Pusher - Tractor Props

[Murocflyer]

Looking for a good reference site that describes/discusses the different types of props and how they are used.

Google is letting me down. Can anyone help?

Thanks,

Frank

[vintage1]

Well the propellors are the same. Do you mean why use a pusher ARRANGEMENT?

It's been proposed as aerodynamically cleaner many times, but has always foundered on the practical problems of how to protect the pilot from a large lump of engine right behind, in a crash. Plus issues of cooling the engine ..plus issues of balance.

[Murocflyer]

I'm looking for a reference site that discusses the difference between the two props. I know APC makes pusher props, and the EZ* comes with pusher, but I can't find a site that discusses the difference besides how to install them.

Frank

[slipstick]

Both props are intended for use on an engine/motor rotating anti/counter-clockwise(looking through the prop towards the motor). A tractor or conventional prop is for the prop at the front of the plane pulling it along, a pusher assumes the prop is behind the plane and engine pushing the plane along.

If you mean physical differences it is purely that the blades angle the opposite way when you look at the side of the prop. Everything else is identical.

For electrics we don't generally use pusher props because electric motors, unlike IC motors, are able to rotate in either direction so we use a tractor prop rotating clockwise.

Steve

[nmasters]

A pusher is less efficient than a tractor by at least 10%. Also the propelor acts as a fin so if it's forward of the CG it's destabilizing. A very crude estimate of the stability effect of a prop is to pretend it's a fin with about ½ the propelor disk area. If you just have to know the details ask Joe & Don (http://search.atomz.com/search/?sp-q=pusher&sp-a=sp10001091&sp-k=ASK+Joe+and+Don&sp-advanced=1&sp-p=all&sp-w-control=1&sp-w=alike&sp-d=custom&sp-date-range=-1&sp-start-month=0&sp-start-day=0&sp-start-year=&sp-end-month=0&sp-end-day=0&sp-end-year=&sp-x=body&sp-c=10&sp-m=1&sp-s=0)

--Norm

[Murocflyer]

Thanks for the link Norm, I had found that one last night.

As I like to post reference links when providing answers to questions, I wanted to find a site that discussed the differences between a pusher prop and a tractor prop to help explain that. But I just can't seem to find a site that breaks that down and explains it.

I gotta believe there is one out there.

Frank

[nmasters]

I guess I just don't understand the question. As Steve said there's not much physical difference in the actual design of the props except for the direction of rotation. In that site search I gave the first hit explains the differences between pushing and pulling pretty well. The others highlite various details

[Murocflyer]

That's what I am looking for. A reference site that explains the physical differences between a pusher and puller prop and how to tell them apart.

It's nice to have a reference link when providing info.

Thanks,

Frank

[JetPlaneFlyer]

That's what I am looking for. A reference site that explains the physical differences between a pusher and puller prop and how to tell them apart.

It's nice to have a reference link when providing info.

Thanks,

Frank

There is no inherant physical difference between a pusher prop and a tractor prop. Providing you have a motor that can spin in either direction a pusher can be use as a tractor and visa versa...

[Murocflyer]

There is no inherant physical difference between a pusher prop and a tractor prop. Providing you have a motor that can spin in either direction a pusher can be use as a tractor and visa versa...

True, but lets say the motor can only turn in one direction.

Is there a site that explains the difference between those two props?

Frank

[nmasters]

I haven't bought a prop in a long time so didn't remember this right away. Plastic props that have the manufacturer's name and size molded in have that text on the suction side i.e. the side that faces forward. The little Thimble Drome props that I have in my hand right now also have turbulaters near the root on the suction side. The turbulaters are little crescent moons with the convex curve pointing toward the leading edge. The pusher has "L.H." for left hand rotation

--Norm

[BMatthews]

True, but lets say the motor can only turn in one direction.

Is there a site that explains the difference between those two props?

Frank

You won't find one because the ONLY difference is that one is left hand pitched while the other is right hand pitched.

As already mentioned they can both be used in either application as long as the motor can turn them the right way. If you're stuck with a motor that is timed to only run one way or an engine that is stuck the same way then you need pusher props because they are pitched so that they can be mounted that way.

If you lay a pusher and tractor on the table in front of you they both have the size numbers molded or printed on the side that is intended to face forward. That being the convex side of the blade. At this point you'll notice that the pitch angles are mirrored to each other to allow turning in their respective directions. You'll also see that the pitch twist towards the tips is the same with the angle to the table becoming flatter towards the tips.

That's it. Nothing else to see. Any other variations will be due to the maker of the prop. Some testing of similar sized but various patterns may show you one works a little better than the others for your specific model and motor/engine.

[Murocflyer]

OK, thanks for all the responses and info fellas. This will now be my reference site when any one asks about them.

Thanks again,

Frank

[slipstick]

Just to make it completely clear (I hope) there is no difference other than what's in the pictures (actually mirror versions of the same picture stolen from Martin Hepperle's site).

So it's VERY easy to tell a tractor prop from a pusher prop.

Steve

[MCarlton]

As far as I understand it, if using an IC engine or a retimed Electric Motor running in reverse, you don't even need a pusher prop, you just move a tractor prop to the back, keeping it in the same orientation.

[BMatthews]

That's one great aspect of using brushless. There is NO timing since there's no brushes. The timing is all handled by the controller which doesn't care at all if it's going one way or the other.

As for the engines if you turn the engine around so it's facing backwards then you need the pusher prop or you need a left hand ported crankshaft (or rotary disc) or a reed valve controlled intake or one of the engines that has a bolt on front and where you can re-attache it with the carb angled 90 degrees to the side (not sure WHICH side). If yoiu can do any of those things in order to make the engine run clockwise as seen from the crankshaft end then you can use a regular tractor prop turned around backwards. Just remember to flip it the right way..... :D