FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1914
1914 - 0770.PDF
JULY 17, I9H- Edited by V, The Steering Competition for Models. THIS competition, which was held on Wimbledon Common on July nth, was an extremely disappointing one, so far as the number of competitors was concerned. The tests were : (A) Straight flight ahead. (B) Figure of eight. The last really amounted to two consecutive circles, one right-handed and the other left-handed, or vice versa. Only one competitor, Mr. J. E. Louch, was successful in accom plishing both tests. Mr. Louch made a very fine straight flight of at feast 150 yards before the model turned at all; only 50 ya'ds was necessary to qualify ; his first attempt at a figure of eight was unsuccessful, the model quickly coming to the ground, but his second attempt was quite successful. The mechanical device adopted by Mr. Louch was very neat and simple but quite efficacious, and struck us as being the best we have yet seen. The model was of the canard type, and the most reliable and efficacious way of steering such a model is, in our opinion, by means of canting the elevator ; the machine is supposed to be like Mr. Louch's one with twin propellers. Presuming the propeller thrust equal and the wings free from warp, &c, then with the elevator (preferably of the dihedral angle type) set symmetrical, i.e., without cant to either side, the machine will fly straight. Cant the elevator in either direction, and the machine makes a right or left handed circle according to the direction in which the cant is made. Let us assume the machine started with the elevator so canted as to cause the machine on rising to make, say, a right-handed turn, then if the elevator be suddenly pulled over so as to have an opposite cant the model will at once commence to describe a curve in the opposite direction, and will continue circling in this sense so long as the elevator suffers no further alteration, until the motive power runs down. The final setting of the elevator at a given angle of cant presents no difficulty, if we imagine a certain restraint against which it is held fairly tight by means of some form of stretched spring. A further extension will place the elevator m a normal lateral position, and a Still further extension pull the elevator over so as to have a cant in the opposite direction. Let us suppose that it is held iti this latter position by means of a wire bolt or pin, which when withdrawn permits the spring to pull the elevator over to the other side. This again presents no difficulty so long as the pin is pulled out and the elevator spring released after the model has risen and com pleted a circle in one direction, either clockwise or anti-clockwise, as seen from below. The manner in which Mr. Louch drew out the pin was as follows : A thread was attached to the pin, and this thread was wound round the thin axle of a cogwheel about an inch in diameter and containing therefore a good number of teeth, this cogwheel was turned by means of a worm or thread on a wire axle, one revolution of the latter causing the toothed wheel, the axle of which was transverse to the Juselage, to turn to the extent of one tooth. The axle carrying the worm ran fore and aft of the fuselage, and was rotated by a twisted band of rubber whose speed was checked or " braked" by a little fan or propeller. This propeller, if we remember correctly, was further reduced in speed by its turning the opposite way, to which its travel through the air would cause it naturally to turn, if free to rotate in either direction. When the machine was released to run along the ground and rise, the little fan brake and motor was also released, with the result that after a certain time the elevator sprung over as already stated. The time, no doubt determined by trial, can obviously be con trolled by the motor, size of fan brake, $i« of COg-Wheel axle, &c, Mr. H. Bedford also succeeded in making his machine describe the requisite figure of eight, but failed to obtain the requisite 50 yds. straight flight in the three trials permitted. Mr. Bedford's method of control was by means of a movable fin in the rear, actuated by means of a small rubber motor and propeller brake. The movement of the fin or rudder in this case was gradual. Mr. H. W. Sykes» Aero Show Ornlthopter Model. The principle upon which this machine is based is that in order to obtain flight in a horizontal straight line the pressure on the underside of the wings must remain constant during both up and down strokes. This is brought about, in the case of a bird, as follows : During JOHNSON, M.A. the down stroke the wings are set at a negative angle, as at D in the accompanying figure, in which the arrow shows the direction of flight. The wind pressure forms, at right-angles to the wings, a pressure, P, which may be resolved into vertical and horizontal components, L and T. The former produces the " lift " or sus- tentation against gravity and the latter the forward impulse. At the bottom of the down stroke the wings are turned to a positive angle as at U in the diagram. The bird is carried along by the kinetic energy acquired during the down stroke, and the (relative) wind striking the under side of the wings produces a reaction, P', at right-angles. This reaction, P', resolves into vertical and horizontal components, L' and T'. T' is the " drift " or resistance to forward motion, and must be overcome by the kinetic energy of the bird, and L' is the " lift." This force, L', lifts the wings without any muscular effort being exerted, and if they were left limp they would be raised without doing any useful work in sustaining the bird, but if the upward movement is resisted, muscularly or otherwise, the result is a susten- tation of the whole bird in proportion to this resistance. And if, instead of being a mere braking force, this resistance consists of the stretching of an elastic cord, or some other means of storing energy, the energy so stored can be given out during the down stroke, thus materially assisting the muscles. This appears to be the function of the " pectoral cords " of a bird—a most important organ of flight and one which does not seem to be possessed by non-flying creatures. In the case of the model the turning of the wings is brought about by driving the two spars thereof by two cranks, the forward one of which has a certain angular advance on the rear one ; conse quently the front spars reach the top and bottom of their stroke and begin the reverse movements before the rear ones, with the result that the front edge of the wing is below the rear one during the down stroke and above it during the Tip stroke, or, in other words, the wing is inclined downwards towards the front during the down stroke and upwards towards the front during the up stroke. The wings assume a helical form, and are, in fact, two one-bladed screw propellers going in opposite directions, and their direction and pitch are constantly " alternating " periodically. During the down stroke the " propeller torques " furnish the lift, and during the up stroke the negative torques, or resistance to rotation, produce the lift. The duty of "pectoral cords" is performed by springs. The engine power should be shut off during the up stroke, a thing which is impassible with a rubber motor, but which would be quite easy with a petrol one. In this model the front wing spars are pivoted at a point below the horizontal centre line and the rear spars above it, imparting a Mr. M Sykes' Olympian ornithopter model. backward and forward component to the motion of the wings—a rowing action—to assist in the propulsion. The down stroke of the wings should be faster than the up stroke to generate the kinetic energy requisite to carry on with during the up stroke, but it is impossible with an ungoverned elastic motor, whose speed depends solely upon the resistance with which it meets. A simple balance gear, analagous to that in the back axle of a 770
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
