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Thread: Question Aerodynamic troubles during a test flight with a Kitfox3

  1. #1

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    Question Question Aerodynamic troubles during a test flight with a Kitfox3

    Hi to Everybody,

    I just acquired a Kitfox3 from 1991. The previous owner is dead, I do not have all the history of the device. I reviewed the Rotax582 which works well. This week test flight in calm conditions, 2 pers on board, after take-off, initial climb and wind cross branch without worries, during the branch wind back in level with 60Knt, departure in fluetter of the whole cell. Phenomenon strong enough that required an emergency. During this maneuver, in base and tight final, the response to the controls is uncertain with a tendency of the plane to dive on the left that it was necessary to counter strongly to compensate during all the final and the posed one. No finding of particular problem on the controls, the shutters, the control surfaces nor other elements. Unable to identify the cause, we are now investigating to solve the problem and fix it. Another clue, we found an unexplained rear centering which implied a thrust of the stick to stitch to hold the machine level ..
    I would be very enjoy to make fly good this kitfox after all the work I made on!!
    Thanks all for your help
    Good flights

    Chris
    ChrisFlyer

  2. #2

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    Default Re: Aerodynamic troubles during a test flight with a Kitfox3

    You should probably post this in the general discussion area along with photos of your airplane. Do you know which control surface was fluttering? Are the weights on the flapperons? Is there any play in the flapperon mixer? Same with the elevator.

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    Default Re: Aerodynamic troubles during a test flight with a Kitfox3

    Quote Originally Posted by CoClimber View Post
    You should probably post this in the general discussion area along with photos of your airplane. Do you know which control surface was fluttering? Are the weights on the flapperons? Is there any play in the flapperon mixer? Same with the elevator.
    Hello,
    thank you very much for your answer. I will actually put the message in the topic.
    The flutter was very strong at the cell and felt strongly in the cockpit. Not a priori in flight orders.
    The elevator was in neutral the phenomenon was amplified when we tried to slightly out.
    There was no fuel in the wings. The weights are, a priori, on the flappers. No play in the flapperon mixer but we will check again. I attach photos.
    Attachment 23344KitFoxMeaux2.jpg


    Best regards
    Attached Images Attached Images
    ChrisFlyer

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    Default Re: Question Aerodynamic troubles during a test flight with a Kitfox3

    The only time I ever had flutter in one of these planes was when the adjustable trim tab cable broke, and the tab started flopping up and down. That made the joystick jerk from front to back. What do you mean when you say the flutter was at the cell? What is the cell? Also, which way did the joystick move? JImChuk

    PS that was on my Avid Flyer MK IV. Not the same exactly as the Kitfox 3, but very similar.

  5. #5
    Senior Member Av8r_Sed's Avatar
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    Default Re: Question Aerodynamic troubles during a test flight with a Kitfox3

    I would pull out the seat pan and go through the controls carefully, comaparing against the Model III diagrams. You're looking for free play, binding, friction, reversed linkages. Originally mine had some binding and I found one of the rod ends bent and soon to fail. The goal is to get it to operate smoothly, with as little play as possible from the control stick through to the flaperons and elevator. Pay particular attention to how the flap hand interacts and make sure it can't move unless you move it. Most people install some sort of stop on the flap handle movement.
    -- Paul S
    Model III SN910
    582 IVO Med

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    Default Re: Question Aerodynamic troubles during a test flight with a Kitfox3

    Quote Originally Posted by avidflyer View Post
    The only time I ever had flutter in one of these planes was when the adjustable trim tab cable broke, and the tab started flopping up and down. That made the joystick jerk from front to back. What do you mean when you say the flutter was at the cell? What is the cell? Also, which way did the joystick move? JImChuk

    PS that was on my Avid Flyer MK IV. Not the same exactly as the Kitfox 3, but very similar.
    Hi,
    Thank you for your answer.
    In our case, no cable break, but can actually be a little play in the flappers. One of the causes of the beginning in fluttering.
    I mean cellule (all the part exept wings). But the pilot with me told me that the wings had flutted also. The joystick did not move to be effective during
    the fluttering but it was very hard to control the plane to land. Even with very experienced test pilot on the command (a friend, not me !!)
    During the landing, out of tight corner very short the aircraft had a tendency to want to dive left, it was necessary to find a compromise
    of flight with the handle very left and a weak response of the controls We also found after the flight that the joystick must be very forward on neutral position and the elevator lowered to stay level.
    So there is a problem of back centering that we do not explain.
    Best regards
    ChrisFlyer

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    Default Re: Question Aerodynamic troubles during a test flight with a Kitfox3

    Quote Originally Posted by Av8r_Sed View Post
    I would pull out the seat pan and go through the controls carefully, comaparing against the Model III diagrams. You're looking for free play, binding, friction, reversed linkages. Originally mine had some binding and I found one of the rod ends bent and soon to fail. The goal is to get it to operate smoothly, with as little play as possible from the control stick through to the flaperons and elevator. Pay particular attention to how the flap hand interacts and make sure it can't move unless you move it. Most people install some sort of stop on the flap handle movement.
    Thanks Paul for your answer and solutions,
    I do not have the pattern and diagram of model 3, can you tell me where to find them.I unfortunately did not have much information with this device.
    We will follow your advice and review the orders to achieve this minimum free play.
    An idea also on the problem of centering or balance when no element has been modified and weight displaced?

    An other question: what is approximatly the take off length with the Rotax582 on clean grass track?
    If we success to make fly this machine correctly, I would like to use it on track of 400meter (1200ft). Our take-off test seemed longer.

    Best regards,
    ChrisFlyer

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    Default Re: Question Aerodynamic troubles during a test flight with a Kitfox3

    Did you check your weight and balance? If your center of gravity is too far back, your airplane will be uncontrollable. If you are pushing the stick forward to stay level, I suspect the cg is too far back and that you are lucky to have landed.

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    Default Re: Question Aerodynamic troubles during a test flight with a Kitfox3

    Exatly! We know it and we will do it. But no change one the originale machine. Did not allow us to imagine a problem of centering.
    ChrisFlyer

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    Default Re: Question Aerodynamic troubles during a test flight with a Kitfox3

    I'm not sure if the Kitfox 3 is the same, but a Kitfox 4 has different bolt holes on the front of the horizontal stabilizer for setting the incidence on the stabilizer. I would check that out as well if you have to use a lot of forward or rear stick to stay in level flight. Here is a picture of my Kitfox 4 project horizontal stabilizer forward mounting point. JImChuk
    Attached Images Attached Images

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