** Kline-Fogleman (KFm) Airfoils - Building/Flying Discussion ** - Page 369 - RC Groups
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This thread is privately moderated by jackerbes, who may elect to delete unwanted replies.
Feb 15, 2013, 02:47 PM
just Some Useless Geek
If you guys are gonna divert into AP discussions you should head over to the aerial photography forum and poke around there. Lots of talk about video gear, onboard storage vs over-the-air streaming, etc. Good stuff.
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Feb 15, 2013, 04:06 PM
Nah, ur right... ap is the mission, KFm is the tool.
I very much like the mucho steps on the last ap craft presented and would certainly consider doing that, myself.
25, 50, and 75 steps sounds ez enough and probably increase strength of the wing plenty for a slow flyer.
I won't be getting carbon fiber arrows for a wing unless there are no other options.
...although I did put out the word for broken fishing rods! lol
Feb 15, 2013, 05:24 PM
What could possibly go wrong?
nickchud's Avatar
So before we lose the AP guys, I'm interested in mission statements.

There are planes that fly like a buzzard and other planes that fly like a falcon. There are planes that fly like WWI fighters and quite different planes that fly like WWII fighters or modern jet fighters. Then we've got pylon racers and 3D aerobats. Canards, flying wings, bi-planes and tri-planes, cargo planes and seaplanes. I love the variety.

I'm interested in our thoughts about horses for courses. It seems there's a KF style for every purpose. I notice that the FPV videos come from a flying wing with a fairly high aspect ratio. Is that because it's the most stable - I would have expected something more like a classic giider for that purpose.

So, if you've designed a plane with a specific purpose, how did you arrive at the airfoil and the wing plan?

Feb 15, 2013, 09:28 PM
Registered User
conbones's Avatar
cf arrow shafts would work a treat but unless they come cheep fg driveway reflective marker rods from home depot (the thin white ones) work great, they are cheap. Or a fishing rod would be worth trying i suppose, i would try it. About the horse so to speak, i wanted to drop parachute men and i havent seen to many kfm swept wing bombers. So i went from their . i had four hextronic dt750 bl motors and a couple 30 amp eflight esc's and a 3200 4s lipo and several pairs of servos. The wing is cut from three sheets of Adams ready board. The sweep was determined by the size of the dtfb, its 30 inches each half which adds up to a total span of sixty inches. i wanted it to glide a new york mile with plenty of lift so i decided to go with a flat bottom foil and multi step kfm with a little reflex at the tips for added stability the fuse is a30 inch long three inch square dtf tube.( all of the DTFB has the paper removed and laminated with sealing or packing tape) thier is a 1"x3"x25" foam block glued inside the fuse for rigidity and it give you something to strap your bats to and makes a good base for landing gear.i am sure it will carry fpv gear no problem. i bet you can carry 4-6 2200 mah lipos, they advertize 900g of thrust on 11" prop . sorry if i was long winded, thanks for reading.
Feb 15, 2013, 10:15 PM
jackerbes's Avatar
Originally Posted by A Useless Geek
If you guys are gonna divert into AP discussions you should head over to the aerial photography forum and poke around there. Lots of talk about video gear, onboard storage vs over-the-air streaming, etc. Good stuff.
We're talking about a FPV platform with a KF airfoil. And as far as I am concerned, that is on topic enough for this forum.

Feb 16, 2013, 03:18 PM
It's difficult, Jack, to keep everyone happy in an open forum. :-)
Personally, I view it as a round-table with plenty of latitude for related anecdotes and a certain amount of levity.
Well, upon checking... this happens to be the 'build/flying discussion' and the -other- KFm thread is labeled 'advanced theory/design' which would possibly be the more appropriate place for those insistent upon Robert's Rules of Order, and such stringent guidelines for participation.

All the while, my collection of asian plastic is growing and with a bit more reading and a few more small parcels (following the China New Year celebration) I should be able to construct a small RPV model ! :-)

I like the heat-bent fff undercamber wings, yet would like the ability of more cargo, so have considered the Armin wing, and of course the KFm.

Con's multi-step KFm does offer very simple construction and decent strength without resorting to carbon fiber.

I do have a certain amount of boxwood on hand which I could pass over the tablesaw and make some lite-weight wood girders for strength in substitute for the CF. Might try that, but my tablesaw is presently buried, deep inside the bowels of my garage, and I would not want to get wood dust all over everything in there! NOT good!!!

I'm thinking a thin strip, placed against the first step of a KFm-3, held in place by the member that institutes the second step, would be sufficiently strong, and hopefully lite-weight. :-)

I must find more information on wing thickness best for lift, and aspect ratio of chord vs span for best slow speed and stability performance. because I've forgotten all the formulas and can't really rely upon TLAR any longer...

All told, Fun stuff!
Feb 16, 2013, 11:52 PM
jackerbes's Avatar
Originally Posted by rusty case
It's difficult, Jack, to keep everyone happy in an open forum. :-)
Personally, I view it as a round-table with plenty of latitude for related anecdotes and a certain amount of levity. ..<snip>...
When I read posts here I have a button next to the Quote button that no one else has. It is the Delete button. And that is because I am the moderator for the thread and can delete any or all posts if I want.

I have never once deleted any posts and have never even asked anyone to back off or watch their mouth or manners. And that includes one glider pilot guy that went out of his way to come over here, make some false accusations, and try to pick a fight with me...

This is a wonderful, well mannered forum. And A Useless Geek is entitled to his opinion. I think my reply to his post balances his request and just leaves things as they were. I read no anger into his post and hope he reads none into mine. We don't have to agree on everything.

If you want to try to get your build more "regimented" to what works, look at the percentages for thickness and step locations in the figure in the opening post. If you are anywhere near to those numbers you'll do fine and by happy. We have only had one or two guys that tried a KF build, claimed that it did not work, and went away mad. And those were guys that tinkered with the details too much and got way off the "what is know to work" track. And, generally speaking, we were glad to see them go...

I use spars from Home Depot most of the time now, pine, oak, whatever looks like it will work. And I put spars under the steps or behind the steps, or just somewhere near the mid chord and as needed to get some strength. I also move the steps a little when it seems like a good idea and that never seems to hurt anything.

If we wanted to have a "Most Challenging and Worst Flying Ever KF Wing Build Contest" here it would be tough. I would start with a piece of lineoleum flooring, use no spars, and have the step facing forward to feel like I would have a chance on winning that that one...

Last edited by jackerbes; Feb 17, 2013 at 10:30 AM.
Feb 17, 2013, 09:35 AM

I really do wish I had taken the time to develop photoshop skills, Jack... but I never did.
Flying a brick would make a neato graphic !

A linoleum tile would indeed be fun, especially with a step reversed !

I'd like to photoshop one of the new HUGE GE turbofans into the center of a common billboard. with an empenage somehow grafted to it... unsure how I might incorporate a KFm step! lol

Tnx for the advisory to go back to No. 1 in the thread. I shall.
Back to basics, as always! :-)

I am retired, and spend far too much time here at the keyboard.
Learned a lot, since I have read many threads in their entirety!
I suppose retention becomes a problem! lol an obvious problem!

Most recently I have begun reading in the micro & mini threads... Vapors and such...
then I watched a few fellows with the indoor flyers and some are doing no more than prop flying... So now I'm wondering just how slow someone can actually fly a wing.

That might be where some fun experimentation can be done with the KFm???

I must study more!
Feb 17, 2013, 06:21 PM
Standing Athwart History
roo_ster's Avatar

Finished my KFm3 36"WS flying wing:

I have built 24" WS flying wings with KFm2 and KFm4. KMm4 is by far the most "point and shoot" and aerobatic. KFm2 can be built the lightest and makes for a nice light park flyer wing.

I built a KFm3 FW for use in non-FPV aerial photography. I wanted a strong, high-lift wing with plenty of thrust to move camera gear and lipos. It does do that. The KFm3 is inherently strong and provides a thick airfoil. It doesn't like inverted flight as well as the KFm4 and this wing has an inherent bias toward staying upright. I think that a function lf the sweep and the KFm3.

Not the most aerobatic wing, but it is a steady flier and ought to provide a nice, portable platform for my gear.

[I also have a larger "hauling" plane in the works. It will have a 44"WS, wide & thick KFm3 airfoil, and pusher prop/twin boom 6-ch configuration with throttle/aileron/rudder/elevator/flaps/bomb drop . It will tote camera gear, bigger lipos, and bomb drop rather prodigious amounts of candy or whatever.]

his shows the steps pretty clearly:

Feb 18, 2013, 05:28 AM
What could possibly go wrong?
nickchud's Avatar
Thanks Roo_ster

That's useful information about the performance of KFm2, 3 and 4. Do we ever need any others?

Feb 18, 2013, 06:17 AM
Vote F5J Gracia for FPV
sgrouts's Avatar

help needed...

Hi ,
I made a 63" kfm2 wing for fpv use and I am having trouble with cg.
The full details and images are here:

If anyone could spend a few minutes to read the details, see the images and give me an advice I would highly appreciate it.
Thank you.

Feb 18, 2013, 07:42 AM
What could possibly go wrong?
nickchud's Avatar

Here's a really useful website. If you scroll about 2/3 down the page you'll see some diagrams that might help. Plus it's worthwhile reading all that stuff about stability. You'll see that it's usual to find the AC and then allow a "static margin" by putting the CG about 10% in front of that.

I think you'll find that several people on this thread would recommend moving the CG a little further back for KF type airfoils. Not too far, maybe for your model about half an inch at first. It should be perhaps 5% in front of the AC IMHO.

Good luck

Feb 18, 2013, 11:14 AM
Registered User
davereap's Avatar
After seeing goldguys recommendation for an epp indoor combat delta called the imp, I made one. but looking at it I thought it was similar enough to the ME163 to be worth a draw up more to scale and for a KF wing..so here it is below
and here is the imp thread ..
Last edited by davereap; Feb 19, 2013 at 12:43 PM.
Feb 18, 2013, 11:32 AM
Nice little plane, Dave!
Feb 18, 2013, 12:35 PM
just Some Useless Geek
Jeez Loise, you guys! Relax! I was just suggesting that you'd get better participation from the AP community if you were to discuss the AP aspects over on that forum. I'm not trying to boot anybody out of here. Oy! Take a swig off that beer, willya?!?

On the other hand, it would be nice to draw some of the AP discussion over here so that AP folks could benefit from the advantages of the KF...

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