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Gull Wings - pros / cons / nasty habits?

Old 06-18-2014, 02:35 AM
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mclarkson
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Default Gull Wings - pros / cons / nasty habits?

I'm playing around with a design with a lot of polyhedral for a trainer-type slow flyer. But I keep thinking of flipping things sideways, sort of, to produce a gull wing polyhedral wing.

What I don't know is if that's a good, bad or indifferent thing. There are 'gull wing' planes out there, especially a lot of older gliders, but also the Stinson Reliant and Corsair.









I'm not talking about planes with anhedral (although the wing tips will be anhedral to the inner wings, they will still have a dihedral tilt with respect to the ground.)

I know that the various planes I've mentioned use the gull wing arrangement for various reasons (e.g. landing gear clearance) and the Corsair is actually an inverted gull wing, but is there any particular reason to not use them on a trainer / slow flyer?
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Old 06-18-2014, 02:58 AM
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Examples from some 3D 'sketches' I've been playing around with:



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Old 06-18-2014, 03:41 AM
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Wrongway-Feldman
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I've had both a corsair and a reliant and both were very stable flyers.
I can't remember where I read it but I understand a polyhedral wing is best suited in a high wing configuration. I'll try to find the page where I read it. If I remember correctly it has something to do with the pendulum of the fuselage under the wing.
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Old 06-18-2014, 04:06 AM
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That'd be great. It's my understanding that, the lower the CG is relative to the wing, the greater the dihedral effect is. That's why high-wing heavy lifters like the Antonov AN-255 have significant anhedral to prevent them becoming too roll resistant. Nonetheless, I see old free-flight models, and newer trainer types, all the time that feature a bunch of tip polyhedral, or a bunch of dihedral, with very low relative CG.



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Old 06-18-2014, 05:45 AM
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JetPlaneFlyer
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Polyhedral (like the Old Fogey or the first of your 3D sketches) is a little more efficient that conventional 'straight dihedral because it places the dihedral close to the tips where it is more effective due to having a longer lever arm to work on. This is why you see it often used on RC sailplanes.

True gull wing like the Minimoa is less efficient than conventional dihedral because the dihedral is inboard where it only has a short moment arm. Gull wing is usually used for 'non-aerodynamic' reasons, such as raising the wings up to increase ground clearance.
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Old 06-18-2014, 08:52 AM
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Or cuz it looks wicked cool!
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Old 06-22-2014, 04:31 AM
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Abuelo
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From what i've read on the Corsair, the inverted gull wing was intended to accomplish two things:

- To get the wing to fuselage angle close to 90 for reduced drag.,
- And to get the fuselage up higher for ground clearance for the prop.
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Old 06-22-2014, 04:52 AM
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Inverted gull of the Corsair was mostly for prop clearance while keeping the landing gear short. Essentially the airplane was designed around the most powerful engine available.

The way the Corsair's wing meets the fuselage creates issues with stall and spin recovery.
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