os 55 ax sideways
 

I know and have read that this 55 ax does not like to run inverted especially with a pitts muffler. have not tried with the stock pipe. anyone have any luck running this thing sideways with stock muffler? was gonna put it in a sport wm mustang just for fun, and I think it would look better sideways than straight up in the mustang . please help its the only project I have going right now, don't want to waste time putting it sideways if it wont run right . thanks all

It should run fine with enough cooling air.

My OS .55 is a great engine, really powerful, but is really touchy on carb settings even side mounted. Seems to need lots of warm up. Should probably stay away from the Fuel fillers which go in the carb line. Inverted engines just seem to be tough to get right, but some people have great luck once the engines are tuned correctly. That said I have a 20 year old Pilot Twin with 2 inverted K&B 28s that have settled down fairly well.

Good Luck - Darryl

It should not be a problem using the engine at any position on a plane. Fuel tank location and how far away it is from the engine can sometimes be an issue though. But if I remember correctly, OS put on a carburetor that has a really large venturi opening in it, and that affects how well it can draw fuel. Especially with larger propellers where the engine doesn't turn RPMs as fast as with smaller props. Many of the Pitts mufflers do not have enough back pressure or muffler pressure to help the engine draw fuel. Usually with the Pitts mufflers you have need to restrict the exhaust outlets more, sometimes they almost block one outlet completely. The engines are sensitive to needing more muffler pressure going to the fuel tank. If you get good muffler pressure and don't try to use the larger props, the engines then tend to work well in any position on the airplane. When some folks remove the internal muffler baffles on the stock muffler, they start running into fuel draw problems too. A few folks have replaced the carbs on their engines with carbs that had a smaller venturi and that helped too.

Once it is running it doesn't care what position it is in. Getting a good prime is more of a problem when sideways or inverted though. They need to be internally wet to fire and a couple of flips with a finger over the carb intake or muffler exit doesn't do the trick because the fuel drops just run out of the carb and onto the ground. So when cold, without the glow ignitier on yet, 1/8 throttle or so, and covering the intake to choke it, spin the motor for about 20 seconds with the electric starter. This will actually suck some fuel into the engine. Then apply the glow power and it should fire.

The carb that came on the original OS 55AX is one of the best OS ever produced. The main factor as is with most of these muffler pressured glow engine is carb relation to the tank. The closer the carb is to tank center-line, the better it will run from start to finish. Of course there may other issues as mentioned earlier like non-stock muffler pressure or poor cowling airflow.

I've got 2 OS .55AXs. I've had them mounter in several planes, always sideways. They run great. As a previous poster said, they're the best OS ever made. Just don't set it too lean on takeoff. If you're leaving a slight smoke trail, that's perfect. It will lean out during flight as fuel burns down.

I do recommend a castor blend fuel for OS ABC (or whatever) engines. I use Omega 10%.

They also respond well to a Jett tuned muffler. I gained 1,700 rpm on an 11-6 APC. 1,500 on the 11-7.

Edit: Correction, I did have a .55 mounted upright. I had one on a Tango, the one in the Avatar. Great little airplane.