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JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Thu Apr 05, 2007 4:06 pm Post subject: Kolb Wing Attach Points

The two pins on each end of the wing strut have the most force on them then the pins in the center section, but not a huge amont... The two strut pins have something like 25 % more force on them than the pin that attaches to the wing center section.    But the huge bending moment caused by that large 1 inch gap makes that one the one that will fail first...   What it takes to bend that pin at a one inch spread, I cannot find a spec on that anywhere.   I would be ok with this on a FireStar, or FireFly, but not on a heavy MK III.  Have you ever seen how thick the wing attach bolts are on a J-3 Cub, they are about twice the streingth of what the MK III is for the same weight class plane.



To help this, I have gone to NAS hardware which is about 20 % stronger than AN hardware, and I am using a bolt and nut, so that if it does bend, one end will not pull out.   I will be drilling that out and going to a bigger diameter bolt there just to be sure.   I would also like to drill out and go one size bigger bolts on the strut ends, but it it might remove to much material from the ends and cause weakness in the 4130 metal of the wing strut end, so I will not.    These have much less bending moment, so are not as likely to fail as the center section as can be seen in the pictures below.   Larry had a good idea of putting a spacer in the lower attach point pin to keep the stress to one side of it.   That will put almost all the stress on one side of the fitting, but will keep that bolt stressed in sheer instead of bending force.  I will use a bunch of washers to do this.   I will also be careful to make sure I do not put to many in so that it does not cause this fitting to be tight.   Making this tight instead of free floating could cause fatigue on the strut end and cause a fialure over time.   Remember the tail that fatigued fialed when its foward fitting was not allowed to float free ?



Attached are pictures so you all can see what I am talking about, and if any one has any more ideas or sees something I dont by all means respond to this thread.



Michael Bigelow

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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

pj.ladd(at)btinternet.com
Guest

Posted: Fri Apr 06, 2007 2:37 am Post subject: Kolb Wing Attach Points

What it takes to bend that pin at a one inch spread,........   on a heavy MK 

III. >>



Hi Michael,



I can give you something to work on.



If you accelerate a Mark111 with a Jabiru engine full throttle over about 50 

yards from a standing start and hit a vertical RSJ with the port wing just 

outside the lift strut attachment point it will bend the front attachment 

pin approc 3/16 of an inch. It will also distort the cockpit cage.



Dont ask...



Cheers



Pat



do not archive

Eugene Zimmerman

Joined: 10 Jan 2006
Posts: 392

Posted: Fri Apr 06, 2007 4:10 am Post subject: Kolb Wing Attach Points

OUCH !     THAT  HURT !

On Apr 6, 2007, at 6:36 AM, pat ladd wrote:



 	  Quote: 	
		   If you accelerate a Mark111 with a Jabiru engine full throttle over  

 about 50 yards from a standing start and hit a vertical RSJ with  

 the port wing just outside the lift strut attachment point it will  

 bend the front attachment pin approc 3/16 of an inch. It will also  

 distort the cockpit cage.

FS2Kolb(at)aol.com
Guest

Posted: Fri Apr 06, 2007 4:42 am Post subject: Kolb Wing Attach Points

Whats an RSJ?

  

 In a message dated 4/6/2007 4:37:38 A.M. Mountain Daylight Time,  pj.ladd(at)btinternet.com writes:

  	  Quote: 	
		  If you    accelerate a Mark111 with a Jabiru engine full throttle over about 50    

yards from a standing start and hit a vertical RSJ with the port wing just    

outside the lift strut attachment point it will bend the front attachment    

pin approc 3/16 of an inch. It will also distort the cockpit    cage.



Dont ask...



Cheers



Pat



do not archive  	


 

  



See what's free at AOL.com. 

  [quote][b]

MKIIIX040

Joined: 31 Mar 2006
Posts: 123
Location: Millinocket, Maine

Posted: Fri Apr 06, 2007 5:14 am Post subject: Kolb Wing Attach Points

Whats an RSJ?

  

 Recreational sport Jaguar

  

 do not archive 

 Vic

   [quote][b]

_________________
MKIIIX040
912UL

a58r(at)verizon.net
Guest

Posted: Fri Apr 06, 2007 9:43 am Post subject: Kolb Wing Attach Points

RSJ= Real Stout Joist

 regards,

Bob N.    FireFly 070 Old Kolb

http://www.angelfire.com/rpg/ronoy/



do not archive



 



 [quote][b]

David.Lehman

Joined: 10 Jan 2006
Posts: 265
Location: "Lovely" Fresno CA

Posted: Fri Apr 06, 2007 12:09 pm Post subject: Kolb Wing Attach Points

Mike...

  

 Take a look at what holds the Luscombe (heavier than a Cub) wing spar to the fuselage carry-through...  An aluminum pin, drilled at both ends and held in place with cotter pins...

  

 DVD

  

 do not archive



 

 On 4/5/07, JetPilot <orcabonita(at)hotmail.com (orcabonita(at)hotmail.com)> wrote: [quote]--> Kolb-List message posted by: "JetPilot" <orcabonita(at)hotmail.com  (orcabonita(at)hotmail.com)>



The two pins on each end of the wing strut have the most force on them then the pins in the center section, but not a huge amont... The two strut pins have something like 25 % more force on them than the pin that attaches to the wing center section.    But the huge bending moment caused by that large 1 inch gap makes that one the one that will fail first...   What it takes to bend that pin at a one inch spread, I cannot find a spec on that anywhere.   I would be ok with this on a FireStar, or FireFly, but not on a heavy MK III.  Have you ever seen how thick the wing attach bolts are on a J-3 Cub, they are about twice the streingth of what the MK III is for the same weight class plane. 



To help this, I have gone to NAS hardware which is about 20 % stronger than AN hardware, and I am using a bolt and nut, so that if it does bend, one end will not pull out.   I will be drilling that out and going to a bigger diameter bolt there just to be sure.   I would also like to drill out and go one size bigger bolts on the strut ends, but it it might remove to much material from the ends and cause weakness in the 4130 metal of the wing strut end, so I will not.    These have much less bending moment, so are not as likely to fail as the center section as can be seen in the pictures below.   Larry had a good idea of putting a spacer in the lower attach point pin to keep the stress to one side of it.   That will put almost all the stress on one side of the fitting, but will keep that bolt stressed in sheer instead of bending force.  I will use a bunch of washers to do this.   I will also be careful to make sure I do not put to many in so that it does not cause this fitting! 

to be tight.   Making this tight instead of free floating could cause fatigue on the strut end and cause a fialure over time.   Remember the tail that fatigued fialed when its foward fitting was not allowed to float free ? 



Attached are pictures so you all can see what I am talking about, and if any one has any more ideas or sees something I dont by all means respond to this thread.



Michael Bigelow



--------

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



[b]

_________________
Ã´Â¿Ã´

"Both optimists and pessimists contribute to the society. The optimist invents the aeroplane, the pessimist the parachute."

--- George Bernard Shaw

d-m-hague(at)comcast.net
Guest

Posted: Fri Apr 06, 2007 6:30 pm Post subject: Kolb Wing Attach Points

At 08:06 PM 4/5/2007, JetPilot wrote:

 	  Quote: 	
		  



The two pins on each end of the wing strut have the most force on them 

then the pins in the center section, but not a huge amont... The two strut 

pins have something like 25 % more force on them than the pin that 

attaches to the wing center section.    But the huge bending moment caused 

by that large 1 inch gap makes that one the one that will fail 

first...   What it takes to bend that pin at a one inch spread, I cannot 

find a spec on that anywhere....

To help this, I have gone to NAS hardware which is about 20 % stronger 

than AN hardware...


	


I've been kinda wondering about that too, so I looked at the numbers.  On 

my Ultrastar, the wing attachment with the 1" gap is in the rear, using a 

1/4" diameter clevis pin.  That pin is rated at 7360# double shear, which 

would seem to be no problem... but it's not really loaded in 

shear.  Bending is indeed another matter.  Figuring the bending loads on 

that pin very roughly, if the fitting is exactly in the center and is 1/8" 

thick, the clevis pin will hold 877# (with no safety factor).  If you can 

space it all the way to one side, then the single shear strength of 3680# 

would be in effect... but on the Ultrastar you can't control where it ends 

up.  However, on the US this attachment sees only drag loads so it's 

probably OK... though there would be added loads due to aileron 

deflection.  Does make me wonder if there was ever a published maneuvering 

speed for this plane, though...



If the gap at a fitting is less than 1", the bending stresses on the pin go 

down proportionately.  A 5/16" pin is 1.56X as strong in shear and 2.44X as 

strong in bending; a 3/8" pin is 2.25X and 5.06X, respectively.  Good 

design practice dictates that a fitting be designed so that it can be 

drilled out for the next larger size fastener if necessary (in case of 

wear), but not necessarily the next size over that.



On the lift strut and inboard wing attachment at the main spar, the wing 

strut takes  the bulk of the vertical load (exactly all the vertical load 

if it attaches exactly at the midpoint of the wing panel).  However, the 

tension in the lift strut is twice the vertical load (assuming a strut 

angle of 30°, which is about right), thus the tension in a lift strut is 

approximately equal to the airplane's weight plus any tail downforce.  I 

don't know how much gap there is on the later models' strut attachment but 

on the US it's a pretty close fit.



On the forward wing root attachment, there's little or no vertical load, 

but it has to oppose the inward force from the lift strut, which is the 

strut tension times cos(30) or 87% of the plane's weight... so that's the 

force on that pin or bolt.



Of course, none of the above takes into account flight load factors or 

required safety factors.



I don't know the specs of the NAS hardware you're using, but I'm not sure I 

like that idea... I hate to second guess the designer, especially on a 

proven design, and a stronger bolt will be more brittle... fatigue may 

become an issue, especially if the bolt gets worn or nicked.



Eeek, too much thinking for a Friday night... 



                                 -Dana

--

--

The citizens of the United States are getting the government they deserve. 

The problem is that I'm also getting the government they deserve.

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Fri Apr 06, 2007 7:35 pm Post subject: Re: Kolb Wing Attach Points

Hi Dana,



That is a very good analisys of the loads on the pins, where did you get the figures for bending the pins across 1 inch ?   According to your figures, the pin is only 1/10 th as strong when the load is bending instead of sheer, which seems about right.



There is very little force on the trailing edge attachment of a Kolb, I would not worry at all about that.   My MK III weighs almost 3 times what the Ultrastar and the Firefly do, but uses the same size pins...  What is not an issue on some planes could be on others.



The one thing I think you got wrong is the stress on that center pin that I am talking about.  It is more than the weight of the airplane.  With the struts at 45 degrees it would be the the same as the aircraft weight, having the strut go out at a 60 degree angle from vertical makes it 1.7 times the weight of the plane, or 1700 pounds at 1 G on my MK III.   The spar is being forced inwards by the struts at a 60 degree angle from the load, I think you just used the wrong part of the triangle.   



NAS 6600 hardware is used as aircraft structrual bolts, and is used in many airplanes for very high stress wing spar attachment ( Low wing planes with no struts ).   This type of bolt was recommended to me by an airline structrual inspector.    I searched the applications and confirmed this to be true before switching bolts.  



To put the next size bigger pin in, I will have to be careful to drill the holes larger only inwards, taking care not to make the holes any closer to the edges, but there is plenty of material to do this.  See the attached picture.

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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

Steve Boetto

Joined: 11 Jan 2006
Posts: 365

Posted: Sat Apr 07, 2007 4:16 am Post subject: Kolb Wing Attach Points

In a message dated 4/6/2007 11:36:33 P.M. Eastern Daylight Time,  orcabonita(at)hotmail.com writes:

  	  Quote: 	
		  To put    the next size bigger pin in, I will have to be careful to drill the holes    larger only inwards, taking care not to make the holes any closer to the    edges, but there is plenty of material to do this.  See the attached    picture.



--------

&quot;NO FEAR&quot; -  If you have no    fear you did not go as fast as you could have  !!!

	


 

 Mike,

 What you propose to do is not that easy. You may end up with loose out of  round holes in your pursuit to improve a tested design. As an alternative you  might consider using spacers or washers to fill the gaps. If you carefully trim  a spacer to a snug fit you will be able to tighten your bolt without deflecting  the main tabs. Deflecting the tabs would also worsen your situation.

  

  

  

 Steve B

 do not archive



See what's free at AOL.com. 

  [quote][b]

d-m-hague(at)comcast.net
Guest

Posted: Sat Apr 07, 2007 4:33 am Post subject: Kolb Wing Attach Points

At 11:35 PM 4/6/2007, JetPilot wrote:

 	  Quote: 	
		  



That is a very good analisys of the loads on the pins, where did you get 

the figures for bending the pins across 1 inch ?   According to your 

figures, the pin is only 1/10 th as strong when the load is bending 

instead of sheer, which seems about right.


	


I just treated the pin as a small beam in bending, supported at the ends, 

and calculated the stresses.



 	  Quote: 	
		  There is very little force on the trailing edge attachment of a Kolb, I 

would not worry at all about that.   My MK III weighs almost 3 times what 

the Ultrastar and the Firefly do, but uses the same size pins...  What is 

not an issue on some planes could be on others.


	


At low AOA (i.e. cruise) the loads are very low.  At high AOA the drag 

loads can become significant... I guess a good reason not to do high speed 

accelerated stalls or snap rolls in these planes.. . 



 	  Quote: 	
		  The one thing I think you got wrong is the stress on that center pin that 

I am talking about.  It is more than the weight of the airplane.


	


No, remember that each wing holds only half of the plane's weight.



 	  Quote: 	
		  NAS 6600 hardware is used as aircraft structrual bolts, and is used in 

many airplanes for very high stress wing spar attachment ( Low wing planes 

with no struts ).   This type of bolt was recommended to me by an airline 

structrual inspector.    I searched the applications and confirmed this to 

be true before switching bolts.


	


It may very well be fine, probably is, I haven't seen the actual specs for 

those fasteners.



Hopefully I can get some work done on my plane this weekend (including 

replacing all the fasteners we've been discussing with new ones) so I can 

have it done in time for Homer's fly-in...



                                 -Dana

--

--

The citizens of the United States are getting the government they deserve. 

The problem is that I'm also getting the government they deserve.

worrybear(at)verizon.net
Guest

Posted: Sat Apr 07, 2007 5:01 am Post subject: Kolb Wing Attach Points

---

d-m-hague(at)comcast.net
Guest

Posted: Sat Apr 07, 2007 5:28 am Post subject: Kolb Wing Attach Points

At 09:01 AM 4/7/2007, DANIEL WALTER wrote:



 	  Quote: 	
		  I believe it was the Ultrastar wing that was tested to failure, I think the

pins in question all surived.  Dennis would know for sure.


	


Yes, he beat on it until the drag strut (which the pin is on the end of) 

failed in compression.  The design was changed to reinforce the drag strut 

and they called it good enough.



Took balls with only a hand thrown parachute...



                                 -Dana

--

--

The citizens of the United States are getting the government they deserve. 

The problem is that I'm also getting the government they deserve.

pj.ladd(at)btinternet.com
Guest

Posted: Sat Apr 07, 2007 5:40 am Post subject: Kolb Wing Attach Points

RSJ= Real Stout Joist>>

  

 Hi Bob,

 well.. it was certainly stout enough that the roof  didn`t fall on me when I hit it.

  

 Cheers

  

 Pat

  

 do not archive

 



   [quote][b]

pj.ladd(at)btinternet.com
Guest

Posted: Sat Apr 07, 2007 5:41 am Post subject: Kolb Wing Attach Points

Whats an RSJ?>>

  

 Hi ,

 sorry, different language. Rolled Steel Joist. You  call them `I` beams, I think.

 Cheers

  

 Pat

  

 do not archive

 



   [quote][b]

NeilsenRM(at)comcast.net
Guest

Posted: Sat Apr 07, 2007 7:22 am Post subject: Kolb Wing Attach Points

Oh come off it.



There are hundreds of Kolbs out there and there are even a few Kolbs that 

have thousands of hours on them with in-flight loads over gross and the has 

never been even a bent pin (from flight loads). That's not to say there 

isn't maybe a good idea to put spacers in but....



Also that plane that Dennis folded the wing on was one of the newer kolbs 

(maybe a MKII). He had to really really work at it to get it to fail. Also 

they didn't just fix the drag strut and call it good enough!!! They fully 

inspected the wing. If the attach point pins were bent in any way they would 

have fixed that also. This wasn't just some required test that they went 

thru (it isn't required and no one else cared enough to do this). The point 

was they cared enough make sure it was safe. Just don't go fixing something 

not broken and make it fail



Rick Neilsen

Redrive VW powered MKIIIC



---

Steve Boetto

Joined: 11 Jan 2006
Posts: 365

Posted: Sat Apr 07, 2007 10:22 am Post subject: Kolb Wing Attach Points

In a message dated 4/7/2007 11:23:33 A.M. Eastern Daylight Time,  NeilsenRM(at)comcast.net writes:

  	  Quote: 	
		  That's    not to say there 

isn't maybe a good idea to put spacers in    but....

	


 

 Hi Rick,

  

 I agree with you that no change is required but the idea of the spacers was  to give some peace of mind to those that do not believe in the tried and tested  method. I also think that if done improperly the spaces could cause harm.   For the record, I use the factory method.

  

  

 Steve B



See what's free at AOL.com. 

  [quote][b]

d-m-hague(at)comcast.net
Guest

Posted: Sat Apr 07, 2007 10:24 am Post subject: Kolb Wing Attach Points

At 11:22 AM 4/7/2007, Richard & Martha Neilsen wrote:



 	  Quote: 	
		  There are hundreds of Kolbs out there and there are even a few Kolbs that 

have thousands of hours on them with in-flight loads over gross and the 

has never been even a bent pin (from flight loads). That's not to say 

there isn't maybe a good idea to put spacers in but....



Also that plane that Dennis folded the wing on was one of the newer kolbs 

(maybe a MKII). He had to really really work at it to get it to fail.


	


No, it was an Ultrastar:

http://forums.matronics.com/viewtopic.php?p=19920



I'm not worried about it, myself... as an aeronautical engineer, I was 

curious about it from an academic standpoint.  I'm leaving my plane stock, 

as designed.



                                 -Dana



--

--

The citizens of the United States are getting the government they deserve. 

The problem is that I'm also getting the government they deserve.

WillUribe(at)aol.com
Guest

Posted: Sat Apr 07, 2007 12:07 pm Post subject: Kolb Wing Attach Points

Greetings, 

 In the 11 years I have been a list member, every once in a while, I  read with great amusement how people want to change Homer's design because they  feel they can do a better job. IMHO nothing is going to just break if  you build it to plans so stop worrying so much.

 Regards,

 Guillermo Uribe

 FireStar II N4GU

 El Paso, TX

 



See what's free at AOL.com.

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lcottrell

Joined: 29 May 2006
Posts: 1494
Location: Jordan Valley, Or

Posted: Sat Apr 07, 2007 12:14 pm Post subject: Kolb Wing Attach Points

 	  Quote: 	
		   I'm not worried about it, myself... as an aeronautical engineer, I was

 curious about it from an academic standpoint.  I'm leaving my plane stock, 

 as designed.



                                 -Dana




	




Then one could safely surmise that you just enjoy being a "Devils Advocate", 

or something painful like that!  :-/



The most likely failure of any part in a Kolb is always going to be the 

brain.



Larry, Oregon

do not archive

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