February, 1935 AIRCRAF T ENGINEERING 49 A Weil-Known German Strut to be Manufactured in England LICENCE has lately been obtained to manufacture in England the "Faudi " compressed-air landing legs. Of German origin, this type of undercarriage strut has already been widely used in tha t country, where it is fitted on th e Luft Hansa Junker s used on the Croydon service and the Heinkel H.E.70. It is also well known in France and is being manu factured in Japan. In England it is being made by Turner's Motor Manufacturing Co., Ltd., of Wulfruna Works, Lever Street, Wolverhampton, who are the concessionnaires. This firm is already in production and a number of test sets are being supplied to various aircraft firms. Many systems have been devised for aero plane undercarriages. Commonly used types comprise rubber; rubber combined with oil damping ; spring, with oil or friction damping; affected by temperature and emulsifies in and compressed air and oil. contact with air. Its weight has also to be I n the commonly used rubber suspension, the added to the weight of the oleo leg. The air- main disadvantage is that the rubber takes a plus-oil strut can only be mounted in one permanent set in service with consequent mis position, whereas the Turner compressed-air alignment of the undercarriage members. It stru t can be mounted upside down if required. also perishes and is unsuitable for a tropical climate. Rubber suspension units suffer from With compressed air it is claimed that an excessive weight. ideal condition arises; air is a compressible medium and will easily pass through restricted The spring suspension with oil or friction valves, while a light reaction is obtained on damping also fails on account of excessive landing, which is progressive through the stroke weight. The larger the energy to be absorbed, of the piston. the heavier the spring. The Turner air suspen The action of the system is as follows:— sion system will, it is claimed, make an immense The suspension legs are filled with compressed saving in weight especially in large aeroplanes. air only from pump or air bottle through a The oil-plus-air system uses compressed air valve (FZ1) suitably mounted on top of the to retain the piston and relies on oil to take the cylinder. The air forces the piston (25) down landing shock and damp out vibration. Oil wards until a predetermined pressure is reached. cannot be compressed and consequently the A mark can be made on the protruding piston energy has t o be absorbed by forcing oil through rod (3) so that it is possible to ascertain at a restricted orifices. glance if th e correct pressure is being maintained The greater the landing shock the greater the in the cylinder in subsequent service. resistance to the oil with consequent shock to the aeroplane and undercarriage. Oil is When the aeroplane alights, the first move ment of the compression stroke compresses the air in the upper cylinder (1). As this pressure increases, the force overcomes the spring behind the mushroom valve (11) and the air is free to flow through the piston into the annular space behind it ; considerable turbulence of the air occurs during this operation which has the effect of absorbing energy, in addition to the passing of air through suitably disposed orifices. When the energy of the first landing shock is completed, the very high pressure of air acting on the piston head returns the piston to its original position. To accomplish this, it has to displace the air which has been forced into the annular space round the piston rod during the compression stroke. The mushroom valve is closed by this returning air and the air can only flow back again through one small hole in this valve (11). This restriction to the air on the return stroke has the effect of absorbing energy and damping out vibration. The size of this aperture can be varied so as to provide suitable shock absorbing qualities for different types of aircraft. The operation of the strut, therefore, consists in the absorption of energy progressively on bot h the compression stroke and the return stroke. A smooth landing results with effective reduction of rebound. Maintenance simply consists in taking care tha t the packing which serves as a seal between piston and cylinder does not become dry.
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Feb 1, 1935
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