Generally, the atmosphere is drier at altitude and leads to premature brush wear,
(And the generation of more ozone due to lack of pressure, I am led to believe)
But there is a lot more to it than that, brush design and material etc.
The way technology has evolved in the automotive industry you'd probably
Find an automotive alternator that would last quite well on a aircraft now, after all, they were automotive originally, and automotive have built in Reg's and the ability to change brush's quite easily.
There are many brush grades now, but with the cost of certifying I guess we are
Stuck with the status quo.
Last edited by Perspective; 5th Oct 2014 at 20:59.