Kline-Fogleman Modified (KFm) Airfoils

[Rocketdork]

KFm is the correct term for the airfoil itself , the number dictates which specific design you are using.

KFm airfoils exploit a vortex that forms in the stepped areas of the foil, creating a frictionless cushion the air can travel over more easily.

Definitely not friction-less, at least at the temperatures we fly, zero friction is not achievable. Google superfluid to find how zero friction can be achieved.

The step induces a low pressure area behind it, the low pressure induces a vortex as the air tries to fill it, the vortex will induce drag. However, the vortex will be stable and as a result, act as a sort of a wing surface. KFm Airfoils tend to be high drag, but at the same time, generate a decent amount of lift at low Reynolds numbers. Additionally, they are very easy to build and are very tolerant of errors in their shape.

Traditional airfoils sometimes use "turbulators" to ensure that the laminar flow detaches at a controlled point (and speed) and is stable. This allows for predictable characteristics. The KFm airfoil seems to take this principal to a logical extreme. I'm reminded of a rocket nozzle called an "aerospike". In a sense, it seems to operate on the same principle, while being completely different.

 

[Heli-Yeah!]

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.

@ Rocketdork

Thank you for pointing that out. I have omited it from my earlier response, so that it will not mislead others looking for useful information.

The Aerospike looks very interesting! Let's scale one down, strap it to a foamy, and blast it off into "never".