Originally Posted by
spaceworm
I built a Goldberg Eagle (original, not the II) for a cousin and helped him learn to fly. The iron piston OS 40FP he put in the plane vibrated so much the Monokote drummed like a rock band. I changed the prop to a carefully balanced one and it did the same. He gave up flying and i lost touch with him. But I wold never consider buying an OS FP engine after that. When did they stop putting iron pistons in the FP series?
I have one with an iron piston too. They will vibrate a bit more than an ABC or aluminum ringed one if revved high. That is just the nature of the beast. The old Fox .35s were nasty for vibrating, I had to put cheek cowls on so the plane would not shake. Later I changed to the LA .25s and vibration was not an issue at all. I think it is just the counterbalance of the crank being too small in the Fox's case. A friends baffle piston OS .25 made my hand tingle from launching it with a smallish 8-6 prop. My FP .40 is in a control line stunt plane and it had an 11-6 or 11-7 when I bought it. It did not vibrate excessively, but flew nicer for stunting at least, with a 12-4. Could be that the old motor your cousin had had a bent shaft from a crash or something maybe too, if it was not new.