Model Airplane guys? Help!

[Tim Clarke]

So I have mostly finished a Radial model engine. I got a prop at the local toy&hobby shop. The hub I built was 7/8 od. The prop has about a 3/4" hub. As you can see from the photo I'm going to hit daylight when I drill for the bolts. So what to do? Anybody know a brand I should look for? The one I have is Master Airscrew.

[danlb]

My first thought is to make a hub that fits the prop. I suggest this since you have the design for the current hub and should be able to scale it down.

No picture, BTW.

[Tim Clarke]

Okay I'll try the photo again

[johnc]

I built the same engine a few years ago and used a prop from this company. http://www.zingerpropeller.com The size 9-7 worked well with the .875 hub.

Nice job with the build!

[Paul Alciatore]

That looks sweet. I have always wanted to build something like that.

[Beazld]

What size prop are you looking for? Diameter? Pitch? Maybe I have something you can use.

[Noitoen]

You could just use 2 short pins at the back flange and turn the front washer to fit the prop's hub.

[Tungsten dipper]

You could just use 2 short pins at the back flange and turn the front washer to fit the prop's hub.

I think it's more about the appearance than the function.

[Noitoen]

I think it's more about the appearance than the function.

One more reason. Use short studs and nuts on the washer.

[BCRider]

For running the engine do not drill the prop even if you get one with a bigger hub area that matches or is a touch bigger than the drive washer. You'll cut too many of the wood fibers that hold the blades from turning into knife like projectiles.

I'm sure you're aware that the common method for model engines is some manner of knurling or other on the front of the drive washer so it bites into the wood or plastic. The single center nut on the shaft providing all the tightening force needed.

Some larger size props intended for big gas engines that do use multiple small bolts can be had. But they would likely be too big for the power of the engine. But one of those with a suitable hub could be cut down as a display prop. But for running the engine put in some cut straight knurls either radially like spokes of a bicycle or just flat cut directly across the face to get all the grip you need.

[DICKEYBIRD]

Isn't that a compressed air engine? Shouldn't need to worry about throwing a blade off a drilled hub.

If you can't find a prop with a large enough hub, get a couple of the ones that look about right, cut them apart & make a custom 3 or 4-blade hub. They used to be available on the market like that. I forget the brand name.

[BCRider]

DOH! ….. I'd forgotten that this is an air engine. Yeah, in that case just buy a larger size prop with a hub that is big enough that it's a touch bigger than the drive and holding washers so there's a bit of extra meat for the hole drilling. And if you don't like the size of the prop cut the blades down and reshape the new tips.

A steam or compressed air motor doesn't have to worry about being lugged down like an IC engine does. In fact I daresay that a steam or compressed air motor is BETTER when lugged down so that the cylinder dwell times are the flow limit instead of trying to flow too much too fast through the feed lines and valves. So a bigger prop won't hurt things at all.