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Dihedral stabilizers

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Kevin Brooker
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Re: Dihedral stabilizers

Postby Kevin Brooker » Fri Nov 17, 2017 1:28 pm

Distance from the CE does matter. The same force ten time the distance has a ten fold effect. It is just a lever. Move the stab farther away and it can be smaller and have less angle of incidence which should reduce drag. The compromise is the fuse needs to be stiffer which adds weight and length adds wetted area. Winglets are usually at the tops of a plane and intended to reduce the vortex created by the fluid below the wing from mixing with the fluid above the wing. This mixing creates a vortex which is really just a parachute and slows the craft. The vortex is created by the spanwise flow of fluid over the wing. As you move closer to the tips the flow becomes more parallel to the span. The winglet "tricks" the fluid into acting like there is more span. A higher aspect ratio is more efficient in terms of induc drag to lift ratios. The cost is parasite drag and stiffness.

The mast had very little to do with yaw control. It is too close to the CE to be significantly helpful. If you take a foil and keep it horizontal and move it in the direction of the wingtip instead of the nose there is zero moment of yaw. The craft is simply skidding sideways. The mast will resist the skid but not add yaw stability. What the mast is doing is acting like a daggerboard or keel on a sailboat.

In addition to rolling (tilting) the foil away from the kite to counter its pull, the mast also helps resist this sideways pull. When the foil is rolled if the mast gains an angle of attack to the water some lift is generated which can cause the setup to move towards the wingtip. A yawning motion created by the rider or a wave which will dictate if the mast lift moves the foil towards the surface or the seabed.

In horizontal flight, yaw input by the rider will create a lift component to the mast. Because of the thin profile more drag will be produced than lift. This drag will impart a rotation to the foil ad it tries to realign itself with the flow which is yaw stability but very ineffective compared to the chord of the mast since it is usually mounted near the CE. The same width chord mounted at the stab would have a massive amount of yaw stability due to the lever by comparison and this is most likely not desirable as it might make the board difficult to turn

revhed
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Re: Dihedral stabilizers

Postby revhed » Tue Nov 21, 2017 3:01 pm

tegirinenashi wrote:
Tue Nov 14, 2017 4:25 am
Stabilizer main function is pitch stability. For that matter, yaw stability is the duty of the mast, and roll stability is responsibility of the main wing. Dihedral (or anhedral) stabilizer makes no sense whatsoever.
As for statement one, YES!
But for sure without a doubt, yaw stability is also affected by the stab, like MANY others been there done that.
And anhedral, spelled correctly, as well as dihedral also will affect stability and "loosness" of a given setup.
We have MANY years ago tested exactly the same wings and stabs flat, di, an, hedral and know that even small amounts on upswept and downswept stab wing tips WILL affect yaw AND roll stability.
Try it yourself if you are able to have exactly same surface area, cord, profile stabs flat vs up swept wing tips and down swept to feel for yourself.
Have a read and maybe learn something?
https://en.wikipedia.org/wiki/Dihedral_ ... )#Anhedral
R H

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Kamikuza
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Re: Dihedral stabilizers

Postby Kamikuza » Tue Nov 21, 2017 3:08 pm

revhed wrote:
Tue Nov 21, 2017 3:01 pm
tegirinenashi wrote:
Tue Nov 14, 2017 4:25 am
Stabilizer main function is pitch stability. For that matter, yaw stability is the duty of the mast, and roll stability is responsibility of the main wing. Dihedral (or anhedral) stabilizer makes no sense whatsoever.
As for statement one, YES!
But for sure without a doubt, yaw stability is also affected by the stab, like MANY others been there done that.
And anhedral, spelled correctly, as well as dihedral also will affect stability and "loosness" of a given setup.
We have MANY years ago tested exactly the same wings and stabs flat, di, an, hedral and know that even small amounts on upswept and downswept stab wing tips WILL affect yaw AND roll stability.
Try it yourself if you are able to have exactly same surface area, cord, profile stabs flat vs up swept wing tips and down swept to feel for yourself.
R H
OMG next thing you know, you'll be calling it a mast and I'll be calling it a strut :D


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