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Cobra Trailer Spare Tire mount failure



 
 
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  #1  
Old September 20th 09, 06:56 PM posted to rec.aviation.soaring
Barny
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Posts: 95
Default Cobra Trailer Spare Tire mount failure

Just a warning to check your trailer spare before a trip and along the
way at gas stops. My 1998 trailer spare tire mount broke on a highway
trip. The wheel is mounted on the frame that holds the glider nose in
place. Two 8mm bolts welded to the nose cone frame hold the wheel to
the frame. One bolt sheared and the other broke away at one of the
welds. I was extremely lucky that the wheel didn't go through the
canopy or damage a wing. The wheel was dangling on the remaining bolt
with the broken weld, the tire tread was 5mm from the wing. It didn't
touch the wing or canopy, so I was "spared" a horrific tragedy.
I had a small shop weld two new 8mm bolts in place. I then added a
third mount to the Cobra design to keep the wheel from rocking on the
existing mount. I suspect the wheel weight rocking caused the
failure. The third leg is very easy to make and install yourself.
Use a small metal bar from a home improvement store, two bolts,
washers and nuts. Photos of the broken mount and new third leg can be
seen he
http://www.flickr.com/photos/brucebarnard/
  #2  
Old September 20th 09, 07:43 PM posted to rec.aviation.soaring
Mike the Strike
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Posts: 952
Default Cobra Trailer Spare Tire mount failure

Mine failed in the same way. It seems to be a design feature of the
Cobra, like the hydraulic ramp jack.

Mike
  #3  
Old September 20th 09, 08:37 PM posted to rec.aviation.soaring
JJ Sinclair
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Posts: 388
Default Cobra Trailer Spare Tire mount failure

On Sep 20, 11:43*am, Mike the Strike wrote:
Mine failed in the same way. *It seems to be a design feature of the
Cobra, like the hydraulic ramp jack.

Mike


I never did like suspending all that weight with no part of the tire
resting on the floor, ala Komet.
JJ
  #4  
Old September 20th 09, 11:44 PM posted to rec.aviation.soaring
JJ Sinclair
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Posts: 388
Default Cobra Trailer Spare Tire mount failure

On Sep 20, 12:37*pm, JJ Sinclair wrote:
On Sep 20, 11:43*am, Mike the Strike wrote:

Mine failed in the same way. *It seems to be a design feature of the
Cobra, like the hydraulic ramp jack.


Mike


I never did like suspending all that weight with no part of the tire
resting on the floor, ala Komet.
JJ


My fix was to mount the spare flat on the floor under the fuselage
nose. This means I would have to remove the fuselage to get the spare
out, but I have only had to change one tire in 35 years. Now, watch me
blow a tire next week on my way to Williams!
JJ
  #5  
Old September 21st 09, 05:05 AM posted to rec.aviation.soaring
Larry Goddard
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Posts: 66
Default Cobra Trailer Spare Tire mount failure


"Barny" wrote in message
:

Just a warning to check your trailer spare before a trip and along the
way at gas stops. My 1998 trailer spare tire mount broke on a highway
trip. The wheel is mounted on the frame that holds the glider nose in
place. Two 8mm bolts welded to the nose cone frame hold the wheel to
the frame. One bolt sheared and the other broke away at one of the
welds. I was extremely lucky that the wheel didn't go through the
canopy or damage a wing. The wheel was dangling on the remaining bolt
with the broken weld, the tire tread was 5mm from the wing. It didn't
touch the wing or canopy, so I was "spared" a horrific tragedy.
I had a small shop weld two new 8mm bolts in place. I then added a
third mount to the Cobra design to keep the wheel from rocking on the
existing mount. I suspect the wheel weight rocking caused the
failure. The third leg is very easy to make and install yourself.
Use a small metal bar from a home improvement store, two bolts,
washers and nuts. Photos of the broken mount and new third leg can be
seen he
http://www.flickr.com/photos/brucebarnard/




Do you ever use a motorhome to pull the trailer? I have known of
another one that failed which had been pulled almost exclusively by a
motorhome with its significantly greater tossing about of the trailer.


Larry






  #6  
Old September 21st 09, 05:15 PM posted to rec.aviation.soaring
JS
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Posts: 1,384
Default Cobra Trailer Spare Tire mount failure

There have been a couple of other versions of the Cobra spare tire
mount.
Under the nose on the floor works if there is room (vintage 1988) If
the tire is too large you'll need a towel over it so the glider belly
doesn't turn black. As JJ mentions, the fuselage comes out to get to
the spare, but not a headache the one time I used it.
Bolted (upright, across the trailer) to the front of the vertical
tube holding the nose cone (vintage 1999) works too, if there is room
behind the storage bin.
Jim
  #7  
Old September 21st 09, 11:53 PM posted to rec.aviation.soaring
Barny
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Posts: 95
Default Cobra Trailer Spare Tire mount failure

Cobra should extend the top steel tube another 20mm in both directions
to capture the bolt with holes. Then tack weld the bolt heads for anti
rotation. The wheel has plenty of clearance for a longer cross-tube.
You still need the third leg to prevent bolt fatigue failure from the
constant rocking.
  #8  
Old September 22nd 09, 04:04 PM posted to rec.aviation.soaring
mattm[_2_]
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Posts: 167
Default Cobra Trailer Spare Tire mount failure

On Sep 21, 6:53*pm, Barny wrote:
Cobra should extend the top steel tube another 20mm in both directions
to capture the bolt with holes. Then tack weld the bolt heads for anti
rotation. The wheel has plenty of clearance for a longer cross-tube.
You still need the third leg to prevent bolt fatigue failure from the
constant rocking.


I'm reading all of this with interest. My new plane (ASW-19) lives in
a Cobra trailer (older -- it has ASW-24 stickers on it). The previous
owner
found that the fuselage is too long to fit very well, and ended up
rotating that
upright column 180 degrees to get things to fit. However, the spare
tire
mount bolts now point back toward the plane so the spare can't be
mounted (the box doesn't fit either but that's another story). For
the moment
the spare is riding in the under-trailer storage box behind the main
axle,
but that causes cg problems for the trailer (tongue weight is like a
feather).

I'm looking for ideas how to mount the spare up front now. The under
nose
option above sounds promising -- how do you anchor down the tire? I'm
also
thinking of using some angle iron so that the tire can hang on the
front of the
column, but it will be more vertical. Will it fit?

Thanks,
-- Matt
  #9  
Old September 23rd 09, 06:42 AM posted to rec.aviation.soaring
JS
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Posts: 1,384
Default Cobra Trailer Spare Tire mount failure

A 14" wheel and tire will just fit vertically across the trailer
without contacting the wing. If it's 13", as many older trailers were,
there will be plenty of room. Mount it so the tire rests on the floor
so there is less stress on the anchoring bolts and upright.
It sounds like you've already had to remove the storage bin, so
forward space may be at a premium. An earlier (1988) trailer fit the
13" wheel between the tracks and under the glider's nose, lying on the
floor with a bolt through it and secured with a wing nut. Best to
reinforce the floor to do that mod. A thin alloy plate on the
underside should do the trick. You may also find the fuselage will rub
the spare tire if the tire is too wide (perhaps anything above a 185)
so use a narrow tire for the spare.
Incidentally for anyone with 13" wheels who would like more ground
clearance, Spindelberger builds a lift kit (25mm or 50mm height) which
goes between the axle and frame. Much less scraping the tail, and if
you have a storage drawer it will last longer. I think the kit was
only 60 or 80 Euros and was easy to install on an empty trailer
sitting on four jack stands. It will be a special order item.
Jim


I'm looking for ideas how to mount the spare up front now. *The under
nose
option above sounds promising -- how do you anchor down the tire? *I'm
also
thinking of using some angle iron so that the tire can hang on the
front of the
column, but it will be more vertical. *Will it fit?

Thanks,
-- Matt


  #10  
Old July 17th 15, 07:31 PM posted to rec.aviation.soaring
[email protected]
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Posts: 580
Default Cobra Trailer Spare Tire mount failure

Six years later, in my 1992 Cobra the vertical post that holds the fuselage nose cone and the spare tire broke at the base, allowing the whole assembly to topple backwards when the fuselage was removed. Apart from cracking the thin wall of the storage bin, no consequential damage.

The post is retained by two vertical, upward-facing bolts at the base, their heads welded onto the "U" bracket that secures the aft end of the trailer tongue. One of the bolts broke off leaving the head still attached. The other weld failed, allowing the bolt to break loose.

It's just one more thing to inspect periodically. If your trailer is similar (every Cobra/Komet seems to be slightly more evolved), pull the fuselage out and climb up into the trailer. Then go forward with a flashlight and check the bottom of the post to ensure both bolts are solid. Rock the nose cone/spare tire to make sure. If you reach in from the front door and try to yank on the tire or nose cone when the fuselage is in the trailer, the fuselage will prevent movement from side to side or backward and a single bolt will prevent it from rocking forward even if the other bolt is broken.

One nice change: this stuff usually happens at a contest.

BTW, I didn't want to deal with removing the wings/fuselage, then towing it over to have someone weld it all up again (and tell me it's a bad design--which it is, notwithstanding the 20+ years it sufficed). So I drilled through the bracket and tongue where the upward-facing bolts had been welded and replaced them with downward facing Grade 8 bolts secured with washers/nuts inside the tongue. A little awkward to reach in there but it will do for a while. I plan to reinforce the post and possibly move the spare tire to another location per the discussion in the 2009 thread.

Chip Bearden
ASW 24 "JB"
U.S.A.
 




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