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Leading edge failures

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jimh474(at)earthlink.net
Guest

Posted: Sun Mar 05, 2006 3:06 pm Post subject: Leading edge failures

Folks;



All this hysteria of failing leading edges, is blown way out in space.



I know of two, one I am very close to and the other I didn't know the 

individual.



Both instances, the Firestars were flown hard and put away wet too many 

times.



How many Firestars have been built and flying, thousands.



On the instance that I am close to, the cause was failure of the 5/16 

diagonal leading edge braces, failure cause, more than likely failure from 

vibration.



Once these diagonals are no longer attached, under the right conditions, the 

leading edge of the wing more than likely shifts  to outboard end of the 

wing, causing the ribs to get out of column and once this starts the leading 

edge folds back and creates an instant spoiler. The wing tip bow will not 

keep the ribs in column in the stock configuration. It doesn't make any 

difference whether it is a 5 rib or 7 rib wing. Once those diagonals go the 

leading edge is free to move at some time. Then again it may not.



The best fix is to use 1/2 .058 wall aluminum tubing to replace the 5/16 

braces. Do not flatten the attaching ends all the way, leave about an 1/8 

inch opening in the ends of the tube. Add the aluminum angle to the outboard 

rib along with replacing the bow tip tube braces with the 1/2 material and 

place a 062 aluminum web connecting the two bow supports.



All you wizards that don't believe that vibration causes fatigue better take 

a hand full of smart pills.



Jim Hauck

planecrazzzy
Guest

Posted: Sun Mar 05, 2006 4:58 pm Post subject: Re: Leading edge failures

Hi Jim,

           So let me ask this.....The leading edge that almost "touch" each other in the wing gap area.....Should there be something that connects these two together for a little added support during flight ?



    After reading your post....I think "it wouldn't hurt"



                       Gotta Fly...

                                        Mike in MN

jimh474(at)earthlink.net
Guest

Posted: Sun Mar 05, 2006 5:13 pm Post subject: Leading edge failures

That still won't solve the problem, as both leading edges would move 

together. The only fix is making sure you have diagonal bracing on each 

wing.



On 3/5/2006 7:58:53 PM, kolb-list(at)matronics.com wrote:

 	  Quote: 	
		   



 Hi Jim,

 So let me ask this.....The leading edge that almost "touch" each other in

 the wing gap area.....Should there be something that connects these two

 together for a little added support during flight ?



 After reading your post....I think "it wouldn't hurt"



 Gotta Fly...

 Mike in MN



 --------

 The more people I know....

 The more I like MY DOG

 .

 .

 .

 .

 .Do not archive





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=19780#19780

Eugene Zimmerman

Joined: 10 Jan 2006
Posts: 392

Posted: Sun Mar 05, 2006 6:37 pm Post subject: Leading edge failures

On Mar 5, 2006, at 6:03 PM, JW Hauck wrote:

 	  Quote: 	
		  

 All you wizards that don't believe that vibration causes fatigue  

 better take

 a hand full of smart pills.



 Jim Hauck


	


Jim,

Whose Kolb airframe has more high stress hours on than brother John's?

How close to catastrophic failure is his plane today?

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Sun Mar 05, 2006 7:46 pm Post subject: Re: Leading edge failures

 	  jimh474(at)earthlink.net wrote: 	
		  



The best fix is to use 1/2 .058 wall aluminum tubing to replace the 5/16 

braces. Do not flatten the attaching ends all the way, leave about an 1/8 

inch opening in the ends of the tube. Add the aluminum angle to the outboard 

rib along with replacing the bow tip tube braces with the 1/2 material and 

place a 062 aluminum web connecting the two bow supports.



All you wizards that don't believe that vibration causes fatigue better take 

a hand full of smart pills.



Jim Hauck 	




Jim is very right about this.  John Hauck recommended these modifications to me and I have all of these along with the rib streingthening on the wing of my MK-III...  One just needs to look at the design to see that this made a lot of sense.  I also read about some cases of wingtips buzzing at high speeds, its obviously an area that needed streingthening.  All this only added a couple pounds of weight  and I will not have any problems in these areas in the future.    



Michael A. Bigelow

_________________
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!

Kolb MK-III Xtra, 912-S

Eugene Zimmerman

Joined: 10 Jan 2006
Posts: 392

Posted: Sun Mar 05, 2006 9:13 pm Post subject: Leading edge failures

On Mar 5, 2006, at 8:12 PM, JW Hauck wrote:



 	  Quote: 	
		   



 That still won't solve the problem, as both leading edges would move

 together. The only fix is making sure you have diagonal bracing on  

 each

 wing.


	


Jim,

Let me run my perspective on the issue of Kolb rib failures.



I do not want to minimize the critical importance of the integrity of  

the leading edge diagonal bracing to keep the ribs in column or to  

get into an argument about what happened to John's wing, but I do  

believe there is another scenario of failure that is much more likely  

than the conclusion that the leading edge failure was initiated by  

failure of the lateral diagonal braces.



Let me point out that  properly installed and finished fabric  

covering is itself an extremely strong medium resisting lateral  

movement of the leading edge UNLESS for some reason it loses its  

tension in one dimension or another but especially in the fore and  

aft direction.



I submit that initial failure mode of the Kolb leading edge is much  

more likely due to the compromise of the curved upper rib tube under  

excessive compression load during a high speed, high wing loading  

situation. As speed increases center of lift moves forward so that  

much more of the load is carried by the front part of the rib.  An  

increased portion of the load is transferred to the spar by an  

increased compression load carried through a tube that by design   

and  of necessity is already out of column it suddenly buckles and  

breaks allowing the leading edge to move back and up into the already  

excessive high speed air flow above the wing.



Such sudden failure  would of course also destroys all diagonal  

braces pulling the leading edge sideways as they fail.



Just picture what would happen to the ribs if a wing  were loaded  

with sand bags  to 4 G all of them ahead of the spar??



In my opinion,,,,,,,,,,,,,,,,,,,, avoid excessive air speed and there  

should be no worry about Kolb rib failure.

Kirk Smith

Joined: 10 Jan 2006
Posts: 78
Location: SE Michigan

Posted: Mon Mar 06, 2006 12:21 am Post subject: Re: Leading edge failures

"Once these diagonals are no longer attached, under the right conditions, the 

leading edge of the wing more than likely shifts to outboard end of the 

wing,"

What would cause this shift?

 "causing the ribs to get out of column and once this starts the leading 

edge folds back and creates an instant spoiler. The wing tip bow will not 

keep the ribs in column in the stock configuration. It doesn't make any 

difference whether it is a 5 rib or 7 rib wing. Once those diagonals go the 

leading edge is free to move at some time. Then again it may not. 



The best fix is to use 1/2 .058 wall aluminum tubing to replace the 5/16 

braces. Do not flatten the attaching ends all the way, leave about an 1/8 

inch opening in the ends of the tube. Add the aluminum angle to the outboard 

rib along with replacing the bow tip tube braces with the 1/2 material and 

place a 062 aluminum web connecting the two bow supports. "

After removing the 5/16 braces one could test the leading edge for lateral strength. Would be interesting to see how much strength the fabric lends to lateral support of the leading edge.

ul15rhb(at)juno.com
Guest

Posted: Mon Mar 06, 2006 5:56 am Post subject: Leading edge failures

The Original Firestar had a 1.5" .028" leading edge tube with no diagonal bracing to the 5" spar except for a short 5/16" length near the root. The fabric kept the nose ribs from moving laterally. I built mine with 1.5" .035" and 3- 3/8" diagonals in the middle of the wing to the spar.



Ralph

Original Firestar

19 years flying it

-- Eugene Zimmerman <etzim62(at)earthlink.net> wrote:


On Mar 5, 2006, at 8:12 PM, JW Hauck wrote:



 	  Quote: 	
		   



 That still won't solve the problem, as both leading edges would move

 together. The only fix is making sure you have diagonal bracing on  

 each

 wing.


	


Jim,

Let me run my perspective on the issue of Kolb rib failures.



I do not want to minimize the critical importance of the integrity of  

the leading edge diagonal bracing to keep the ribs in column or to  

get into an argument about what happened to John's wing, but I do  

believe there is another scenario of failure that is much more likely  

than the conclusion that the leading edge failure was initiated by  

failure of the lateral diagonal braces.



Let me point out that  properly installed and finished fabric  

covering is itself an extremely strong medium resisting lateral  

movement of the leading edge UNLESS for some reason it loses its  

tension in one dimension or another but especially in the fore and  

aft direction.



I submit that initial failure mode of the Kolb leading edge is much  

more likely due to the compromise of the curved upper rib tube under  

excessive compression load during a high speed, high wing loading  

situation. As speed increases center of lift moves forward so that  

much more of the load is carried by the front part of the rib.  An  

increased portion of the load is transferred to the spar by an  

increased compression load carried through a tube that by design   

and  of necessity is already out of column it suddenly buckles and  

breaks allowing the leading edge to move back and up into the already  

excessive high speed air flow above the wing.



Such sudden failure  would of course also destroys all diagonal  

braces pulling the leading edge sideways as they fail.



Just picture what would happen to the ribs if a wing  were loaded  

with sand bags  to 4 G all of them ahead of the spar??



In my opinion,,,,,,,,,,,,,,,,,,,, avoid excessive air speed and there  

should be no worry about Kolb rib failure.

 

 

 

Try Juno Platinum for Free! Then, only $9.95/month!

Dave Bigelow

Joined: 29 Jan 2006
Posts: 103
Location: Kamuela, Hawaii

Posted: Tue Mar 07, 2006 1:08 am Post subject: Re: Leading edge failures

Not to beat this topic to death, but.....



Another way to stiffen up the leading edge of the wing and to keep the ribs in column is to cover from the leading edge back to the high point of the airfoil with thin fiberglass sheet or aluminum.  Rivet the thin sheet to each rib and false rib at about two inch intervals.  It adds a couple of pounds to each wing, but really stiffens up the structure.  It also eliminates the sag between ribs and makes for a cleaner airfoil.  Do the fabric over the entire wing after the leading edge covering is intalled.



I built my FS2 wing this way, and I can guarantee that the ribs and leading edge are not going have any spanwise movement.  I think this would be the most simple and structurally sound modification for a 5 rib wing.  It does involve recovering the wing.

FS with Fiberglass LE Covering.jpg

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_________________
Dave Bigelow
Kamuela, Hawaii
FS2, HKS 700E

John Jung

Joined: 10 Jan 2006
Posts: 108
Location: Surprise, AZ, USA

Posted: Tue Mar 07, 2006 6:52 am Post subject: Re: Leading edge failures

 	  Eugene Zimmerman wrote: wrote: 	
		  I submit that initial failure mode of the Kolb leading edge is much more likely due to the compromise of the curved upper rib tube under excessive compression load during a high speed, high wing loading situation. As speed increases center of lift moves forward so that much more of the load is carried by the front part of the rib.  An increased portion of the load is transferred to the spar by an increased compression load carried through a tube that by design and  of necessity is already out of column it suddenly buckles and breaks allowing the leading edge to move back and up into the already excessive high speed air flow above the wing.



Such sudden failure  would of course also destroys all diagonal braces pulling the leading edge sideways as they fail. 	




Group,



Eugene's explaination makes the most sense to me. I have been trained as a mechanical engineer and I am a Kolb flyer and builder/rebuilder.



I do not mean to alarm anyone by comenting on possible wing failures. But I also would not suggest that the risk is not higher when someone flys over the gross weights set by Kolb. I flew my original Firestar at about 600 pounds when I carried extra gas and camping gear. I accepted the extra risk on those flights. If I had to fly every flight at a gross weight  substancially higher than that, I would have sold the plane and bought a Firestar II. That's what I did, but for different reasons. Just my opinion. Everyone has there own tolerance for risk.

_________________
John Jung
Firestar II N6163J
Surprise, AZ

herbgh

Joined: 10 Jan 2006
Posts: 145

Posted: Tue Mar 07, 2006 6:54 am Post subject: Leading edge failures

Dave



   How did you keep the Glass/metal from puckering between ribs back

toward the maine spar?  Did you attach it to the spar?  I am building a

set of single lift strut wings for my Firefly and have thought about

using a leading edge d cell configuration.  I will wrap .016 2024-t3

around my wings since I already have it..  Actually thinking about

metallizing the whole wing!  Likely as cheap as fabric and the stitts

process..    Herb 



On Tue,  7 Mar 2006 01:08:09 -0800 "Dave Bigelow"

<up_country(at)hotmail.com> writes:

 	  Quote: 	
		   

 <up_country(at)hotmail.com>

 

 Not to beat this topic to death, but.....

 

 Another way to stiffen up the leading edge of the wing and to keep 

 the ribs in column is to cover from the leading edge back to the 

 high point of the airfoil with thin fiberglass sheet or aluminum.  

 Rivet the thin sheet to each rib and false rib at about two inch 

 intervals.  It adds a couple of pounds to each wing, but really 

 stiffens up the structure.  It also eliminates the sag between ribs 

 and makes for a cleaner airfoil.  Do the fabric over the entire wing 

 after the leading edge covering is intalled.

 

 I built my FS2 wing this way, and I can guarantee that the ribs and 

 leading edge are not going have any spanwise movement.  I think this 

 would be the most simple and structurally sound modification for a 5 

 rib wing.  It does involve recovering the wing.

 

 --------

 Dave Bigelow

 Kamuela, Hawaii

 FS2, Rotax 503 DCDI

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=20054#20054

 

 

 

 

 Attachments: 

 



http://forums.matronics.com//files/fs_with_fiberglass_le_covering_827.jpg
	


 	  Quote: 	
		   

 

 

 

 

 

 ============================

 

 

 

  

  

  

 

 

 

 

 


	




Its what we learn after we know everything that is the most important.

eagle1(at)commspeed.net
Guest

Posted: Tue Mar 07, 2006 8:12 am Post subject: Leading edge failures

I also built my FS II that way. I used thin roof flashing from the hardware 

store. Makes a  nice clean wing leading edge.

       AZ. Bald Eagle.



---

Eugene Zimmerman

Joined: 10 Jan 2006
Posts: 392

Posted: Tue Mar 07, 2006 9:23 am Post subject: Leading edge failures

On Mar 7, 2006, at 11:11 AM, George E. Thompson wrote:



 	  Quote: 	
		   I also built my FS II that way. I used thin roof flashing from the  

 hardware

 store. Makes a  nice clean wing leading edge.


	


Until it get a dent or two.

herbgh

Joined: 10 Jan 2006
Posts: 145

Posted: Tue Mar 07, 2006 3:17 pm Post subject: Leading edge failures

Gene

   One way to mask the dents is to overlay the aluminum with felt.  The

dent is still there but the felt maintains the normal curve.. 

    Lets see---Aluminum or Fiberglass sheet d cell and felt... By gosh I

think we have likely soothed  everyones fears..   Herb 

On Tue, 7 Mar 2006 12:22:00 -0500 Eugene Zimmerman

<etzim62(at)earthlink.net> writes:

 	  Quote: 	

 <etzim62(at)earthlink.net>

 On Mar 7, 2006, at 11:11 AM, George E. Thompson wrote:

 > I also built my FS II that way. I used thin roof flashing from the 

 > hardware

 > store. Makes a  nice clean wing leading edge.

 Until it get a dent or two.

Its what we learn after we know everything that is the most important.

Dave Bigelow

Joined: 29 Jan 2006
Posts: 103
Location: Kamuela, Hawaii

Posted: Wed Mar 08, 2006 12:50 am Post subject: Re: Leading edge failures

I used fiberglass rather than metal to avoid the dent problem.  It takes some work to smooth the fiberglass sheeting over the ribs without wrinkles.  The natural stiffness of the fiberglass prevents sagging between the ribs and false ribs.  It is not attached to the main spar and does not act as a D-tube.  It just stiffens up the leading edge structure and makes for a smooth sag free airfoil.

_________________
Dave Bigelow
Kamuela, Hawaii
FS2, HKS 700E

Kirk Smith

Joined: 10 Jan 2006
Posts: 78
Location: SE Michigan

Posted: Wed Mar 08, 2006 7:54 am Post subject: Re: Leading edge failures

"Another way to stiffen up the leading edge of the wing and to keep the ribs in column is to cover from the leading edge back to the high point of the airfoil with thin fiberglass sheet or aluminum. Rivet the thin sheet to each rib and false rib at about two inch intervals. It adds a couple of pounds to each wing, but really stiffens up the structure. It also eliminates the sag between ribs and makes for a cleaner airfoil. Do the fabric over the entire wing after the leading edge covering is intalled. 



I built my FS2 wing this way, and I can guarantee that the ribs and leading edge are not going have any spanwise movement. I think this would be the most simple and structurally sound modification for a 5 rib wing"

Have you noticed any cracks forming in the ribs where the rivets are? 



Do not archive

jbhart(at)onlyinternet.ne
Guest

Posted: Wed Mar 08, 2006 11:18 am Post subject: Leading edge failures

At 07:54 AM 3/8/06 -0800, you wrote:

 	  Quote: 	
		  



"Another way to stiffen up the leading edge of the wing and to keep the ribs in column is to cover from the leading edge back to the high point of the airfoil with thin fiberglass sheet or aluminum. 




	


Kirk, & Kolbers,



This thread has really been interesting.  To stabilize the leading edge wing 

tube, the FireFly uses one 5/16 OD 0.035 inch thick tube brace starting next 

to the most inboard rib from the nose tube back to the center line of main 

spar at about a 45 degree angle.  Two other shorter braces using the same 

size tubing attach to the upper and lower nose rib tubes of the inner most 

rib to stabilize the nose rib against the pull of the shrunk fabric.  

Addition nose rib column stabilization comes from the fabric. 



I question the need for an increase in stiffening the wing leading edge.  

Basically, where is the sideways load going to come from that will cause the 

nose ribs to be forced out of column?  During normal or abusive flight (high 

g loads), how is the leading edge tube going to forced sideways to move the 

ribs out column?  



The only way I can see a leading edge tube diagonal bracing failure is if 

the outer wing was to strike the ground or the leading edge tube struck some 

fixed object.  Then one should cut an inspection hole through the fabric 

next to the inboard nose rib to view all three braces.



If I wanted to increase nose rib strength, I believe you would get more for 

less weight by adding 1/2 by 1/2 aluminum angle to each nose rib to help 

carry rib compressive loads.



Some musings on a cold wet day.



Jack B. Hart FF004

Winchester, IN

Kirk Smith

Joined: 10 Jan 2006
Posts: 78
Location: SE Michigan

Posted: Wed Mar 08, 2006 1:52 pm Post subject: Leading edge failures

Jack?Kolbers

 	  Quote: 	
		   This thread has really been interesting.  To stabilize the leading edge

wing
	


 	  Quote: 	
		   tube,


	


I think so also Jack. The physics of how are little planes work is always

interesting.

jdm(at)wideworld.net
Guest

Posted: Wed Mar 08, 2006 1:52 pm Post subject: Leading edge failures

If you exert pressure on the leading edge until it fails it won't break the 

rib tubing. It has to bend.  Since being "in column" is not an exacting 

concept, it will fold up by swinging to one side or the other favoring the 

easiest route to go since it's not built perfect.  There are no external 

forces to push it other than the LE collapsing and "swinging out of column 

under the path of least resistance under the g force applied to it.  Adding 

cross braces will keep this from happening and under enough force the 

leading edge would just crush upward.  The question is at what point will it 

fail?  Out of column at 6 g's?  If supported crush upward at 12g's I don't 

know but I called BRS today and they e-mailed me pictures for installation 

of the canister to the root tube.  I generally fly at 1,000 AGL so I feel 

safer now with the cute.



If you want to see how this will happen if you can't visualize it, go to the 

hanger of the guy who is building one. Take three of your buddies along. 

Assuming his plane is framed out and assembled but not covered, have 

everyone line up on the leading edge with the wing achored to the ground by 

tying the spar tube to the floor so it can't move.  Now all at once push 

straight up on the leading edge as hard as you can until the leading edge 

fails.  You will see that it has to swing one way or the other.  It helps to 

have a few beers first.  Oh, don't forget to leave a note for the owner how 

his sacrifice educated you and all the readers here!



---

Eugene Zimmerman

Joined: 10 Jan 2006
Posts: 392

Posted: Wed Mar 08, 2006 4:56 pm Post subject: Leading edge failures

On Mar 8, 2006, at 4:50 PM, John Murr wrote:



 	  Quote: 	
		   I generally fly at 1,000 AGL so I feel

 safer now with the cute.


	


Why ,,,,,,,,,,,,,,,,,,, is she a terrorist or somthin?

Who is this cute yer talking about?



do not archive

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