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Aviation History
1921
1921 - 0119.PDF
FEBRUARY 17, 1921 CAMBRIDGE UNIVERSITY AERONAUTICAL SOCIETY (OFFICIAL ORGAN, "FLIGHT") ON January 19, 1921, a paper was read by Major Orde Lees, O.B.E., A.F.C., entitled "Positive-Opening Parachutes" The lecturer referred to the first historic mentioning of the parachute by that great Italian, Leonardi da Vinci, who, he said, had completely anticipated the modern parachute. He then mentioned the many inventions relating to para- chutes, and pointed out how a great number of these were doomed to failure owing to the imperfect understanding by the inventors of the fundamental principles involved. The chief reason for so many of these inventions being ineffective was insufficient area to check the fall to any appreciable extent. " The plane projection," the lecturer said " of the standard 28 ft. diameter parachute is much less than the actual area of the silk, being contracted to 18 or 20 ft. with a 1601b. load." Major Orde Lees then referred to the different ways in which parachutes open, according to the manner of packing. Progressive opening is good, while " explosive " opening is bad, imposing great stresses on the fabric and carrying with it the danger of splitting the parachute. The general belief, the lecturer said, that one of the greatest dangers of parachuting is failure to open, is fallacious. By far the greatest danger is in landing or, in the case of a jump from an aeroplane, getting entangled in parts of the machine. The advantage of the positive-opening type of parachute is not so much that it reduces the very remote chance of failure to open, but that it can be depended upon to open after a short drop. He then mentioned that parachutes of the non- positive-opening type, although rarely failing to open, have been known to fall considerable distances before opening, and that for real useful life-saving properties jumps might frequently have to be made from heights below 1,000 ft. While a short " free fall " is desirable for this reason, the really important advantage of the positive-opening type of parachute is that it makes the length of free fall a constant. One knows where one is. On the other hand, if the parachute opens too soon, there is greater danger of it becoming entangled in the tail of the aeroplane. Major Orde Lees related a number of remarkable parachute drops, in some of which free falls of many hundreds of feet were made without injury to the occupant. As an instance of extraordinary determination and pluck, he mentioned a parachute descent by Miss Sylvia Boyden at Copenhagen on October 3, 1920. The wind was blowing at a velocity of 60 m.p.h., and the young lady jumped from a height of 1,000 ft. The parachute drifted 9,300 ft., and by the most amazing luck she just passed over a lake and landed on its farther shore by letting go when still 15 ft. from the ground. " As a matter of fact," the lecturer said, " she landed with exactly the same force as if she had hurled herself off the roof of an express train going at full speed. You will admit that this young lady of 21 has rare pluck. Several friends tried to dissuade her, but she insisted upon doing it because there were 10,000 people waiting to see it, and she said she wasn't going to let them think that an English girl was afraid of a little thing like that. The ' little thing ' was certainly the most daring parachute descent ever undertaken." In conclusion, the lecturer referred to three main types of encased parachutes. The normal type is contained in a casing and is dragged over an aluminium disc by the relative motion between the falling aviator and the machine. It is therefore positively extended. The second type referred to is the knapsack parachute. In this the container is attached to the aviator's person, and the parachute is extracted automatically, either by a cord attached to the aeroplane or by a miniature parachute, liberated at the moment of, or shortly after, jumping. " In some makes of this type," the lecturer said, " it is necessary for the aviator to pull a ring on his chest after jumping, to rip open the case containing the parachute, which puts it out of cou^rt for passengers at once. On the other hand, this type of parachute has the undoubted merit of being far less likely to get foul of the aeroplane than other types, especially in spins and nose dives, though it must be remembered that in a spin even the smallest machine takes as much as three to five seconds to make a complete revolution, and that that is time enough for any type of parachute to function and get clear. " The third class, for which great hopes are entertained, has never yet materialised. In it lies a chance for inventors. It relates to a type termed soaring parachutes, where the parachute is shot upwards above the machine, opens, and extracts the man bodily from the aeroplane. " The provision of parachutes will not, of course, increase or decrease accidents, but there is a certain amount of truth in the assertion that the provision of life-saving devices, and especially their visible and tangible exhibition, will have the effect of emphasising the fact that accidents do occur. It is merely a question of development and of educating the public as to what is best for it. If lifebelts and lifeboats on ships ever had the effect of deterring passengers, certainly the exact opposite is now the case. Passengers demand that all ships shall have adequate life-saving appliances, and, in time, it is equally certain that the same must, and will, in even greater degree, be the case with aerial transport. Unless aerial transport is going to die out altogether, which is unthinkable, passengers will, sooner or later, refuse to travel by aircraft unless they are equipped with proved life-saving appliances." "Some Problems in Aeronautical Research " Under this title a paper was read before the Society on January 26, 1921, by Air Commodore H. R. M. Brooke- Popham, C.B., C.M.G., D.S.O., A.F.C. Unfortunately, the Air Commodore's manuscript is not available at the moment, and we are therefore unable to publish extracts from it this week. We hope, however, to have an opportunity of examining the paper shortly, when we shall endeavour to deal with it in FLIGHT. On February 2, 1921, a paper was read, entitled "Some Requirements of the Modern Aeroplane," by Sir Richard Glazebrook, K.C.B., F.R.S., F.R.Ae.S. The paper was mainly of an elementary character, and Sir Richard outlined the broad fundamental principles of aero- dynamic and structural design, giving the fundamental formulae for lift and drag, and mentioning the progress that has been made in the development of wing sections with a high maximum lift coefficient to give low landing speed for a heavy wing loading, referring, among others, to the new Handley Page wing in which the maximum lift coefficient is very much greater than that of any known ordinary aero- foil. Sir Richard also drew attention to the importance of engine reliability, and pointed out that of almost equal importance is light weight per horse-power, as the engine, fuel and oil form a great proportion of the total load carried by the machine, and consequently the lighter these are, the more lift is available for carrying useful load. While, thus, it is important to keep the engine and structure weight as small as possible, the machine must be amply strong for safety, and Sir Richard referred to such matters as factors of safety and load factors, and pointed out the different attitudes and manceuvres of an aeroplane that have to be taken into account when making stress calculations. He also dealt in some detail with the design and use of accelero meters for determining the forces set up in a machine executing various manoeuvres such as looping and flattening out after a dive. If it were possible for a machine to be dived at twice its normal speed, and if the pilot could flatten out instantaneously without any change of speed, the forces on the aeroplane would be increased twelve to sixteen times, and the machine would have to be twelve to sixteen times as strong as for horizontal flight. In practice this cannot, of course, happen, as the aeroplane will not be diving at twice its normal speed, nor can the pilot change its motion instantaneously, but still, this theoretical consideration shows that quite extraordinary stresses may be met with during rapid manceuvres. .While dealing with the findings of the Committee on Load Factors, Sir Richard mentioned that a stable machine is allowed a smaller load factor than an unstable one, and referred to the difference of opinion which exists among pilots as to whether a stable or an unstable machine is to be preferred for military work. "For commercial aircraft." Sir Richard said, " there can be no doubt. A stable aeroplane in which the pilot for a time loses control from any cause, flies on ; if the engine stops it puts its nose down and glides gradually to earth and may make a safe landing ; the unstable machine gets into a spin and crashes." One condition in which the unstable machine may score is in the case of landing. When near the stalling speed, the stable machine will try to get its nose down so as to gather speed. The pilot may have to exert considerable force to overcome this tendency, whereas the unstable machine may be coaxed into keeping on an even 119
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