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Aviation History
1911
1911 - 0385.PDF
APRIL 29, 1911. in reference to the method of mounting the gyroscope on the aeroplane, that the latter would be able to swing either laterally or longitudinally without in any way affecting the former, and then later on he remarks that it (the gyroscope) comes into operation on the plane tilting. To me this seems somewhat contradictory, but it may be that I have not quite- grasped his meaning. He also writes that on the plane tilting the point marked A in his diagram makes contact with either B or C. Quite true, but surely he will have the same contact made when the nose or tail of the machine dips, owing to the gyroscope's precessional movement, a fact which may possibly spoil the desired effect. No doubt this could be easily remedied by employing a somewhat different method of attachment. Gloucester Street. A. PERCY BRADLEY. 1/tiCfiT] Dipping: Front Edge. [II53] By your note to my letter (1126) I feel I cannot have made myself clear concerning the dipping front edge. You say that the energy taken from the up current roust give a dynamic lift. With this I entirely agree, but it seems to me that, seeing that this lift comes from destroying the momentum in the up current, just as much negative lift (or downward force) must be produced in giving the air this upward momentum. This follows from the principles of dynamics, for no other forces act on the air except those between it and the aeroplane. Thus the net lift is given only by the final downward momentum of the air represented by the trailing angle. Wimbledon. B. BRUCE-WALKBR. [The energy in the up current certainly has to be paid for as we have already explained, but it does not necessarily have to be paid for by a corresponding negative pressure on the plane itself. Our own view is that the thrust of the propeller is the particular coin in which the debt is discharged.—ED.]. Propeller Action. [1154] Does the pilot of a Bleriot monoplane feel a draught from the tractor in front of him while he is in flight ? Also does a propeller screw itself through the air, pushing the aeroplane before it, or does it derive its motion forwards by the reaction of the volume of air it sends back ? I am totally ignorant of these matters, and have had no satisfactory explanation as yet. Knightsbridge. P. R. H. [The draught from a tractor screw naturally augments the ordinary draught due to the flight velocity. A propeller exerts a thrust by virtue of the volume of air that it discharges to the rear. As the result of the thrust it proceeds bodily through the air, hence it is equally correct to say that a propeller does screw itself through the air. But it must never be overlooked in dynamics that fluids are incapable of offering an abutment except while being accelerated, hence the reason for the slip stream or draught from a propeller, which represents the accelerated volume of air that has by virtue of its acceleration served as an abutment for the wedge-like action of the propeller blades. In the mechanics of solids this idea of slip finds no place in the ordinary screw and nut motion,—ED.] Pendulum Stability. tII55] In reference to Mr. Johnson's letter (1120) on pendulum stability, as regards lateral stability the pendulum connected with the balancing tips would be all right when flying in a straight line, but for turning it would interfere with the control. For instance, supposing the airman wanted to turn to the right, he would want to " bank " the machine left side up and right side down. The right side being low the pendulum would automatically pull the right balancing tip, thus bringing the machine on an even keel and nullifying the " banking " operation. As regards longitudinal stability, a pendulum connected with the elevator would be all right if it did not interfere with the airman's control in that direction. I think it is better as it is, for both lateral and longitudinal control to be under the direction of the airman, as it is all done with one lever, and I should think comes to him as naturallv as riding a bicycle. W. H. NORTON. Redhill. Classification of Aeroplanes. [1156] I think Mr. Twining's idea excellent, but why not make the second figure (which represents the main planes) in large tvpe, to show which are the large planes. The figure "o" would then be unnecessary to indicate the absence of an elevator. Scarborough. PERCY SWAINS. MODELS. Model Monoplane. [1157] I was rather startled to see some drawings of a model monoplane accompanying letter 999 from " J. C. B.," for at first sight they appeared to be the same as my own, only on mine it will be noticed the ends of planes are cut off in an opposite sense ; the elevator is also distinctly different, mine being divided into two pieces with a wire rod between them. My monoplane is made •! Vs in. square American poplar and is propelled by two " Aerospeed " 8 in. propellers, the planes have a slight camber and are covered with fine silk. The wood, propellers and silk were purchased from A. Melcombe, Bedford. I cut the ends of my planes off as a help to the stability of the model. My longest flight has been 341 ft. while the machine has remained in the air for 43 sees. Cainscross. HARRY S. D. GABB. Models at Olympia and our Prize Scheme. [1158] Being an exhibitor in the Model Section at the recent Aero Show I was naturally interested in your article "Models at Olympia" which appeared in your issue of April 15th. Although I am bound to admit the article in question was very ably written, I cannot find myself in agreement with all the state ments it contains. The fact that no prize was given for originality of design was, as you say, unsatisfactory. It seems to me the reason of this was not that insufficient encouragement was given to inventors in advance announcements, but rather that the judges were not looking out for originality. Surely the reason for holding exhibitions of all kinds is to- encourage original ideas and advance the particular industry with which they are connected. Yet I find at this last and previous shows, the prizes have all been awarded to copies of existing "flyers" (if we exclude the model exhibited by Mr. Bragg Smith in last year's exhibition, which, I believe, was an original design) or to "toys." It was the absence of a definite and clear purpose in the nature of the judging, and not in the models, that was " the most unfortunate feature." I sincerely hope the prize scheme you anticipate carrying out will be successful in bringing to the front something " progressive," but to my mind it has its weak points. It may be that writing essays is " conducive to the acquisition of an intelligent appreciation of the why and wherefore of things." and there is no doubt that flight is based upon the great science of aero dynamics. There are scores of people, however, who could write miles of copy on aero-dynamics and similar sciences and yet not have the slightest notion of the practical or mechanical side of building an aeroplane. It is more likely that the study of this particular science, and writing essays thereon, will do a good deal towards developing a scientific vocabulary (as is shown by some of the letters which appear from time to time in your journal), but the use of a few scientific terms and pseudo-scholastic phrases does not prove that one understands the scientific principles. It is doubtful if the Wright Brothers knew very much of aero dynamics when they produced their first " flyer," and a study of the 387
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