Warning! This site requires Javascript. Learn how to enable it here.

what kf airfoil should i put on ?

Discussion in 'Scratchbuild Talk' started by Tony_Pham, Apr 21, 2010.

  1. Tony_Pham

    Tony_Pham Rookie

    Posts:
    389
    Likes:
    0
    Points:
    0
  2. I have installed four KF airfoils now and like all of them with the exception of the one I installed on my X-20. Basically the KF airfoil caused too much turbulence over the control services at slow speeds and I was unable to gain control before crashing. Without the KF things seemed fine but with it it was hard to launch without crashing. I’m planning on rebuilding my X-20 without KF airfoils. I have a feeling your delta wind plane will have similar problems.

    Mark
  3. kaptondave

    kaptondave Rookie

    Posts:
    1,012
    Likes:
    2
    Points:
    0
    Try it and see. You can just tape it on, and remove it if not satisfied, but get it flying without first.
  4. Sonicjet

    Sonicjet Rookie

    Posts:
    870
    Likes:
    3
    Points:
    0
    ...you did something wrong...did you sand the leading edge?
    Use a KFm2,always works.
  5. DJRubberCow

    DJRubberCow Cadet

    Posts:
    874
    Likes:
    0
    Points:
    16
    KF2 vs KF4

    From the way the KF's were shown by Dave, I really did not understand why anyone would want a KF2 if you can go with a KF4 because according to dave, the KF4 behaved better in about any category. And don't tell me that 1oz of weight is doing that much of a difference
  6. Sonicjet

    Sonicjet Rookie

    Posts:
    870
    Likes:
    3
    Points:
    0
    About the weight,You would be surprised.
    KFm4 does not stall as well and does not make lift until you pull back on the stick.
  7. peckair

    peckair Rookie

    Posts:
    787
    Likes:
    0
    Points:
    0
    But they're better for arobatics.:D
  8. RCPlattu

    RCPlattu Airman

    Posts:
    283
    Likes:
    28
    Points:
    28
    I think planes that are built for silly flying (3D stunts) usually (should) have symmetric airfoils. That would be KFm4.
  9. Tony_Pham

    Tony_Pham Rookie

    Posts:
    389
    Likes:
    0
    Points:
    0
    so KF 2 for slow fly and KF 4 for silly flying (3d stunts ?)
    if yet i might put kf2 on it first cause i am a noob flyer ( my cousin say i cutting grass more than cutting the air ) lol
  10. weldblast

    weldblast Rookie

    Posts:
    36
    Likes:
    0
    Points:
    0
    Hey what would happen if you put the kf3(you know the heavy lifter) on both sides of the wing like the kf4 except that it has the double step on both sides? Sorry I don't have a picture.
  11. Tony_Pham

    Tony_Pham Rookie

    Posts:
    389
    Likes:
    0
    Points:
    0
    i dunno maybe nothing happen ( heavy lift on both side ) that just a guess.
  12. RCPlattu

    RCPlattu Airman

    Posts:
    283
    Likes:
    28
    Points:
    28
    I wouldn't say KF 2 is just for slow flyers. Didn't someone say it reduced drag compared to flat foam?

    KF 3 on both sides... I thinks it's worth trying. If you have seen some of the balsa 3D planes some of them have very thick symmetric airfoils.
  13. poplharris

    poplharris Ace Pilot

    Posts:
    1,988
    Likes:
    156
    Points:
    63
    I agree with kaptondave, I love compairing how the plane flies with and without the airfoils. I tried this on my F18ezb and did notice a big difference particually at high speed. Or as high speed as one can get with this particular bird.
    thanks
    Don
  14. DJRubberCow

    DJRubberCow Cadet

    Posts:
    874
    Likes:
    0
    Points:
    16
    Well I would say as the KF3 produces considerably more drag than the KF2, two KF3s would create even MORE considerable drag than a KF4. I assume it's like flying a whiteboard flatwise :)
  15. Dredogol

    Dredogol M0DERATOR - (aka "Dred")

    Posts:
    998
    Likes:
    4
    Points:
    0
    With lift, there is drag.
    That is just a fact...

    But yes, if it is an 3D aerobatic plane, use a KF-4.
    If you use KF1, 2, or 3, the plane will have a tendency to "flip" to the side with greater lift.
  16. DJRubberCow

    DJRubberCow Cadet

    Posts:
    874
    Likes:
    0
    Points:
    16
    Which just about sums up the theory that lead to my post :)
    However I always ask myself if drag and lift always rise equally. Take the KF airfoil in comparison to the default airfoil for example. Dave once stated that the KF has considerably less drag than a default airfoil because it's "air hitting air" rather than "air hitting wing". A lift to drag x/y diagram would be nice for the different types of airfoil out there
  17. Dredogol

    Dredogol M0DERATOR - (aka "Dred")

    Posts:
    998
    Likes:
    4
    Points:
    0
    Drag and Lift are not equally proportional.
    The contour / design of the airfoil greatly affects the Lift / Drag ratio.

    The KF airfoil is pretty much based on making a negative air pressure bubble, where air glides over air... yes.

    If you want scientific data of the various KF airfoils... ask your local University to see if you can borrow / test them in their wind tunnel facilities! :lol: (good luck with that).
  18. RCPlattu

    RCPlattu Airman

    Posts:
    283
    Likes:
    28
    Points:
    28
    Yeah it's the "air bubble" that seems to be the best and worst part of the KF airfoil. Drag is lower but the bubble isn't umm... stable and solid as a normal wing surface is. This is just an semi-educated guess but I think the shape and stability of the bubble depends heavily on the air speed. Another guess: unstable bubble generates a lot of drag and a lot less lift. Third guess: there's a narrow-ish sweet spot in the air speed where the bubble is optimal and can possibly outperform a normal airfoil with an equivalent shape.
  19. Dredogol

    Dredogol M0DERATOR - (aka "Dred")

    Posts:
    998
    Likes:
    4
    Points:
    0
    Exactly, and well said Lattu! :)
Similar Threads
Forum Title Date
Scratchbuild Talk What should i do with the pecked lines or KF airfoil? Jul 21, 2012
Scratchbuild Talk Airfoil Jul 9, 2014
Scratchbuild Talk f35 v3 kf airfoil Oct 1, 2013
Scratchbuild Talk Marion Airfoils Open House Aug 24, 2013
Scratchbuild Talk KF Airfoil? Jul 12, 2013
Scratchbuild Talk Airfoil School Project-Open for Suggestions Apr 19, 2013

Share This Page

string(1) "1"