High Efficiency Hydraulic Power Transfer Units for Multisystem Aircraft Available to Purchase

Fully powered flight controls are common among many aircraft, both military and commercial. Multiple pumps are generally employed to provide these flight controls with a redundant power source in addition to many other aircraft services. The prime hydraulic source in most cases is the engine‐driven pump. It is driven directly by one of the aircraft's engines and offers the most efficient method of converting engine horsepower to hydraulic horsepower. The secondary hydraulic power source is generally not as efficient. It must derive its power from a source other than that which powers the prime pump. Present transport aircraft have utilised bleed air, ram air, electrical power, or hydraulic power to drive this redundant pump. All have demonstrated poor power‐transfer efficiency when compared to a mechanically coupled pump. This inefficiency generally results in increased cost, weight, and complexity to the aircraft. The inadequate performance of existing hydraulic power transfer units was of particular concern. This paper will address the performance problem as well as the Douglas approach to improve it.