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Cobra trailer stuck closed



 
 
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  #11  
Old June 10th 18, 01:22 PM posted to rec.aviation.soaring
[email protected]
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Posts: 1,738
Default Cobra trailer stuck closed

On Sunday, June 10, 2018 at 4:30:12 AM UTC-4, Jim White wrote:
At 03:22 10 June 2018, AS wrote:
On Saturday, June 9, 2018 at 9:21:30 PM UTC-4, Steve Koerner wrote:
Uh-oh, someone doesn't understand how gas springs work:


I do - I used to design similar devices....
Uli
'AS'

It might help to unbolt the hinges and lift the lid evenly with two
winches?


LAST resort only.
Putting top back on is a very big deal.
UH
Ads
  #12  
Old June 10th 18, 02:16 PM posted to rec.aviation.soaring
Dave Nadler
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Default Cobra trailer stuck closed

On Saturday, June 9, 2018 at 5:42:23 AM UTC-6, Auxvache wrote:
... So, I'm trolling for ideas...


Sell it as is where is?
Bidding starts at?
  #13  
Old June 10th 18, 02:20 PM posted to rec.aviation.soaring
Dave Nadler
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Posts: 1,292
Default Cobra trailer stuck closed

On Saturday, June 9, 2018 at 5:42:23 AM UTC-6, Auxvache wrote:
...So, I'm trolling for ideas...


Seriously, be VERY careful.
Even with an over-head hoist, incrementally support the top with 2x4s
under top's edge-channel to ground, and keep the trailer attached to a car
(with brakes/park set).

Most likely you're going to have to repeat this;
1rst time to get the old stuff out, 2nd time to install new struts.

Careful!
And don't forget to post pictures ;-)
  #14  
Old June 10th 18, 04:49 PM posted to rec.aviation.soaring
George Haeh
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Default Cobra trailer stuck closed

The manufacturer does this all the time. It would be worthwhile contacting them for the correct procedure and equipment.
  #15  
Old June 10th 18, 05:46 PM posted to rec.aviation.soaring
Steve Koerner
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Posts: 376
Default Cobra trailer stuck closed

On Saturday, June 9, 2018 at 8:22:46 PM UTC-7, AS wrote:
On Saturday, June 9, 2018 at 9:21:30 PM UTC-4, Steve Koerner wrote:
Uh-oh, someone doesn't understand how gas springs work:


I do - I used to design similar devices....
Uli
'AS'


Well Uli let's talk gas springs for a moment...

If you actually did understand how gas springs work - the everyday gas springs used for car tailgates and glider canopies and Wing Riggers and Cobra trailers - then you would know what a silly suggestion that was. Gas springs already have a controlled leak across the piston. That is what establishes their wonderful damping property. Once stopped, there is no pressure differential across the piston at all. The nominal force produced by a gas spring does not relate to pressure across the area of it's piston (as is the case for a pneumatic drive cylinder); the gas spring force arises from the pressure exerted across the cross-sectional area of the rod itself.

Anyway, don't feel too bad about getting this wrong. I did a google search so that I could provide a link for you. Amazingly, virtually every little story that came up about how gas springs work on the internet was also wrong -- including the wikipedia article on gas springs and a bunch of youtubes on the subject. It wasn't until I downloaded a lengthy manufacturers catalog that I came upon actual sound science that tells the story correctly:
http://pdf.directindustry.com/pdf/di...57-175377.html

So back to the original poster's issue: You do not need to worry about pressure leaked to the wrong side of the piston and holding the clamshell down.. That is a red herring of the highest order.



  #16  
Old June 10th 18, 07:26 PM posted to rec.aviation.soaring
Scott Williams
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Posts: 128
Default Cobra trailer stuck closed

On Saturday, June 9, 2018 at 6:42:23 AM UTC-5, Auxvache wrote:
Anyone have any experience with the gas strut failing in the compressed position? My 2002 fiberglass top didn't quite open fully on its own in March, so I ordered replacement struts. Unfortunately, the next time out the top only opened a few feet, then progressively less as I tried to lower and then raise it. Now it is stuck closed and will not open even a crack despite two people hauling on it. Did I mention the glider is still inside? I can't get to the strut from the front door with the fuse and wing in the way.

So, I'm trolling for ideas on how to force the top open without damaging something. Thanks in advance.


Why does my cobra top not slowly close? it stays open until I drag it down.
I must admit ignorance of the internal demon that makes it work.
respect,
Scott
  #17  
Old June 10th 18, 10:26 PM posted to rec.aviation.soaring
Steve Koerner
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Posts: 376
Default Cobra trailer stuck closed


Why does my cobra top not slowly close? it stays open until I drag it down.
I must admit ignorance of the internal demon that makes it work.
respect,
Scott


Because it has two gas springs holding it up.

Or are you asking how does a gas spring work? That particular question was just answered and a link provided to a concise explanation with diagrams.
  #18  
Old June 10th 18, 10:30 PM posted to rec.aviation.soaring
Auxvache
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Posts: 24
Default Cobra trailer stuck closed

On Saturday, June 9, 2018 at 7:42:23 AM UTC-4, Auxvache wrote:
Anyone have any experience with the gas strut failing in the compressed position? My 2002 fiberglass top didn't quite open fully on its own in March, so I ordered replacement struts. Unfortunately, the next time out the top only opened a few feet, then progressively less as I tried to lower and then raise it. Now it is stuck closed and will not open even a crack despite two people hauling on it. Did I mention the glider is still inside? I can't get to the strut from the front door with the fuse and wing in the way.

So, I'm trolling for ideas on how to force the top open without damaging something. Thanks in advance.


Thanks very much everybody for the helpful replies. FWIW, the top definitely feels actively pulled down, not just mass + gravity. We'll try lifting and blocking it in steps as suggested. And yes photo documentation--probably going to be good for some laughs...
  #19  
Old June 10th 18, 10:46 PM posted to rec.aviation.soaring
Steve Koerner
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Posts: 376
Default Cobra trailer stuck closed

On Sunday, June 10, 2018 at 2:30:34 PM UTC-7, Auxvache wrote:
On Saturday, June 9, 2018 at 7:42:23 AM UTC-4, Auxvache wrote:
Anyone have any experience with the gas strut failing in the compressed position? My 2002 fiberglass top didn't quite open fully on its own in March, so I ordered replacement struts. Unfortunately, the next time out the top only opened a few feet, then progressively less as I tried to lower and then raise it. Now it is stuck closed and will not open even a crack despite two people hauling on it. Did I mention the glider is still inside? I can't get to the strut from the front door with the fuse and wing in the way.

So, I'm trolling for ideas on how to force the top open without damaging something. Thanks in advance.


Thanks very much everybody for the helpful replies. FWIW, the top definitely feels actively pulled down, not just mass + gravity. We'll try lifting and blocking it in steps as suggested. And yes photo documentation--probably going to be good for some laughs...


Even with no pressure in the cylinders, you'll still have damping force that will be resisting the rate of motion. If you lift slowly enough the damping force approaches zero; then all you'll have is gravity to deal with.
  #20  
Old June 11th 18, 12:36 AM posted to rec.aviation.soaring
Steve Leonard[_2_]
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Posts: 918
Default Cobra trailer stuck closed

On Sunday, June 10, 2018 at 8:16:04 AM UTC-5, Dave Nadler wrote:
On Saturday, June 9, 2018 at 5:42:23 AM UTC-6, Auxvache wrote:
... So, I'm trolling for ideas...


Sell it as is where is?
Bidding starts at?


I will give a hundred dollars for it.
:-)

Steve Leonard

I have dealt with two Cobra trailers that have had one strut "blow out". one was spectacular sounding. Closed the lid, then PSSSSSSSTTTT! Thought I had pinched and popped a tire! The other died when I was not there, so don't know how quickly it went. Replacing them one at a time on a metal topped trailer for a 15 meter glider just required a prop to hold it open. Glider was out, no big deal. The one on the ASH25 trailer, well, that was another story!
 




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