Low Dihedral, Polyhedral (gliders)  
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All Forums >> RC Airplanes >> Aerodynamics >> Low Dihedral, Polyhedral (gliders)
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Low Dihedral, Polyhedral (gliders) - 3/10/2002 1:33:53 PM   
wildblueyawner


 

Posts: 197
Joined: 2/16/2002
From: Covina, CA,
Status: offline 		Re gliders,

1) What is the benefit of a low, or no, dihedral wing, given its generally greater tendency for spiral instability and tip stalling in turns >> Aero efficiency? Some other controllability issue?


2) Are polyhedral wings used mainly for their greater roll stability and turning ability, or is there actually some L/D benefit, at least to offset the added interference drag?

I believe it was Bob Dodgson (of Dodgson Designs) who was a proponent of DIHEDRAL thermal designs over polyhedral, for reasons I don't recall.
       Post #: 1

Low Dihedral, Polyhedral (gliders) - 3/10/2002 6:59:26 PM   
Ollie


 

Posts: 958
Joined: 12/8/2001
From: Punta Gorda, FL
Status: offline 		Dihedral and polyhedral produce yaw-roll coupling and lateral stability. For every polyhedral arrangement, there is a dihedral that produces the same yaw-roll coupling and lateral stability as the polyhedral does. Polyhedral will tip stall at a lower angle of yaw than dihedral with the equivalent yaw-roll coupling and lateral stability.

Another possible advantage of dihedral over polyhedral is that it avoids the weight and complication of the structure to join wing panels.

The desirability of polyhedral or its equivalent depends on the purpose of the aircraft. Yaw-roll coupling and lateral stability need to be very limited in aerobatic aircraft, for example.

_____________________________

Regards, Ollie

(in reply to wildblueyawner)
       Post #: 2

Low Dihedral, Polyhedral (gliders) - 3/16/2002 4:39:34 AM   
dhrider


 

Posts: 22
Joined: 2/25/2002
From: Northglenn, CO, USA
Status: offline 		look what I found 2 cents

on a flat or little dihedral ship its more efficient in a straight line but requires more work in a turn to keep it from spiraling in - that said a well designed and trimmed machine will make this easier.

A machine with lots of dihedral will be more stable in a turn and will return to upright flight.

What are you looking for in your shipp??

(in reply to wildblueyawner)
       Post #: 3

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