Cobra Trailer

Thanks for all the input. I like the move to a warmer part of the
country.

They are the square struts and seem to work well when it's warmer and
stay up without any indication of falling.

We need to open them when it's cold to do some work so we can fly when
it's warmer.

Bob


On Dec 4, 4:39 pm, Tony Verhulst wrote:
wrote:
My Cobra trailer is difficult to open and close in colder weather. It
seems to be with the struts. Any suggestions?On the other side of the coin.... I had a strut fail last season on my
almost 20 year old Komet trailer. Fortunately, the shell was not open
with the glider partially removed at the time. That would have been bad.
I simply showed up one morning and the shell was VERY difficult to raise
and would not stay up.

Tony V.

I have a Komet trailer whose top will barely stay up in cold weather. I
know, I need to replace the gas struts. I figure winter is a good time to
do this since the struts expand with less force when cold.

To get the trailer open with less effort, try making a tube around the cold
struts with plastic sheet and duct tape and then direct hot air from a hair
dryer through the tubes to heat the struts.

Here's a trick I've used to replace smaller struts; compress them with a
drill press and lock the spindle to hold the strut compressed. Use safety
wire to secure the strut at the compressed length - don't put the wire
through the mounting holes. Bolt the strut in place and then cut the safety
wire. The same proceedure can be used to safely remove the old struts. Be
careful, there's a lot of energy in a compressed strut.

Whenever I'm faced with an OEM part replacement, I look around to see if the
money could be better spent on an upgrade. One thing that caught my eye is
the 12V electric ball screws that boat people use to open hatches. These
things are often on E-bay for less than $100. A pair of them could easily
open the Komet top. How cool would it be to open a trailer by just pushing
a button.

Bill Daniels


wrote in message
ups.com...
Thanks for all the input. I like the move to a warmer part of the
country.

They are the square struts and seem to work well when it's warmer and
stay up without any indication of falling.

We need to open them when it's cold to do some work so we can fly when
it's warmer.

Bob


On Dec 4, 4:39 pm, Tony Verhulst wrote:
wrote:
My Cobra trailer is difficult to open and close in colder weather. It
seems to be with the struts. Any suggestions?On the other side of the
coin.... I had a strut fail last season on my
almost 20 year old Komet trailer. Fortunately, the shell was not open
with the glider partially removed at the time. That would have been bad.
I simply showed up one morning and the shell was VERY difficult to raise
and would not stay up.

Tony V.

Whenever I'm faced with an OEM part replacement, I look around to see if the
money could be better spent on an upgrade. One thing that caught my eye is
the 12V electric ball screws that boat people use to open hatches. These
things are often on E-bay for less than $100. A pair of them could easily
open the Komet top. How cool would it be to open a trailer by just pushing
a button.

I prefer to keep things simple and got factory replacements struts.
Pricey at US$125 each - but I don't have to worry about having power at
the trailer. To each his own, of course. But you're right,it would be
way cool :-).

Tony V.

Tony Verhulst wrote:
Whenever I'm faced with an OEM part replacement, I look around to see if the
money could be better spent on an upgrade. One thing that caught my eye is
the 12V electric ball screws that boat people use to open hatches. These
things are often on E-bay for less than $100. A pair of them could easily
open the Komet top. How cool would it be to open a trailer by just pushing
a button.

I prefer to keep things simple and got factory replacements struts.
Pricey at US$125 each - but I don't have to worry about having power at
the trailer. To each his own, of course. But you're right,it would be
way cool :-).

Tony V.
The trailer that I saw with the Duster that JJ built had a clamshell
fitted with jet canopy hydraulic lifters. That was very interesting
and easy to use.

Frank W.

Tony Verhulst wrote:
wrote:
My Cobra trailer is difficult to open and close in colder weather. It
seems to be with the struts. Any suggestions?

On the other side of the coin.... I had a strut fail last season on my
almost 20 year old Komet trailer. Fortunately, the shell was not open
with the glider partially removed at the time. That would have been bad.
I simply showed up one morning and the shell was VERY difficult to raise
and would not stay up.

Same thing happened last year to my ~3 year old Komet. :-(

So I replaced both and now have a spare. Well "I replaced" being "left
the trailer and new struts with Rex" of course. :-)

Jeremy

Eric Greenwell wrote:
The struts in my Cobra are 12 years old and just as strong as when I got
it; the ones in my mini-van generally go 8-10 years. I think the metal
pieces around Bob's struts need cleaning and grease, as bumper
mentioned. My trailer needs it every 5 years or so, or it gets a bit
balky regardless of the temperature.

I'm with Eric. MY Cobra trailer is nearly 15 years old and the struts
are still incredibly strong. My ASW 24, on the other hand [it was an
extra-cost accessory that came with the trailer ], has a gas spring
that holds up the canopy that has needed replacing for some time (I
haven't been brave enough to dive into the assembly yet). The gas
spring in my LS-3 landing gear seemed to go 3-4 years before it got
soft. And, worst case, I had a spare LS-3 gas spring in my tool box for
some years that was marginal by the time it was needed to install it.

I've never opened my Cobra's square tube linkages where the gas springs
live but I suspect one reason for the longevity is that the springs are
mounted so that the lubricating oil is always around the piston rod and
seal rather than up at the higher end of the cylinder where it doesn't
do any good. IIRC, one problem with my LS-3 gas spring was that it was
mounted so that it was in the "correct" position when the gear was
extended but upside down when retracted (or vice versa). On my Cobra
trailer, it's easy: just mount them in the correct position and they're
always oriented that way.

Dust and grit that settle on the piston rod and abrade the seal also
shorten the life. My Cobra springs are inside the trailer but the ones
on my 1978 Komet trailer were mounted unprotected from the weather
outside the trailer. I believe they also changed orientation as they
extended meaning that the oil was at the wrong end of the cylinder part
of the time no matter what.

It also could be that gas spring technology is simply better now than
it used to be.

Chip Bearden
ASW 24 "JB"

wrote:


I've never opened my Cobra's square tube linkages where the gas springs
live but I suspect one reason for the longevity is that the springs are
mounted so that the lubricating oil is always around the piston rod and
seal rather than up at the higher end of the cylinder where it doesn't
do any good.

Gas spring manufacturers say to mount the rod on the bottom for that
reason, something I didn't appreciate when I replaced them on my
mini-van the first time. The second set of replacements has lasted a lot
longer!

The small gas spring (like the one on the front Cobra door) on my
engine's retraction system seems to need replacing every 5 years. I
attribute this to the high engine bay temperatures after the engine
retracts and the doors close.

The temperature range I've see specified for gas springs is -30 F to
+175 F, unless you pay extra. I cautiously avoid opening my trailer at
either extreme .

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

You seem to have much better luck with gas struts than
I do.
The two struts that hold open the rear hatch on my
Mercedes ML lost all their power at the first cold
snap after 3 years. The replacements failed after
two years. The two struts on my Mercedes SLK had to
be replaced after 4 years because they would no long
hold the trunk lid up. The two big struts on my Avionics
trailer fail to hold up the lid starting this fall
after 6 years. The gas strut holding the canopy open
on my SZD-59 failed to hold the canopy open this fall
after 5 years. Every one of these struts is mounted
with the rod end down.
Guy

One more factor: in my experience, gas springs tend to deteriorate over
time to about half their original force and then plateau (although
that's a generalization based on a relatively few measurements). I
assume that's because the high gas pressures leak down only to a
certain extent, not to atmospheric pressure/zero. In that case, springs
that are overdesigned (i.e., higher-than-necessary pressures and/or
larger cylinder bores) might still be adequate for the job even after
degrading substantially.

I wouldn't necessarily advocate replacing a weak cylinder with one that
is substantially stronger than the OEM's spec. The mounting points may
not be designed for those loads. And it might not be desireable, for
example, if the hood of your automobile sprang up and hit you in the
face when you released it. But the gas spring manufacturers sell
just about any combination of compressed length, extended length,
mounting type, diameter, force, etc., so it's possible.

Chip Bearden
ASW 24 "JB"

Hmmm, there's the potential for entertainment value here! Let's if I have
the mental image straight . . .

On my 4 year old Cobra, the stock springs are already so strong that I get
light in my tennies a hangin' on trying to close the lid. If they were much
stronger, I'd lose, get launched, or both. (g)

bumper

wrote in message
oups.com...
One more factor: in my experience, gas springs tend to deteriorate over
time to about half their original force and then plateau (although
that's a generalization based on a relatively few measurements). I
assume that's because the high gas pressures leak down only to a
certain extent, not to atmospheric pressure/zero. In that case, springs
that are overdesigned (i.e., higher-than-necessary pressures and/or
larger cylinder bores) might still be adequate for the job even after
degrading substantially.

I wouldn't necessarily advocate replacing a weak cylinder with one that
is substantially stronger than the OEM's spec. The mounting points may
not be designed for those loads. And it might not be desireable, for
example, if the hood of your automobile sprang up and hit you in the
face when you released it. But the gas spring manufacturers sell
just about any combination of compressed length, extended length,
mounting type, diameter, force, etc., so it's possible.

Chip Bearden
ASW 24 "JB"