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Aviation History
1913
1913 - 0833.PDF
AUGUST 2, 1913 (/ycHfj Some Experiments with Models. MINVALLA, A.S.M Edited by V. E. By PHEROZE E. J. FOR some years past I have carried out a large number of experi ments with models, and in case any of your readers would like to avail themselves of the results of my experiments, I set out a few designs, &c., of various machines I have constructed. Figure A is a dart-shaped monoplane in which the wings are attached to the fuselage in a somewhat novel way. The body consists of two spars, but the elevator and main planes are fixed in between the two longitudinals, which are specially bent (Fig. B) to the camber of the wing surfaces. Fig. B. Figure C shows the plan, end view and blade sections of the carved propeller used on this machine, which has made some good flights. It invariably turns, however to the right. I have hxed JOHNSON, M.A. if a sudden gust occurred. But in this machine the dangers of a- side-slip are minimised to a great extent, for this reason. If the machine is blown sideways and downwards, the air pressure on the curved surface nearest the ground would to a considerable degree break the rate of descent, and the upper curved top end (being brought down at such a speed), would consolidate the air under it, and so create support for the machine. Hence any tendency to bank over too far is immediately checked. In the case of small oscillations, for a similar reason they are prevented [notprevented, but damped out.—V.E.J.], the foregoing accounting for the steady flights I have had with this machine. [The stability of the Bragg-Smith model is attributed by it9 inventor to the following causes. The top plane is approximately straight, the lower plane having its end curved up to meet the upper. Thus when the machine is tilted laterally by a side gust a greater projected area of sustaining surface is presented on that side of the machine which is lowest, while the opposite side assumes a more or less vertical position, with the result that the sustaining effect on that particular side is decreased, the machine automatically regain ing its normal position. The above functions being performed by the lower curved plane, the especial function of the upper being, not only to provide adequate sustaining surface, but to damp out the lateral oscillations, which he found to occur when a single curved surface is used. The longitudinal stability is attained by setting the small surface (elevator) at an angle of incidence of about 50 to the main planes.—V.E.J.j Figure E, Nos. 1-6, shows a selection of paper gliders with which I have experimented. No. 1. This is made in 3 parts :|body, wings, empennage. Part 1 is made by cutting out of a thick piece of paper (I find the backs of stiff exercise books answer admirably), and folding a narrow double strip of the length required, then shaping it into a streamline form by joining the two front and rear ends with some stamp paper hinges. Then slots are cut of the required camber through both sides, and the wings are slipped through and fastened with hinges similarly for the empennage. In this way I find you can best test the various Plan Fig. c. the rudder to the left, turned the left wing down, and the right up, but it still turns to the right. A notice able feature is the large angle at which it banks when turning. I can attribute it to no cause. I have taken tracings of both wings ; they coincide exactly, their camber is identical; so I do not think there can be any possibility of the trouble arising from that quarter. [Our contributor does not state in which direction the propeller rotates, clockwise or anti-clockwise ; in a model of this character we should expect the reaction of a single -V.E.J.] My next model was a biplane of the character shown in Plan D, the lower wing being turned up to meet the upper surface, thus forming a quadrant on either end of the machine's surfaces. This machine was exception ally stable both longitudinally and laterally, and was practically free from all tendency to dive or oscillate. I am not aware that this idea has been broached by anyone at all, bar Mr. Bragg-Smith, but I think my machine is considerably different from his. * It appears to me that the stability of this model is due to the following causes. The machine is travelling at a uniform velocity in a certain direction (say) directly at right angles to the wind, which Z&eanS that the pilot has ever to be on his guard against a side-slip, Fig. propeller to be very marked.- wing shapes (the best being the one given in Plan E, No. 1), and various other factors. This model was extremely stable laterally, but would dive, when launched from about 6 ft. to within 2 ft. from the ground, and then flatten out and glide for 8 to 12 ft. All these experiments Fig. a.
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