Some day I'd like to build a large scale Dehavilland DH2, a WW1 pusher-type airplane. Can I consider a glow engine for this project? Or should I just go electric?

Can a glow engine run backwards? Or do you buy a special prop for it so it can run normally but push air instead of pulling it?

Thanks!

Charles.

You only need to buy a pusher prop, ie., Master Airscrew. The prop will have the letter P next to the diameter and pitch numbers. You will need to consider limited taxi time with a pusher, the engine gets very hot very quickly on the ground.

As roary said, pusher props are available but the range is much more limited if you want to get fussy about them. A heli engine with the large heat sink head would help keep it cool. But if you have an engine with a removeable front end then you can change it the way I've done in the photo. This allows the engine to run in reverse as well as it does normally and then you simply use a normal prop but put it on backwards. Personally I'd never use a plain bearing engine as a pusher because the crank is always pushed back against the crankcase and the shim thrust washer isn't really designed for continuous use.

Hello Downunder; You'll have to show me how that "regular prop put on backwards" works.

Simple, just turn it around so the blunt edge is at the front when the engine is rotating clockwise (as viewed from the front of the motor).

By rotating the front housing of the engine through 90 degrees, you effectively convert the intake timing to allow the motor to run in a clockwise direction -- the opposite of normal. This was one of the really cool things about the OS FSR 40 and 45 engines (as well as others). They had a bolt-on front housing so you could convert them to pusher operation really easily. I did it on several occasions with great results.

These days however, most engines have a one-piece crankcase casting so can't be modified without a new crankshaft.

A reverse-rotation camshaft can be ordered for some 4-stroke engines (Saito for example).

If you've got a plain old 1-piece crankcase 2-stroke however, it's just easier to buy a pusher propellor.

As someone else pointed out though, watch for overheating on the ground. The *vast* bulk of the air that is drawn into a propellor comes in from the side -- not the front (believe it or not) and this means that there's very little air "sucked" over the engine when it's on the ground -- so it gets real hot, real quick.

I had to laugh; downunder brought up some knowledge of the fsr engines that I had forgot years ago. He is right; just rotate the front case 90 degrees and the crank timing will work in the other direction. Funny, some of the thngs you relearn.

Good idea, Downunder....[sm=thumbup.gif]

The carb can draw some clean air as well, rather then being stuck "behind"
the cylinder. I might try that with an OS 60FSR in my new pusher plane.

FBD.

Although this is probably not appropriate for the DH2 (yet I am considering putting my jett 76L in the DR-1 VK triplane), Jett offers all of its engines in reverse-rotation configuration. Just a matter of ordering it that way with the clockwise crankshaft.

As noted, the huge advantage here is prop selection. There is a very limited selection of 'pusher' props on the market. The reverse rotation engine allows you to use any standard tractor prop, installed with the curved surface facing forward into the flight path. You have the ability to select the prop that performs best in that application, rather than compromising.

K&B use to sell reverse-cranks, as well did a few other mfgs. These were mainly used by folks wanting counter-rotating engines on twins... often overlooked as pusher engines. And as shown, those engines with bolt-on front ends can be rotated - this has been done many times over the years.

Dave..... that FSR sounds like just the ticket there

Bob

How bout taling Dubb in building a four stroke for that Tripe?

Nah... he is not a 4c type of guy. Too many parts. The chinese seem to have those figured out pretty well as it is.
Fitting a 4c into the VK trip is a serious pain in the butt. I did that on the Camel and it was a big mistake. Engine size/weight/position/cooling are important, and it needs a 14" dia prop - flys best that way. Tripe use to have a ST bluehead in it. Now has an old webra 61 (altered a bit - tiny carb) - a bit too heavy. The 76L actually fit in there nicely, and it outperforms that blue head and webra on a 14x6, and is lighter. Might be a fun experiment. The plane is somewhere around 15 years old now.

ok.. enough.... getting a bit OT here.... [&:]

The VK tripe is a bit smaller, but a 4 cycle fit nicely in the slightly larger GP Dr-1.