KFM airfoil

[Blackbird]

I was planning on trying a kf airfoil for my upcoming scratch build.
I particularly like the kfm3 airfoil design, but I wasn't sure how to build it.
I was thinking that on a flat piece of depron (that's all I get to use) I could lay another piece, and then fold the front of the first piece of depron over the second piece but not enough to completely cover it. This is my idea of making the airfoil, but honestly, I don't know how.
Some instructions on how to build the wing would be much appreciated.
I'm using 6mm depron and I don't have access to any other material and balsa is too expensive where I live.
I was wondering if it's even possible with 6mm.

Thanks in advance!

 

[engineer]

Well, I think its pretty straight forward, and i think possible with a wide range of materials including depron.
So, KFm3 has 2 'steps', the first one is anywhere from 1/4 chord to 1/2 chord, and height of less than 10% of chord (1 inch high for a 10" chord). The second 'step' reaches from the end of the first step to 3/4 chord. Sometimes a sort of 'riser' can be used under the higher edge of the second step.

I just made my first one today, it was pretty easy.
My steps were:
1) Determine root chord (I chose 9" as my average chord, and decided to go a length of 3.25" for the first step).
2) I cut out 2 other parts of the steps, one thin strip as riser (0.5"x28") and the second step (3.25" x 28"). The .25" extra on both of the first and second steps will overlap.
3) I glued the riser strip down to my bottom surface at 3.25" from leading edge.
4) I glued the second step to the top of the riser strip and to the roughly-2/3 chord distance from the leading edge (it will be slanted down somewhat).
5) I added glue to the leading edge and top of the higher-side of the second step and sloping to the leading edge. (I used a folded leading edge, so my piece of foam was 12.25", folded at 3.25" to make the first step, and the remaining 9" were the underside)
And done!
I hope I wasn't too wordy! I've not tried these yet, but i hear they're pretty forgiving if you get even close to the design.
Good luck!

 

[Blackbird]

Thanks for the info!

 

[Aj114]

Hey all,
Im planing to build a kfm 2 airfoil with a 2m wingspan... im planning to put my aluminum spar rod just behind the 50%chord out of the wing it will snug just behind the top section trailing edge.
Will anyone know if that location will provide sufficient strength for my trainer.... will not be flying aggressively.
Do you recommend puting the spar in a different location? Somewhere simple ofcourse.
I was interested in the arma wing.... however i found the kfm2 airfoil being just as easy to do.
I'd like to hear your opinions!
Thanks

 

[leaded50]

KFm airfoils

 

[Aj114]

Great

 

[Merv]

The Kf family of airfoils are easy to build and are a huge improvement over a flat wing. None of the dimensions are critical, most of my steps are about 1/3 of the wing cord. I prefer a thicker wing, usually 10-15% of the wing cord.

 

[Piotrsko]

Built a 40" span kfm wing using my table saw and chopsaw on DTFB and @Hai-Lee plans. Bloody thing is indestructible, doesn't need a spar, took about an hour to build but for some stoopid reason prefers to fly inverted hands off.

 

[Aj114]

Built a 40" span kfm wing using my table saw and chopsaw on DTFB and @Hai-Lee plans. Bloody thing is indestructible, doesn't need a spar, took about an hour to build but for some stoopid reason prefers to fly inverted hands off.

Hahahahaha i love it!

 

[Aj114]

The Kf family of airfoils are easy to build and are a huge improvement over a flat wing. None of the dimensions are critical, most of my steps are about 1/3 of the wing cord. I prefer a thicker wing, usually 10-15% of the wing cord.

Ok
Im going to give it a go a 2m wingspan with a 30cm chord.

 

[Aj114]

Decided to stick with the 1m x 20cm wing...

 

[Aj114]

 

[Aj114]

Any ideas for control throws for maiden flight?

 

[Merv]

Great looking plane.
Start with the CG @ 25% of the wing cord & throws 15-20 degrees.

 

[Aj114]

Thanks
Will do