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Aviation History
1920
1920 - 0192.PDF
FEBRUARY 12, 1920 or\aer\c [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. PARACHUTES—POSITIVE AND NON-POSITIVE [1992] In the correspondence recently published in FLIGHT relating to parachutes for use from aeroplanes, Mr. E. R. Calthrop has clearly stated the great advantage offered by " positive " opening in providing certainty of opening within a known limited fall, so that the apparatus may be relied upon to function from a small attitude. In a previous letter Lieut.-Col. Holt most pertinently pointed out that types of " positive " opening parachutes which require to be gradually withdrawn from their case for the full length of their rigging and silk body before becom- ing detached from the aeroplane may be very suitable for exhibition drops under the favourable conditions of selected types of machines flying level and under control, but that there is a most serious danger of such an apparatus becoming entangled with or damaged by the aeroplane when its use is attempted as a means of escape from a machine that, being out of control, will probably be in a spinning dive or per- forming other unsuitable evolutions. That this danger is very real is borne out by the large number of cases in which the silk bodies of such parachutes have been ripped by the tailskid of the aeroplane when tested from fast machines, even when flying under control. But Lieut.-Col. Holt is surely mistaken in basing upon these occurrences a sweeping condemnation of all parachutes having " positive " opening. The technical disasters (for- tunately only with weights and dummies) have not been due to " positive " opening, but to failure in the essential feature of,instant detachment from the aeroplane. Most types of parachute that by instant detachment from the aeroplane avoid the possibility of entanglements or tearing are subject to the disadvantage of uncertain length of fall before opening, and such heavy shock when opening takes place that many silk bodies have burst during tests. In a short article published in FLIGHT in 1918, under the pseudonym " E. Forgeron," the writer outlined the essential characteristics for a satisfactory aeroplane parachute by placing foremost the necessity of avoiding entanglement with the machine (as urged by Lieut.-Col. Holt), and, secondly, that of positive opening (as advocated by Mr. E. R. Calthrop), with other desirable features, such as small shock, light weight, easy packing and moderate price. These essentials were practically attained by a special aeroplane parachute manufactured by Spencer and Co., , which, in the spring of 1919, was subjected to a series of official Government trials, when it was demonstrated to give complete detachment in bulk of the silk body and rigging from the aeroplane instantly the weight of the load tightened the sling combined with " positive" action, so that the opening was perfectly regular and certain. Without the use of any special means of attachment this " Salvus " parachute - easily cleared the fast " Bristol Fighter," which had hitherto * ripped the silk body of every " positive " opening parachute, whilst stop watch and cinema film showed the regular sequence of functioning in the opening, and dynamometer tests showed • the shock of opening to be unusually small. With the eventual advent of commercial flying on a large scale, aerial lifebuoys will have to be considered, and it would be advantageous and an encouragement to inventors if the Government, the aircraft constructors, and the in- surance companies could jointly agree upon the relative importance of various items of performance and arrange for open trials to be made on an equal competitive basis, with definite marks given for specified items. Price, weight of complete attachments to machine and passengers, time required and apparatus necessary for pack- ing could be readily compared ; shock of opening recorded by dynamometer, and regularity of opening judged by a series of drops from a low height, such as 200 ft., flying level at varying speeds and recorded by stop watch and cinema film ; clearance from machines by drops when climbing and diving ; comparative opening and speed of fall of various types by simultaneous drops from a large machine. It might also be possible, by utilising obsolete and damaged wings (that would otherwise be scrapped) attached to light, rough frames and dropped from kite balloon, to simulate a helpless machine diving out of control, and judge the risk of entanglement. ERNEST E. SMITH, A.M.I.Mech.E. [1993] I sincerely hope that Col. Holt has not read any personal acrimony to himself in my letter appearing in your issue of January 15, for most certainly none was intended, and I hope sooner or later to have the pleasure of making his personal acquaintance. We are both working to one end, and my argument is directed purely ad rem. In his letter in your current issue of January 29, Col. Holt mistakenly attributes to me the coining of the word " positive '' in relation to the opening of the body of a parachute. My inaugural claim for my parachutes was " automatic open- ing," but the terms " positive opening " and " non-positive opening," originating with Major T. Orde Lees, emanated from the Parachute Section of the Air Ministry, and, being official descriptions widely understood, I have latterly used them in preference to my own earlier distinctions of " automa- tic " and "ordinary," i.e. "non-automatic," opening. I think it must be generally agreed that all parachutes, of whatever kind, size and make, must fall into one or the other of the two categories " positive " or " non-positive " opening It is a good and scientific distinction, and I cannot yet conceive of a third. Even Col. Holt's " anti-suction " parachute (to seeing which I shall look forward with interest), if it opens each time the same way, and at the same depth of fall, without variation except in'ratio to load and the speed of the aeroplane, must necessarily have " positive opening " as understood by experts, whether he fancies the term or not. Col. Holt takes exception to my use of the word " infallible " in connection with " positive opening." Unless it is in- fallible in its opening, a parachute is not entitled to be de- scribed as provided with " positive opening " ; but to be infallible, the opening mechanism must be so simple as to be absolutely reliable in its action. I do not claim that it is impossible for any other than my " Guardian Angel " Para- chutes, to have " positive opening " ; but I do claim that in an eight years'search for positive opening mechanism, when others were not concerning themselves in any such problems, I have invented and patented all the simplest forms of it, and that other forms must now be necessarily more complex, and their use be attended with greater risk. If the external air is led in large volume into the interior of any parachute body provided with tangle-proof rigging, it follows that it will open to its full extent as infallibly as that a cork, tossed on the water, will float. Neither can do anything else. In order, so it would seem, to contest the infallibility of positive opening, the value of which was the theme of my last letter to you, Col. Holt refers to " a bad disaster in the United States " owing to the parachute rope becoming en- tangled in the aeroplane's " bloater." This disaster had nothing whatever to do either with positive opening, or in any way with the parachute. The claim I made was: " There is no case known of a positive opening parachute failing to open exactly as it was designed to do "; and to that claim I adhere. This is not the first occasion on which a somewhat unfair reference has been made to happenings which have occurred when " Guardian Angel " parachutes were being carried, and I think the time has come for a perfectly explicit statement to be made upon the subject. There have been three fatalitie* from aeroplanes which were carrying " Guardian Angel" parachutes ; but in not one of these cases was the parachute in any way at fault. The first casualty was due to the breakage of a standard pattern doghook of malleable iron in the rope connecting the parachute container to the aeroplane. The doghook was originally tested to one ton, and had been used a dozen times with loads heavier than that on the occasion of the accident. Examination showed that the broken arm contained a hidden flaw which was the cause of the accident. The Coroner's jury absolved all concerned from any blame. As the con- nection between the container and the aeroplane had thus been severed, it fell, unopened and inoperative, with the _ua- 192
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