ARMOR is a joint University/ Industry UAV project that has been in development for some years in Portugal. On a quest for safety and redundancy a twin-engine arrangement has been sought for the propulsive unit, the two engines driving the same pusher propeller. This solution is unheard of. Hence, several points concerning the behaviour of the ensemble of the engines had to be studied: start up of each engine, stability and response of the ensemble for a variety of working conditions, response of one engine to a malfunction (or complete failure) of the other, and strategy of load partition between the two engines. An experimental programme was set up to investigate these points. Two model engines were assembled in a dedicated stand, driving the same shaft through sprag clutches. The dedicated stand was mounted in an engine test bed. The tests showed that: 1. the engines could be started independently, with no interference with each other, but (obviously) they could not be started using the common shaft as the driving input; 2. there were no stability problems in steady-state conditions, and momentary perturbation were dealt with satisfactorily; 3. when one engine was stopped it was possible, by manually increasing the throttle opening, to restore the previous load and speed conditions; 4. fuel consumption of the ensemble did not change appreciably when the two extreme situations of load partition were used (i.e. both engines with half-load, and one engine with full load and other on - virtually - zero load). The results obtained indicate that this is a viable solution. Tests with the full size engines to be used on the prototype aircraft should then follow.
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