put forward by Mr. P. A. Hearne in Flight, April 12th. I am afraid I do not see the point in Mr. Stone's obscure reference to a motor car engine, and I think he must have failed to realise that while the b.h.p. developed by a recipro- cating engine under a given set of conditions is constant, the thrust h.p. developed by a constant-thrust jet engine depends on the forward speed. This means that although a Napier "Sabre" engine may evelop 2,400 b.h.p. on the test bed, a jet engine of 2,4001b. i thrust will only develop 2,400 h.p. when travelliqg at Si m.p.h., as shown by the formula in my previous letter. Mr. Stone's statement that " there is no question of efficiency to consider" is quite wrong, however, since I was, of course, referring to the propulsion efficiency. Since Mr. Stone has presumably never heard of this, I would state that the propul- sive efficiency depends on the difference between the velocity of the aircraft and the velocity of the jet efflux, the greater the difference the lower the efficiency. Thus, if we assume, for the sake of argument, that the velocity of the efflux is the same at all forward speeds, it is obvious that the lower the speed of the aircraft the lower the propulsion efficiency. Perhaps it might have been better, however, if I had used the word " per- formance " instead of "efficiency," since the performance is usually based on the horse-power available, and it is one of the inherent characteristics of the jet engine that the horse-power available at low forward speeds is also low. 1 am afraid the facetious reference to my asumption that the fuel consumed per hour would be found by trial rather leaves >•<• cold. Is there anything impossible in fuel-consumption %ht tests? 1 must emphasise at this point that my method of comparing fuel consumptions is not based 011 practical experience but on the use of common sense and a little mathematics, and I think this dimculy could easily be cleared up if some expert could tell us how the fuel consumption per t.h.p./hr. of a jet engine is determined in practice. Or is it still a secret? Concerning Mr. Stone's last point, I am completely mystified as to how he deduces that the horse-power of a jet engine in- creases as the cube of the speed, and I am sure we should all be very grateful if he would give us a mathematical proof of it. Just what the resistance of the body has to do with the thrust developed inside the jet engine rather escapes me, but perhaps he would be good enough to explain this also. S. H. W. PRINCE. AIR ARM PARADOX Sidelight on the " Agamemnon " Trial AS the pilot\of the aircraft from which the Agamemnonwas bombed in the trial referred to by Mr. Hurren in "Air Arm Paradox" (Flight, April 26th) it occurs to me that some further details of the trial might be of interest. The bomb-aimer was Grp. Capt. J. K. Wells, A.F.C., who, I am glad to say, is still going strongly; in fact I saw him only a few days ago. The aircraft used were Handley-Page 0/400S and the second machine shed an airscrew when well away from Gosport—our base—but was safely brought back there by Fit. Lt. Sawyer who, I believe, is now with Fairey, at Hayes. The failure of the electric signalling device (red, yellow and green lights) occurred about half way out to the target area of the Isle of Wight, but fortunately I had a small ball of string in the pocket of my "Sidcot," and tying the loose end to my right ankle, I threw the ball back to Wells, who was lying prone on the floor about six feet behind me; he then released enough string to enable me to tie the other end to my left ankle after I had cut off the surplus. Zero hour had almost arrived by this time and we had only a few minutes' practice with the makeshift before starting our first official "run up." I was intrigued to find how extremely sensitive the ankles were to the feel of the string, as the slightest tension could be felt instantly. I never had the least doubt that aircraft would establish complete mastery over surface ships, and it seemed to me only a matter of increasing the size of the bomb (or torpedo) and attacking with a hundred or more aircraft from all points at once to make destruction a certainty. I tried frequently to convince '' non-believers'' of my views by published articles and wordy arguments, but fear I did not make many converts. Apart from bombing, I have often wondered what is the record number of different types of aircraft flown by a test pilot. I have flown 126 myself and know at least one well- known director of a famous aircraft manufacturing company who has exceeded my total by a considerable margin. My list includes single- and multi-engined flying boats, seaplanes, amphibians, fighters, bombers, etc., many of which, I expect, have never been heard of by the pilots of to-day. My last flight was in 1938 after an innings of 23 years, but I would much appreciate the opportunity of trying a few of the latest products of the aircraft industry; I fear, however, the chance of this is remote. . C. A. RE A. "TUNS" AND "GALLUNS" Confusion Over U.S. and U.K. Measures I AM sure many people feel the same difficulty as I do owingto the prevailing confusion between British and United States tons and gallons. Those who have been initiated into the myster ' are forced to adopt the cumbersome practice of specifying Imperial gallons, U.S. gallons and U.S. tons in order to avoid pitfalls. As for the uninitiated, whose name is legion, they are doomed to dwell in confusion and error. As a practical and easy means of clearing up the muddle, 1 would suggest that the spelling of U.S. tons and gallons might with advantage be changed to "tuns" and " galluns" (or perhaps "galuns"), respectively. This will offend nobody, least of all the Americans, since in the United States the spell- ing of many common words has been Americanised, as, for instance, "tho," "thru," "color," " nite " and "aluminum." " Tuns " and " galluns " will, therefore, have plenty of friends and will not feel lonely. I hope this modest suggestion will be considered by the authorities concerned, both in England as well as in the United States, and some action taken in order that confusion may be avoided in the future. "GARUDA."
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