Editing Auxiliary power unit (section)

====Gearbox section====
The [[gearbox]] transfers power from the main shaft of the engine to an oil-cooled generator for electrical power. Within the gearbox, power is also transferred to engine accessories such as the fuel control unit, the lubrication module, and cooling fan. There is also a starter motor connected through the gear train to perform the starting function of the APU. Some APU designs use a combination starter/generator for APU starting and electrical power generation to reduce complexity.

On the [[Boeing 787]], an aircraft which has greater reliance on its electrical systems, the APU delivers only electricity to the aircraft. The absence of a pneumatic system simplifies the design, but high demand for electricity requires heavier generators.<ref name=nobleed1>{{cite web|last=Sinnet|first=Mike|title=Saving Fuel and enhancing operational efficiencies|url=http://www.boeing.com/commercial/aeromagazine/articles/qtr_4_07/AERO_Q407_article2.pdf|publisher=Boeing|access-date=January 17, 2013|year=2007}}</ref><ref name=Design_News_20070604>{{cite news |url=http://www.designnews.com/document.asp?doc_id=222308 |title=Boeing's 'More Electric' 787 Dreamliner Spurs Engine Evolution: On the 787, Boeing eliminated bleed air and relied heavily on electric starter generators |publisher=[[Design News]] |date=June 4, 2007 |editor=Ogando, Joseph |access-date=September 9, 2011 |archive-date=April 6, 2012 |archive-url=https://web.archive.org/web/20120406062451/http://www.designnews.com/document.asp?doc_id=222308 }}</ref>

Onboard solid oxide fuel cell ([[SOFC]]) APUs are being researched.<ref>{{cite journal |last=Spenser |first=Jay |date=July 2004 |title=Fuel cells in the air |journal= Boeing Frontiers |volume=3 |issue=3 |url=http://www.boeing.com/news/frontiers/archive/2004/july/ts_sf7a.html}}</ref>