Cobra Trailer Spare Tire mount failure

[Barny]

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 here:
http://www.flickr.com/photos/brucebarnard/

[Mike the Strike]

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

Mike

[JJ Sinclair]

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

[JJ Sinclair]

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

[Larry Goddard]

"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 here:
> 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

[JS]

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

[Barny]

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.

[mattm[_2_]]

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

[JS]

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

[[email protected]]

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.

[Jonathan St. Cloud]

Anyone have any experience with the option offered by Cobra of mounting the spare under the trailer behind the axial?


On Sunday, September 20, 2009 at 3:44:45 PM UTC-7, JJ Sinclair wrote:

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

[[email protected]]

On Friday, July 17, 2015 at 8:43:15 PM UTC+1, Jonathan St. Cloud wrote:
> Anyone have any experience with the option offered by Cobra of mounting the spare under the trailer behind the axial?
>
>

I don't have experience of that Cobra option and don't know how it is designed. I have, however, been under a trailer that needed to be jacked up by the roadside to unbolt an under-mounted spare and it was a very worrying experience as passing vehicles blew the trailer about. I would only have an under trailer spare if the the design is such that the spare is in a cradle so that, no matter how flat the tyre, the wheel could be slid out from the side without any need to go or reach underneath.

John Galloway

[[email protected]]

I have that option, I put a plate on the inside of the trailer to help carry the load. The real problem with the initial installment is the bolts are too short and it is a real tussle to get the wheel off the bolts because as soon as one or two are loose the tire shifts against the remaining bolt and this can cause the threads to be damaged. Additionally, it is almost impossible to get the flat tire back on the bolts because of weight and short bolts. BUT, better than having the tire break off the original mount and fall on the nose of the glider.
Boise, ID

[Mark628CA]

I have an early (1983) Cobra trailer originally built for a Ventus. It is the smallest (width and height) clamshell I have ever seen. It has been retrofitted for my Pegasus, and if it was 1/4 inch smaller in any dimension, the glider would not fit inside. So, I can't keep a spare inside due to space limitations.

As a result, I built a spare tire carrier that is mounted on the side of the trailer just behind the right fender. I keep a dedicated screw jack with handle and a lug wrench and handle inside the front hatch. The last time I had a flat (actually a tread separation) on the road, it took eight minutes to swap the tire.

I didn't have to unload the fuselage or anything else. I keep a vinyl cover over the spare, but they only last a couple of years. So I spend $20 for a new one when it deteriorates.

Your best insurance concerning flat tires is to not let them get over a few years old. The tread depth may be (and probably is) just fine. What kills tires is age, oxidation (ozone) and ultraviolet exposure. A hundred bucks on a cheap set of radial tires every two or three years is cheap insurance for your $50,000 investment. I also don't bother with "ST" or trailer tires, as they are more expensive and (in my opinion) don't offer any more protection, reliability or longevity.

A lot of this comes from my own experience, as well as from airshow pilot Bob Carlton, who has been dragging glider trailers to airshows around the country for twenty years, logging as many as 30,000 miles or more every year.

Anybody want to buy a slightly used enclosed trailer for a 13 meter glider? Only 650,000 miles. Good tires.

[howard banks]

One time some years back when this fatigue failure mode came up on RAS I asked Mark Mocho about it. He created an external spare wheel mount on the side of the trailer, just in front of or closely behind the wheel (can't recall which). Put on a cover to keep the sun off the tire. Worked well.
Don't have it on present Cobra, though perhaps should.
Ask Mocho at M&M Fabrication.
HL.





On Sunday, September 20, 2009 at 11:56:12 AM UTC-6, Barny wrote:
> 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 here:
> http://www.flickr.com/photos/brucebarnard/

[Andrzej Kobus]

The tire is in front of the axle not behind in that option.

[Mark628CA]

I am in awe of the marketing penetration of M&M candies. My business is "MM Fabrication." 95% of the people who write checks, offer references or email me always write "M&M."

Wish I had thought of it first.

[[email protected]]

> As a result, I built a spare tire carrier that is mounted on the side of the trailer just behind the right fender.

Mark, have you had any wear or bending of the cobra trailer wall?

Also, kits, pics, do you sell????

I also have a 85 cobra with spare under the fuselage inside. Would like to go outside.

Kevin
92

[Mark628CA]

Harbor Freight has a spare tire bracket that looks like it will bolt to the side of the trailer. If I built a kit, it would look a lot like this and cost more, so you might as well try this one:

http://www.harborfreight.com/trailer-spare-tire-carrier-93341.html

Be sure to locate it where the bolt heads on the inside of the trailer wall will not interfere with the wing dollies or the wing itself. I recommend using round head carriage bolts. It may be obvious to most people, but do not drill through the trailer side without taking your wing out first.

Mine is located just in front of the right fender. I have not seen any evidence of bending, but try to support the tire in such a way that it is not cantilevered. There are other types Like this one:

http://www.etrailer.com/Trailer-Cargo-Control/Redline/413200.html

It can be mounted vertically, so the load is spread over a larger area of the sidewall.

[HGXC[_4_]]

On Friday, July 17, 2015 at 9:25:10 PM UTC-4, Mark628CA wrote:
> I have an early (1983) Cobra trailer originally built for a Ventus. It is the smallest (width and height) clamshell I have ever seen. It has been retrofitted for my Pegasus, and if it was 1/4 inch smaller in any dimension, the glider would not fit inside. So, I can't keep a spare inside due to space limitations.
>
> As a result, I built a spare tire carrier that is mounted on the side of the trailer just behind the right fender. I keep a dedicated screw jack with handle and a lug wrench and handle inside the front hatch. The last time I had a flat (actually a tread separation) on the road, it took eight minutes to swap the tire.
>
> I didn't have to unload the fuselage or anything else. I keep a vinyl cover over the spare, but they only last a couple of years. So I spend $20 for a new one when it deteriorates.
>
> Your best insurance concerning flat tires is to not let them get over a few years old. The tread depth may be (and probably is) just fine. What kills tires is age, oxidation (ozone) and ultraviolet exposure. A hundred bucks on a cheap set of radial tires every two or three years is cheap insurance for your $50,000 investment. I also don't bother with "ST" or trailer tires, as they are more expensive and (in my opinion) don't offer any more protection, reliability or longevity.
>
> A lot of this comes from my own experience, as well as from airshow pilot Bob Carlton, who has been dragging glider trailers to airshows around the country for twenty years, logging as many as 30,000 miles or more every year.

[[email protected]]

Thanks,

Did you do a flat plate or anything inside to reinforce instead of metal pieces like in on the harbor freight design?

Kevin

[BobW]

On 7/18/2015 9:15 AM, Mark628CA wrote:

> It may be obvious to most people, but do
> not drill through the trailer side without taking your wing out first.

Ha ha ha! Years ago I was drilling out rivets on both sides of an HP-14
aileron rib. All went as planned until on the second side near the trailing
edge. When the drill broke through it happened to be perfectly aligned with
the rivet hole on the (nearby) opposite side, a possibility I hadn't
considered. I still have the scar in the palm of my other hand from the chunk
of muscle and tissue that was attached to the drill bit upon extraction. At
least the sheet metal holes ended up round and not oversize...

Bob W.

[Mark628CA]

Kevin-

I didn't reinforce the inside, as the extruded aluminum sidewall of the trailer is pretty stiff and the round head bolts have a pretty large bearing surface, but then the design I used is more like the second example from Etrailer.com. It spreads the load pretty well from top to bottom. I think even the Harbor Freight model would work, but a lot depends on how heavy the spare is and whether it sticks way out, increasing the lever arm. Rough roads will also exaggerate the load, which is why I would prefer the Etrailer model.

[2G]

The problem with this design has 2 major problems:

1. The stress generated by the motion of the spare fore and aft is directly transmitted to these 2 8mm bolts.

2. The 8mm bolts are welded to the mount. Welding changes the metallurgical nature of the bolts, embrittling them at the weld (https://en.wikipedia.org/wiki/Hydrogen_embrittlement).

Your fix solves the first problem by adding a 3rd mounting point, but does nothing about the 2nd problem. At least if the weld breaks again you have redundancy. I would prefer to see a flat plate welded to the upright pieces (wand gussets for more lateral strength) with the bolts attached by lock nuts (no welds). Then you know you will have their full strength. A loose tire banging around the inside of the trailer can do an incredible amount of damage, so a design overkill is clearly warranted.

My Cobra trailer has this same inadequate spare tire mount, but it is not used. Instead, the tire is sitting on the floor upright, secured to the storage bin by a single large threaded rod.

Tom

[[email protected]]

Good suggestions all around. Has anyone tried mounting the spare on top of the trailer?

Mark

[[email protected]]

On Tuesday, July 21, 2015 at 7:17:16 PM UTC-4, wrote:
> Good suggestions all around. Has anyone tried mounting the spare on top of the trailer?
>
> Mark

How about putting the spare in the storage box under the trailer, will it fit?
Glen

[Papa3[_2_]]

I did the under-side mod this weekend as well. Made up a backing plate to help spread the load on the inside of the trailer. I mounted mine just behind the axle to avoid interfering with the surge brake mechanism. 4 grade 8 bolts poking down through the floor locked in place with jam nuts and fender washers on the bottom. Rim goes through the lug holes and held in place with 4 more nylock nuts with washers. Bought an aftermarket spare tire cover to keep everything from getting too messy - we'll see how/if that hold up. While I don't love the idea of crawling under the trailer, I figure that the flat tire can temporarily sit in the front of the trailer until we get to a convenient location to repair and put everything back where it belongs. In 25 years of trailering gliders I've only had 2 flats while on the road (maybe I've been lucky?), so hopefully it's a rare event.

[[email protected]]

Just to close the [recent] loop, I mounted my spare flat on the floor under the nose of the glider. BTW, I was able to "reuse" the hole in the trailer floor where a bolt securing a bracket under the floor was already secured. The bracket is a simple strut that supports the brake rod about half way back from the coupler to the axle and keeps it from flapping around. I noticed that the bracket had been bent back by a previous collision with something under the trailer, not seriously but enough that it would have given me pause to locate the spare tire there. There's not much load on the bracket or the spare tire.

I have 13" wheels but went up one size in tire the last time I bought them to get more ground clearance (don't recall the size). As a result, the tire is JUST small enough to lie flat between the wings and not interfere with the spar dollies rolling in and out. Conceptually, the factory mounting the tire above the nose cone gives a lot more flexibility because there's more width there (due to the wing root shape) and the dollies are irrelevant. But obviously the load on the mount is a lot higher.

Chip Bearden
ASW 24 "JB"
U.S.A.

[[email protected]]

And, yes, getting at the spare will require pulling out the fuselage on the side of the road. But that's a reasonable price to pay for me even though I've had more than a few trailer flats over the years.

Chip Bearden
ASW 24 "JB"
U.S.A.

[6PK]

On Tuesday, July 21, 2015 at 5:57:59 PM UTC-7, wrote:
> On Tuesday, July 21, 2015 at 7:17:16 PM UTC-4, wrote:
> > Good suggestions all around. Has anyone tried mounting the spare on top of the trailer?
> >
> > Mark
>
> How about putting the spare in the storage box under the trailer, will it fit?
> Glen

That is exactly where I keep mine. With the jack and all the other tools needed.
P.S. I find this box cumbersome for regular use. The rollers tend to not work too well after a while, but is a perfect place for the spare.