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Old Mar 15, 2011, 06:03 PM
Multi Rotor Maniac
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Australia, VIC, Melbourne
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Flying wing pusher prop - wing turbulence effect

I was wondering how does the turbulence generated from a flying wing effect a rear mounted pusher prop? Most flying wing pusher prop designs (such as zagis or swifts) have the motor mounted at wing level therefore the turbulence passes directly into the prop area.

Would there be any noticeable difference if the motor was mounted above the wing some distance (for example mounting a motor a few inches higher so that a 6 inch prop is entirely above the wing)? Would it be more efficient? Quieter?
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Old Mar 15, 2011, 06:19 PM
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Noise. Probably some efficiency loss.
Mounted higher > less noise, maybe...mmmmmaybe more efficient. But the full drag of the motor probably would kill that minor gain let alone all the problems with thrust angle generated.

Taken to extreme > put it on the nose. Quiet and efficient. Yes, there are wings with tractor drive systems for just that reason.
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Old Mar 15, 2011, 11:12 PM
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http://www.rcgroups.com/forums/showthread.php?t=990745
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Old Mar 16, 2011, 04:26 AM
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I was reading through the thread that nmasters posted, and following some links, and came to this image: http://www.rcgroups.com/forums/attac...mentid=2306757

Mounting the motor up to 1/4 prop diameter over the wing as in the last frame sounds like a decent idea for reducing the noise, but the efficiency might not increase, since now the motor isn't pushing along the correct axis, and you have to compensate by angling it so it blows a bit upward. the basic idea is that the thrust line should go through the center of gravity, or in the vicinity at least

I wouldn't go more than half the prop diameter above. The thrust line issues get worse the higher you get.
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Old Mar 16, 2011, 04:52 AM
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Cheers thanks for the info. The reason i was thinking about mounting the motor higher is because im attaching a fuz to my wing. This will provide about 80mm of usable space to mount the motor. Drag issues will not be a concern.

Think I will stick with similar designs and mount the motor just above the wing. So with mid mounted pusher designs such as the skywalker, do they have to adjust the thrust angle?
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Old Mar 16, 2011, 09:00 AM
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Mid mounted motor

Hi,
Any info on the thrust angle for a mid wing mounted motor set above the CG?
Go with throttle/elevator mix?
Where does up thrust from nose mount change to down thrust from rear mounted if prop is a same angle to horizontal,
or is it neutral by CG?
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Last edited by CaribbeanBlue; Mar 16, 2011 at 09:05 AM. Reason: clarification?
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Old Mar 16, 2011, 10:18 AM
internet gadfly
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Quote:
Originally Posted by meshyx View Post
Mounting the motor up to 1/4 prop diameter over the wing as in the last frame sounds like a decent idea for reducing the noise, but the efficiency might not increase, since now the motor isn't pushing along the correct axis, and you have to compensate by angling it so it blows a bit upward.
The thrust lost due to angling the thrust line a few degrees is actually surprisingly small as explained in this thread. Most full size 'wings have some angle either to get the prop hub away from the trailing edge or because of engine shaft offset. I know of one that has the prop tilted 14 degrees when the plane is sitting on its landing gear but the wing also has 7 degrees of incidence so you subtract the incidence angle from 14 to get the angle to the chord.

--Norm
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Old Mar 16, 2011, 10:27 AM
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Quote:
Originally Posted by CaribbeanBlue View Post
Hi,
Any info on the thrust angle for a mid wing mounted motor set above the CG?
Go with throttle/elevator mix?
Where does up thrust from nose mount change to down thrust from rear mounted if prop is a same angle to horizontal,
or is it neutral by CG?
The thread I pointed to in my last post also talks about pylon mounted engines but not in relation to flying wings. Basically don't do it. 'Wings don't have enough pitch authority to compensate for the torque that the high thrust line and if the prop is directly above the CG no amount of downthrust will trim it out.

--Norm
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