Cobra Top Hinge Bolt Failure - Revisit

On Wednesday, May 15, 2013 4:29:14 PM UTC-4, wrote:
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

Um, I designed it with Alfred, its not yet an official product.
I'll try get in touch with them next week and see if they will
make these generally available. Key is the ability to jack the
front back into position and hold it there...

You could weld up your own, not at all high-tech here !

Hope that helps,
Best Regards, Dave

Ah, I see, well its a good idea. Was just thinking how I could possibly fabricate something similar. Mine is not nearly as bad as the one shown in blue, but I could stand to move it 1/4".

On Wednesday, May 15, 2013 4:50:45 PM UTC-7, wrote:
Ah, I see, well its a good idea. Was just thinking how I could possibly fabricate something similar. Mine is not nearly as bad as the one shown in blue, but I could stand to move it 1/4".

Dave, on my trailer the hinge plate is at an angle w.r.t the side rails. How did you deal with that in terms of jack bolt alignment? Is the jack bolt in your design perpendicular to the hinge plate?

Thanks,

PS. I am glad I am looking at this because my hinge plate bolts, while not broken, were certainly bent. and corroded.

This solution is close but not quite complete. I've studied this a fair bit and the side rails of the cobra trailer, at least mine is not quite as stout as one would think. You can actually flex it with just your hand. Its only 1/16th inch material and unclear how well mounted to the lid. I am concerned about buckling the side rails for trailers with large displacement issues once you start cranking on the jack. If it buckles, you're screwed.. Interestingly the trailer top struts are not mounted to the side rails. They actually mount to a cross member that is glassed to the lid. I think something like this cross member should be added to the location of this jacking mechanism to help distribute the load to more than just the rail. This will also be synergistic in taking vertical loads associated with the jack for those that have an angle to deal with (rail w.r.t to the hinge plate of about 5 degrees) instead of torsionally loading the side rail.

On Wednesday, May 22, 2013 1:09:29 AM UTC-4, wrote:
This solution is close but not quite complete...

This solution mirrors current Cobra production, which adds a
block screwed to the side rail and pressing against the hinge
plate. Thus compression loads (not torsional) are carried
just as with new trailers...

The side rails are not enormously stiff and vary depending
on the top (different models have different extrusions).
However, they don't seem to buckle...

Hope that helps,
Best Regards, Dave

Interesting. Okay, well, mine has both a wimpy side rail and an angle to deal with so I have the worst of all worlds. Correct there is a compressive load component but because of the angle I have vertical component. The resultant is a vector load that is not aligned with the side rail, hence the torsional component I am having to deal with that twists the rail. I have no choice but to add a cross member. What can you do, Spindelberger had a design flaw that exposes itself over time.

On Wednesday, May 22, 2013 5:35:43 AM UTC-7, Dave Nadler wrote:
On Wednesday, May 22, 2013 1:09:29 AM UTC-4, wrote:

This solution is close but not quite complete...



This solution mirrors current Cobra production, which adds a

block screwed to the side rail and pressing against the hinge

plate. Thus compression loads (not torsional) are carried

just as with new trailers...



The side rails are not enormously stiff and vary depending

on the top (different models have different extrusions).

However, they don't seem to buckle...



Hope that helps,

Best Regards, Dave

I have to deal with a ~2000 vintage Cobra for a 2-seater. Examination of the top and hinge plates showed no problem - yet. However, the explanations here helped visualize the problem - and, maybe, a potential alternative solution. Basically, I'm thinking of a system that forces the top to close in perfect alignment with the bottom.

If the main problem is a constant forward force on the hinges with the top closed, then why not use "something like" the already present alignment tabs near the front of the trailer to take up the load instead of the hinges? If a top had already moved forward, wedged tabs would force the top back aft as it was closed. All it would take is a pair of ball bearing studs on the insides of the bottom half of the trailer. This way, there would be no horizontal load at all on the hinges. If I'm imagining this right, the ball bearing studs and wedged tabs would be far enough forward the glider wings couldn't contact them.

It should also be possible to implement a wedge and roller on the outside of the trailer back near the lift struts. This would force the latches into alignment while relieving pressure on the hinge plates.

Of course, this wouldn't help with the top open.


On Wednesday, May 22, 2013 6:35:43 AM UTC-6, Dave Nadler wrote:
On Wednesday, May 22, 2013 1:09:29 AM UTC-4, wrote:

This solution is close but not quite complete...



This solution mirrors current Cobra production, which adds a

block screwed to the side rail and pressing against the hinge

plate. Thus compression loads (not torsional) are carried

just as with new trailers...



The side rails are not enormously stiff and vary depending

on the top (different models have different extrusions).

However, they don't seem to buckle...



Hope that helps,

Best Regards, Dave

On Wednesday, May 22, 2013 2:21:07 PM UTC-4, Bill D wrote:
why not use "something like" the already present alignment tabs
near the front of the trailer to take up the load instead of the
hinges? If a top had already moved forward, wedged tabs would
force the top back aft as it was closed. All it would take is
a pair of ball bearing studs on the insides of the bottom half
of the trailer. This way, there would be no horizontal load
at all on the hinges. If I'm imagining this right, the ball
bearing studs and wedged tabs would be far enough forward the
glider wings couldn't contact them.

It should also be possible to implement a wedge and roller
on the outside of the trailer back near the lift struts.
This would force the latches into alignment while relieving
pressure on the hinge plates.

Of course, this wouldn't help with the top open.

Wedge/roller behind the lift struts would take the side
load in tension which would be good. Probably could be
done on the inside. Needs a gradual taper otherwise
you won't be able to close the trailer.

I simply created an adjustable version of what
Spindleberger currently builds in new trailers...

Hope that helps,
Best Regards, Dave

On Wednesday, May 22, 2013 1:09:18 PM UTC-4, wrote:
Interesting. Okay, well, mine has both a wimpy side rail and
an angle to deal with so I have the worst of all worlds.
Correct there is a compressive load component but because of the
angle I have vertical component. The resultant is a vector
load that is not aligned with the side rail, hence the torsio
component I am having to deal with that twists the rail.

Aarrggg - I see. The bits line up better in my trailer,
consequently only minor torque.

I have no choice but to add a cross member. What can you do,
Spindelberger had a design flaw that exposes itself over time.

Right. The best solution would be remove the top and reinforce
the corner - not so easy ! Which is how I arrived at the solution
for my trailer - I could implement this without an overhead hoist.

Hope that helps,
Best Regards, Dave

Just thought I would report - I was able to fabricate some parts out of aluminum channel and steel channel based on Dave's design and document. Mine was done without welding since I am not a welder, but riveted to the side rail. An additional piece of aluminum sq tubing was added to the shell behind the side rail as piece of mind should the side rail want to twist. I am happy to report that after gradually torquing the jacking bolt, and shifting the top maybe 1/4 inch, the shell closes a lot better. I needed it more on one side than the other and this design helps addresses it well. I highly recommend this approach if you find the closing the trailer top is difficult on your fiberglass Cobra and see clear evidence of the top shifting fwd. It took me one week, couple hours each evening to fabricate the pieces and I'm not a machinist.

Darren