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Aviation History
1946
1946 - 0377.PDF
FEBRUARY 21 ST, 1946 FLIGHT 199 CORRESPONDENCE The Editor due* not hold himself responsible for the views expressed by correspondents. The names and addresses of the writers, not necessarily for publication, must in all cases accompany letters. IN PURSUIT OF SAFETY Pre-war British Rotor Patents TN Flight, January 24th, the Vvriter observed a letter from Jl S. H. Goodright suggesting retractable rotors for airliners. It might perhaps interest your correspondent and others, to (iearn that this idea, broadly, is now some ten years old—if not older. The writer's patent No. 499,632 (applied for on April 14th,1938) is the oldest and the pioneer British patent on this subject. This was followed by Patents of Addition Nos.524.9J3 an<J 568.505. The broad idea was first patented by others in the United States several years before 1938. Thewriter's patents deal with the technicalities of aircraft stability as affected by the extension and operation of the rotor (orrotors), not with merely the broad idea of an extensible and retractable rotor for fixed wing aircraft, to which the Americanpatents are limited. Tht original patent was placed before all the leading air-craft manufacturers in Britain, United States, Germany, Italy, France, Holland and Japan, and also before the Air Ministriesof all those countries. Strange to relate, it was the British ho took the greatest interest in the idea. The consensus; opinion among British manufacturers was that the idea, oroadly, was good, but they were not -prepared to spend thelarge sum of money involved in the long-term research necessi- tated by this project, and there, for the present, the matterrests. E. V. HAMMOND. R.A.F. SLANG Strips Were Torn Before 1928 I HAVE read with some amusement the explanations regard-ing the slang "tearing off a,strip." One of your corre- spondents states it was derived from the Cardington balloonin 1939-40. 1 myself, in company with many others, used this slangexpression with great regularity at Halton in 1928, and we had it handed down by previous entries. At one time, whenever anyone " shot a line " he was greetedwith that rather rude noise commonly known as a "rasp- berry."As we all know, this sound is very much like tearing a strip of cloth. So when anyone gave us the " bull," a wag wouldalways invite us to "tear him one off"—and believe me we always did ! By the way, another slang expression used extensively is"gen," and I have heard many and varied stories as to its derivation.It was first started as anything \ hich was common know- ledge or anything on orders for the '' general information.''The individuals who used to spread this information, some- times with a few odd statements concerned with their ownwishful thinking, were greeted with "Here comes the gen- man." Now, however, it is applied to many things, mostly to peoplewho are usually well informed in their particular sphere. EX-HALTON BOY. SPEED AND THRUST Power Developed versus Work Done THINK "Indicator" rather misses one point in his explana-tion of the connection between thrust and horsepower in Flight, January 17th, and will tend to leave some confusion inthe ordinary person's mind. He compares a Merlin engine being "revved up" on theground with a jet unit running under similar conditions, and states that the former is developing a large quantity of power,while the latter is developing none. Surely a layman would be justified in making the following comment on that state-ment:— "You say that the jet unit on the ground is giving no power (i.e., doing no work) because, although a largethrust is being created, the engine itself is not moving for- ward. Why then should we not say that the Merlin engine,too, is doing no work, since it is not moving forward either?" The essential point is, of course, that we must be carefulto recognise clearly the distinction between total power de- velopeu and power usefully employed, and to make sure that l'nc!i we are comparing two engines under certain conditions h. we are considering the same type of power or work in eachcase. Another point is that we must compare similar types of unit,i.e., things tfiat can do the same job. It is of no more use to compare a jet engine with a Merlin engine by itself, thanto compare a capstan lathe with a milling machine. A Merlin engine by itself cannot produce thrust (except for a smallamount of exhaust thrust perhaps), but only torque, whereas a pure jet unit has no available torque, but gives a largethrust. The airscrew fitted to the Merlin engine is the means for converting torque into thrust, so that for comparison withthe jet uuit we must consider the Merlin-airscrew combination as a whole. If we make the comparison on a total work basis, then wemust say that both engines are doing work. The Merlin-air- screw combination is throwing backwards a large quantity ofair with a medium velocity, while the jet unit is sucking in a smaller quantity oi air, but is blowing it out at the backwith a much greater velocity—if that isn't doing work, I don't know what is! We can easily estimate the total power of "Indicator's" jet unit on this basis. F01 instance, suppose that the unit, in order to develop its 2,ooolb. of static thrust, were pushing out 401b. of air (exhaust gas) per second at a speed of 1,600 it./sec. The horsepower ejected in the air is then equal to W»a 40 x (i,6oo)2 — ^ 1.— = 2 2 x g X 550 2 x 32.2 X 550 On the other hand, if we are to compare the units on abasis of useful power, i.e., power usefully employed in moving the engines (and their attached aircraft!) forward, then wemust say that neither unit is developing any power, because neither is moving.The apparent paradox of our having supposed originally that the Merlin was giving 2,000 b.h.p. is easily explained whenit is remembered that that figure represents the total power available, and not necessarily the amount usefully employed.This latter depends on the propulsive (or Froude) efficiency of the airscrew, which is defined as tlie ratio of the power use-fully employed to the power supplied in the airscrew shaft, and which is zero when the aircraft is at rest, just as the pro-pulsive efficiency of the jet unit is zero when it is at rest. THOMAS D. ROBERTS.[" Indicator " writes; " I agree with Mr. Roberts' further clarification, but I was really intending to be faintly ironic.Perhaps I should have explained that the " work " being done by the piston engine was. that of turning the airscrew.] AIR ACCIDENTS Mistake to Disband R.O.C. IN the past few weeks I have, in company with many others,been greatly perturbed by the seemingly ever-increasing number of air crashes that have occurred in this country. Itis not my intention, however, to attempt to lay the blame for these mishaps at any particular door, nor to try to trace themback to any definite cause. Rather would I put forward a suggestion for the prevention of one of the most lamentablefeatures of the majority of these crashes—the time lag between the actual crash and its subsequent discovery. Surely the remedy for this lies in the immediate setting upof an organisation, comparable in size and scope with the Royal Observer Corps, for the plotting of all aircraft flying over theBritish Isles. During the war, besides giving warning of enemy aircraft, the Observer Corps kept track of all aircrafteither seen or heard by their posts, and in the event of a crash were able to notify the appropriate authorities within a matterof minutes, thus saving the lives vl many Allied airmen. But with a state of war no longer existing the Government sawfit to disband, or, to quote an official euphemism, "stand down" the R.O.C., with the result that, theoretically at least,any machine can fly over the whole length of this country and no one is the wiser.In addition to the inestimable benefit that speedy location and rescue would give to the occupants of crashed aircraft,in view of the enormous success of the R.O.C. in "homing" lost aircraft, and in preventing aircraft crashing into highground, I venture to say that, with an organisation such as the Royal Observer Corps restarted, the number of air crasheswould drop considerably. G. A. B. SHORT.
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