THE AIRWAY

Sun (Auckland), Volume III, Issue 674, 28 May 1929, Page 14

THE AIRWAY

By "TUB ROC ”

Slot and Interceptor Control

WHILE tlie automatic slot which is fitted to the majority of airplanes in the Dominion gives lateral stability when a plane is in a stalled condition, thus preventing the incipient spin, it by no means makes the lateral control as powerful as might be desired. This difficulty has now boon overcome, however, by a new invention, the “interceptor.’’ which is a very simple addition to the Handley-Page automatic slot, and is another remarkable contribution toward the safety of flying.

TI7HEN a plane is normally stalled, that Is, loses flying speed, it either nose dives or heels over into a spin. At and beyond the stalling angle there is no way of controlling the plane, for theoretically, it is inert, a dead weight falling through the air. It becomes controllable again only by diving in order to regain flying speed, and by neutralising the controls the plane will come out of the spin. Thus when flying at a reasonable height the cool, calm and collected pilot does not have any difficulty in regaining control should his plane lose flying speed and spin. But even so, many serious crashes have resulted. FUNCTIONS OF SLOTS With the automatic slots it is possible for the plane to go on flying even though it has, normally, lost most of its flying speed. This may be said to be done by capturing the force of gravity, as the plane begins to sink through the air toward the earth, and converting it into lift. In other words, the slots pull the centre of lift forward and so enable the plane to keep on flying at speeds so low that they do not register on the air speed indicator. Flying at such low speeds, however, makes the ailerons sluggish and of little use in controlling the plane. When used they have to be worked so extremely that considerable rudder is necessary to offset the tendency to turn, and in the case of an emergency they are too slow. Now, if one slot were closed and one opened, the wing with the closed slot would immediately stall, assuming the plane to be at a normal stalling angle, while the wing with the open slot would continue to lift. It is thus plain that if one wing dropped the way to raise it would be to close the opposite slot; the dropped wing would then continue to lift, while the high wing would stall and drop, and a level keel could thus be attained.

It is precisely this effect which the interceptor slot attains. THE “INTERCEPTOR”

The interceptor slot is a long, narrow plate, situated at the wing tips behind the normal automatic slots on the leading edge. In its normal position it is hidden in a recess in the wing, parallel and close to the front spar. To it are attached three rods working on springs and fastened at the other end to the aileron. When the aileron is lifted the rods push against the interceptor plate and cause it to rise vertically. A plane is flying along with its slots open. Suddenly the right wing drops. The pilot immediately raises the left aileron and depresses the right. This movement or the control stick causes the interceptor slot to spring into a vertical position. The effect of this narrow’ panel is to destroy the effect of the automatic slot in front, causing the air to eddy and flow’ off over the upper surface of the wing, which in turn results in a loss of lift and increases the resistance of the wing. In other words, the left wing stalls, and, as it falls level with the right, which is maintaining its lift, the pilot centralises his controls, the interceptor closes and the plane resumes normal flight. A convincing demonstration of the slot and interceptor control was given in England last month by one of Handley Page’s test pilots, flying a D.H. Moth with the new arrangement. After going up to a height of a few hundred feet, the pilot put the nose of the machine up at an alarming angle and then proceeded to operate the lateral controls, first standing the machine on its right wing tips and

then on its left. Sinking all the while, the Moth was obviously under perfect—and very powerful—control in spite of the fact that its nose was held up and the actual angle ot attack well above the stalling angle.