Cobra top hinge plate bolt failure

Last year "YO" told us about how he nearly lost his trailer top after
both bolts securing one trailer top hinge plate failed. Of course I
checked my bolts and all four were secure at that time.

Yesterday I arrived at the club field and had a problem releasing the
left rear top latch. Sure enough the outer bolt on the left hinge
plate had failed and this allowed the top to move back slightly and
bind up the rear latch. I was able to find replacement bolts at a
local hardware store. 5/16 x 3.5 inch are very close to the
diameter the original metric bolt and provide more load bearing
unthreaded shank.

The bolts in question go through the front handles, the trailer glass
top, the trailer top frame (with an internal spacer block), a spacer
plate, and then the main hinge plate. All the parts try to misalign
under load. With the help of 5 people I was able to align all the
pieces well enough to get the new bolt in and was then able to rig and
fly the task.

Another isolated failure? No. While I was working on it GW walks up
and says he found the same bolt failed on his trailer the previous
evening. My trailer is 9 years old and GW's I think 10 years old.
Both are glass top but I don't know if that is significant. So 3
known failures of these bolts.

Do you feel lucky?

Andy (GY)

On May 16, 10:40*am, Andy wrote:
Last year "YO" told us about how he nearly lost his trailer top after
both bolts securing one trailer top hinge plate failed. *Of course I
checked my bolts and all four were secure at that time.

Yesterday I arrived at the club field and had a problem releasing the
left rear top latch. *Sure enough the outer bolt on the left hinge
plate had failed and this allowed the top to move back slightly and
bind up the rear latch. *I was able to find replacement bolts at a
local hardware store. *5/16 x 3.5 inch *are very close to the
diameter *the original metric bolt and provide more load bearing
unthreaded shank.

The bolts in question go through the front handles, the trailer glass
top, the trailer top frame (with an internal spacer block), a spacer
plate, and then the main hinge plate. All the parts try to misalign
under load. *With the help of 5 people I was able to align all the
pieces well enough to get the new bolt in and was then able to rig and
fly the task.

Another isolated failure? *No. *While I was working on it GW walks up
and says he found the same bolt failed on his trailer the previous
evening. My trailer is 9 years old and GW's I think 10 years old.
Both are glass top but I don't know if that is significant. *So 3
known failures of these bolts.

Do you feel lucky?

Andy (GY)

I was just about to post something on this very topic,
as I'm about to do some work related to this...

1) Spindelberger has had only one other failure of
this bolt reported to them; actually while I was with
them a few weeks ago and they were very surprised and
thinking maybe a bad batch of bolts.

2) The gas struts that open the trailer top push
the top FORWARD when closed. This puts a load on
these bolts and over time the top actually moves
forward. When this happens you will notice the
rear latches don't line up with the top and are
hard to close.

3) Do NOT remove these bolts without clamping the
trailer top down and restrained from moving
forward. If you undo the bolts without restraining
the top, even on just one side, even just one bolt,
the gas strut will deliver you a nasty surprise
(as happened to me on the highway to Hobbs).
CAREFUL !

4) Spindelberger has replacement hinge parts
with a bend to move the top aft and gave me a
set.

5) I'm designing a clamp to safely hold the top
during replacement of the hinge and bolts...

When I get this sorted I'll post something with
pictures. Not this week as we're having contest
weather.

Hope this helps,
Best Regards, Dave "YO electric"

I have a cobra glass top of this vintage so this has my interest.

Did the bolt break or shear at the location where the thread ends and
solid shank starts?

Where the new bolts you used "grade 8"?

I would not use stainless bolts as they are softer and will shear much
easier than
a "grade 8" heat treated bolt.

By the way 5/16" is exactly the same size as 8mm, difference is only .
002, less
than a hair thickness. And I would trust the heat treatment of a grade
8 5/16" bolt over a class 12.9 metric bolt.

I think I would get bolts long enough to have a solid shank all the
way thru the structure causing the misaligned stress
you decribe and only enough thread on the back side to hold the washer
and nut.

I'll be checking mine if it ever quits raining.....................

Joe Simmers

On May 16, 3:23*pm, joesimmers wrote:
I have a cobra glass top of this vintage so this has my interest.

Did the bolt break or shear at the location where the thread ends and
solid shank starts?

Where the new bolts you used "grade 8"?

I would not use stainless bolts as they are softer and will shear much
easier than
a "grade 8" heat treated bolt.

By the way 5/16" is exactly the same size as 8mm, difference is only .
002, less
than a hair thickness. And I would trust the heat treatment of a grade
8 *5/16" bolt over a class 12.9 metric bolt.

I think I would get bolts long enough to have a solid shank all the
way thru the structure causing the misaligned stress
you decribe and only enough thread on the back side to hold the washer
and nut.

I'll be checking mine if it ever quits raining.....................

Joe Simmers

My bolt failed at the thread to plain shank intersection. I have not
yet found the nut and threaded end. The plain shank length of the
original bolt is far too short and any shear load it taken at the
intersection rather than on the full shank diameter.

I don't know what grade the replacement bolt is. At the time I was
very pleased to find there was a hardware store within 10 miles of the
glider port. I have been flying there for over 20 years and had no
idea the store was there. To then find they had socket cap bolts of
the required size and length was beyond my expectations.

For the emergency repair at the glider port I was able to insert a #2
Phillips screw driver to pin the parts and then open the trailer. I
had 4 people at the aft end holding the top up and one person pulling
down on the front of the top. That allowed the bolt to slip in. Had
the other bolt failed it could have been ugly.

GW inserted a new bolt in his solo with the help of a clamp to pull
the parts into alignment. I had people available but no clamp.

Andy (GY)

On May 16, 7:40*am, Andy wrote:
Last year "YO" told us about how he nearly lost his trailer top after
both bolts securing one trailer top hinge plate failed. *Of course I
checked my bolts and all four were secure at that time.

Yesterday I arrived at the club field and had a problem releasing the
left rear top latch. *Sure enough the outer bolt on the left hinge
plate had failed and this allowed the top to move back slightly and
bind up the rear latch. *I was able to find replacement bolts at a
local hardware store. *5/16 x 3.5 inch *are very close to the
diameter *the original metric bolt and provide more load bearing
unthreaded shank.

The bolts in question go through the front handles, the trailer glass
top, the trailer top frame (with an internal spacer block), a spacer
plate, and then the main hinge plate. All the parts try to misalign
under load. *With the help of 5 people I was able to align all the
pieces well enough to get the new bolt in and was then able to rig and
fly the task.

Another isolated failure? *No. *While I was working on it GW walks up
and says he found the same bolt failed on his trailer the previous
evening. My trailer is 9 years old and GW's I think 10 years old.
Both are glass top but I don't know if that is significant. *So 3
known failures of these bolts.

Do you feel lucky?

Andy (GY)

This happened to a friend of mine also exactly as you describe. So
make that 4 cases.

On May 16, 6:23*pm, joesimmers wrote:
Did the bolt break or shear at the location where the thread ends and
solid shank starts?

...

I think I would get bolts long enough to have a solid shank all the
way thru the structure causing the misaligned stress
you decribe and only enough thread on the back side to hold the washer
and nut.

But, note that the load is not just in shear.
These 4 bolts are taking the total force of the
compressed gas springs in tension...

Best Regards, Dave "YO electric"

I think that all hardware store socket head cap screws are going to be
grade 8 or equiv. so I don't think you have to worry about that.

My bolt popped in the middle of the threaded length which apparently
is not where Andy's bolt broke. That supports my impression that it
is primarily a tension failure rather than a shear failure.

The type of clamp that I used successfully by myself is called a "Kant
Twist" 4 1/2" machinist clamp. These are sold at www.use-enco.com and
lots of other suppliers. So I'm not so sure that designing a special
clamp is needed. What does need designing is a scheme to get a
couple more bolts into that plate. The design is flawed and
dangerous.

Steve Koerner (GW)
www.wingrigger.com

On May 16, 8:08*pm, Steve Koerner wrote:
The type of clamp that I used successfully by myself is called a "Kant
Twist" 4 1/2" machinist clamp. *These are sold atwww.use-enco.comand
lots of other suppliers. *So I'm not so sure that designing a special
clamp is needed. * What does need designing is a scheme to get a
couple more bolts into that plate. * The design is flawed and
dangerous.

Steve Koerner (GW)www.wingrigger.com

Hmm - I planned to clamp with surfaces:
- bottom: grab the front inside the extrusion slot
- top: fix the angle on top of the alum frame
Nothing fancy, just a couple parts with holes
preventing clamping surfaces rotating and a bolt...

Did the kant-twist end fit inside the front's slot ?

Thanks,
Best Regards, Dave

It looks like YO and I were both commenting at the same time to the
effect that it is more likely a tension failure. However I don't
agree that the gas spring force has much to do with it. The gas
spring force is small compared to the strength of two 5/16 cap
screws. I suspect it has more to do with the inertia of the lid in
longitude with some combination of vibration and road bumping creating
the load. Heaven knows my trailer has seen some bumpy roads.

GW

On May 16, 5:18*pm, Dave Nadler wrote:
On May 16, 8:08*pm, Steve Koerner wrote:

The type of clamp that I used successfully by myself is called a "Kant
Twist" 4 1/2" machinist clamp. *These are sold atwww.use-enco.comand
lots of other suppliers. *So I'm not so sure that designing a special
clamp is needed. * What does need designing is a scheme to get a
couple more bolts into that plate. * The design is flawed and
dangerous.

Steve Koerner (GW)www.wingrigger.com

Hmm - *I planned to clamp with surfaces:
- bottom: grab the front inside the extrusion slot
- top: fix the angle on top of the alum frame
Nothing fancy, just a couple parts with holes
preventing clamping surfaces rotating and a bolt...

Did the kant-twist end fit inside the front's slot ?

Thanks,
Best Regards, Dave

Dave -- I am not really visulizing all this. Probably because I dealt
with it in the dark holding a flashlight. If you've worked through a
plan, it's probably a good one. It does seem like one of the jaws on
the clamp was fatter than I wished it were. So that is probably what
you are referring to. On my hinge plate, I was able to get the holes
to allign though even without the jaw stationed exactly where I wished
it would go. That might not be the case if the plate is positioned
just a little different on your trailer.

GW