Maxthelion wrote:If the engine doesn't stop firing when it's got both mags off, you learn that one of the P leads is disconnected, leaving you with a permanently live mag and therefore prop. But you're quite right, it is a great way to wake up the neighbourhood.
But I learned that with the one by one method. Mag left - 50rpm drop. Mag right - no drop. Therefore left mag not shorting out. Inspection under the bonnet confirms broken wire. This actually happened six months ago. We put a big "live mag" sign on the prop till it was fixed.
What can i learn from a dead cut that I *can't* learn one by one?
Charles Hunt wrote:Surely it's only a momentary thing. You flick the switch, hear the revs starting to fall and switch it back. 1/4 second maybe?
At 1200rpm , 1/4 second is 5 revolutions, 10 power strokes in a 4 cylinder engine. That's a lot of fuel/air mix!
Boxkite wrote:But, in answer to some of the enquiries about a dead-cut test, if you don't detect a mag drop, how do you know the switches are even working??
The answer is a deadcut test by switching off both mags together.
If I don't detect a drop at all *something* is wrong and I investigate further. Or rather an engineer does. But if I have detected a drop, no need to do the dead cut.
I do accept that not all engines are the same and some may not show a drop on one mag. So different rules may apply then.