Jester241

I'm building a biplane(sig hog bipe),and am wondering what will happen if I point my exhaust straight down(ST .91 4stroke)? I screwed up and put my onboard glow on the exhaust side of the plane and down want to cover it in oil or the rest of the plane for that matter. I'm just wondering if pointing it down with tend to push the nose up in high throttle flight or during takeoffs with the exhaust pressure. I noticed on one of my other planes that pointing the exhaust down more changed the elevator trim during flight.

I've seen other bipes with the pipe pointing straight down and they didnt seem to fly screwy. Just some some more opinions on this. Engine is mounted upright,so the exhaust will be coming out of the side of the fuse and pointing down as opposed to coming straight down the middle of the fuse like I could if it was mount sideways.

Nathan King

You won't notice the difference. The engine will run fine and the aircraft will fly the same. You'd have to have some crazy exhaust pressure for the airplane to pitch up like that.

chashint

I point the exhaust straight down on all of my four strokes.
I have seen others do it differently but I really don't want the exhaust blowing up in my face when I am cranking the engine or checking the RPMs.

Stick40

I think he is refering to the drag produced by the huge mufflers ST engines have. This wont effect the proformace in a noticable manner. I had a ST 51 on a Stick 40 with the exaust pointing straight down. Flew Great!

Stick 40

r2champion

I think he does mean from the exhaust pressure itself, not drag.

Point the exhaust to whichever orientation is best for you, the difference will be negligable.

bruce88123

Pointing it FORWARD is not recommended though.

carrellh

If the muffler is big enough, it might be possible for it to act like a forward elevator. In that case making it level with the engine thrust line would probably be best.