AirplaneDesign.aero

crschro · Newbie Joined: 04 Mar 2005 Posts: 1

So I've taken numerous stability, control and aerodynamics classes but the pros and cons of Pusher Props has never been discussed. I'm wondering what the drawbacks of a Pusher are and why they aren't used more often?

joshua.montgomery · Posted: Tue Mar 08, 2005 1:47 pm Post subject: Tractor or Pusher

A couple reasons for NOT using a push prop.

1. Takeoff rotation: in a pusher config. one has to be very careful to avoid prop strike.

2. Crashworthy ness: To address 1 (above) you have to set the engine up and behind the passengers. In a crash, this engine has the potential to come down into the passenger compartment and hurt people.

3. Cooling: In a tractor configuration cooling air is drawn from the free stream behind the prop. In a pusher ductwork is required to duct the cooling flow from the free stream.

4. Tradition: never discount the importance of tradition in aircraft design. "That is the way we have always done it!" is a phrase that rings out over and over in certain companies. Is this a good thing? Yes and no. Yes because having experience with the configuration lets engineers build safer aircraft. No because sometimes a pusher or another non conventional geometry makes sense.

steven42 · Newbie Joined: 05 Oct 2008 Posts: 2 Location: New Zealand

The tractor configuration has the extra drag of having the fuselage in the accelerated prop wash. If all else was equal a pusher aircraft would be faster, but it is not because boundry layer air from wings or elevator degrade the propeller efficiency. When the boundry layer air encounters the outer third of the propeller diameter the slow speed of the air reletive to the craft causes the propeller blade to stall. The efect of this is two fold. 1 there is no thrust produced by the blade untill corect flow is established. 2 the drag on the blade is incresed, loading the engin with no gain in this region. My question is, knowing this, and how much efort jet engin installations go to stop boundry layer air from being ingested, has there been any investigation into the effect of devertind the boundry layer air away from the outer third of pusher propeller?
If any of my assumptions are wrong please feel free to put me right.
I welcome comment.