MODEL AEROPLANE NOTES.

Dominion, Volume 30, Issue 143, 13 March 1937, Page 23

MODEL AEROPLANE NOTES.

-BY

"AILERON"

Controlled Petrol Model Flying. Before discussing this, it is amusing to note that the record for outsize petrol “models” is held by an English aero club. A low-wing two-seater monoplane with a I’objoy engine was started carelessly. It promptly took off and climbed to about 150 ft., and completed two circles, flying empty, before hitting the ground and catching fire. This sort of thing arouses the envy of all who fly petrol models of , a mere Oft. wing span. A few days ago, a Wellington builder was testing a new model. Flying at Lyall Bay. and thinking that he had only a little petrol in the tank, he let the model take off. It flew out to sea aud has not been recovered. The loss of this model, worth about £B, focusses attention on the absolute necessity, in nearly all cases, of having a certain means of limiting the time of flight of petrol models. There are, broadly speaking, three methods. The first method is to restrain the model by means of a cord. This may be attached to the rearmost point of the fuselage. If the model is not correctly adjusted, it may thus be prevented from getting more than a foot or two off the ground. Conversely, the cord may be attached to the wing tip. or fuselage underneath the wing (at the centre of gravity), I and the model can thus be made to circle. A refinement of this method is to attach the cord to the arm of a knife switch, so that any slight pull will cause the switch to open, stopping the motor. , This is handy for take-off and landing tests in comparative safety. The second method is to have some mechanism, independent of the motor, to break the ignition circuit at any given time. This method is especially handy for free flying iu a small area. One way is to have a small, light clockwork motor, geared up to a fast final drive, which is then slowed by a fan till the winding shaft unwinds at tlie rate of about one revolution every two minutes. A brass disc, witli a break in the rim. is mounted here, and a conducting arm, insulated from the rest of the mechanism, bears against the rim. It is now easy to mark the disc, indicating for how long it may revolve before the arm reaches the break in the rim and cuts the circuit. Any desired length of motor run may thus be obtained. Variations of this idea include the use of

a screwed shaft, along which a nut, bearing an arm, is made to travel. By varying the length of the conducting strip on which the arm bears the motor run can again be timed accurately. It should he possible to rig a wind-driven propeller to take the place of the clockwoork motor, but this, while lighter, would be considerably more difficult of construction. The third method consists iu the use of a small graduated petrol tank. This is best made of glass or celluloid tubing, about jin. to Jin. diameter, connected by rubber tubing to the engine (in the case of a gravity feed). 'Where suction feed is used, a tank of larger diameter mav be used, with the petrol pipe extending down inside it. Be sure to put air holes in the tank cap. By a system of trial and error, the exact height to which to fill the tank Cor any length of motor run may lie found, and marked on the tank itself. This method is almost foolproof, and can only fail when the throttle closes slightly in the air, which may result iu much legs petrol consumption while still allowing the model to fly level. In the last two methods, the best course is to start the motor, allow it to run while the indicator moves to the desired position and then launch the model, thus making sure that both timing device and motor are functioning properly before a flight is attempted. It is to be hoped that more general use of these methods will result in more reasonable tactics being employed by petrol model flyers. One can recall at least two instances where uncontrolled flying has resulted in damage to property —material damage, for which compensation had to be made.