1984-10-01

Airplane Mounted Accessory Gearbox Design 841605

Since the advent of lightweight, high thrust jet engines developed for modern combat aircraft, the trend has been to delete accessory drive pads from engines and to furnish engines with provisions only for driving a power takeoff shaft or PTO.This has created the requirement for a new accessory to provide drive pads for such items as jet fuel starters, air turbine starters, hydraulic pumps, fuel pumps, AC generators and provisions for a PTO shaft for connection to the engine.This new accessory is an airframe mounted accessory drive or gearbox (AMAD or AMAG). While involving no new principles of design, it has suffered a plethora of costly and time consuming design and development problems. These problems are mainly due to the transfer of gearbox design and performance responsibility from the engine manufacturer to the airframe and gearbox manufacturers, who often lack the indepth design and system expertise to conceive and direct a timely and trouble-free AMAD/AMAG program.This is especially true where input shaft speeds and drive pad speeds are now reaching 17,000 and 25,000 RPM, respectively and where gear and bearing loads are increasing at the same time due to higher accessory loads and speeds.Further, acceleration and deceleration input speeds of 3600 and 5000 RPH/second are typical thus presenting potential bearing skid problems.In these cases not only are bearing and gearing designs demanding but their integration into the gearbox design as a whole and particularly with regard to lubrication and control of increased heat rejection, is a task not to be underestimated.This paper gives broad coverage to the many areas of gearbox design and provides to the engineer and his management a compilation of specialized engineering experience and program guidance that when followed will result in timely and successful AMAD/AMAG projects.

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