[&:]Does it matter what direction a glow engine is run? Can a glow engine be run backwards or will it fall apart?[:@]

It absolutely matters. Some of my larger engines (usually the ones that I flip-start) will start backward. Although they run backward, they have no power and no real accelleration capability.

If you need to setup an engine in a pusher configuration, you need to buy a pusher prop to get reverse thrust.

You won't get one to run backwards very long. The port timing is set up for right hand rule rotation, and if it starts backwards it'll run, but won't pull anything.

Good luck
Dave Olson

Thanks for the info....
I understand engine timing as it applies to an engine with valves but how does the stupid glow engine know what direction it is operating in? All it does is suck & blow
My theory on this was that the piston is doing the same thing no matter what direction it was turning????
I gather then that crank shaft direction affects flow within the engine & this restricts performance.. Do I have this correct. I find no other reason to explane the loss of performance.
Is it a reasonable assumption that if the engine had the intake & exaust ports moved to the opp side then the performance would be the same???[:-]

do they make engines that run opposite? How are the twin engines set up?

There are one or two glow engines designed to run "backwards", or that can be converted to do so, but fewer than there use to be.

All the twins that I've seen just use two identical engines rotating in the same direction.
Dennis-

Do full scale twins run the same direction also? I always assumed they'd be opposite to counter balance the torque. I bet those are fun to take off.

Here's an answer, probably not the one you want to hear.

The P-38 was designed with counterrotating props. The first order was made by the British, who specified identical engines both turning the same way (without turbochargers, too.) After some wind tunnel work, the counterrotating engines were switched from side to side, so the prop turns away from the top of the canopy, rather than toward it. You could build a scale, correct engine rotation P-38 in any of those configurations.

I understand the ordinary full scale twin has props that turn toward the canopy on top.

Twinman has addressed the counterrotating question at length, in a thread on the twins forum. I'll let you do the search. You'll find there that some will spend the money to have correctly counterrotating engines, and some won't. One of the high dollar items is the reverse pitch propellor, for the left-hand-rotation engine.

Good luck
Dave Olson

The only thing you need to change on a typical 2-stroke to make it run fine backwards is the crankshaft. It's the intake port cut in the crankshaft that "knows" forwards from backwards, everything else can go either way. You used to be able to buy replacement cranks, and maybe you still can, though I haven't looked for any.

As for moving the exhaust ports around, that's also possible. There used to be some engines (the old OS .40FSR was like this, I have a couple), where the front housing screwed on instead of being a one-part crankcase. This allowed you to take the front housing and backplate off the engine and swap them around, making the exhaust come out the other side. It was also possible to flip the carb 180 on it's mounts to move the throttle linkage to the other side of the engine as well (with or without changing the exhaust). So, with just a crankshaft, and some quick work with the hex drivers, you could have two totally mirror image engines.

As I understand it, the reason the brits wanted the p-38 engiens to both turn in the same direction was for spare parts inventory. If both engines went the same way, then you had exactly the same engine on both sides. If you had two planes, each with a dead left engine, you could pull one engine and put it on the right side of one plane and have a servicable fighter. With counter-rotating engines, you couldn't do that. Since the brits would have to ship in spare parts past the U-boats and so on, getting spare parts count down was really important.

Don't mean to hijack, but if you put a pusher propellor on a regular engine (ie, one that doesn't rotate backwards), it would push the plane? I had always thought the direction of the engine was necessary to accomplish that. [&:]

Put a pusher prop on a normal plane, it will push it backwards.

Full scale twins have all sorts of setups. There are some counter rotating that the descending blade is to the center for safer single engine performance, some like the P-38 mentioned have them going the other way for more maneuverability in a fight, and most have both engines spinning the same way, making the left engine more critical than the right if it were to quit. It all depends on the manufacturer and the engine. Most of the turbines I have flown spin the same way. The counter rotating ones are usually the trainer types and light twins.

If you put a pusher prop on a "backwards" engine, you get a "pulling" engine again. If you have a twin with counter rotating engines, one prop will be a "pusher". Really, "pusher" and "tractor" props are mis-labeled. It would be better to call them "right hand" and "left hand", to tell what direction to turn them to produce thrust in a particular direction. But since all the moden model engines turn in the same direction, you can label them "pusher" and "tractor" and get away with it.

I thought so Montague.



I am a bit confused. I accidently bought a pusher prop about a week ago, didn't see the little "p". It was the same price as the normal props. How is this high dollar?

Wings

In the smaller sizes, the pusher props aren't really any more expensive. However I suspect (haven't looked though) that in the larger sizes used by the giant scale guys, the price goes up dramatically.

Some of the old SupreTigres will run backwards. My 3250 for example has a bolt on front crankcase. By rotating the front of the crankcase 90 degrees the timing is correct to run the other way. All the old .60s-.75s & .90s had the removable front crankcase. They will also run just fine the other way.

David