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Al-Ko Trailer Tongue failure



 
 
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  #11  
Old July 8th 16, 03:36 PM posted to rec.aviation.soaring
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Default Al-Ko Trailer Tongue failure

On Friday, July 8, 2016 at 2:43:03 AM UTC-5, Per Carlin wrote:
On Friday, July 8, 2016 at 4:31:04 AM UTC+2, wrote:
Remember that "tensile strength" measures a bolt under a longitudinal load. What you are seeing in this instance is a failure under "shear load." Two entirely different situations, and one of the main reasons that aircraft bolts (AN) are not the same as "Grade 8" or the European (DIN) equivalent.. High tensile strength bolts often exhibit less than desirable brittleness under shear load.


I think Mark is close to the root cause of the failing bolts. It is not the strength of the bolts itself that makes in brake (sounds funny, I know).
In the bolt-configuration in the initial post is the function of the bolts to hold the Al-Ko tongue tight to the square bar, the friction between the tongue and the bar makes the strength.
If the friction coefficient is low (fat, grease, dirt) or bolts is not tight (loosen by vibrations, deformations etc) is the friction between the tongue/bar low and a shear stress occurs on the bolts. The bolts are not dimensioned for this and will brake by fatigue.
This is a common problem on Cobra trailers(the nose-cone / spare wheel holder), the bolts a not tighten enough from the factory and / or they vibrate loose on the road.


Per is right, a properly engineered bolted connection is never meant to hold shear loads. The longitudinal tension in the bolted connection should press the pieces together with a force that causes friction sufficient to withstand the bending moment.
  #12  
Old July 8th 16, 03:40 PM posted to rec.aviation.soaring
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Default Al-Ko Trailer Tongue failure

I've often thought that the source of many trailer failures here in the U.S.. is partly that we just drive a lot more miles/kms than the typical European customer. I just got back from a nearly 5,000 mi. round trip to Nephi. And I've made numerous trips west with this trailer. How common is that in Europe?

The nose cone/spare tire holder on my Cobra failed last year and fell over (fortunately without damage) not because of a failed or loose bolt but because of a failure of the weld at the base of the supporting post. I had a failure many years ago of an Al-Ko tongue on a Komet trailer when the welds that secure the front tongue bracket inside the trailer broke.

Cobra/Komet designs have continued to improve each year since we first saw their appearance here (in the 70s?). But it seems like many of those improvements are in response to "destruction testing" performed by helpful U.S. owners. Is our experience shared by owners in similarly wide-open regions such as, say, Australia?

Chip Bearden
ASW 24 "JB"
  #13  
Old July 8th 16, 03:55 PM posted to rec.aviation.soaring
Dave Springford
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Default Al-Ko Trailer Tongue failure

In response to Eric's comments about whether or not the bolt broke, I can not say for sure, but the bolts are secured with ny-lock nuts that should prevent an inadvertent loosening of the nut.

The vertical bolt in the picture attaches to a plate on the bottom side of the upper (inverted) U-shaped piece of the tongue. This plate then butts up against the edge of the square tube that forms the inner piece of the tongue and it appears to be there to prevent the two pieces of the tongue from moving fore and aft against each other, or perhaps for alignment during installation.

  #15  
Old July 8th 16, 05:05 PM posted to rec.aviation.soaring
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Default Al-Ko Trailer Tongue failure

On Friday, July 8, 2016 at 10:26:09 AM UTC-5, Eric Greenwell wrote:
wrote on 7/8/2016 7:36 AM:
Per is right, a properly engineered bolted connection is never meant
to hold shear loads. The longitudinal tension in the bolted
connection should press the pieces together with a force that causes
friction sufficient to withstand the bending moment.


Bolts are routinely used in shear, from toys to airliners. On my glider,
the tail wheel, landing gear, and propeller are fastened with bolts in
shear, along with many other items.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorg...ad-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/...anes-2014A.pdf


Sorry Eric, you are wrong. Pretension (torque) on the bolt results in parts being pressed together. That force with a coefficient of friction normally being assumed at 0.1 results in the parts staying together without slippage. Shear can only occur if the parts slip, a properly designed connection never does.
  #16  
Old July 8th 16, 05:29 PM posted to rec.aviation.soaring
Craig Funston
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Default Al-Ko Trailer Tongue failure

On Friday, July 8, 2016 at 9:05:24 AM UTC-7, wrote:
On Friday, July 8, 2016 at 10:26:09 AM UTC-5, Eric Greenwell wrote:
wrote on 7/8/2016 7:36 AM:
Per is right, a properly engineered bolted connection is never meant
to hold shear loads. The longitudinal tension in the bolted
connection should press the pieces together with a force that causes
friction sufficient to withstand the bending moment.


Bolts are routinely used in shear, from toys to airliners. On my glider,
the tail wheel, landing gear, and propeller are fastened with bolts in
shear, along with many other items.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorg...ad-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/...anes-2014A.pdf


Sorry Eric, you are wrong. Pretension (torque) on the bolt results in parts being pressed together. That force with a coefficient of friction normally being assumed at 0.1 results in the parts staying together without slippage. Shear can only occur if the parts slip, a properly designed connection never does.


Herb,

There are some cases where friction is what is relied on for a bolted shear connection, but these are very special cases and require specific installation procedures. In building structures, these bolts are designated ASTM A325 SC or ASTM A490 SC. The "SC" designating slip critical. In order to perform as slip critical connections there needs to be enough capacity in the bolted sandwich to allow the bolt to yield slightly in tension during tightening. This provides a consistent preload to develop the friction. This type of connection is impossible to achieve when bolting though a hollow tube unless there is a bearing sleeve through the tube to allow development of full tension in the bolt. Without the bearing sleeve the bolt simply crushes the tube and sufficient clamping force is never achieved. Many buildings and other structures are designed and constructed using bolts in shear without relying on friction between the faying surfaces. Slip critical bolting (friction bolting) is a nice solution when cyclic loads and fatigue are a consideration because it eliminates the movement that happens when bearing bolts (bolts in plain shear) are cycled from one load direction to another. Cyclic loading can also be accommodated by interference fit bolts, but the degree of accuracy required in fabrication is too expensive for all but specialty applications.

Best regards,
Craig Funston, P.E. , S.E. , P.Eng.

  #17  
Old July 8th 16, 08:34 PM posted to rec.aviation.soaring
Craig Funston
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Default Al-Ko Trailer Tongue failure

On Thursday, July 7, 2016 at 2:21:21 PM UTC-7, Dave Springford wrote:
On my way home from Nephi (towing my trailer with the RV) I stopped for fuel and found one of the bolts that holds the Al-Ko trailer tongue together was gone as can be seen in the picture he

http://www.foxonecorp.com/images/20160703_154501.jpg

In the picture you can see the front hole that has been vacated by the bolt. Fortunately, the second bolt didn't fail before I stopped for fuel and also fortunately, five minutes down the road was a well stocked hardware store. So I was back on the road an hour later.

The original bolts are M12 x 100 with an 8.8 rating giving a tensile strength of 800 MPa (116,000 PSI). The holes in the tongue will accommodate a 1/2 inch bolt so I installed 1/2 x 4 inch grade 8 bolts with a tensile strength of 150,000 psi.

These imperial bolts are about .02 inches larger in diameter than the M12 and also about 30% stronger, not including the added effect of the extra diameter.

I emailed with Alfred Spindelberger and he indicated there is no harm in using stronger bolts.

So... my suggestion to those that tow their trailer with an RV is to check the bolts on the tongue, and maybe just go ahead and replace them before yours fail. It also might be a good idea to replace them every 4-5 years if you tow a lot with your RV (my trailer was new in 2012). Then, keep a spare set of 1/2 x 4 grade 8 bolts in the trailer just in case.

A few dollars in bolts might save you thousands in repairs!

Now, at every fuel stop, as well as visually checking tires and wheel hub temperature on the trailer, I'll also be checking the bolts.


Dave,

Did the vertical bolt ahead of the horizontal ones fail as well or did the nut come off the bottom? That's usually the primary load path for the vertical prying loads introduced by coupling the hitch assembly with the drawbar.
  #18  
Old July 8th 16, 09:07 PM posted to rec.aviation.soaring
Craig Funston
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Default Al-Ko Trailer Tongue failure

On Friday, July 8, 2016 at 7:55:50 AM UTC-7, Dave Springford wrote:
In response to Eric's comments about whether or not the bolt broke, I can not say for sure, but the bolts are secured with ny-lock nuts that should prevent an inadvertent loosening of the nut.

The vertical bolt in the picture attaches to a plate on the bottom side of the upper (inverted) U-shaped piece of the tongue. This plate then butts up against the edge of the square tube that forms the inner piece of the tongue and it appears to be there to prevent the two pieces of the tongue from moving fore and aft against each other, or perhaps for alignment during installation.


Dave,

Just saw your comment on the vertical bolt. Please ignore my prior note.
Craig
  #19  
Old July 8th 16, 09:08 PM posted to rec.aviation.soaring
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Default Al-Ko Trailer Tongue failure

Rather than drifting this thread on into principles of bolt engineering, instead lets focus the on the real problem. The new Al-Ko tongue design again leads to concerns of possible tongue failure. The old style Cobra round tongue also has a history of failures and also generated the same concerns. As Cobra trailer owners, we should be campaigning Spindelberger to provide better engineered tongue components. A new, well optioned, Cobra trailer can easily cost $20,000 or more. The last thing I expect to do after taking delivery of a new trailer is upgrading tongue bolts.

On Thursday, July 7, 2016 at 5:21:21 PM UTC-4, Dave Springford wrote:
On my way home from Nephi (towing my trailer with the RV) I stopped for fuel and found one of the bolts that holds the Al-Ko trailer tongue together was gone as can be seen in the picture he

  #20  
Old July 8th 16, 10:13 PM posted to rec.aviation.soaring
Casey[_2_]
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Default Al-Ko Trailer Tongue failure

On Friday, July 8, 2016 at 4:08:38 PM UTC-4, wrote:
Rather than drifting this thread on into principles of bolt engineering, instead lets focus the on the real problem. The new Al-Ko tongue design again leads to concerns of possible tongue failure. The old style Cobra round tongue also has a history of failures and also generated the same concerns. As Cobra trailer owners, we should be campaigning Spindelberger to provide better engineered tongue components. A new, well optioned, Cobra trailer can easily cost $20,000 or more. The last thing I expect to do after taking delivery of a new trailer is upgrading tongue bolts.


Right On. I can't believe they are still using steel wheels with hub caps. Nice aluminum rims are not even an option. Not sure if current hubs come with bearing buddy/quick lube fittings. But if not that is amazing as well.. A shot of synthetic grease every couple of years and one would never need to replace bearings or have to open bearing cap.
 




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