What's the different between a pusher and puller props?
 

Ok.. Other than the obvious 1 pushes, the other pulls. What's the difference?

If one looks at the airplane from the front, they both rotate the same direction.

Is the shape different?

The reason I'm asking is, if I build an airplane that requires a pusher prop, and I can't find a "pusher" prop of the correct dimensions. Will a puller prop work in its stead?


I know it may seem like a naive question... but I just "don't know."



Thanks in advance,

Lyndon

RE: What's the different between a pusher and puller props?
 

You can't just mount a tractor prop on an engine that is facing backwards because the engine needs to rotate the wrong direction for the prop. So you either need a pusher prop, which is different only in it's direction of rotation, or an engine that rotates the wrong way, and use a tractor prop.

RE: What's the different between a pusher and puller props?
 

A tractor prop mounted on a pusher motor will move the plane towards the tail, even if it's reversed on the motor.
The direction of rotation of the motor must be reversed to use a tractor prop as a pusher.
Some i.c. motors have the front plate seperate, and it's possible to rotate that so the motor will run "backwards".
Electric motors, just plug them in "backwards"*, and use a conventional tractor prop.
.
* reverse any two of the three leads with a brushless motor to reverse its rotation.

RE: What's the different between a pusher and puller props?
 

I knew that the rotation of a "tractor" motor in a "pusher" orientation is opposite direction of a "tractor" motor in "tractor" orientation. I had hoped I had said that correctly in my first post. Guess I didn't... Sorry.

The way I see it, there are two kind of engine/prop "pusher" configurations possible.

1. A "tractor" motor mounted backwards in a pusher orientation with "pusher" prop.

2. A "pusher" motor (spinning in opposite direction of a "tractor" motor), with a "tractor" prop.


Either configuration, the lettering on the prop must be facing the front of the plane.


That being said, I'm thinking more from a pure aerodynamic standpoint. Say you have a 10-6 prop on both of the above setups. Would the shape of the prop bladed differ? Like the rate of twist, thickness of prop blades, etc.

I hope that makes more sense this way...

RE: What's the different between a pusher and puller props?
 

Not only must it be a pusher prop, but something else to watch out for is to get it on the right way.

With a regular (tractor) prop, the lettering and/or Logo (Indicated by the red line in the picture) is facing forward - away from the engine

I have seen many people install a pusher prop with the lettering also facing away from the engine. In MOST cases, manufacturers put the lettering facing the FRONT of the plane.

RE: What's the different between a pusher and puller props?
 

We're stuck with what is available.
On my push-pull Senior Kadet/Cessna 337, the front prop is a 10x5 tractor, the rear prop is a 10x6 pusher. Both by Zinger. Both engines are OS 40FPs.
There isn't a large selection of pusher props.

RE: What's the different between a pusher and puller props?
 

The shapes of the blades would not differ. The same propeller theory applies to both tractor and pusher props. There are aerodynamic results on the aircraft however, like no slipstream effect, if there is no tail in the slipstream, etc..

RE: What's the different between a pusher and puller props?
 

What was really interesting to me-- was the airflow to/from the prop-- on a twin boom pusher design I tried in two different sizes.
the fuselage pods were smooth 10-1 teardrops and on c/l of wing - so airflow to ptop,was about as smooth as I could do it

the downstream flow in both cases was from prop tips - -inward to a small spiral -just like water going down a drain. I held a piece of string in front -above and downstream and watched it's angle to determine the airflow - a poor man's windy tunnel . seemed accurate to me .
Rather than fret on prop blade design --I now try to get smoothest path to /from prop. see picture of EDGE
I really think that makes more difference than typically supposed and based on peformance of the model I will persue this approach.

RE: What's the different between a pusher and puller props?
 

Off topic: How do you like those tip plates?

Cooling drag can be HUGE. Racers know that too.

RE: What's the different between a pusher and puller props?
 

Note the scale openings got blanked.
on my new pattern plane 'mommacass', a modified Cassut lookalike, the frontal opening is tight to the cylinder of the 40 cc ZDZF3A -it is an extractor setup . cowl is tight to sides of cyl. no cheekcowls (why in the ---some "pattern planes have those blips on eiher side of cowl is beyond me.)
the tip plates :
it may sound strange -but the EDGE with 4" cut from each panel and the tip plates is better in all maneuvers than the stock setup - there is no hint of being higher in wing loading.-tho it is .
knife edge and or knife edge loop is easy and in knife flight, fuselage is at a very low AOA .
even at low/moderate speeds
cg is at 30% MAC
The high power and engine response may cloud my overall asessment but low speed flying just seems very light. super quick roll response and stop