DIY woody queestions

[knyfe]

Ok I started my DYI and based it on:
http://www.seabreeze.com.au/News/Kitesu ... 49403.aspx

Now Of course I didnt use the crazy air profile they recommended for the main foil but the Eppler 817 and tried to make the correct deflection / inflection points of the foil as good as I can manually. Now two questions:

- the plan doesnt give any details on size and shape of the rear wing at all. Should I just scale the front wing down to 30*10 cm?

- the plan states that one should mount the rear wing upside down to counteract the front wing pitching. Now that sounds fishy to me ... Whats your read?

THNX, G

[Hawaiis]

10cm x 30cm for the rear sounds about right.
I am a believer of symmetrical foil for both front and rear at 0 degree angle.
The reason is at different speed the lift produced by asymmetrical foil will be different.
If you have the front one pitching up and rear pitching down, it just pronounce the Kangaroo effect. Unless you are an experienced racer, able to control the positive lift into higher upwind angle.

[knyfe]

As far as I recall there is no plane with inverted rear wing At least thats my experience. So good, I will stick to it - both wings the same orientation.

I also plan to have two 3-2mm thick 12cm wide aluminum sheets as a mast. mount them Left /Right on the fuselage and then full width of the board (~30cm apart) on the board. Should be way more stable then a single much ticker mast as I have a force triange. Anyone tried that before?

G

... amazing how fast one progresses over one weekend. I nearly have all stuff together after a few hours...

[Peter_Frank]

As far as I recall there is no plane with inverted rear wing At least thats my experience. So good, I will stick to it - both wings the same orientation.

I also plan to have two 3-2mm thick 12cm wide aluminum sheets as a mast. mount them Left /Right on the fuselage and then full width of the board (~30cm apart) on the board. Should be way more stable then a single much ticker mast as I have a force triange. Anyone tried that before?

G

... amazing how fast one progresses over one weekend. I nearly have all stuff together after a few hours...

Dont make an asymmetrical rear stabilizer...

And IF you have made one, then you better turn it upside down, as you can not change the relative aoa to the front wing, like on planes.

IMO it does not make sense to use a symmetrical wing (front), as we never ride with zero or negative lift, thus no net advantages.

But using almost symmetrical wings makes sense sometimes, as we ride with really low lift, if going fast and not upwind

PF

[knyfe]

Oha, juuust in time. I made a lot today but didnt get to the rear stabilizer. Made the front wing, the fuselage and the mounting of both of them as well as the masts (2). The is where I cleaned the garage:

So for the rear I should stay close to symmetrical then? Ok, I certainly will follow your advice. I already printed the small version of the Eppler. So good that you stepped in!!!

One other question with respect to the mounting position of the mast relative to the back foot position: Should it be right under the rear or slightly (2 or 3inches) behind?

G

[Hawaiis]

If you stay with the twin strut design, be ready for more drag. A single strut has half the surface area, will be more efficient. I would move the front wing back to just in front of the strut.

[knyfe]

THNX for the comment. I will leave some room to shift the wing / tower attachment around as needed.

For sure I will stay with the twin design but I want to see how stable it is before I start to make them thinner. Practically I doubt that the 2X2mm will have more drag than the standard 15-25mm width single tower. I doubt that surface are is the driving factor here. But hey lets see



G

[revhed]

Ok I started my DYI and based it on:
http://www.seabreeze.com.au/News/Kitesu ... 49403.aspx

Now Of course I didnt use the crazy air profile they recommended for the main foil

- the plan states that one should mount the rear wing upside down to counteract the front wing pitching. Now that sounds fishy to me ... Whats your read?

THNX, G

The given F wing profile would work just fine, but ypur choice is better.
We always use either epp 817 or ep222 or a combination for the R wing as well , but sure a sym will work, and yes upside down!
Never even seen a sym F wing but again it will work, but how well?
They do work well for 3d helis though and needed!
As far as I can see all the factory foils use asym F wings and Almost all use asym R wings as well.
Why not haf the struts width, say 5 cm, and half the thickness, say 6mm instead of using a single strut spec for the 2?
As H said you will have twice the surface area therefore twice the surface friction, and note that airchair Many, MANY years ago gave up on the 2 V strut idea.
But maybe they did not half all the specs like I said, I thought of this as well a few years back, so go for it and let all of us know.
It would seem that a V twin strut could be made lighter, thinner and maybe MUCH stiffer in both twist and flex, as well as hydrodynamically better?
Sometimes an idea that was given up on was a good one only not fully thought out?
A thought about almost sym F wings, the t speer 105 is close and the numbers look great!
H wrote;
I am a believer of symmetrical foil for both front and rear at 0 degree angle.
The reason is at different speed the lift produced by asymmetrical foil will be different.
If you have the front one pitching up and rear pitching down, it just pronounce the Kangaroo effect. Unless you are an experienced racer, able to control the positive lift into higher upwind angle
I am sorry but I disagree with all of that!
R H

[knyfe]

finished up my little side project today ... well mostly. I want to see how it rides first before I spend more time to make it pretty. The two legged mast turned out to be really stiff. I picked a good aluminum from a lid of an "undisclosed" but expensive instrument

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after the first swimming test in the hot-tub I will add some additional floatation on top of the board - juust in case.

As I will be a novice in foiling I probably start with a front strap but none in the back so I dont kill myself on the first rides. Any other suggestions to minimize the pain?

G

[Hawaiis]

from the photo, your foil is still too far forward, it need to move back 4-6 inches, maybe you can mount the twin struts right behind the front wing, like most foils.

Helmet, impact vest and a full 3mm wetsuit will help with learning.