Many aircraft in use today require the presence of an auxiliary power unit at one stage or another during their operation. Generally speaking, the function of the auxiliary power unit is to provide electrical and/or hydraulic power to aircraft systems when the aircraft's main engines are not in operation.
Additionally, in aircraft operating environments, it is also desirable in many instances to have a source of compressed air that may be utilized, for example, in starting the aircraft's main propulsion engines or in providing compressed air to aircraft systems that ordinarily would receive compressed air as bleed air from their main propulsion engines.
Further, not infrequently, such environments also require an air turbine starter for initiating operation of a turbine and/or an air turbine starter motor which is much the same as an air turbine starter but is adapted to be operated more or less continuously.
Needless to say, to provide all the equipment necessary to perform the foregoing functions is quite expensive, and where such equipment is on board the aircraft, it lessens the load carrying capability of the aircraft, all other things being equal, because of the weight of such equipment.
The present invention is directed to overcoming one or more of the above problems.