FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1925
1925 - 0526.PDF
AUGUST 13, 1925 ON THE PREVENTION OF ACCIDENTAL STALLING By M. L. BRAMSON, A.C.G.I., M.I.Ae.E. THE problem of abolishing the type of accident which is caused or aggravated by involuntary stalling may be stated as follows : to devise means whereby the stalling of an aeroplane is rendered impossible, otherwise than as an act of volition on the part of the pilot, subject to the condition that the complete control by the pilot of his machine must in no circumstances be impaired. Let us examine this problem in principle in order to dis- cover, if possible, a logical solution. In the first place it is clear that if we can convey a warning to the pilot which— (1) cannot fail to reach him,(2) cannot be misunderstood, and (3) reaches him at the right moment ;then we can solve the problem. Kind of Warning.—In considering the kind of warning re- quired to comply with (1) and (2) we must remember we are dealing with the human element. It is a matter of physiology. Man has five senses, and if you want to convey a message to him you must appeal to one or more of these. Two of them, taste and smell, we must rule out for obvious reasons. We are, therefore, left with sight, hearing, and touch. Sight and Hearing.—Taking these in the order mentioned, let us find out whether a visual warning will do. Now, in practice, it is impossible to produce a visual signal covering the pilot's field of vision in all directions. If, therefore, he happens to be looking in some direction other than that from which the signal is coming, it will not reach him. Conse- quently, no visual warning can comply with condition (1). This is borne out by experience. The presence on the dash- board of a perfectly reliable Air Speed Indicator has not, unfortunately, proved a sufficient safeguard against in-voluntarv stalls. Likewise, on account of the noise on board an aeroplane,a sound signal might fail to reach the pilot. Sense of Touch.—And so, by a process of elimination, wearrive at the conclusion that if the warning is to be infallible, it must be conveyed to the pilot through his sense of touch.Now there is one part of the body of the pilot, and one only, which is in constant sensitive touch with the doings of hismachine, namely, the hand which holds the control column. Moreover, we have stipulated that the warning which shouldmake him move the control column forward must be in- capable of being misunderstood. It is, therefore, logical to transmit the signal to the pointwhere action is to be taken, and in the sense (that is forward) in which action is to be taken. In other words, a signalconsisting of a force suddenly applied to the control column in a forward direction is the one type of signal which canneither fail to reach the pilot nor be misunderstood by him. In practice such a force may be derived from mechanical,hydraulic, pneumatic or electro-magnetic sources, and limited to such a magnitude that the pilot can overcome itif he so desires. The Right Moment.—There remains the question of ensuringthat the warning is given at the right moment. In a recent article on " Accidental Stalling," the writer pointed out thatthe " Stalling Incidence " is a constant for any given machine, whereas the stalling speed varies with the static and dynamicloading. It follows that the application and discontinuance of the warning force must depend upon the angle of incidence.We thus arrive at the following conclusion : Involuntary stalling may be eliminated by any device which informs thepilot in the manner described whenever the angle of incidence reaches a pre-determined value near, but below the stallingincidence. THE SAVAGE-BRAMSON ANTI-STALL GEAR A New Device with Great Possibilities IT is by now generally admitted that a very large proportionof aeroplane accidents are due to nose dives or spins following upon accidental stalls close to the ground. It is also admittedthat a skilled pilot will practically never stall his machine accidentally near the ground unless he happens to be pre-occupied, such as, for instance, with looking for a suitable field in which to make a forced landing. If, therefore, meanscould be devised for reminding the pilot that he was approach- ing stalling point, many crashes would in all probability beavoided. In the preceding article, Mr. Bramson has outlined the considerations which led him to adopt the particularanti-stall gear, of which he is the inventor, and which is described below, Mr. Bramson's argument is so logical andconvincing that we need not elaborate it here beyond stating that it appears to be an incontrovertible fact that a systemby which the " reminder " to the pilot reaches him through the joy-stick, in other words, through the one spot at whichhe is always, under all possible conditions, in close touch with his machine, must necessarily be preferable to any formof aural or visual system. To this advantage must, of course, be added the fact that in the Savage-Bramson anti-stallgear one has not only a " reminder " to the pilot, but also a mechanism which moves the controls in the appropriatemanner. Mechanism of the GearThe actual mechanism of the gear itself is very simple, and consists essentially of a cylinder and piston with rigid con-necting rod attached to the joy-stick, and a double-acting pneumatic relay mechanism, in principle similar to thatemployed in organs, etc., while a small release valve, operated by a vane, completes the equipment. One of our sketchesshows the apparatus installed in the machine, and the sectional drawings show the details of the mechanism. Normally, the pneumatic relay, a section of which is shownin the upper right-hand corner of the sectional drawings, is in the " up " position, kept there by the small adjustableleak which admits air under pressure from a reservoir mounted in the fuselage to the underside of the flexible diaphragm. Inthis sectional view the upper tube communicates with the reservoir, while the lower tube communicates, via tubes insidethe wing of the aeroplane, with the vane-operated release valve. The latter is mounted on one of the interplane struts, and itwill be seen that not onlv can its relative incidence be altered, but also the number of degrees through which the vanemoves before the release valve is opened, so that very fine adjustment is possible. The vane is set to operate at anangle of incidence slightly below the stalling angle, and with the adjustment provided it is possible to vary within quitewide limits the number of degrees before stalling at v hich the mechanism comes into operation.When the machine approaches the stalling angle, or rather the angle at which the relay is set to operate, the wind strikesthe lower surface of the vane, which consequently lifts and opens the release valve. The pressure below the flexiblediaphragm then drops to atmospheric and the pneumatic relay moves into the " down " position (in which it i? shownin the sectional drawings). The pressure from the reservoir then reaches the cylinder and pushes the piston back, theconnecting rod communicating to the joy-stick a sharp blow which pushes the stick forward. By suitably choosing thepressure in the reservoir, the size of piston, and the distance below the joy-stick pivot at which the piston is attached, anydesired pressure can be exerted on the joy-stick. In practice this pressure is so adjusted that the pilot can overcome itshould he so desire, but the sharp blow is quite unmistakable, and cannot possibly pass unnoticed by the pilot. With the control stick forward the machine presentlyreaches the angle at which the vane again moves down and closes the release valve. When the pressure on the under-side of the diaphragm moves the relay valve into the " up position, the cylinder once more communicates with theatmosphere. We recently had an opportunity of seeing Mr. Bramsonflying one of Major Savage's S.E. 5's at Hendon, and carrying out various evolutions, and in no instance did the gear fail tooperate. Being based upon angle of incidence, and not upon air speed, the gear acts correctly irrespective of loading, and sosensitive has it been found that the pilot can detect a difference according to whether his tanks are full or half empty. The Savage-Bramson anti-stall gear, which is so simple thatthere is nothing to go out of order, while in any case, if some- thing did fail, the pilot would be no worse off than he wouldbe without the gear, seems to us to promise to go a very long wav towards reducing crashes due to stalling near the ground,and as the weight of the present model is only about 5 lbs., it can be mounted without serious addition of weight on even 526
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
