aileron flutter !!!! help !!!

[herman pahls]

Hello Mike
I believe I have shared this info. before on this forum.
This may not be your issue but it is easy to check with 4 foot long sticks clamped to the bottom of your flapperons as outlined in the model 2 manual.
As has already been mentioned, check your flapperon rigging at the position that you cruise at.
I also have a Model 2 Kitfox that I have been flying for 19 years.
The first 14 years with a Rotax 532 and then I tried a Jabiru 2200.
Since my Model 2 did not come with an elevator trim tab, I trimmed for cruise using minor adjustments of the flapperons.
With the added 20-25 pounds weight of the Jabiru the CG was still in range but now more forward.
I compensated the nose down tendency with trimming the fapperons for hands off flight in cruise as I always had with the 532.
I just did not realize how much I had reflexed them for hands off flight.
The old Kitfox kits did not make provisions for flap lever positions like the newer kits do.
What used to be a fun airplane to fly became almost miserable to fly.
The ailerons became very heavy, one wing became heavy, the stall speed increased and coordinated flight was difficult.
Then I experienced scary flapperon flutter in turbulence and grounded the airplane.
I asked the same questions you have and was given the same advice which is all very good and I followed.
Then a Kitfox owner in Idaho asked whether or not my flapperons were reflexed.
I went back to the manual and found that my flapperons at cruise were refexed way out of specs.
I have since made a mark where the flap handle should be when the flapperons are rigged properly.
The airplanes former good flight characteristics immediately returned except I needed to add weight to the tail to trim the airplane (or a trim tab).
I have not had flutter since but admit I get nervous every time I get into turbulence.
It is embarrassing to admit that I fought this problem for almost 2 years before the flutter incident grounded me and I did not make the simple connection between flap handle position and bad flight characteristics.
I thank this forum for my solution and hope you find the same so you can enjoy your Kitfox.
Herman

[mikegregory]

Hi Herman . Thankyou for your help & advice . I really find that interesting . Can you please explain exactly how to check the flapperons ? & what position they should be ? & as for the flaps ? I was told never to use them ? But am even unsure of the actual off position for my plane ? Mine seems very heavy in roll . I thought this was normal ? Now im thinking maybe it's not ?? Thankyou again

Mike

[Dave Holl]

Can you explain what you mean by reflex is it negative angle of attack? Ie flaperons TE up from neutral position?

[PapuaPilot]

Dave,

That is correct. If the ailerons are reflexed it means the trailing edge is up and the ailerons are at a negative angle of attack.

[herman pahls]

Mike
Reflex is as described in post #33 and #34.
Did the Model 2 build instructions come with your Kitfox?
Adjusting the incidence of the flaperons is described in the Covering and Finish section under Rigging, page CF-18.
I would post the page but have no idea how to at my computer skill level.
The process of setting the "Flaperon Neutral Position Rigging Details" is quite simple.
Assuming you have the flat bottom Flaperons like my Model 2 came with, lightly clamp a light weight wooden dowel to the bottom of each flaperon, positioning the dowels at 90 degrees to the flaperons and just outboard of the lift strut attach brackets.
This location is used due to the twist in the wing.
Before moving your flap handle from your normal flying position, measure how far the top of the dowels are from the bottom of the front wing spar.
Then move the flap handle so that there is 1 inch from the bottom of the front wing spar to the top of the wooden dowel.
Fabricate a stop so the flap handle can not go further down and allow the flaperons to start reflexing.
I can take photos for you on my I Phone and email to you or better yet, if some one could teach me how to get photos from my phone to this thread.
If you find that you have been flying with significantly more than the 1", you may have found your problem as I did.
I would test using a long runway a few feet off the ground.
If I can be of further help let me know.
Let us know what you find out.
Herman

[mikegregory]

Hi Herman . Thankyou . Yes I understand that & I'll ho & check that . Many thanks . Most appreciated
Mike

[mikegregory]

right well !! i checked the flapperon reflex position , & i found out , that i have been flying it way out !!! i thought i had it in the neutrol position ? (no flap) but when i checked it , with straight edges , under the flapperons , instead of getting a gap of 1 " at the leading edge spar , it was more like 7 " !!! so i had been flying with negative angle of attack !! , what efect would this have ??? & would it have caused my original flutter problem ?? or at contributed to it ??
mike

[herman pahls]

Mike
The answer is yes and yes, 7 inches is a lot of reflex and it most likely caused the flutter and a very poor handling Kitfox if your excessive reflex had the same negative impact as it had on my Model 2.
With the stick centered left to right, set the flap handle so you have 1" between the dowels and the spar and make a positive stop so the flap lever will cannot be moved further down.
I expect you to have a totally better handling Kitfox.
You will probably have to reset the wing incidence and add weight to the tail or a trim tab on the elevator since reflexing the flaperons trims the airplane nose up.
Take out the reflex and the nose will be heavy.
Herman

[mikegregory]

Thanks hermon . It's almost a relief to find something . & I'm almost eager to get in it & try it out . I have a trim tab fitted . & at this time level flight is at neutral trim . Landing is full up trim . So I'm a little concerned that I'll run out of up trim now I've taken out reflex ??

[jrevens]

Thanks hermon . It's almost a relief to find something . & I'm almost eager to get in it & try it out . I have a trim tab fitted . & at this time level flight is at neutral trim . Landing is full up trim . So I'm a little concerned that I'll run out of up trim now I've taken out reflex ??

Double check your weight & balance.