This Note describes the design and construction of a “ Tilting Test Bed ” for helicopter engines for Alvis Ltd., for which some onerous requirements were laid down (Fig. 1). The most important of these were that:—

1. (i) Readings of engine torque and b.h.p. must be given by a dynamometer, so as to provide accurate data.

2. (ii) The engine, and therefore the complete test plant, must be capable of being tilted, while running, through 120°—from the horizontal to the vertical and 30° beyond.

3. (iii) During the tilting process the engine throttle setting must remain unaffected and the readings of torque, b.h.p., fuel consumption, and so on, continue with unaltered accuracy.

4. (iv) A powerful fan must be incorporated, for cooling certain types of engine not provided with selfcontained fan, and the air-blast must continue unchanged during tilting.