mrc
Just wondering, is there a KF foil upgrade for the Extra 300 - has it been tried or isn't it necessary on this particular type of model
Quote 0 0
DJRubberCow
The Extra 300 is not built for aerodynamic flying - it's a 3D plane. It only flies by motor power and control surfaces - an Airfoil would defeat its own purpose on this plane - Even the original Plane has nearly no airfoil.
Quote 0 0
kaptondave
The X-31 (on edit ; I meant Extra 300) flies on its wing just as all airplanes do. If it did not it would not be an airplane. It can sustain horizontal flight and fly patterns. A KF3 airfoil should work just fine. I have never seen an official RCP upgrade for it but it would be very easy to make one yourself. It is just a matter of cutting the right shape out of Depron and gluing it on the top surface of the wing, with the proper step at the rear. Look up Scott's KF videos on You Tube. He has one that covers all of the KF designs and also one, as I recall, on the F-22.

http://www.youtube.com/user/RCSuperPowers#p/search/7/6H-s7yuJcwk
Quote 0 0
Dredogol
He was talking about the Extra 300, not the X-31

Also, the Extra 300 should not use any KF airfoils, because there is no real performance boosts.

The KF airfoils do a LOT of benefit on Trapezoidal (diamond) and Delta shaped wings.

For the Straight / Swept-back wing designs... the KF actually makes the wings heavier, and produce very little added benefit ... just more weight.

KF-2 (top only) is good overall, and the KF-4 (top + bottom) works best for sporty planes that needs a lot of control with added KF-2 lift benefits.

KF-1 and KF-3 are special purpose airfoils. You can read up on more the KF-airfoils here:
http://www.rcpowers.com/forum/showthread.php?t=2445/

HTH
Quote 0 0
kaptondave
Sorry, I knew he was talking about the Extra 300 but my brain was not fully awake at the time I posted earlier. I agree that the KF-2 would be the better choice but not that KFs are effective only on delta wings. There are a lot of conventional-wing R/C planes flying with them, including one that I have, and it flies very well..

The OP asked if they were necessary. Obviously not, but it would be fun to try.
Quote 0 0
squishy
Kf4 would be best for the extra, so it remains a 3d plane...
"Education is not about filling buckets; it is lighting fires." W.B. Yeats

http://www.youtube.com/user/squishy654
Quote 0 0
mrc
Replies and links are greatly appreciated.
Thanks, I understand why the extra 300 doesn't need them, however I may still stick some on (KF4) with double sided tape just to see what happens. Will post the results.
Quote 0 0
rodrigo
here are a excellent article from Richard Thompson about KF airfoil, which makes a comparison with different profiles including conventional profiles

http://www.rcgroups.com/forums/attachment.php?attachmentid=1935546

For me, the KF airfoils are always welcome, you gain lift, improve slow flights, better handling even with lot of wind (+15 knot probe it in my eurofighter!!) and lot of other thinks, and also produce a stronger wing (better resistance to crash and less curvature of the wing)
for lost a bit of performance for a little extra grams and drag increased
good luck!

tx Futaba 9CAP & 8U
Quote 0 0
mrc
Excellent article, many thanks for the link - It was very useful.
Quote 0 0