Looking at some plans(Palmer OV-10 Bronco) which calls for 2-.80 4S Saitos. I have the 2 engines but am a bit confused as to how to make an engine run backward. Doesn't seem to be a problem with a 2 stroke. I must be missing something, brain maybe! Bill S.

It's not necessary to have counter rotating engines on a model.

You need a reverse roatation cam to reverse a 4-stroke, but as Mike stated, not necessary. If you can find the correct props for counter-rating engines, they are kool.

BillS:

Reversing a Saito engine can be done either of two ways.

On the "Big Block" engines where the exhaust and intake both attach in an internally threaded port in the cylinder, all you have to do is switch the inlet and exhaust manifolds. Instant reversal. It also gives you symmetric engines, so you can have the cylinders both on the fuselage side of the nacelle and have the exhaust on the bottom.

If yours is a big block with the o-ring sealed intake or a mid series it's still easy, but you can't get the symmetry the others allow. Just change the camshaft. Check the parts listing for your engine, then go to the parts listing for a twin in the same series. If you picked the right one, you'll find the right cam has the same part number as your single, order the left cam and install it, you have reversed the engine. If your engine has more than a few minutes running time, it is strongly suggested that the tappets be replaced at the same time.

The big block engines can also be reversed by changing the cam. Or if you want the symmetric engines without reversing, use the reverse cam with the reversed ports. One cancels the other, you will have the symmetric engines and still have conventional rotation on both.

The props for reversed rotation? Zinger has what you want, if you can't use the Master Airscrew or APC pushers to match the tractor prop on the other engine. Most of the Zinger pushers are wood, and some people don't like wooden props.

Bill.

Ditto.

It is extremely glamorous, but completely unnecessary to have counter-rotating props. And, in my opinion, way too much hassle.

I am stunned and awed, however, by Bill's discourse on Saito's. There's an awful lot of information packed in that little post! I like Saito's and I'm tempted to set up a twin as you suggest, just for the intrigue (and, yes) glamour of it all!

mt

It certainly would seem very cool! I have to digest Bill's data a tad and check my engines. I love the sound of the big 4 stroke but have never heard two going at the same time. The C.R. props at a low idle would turn a few heads!

All:

I have one (the conventional rotstion) F-120 done, the reversed/symmetric FA-120 is part of my "Saito Magnum Opus" that I'm working on. There will be complete pictures and procedures.

Bill.

Oh, just one more point against counter rotating engines. Very few full scale planes had them. One notable exception is the P-38, and its engines were backwards of what ease of single engine flight requires.

But I still like counter rotation.

Bill.

What were the advantages, reason for counter-contra?-rotation. You say you like them, why? Other than Koolness on a scale plane. Gotta remember to reverse that starter each time tho! Hmm, which one goes right and which one, left? Oh, oh, my plane's flying backward!

SmallBill:

If you have a twin with the left engine only running, the offset thrust tends to pull the plane to the right and the torque tries to roll the plane to the left. The two forces are opposing, making the airplane easier to fly than on the right engine only, where the two forces add. Provided both engines are conventional rotation.

Since this airplane is easier to fly with the left engine only, the left engine is referred to as the "Critical" engine. Losing the left is more a crisis than losing the right.

With counter rotating engines it doesn't matter which engine fails, the torque and thrust are subtractive for both engines.

The P-38 is a special case. With the right engine reversed there were bad turbulence problems, so it had the left engine reversed. Yes, this made the plane equally hard to handle with either engine out, but techniques were developed using this to increase the maneuverability of the plane; playing with the throttles gave it yaw capabilities that astounded the Jap fliers just before they died.

Bill.