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Canard design/setup

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joyrider1
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Canard design/setup

Postby joyrider1 » Sat Jan 16, 2016 5:36 pm

From time to time the canard design/setup is mentioned as a concept for KBHF.

I am extremely skeptical that canard will work for KBHF. Because: In a typical canard setup the strut/mast would be in front of the main lift producing (here: rear) wing? If you assume that in KBHF the center of gravity is almost directly above the main (canard: rear) wing, the center of gravity would be aft of the mast/strut in a canard setup. Experience showed that the stability in yaw increases with the mast being more aft of the center of gravity?
Another DIY experiment: Try to ride a kiteboard (wave oder TT) with one or several big fins (surf fins, not the small TT style) in the nose of the board (…or just turn your wave directional board…) for a longer ride. Keep the fins in water all the time and try to go fast. As soon as the fin “catches” just a little bit to one side or the other your ride goes out of control.

Just my 02 cents, not trying to destroy anyone`s dreams about a canard KBHF. It just cannot have the strut/must in front of the main lifting wing? If someone solves this problem: Respect!!! And curious how the design would be….

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Peter_Frank
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Re: Canard design/setup

Postby Peter_Frank » Sat Jan 16, 2016 6:05 pm

I think you are absolutely right.

Without the strut (R.H, I dont care what its called, but being polite one always use the term the original poster use :D ), a Canard design could work and give you more overall lift with the same total wing area.

In normal Canard design, the yaw is a problem though, and you need an elongated fuselage behind the rear main wing, with a rudder for simple yaw stability (and maybe as a control surface).
It is more practical to use a rearward swept main wing and use winglets (or tip rudders) as they give you the lacking yaw stability, and might also give you the classic winglet efficiency advantage at a certain AOA.
And if clean winglets, then use the ailerons for turning without the rudder - simpler and works okay.

So placing a strut on top of a straight or rearswept main wing will be bad as it is forward of the desired sideways COE :(

Maybe a trick could be to use winglets/upswept tips, and have the strut go more diagonal rearwards up to the board, instead of angular as most uses ?

8) PF

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Re: Canard design/setup

Postby revhed » Sat Jan 16, 2016 7:22 pm

Peter_Frank wrote: but being polite one always use the term the original poster use
Without being antagonistic :D why not let us be respectful and polite to MR MIKE MURPHY who calls the vertical element of a hydrofoil a STRUT simply because that is the best word to call it in english, like MANY years ago!
http://www.nextfoils.com/strut-6061-t6/
http://www.nextfoils.com/
R H

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Re: Canard design/setup

Postby ronnie » Sat Jan 16, 2016 9:31 pm

Logically, when the angle of attack is increased by raising the nose of the board, you want the centre of lift to move aft.

To get that to happen with 2 positive lifting wings, would require that at higher angles of attack, the rear wing would produce proportionately more lift than the front wing.
For a 1 metre mast/strut, the centre of lift would need to move aft by about 17mm for each degree increase in the angle of attack.

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Re: Canard design/setup

Postby Bille » Mon Jan 18, 2016 6:17 pm

ronnie wrote:Logically, when the angle of attack is increased by raising the nose of the board, you want the centre of lift to move aft.

To get that to happen with 2 positive lifting wings, would require that at higher angles of attack, the rear wing would produce proportionately more lift than the front wing.
...
I think you could get that to happen , by playing with different airfoil thickness, and % cord for
the high-point, on each wing ?

The canard on the VariEze airplane, works quite well , and the plane is really fast, (200mph) ; but
the main lifting wing in the rear, requires a good bit of sweep to work. It also has rather
large vertical rudders on each wing-tip for stability.

https://www.google.com/search?q=varieze ... cQ_AUIBigB

Bille

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Re: Canard design/setup

Postby ronnie » Mon Jan 18, 2016 8:02 pm

Bille wrote:
ronnie wrote:Logically, when the angle of attack is increased by raising the nose of the board, you want the centre of lift to move aft.

To get that to happen with 2 positive lifting wings, would require that at higher angles of attack, the rear wing would produce proportionately more lift than the front wing.
...
I think you could get that to happen , by playing with different airfoil thickness, and % cord for
the high-point, on each wing ?

The canard on the VariEze airplane, works quite well , and the plane is really fast, (200mph) ; but
the main lifting wing in the rear, requires a good bit of sweep to work. It also has rather
large vertical rudders on each wing-tip for stability.

https://www.google.com/search?q=varieze ... cQ_AUIBigB

Bille
It may be possible to get +&+ aerofoil wings that do shift the lift aft when the AOA increases, but to do that may force design away from the more efficient foils.
The canard configuration +&+ does seem like it would be very difficult to get to work right for a kite foilboard and it may never be able to equal what is already available with +&- wings.

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Re: Canard design/setup

Postby DidierM » Thu Jan 21, 2016 2:47 pm

I really love those posts that discuss how KBHF works, simple design but hard to understand ! Thanks PF and others...
My 2 cents.
joyrider, since for a canard configuration the center of lift remains close to the main wing, is there an obvious reason to move the strut? Why not just keep it behind the main wing..?. Now yes there is a yaw stability issue with the added canard far ahead of the main wing...

PF, yes for a backwards elongated fuselage, but swept wings are so inefficient....They seem to have nearly disappeared in most recent designs.
Not sure that a canard can give you more overall lift since, for stability reasons , the rear wing must operate at a lower AoA than the front wing (negative decalage). So when increasing the AoA the canard may stall before the main wing can reach its max loading.

Ronnie, with varying AoA the center of lift moves because of the decalage angle between front and rear wings. This happens even with 2 positive lifting wings, so imo very similar for canard and regular KBH configurations.


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