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"

Hi Guys - Spindelberger is looking into this.
It would greatly assist if you could:

1) Take close-up photographs of broken bolt ends
and email them to me.

2) Send me the broken bolts (which I will forward
on to Spindelberger):
Dave Nadler
97 Central Street
Acton, MA 01720

3) Somebody go help JJ get a picture of the rivets
he replaced and email them to me...

Thanks !
Best Regards, Dave

PS: I'm on the road so a bit hard to reach.
Going to PA for a few days, where no doubt
it will rain as they've gone and called
another contest...

Does opening the top allow you to do individual bolt replacement with
no additional clamping? i.e the struts are fully extended and the
'lift' vector is almost vertical.

KK

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 !


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

On May 22, 6:17*pm, Ken K wrote:
Does opening the top allow you to do individual bolt replacement with
no additional clamping? i.e the struts are fully extended and the
'lift' vector is almost vertical.

KK







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 !

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

No ! No !!
To clarify #3:
Best to OPEN the top AND THEN clamp the front down...

The "lift vector" is NOT non-existent;
CG of top is AFT of strut attach point and
front of top will pivot around the strut attach
(upwards) and push forward as well...
Unless it is well clamped !
Look at the picture he
http://www.nadler.com/public/2010_Hobbs/2010_Hobbs.html

Hope that helps, From soggy Ridge Soaring,
Best Regards, Dave "YO electric"

On May 22, 3:17*pm, Ken K wrote:
Does opening the top allow you to do individual bolt replacement with
no additional clamping? i.e the struts are fully extended and the
'lift' vector is almost vertical.

KK







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 !

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

What Dave said!

However the clamp does not need to be anything special. I changed my
bolts yesterday using a 2.5 inch C clamp that was quite a bit less
substantial than the one shown in Steve (GW)'s write up.

Trust us - It's far easier to clamp the parts while they are in
alignment than to try to get them back into alignment if you try
without clamping!

Andy (GY)

I have just checked my UK based 15M 1999 Cobra trailer (glass sandwich
top). This has only been towed on reasonably smooth roads (excluding the
odd field) and only very occasionally opened in strong winds .
There is some slight compression to the glass shell at the outer mounting
holes on each handle. When checking the bolt tightness I noticed that the
nuts on the outside mounting bolts (inside the trailer on the hinge plate)
are both not square to the hinge plate as though they were fitted at a
slight angle. (approx 1mm gap is at the top of the bolt ) .
I have vague recollections they had always been like this and assumed at
the time that this was because it was not possible to square everything up
when mounting the bolts at the factory. However, I now wonder if the lid
has moved up slightly inclining the outer bolts.
I “gently” tightened all the bolts a couple of turns (using a small 6”
spanner to limit torque) so it would appear that they were working loose.
I was in a hurry when I did this and seem to remember the extra torque
reduced the gap at the top of the inclined bolts.
Few of questions
- Has anyone else noticed if any of their hinge mounting bolts were at a
slight angle when delivered ?
- Does anyone have a “method” of judging how tight to do these bolts
should be. I am loath to snap them or do more compression damage before I
get round to re-enforcing the handle area and fitting stronger bolts.
- Regarding clamping the hinge to the aluminium cross member. When the
bolts are removed what stops the aluminium cross member from ripping out
of the top shell. I assume it is glued in ?

On May 23, 7:48*am, Ian Reekie wrote:
When the bolts are removed what stops the aluminium cross member from ripping out
of the top shell. I assume it is glued in ?

It is riveted to the top side rails. However one US owner has found
all rivets sheared. All mine seem ok.

In any event you should only change one bolt at a time!

Andy

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)