aileron flutter !!!! help !!!

[mikegregory]

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

[Danzer1]

Didn't you have some of these issues before? Have you completely gone through the rigging and controls to make sure everything is correct per the manufacturers specs?

Also as the engine stopped - is it possible you had a little bit of water in the fuel - as you haven't flown it for some time? If it was fuel starved - it could cause shuddering.

Also keep in mind an engine will act/run differently when running under load (in the air) than it will static (not moving on the ground).

[mikegregory]

hi danzer , thanks for your reply , no , never had any issues before , ive not long , only done less than 10 hours in it , but never had any issues at all before ! all rigging etc seemed ok , i fold the wings for hangerage , but as usual it was simply putting the wing pins in & putting the turtledeck on , i checked everything after , but cant see anything obvious , i guess water could have been an issue ?? but why would it make the wings / ailerons shudder so bad ?? thanks anyway
regards
mike

[Danzer1]

Mike,

This thread was yours: http://www.teamkitfox.com/Forums/showthread.php?t=4739 You mentioned some of that same issue today "& the plane started to drop to the left".

If the engine is running rough for any reason, the resulting vibration amplifies the further away it gets from the source and to the components that flex the most - so seeing it outboard on the wings would not be out of line.

Good Luck

[mikegregory]

danzer , thanks again , yes thats right it did used to drop a left wing , but i believe that was due to it being set up for a previous owner who flew from the right seat , i adjusted the incidence a little & now its ok ? i think ? but today it was definate flutter on the ailerons , but as you said , & now thinking about it , the instrument panel shuddered badly also , so maybe it was water ? rough running engine ? that shook the whole airframe & made the ailerons flutter so badly ???
regards
mike

[Geowitz]

If the engine shut off on it's own I would start there. Something intermittent could be going on with your ignition or fuel delivery. Engine problems can definitely create a lot of vibrations in these planes and make it look like something else. I doubt this is a flutter or rigging issue. Your previous issue was about a heavy wing/incidence and again, I doubt it has anything to do with this. I'm betting on bad ignition connections, but check fuel too.

[cubtractor]

To make sure we understand this correctly, did the shuttering stop completely when the engine quit or did it continue after the engine shut down then stopped when the airspeed slowed?

[mikegregory]

Hi cub. I can't be sure , it all happened so quick & was a bit of a blur . But I think it continued to flutter for a while after the engine stopped . It all seemed to be hard to control & settle , but maybe that was my nerves ?

[Av8r3400]

Check all flapperon bearings and the tightness of the turtleneck bearings. They all should be snug with no play.

Check the rib tails for breakage.

Check all rodend bearings throughout the control system.

[mikegregory]

Hi av8 . Thanks for your help . Can I ask how do I check all these bearings ? What exactly am I looking for. There is dome play with ailerons. But hard to determin what's acceptable & what's not ? Even my inspector just said "check everything" . But I'm not sure exactly what to check ?

Regards
Mike

[Dave Holl]

Have the flaperons got the weights fitted and are they secure? I don't believe there should be any backlash in the aileron circuit. Get someone to hold the control stick central and then see how much lost movement in each of the flaperons I don't think there should be any

[Av8r3400]

First give it the "wiggle" test. There should not be any play in the bearings on the flapperons and the turtle deck bearings should be snug to the shaft passing through them.

Loose bearings on the turtle deck of the early models 1-3 have been known to cause flapperon flutter.

Broken rib tails have also been known to induce flutter.

Both of these are common issues that can be easily overlooked.

[Av8r_Sed]

Just checking, but you do have the flaperon mass balance counterweights installed, correct?

[Dave S]

Mike,

This may help with some your flutter question; it is a link to the FAA Advisory circular for testing home built experimental aircraft. On pages 52 & 53 as marked on the bottom of the page (pages 59 and 60 of the PDF document) there is guidance on analyzing and dealing with control surface flutter.

http://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/media/ac90-89a.pdf

Not an exhaustive engineering piece by any means; but a good primer on the subject.

Sincerely,

Dave S
KF7 Trigear
912ULS Warp Drive
St Paul, MN

[jrthomas]

A friend of mine had a GSC wood 3 blade prop on a 582. One blade would slip and the pitch change would cause it to vibrate like crazy. Just a thought. Good luck. James Thomas

[mikegregory]

Thanks everyone do far . Yes there are counter weights on the flapperons & are secure . There is some play in the flapperons when the stick is held firm . Maybe this is an issue ? But if it is & I did experience flapperon flutter . Would the instrument panel shudder like it did ? . Mike

[Av8r3400]

Yes, I believe it would. The panel is not rigidly mounted and will move if the entire airframe is vibrating from a flutter.

We're you getting a vibration in the control stick, too?

You need to track down where the play in the stick is coming from. That's critical.

[mikegregory]

Hi av8 . Actually I font recall the stick shuddering at all . Which would suggest excessive playiI guess ? Maybe the engine cutting was an extra issue ? I'm not looking forward to flying it again !

[Dave Holl]

Hi
There has been some very good suggestions so far but before you fly the aircraft I think you must remove all play in the aileron circuit that probably means at least replacing all of the bolts in the pushrods and mixer circuit I would also critically inspect the rose joints and repace any that show any movement, check the rivet security on the flaperons torque tubes and ensure no movement in the removable connections.
It is possible it is engine related and if you have done the work on the flaperons circuit that would be one less thing to worry about as obviously flutter can cause an in flight break up very quickly.
I have experienced violent engine vibration and the inst panel really did shake(not on a kitfox though) and the fact that you had an engine issue is probably what caused the vibration but better safe than sorry.
Hope it goes ok
PS would be worth getting onto the mcbeens and get their views as I am sure john would give you some specific advice!

[Av8r3400]

I'd agree with Dave, now. Aileron flutter would shake the heck out of the stick. You'd remember that, I would expect.

Inspect for the play in the stick and repair that, but look to your engine for issues.

[Danzer1]

Mike,

I'd be concerned about flying it too! And you may also have more than one issue. You purchased this used and haven't provided much history information. Lets start from the beginning. I recall, you bought this about 8 months ago.

What have you inspected, adjusted, replaced, serviced since you bought it?

Did it have any issues in your pre-purchase flight/inspection?

Did the previous owner have any known issues with it?

Was he/she also the builder?

How many hours total on the aircraft? How many hours prior to your purchase?

Was the engine a new install or used from another aircraft?

Are the log books complete and has all maintenance been performed?

How long did it sit without being run or flown?

I do have a point here, but need to know the history to go into detail.

[mikegregory]

Hi . Right well . Since owning it . All I did was tweak the wing incidence a bit , as the previous owner/builder flew from the right seat . so it had a turn to the left . Apaft from that it's been fine since I owned it , all I can see is a very slight bit of play in the wing root nylon pieces . That stop the flapperons from flexing . When the stick is fixed . I can manually flex each flapperon maybe 12mm each way . The linkages seem ok . But the gap in nylon (1 bit in turtle deck each side) seems to be the cause of the flex . Any ideas ?

[mikegregory]

Just to confirm . The nylon plates ( or whatever the correct name ? ) that sandwich the main control arm of each flapperon at wing root . That is where there should be no play ? There's a tiny bit on each side of mine . Maybe that's enough to cause flutter ? I did cut a small amount away when I first bought the plane , as the flapperons would snag as I folded the wings ! Never had any flutter or violent shuddering though ? Until now !

[Av8r3400]

Those nylon pieces are what I refer to as the "Turtledeck Bearings" and they are super mission critical. I know of several instances where flexing of the flapperons from loose turtleneck bearings on early Kitfoxes (1-3) will induce aileron flutter.

12mm is nearly 1/2" which in my mind is an extreme amount of flex. These bearings should be snug to the flapperon horns not allowing any flex, while not binding the rotational motion of the horns.

You definitely need to repair this.

[Av8r3400]

The lower half of these bearings is usually mounted on a hinge or is removable in order give clearance to fold the wings.

The upper half is mounted to the turtledeck and is removed for the folding process.

[Danzer1]

Mike, I'd love to help, but to be blunt, you've only answered one question of my many. Rather than me spend a lot of time writing a book of "what ifs" it would be more effective if you'd help the cause, so we can narrow it down. You could possibly have more than one issue.

Besides the other questions, here's a couple more (and I'll probably have a few more):D:

Why did the previous owner fly it from the right side?

Was the Jab 2200 the original engine on this aircraft?

Greg

[Peteohms]

When I bought my Kitfox 3-912, the "Hatchback bearing's were worn and cracked. They were really not functional. I flew that way for probably 50 hrs with no indication of any problem. Eventually I made new ones. I noticed no difference. I have more than 650 hours flying my Kitfox. I'm not saying don't replace the bearings, just that they made no difference in my plane.

[mikegregory]

Thankyou av8 . Most appreciated . & I'll get onto that asap .
Danzer . I'm sorry but I only have a mobile phone to use internet & it's not easy to read , remember & reply to lots of questions .
The previous owner/builder sat on the right as he was used to having a throttle on the left . The only changes I made was tweak the incidence due to a left turn. & move the elevator trim from right side to left . The jab engine was not original . It started with a 582 , the plane has done 350 hours . The jab was zero houred . Dr built & installed & has now done 60 hrs . & runs very well . The plane is 20 years old , I'm 2nd owner . Log book complete & I assume aircraft maintained ? & I hadn't flown it for 4 months but have ran the engine every few weeks . :)

[Danzer1]

Mike - as I suspected! One more question and then I'll give you my thoughts.

What propeller is on it? What length? And has it ever been electronically "balanced"? Okay that's 3 questions:).

Greg

[mikegregory]

Hi Greg , right well the prop is a 1 off . The previous owner/builder had it made for him . I believe it's fairly fine pitch so he could get out a short strip easier . It's I believe 60" but don't know the pitch . & I balanced it myself recently . :) Thankyou for your help
Mike

[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.

[herman pahls]

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

[mikegregory]

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 !

[Dave Holl]

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

[mikegregory]

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:)

[SkyPirate]

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

[mikegregory]

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

[SkyPirate]

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

[mikegregory]

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 ?

[Dave Holl]

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.

[ChrisKitfox]

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.

23580
Actual neutral position with 3"

23581
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???)

[Bigshooter]

what did you end up doing to fix the issue?


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.

23580
Actual neutral position with 3"

23581
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???)

[ChrisKitfox]

what did you end up doing to fix the issue?

Hello, I solved the problem by carrying out a check of the adjustment of the angle of attack of the flaperone in neutral position. The adjustment of the machine as I had recovered it, and despite the seller's comments, was beyond all tolerances. The flaperons were nosediving at too high an angle. This generated turbulent and disruptive flows during flight between the trailing edge of the wing and the flaperons which generated the Futer phenomenon from a certain speed.

Take care to this problem!

Good flight!