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.

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

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

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.

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.

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

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.

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

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.

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...ier-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-Carg...ne/413200.html

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