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Cracking in tubing and welds?

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jindoguy(at)gmail.com
Guest

Posted: Tue Nov 06, 2007 5:56 pm Post subject: Cracking in tubing and welds?

Grant, My Mk III is serial number 43. I've had it down for quite awhile to rebuild the electrical and fuel system and do a thorough inspection. I've found three spots worth checking. 

1. If your fuel tank taps come out of the bottom of the plastic tanks, as mine did, check the rubber grommets for cracking. Mine were just about cracked through to the hole. How they didn't leak was just pure luck. Newer Mk III's have the taps on the top of the tank. Still a good idea to check the grommets. 

2. Check how the trim system is hooked up. Mine had a cable that went from the spring all the way back to the elevator bell crank and then back forward again to the cockpit bell crank. When the trim lever was pulled back it caused the return cable to go slack and bang around inside the tail boom and the connection from the pedals went through the trim spring. The current system goes from the trim spring to a tab on the fwd side of the cockpit bell crank, then separate cables go from the cockpit bell crank to the elevator bell crank. 

3. Water can gather at the low point of the cockpit right where there is a weld cluster. Mine was rusty and a pain to clean up. I used thin strips of emery cloth and put a matching strip of duct tape on the cloth side so the edges wouldn't abrade the cloth as I pulled it back and forth to get the rust off the bottom of the cluster. Otherwise a Dremel Tool with their little wire wheel took off all the rust on the top, sides and back. Work a piece of plastic between the cluster and the cloth, then space the cloth away from the cluster with something thin, I used tongue depressors, and slobber on some anti rust paint. Let dry and remove the spacers and the plastic. 

Install the aileron counter weights, really important. Someday I'll figure out how to upload that few seconds of video I have of the ailerons flapping up and down as I did a fly by of the strip.

I guess that was really four things. No cracked welds, though. 



Rick



On 11/6/07, grantr <grant_richardson25(at)yahoo.com (grant_richardson25(at)yahoo.com)> wrote:[quote] --> Kolb-List message posted by: "grantr" <grant_richardson25(at)yahoo.com (grant_richardson25(at)yahoo.com)>

 	  Quote: 	
		   My main concern for safely in our aluminum and chromoly tube structures is cracking of tubes and welds. 



 They unusually occur in those hidden areas that are hard to inspect.


	




I saw this posted under the chutes thread. Is this something to be overly concerned with?



Do motorcycles have the same issues? Ive just never heard of this in cycles. I thought metal fatigue was not that prevalent in our light non aerobatic planes. 



My plane does not have a chute and my instructors challenger does not have a chute..



I do plan on finding a used one to put on it later just in case.



Thanks,

Grant





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slyck(at)frontiernet.net
Guest

Posted: Wed Nov 07, 2007 5:44 am Post subject: Cracking in tubing and welds?

The most overlooked tube is the lift strut carry-through, -that  

single tube passing at the bottom,

beneath your sphincter musckles.  That guy connects the total lift of  

the struts and could

cause those musckles to contract considerably if it fails.



Seatbelts?  yah, I am a firm believer, and I want you motorcycle guys  

to buckle up too  



BB

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jb92563

Joined: 23 Mar 2007
Posts: 314
Location: Southern California

Posted: Wed Nov 07, 2007 1:21 pm Post subject: Re: Cracking in tubing and welds?

It was me that posted the comment about cracks and welds on the safety & chutes thread.



There are no issues that I know of, just merely pondering the hypothetical modes of failure based on what little experience I have in my Kolb Ultrastar, that would require a deployment.



I was told by others on this list when I was buying my plane, to look for corrosion in the tubes since they are not protected internally.



I was also told to look for weak looking welds that may have resulted from a home repair by a poor welder.



Cracks are more an issue with some types of aluminum parts, as I had a cracked wing rib that failed at a rivet hole on the leading edge of the wing.



It buckled due to overshrinking the fabric at the wing tip.



No need to be overly concerned, just perform good preflights and check some of those high stress areas regularly and make sure the corrosion protection is replaced in those rare areas that start to rust.

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_________________
Ray

Kolb UltraStar (Cuyuna UL-202)
Moni MotorGlider
Schreder HP-11 Glider
Grob 109 Motorglider

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John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Sat Nov 10, 2007 10:47 pm Post subject: Cracking in tubing and welds?

| Cracks are more an issue with some types of aluminum parts, as I 

had a cracked wing rib that failed at a rivet hole on the leading edge 

of the wing.

|

 |

| No need to be overly concerned, just perform good preflights and 

check some of those high stress areas regularly and make sure the 

corrosion protection is replaced in those rare areas that start to 

rust.

|

| --------

| Ray

Ray:



I believe cracks are more an issue of both aluminum and 4130 parts, 

especially fuselage welds.  The nature of a two stroke engine 

encourages stress cracks through high frequency vibration.



Personally, I would be more concerned with internal 4130 tube 

corrosion than external.  External corrosion I can see and fix. 

Internal I have no control over unless I use tube seal to prevent.



john h

mkIII

Nellis AFB, Nevada

Big air show here tomorrow and Sunday.  Happened to arrived here this 

morning and was surprised by the old War Birds that were flying in 

Nellis traffic.

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_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

jbhart(at)onlyinternet.ne
Guest

Posted: Sun Nov 11, 2007 7:33 am Post subject: Cracking in tubing and welds?

At 12:25 PM 11/9/07 -0800, you wrote:

 	  Quote: 	
		  

I believe cracks are more an issue of both aluminum and 4130 parts, 

especially fuselage welds.  The nature of a two stroke engine 

encourages stress cracks through high frequency vibration.




	


Ray,



What causes the shake of the cage is the reaction force caused by engine 

power pulse.  Since the engine is geared most of the reaction forces 

transferred to the cage are caused by the flywheel reaction of the propeller. 

 The lighter or lower inertia propeller is more easily accelerated and 

de-accelerated, therefore there is less reaction force transmitted through 

the mounts and on to the cage.



If the vibration amplitude is so low that it does not exceed the cage metal 

yield stress, vibration frequency is a non issue.  Has anyone any 

documentation that a Kolb fell out of the sky because of a cage failure?  

If you are really concerned about this go with the lowest inertia propeller 

you can find.



Jack B. Hart FF004

Winchester, IN

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Wade Lawicki

Joined: 27 May 2007
Posts: 31
Location: Nashville Tn.

Posted: Sun Nov 11, 2007 8:19 am Post subject: Re: Cracking in tubing and welds?

I believe that the weld quality from the factory welded cages has never been a concern but, where i would be concerned is the older and used Ultrastars that were welded by the builder themselves with unknown credentials. I have seen 2 that were very bad and 1 of them did end up in a fatal crash. 

  Even though most of us are very competent  and conscientious builders, the nature of our small planes attracts builders of all levels of experience , even some with none!  Being extra thorough is never a bad thing.



Fly Safe,   Wade

do not archive

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herbgh

Joined: 10 Jan 2006
Posts: 145

Posted: Sun Nov 11, 2007 9:16 am Post subject: Cracking in tubing and welds?

Jack and all



  I think an engine mount that places the lord isolators in line with the

crank shaft  center would be a great help.    Herb 

 

On Sun, 11 Nov 2007 10:42:11 -0500 "Jack B. Hart"

<jbhart(at)onlyinternet.net> writes:

 	  Quote: 	
		   

 <jbhart(at)onlyinternet.net>

 

 At 12:25 PM 11/9/07 -0800, you wrote:

 >

 <jhauck(at)elmore.rr.com>

 >

 >

 >I believe cracks are more an issue of both aluminum and 4130 parts, 

 

 >especially fuselage welds.  The nature of a two stroke engine 

 >encourages stress cracks through high frequency vibration.

 >

 

 Ray,

 

 What causes the shake of the cage is the reaction force caused by 

 engine 

 power pulse.  Since the engine is geared most of the reaction forces 

 

 transferred to the cage are caused by the flywheel reaction of the 

 propeller. 

  The lighter or lower inertia propeller is more easily accelerated 

 and 

 de-accelerated, therefore there is less reaction force transmitted 

 through 

 the mounts and on to the cage.

 

 If the vibration amplitude is so low that it does not exceed the 

 cage metal 

 yield stress, vibration frequency is a non issue.  Has anyone any 

 documentation that a Kolb fell out of the sky because of a cage 

 failure?  

 If you are really concerned about this go with the lowest inertia 

 propeller 

 you can find.

 

 Jack B. Hart FF004

 Winchester, IN

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