When I made my Ugglan I varied the KF-spar height (KFm2) so that its height related to the wing chord (5%) along the wing. This meant the KF-spar was considerably higher at the wing root then on the wing tip. Though I haven't seen this on other deltas with KF-profile. Most seem to use the same spar height along the whole wing span.

Anyway, the Ugglan with varied KF-spar height flew very stable and I will continue to use the KFm2 in other projects as well.

On a tapered wing , not varying the spar height would make the tips "relatively Thicker" and provide more lift in that area, increasing the roll stability, decreasing the tendency to tip stall ... (wheelbarrow effect)... Besides tapering a spruce spar is a PIA on a 2 hour Foamie...

OK thx guys. Im going to rebuild with some FFF to go with the thinner idea.

gpw wrote:

"..tapering a spruce spar is a PIA on a 2 hour Foamie..."

Some builders can tolerate a higher level of pain than others. If you haven't seen any of boopidoo's work yet check out the one he mentions:

https://www.rcgroups.com/forums/show....php?t=1019466

That is probably one of the best flying and most sophisticated foamies I've seen.

Jack

Postponing the build on the plank because the airframe is way too heavy. and starting a canard with a KFm4 or KFm2 (not sure yet) wing. It will be a version of the Georgia Goose. Paper over foam fuselage, for strength, with white foam and FG Tape for the wing and canard. 48" span with BP21 and 3s power train. I'll post details when I have them here and on the Canard thread.

Will advise on progress if the new typhoon lets me get anything done.

Steve.

Hey, jackerbes, that boopidoo plane you mention looks very similar to the original XYZ, but is constructed completely differently.

It is an interesting plane and really a nice flier too. I'm used to thinking of delta looking planes as needing to be fast to have much stability but that one is not that way at all. The large roomy fuselage really makes it a nice FPV and video down link platform. The thing is like a flying truck as far as having room and cargo capacity to play around with things.

I'm sure the piloting skills have something to do with it but it really looks smooth and stable in the air.

Jack

Originally Posted by j2m2t2

Is there a difference between the folded leading edge and a KF-m step? Does the spacer make the foil? The pic below shows fold and KF, do they perform differently?

Interesting, all of my builds but one have been sans-spar. The second illustration labeled "folded LE". That is, without the "filled in step".
Using FFF @ 1/4", I have had some excellent gliders.
Do you guys think the use of a spar as spacer would offer better glide/lift?
jp

The KF step works well at a variety of step depths, but I dont think anyone has tried to quantify the depth vs the glide
We know where the steps work as %ages of the chord
We know fairly well the wing thickness %ages ...but depths v glide ??

I am one of those who uses a constant depth step all along the wing as an example ive recently used a 9mm deep step, (1/4 balsa + 3mmdepron) top and bottom. over a 6mm depron centre layer, along a KFm4 zagnutz wing..chord at tip is 220 mm chord at root is 300mm ..so each step is 4.5% at tip and 3.3% at the root..
To gesstimate the overall step depths I use the tip chord only and aim for about a 10% thickness wing..in this case it was 12% at the tips and 8.7% at the root..
If I had made that as a KFm2 it would have only had one 12mm step of 1/4 balsa + 6mm depron as a top layer..different %ages but it would work ok
Ive also tried 12mm steps on a constant 380mm chord. only two steps at 3% . and an overall 9% thickness on the wing
All my builds use balsa spars under the depron at the steps, either 3/16 or 1/4 thick, then using 3 or 6mm depron I get the step depth..this has worked well on planes 24-72" span.
All my wings are reinforced with colored packing tape at LE TE and step locations which makes for a very tough wing, despite being made from depron.
So at the step it is a tape,depron, balsa, depron,balsa depron, tape muti layered sandwich, which turns out very stiff and strong

I never worry too much about the depths since all so far have worked well. BUT I wont use a too deep step never mind the chord. A step depth of 12-15mm is the maximum I will use. I know that will work..
Steve below uses 1/2" steps for his builds.. 12.5mm

Ive even put a KFm4 section using two 12mm steps tapered down to the thickness of just the depron near the edges, both steps at 50%, onto a circular 36" Nutball with great results..thats my favorite hack, great fun

Hey guys,
I'm off and running on a canard project. We had a blackout all day so didn't get much done but here's a picture of what I have so far. Details here on the Canard thread...
https://www.rcgroups.com/forums/show...5#post13259001

Dave the new highly modded plank based on your Nifty is on hold due to serious weight problems.

I'd like to finish up the canard tomorrow if possible.

Steve.

My friend, Tony Chang (Ghostfit), just sent me a video of a ten year old boy flying a SlowStick with a KFm2 airfoil. The boy does an outstanding job of flying and landing. I thought you might like to see this video...

Corostick RC plane flown by 10yr-old (5 min 8 sec)

Steve
I wouldnt worry too much about being a bit heavy..RCfoamfighters builds are way heavier, they fly well with their KFm sections, even if they go at about 100mph tops, they still slow enough to land with no problems

If you "feel the need for speed" do check out their designs at http://rcfoamfighters.com/blog/
They use some interesting build methods with the KFm sections..This makes for a heavier AUW, and a much higher flying speed.. Some very good planes there, but they are not slow enough for my field, which gets a lot more pedestrian trafic, and needs to be kept free from complaints on safety or noise issues

"..I dont think anyone has tried to quantify the depth vs the glide..."

You're right about that.

There have been some builds where the results experienced seemed to provide some insight. The Zagnutz was the first Tony65x55 KFm build and was, of course, a KFm1 bottom step design. The Zagnutz plans show and scale out to it having a 1/4" square spar and one layer of FFF foam resting on the spar.

The PB III FFF seems to vary in thickness from about .190" to .230" from one bundle to another.

Built in FFF with a 1/4" square spar, that would put the step height on Zagnutz at .440" to .480" and the wing thickness at .630 to .690". That puts the step height at 4.4% and the wing thickness at 6.3% of the 11" chord.

As we all know now, the Zagnutz flew very well in that configuration and there was little else to compare it to. That first figure that Tony65x55 put out with the KFm1 to KFm4 airfoils mentions a 7-9% thickness range for the KFm1 but it was already evident that thinner would work.

Early in the Zagnutz thread one of the builders got the step height up to around 1/2" or so the the plane seemed to suffer for it. So at that point it was sort of decided that 3/8" or so was a good maximum for the KFm2 step height.

As I read Dave's numbers I see things that confirm the validity of the numbers that emerged from the Zagnutz but I also see that variations from them have worked well too. I also see things that contradict that "3/8" maximum step height" mentioned earlier.

This one confuses me though:

"..Ive also tried 12mm steps on a constant 380mm chord. only two steps at 3%..."

Should that be "two steps at 30%"? In a KFm4 top and bottom configuration?

I think I'll quit saying much about what does not work or the "best way" to build the different variations simply because it seems that almost everything will work for someone and in one build or another and using one material or another.

I think I'm seeing that as the material in the wing center panels gets thicker the step heights can also be higher. And that maybe there is some level of consistency in having lower steps with thinner materials.

But short of getting a wind tunnel and building test air foils in the various combinations and testing, I don't think any real clear "rules of thumb" will emerge. And it may be that the "rules of thumb" will be very wide in ranging and tolerant.

What a great venue for experimentation!

Jack

Originally Posted by jackerbes

It is an interesting plane and really a nice flier too. I'm used to thinking of delta looking planes as needing to be fast to have much stability but that one is not that way at all. The large roomy fuselage really makes it a nice FPV and video down link platform. The thing is like a flying truck as far as having room and cargo capacity to play around with things.

I'm sure the piloting skills have something to do with it but it really looks smooth and stable in the air.

Jack

Thanks!

Yes the Ugglan design flies very good but it's still a delta and if you point it the wrong way it will crash if you're at too low altitude. I experienced this a couple of weeks ago when I suffered from failsafes and crashed because I didn't keep my cool. But the error (apart from some radio error) was my own, not the design.

I'm on my way to design another UAV/FPV model but this time I'll use dihedral combined with the KFm2 which I like a lot.
https://www.rcgroups.com/forums/show....php?t=1118891

BTW, I've made some drawings of another delta with the KFm4 wing, designed by berthrsd. This one is a really fast one and rolls super fast. I've built one myself but haven't yet installed Rx. The construction is really easy but it's a rigid and sturdy construction. Try it!
https://www.rcgroups.com/forums/show....php?t=1098863

Originally Posted by jackerbes

....What a great venue for experimentation!...Jack

Well said! I wonder if my smaller steps are more conducive for the extra steps I have had success with?
jp