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Fuselage Fabric Wrinkles

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trevorkebb(at)earthlink.n
Guest

Posted: Wed Jun 07, 2006 7:40 pm Post subject: Fuselage Fabric Wrinkles

Hello Folks:



I am an  old time member of the Kitfox List from about 8 years ago; just returned to the  US and newly signed up. I need some advice.



A few days ago, after having  folded the wings on my 310-hour Model IV 1050, I noticed some subtle  longitudinal (front-to-back) wrinkles on the top fuselage fabric, in the bay  that starts about a foot in front of the vertical stabilizer. I have never seen  them before and cannot think of any reason, or abuse to the plane, that could  have caused them to appear. The wrinkles smooth out a bit when the wings are  swung out for flight. It is surely not temperature related, and no one to my  knowledge has ham-fistedly handled the plane in a way that would bend tubing. It  is always hangared and my hangar mate's plane has been off getting its annual  and some new paint for the last

2 weeks.



My initial thought was that I  had a broken weld somewhere, tempered somewhat by the knowledge that I have not  heard of this happening to any other Kitfox. I spent an hour yesterday visually  looking over, then pulling and pushing on the individual tubes inside the  fuselage that I could reach from the opening below the turtledeck and through  inspection holes, and pushing against those I could not reach with a wooden  stick. I found none loose. Then a Pitts owner and I spent about an hour trying  to torque the fuselage weldment any way we could, by the vertical and horizontal  tails, pushing down on the fuselage, by the wingtips with wings out, by the  wings when folded, etc., and we could not find any combination that would  increase or make any visually discernible difference in the wrinkles, nor were  there any abnormal airframe sounds or clicking. These crude tests don't  eliminate the possibility of a broken weld but do diminish it.



The  wrinkles are to me a rather strange anomaly -suddenly there for no apparent  reason.



Has anyone on the List come across anything similar? Any advice  on further checks I could make?



Thanks in advance.



Robert  Beck



PS Hi Ron!

smokey_bear_40220(at)yaho
Guest

Posted: Wed Jun 07, 2006 8:59 pm Post subject: Fuselage Fabric Wrinkles

Hi Robert,



I'd immediately assume the same things you did, that

there is some flexing going on there.  Usually the

fabric tension doesn't release enough under normal

flex to wrinkle.  That would create a problem on our

wings and tail surfaces!



Is that the bay with the lift handle?  Just a

thought...



Because that is a small width of fabric back there, a

smaller flex would show quicker, in my opinion.



Not sure if you tried this, but put a straight edge to

the tubing between welds on either side of the

wrinkles and see if they are drawn in.  Then push on

these tubes 1/2 way between welds and see if the

fabric shows a change.  If the fabric had been too

tight to begin with, the tubes could have curved in

and began flexing over time.



Check with another same model Fox and see how straight

they are so I don't mislead you, if they are meant to

be curved on your model.  I think they are nearly

straight between bays?



Those are the only additional raw checks I can think

of.



Kurt S.  S-5



--- W & R Beck <trevorkebb(at)earthlink.net> wrote:



 	  Quote: 	
		   Hello Folks:

 

 I am an old time member of the Kitfox List from

 about 8 years ago; just returned to the US and newly

 signed up. I need some advice.

 

 A few days ago, after having folded the wings on my

 310-hour Model IV 1050, I noticed some subtle

 longitudinal (front-to-back) wrinkles on the top

 fuselage fabric, in the bay that starts about a foot

 in front of the vertical stabilizer. I have never

 seen them before and cannot think of any reason, or

 abuse to the plane, that could have caused them to

 appear. The wrinkles smooth out a bit when the wings

 are swung out for flight. It is surely not

 temperature related, and no one to my knowledge has

 ham-fistedly handled the plane in a way that would

 bend tubing. It is always hangared and my hangar

 mate's plane has been off getting its annual and

 some new paint for the last

 2 weeks.

 

 My initial thought was that I had a broken weld

 somewhere, tempered somewhat by the knowledge that I

 have not heard of this happening to any other

 Kitfox. I spent an hour yesterday visually looking

 over, then pulling and pushing on the individual

 tubes inside the fuselage that I could reach from

 the opening below the turtledeck and through

 inspection holes, and pushing against those I could

 not reach with a wooden stick. I found none loose.

 Then a Pitts owner and I spent about an hour trying

 to torque the fuselage weldment any way we could, by

 the vertical and horizontal tails, pushing down on

 the fuselage, by the wingtips with wings out, by the

 wings when folded, etc., and we could not find any

 combination that would increase or make any visually

 discernible difference in the wrinkles, nor were

 there any abnormal airframe sounds or clicking.

 These crude tests don't eliminate the possibility of

 a broken weld but do diminish it.

 

 The wrinkles are to me a rather strange anomaly

 -suddenly there for no apparent reason.

 

 Has anyone on the List come across anything similar?

 Any advice on further checks I could make?

 

 Thanks in advance.

 

 Robert Beck


	


__________________________________________________

rliebmann(at)comcast.net
Guest

Posted: Thu Jun 08, 2006 5:53 am Post subject: Fuselage Fabric Wrinkles

Hi Robert,

  

 Send me your new e-mail address directly. I'd like  to fly to Lewis and see your Fox. I think that the wrinkle is caused  by temp & or humidity. I have seen it before.

  

 Ron

  

 DO NOT ARCHIVE

 [quote]   ---

mike
Guest

Posted: Thu Jun 08, 2006 5:58 am Post subject: Re: Fuselage Fabric Wrinkles

I had an area in the rear section behind the rudder cable exits, both sides, I didn't get excited about it and took a little hobby heat gun and run over the area until the area was smooth.  Had the same type of thing up on the tank area, did the same thing.

trevorkebb(at)earthlink.n
Guest

Posted: Thu Jun 08, 2006 1:35 pm Post subject: Fuselage Fabric Wrinkles

Kurt:



Thanks for your reply.



No, the wrinkles are in the larger bay just in front of the handle, a bit to 

the right side longeron, which is quite a long, unsupported tube. The right 

longeron shows a tad more bend than the left, both of them having had very 

slight bends after fabric shrinkage, since the plane was built. It is 

probably that right side top longeron tube. The question is, why does it 

suddenly have a bend in it?



I spent another few hours the other day checking every weld I could get to 

with either my hand, a push-stick, or a mirror and light, all the way from 

the tailwheel to the primary cockpit structure, and could come up with no 

squawks.



So today I went flying for 2 hours. No noticeable difference in trim.



It's a mystery.



Robert Beck

---

temco(at)telusplanet.net
Guest

Posted: Thu Jun 08, 2006 2:16 pm Post subject: Fuselage Fabric Wrinkles

Robert



This may be a bit of a stretch, but, have you looked at the two wooden

stringers along the side of the fuselage that runs from just back of the

doors to near the horizontal stabilizer. Perhaps one of these has warped or

broken causing the fabric ripple.



Just a thought



Ted 

Edmonton, Ab 

Subject: Re: Fuselage Fabric Wrinkles






Kurt:



Thanks for your reply.



No, the wrinkles are in the larger bay just in front of the handle, a bit to



the right side longeron, which is quite a long, unsupported tube. The right 

longeron shows a tad more bend than the left, both of them having had very 

slight bends after fabric shrinkage, since the plane was built. It is 

probably that right side top longeron tube. The question is, why does it 

suddenly have a bend in it?



I spent another few hours the other day checking every weld I could get to 

with either my hand, a push-stick, or a mirror and light, all the way from 

the tailwheel to the primary cockpit structure, and could come up with no 

squawks.



So today I went flying for 2 hours. No noticeable difference in trim.



It's a mystery.



Robert Beck

asq1(at)adelphia.net
Guest

Posted: Thu Jun 08, 2006 2:34 pm Post subject: Fuselage Fabric Wrinkles

Robert,

  Was it towed over rough terrain(or road)?  Larry



---

Ceashman(at)aol.com
Guest

Posted: Thu Jun 08, 2006 2:53 pm Post subject: Fuselage Fabric Wrinkles

>No, the wrinkles are in the larger bay just in front of the handle, a bit to 

 	  Quote: 	
		  the right side longeron, which is quite a long, unsupported tube. The right 

longeron shows a tad more bend than the left, both of them having had very 

slight bends after fabric shrinkage, since the plane was built. It is 

probably that right side top longeron tube. The question is, why does it 

suddenly have a bend in it?

 
	


Hi Robert.

 Are you sharing a hangar?

 The bend is in the top longeron tube opposite side to the ground moving handle. Could someone have tried to shove the plane with the chocks in place or the tail wheel locked and did not know what he was doing?

  

 Could something heavy have fallen on the side of the plane, any traces of surface paint damage in the area?

  

 Have you had a real heavy tail wheel first three point landing recently?

  

 I believe the fabric can expand if you place too much heat, but that is noticed at the exact moment of shrinking, incorrectly. And the direct sun could not effect it, even though the color is very dark because it would not reach the temperature of expansion.

  

 You must have been flying too close to the sun!

 Eric.

trevorkebb(at)earthlink.n
Guest

Posted: Thu Jun 08, 2006 7:25 pm Post subject: Fuselage Fabric Wrinkles

Eric:

  

 No, my hangar has been empty but for my plane for the last few  weeks as my hangar-mate's Spam Can is up at Kenosha getting an  annual. And paint on the repaired lower cowl that was damaged when he  hit a goose. I'll bet that woke him up!

  

 Since I always have my wings folded in the  hangar it is difficult to conceive of any way that the longeron could have been  bent in my absense, as the folded wings pretty much cover that area of the  fuselage, and anything falling, or any ham-handed handling of the plane, would  have shown up as damage to the wings. 

  

 I did have an off-airport landing in a freshly  planted cornfield 2 weeks back (a week before the wrinkles arrived) but  that landing was kiss-my-hand soft  -are we down yet?-  compared to  any landing I have ever done on pavement.

  

 Flying too close to the sun, Icarus,  and no wax to melt  but fabric to soften. That must be it.

  

 Robert

  	  Quote: 	
		     Hi Robert.

   Are you sharing a hangar?

   The bend is in the top longeron tube opposite side to the ground    moving handle. Could someone have tried to shove the plane with the chocks in    place or the tail wheel locked and did not know what he was doing?

    

   Could something heavy have fallen on the side of the plane, any traces of    surface paint damage in the area?

    

   Have you had a real heavy tail wheel first three point landing    recently?

    

   I believe the fabric can expand if you place too much heat, but that is    noticed at the exact moment of shrinking, incorrectly. And the direct sun    could not effect it, even though the color is very dark because it would not    reach the temperature of expansion.

    

   You must have been flying too close to the sun!

   Eric.

smokey_bear_40220(at)yaho
Guest

Posted: Thu Jun 08, 2006 9:47 pm Post subject: Fuselage Fabric Wrinkles

OK Robert,



Maybe one of our engineers can address this better. 

I'm getting old.... 



I think you should make sure that the tubes are not

bent more than half their diameter out of being

straight between welds.  That is my rule of thumb

without the math behind it.  Straight is much better. 

1/2 is the limit and not even nice.



Called "long column bending", a tube really gets weak

in compression if it is not straight.  An upper tube

is usually in tension in flight, but compression on

the ground.  That means it bent more than normal on

the ground because tension in flight would straighten

it.  Only ground contact, inverted flight, or force

bends a top tube.  (I think.  Maybe a side load on the

tail might do it too.)



Folding your wings contributes to this because it

moves more weight to the tailwheel.



If your fabric tension is too high and a tube is bent

to begin with, it takes less compression to bend it

more.



Very hard to bend a straight tube, but it weakens

rapidly if bent past a certain point.  If I remember,

1/2 the diameter is about it before it bends real

easily.  Maybe less.



I added 2 cross braces to my Fox in the bay just

behind the baggage area because I didn't like the

bending there after covering.  I kept mine under 1/8th

inch off straight.  Just a precaution for me.  You

might look at doing the same.  The braces have to be

mounted so that they will not come lose and poke the

fabric when stressed, so take care for that.



Any engineer comments would be appreciated.



Kurt S.



--- W & R Beck <trevorkebb(at)earthlink.net> wrote:



 	  Quote: 	
		   Kurt:

 

 Thanks for your reply.

 

 No, the wrinkles are in the larger bay just in front

 of the handle, a bit to 

 the right side longeron, which is quite a long,

 unsupported tube. The right 

 longeron shows a tad more bend than the left, both

 of them having had very 

 slight bends after fabric shrinkage, since the plane

 was built. It is 

 probably that right side top longeron tube. The

 question is, why does it suddenly have a bend in it?

 

 I spent another few hours the other day checking

 every weld I could get to 

 with either my hand, a push-stick, or a mirror and

 light, all the way from 

 the tailwheel to the primary cockpit structure, and

 could come up with no squawks.

 

 So today I went flying for 2 hours. No noticeable

 difference in trim.

 

 It's a mystery.

 

 Robert Beck


	


__________________________________________________

trevorkebb(at)earthlink.n
Guest

Posted: Fri Jun 09, 2006 5:36 pm Post subject: Fuselage Fabric Wrinkles

Larry, Ted, and Kurt:



No, it hasn't been towed, and the wood stringers are fine all around.



Kurt, I appreciate your insights on tubing. I suppose at some point I will 

cut a hole in the bottom fuselage fabric (Horrors! It's virgin!) and put in 

a couple lightweight crossbraces in to take the bit of sag out of those top 

longerons.



Thanks again, folks.



Robert

 	  Quote: 	
		   



 Robert,

  Was it towed over rough terrain(or road)?  Larry


	


This may be a bit of a stretch, but, have you looked at the two wooden

stringers along the side of the fuselage that runs from just back of the

doors to near the horizontal stabilizer. Perhaps one of these has warped or

broken causing the fabric ripple.



Just a thought



Ted

Edmonton, Ab

janderson412(at)hotmail.c
Guest

Posted: Fri Jun 09, 2006 11:37 pm Post subject: Fuselage Fabric Wrinkles

For future builders I built in a hatch cover behind the turtle deck so I could get into the rear fuse to keep a good eye. To large a are not to be able to check over the life of the fabric....John A.

 

 [quote]   

From:  "W & R Beck" <trevorkebb(at)earthlink.net>

Reply-To:  kitfox-list(at)matronics.com

To:  <kitfox-list(at)matronics.com>

Subject:  Re: Fuselage Fabric Wrinkles

Date:  Fri, 9 Jun 2006 19:47:13 -0500

--> Kitfox-List message posted by: "W & R Beck" <trevorkebb(at)earthlink.net>



Larry, Ted, and Kurt:



No, it hasn't been towed, and the wood stringers are fine all around.



Kurt, I appreciate your insights on tubing. I suppose at some point I will cut a hole in the bottom fuselage fabric (Horrors! It's virgin!) and put in a couple lightweight crossbraces in to take the bit of sag out of those top longerons.



Thanks again, folks.



Robert

[quote]--> Kitfox-List message posted by: "Larry Huntley"

janderson412(at)hotmail.c
Guest

Posted: Fri Jun 09, 2006 11:45 pm Post subject: Fuselage Fabric Wrinkles

 	  Quote: 	
		     

For future builders I built in a hatch cover behind the turtle deck so I could get into the rear fuse to keep a good eye. To large an area not to be able to check over the life of the fabric....John A.

 

  	  Quote: 	
		     

From:  "W & R Beck" <trevorkebb(at)earthlink.net>

Reply-To:  kitfox-list(at)matronics.com

To:  <kitfox-list(at)matronics.com>

Subject:  Re: Fuselage Fabric Wrinkles

Date:  Fri, 9 Jun 2006 19:47:13 -0500

--> Kitfox-List message posted by: "W & R Beck" <trevorkebb(at)earthlink.net>



Larry, Ted, and Kurt:



No, it hasn't been towed, and the wood stringers are fine all around.



Kurt, I appreciate your insights on tubing. I suppose at some point I will cut a hole in the bottom fuselage fabric (Horrors! It's virgin!) and put in a couple lightweight crossbraces in to take the bit of sag out of those top longerons.



Thanks again, folks.



Robert

 	  Quote: 	
		  --> Kitfox-List message posted by: "Larry Huntley"  

	

	


	


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