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questions about pusher props.

Old 08-25-2019, 12:16 PM
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Flight Risk
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Default questions about pusher props.

I have a glow engine I would like to run as a pusher on a flying wing, and have noticed that the selection of pusher / reverse propellers is down from what I used to see.especially in the smaller sizes such as 10-15 inch. There seems to be quite a variety in the big 20-30" sizes, evidently for contra-rotating pattern planes. And there is an abundance of pusher props for electric motors, for obvious reasons, including multi-rotors.
One odd thing I notice is that all of Master Airscrew's pusher props are 3 blades. Why is that? My finding is that 3 (or 4) blade props are much less efficient than 2 blades. I may try one on my wing but wish they were 2 blade. What I need is a 10-11 inch prop with a pitch of 8-10 to allow for ground clearance on a 60 size engine. I did find a 12x9 pusher from Xoar and I cut it down to 11" and will try it in the next few days.
But my main question is what's up with the 3 blade props from Master Airscrew.
And have you found another source of pusher props.

Thanks
Old 08-26-2019, 03:06 AM
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I don't remember who it was I talked to but at least one of the manufacturers will make a pusher in any size they make a tractor. I'm pretty sure was either Master Airscrew or Xoar and this is for the wood props. They just don't advertise the pushers as much since there isn't a great demand for them.

I'd e-mail both of them and simply ask if they can make a pusher in what ever size(s) you need.
Old 08-26-2019, 10:33 PM
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Originally Posted by Appowner View Post
I don't remember who it was I talked to but at least one of the manufacturers will make a pusher in any size they make a tractor. I'm pretty sure was either Master Airscrew or Xoar and this is for the wood props. They just don't advertise the pushers as much since there isn't a great demand for them.

I'd e-mail both of them and simply ask if they can make a pusher in what ever size(s) you need.
Thanks Appowner, after doing more searching someone did mention that Xoar could make any current prop into a pusher. I'll try the few old stock I have and see what might be usable;
Old 08-28-2019, 08:26 AM
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Flight Risk, that's a good handle.
Old 08-28-2019, 01:22 PM
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my guess with most pushers being 3 blade is if since being is a reversed position there may be a lack of speed? if you were to use a 3 or 4 blade prop there is more speed but the downside is there is also a increase in drag between the prop blade so less efficient. this is just my guess i could be wrong
Old 08-28-2019, 05:46 PM
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Originally Posted by z-rc135 View Post
my guess with most pushers being 3 blade is if since being is a reversed position there may be a lack of speed? if you were to use a 3 or 4 blade prop there is more speed but the downside is there is also a increase in drag between the prop blade so less efficient. this is just my guess i could be wrong
A true pusher prop is no more or less efficient than its tractor counter part. Assuming they are both mounted and used properly. Reversing or flipping a tractor does not make it a pusher in case anyone was wondering. But putting either prop on backwards will reduce it's efficiency. In addition, for a given application a 3 blade prop is less efficient than a 2 blade. And for the best performance, try a single blade. The reason is the prop is most efficient when the blades hit perfectly smooth air. However, every blade disturbs the air for the next blade. Thus reducing efficiency. Hence with a 3 blade the air is more recently disturbed when the next blade comes along.

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