Cobra Top Hinge Bolt Failure - Revisit

At 22:21 25 April 2012, wrote:
On Tuesday, April 24, 2012 11:26:45 AM UTC-4, Steve Koerner wrote:
The structure immediately under the handles had clearly collapsed.
There is no such solid material between the inner and outer laminate
on mine.

The backing plate has resolved the problem quite well.

I've looked at my hinge bolts a number of times, but can't detect any
problems. Are there any symptoms that precede bolt failure, i.e. loose
handles?

TIA,

Frank (TA)


We checked all the Glass fibre top (twin skin) Cobra trailers at our site.
(over 10 older trailers ) None had so far suffered a hinge failure.
The most obvious sign of a potential problem is loose bolts which are
easily tightened. One older trailer had a couple of mm slack that could be
tightened out.
I changed the bolts on mine for longer stronger bolts (12.9 spec) that do
not have the thread section across a load bearing junction.
I noticed a lot of corrosion present on the bolts removed from my 13 year
old trailer stored in a English climate. It might be prudent to replace
them after about 10 years depending on local conditions.
I refitted with a aluminium backing plate for good measure but it probably
is not necessary as all the compression between the twin skins seems to
have taken place.

At 22:21 25 April 2012, wrote:
On Tuesday, April 24, 2012 11:26:45 AM UTC-4, Steve Koerner wrote:
The structure immediately under the handles had clearly collapsed.
There is no such solid material between the inner and outer laminate
on mine.

The backing plate has resolved the problem quite well.

I've looked at my hinge bolts a number of times, but can't detect any
problems. Are there any symptoms that precede bolt failure, i.e. loose
handles?

TIA,

Frank (TA)

Check the hold-down clamps at the aft end of your trailer, If the top latch
doesn't match up with the lower attach bracket like it did when
new.....................that means the top has moved forward and may be
setting up the failure mode with the hinge bolts. I found this condition on
both aluminum and fiberglass tops and then found sheared off rivets in the
hinge bolt bracket.

Another item to remember; avoid opening the trailer when a 10+ knot
cross-wind is blowing. An open top acts like a sail and can place
tremendous loads on the hinge bolts.
JJ

At 13:01 26 April 2012, John Sinclair wrote:
At 22:21 25 April 2012, wrote:
On Tuesday, April 24, 2012 11:26:45 AM UTC-4, Steve
Koerner wrote:
The structure immediately under the handles had clearly
collapsed.
There is no such solid material between the inner and outer
laminate
on mine.

The backing plate has resolved the problem quite well.

I've looked at my hinge bolts a number of times, but can't
detect any
problems. Are there any symptoms that precede bolt failure,
i.e. loose
handles?

TIA,

Frank (TA)

Check the hold-down clamps at the aft end of your trailer, If
the top latch
doesn't match up with the lower attach bracket like it did when
new.....................that means the top has moved forward and
may be
setting up the failure mode with the hinge bolts. I found this
condition on
both aluminum and fiberglass tops and then found sheared off
rivets in the
hinge bolt bracket.

Another item to remember; avoid opening the trailer when a
10+ knot
cross-wind is blowing. An open top acts like a sail and can
place
tremendous loads on the hinge bolts.
JJ


As a contributory preventative measure how about doing
something at the aft end to prevent forward movement of the
trailer top during towing? For example, angle the aft trailer-top
clamps at 45 degrees as viewed from the side with the lower
fitment being to the rear.

It would seem that this problem is related to using the trailer on the
road. Steve Koerner's link above states "...lonitudinal loads on the
trailer top hinge plate occur as the trailer and its tow vehicle pass
over bumps on the roadway."

This implies that if the trailer sits at a gliderport most or all of
the time, you may never experience this failure at all. Correct?

- John

John -

Subsequent to that writing, I think I really concluded that the
biggest issue may be the open trailer top in a crosswind as JJ
mentions here and as was discussed in the year ago thread on this
topic. Lots of theories were put forth on the matter.

As JJ points out, the crosswind issue is an avoidable situation
although thermal winds and dust devils can present a surprise at times.

As a contributory preventative measure how about doing
something at the aft end to prevent forward movement of the
trailer top during towing? For example, angle the aft trailer-top
clamps at 45 degrees as viewed from the side with the lower
fitment being to the rear.

There are some pretty strong forces at work here. Two struts that are
strong enough to raise the top, are trying to move the top forward when it
is down. Don't think the latches would last long tyring to fight the
struts. If top mated over steel posts in the lower trailer sides at the
rear, it might be strong enough to resist the forward forces. Spindelburger
is always improving his product and I'm betting we will see a fix on his
new product..........If anyone has enough money to buy one! I was told a
new Cobra cost $40K. Can this be right?
JJ

On Thursday, April 26, 2012 5:36:53 PM UTC-4, JJ Sinclair wrote:
As a contributory preventative measure how about doing
something at the aft end to prevent forward movement of the
trailer top during towing? For example, angle the aft trailer-top
clamps at 45 degrees as viewed from the side with the lower
fitment being to the rear.

There are some pretty strong forces at work here. Two struts that are
strong enough to raise the top, are trying to move the top forward when it
is down. Don't think the latches would last long tyring to fight the
struts. If top mated over steel posts in the lower trailer sides at the
rear, it might be strong enough to resist the forward forces. Spindelburger
is always improving his product and I'm betting we will see a fix on his
new product..........If anyone has enough money to buy one! I was told a
new Cobra cost $40K. Can this be right?
JJ

JJ,

According to my quick perusal of the 2011 price list on W&W, a 15-meter aluminum-topped trailer with some options was around $17K (abt 13-14,000 euros).

TA

Hey Guys, I am noticing signs the top of my fiberglass Cobra is moving forward. I am going to replace the bolts as recommended by many, and may do the backing plate solution as well. The deformation of the fiberglass is worrisome. Can the clamping of the hinge plate and removal of bolts be done with the glider in the trailer? or is it recommended to empty the trailer first?.. for those who have done it.

BTW, I also see what JJ identified and that's the 4 rivets on one side are popped and gone. I wonder if I can realign the frame and get either rivets or small fasteners back in there?
TIA,
Darren

On Wednesday, May 15, 2013 1:06:10 PM UTC-4, wrote:
Hey Guys, I am noticing signs the top of my fiberglass Cobra is moving
forward. I am going to replace the bolts as recommended by many, and
may do the backing plate solution as well.

Which will not help with the top migrating forward.

The deformation of the fiberglass is worrisome.
Can the clamping of the hinge plate and
removal of bolts be done with the glider in the trailer?

Yes, but BE CAREFUL. See below.


I drafted a note for Spindelberger but didn't hear back,
need to chase them...

http://www.nadler.com/Antares/Cobra_...rcement_01.pdf

Hope that helps,
Best Regards, Dave

PS: The part they made for me won't fit many trailers;
there are different extrusions used at the lower edge
of the top.

Wow, that seems like a good solution for me. Hmmm. I called one dealer yesterday and they did not mention this so I doubt they are aware of it. Let us know what you find. Anybody else able to get this part?
Thanks,
Darren