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Cobra trailer stuck closed



 
 
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  #21  
Old June 11th 18, 04:01 AM posted to rec.aviation.soaring
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Default Cobra trailer stuck closed


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!


Most Cobra trailers have a hole drilled through one strut (the port strut for my trailer) so that a pin can be inserted to ensure the top stays fully open. I assume the purpose is safety, to prevent the top crashing down if a strut fails.

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  #22  
Old June 11th 18, 05:14 AM posted to rec.aviation.soaring
Charlie Quebec
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Default Cobra trailer stuck closed

So younke-tbpooking until you found an answer that agreed with you, then ignored all other evidence?
  #23  
Old June 11th 18, 01:26 PM posted to rec.aviation.soaring
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Default Cobra trailer stuck closed

Don't be an ass, CQ. Steve knows his stuff. Gas springs do not just have pressure on one side of the piston. It is the volume of the rod that compresses the gas as it retracts and takes up more space in the cylinder. The small orifice in the piston that allows gas to pass by the piston also regulates the rate at which the rod extends.

WingRiggers as developed by Steve Koerner and now produced by MM Fabrication use gas springs, so the design and mechanics are well understood by us. Plus, we just had to cut a few apart for fun.
  #24  
Old June 11th 18, 07:25 PM posted to rec.aviation.soaring
Bob Kuykendall
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Default Cobra trailer stuck closed

On Monday, June 11, 2018 at 5:27:01 AM UTC-7, wrote:
...Steve knows his stuff...


The guys who designed the 737 rudder PCU knew their stuff.
  #25  
Old June 11th 18, 07:54 PM posted to rec.aviation.soaring
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Default Cobra trailer stuck closed

Irrelevant.
  #26  
Old June 11th 18, 08:18 PM posted to rec.aviation.soaring
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Default Cobra trailer stuck closed

You know.
These forums are degrading into gutter talk and condescension way too often and way too quickly. People being off topic should be immediately blocked. Those with verbal trigger fingers should chill out.
GROW UP !!!
  #27  
Old June 11th 18, 09:20 PM posted to rec.aviation.soaring
Bob Kuykendall
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Default Cobra trailer stuck closed

On Monday, June 11, 2018 at 11:54:14 AM UTC-7, wrote:
Irrelevant.


Fully relevant. Engineers were surprised to discover that under certain conditions of wear and abuse, the PCU would produce outputs that were exactly the opposite of those commensurate with the input conditions.

I've disassembled three or four different types of gas spring (each of my gliders has two), and I'm pretty sure that there are possible failure modes in which the unit resists opening instead of assisting it. They're probably not common failures, but I'd bet solidly against impossible.

Bob K.
  #28  
Old June 11th 18, 09:32 PM posted to rec.aviation.soaring
Charlie M. (UH & 002 owner/pilot)
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Default Cobra trailer stuck closed

In general, yes, forums have some volunteer staff.
RAS seems to be outside this.
I am staff on other forums, good luck on "moderating" on RAS.

Hopefully I don't fall under your negative comments......

Whatever, there IS good info here, just takes some sifting......
  #29  
Old June 11th 18, 10:52 PM posted to rec.aviation.soaring
AS
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Default Cobra trailer stuck closed

On Monday, June 11, 2018 at 4:20:38 PM UTC-4, Bob Kuykendall wrote:
On Monday, June 11, 2018 at 11:54:14 AM UTC-7, wrote:
Irrelevant.


Fully relevant. Engineers were surprised to discover that under certain conditions of wear and abuse, the PCU would produce outputs that were exactly the opposite of those commensurate with the input conditions.

I've disassembled three or four different types of gas spring (each of my gliders has two), and I'm pretty sure that there are possible failure modes in which the unit resists opening instead of assisting it. They're probably not common failures, but I'd bet solidly against impossible.

Bob K.


Just catching up with this thread now and finding the very belittling response by Steve to my suggestion deeply insulting! When I said that I understand the inner workings of a gas spring and that I designed similar devices, than that is fact based. We carefully took apart several different gas springs and then designed a gigantic version of it - the type that holds down the tag-axle of a concrete mixer truck! It had some other functionalities built in but I will not get into that.
Steve is correct in describing the type of spring he took apart and that the kind of behavior as described by the original poster with those types is unlikely but is that the only type? How does he know that this is the type used in that particular trailer?
As other posters mentioned above, the sniping and 'I know it all and the rest of you are stupid for suggesting otherwise' is highly unprofessional and discouraging towards posting anything. The purpose of this and similar fora is to exchange ideas and help each other out in solving issues we have with our equipment; not to pile-drive others.
N'uff said!
Auxvache, good luck in getting the trailer opened up again and please keep us posted as to what you find out.
Uli
'AS'
  #30  
Old June 12th 18, 12:24 AM posted to rec.aviation.soaring
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Default Cobra trailer stuck closed

On Sunday, June 10, 2018 at 5:46:03 PM UTC-4, Steve Koerner wrote:
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.


I like Steve's idea. Maybe use an engine hoist or such on the rear handles with a bit more than top weight( say 200 lb), walk away and see if it starts to creep open.
Another voice hear from.
UH
 




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