This weekend I overheard a rather interesting conversation at an
airfield here, but did not participate myself.
Two guys with a large silver oldtimer that looked like a "Tante JU" (JU
52, had to look it up) with three props were discussing torque issues.
I know that the common way to counteract torque in twin prop (i.e. the
banana heli config) HELICOPTERS is to just counterrotate the blades. On
my own planes I've never bothered, since I never consciously thought
Google searches showed that counterrotating seems to be the common way
to fight it... but why even bother? I'd imagine this here (imagine
that's a plane seen from the front or the rear... with the lines being
Then if the engines counterrotate, it'd be a force distribution similar
to this (depending on which engine goes which way around, I know):
Nice and symmetric. Would there be any difference in flight if the
torque was exactly reversed? I should think not?
But what (roughly) would be the effect of both engines rotating in the
same direction? The forces ought to be like this:
I would imagine it more or less being the same or even a little less
than a single engine's torque effect? The center torque should cancel
each other out. Would the torque be twice that of a single engine with
the combined force of both? A fraction of one engines power? I can't
quite find a straight answer to this via Google.
My main question is really "do I need to know this", but since I am
incurably curious I guess I HAVE to know it nonetheless :)
Btw, the two guys talking about it didn't come to a consensus about the
proper way to work out that three-engine plane's torque :)
- posted 15 years ago