However I do feel that a KF will work as an alternative build. Going back a while flitetest made a good video on airfoils, and the KFm3 wing is tested from about 4 minutes into the video.ĭespite their previous good results flite test has gone forward with a different type of wing construction that is well suited for paper covered foam board. The KFm2 is emulating a lifting section, as is the KFm3, KFm9 and KFm11 So a KFm4 is emulating a symetrical section, as is the KFm6 The basic step idea is that there will be a vortex produced behind each step that fills in the missing gap and lets the air flow over over the wing as though the gap was solid and profiled.
If you look at their shape and then add a line joining the top of the steps going down, or up, to the trailing edge you will see the airfoil profile they are emulating. The most used sections being KFm2, KFm3 and KFm4. Used because they are the quickest and easiest to make, and they fly well. Steps can be raised to give more height and the step effect increases proportionaly with both height and air speed. The height of the step is only determined by the thickness of your foam sheet. Note the percentage thickness refers to each sections total thickness vs the total chord of the wing, and not the height of the step.
#AIRFOIL WING FULL#
Position guide numbers can also be varied, I have a habit of leaving the aileron width out of the full chord measurement, so in effect my steps are moved forward on my wings, the step then is kept clear of the aileron hinge line , I dont want a vortex to affect my control surfaces. I personally won't go above 15% and I prefer to keep the percentage down as close to the recomended numbers as possible. The guide numbers however are open to changes, going thinner will always work, going a bit thicker will often work, go too thick and it wont work.
There are a number of KF variations , These use a combination of layers and positioning to produce a wing that can be made to emulate what are generaly considered normal wing airfoil profiles.ĭrawn up by dick Kline these give some basic guide numbers for the various combinations that have been tried. On there are long threads for both general building and scientific discussions on the topic. KF by the way stands for Kline and Foggleman who were the designers that have been credited with the basic idea,Ī KFm wing uses laminated foam sheets to make a layered, stepped wing. If you build your own models and lack the ability to hot wire cut a wing then a layered KF wing is a must build. Ive been sticking a KF wing on almost 100% of my foam models for several years now. I will say at this point that KF wings work superbly for all powered models, they offer benefits in stability, they reduce stall and give smoother flights. This article will not go into the science behind the idea, but try to give a simplistic explanation of the KF wing.
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