• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

Kline-Fogleman Modified (KFm) Airfoils

Heli-Yeah!

Gremlin on the Wing
#1
I thought a place to discuss the Kline-Fogleman modified airfoil, would be right at home here on the FT forum.

I have not been into planes very long, but already my RC addiction has given me an itch I just had to scratch.
While looking into how to scratch build an airplane, I discovered the KFm airfoils, and how they work.

I like how easily an efficient airfoil can be produced by simply folding, or building up, and stepping down the thickness to a prescribed amount. This makes model building so simple even a Monkey could Fly! :p

I did some modifications to the foil I made (see scratch link above), and I'm not sure how it will effect the lift properties, but I can't ever leave well enough alone, and had to put my "touch" in there.

So what are some of your experiences with KFm airfoils? What have you found to work well, or not so well for you. I would like to learn a lot more about them, as well as provide some good info for others just getting into, or actively building scratch planes.

460px-KFm-Family-descriptions3.jpg
step1.jpg
 

Attachments

#2
Cool - I have a KFM-4 - 4 layers of 3mm depron and 1*3mmCF for reinforcement

Alulah -style wing intended for slope...
 
Last edited:

ananas1301

Crazy flyer/crasher :D
#3
Cool - I have a KFM - 4 layers of 3mm depron and 1*3mmCF for reinforcement

Alulah -style wing intended for slope...
What do you mean with you have a KFM airfoil? Well any Plane has an airfoil (in theory)
Did you want to say that you have a KFM 4 airfoil?
 

ananas1301

Crazy flyer/crasher :D
#5
These airfoils look awesome!
They don´t only look awesome they also give you the certain response to your needs of you choose the right airfoil!
Those airfoils were developed over hundreds of years during experimenting of many scientist, which kept failing and retrying it until they got the basic shape. So it is the heritage we can make use of :)
Just to have a bit of history there :)
 

Heli-Yeah!

Gremlin on the Wing
#8
What do you mean with you have a KFM airfoil? Well any Plane has an airfoil (in theory)
Did you want to say that you have a KFM 4 airfoil?
KFm is the correct term for the airfoil itself , the number dictates which specific design you are using.
 
Last edited:

Heli-Yeah!

Gremlin on the Wing
#9
@ UndCon
I think the KFm-4 would use an odd number of layers, if it tapers down to one layer, and is symmetrical. I love the organic design of the Ahulah! Do you have any pics?
 

colorex

Rotor Riot!
Mentor
#10
I was reading the story of Mr. Kline. He found this design after doing hundreds of paper airplanes :)

It is impressive how something seemingly "unaerodynamic" can perform so well!
 
#11
I have built many planes with the KFM style wings on them. They seem to hold up well and perform well. I build most of my wings out of FFF and use the fold that comes in the FFF. If needed I will layer and sand to get the right shape I want. Also, to get a good curve on the front of the wing, cut a piece of PVC pipe in half and glue in or use the sticky back sandpaper. Works great!
 
#12
For my Depron builds I always use a KFM foil. I use KF2 for planes I want to be floaty, aerobatic and good for high alpha. I use KF4 for planes I want speed, but they still perform great high alpha moves. Currently I am building a flying wing that will have KF7 just to experiment. Also they are great for adding strength to the plane.
 
#13
I actually started with a different profile but ended up with a KFM-4ish profile.

The middle section is actually 2 layers of Depron on my wing. Might not be optimal but it seems to work.

I will build a new Alulah when I get some more CF.



@ UndCon
I think the KFm-4 would use an odd number of layers, if it tapers down to one layer, and is symmetrical. I love the organic design of the Ahulah! Do you have any pics?
 

ananas1301

Crazy flyer/crasher :D
#14
I was reading the story of Mr. Kline. He found this design after doing hundreds of paper airplanes :)

It is impressive how something seemingly "unaerodynamic" can perform so well!
Told ya! Just after experimenting it was found out! That is quite impressive!
 
#15
I have used kfm-2 on several planes and I really like the rigidity it adds, plus it makes them more stable while flying. I recently acquired a foamy version of a p-51 and I'm trying to decide if I should add a kfm-2 or kfm-4. I like the gentle flying characteristics of the kfm-2, but I believe the 4 will make it more responsive for mild aerobatic maneuvers and inverted. I've found if you cut a 45 degree bevel on the step and place it in front of the wing upside down with a piece of good duct tape, drop a line of glue in the bevel, fold it over and let it dry like that it doesn't even need a spar. the combination of the tape, glue, and compressed leading edge of the foam makes it quite rigid. As an added bonus it rounds the LE automatically.
http://www.wattflyer.com/photopost/data/500/medium/KFm_Wing_Fold_Instructions.jpg
 
Last edited:

PaulT

New member
Mentor
#16
I am scratch building a parkjet delta wing plane (old Polaris )
Does the KF design work well with delta wings?
 
Last edited:

Heli-Yeah!

Gremlin on the Wing
#19
I am scratch building a parkjet delta wing plane (old Polaris )
Does the KF design work well with delta wings?
Yes, KFm airfoils can be used anywhere a traditional airfoil would be employed.

what does the % in KF descriptions mean? like the MFm-4 says (6-9% thickness) ???????
I think it is to say 6-9% wing thickness, as compared to Chord length.

is that a small strip of foam or something else between the top and bottom pieces?????
It is simply a spacer to establish the prescribed thickness, most commonly a strip of foam is used. You could use a CF, or Wood spar to build up the step, or just create a void in the length of the wing and insert a removable spar after completing the foil.