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Wing Polyhedral - 1/6/2003 5:36:39 AM   
BBRELAND


 

Posts: 4
Joined: 11/7/2002
From: MS
Status: offline 		Hello All,
I'm presently building a Dynaflite Butterfly with a 99" span wing, and my question is what could I expect if I removed the polyhedral from the wing, but left the dihedral? I see gliders with and without the polyhedral. by the way. this is rudder and elevator only plane. Would appreciate your input. I have been flying for several years so the plane being less gentle wouldn't be a problem.
Thanks,
Butch
       Post #: 1

Re: Wing Polyhedral - 1/6/2003 8:32:50 AM   
BMatthews



Posts: 9005
Joined: 10/4/2002
From: Burnaby, BC, CANADA
Status: offline 		[QUOTE]Originally posted by BBRELAND
Hello All,
I'm presently building a Dynaflite Butterfly with a 99" span wing, and my question is what could I expect if I removed the polyhedral from the wing, but left the dihedral? I see gliders with and without the polyhedral. by the way. this is rudder and elevator only plane. Would appreciate your input. I have been flying for several years so the plane being less gentle wouldn't be a problem.
Thanks,
Butch [/QUOTE]

Common error, I learned that this was wrong when I was a teenager. Cost me a model when I tried just what you're suggesting and it wouldn't turn at all and sidesliped into a barbed wire fence.

Rudder controled models rely on the coupling between the rudder yawing the model and the dihedral converting that yaw into roll. If you remove the outer polyhedral angles then the model will react more slowly to rudder inputs, not faster.

And, as I found out, since the poly is out at the tips where it has more leverage the model will loose much more of it's response than the removed dihedral would suggest at first.

Basically, don't do it. If you're trying to get faster and more powerful response out of the design then move the hinge line to make the rudder larger and use lots of throw. Up to 45 degrees.

_____________________________

Witty saying to be plagarized shortly.....

(in reply to BBRELAND)
       Post #: 2

Wing Polyhedral - 1/6/2003 8:39:50 AM   
BBRELAND


 

Posts: 4
Joined: 11/7/2002
From: MS
Status: offline 		Thanks Bruce,
After reading your post I'll play it safe and build it per the plans.
Butch

(in reply to BBRELAND)
       Post #: 3

Wing Polyhedral - 1/6/2003 9:30:34 AM   
Ben Lanterman



Posts: 1284
Joined: 10/27/2002
From: St. Charles, MO, USA
Status: offline 		I agree with BMatthews. But it also depends on the type of airplane you are working with.

I have several glider type models (rudder-elevator) that came with standard dihedral that always seemed to be less than responsive to rudder. When I cut the wings and put in some polyhedral they became really nice flying models. The turns seemed to be flatter which for a glider was nice.

Years ago I flew in the rudder only class of RC competetion, never won but flew. Those models were of a cabin type fuse with standard (a lot compared to today) dihedral wings. They responded very well to rudder inputs and produced a lot of roll.

The Butterfly fits in the first class of model.


_____________________________

Ben Lanterman

(in reply to BBRELAND)
       Post #: 4

Wing Polyhedral - 1/6/2003 1:06:16 PM   
Daniel Nelson


 

Posts: 87
Joined: 11/20/2002
From: Lancaster, CA,
Status: offline 		I'm not familiar with a Butterfly, but as long as you increase the dihedral you won't need to bend the outer sections up. I've never flown a rudder-elevator that only had dihedral, but as a rough guess above 10 degrees should do.

Of course, you could always break out the ol' trigonometry and calculate how much dihedral you'd need so that the tips are in the same location as in the plans.

Dan Nelson

(in reply to BBRELAND)
       Post #: 5

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