d FLIGHT JANUARY 8 T H , 1942

S H O C K D A M P E R S

The graph shows the torque variations at different speeds plotted from the torsion meter records for the engine with and without the absorbers. The very con-siderable reduction of vibration torque, and therefore of vibratory stress in the shaft and airscrew, over the whole of the flying speed range should be noted.

An outstanding advantage of the tuning methods adopted in this design compared with methods previously employed, which aimed at tuning the absorbers to exact resonance with the troublesome torque order, is that very close manufacturing tolerances on absorber details are not required. Thus, in the present example, satisfactory functioning is obtainable with a tolerance of o.oo2in. on the pin diameter, in the bores of the bushings, in the crank web extensions, and in the absorber rings; and o.ooBin. on the radial distance of the centre of the crank web extension bushing from the axis of the crank-shaft. Furthermore, a series of supplementary tests proved that satisfactory operation would still be obtained with the pins and bushings worn to the extent of 0.005m. on diameter. It is unlikely, however, that wear of this amount would occur in normal service, since the parts are few and ape of extremely simple design, whilst the oil mist inarae the crankcase ensures adequate and efficient lubrication.

Even when there are no really severe resonance zones

in the operating speed range of an engine, considerable benefit can still be obtained by fitting rotating pendulum vibration absorbers. For example, the use of pendulum absorbers to remove the principal torque impulses from in-line engine aggregates is tantamount to endowing the engine with a torque characteristic similar to that of an engine having twice as many cylinders. This is particu-larly advantageous in geared drives, where excessive torque fluctuation at the gear teeth might have serious consequences. The weight represented by an absorber scheme of the type shown in the photographs is frcwr" 2 to 3 per cent, of the engine weight. If, however, advantage is taken of the increased engine smoothness, resulting from reduction of torque fluctuations and internal bending forces, to use smaller scantlings for engine and airscrew components, it is probable that the total weight of an engine will be appreciably reduced when absorbers are fitted.

The results obtained from this De Havilland experi-ment are very encouraging, and now that satisfactory practical and theoretical studies appear to be becoming more generally available, there should be a considerable ^ increase of interest in what is undoubtedly a powerful method of dealing with vibration troubles, especially taking into account the constructional simplicity of the device.

LITTLE FLEAS and LESSER FLEAS Italian Service Carries Strange Cargo

'"FHE carrying of aircraft engines by air is nearly as old -* as flying itself, but except for the Short-Mayo com-

posite the carrying of aircraft on or in another aircraft has not hitherto been a commonplace. The war in the Mediter-ranean has brought into being a special Italian air service, known as the Servizi Aerei Speciali, which has carried many

strange cargoes. It has been.reported that during the first 100 days of its existence the service carried 635,000 lb. of material, 19,185 persons, and covered 1.5 million aircraft miles.

Perhaps the most interesting of all the cargoes carried was a Fiat C.R.42 single-seater fighter, which was trans-ported inside a Savoia-Marchetti S.M.82. The Savoia is, of course, a large aircraft and the Fiat a small one, but nevertheless it is somewhat surprising that space could be found without dismantling the fighter into smaller com-ponents. It will be seen that there is room to stand the wing against the side of the cabin, while the fuselage, with its engine, rests on the floor.

Solving the problem of transporting fighters to a scene of operations outside their range. A Fiat C.R.4? in the fuselage of a Savoia-Marchetti S.M.8z.