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Tail Wire Tangs Breaking And other Tail Brace Issue Contin

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Possums

Joined: 03 Nov 2007
Posts: 247

Posted: Thu Sep 03, 2009 8:21 pm Post subject: Tail Wire Tangs Breaking And other Tail Brace Issue Contin

At 11:15 PM 9/3/2009, you wrote:

 	  Quote: 	
		  



Given the recent very close call by one of our fellow Kolb flyers, 

this issue needs to be brought to everyones attention.-snip-



In professional aviation and the airlines, the absence of accidents 

does not mean that there is not a large danger.   Reports of 

problems, and many near accidents is regarded as an accident waiting 

to happen, and these problems are fixed before people get 

killed.  We have a pattern like this developing with our Kolb Tail wires.


	




I would defer to Dennis as the ultimate authority on any of the 

changes the we "think" might improve the original structural design.

If you change/strengthen  one thing - you weaken another. You just 

move the problem to another area. I only know

of one person who was willing to tear the wings off of a Kolb in 

flight - on purpose (not with sandbags on the ground) and

trust a chute to carry him down. This was done to find the weak link 

in the design. The "weak link" was fixed years ago and

by weak - I mean more G's than you might ever do..

Most of the stuff I have done is cosmetic or just for looks/comfort.

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Possum

flykolb(at)pa.net
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Posted: Fri Sep 04, 2009 4:25 am Post subject: Tail Wire Tangs Breaking And other Tail Brace Issue Contin

Everyone,



I really hope, for all your sakes, that I am not the ultimate authority on

this as I have been out of the loop on this stuff for about 10 years - but I

can perhaps add a little bit of perspective.  The information exchange here

is awesome and I have learned something I did not know and that was the

breaking of the 4-hole tangs on the Rans.  



But, the fact is that adding a turnbuckle does change the dynamics in

several ways (changes are seldom made without consequences), so if you are

going to make a change, realize that your airplane just became MORE

experimental.  The turnbuckles do present a real hazard when folding in the

potential to overstress the tang.  Plus it makes it very easy to

over-tension the wires which places further stress on the tangs.  



I think we are all concerned with safety, but too many times we get too

micro-focused with the safety issues that we can see - not the ones we can't

see.  Homer and I both shared a conviction that having turnbuckes on the

tail wires represented a real safety issue in that forgetting to safety wire

a turnbuckle is something very easy to do.  So, for that and other reasons

we felt they represented a real safety issue.  All our conversations with

Kolb builders over the years has only strengthened this conviction - it is

so easy to overlook something when the airplane gives the appearance of

being fully assembled.  Most of us are amateur builders and mechanics and we

easily forget little details like safety pins, safety wire, lock nuts, etc.

but us professionals forget too.  Ask me how I know.



If I were in the business today, I would probably continue with a 4-hole

tang, but it would be a 4130 tang made just a little thicker - depending

upon application.  Originally we did not use the 4-hole tang or turnbuckles

- nothing is really needed.  But the adjustments make life easier.    



I would still not use turnbuckles for the reasons I previously mentioned in

an earlier email and above.  But I did add double wires to the Slingshot

from the beginning because I felt they were needed for the higher speeds the

SS was capable of going. (I also added a significant internal brace (from

the wire attach point back to the inside corner of the stabilizer) to

properly handle the inward loads imposed by the wire on the leading edge

tube.)  



I don't know all the reasons why other manufacturers may use double wires on

the tail, but I do know the major reason - their tail design requires it -

it is not optional for them.  With a rectangular tail one cannot say that

they have double tail wires for safety - the design requires it.  The light

weight tail structure is not torsionally stiff enough to be held by only one

set of wires.  I can further guesstimate that many times this rectangular

shape is chosen not for aerodynamics - but rather for manufacturing ease.

Many of these tails are just a series of bends in a tube.  This is much

easier, faster and less expensive than the 3-separate tubes the Kolb uses

that must be gusseted and riveted at every corner. 



Homer has always used the triangular plan form on the tail because it will

not stall nearly as easily as a rectangular one will.  So in Homer's mind

aerodynamics (shape) is a safety issue.  Probably not many on the list see

tail planform shape as a safety issue - but Homer did. 



I noticed on the photo of the tail, that another change has been introduced:

the curved leading edge of the horizontal stabilizer - and I have seen these

before too.  This type design, while not being rectangular - it has

definitely been taken out of the triangular scenario with its direct load

paths.  So if one wants a curved leading edge, I would say should have a

double set of wires - depends upon degree of curvature.



I really hope the group can continue to operate in a civil manner - so much

these days is becoming polarized where someone who has a different opinion

is vilified.  This is unfortunate because I don't think anyone of us has a

lock on all the knowledge - so we need to share our little pieces of the

puzzle so we can all see the big picture and hopefully fly more safely. 



Dennis



--

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JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Sat Sep 05, 2009 7:02 am Post subject: Re: Tail Wire Tangs Breaking And other Tail Brace Issue Co

 	  Possums wrote: 	
		  At 11:15 PM 9/3/2009, you wrote:



I only know 

of one person who was willing to tear the wings off of a Kolb in 

flight - on purpose (not with sandbags on the ground) and

trust a chute to carry him down. This was done to find the weak link 

in the design. The "weak link" was fixed years ago and

by weak - I mean more G's than you might ever do..

Most of the stuff I have done is cosmetic or just for looks/comfort.



	




Possums,



You plane does look good, but some of your improvements are not cosmetic  You say you mods were done for " looks/comfort "....   Are you suggesting that you put two sets of tail bracing wires on for looks ? Or that having two sets of tail wires somehow make your plane more comfortable ?  You did a very nice job on your Kolb, it is disappointing to see you join in on the recent ugliness with your last post, and that you would even downplay your own improvements in in your kolb for the sake of fitting in with a few people that are intent on discrediting anything I post.  You have done some really nice things to your Kolb, to downplay them to " Fit In " does a disservice to yourself and those that might think about similar improvements to their planes.



Mike

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

Kolb MK-III Xtra, 912-S

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