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Aviation History
1935
1935 - 1072.PDF
508 FLIGHT MAY 9, 1935. FLYING ON 250 c.c. Villiers Two-stroke Motor Cycle Unit as " Occasional Engine " for a Sailplane : The Outcome of a Startling but Practical Scheme Conceived by Sir John Carden Puzzle—find the power unit J No one would suspect that an auxiliary engine is tucked away within the fuselage of the Carden- Baynes sailplane. SEVERAL attempts have been made from time to time to combine the glider or sailplane and the power-driven type of aircraft in one machine. Many of the ultra-light 'planes which took part in the Lympne competitions some years ago were virtually gliders with small motor cycle engines fitted. Although these machines were remarkably efficient, regarded as aeroplanes, they did not achieve L/D ratios com parable with those which the modern type of sailplane attains. The very fact that the engine and airscrew were exposed to the airstream increased the drag very materially and reduced the efficiency from the sailplane point of view. With a pure and simple glider, on the other hand, a very high L/D ratio is achieved by having a very large wing span, so as to obtain low span loading with consequently low in duced drag. To get into the air such a machine must, how ever, be launched either by a ground crew catapulting it off by means of rubber cords, or by towing behind a motor car or an aeroplane. It is often possible, if a height of some hundreds of feet can be attained initially, for such a machine to reach a region where strong up-currents exist, and by making use of these the pilot can often make cross-country flights of con siderable duration. If the sailplane gets out of one up-current, however, it may not be able to reach another before it has lost too much height, and will then have to land. In most cases this means that the pilot has to telephone back to his starting point, and a car with a trailer has to be sent out to find him and bring him back. All this is something of a handicap to the sailplane pilot, and if means can be found to enable him to regain his base without outside assistance his independence would be vastly increased, and, moreover, he would probably be able to put in many more flights in the course of a day. Sir John V. Carden, who has been a keen amateur pilot for a good many years, and who has owned several aero planes (his present mount is a Miles "Hawk"), has had the brilliant idea of utilising an " occasional " power plant; in other words, his engine is ordinarily mounted in a position out of the airstream; but when it is wanted, either to get the sailplane off the ground initially, or for reaching a region of up- currents, it can be put into operating position and started, the machine then proceeding as an ordinary low-power aeroplane. It might have been thought that to do this would have been a very difficult task. Sir John has, however, schemed out an amazingly neat and simple method. In his work he has had the whole-hearted co-operation of Mr. L. E. Baynes, the de signer of the very successful " Scud " sailplanes, and of the Villiers Engineering Co., Ltd. Mr. Baynes has designed for this extremely interesting development a new high-efficiency sailplane which has been constructed at the Abbott Motor Works, Wrecclesham, Surrey, where Flight last week had an opportunity of inspecting the new craft. Engine Reliability The engine which Sir John Carden is using is a single-cylinder Villiers two-stroke of 249 c.c. capacity. In its normal form ihis engine is, of course, an ordinary motor cycle engine with its cylinder pointing upwards. For the sailplane it was de sired to invert the engine, since by doing this the centre of the crankshaft would be raised, thus giving the necessary airscrew clearance with very small overall height. The Villiers Com pany very sportingly undertook the work of converting tht engine, and the tests which Sir John has had carried out at Wrecclesham have been extremely satisfactory; the engine has run for many hours on end at full throttle without any troubk and without any signs of overheating, the cowling being so arranged that it forms a venturi, while the airscrew blades passing close behind the cylinder help to produce a very strong air current. The mounting of the engine p very simple. Two tubes having a diagonal bracing member run to the crank case and vee tubes to the cylinder head, so that the whole system is perfectly triangulated and a very rigid mounting provided. The Carden engine mounting. 0" the left may be seen the details, while the right-hand view shows the engine in an intermediate position. The cowling has been removed to show the mounting structure. (Flight photograph*)
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