Cobra top hinge plate bolt failure

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)

Just checked my hinge plate bolts and they appear to be OK, but one
nut was just finger tight. A loose nut could/would lead to bolt
failure. Recommend we all check to make sure our hinge plate nuts are
tight.
JJ

On May 17, 11:04*am, JJ Sinclair wrote:
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)

Just checked my hinge plate bolts and they appear to be OK, but one
nut was just finger tight. A loose nut could/would lead to *bolt
failure. Recommend we all check to make sure our hinge plate nuts are
tight.
JJ- Hide quoted text -

- Show quoted text -

I checked my bolts for security last year after YO's report. Don't
remember how much I tightened them, it at all, but the damage was
probably already done. I think the only safe action is to replace the
bolts.

Given Howard's confirmation of fatigue failure I wonder how much wash
boarded dirt roads are a factor. Is this just a Western US hazard? I
didn't even know what a wash board road was until I moved here.

Andy (GY)

On 5/17/2011 11:38 AM, Andy wrote:

I checked my bolts for security last year after YO's report. Don't
remember how much I tightened them, it at all, but the damage was
probably already done. I think the only safe action is to replace the
bolts.

Given Howard's confirmation of fatigue failure I wonder how much wash
boarded dirt roads are a factor. Is this just a Western US hazard? I
didn't even know what a wash board road was until I moved here.

Washboarded roads - maybe. Here's another data point: 1995 Cobra trailer
for ASH 26 E, 160,000 miles of highway driving, and the bolts are not
broken.

Some details:

*note that the ASH 26 E trailer body is 30 feet long, as the 18 meter
wing is only two pieces (tongue is another 4 feet)

*towed almost entirely by motorhomes

*I haven't actually pulled out the bolts to see if they are cracked

*Probably less than 1000 miles of dirt roads, including mostly roads
under repair or construction, and hardly any washboarded roads.

I will replace the bolts as soon as people settle on the best kind of bolt.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

I have 3 Wing Riggers that I need to get shipped out today, but as
soon as I get a chance I intend to investigate changing the bolts to
the next larger size, 3/8" grade 8. Of course that will mean drilling
the holes larger and it will also mean that the head will not be
neatly counterbored into the handle. If that plan works out, I will
post back here.

GW

On May 18, 9:44*am, Steve Koerner wrote:
I have 3 Wing Riggers that I need to get shipped out today, but as
soon as I get a chance I intend to investigate changing the bolts to
the next larger size, 3/8" grade 8. *Of course that will mean drilling
the holes larger and it will also mean that the head will not be
neatly counterbored into the handle. *If that plan works out, I will
post back here.

GW

I'd be interested to hear how that works out. There is a least one
spacer block inside the frame extrusion and it looks like it would
have to be extracted, drilled, and replaced. There may be two each
side. Given the limit access to the extrusion opening it could be a
bit awkward to work the inner blocks.

If I was going to larger bolts I think I'd relocate the handles and
keep them on 5/16 socket cap bolts. They wouldn't need the spacer
blocks as long as a moderate torque was used.


Andy (GY)

If this problem is primarily affecting Cobra trailers with fiberglass
tops, rather than aluminum, I wonder if the difference in thermal
coefficient of expansion between the two materials might be playing a
roll?

On early Stemme S10-VT motorgliders, the spoiler control rods were
aluminum in an otherwise mostly carbon fiber wing. The spoiler over-
center locks were at the fuselage end. As the temperature dropped with
altitude, the spoilers would first start to come open and then
sometimes even open all the way with no pilot input. Problem was
solved by changing the control rods to carbon fiber.

bumper
zz Minden

On May 21, 6:25*pm, bumper wrote:
If this problem is primarily affecting Cobra trailers with fiberglass
tops, rather than aluminum, I wonder if the difference in thermal
coefficient of expansion between the two materials might be playing a
roll?

On early Stemme S10-VT motorgliders, the spoiler control rods were
aluminum in an otherwise mostly carbon fiber wing. The spoiler over-
center locks were at the fuselage end. As the temperature dropped with
altitude, the spoilers would first start to come open and then
sometimes even open all the way with no pilot input. Problem was
solved by changing the control rods to carbon fiber.

bumper
zz Minden

Bumper might be on to something.

Polyester reinforced with glass fiber has a linear coefficient of
thermal expansion of 25 (10^-6 m/m K) while structural steel is just
13. Aluminum is 22.2 which is close enough to steel there may not be
a problem.
Ref: http://www.engineeringtoolbox.com/li...ents-d_95.html

The fiberglass top is, of course, exposed to the direct sunlight while
the steel trailer frame stays mostly in the shade.

Bill D

On May 18, 11:44*am, Steve Koerner wrote:
I have 3 Wing Riggers that I need to get shipped out today, but as
soon as I get a chance I intend to investigate changing the bolts to
the next larger size, 3/8" grade 8. *Of course that will mean drilling
the holes larger and it will also mean that the head will not be
neatly counterbored into the handle. *If that plan works out, I will
post back here.

GW

Why not use the proper metric size?

Peter

On May 18, 11:43*am, vontresc wrote:
On May 18, 11:44*am, Steve Koerner wrote:

I have 3 Wing Riggers that I need to get shipped out today, but as
soon as I get a chance I intend to investigate changing the bolts to
the next larger size, 3/8" grade 8. *Of course that will mean drilling
the holes larger and it will also mean that the head will not be
neatly counterbored into the handle. *If that plan works out, I will
post back here.

GW

Why not use the proper metric size?

Peter

Because they break.

GW