German members: what is a Bürstenabhebung?

[gecko]

I know some German, but this has me stumped. Brush withdrawal? It is supposedly the name of a lever involved in starting an aircraft engine. I'm trying to get a better idea of what it is.

 

[Frosty]

Well, I am not German but the only brushes I can think of (and I don't know anything about engines, dynamo's etc.) are these: https://en.wikipedia.org/wiki/Brush_(electric) Don't ask me why it should be necessary or desirable to remove or lift these but there are probably plenty of people who can shed some light on this.

 

[gecko]

Yeah, it sounds like that kind of thing, but it doesn't make any sense in context unless it is further disconnecting the electrical starter during hand cranking. Maybe???

 

[paulopp]

Yes, the brushes are the electrical contacts in an electrical engine. As they physically grind over the contacts, they are prone to wear and tear. So, the Bürstenabheber temporarily "withdraws" the brushes.

 

[MajorMagee]

I wonder if it has something to do with the Magneto check?

https://www.aopa.org/news-and-media/all-news/2002/january/flight-training-magazine/the-magneto-check

 

[gecko]

Thanks guys, I think I understand now. Electrical current passing through an electrical motor causes the motor to turn (obviously) but when current is not flowing, if the motor is turned by another means (in this case, hand cranking an inertia starter to energize the flywheel) the rotation of the motor will actually cause electrical current to flow, effectively turning a motor into a generator. This could possibly cause problems in the electrical system, so withdrawing the brushes in the motor would prevent the motor from producing an electrical current.