Chas Levin
Western Thunderer
I don't know how other folks deal with this, but I was slightly concerned at the idea that the yellow prop tips might not be (reasonably) uniform in length, so I built a quick jig, based on a rubber washer cyano'd to a piece of thick card with a hole in and some other card discs on the back, so the engine can be stood on the hole, with each prop tip lined up with some pencil marks on the card - sounds more complicated than it is, hopefully these pics make it clear (and each prop tip does align above each pencil line when viewed in real life one by one, they just look odd through te camera):
