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Thread: aileron flutter !!!! help !!!

  1. #41

    Join Date
    Sep 2009
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    coquille oregon
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    Default Re: aileron flutter !!!! help !!!

    Mike
    I agree that re checking the weight and balance is a big must.
    My Model 2 flies and lands best when the C of G is near the rear of the envelope.
    Since I do not have a trim tab on the elevator, my Kitfox is only in hands off trim at cruise speeds.
    My stick pressure is so light I am not concerned about being out of trim at other power settings.
    When I had the Jabiru (weighed 25 pounds more than the 532 including bigger battery and cables to start it) I drilled a new hole and moved the leading edge of the horizontal stabilizer down to help trim for the added weight over the Rotax 532 even though the C of G was in the envelope but had moved forward.
    After I figured out that reflexing the Flaperons is the wrong way to trim out the added nose weight, I added 4 pounds to the tail to get the C-G moved back.
    To summarize the above from my experience flying the same Kitfox for 19 years with 3 different engines that all weighed within 25 pounds of each other.
    Do not use the flaperons or trim tabs to solve weight and balance/ trim issues; use weight.
    Let us know how it flies.
    Herman
    Last edited by herman pahls; 03-19-2014 at 10:47 PM.

  2. #42

    Default Re: aileron flutter !!!! help !!!

    Right ok Thankyou . I'll do that. If I can remember how to do it ? I seem to remember it being a nightmare last time as I didn't really know what I was doing ! I do remember it was nearer the front . Nose heavy ! Due to jab engine & fuel tank in front on instruments . Right behind bulkhead . But surely if it was within limits ? All be it at the front of the range , . The weight & balance will still be the same ? Now I'm confused about that ! On top of everything else !

  3. #43
    Dave Holl's Avatar
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    Mar 2009
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    London England
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    Default Re: aileron flutter !!!! help !!!

    Mike
    Not sure where you are located in the uk but I have some scales and could help you with the weigh. I have not weighed a kitfox but have done a number of other aircraft
    Dave
    Dave Holl
    Building Kitfox MK7
    Rotax 912ULS

  4. #44

    Default Re: aileron flutter !!!! help !!!

    Hi Dave . Thankyou for your kind offer . But im all the way down in Devon. But Thankyou anyway . I think ill be able to do it , after a lot of head scratching

  5. #45
    Senior Member SkyPirate's Avatar
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    Apr 2009
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    Edgar Springs MO
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    Default Re: aileron flutter !!!! help !!!

    Just a guess but with flaperons negative , that tells me the weight and balance is adressed aerodynamically( nose heavy), negative flaperons would take the weight out of the stick
    Chase
    Model 5 OutBack
    912 UL

  6. #46

    Default Re: aileron flutter !!!! help !!!

    Hi skypirate . Sorry for sounding dumb . But what exactly do you mean ? Can you explain that ? I'm confused as to what negative angle of attack on the flapperons will actually do/cause ? & what will happen now there in the correct (neutral) position ? Thanks
    Mike

  7. #47
    Senior Member SkyPirate's Avatar
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    Edgar Springs MO
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    Default Re: aileron flutter !!!! help !!!

    ok Mike,I will try ..if your plane, when you bought it,. the previous owner had the flaperons set to a negative AOA then 2 things happen,..1 you get less lift,..2 you get nose up (if W&B is correct),..or if W&B is not correct you get level flight but it takes more power to hold it,..so as soon as you reduce power you get sink and at a higher rate unless corrected with stick, you could be with in limits "Dry" but you mentioned you have the header tank so if W&B was at limit dry,.then most definitely it would be forward of that with header tank full,
    I would drain all fluids and remove anything from inside of plane that is not needed for safe flight,..weigh it for "dry weight" then I would fill the tanks and weigh it,.. with tanks full I would do a weight and balance without pilot..then with pilot,,then with pilot and passenger,..and it might seem backwards but then I would drain the tanks and repeat the weight and balances with and with out pilot/passenger..the reason I would do it with fuel first,..any weight you added to the plane for correct W&B with full tanks should keep the W&B with in limits with empty tanks,..if you do it with empty tanks first,..since you have a header tank your forward limit measurement if at max forward limit dry, will change with full forward tank and most likely be forward of max forward limit
    Last edited by SkyPirate; 03-20-2014 at 02:51 PM.
    Chase
    Model 5 OutBack
    912 UL

  8. #48

    Default

    Hi skypirate . Sorry for sounding dumb . But what exactly do you mean ? Can you explain that ? I'm confused as to what negative angle of attack on the flapperons will actually do/cause ? & what will happen now there in the correct (neutral) position ? Thanks
    Mike

    Thankyou skypirate . I'll try that . I guess my only concern is weather I'll have any trimming issues with the flapperons now changed ?

  9. #49
    Dave Holl's Avatar
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    Smile Re: aileron flutter !!!! help !!!

    Mike
    If I were you I would do one thing at a time.
    First ensure that the flight controls are rigged as per the specification and that any backlash is addressed.
    Ensure that the flight controls have the correct range of movement.
    Check the correct rigging of the wings including the wing washout and while you are at it check that the wing has the correct sweep not sure what it will be on your aircraft but others on here will be able to advise.
    Check the tail plane incidence and set it to datum as per the build manual.
    With all that done you should have an aircraft correctly set up aerodynamically.
    Next address the weight and balance, weigh the aircraft in its basic config with all fuel removed and all non fixed equipment removed. If you have a good weight and balance pro-forma it should be possible to calculate the various scenarios of pilot and fuel loads to ensure that the weight and balance is within limits,if not address this by adding weight as required again you can calculate this first.
    With this done you are now in a position to start test flying the aircraft thats when the fun begins but it will be worth it in the end.
    Dave Holl
    Building Kitfox MK7
    Rotax 912ULS

  10. #50

    Join Date
    Nov 2019
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    MASSY
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    29

    Default Re: aileron flutter !!!! help !!!

    Quote Originally Posted by mikegregory View Post
    hi all , i have a mk 2 kitfox , & had the fright of my life today !! i took off as normal (not flown for several months ) & was climbing out at around 300ft when all of a sudden the aircraft started to shudder badly , the port wing ( i didnt notice the starboard wing ) started to flutter as did the ailerons , very badly !!! the instrument panel also shuddered badly ! i couldnt control it , & the plane started to drop to the left ! i closed the throttle & tried to slow it down , ( the speed had creeped up to over 80mph ) the engine stopped , i thought my time was up !!! but i managed to restart the engine & gently increased power so i could nurse it back into normal flight , the flutter seemed to stop , but still seemed like it wanted to turn , i very nervously nursed it back around & landed safely , but , ive not got a clue why it happened ? ground running after showed no issues , i taxied it & checked everything , but all seems ok ?? im very reluctent to try flying again untill i have some idea of what happened ?? could it have been some kind of high speed flutter ? as i had let it creep up over 80mph on full power ? but if so , why did the instrument panel shudder also ?? could it have been engine related ?? but why does it seem to run ok after ?? any help gratefully recieved
    mike
    I found this discussion after research because I encountered exactly the same Flueter problem! I bought a Kitfox3 that was stuck more. The son of the former owner who is an instructor tells me that the plane flew in the state but he is not honest, I think. I took all the games in the flaperon control and Kitfox sent me the technical data sheet with the set of 1 to get.When I checked this week, we found a significant difference from the good In the neutral position, we have more 3 "instead of 1. Photos Below I think this may be the cause of the problem of flueter What do you think?
    Thank you for your help.

    Reglage flaperon.jpg
    Actual neutral position with 3"

    IMG_20191205_122050.jpg
    Réglage des flaperons selon les valeurs préconisés par Kitfox. Dans cette position des flaperons, le levier des volets est tirés
    de 17° donc en position neutre les flaperons se retrouvent en négatif de 17°!! (Raison du flueter???)
    ChrisFlyer

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