** Kline-Fogleman (KFm) Airfoils - Building/Flying Discussion ** - Page 323 - RC Groups
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Oct 14, 2012, 12:28 PM
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Dickeroo's Avatar

Trond's KFm4 takes to the skies.

After Trond got it dialed in, his KFm4 Flying Wing performed very well.
It tracked straight and true and seemed easy to handle. Great work.

FPV49v3 KFm-4 Maiden (14 min 17 sec)
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Oct 14, 2012, 02:44 PM
What could possibly go wrong?
nickchud's Avatar

holiday project

Thanks for the advice Thomas and Dave, and all the input from other experts too.

The wing is 3 thicknesses of 3/32" balsa. Very robust indeed, IMO. I like balsa. After all this abuse it's still easy to fix. I guess the AUW is about 12oz. No scales in our holiday place here.

Ready for more fun and frolics!

Oct 14, 2012, 03:37 PM
just Some Useless Geek
Nick -- you might want to take a look at the horizontal stab size, too. The kind of spinning that your plane exhibited is due in large part to lack of stability in the horizontal plane. (The combined efforts of the vert and horz stabs are cumulative.) Try a chuckie with a suitable horizonal stab to begin with. Then just start decreasing the stab size and you'll see what I'm talking about.

I get away with really small horizontal stabs on my trapezoid trainer planes because the rear cluster is hung pretty far back and the dihedral KFm2 main wing is so inherently stable already that the planes need little stabilization to fly properly. Yer Radius has that phunky fixed width tail section and way too little stab/aileron ratio. Uh, oh.
Oct 14, 2012, 08:09 PM
What could possibly go wrong?
nickchud's Avatar
Test flight went very well this afternoon!

Geek! I know your advice is always good. This time however, I beg to differ.... Aileron travel is only 10mm up and down, while the moment for the horizontal stab is considerable. Mine is 405mm from CoG to the LE of the elevator panel. P'raps that's why it seems to be working OK.

I've never tried a gyro before and maybe this isn't the right plane for it. I have it in the aileron channel. I can see it responding correctly by rocking left and right. As soon as I set the "gain" up to even 30% it causes the servo to jitter when I go for any speed. At 60% I get jittering in the propwash as I hold the plane and throttle up. No jittering at 0% even in a power dive.

Any ideas?

Last edited by nickchud; Oct 15, 2012 at 01:52 AM. Reason: correction of the measurement
Oct 15, 2012, 03:43 AM
Registered User
davereap's Avatar
I think I will have to be careful with my radius, Thomas has much bigger fins both above and below that rear wing section, so more stability..
I have virtually no frontal side area having only a 1" spline below the wing, so I may be ok.. If not I will add on a similar fin below the rear wing section
I hope to get a flight in soon when the grass outside has dried up a bit,

servo jitters with gyros are related to the gyro gain, they get it a lot on quad copters..you can see the quad vibrating when the gyros are set too high, the solution is to reduce the gain till it stops...
Have a look at the various trimming videos on quads using the KK2 boards.. there are a few that deal with that adjustment
Last edited by davereap; Oct 15, 2012 at 03:52 AM.
Oct 15, 2012, 05:04 AM
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davereap's Avatar
Maidened the radius ...
video below....
1st section flown at 75% aileron rates second section flown at 40%.. elevator at 80%
OK Movement ...Ailerons +- 20mm right out at the pointy tips... Elevator +- 17mm again at the pointy tips
COG for the maiden at 105 mm .. measured from the front at the root of the semi circular wing..
power a 1700kv blue wonder..3 cells and a 7x3.5 prop...not bad for whizz about but lacking a bit in static thrust

COG definately nose heavy... in flight, as I reduced speed the initial elevator trim was not enough to keep the nose up, and with power off the nose just wanted to drop like mad...
However the elevator is very powerfull and gave more than enough flair in the landing, although the landing was quite fast...
I tried stalling at height but there were no problems.. I finally managed an unintentional stall at the end of the video, I think that was down to its nose heavy setup, and I hit the ground breaking a prop...
It looks like the initial COG I predicted at 125mm obtained from the small scale version is going to be more on the spot..

next time I will be moving the COG till I get a better hands off glide and I am going to change to a 1300kv blue wonder and an 8x4 prop setup
I thought at the start I was on low aileron rates.. so I landed to dial it down , but then found I was flying on my high rates
On the second section I was flying slower, you can see the nose dropping as the trim was less effective and hear me dialing in more up..
Radius model at 500mm span Maiden Flight (3 min 56 sec)
Last edited by davereap; Oct 15, 2012 at 05:25 AM.
Oct 15, 2012, 11:56 AM
What could possibly go wrong?
nickchud's Avatar

Radius or Semi Speed 500

It's a great plane Dave and a good video. I'm continuing to enjoy mine.

However, I can't explain why our CoG positions should vary so much. My maiden flight was set at 120mm and it was completely unmanageable. After a few tries and a considerable battering I came back to repair it.

Based on the Geek's remarks about a phunky tail, I think every plane deserves a cute rear end, so here is my effort to pretty it up a little. Not difficult, since my fins are inboard in line with the sides of my "fuselage". I cut a bit of a waist behind the ailerons and stuck the offcut on the tail.

Oct 15, 2012, 12:38 PM
Registered User
davereap's Avatar
Ive not determined my correct COG as yet...I had another fly, this time using the 1300kv 8x4 setup, but it was far too windy to get it finally sorted..
however I was back at about the 115 location...what I need is a good calm day...
Oct 15, 2012, 06:11 PM
Thomas B.'s Avatar
Great maiden flights and video, Dave!
Maybe the c of g locations must be different for Kfm 2 and Kfm 4 wings. On my 40 cm Kfm2 wing the cg is quite far forward and it still needs a bit of down trim to fly level.
The pictures show my 1,4 times enlarged radius which I hope to fly soon. It has a Kfm 4 wing, wingspan is 55 cm ( Radius 275 ). Control surfaces are a bit smaller.
It is my first Kfm4 wing so I am really curious about it`s flying characteristics.
Oct 16, 2012, 02:11 AM
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davereap's Avatar
I find KFm4 to be steadier and more neutral in flight..and with everything symetrical in section and the motor at a 0degrees thrust line, logically it should need some small amount of up elevator trim to get the angle of attack that enables it to fly... and depending on how nose heavy it is that 'up' will increase as you move the cog more forward..
Related to that, the more nose heavy it gets, the less effective the elevator gets..and the more up trim you need to get it flying nice and level, .. luckily the elevator is very effective on the radius, so I had no problems on the maiden flight with a fairly nose heavy setup..
The biggest problem when fying too nose heavy is that of landing speed..You cant slow the model down enough without loosing the effectivness of the elevator, so to get the flair, the speed has to be kept up higher than neccessary

When I set my COG I like a very slightly nose heavy setup, enough to make for an easy and not overly sensitive flight.. so when I go inverted it takes just a touch of down to hold it level...Thats my preference but everyone is different in how they like to fly..

The KFm2 and the other top step KF sections are all lifting wings, so likely its the lift forces from the wing that make its trim settings so different
Last edited by davereap; Oct 16, 2012 at 02:38 AM.
Oct 16, 2012, 11:24 AM
Registered User
Hi jackerbes, thanks for the info, CoG calculator was great. Test glide proved it was on only about 1/4 inch out. Clever. Cheers
Oct 16, 2012, 12:56 PM
jackerbes's Avatar
Originally Posted by Fly Boy3
Hi jackerbes, thanks for the info, CoG calculator was great. Test glide proved it was on only about 1/4 inch out. Clever. Cheers
Good to hear it worked. I use that calculator all the time. You can set if for any shape of wing and tell it the percentage you want (33% for example) and it will give you the wing area, CG location distance back from the leading edge, etc.

It is much quicker and simpler to use than many of the "real" CG location calculators.

Oct 16, 2012, 02:19 PM
What could possibly go wrong?
nickchud's Avatar

Radius success

There we are..

I'm extremely lucky to have friends and relations to visit in Laguna!

Radius Success (1 min 43 sec)

WS is 500mm and CoG is now at 100m behind the LE at root. LE of the wing to LE of the elevator panel is 500mm. Gyro is set at about 25% gain and I think it helps quite a bit in windier conditions. Tx is a Spektrum DX5, set to High rate. Span of the tailplain is 225mm and the fuse at the waist is 85mm. Fins are 55mm apart and 90mm high. She flies inverted nicely and she rolls slow or fast. If I fly slow and keep the nose up she doesn't stall, just cruises very slowly -- that could be thanks to the gyro, perhaps? Must build one with rudders when I get home.

With my 2200 kv motor and 4.7 x4.7 prop, I only get about 4 and a half minutes flying time out of my 800MaHr 3S1P batteries -- should have brought some bigger ones.

Last edited by nickchud; Oct 16, 2012 at 06:14 PM.
Oct 16, 2012, 06:24 PM
Thomas B.'s Avatar
Nick, great Model and video!
Oct 16, 2012, 06:30 PM
Thomas B.'s Avatar
Ready to go! Radius 275 weighs 400g. Hope to fly it tomorrow.

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