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Al-Ko Trailer Tongue failure



 
 
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  #1  
Old July 7th 16, 10:21 PM posted to rec.aviation.soaring
Dave Springford
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Posts: 235
Default Al-Ko Trailer Tongue failure

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.
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  #2  
Old July 7th 16, 10:55 PM posted to rec.aviation.soaring
JS
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Default Al-Ko Trailer Tongue failure

Glad it had a reasonably happy ending, Dave.
You mentioned RV. Do you think the distance from axle to tow ball was a factor?

Another good set of bolts to inspect are inside the trailer, holding the tongue in place. Once discovered one of the front bolts broken during a drive across the Great Basin.
Jim
  #3  
Old July 7th 16, 11:21 PM posted to rec.aviation.soaring
[email protected]
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Default Al-Ko Trailer Tongue failure

Nice save, F1! I'm towing a 1992 Cobra with the round tongue so I check that for cracks fairly regularly along with the usual hub/tire checks. But I've never towed with a motorhome and I, too, wonder if that's the common factor.

There was a flurry of concern some years ago about these earlier round trailer tongues on Cobras. Has everyone else replaced theirs already, leaving me in the minority? Or did this prove to be an issue only for those towing with larger RVs where some serious leverage could be applied?

Chip Bearden
ASW 24 "JB"
  #4  
Old July 8th 16, 12:02 AM posted to rec.aviation.soaring
Tom Kelley #711
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Default Al-Ko Trailer Tongue failure

On Thursday, July 7, 2016 at 3:21:21 PM UTC-6, 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.


Just went and checked my bolts on my 2006 Cobra trailer. Mine are original and they are 10.9 grade. Pulled behind my motor home with many miles....no problems....yet...thanks for the pictures and glad it turned out safe.

Best. #711.
  #5  
Old July 8th 16, 12:20 AM posted to rec.aviation.soaring
Dave Springford
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Posts: 235
Default Al-Ko Trailer Tongue failure

I'm certain that the towing with the RV is the contributing factor in the failure. The amount of bouncing that I see in the mirrors is astonishing and this certainly puts a significant number of cycles at higher loads on the tongue, than a car, that can lead to either a fatigue or catastrophic failure.

Tom's 10.9 bolts are rated at 145,000 psi so much closer to the imperial grade 8 bolt that I used as replacements than the original 8.8 bolts that were installed in my trailer. These are close to an imperial grade 5 bolt.

So from Tom's experience, I conclude if you tow with an RV and have 8.8 bolts replace them!
  #6  
Old July 8th 16, 02:21 AM posted to rec.aviation.soaring
Karl Striedieck[_2_]
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Default Al-Ko Trailer Tongue failure

My first Duo trailer showed signs of those two cross bolts working, so I drilled a 1/2" hole vertically in that area and installed a grade 8 bolt to hold everything tight. No working thereafter.

I'll so same with replacement Duo/trailer.

Piet Barber has that rig now and he might share pics?

I'll send a picture to Dave who might post it for me. (Thanks in advance Dave!)
  #7  
Old July 8th 16, 02:38 AM posted to rec.aviation.soaring
Dave Springford
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Posts: 235
Default Al-Ko Trailer Tongue failure

Here is Karl's picture showing the location of the additional bolt.

http://www.foxonecorp.com/images/trailer.jpg
  #8  
Old July 8th 16, 03:31 AM posted to rec.aviation.soaring
[email protected]
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Default Al-Ko Trailer Tongue failure

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.
  #9  
Old July 8th 16, 08:43 AM posted to rec.aviation.soaring
Per Carlin
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Default Al-Ko Trailer Tongue failure

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.
  #10  
Old July 8th 16, 03:30 PM posted to rec.aviation.soaring
Eric Greenwell[_4_]
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Posts: 1,029
Default Al-Ko Trailer Tongue failure

Per Carlin wrote on 7/8/2016 12:43 AM:
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.


Can we be certain the missing bolt broke? I would expect the bolt hole
to show noticeable elongation or other damage from shearing the bolt,
especially on the side opposite the break (it would stay in the hole for
while, taking all the pounding, until that side also sheared, or the
bolt simply fell out), but the hole looks undamaged in the photo. Can't
see the other hole, however.

There is vertical bolt in the picture (about where Karl's seems to be),
just ahead of the missing bolt: what is it's function?

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




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