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Pusher vs. Puller propellers

#1
Many times, when looking at various RC planes, the propellers are often in the front or back. If you are designing and building a plane and had the option of either a puller or pusher propeller, is there any difference between the two? If so, how does the position of the propeller affect the flight of the plane? Along the same lines, why are some propellers more in the middle of the plane?

Sincerely,
Dwight
 

localfiend

I like 3D printers...
Mentor
#2
Many times, when looking at various RC planes, the propellers are often in the front or back. If you are designing and building a plane and had the option of either a puller or pusher propeller, is there any difference between the two? If so, how does the position of the propeller affect the flight of the plane? Along the same lines, why are some propellers more in the middle of the plane?

Sincerely,
Dwight
In the days of electric motors, which can spin in either direction with no problems, there won't be any difference between pusher or puller props. Back when gas was more popular, and most engines could only spin in one direction, you would need a pusher prop if the engine was in the back of the plane.


Pusher's are generally seen as more efficient, other than that, there's not a lot of difference. Propellers can be positioned in the middle of the plane for several reasons, most common probably being ease of balancing the plane and adding protection to the propeller.
 
#3
When possible, I like to avoid pushers. Especially high KV ones. While I don't know the scentific reasons, pushers tend to be more loud. When flying at local parks and usually near dusk I don't like to disturb neighbors as much as possible. That doesn't mean I avoid them altogether just not a preference at the local park.

When using a pusher propereller as a single motor puller, just keep in mind that any thrust angle will need to also be reversed.
 

localfiend

I like 3D printers...
Mentor
#4
When using a pusher propereller as a single motor puller, just keep in mind that any thrust angle will need to also be reversed.
Any right/left thrust angle will need to be reversed. Up/Down stays the same, just to clarify, I know you know that.

Loudness of pusher's seems to be directly related to the distance between the back of the plane and the front of the prop. If you can widen that gap without tail heaviness issues it can really quiet things down.
 
#5
As some have stated, the difference between a so called "pusher" or "puller" AKA "tractor" prop is just the direction of rotation. Since electric motors can spin either way you can put a so called "pusher" prop on the front of the plane, or a so called "puller" prop on the back of the plane. Standard rotation props, AKA Puller, AKA CCW (Counter Clockwise Rotation when viewed from the front) are still a bit more available, though that is changing rapidly, at least for the sizes that are commonly used for multicopters, which need both directions of rotation even though they are almost always set up to "pull".

Ultimately your question really isn't about the prop rotation direction, which is mostly arbitrary, but about the design of the aircraft that use them. Most planes are pullers for good reason. It makes good sense to put a heavy motor up front. The propeller also gets to run in "clean air", which means there are no obstructions ahead of the prop to create turbulent airflow and mess up its efficiency. Propellers in the back, or in the middle of the plane are usually done for aesthetic reasons, not because they work better. As mentioned by others, props in slots, or close behind obstructions tend to make excessive noise, which should give you some sense of the negative impact on their efficiency.

Props in front are more likely to break if the plane hits the ground, so some designs put the prop on the back or even in the middle of the plane to protect. A better solution would be to not hit the ground so much. That doesn't apply to combat planes though.

The direction of rotation does create a swirl in the propwash downstream of the propeller. This will have an impact on most planes. Most conventional puller planes will need right thrust or right rudder to keep them straight during a high power climb. There are many reasons for this but they all trace back to torque, the direction of the prop wash swirl, and something called P-factor. If you use a reverse rotation propeller you will want left thrust or left rudder instead. If the prop is in the back, and there is nothing behind it, then prop swirl won't matter, but the torque and possibly P-factor still will. Planes with single propellers are not perfectly symmetrical, just close. Usually the difference is just a click or two of trim, but some designs are more problematic than others.