1981 Cobra trailer gas struts

[David Cleveland]

I have a 1981 Cobra trailer designed for a single seat glider. The trailer design is of the type that has the struts located on the outside of the trailer, with an aluminum top. I am looking to replace the gas struts.

I have contacted Wings and Wheels. They have been very helpful, but they do not carry the struts for this design. They also mentioned that Spindelberger/Cobra do not carry the item.

I am looking for two things. My struts were painted in the past, so I am unable to get the read the strength of the strut. I am also looking for a recommendation for replacement or refurbish.

Thanks

David Cleveland
Salt Lake City

[Dan Daly[_2_]]

On Friday, December 13, 2019 at 7:54:33 AM UTC-5, David Cleveland wrote:
> I have a 1981 Cobra trailer designed for a single seat glider. The trailer design is of the type that has the struts located on the outside of the trailer, with an aluminum top. I am looking to replace the gas struts.
>
> I have contacted Wings and Wheels. They have been very helpful, but they do not carry the struts for this design. They also mentioned that Spindelberger/Cobra do not carry the item.
>
> I am looking for two things. My struts were painted in the past, so I am unable to get the read the strength of the strut. I am also looking for a recommendation for replacement or refurbish.
>
> Thanks
>
> David Cleveland
> Salt Lake City

If you message the factory (Agnes Spindelberger whose e-mail contact info is at https://www.cobratrailer.com/?page_id=1227&lang=en ) with your trailer serial number they will probably be able to help you. They usually go to the SSA Convention (very interesting demos of setting the brakes correctly if you ask) and have brought things like replacement struts with them in the past (there is a 2016 thread where they did that) if you (or a club member) is going. If not, the Euro is down and shipping is relatively cheap.

[JS[_5_]]

On Friday, December 13, 2019 at 4:54:33 AM UTC-8, David Cleveland wrote:
> I have a 1981 Cobra trailer designed for a single seat glider. The trailer design is of the type that has the struts located on the outside of the trailer, with an aluminum top. I am looking to replace the gas struts.
>
> I have contacted Wings and Wheels. They have been very helpful, but they do not carry the struts for this design. They also mentioned that Spindelberger/Cobra do not carry the item.
>
> I am looking for two things. My struts were painted in the past, so I am unable to get the read the strength of the strut. I am also looking for a recommendation for replacement or refurbish.
>
> Thanks
>
> David Cleveland
> Salt Lake City

To me replacement seems easiest.
Open the trailer once with bad struts, close it with good ones the same day.
Do it with the assistance of a hoist if possible. It's easier to access everything and generally less unnerving if the glider is out.
Believe Ralf is the parts contact, but yes, Alfred and Agnes can bring some small parts to the convention. They are a pleasure to deal with.
rdiestertich cobratrailer com
Jim

[Nick Kennedy[_3_]]

Dave
Theres a guy in Canada " Strutwise" who rebuilds your struts at a resonable cost. and quick turnaround.
Google it and you can call him.
Good Luck
T

[Dennis Vreeken]

Just an FYI on strut wise. He is not well and it took a year to get something done . It also ended up wrong as well . YMMV.

[Richard Pfiffner[_2_]]

On Friday, December 13, 2019 at 4:54:33 AM UTC-8, David Cleveland wrote:
> I have a 1981 Cobra trailer designed for a single seat glider. The trailer design is of the type that has the struts located on the outside of the trailer, with an aluminum top. I am looking to replace the gas struts.
>
> I have contacted Wings and Wheels. They have been very helpful, but they do not carry the struts for this design. They also mentioned that Spindelberger/Cobra do not carry the item.
>
> I am looking for two things. My struts were painted in the past, so I am unable to get the read the strength of the strut. I am also looking for a recommendation for replacement or refurbish.
>
> Thanks
>
> David Cleveland
> Salt Lake City

Dave,

https://www.industrialgassprings.com/

Give me a call

Richard
www.craggyaero.com

[[email protected]]

Here is another possible source:
https://store.easylift.com/gas-springs/

[David Cleveland]

On Friday, December 13, 2019 at 7:44:41 PM UTC-7, wrote:
> Here is another possible source:
> https://store.easylift.com/gas-springs/

Great response guys. Thanks.

So, as for response;

Nick: Thanks for the Strutwise lead. I've got a friend of mine here in Salt Lake that confirmed his illness. Too bad. I'll reach out just in case.

Richard: I'll give you a call tomorrow. Thanks.

Jim: I hadn't heard of Easylift. I'll reach out to them on Monday.

I've got a query in with Ralf at Spindelberger, as well as the folks at Wings and Wheels. We'll see what turns up. The last word I received was that Spindelberger records for 1981 are a bit sketchy.

The one remaining issue is that I don't know the original strength of the strut. I know that the design that places the strut inside the trailer calls for a gas strut strength of 900N. The folks at Wings and Wheels said the exterior strut design strength may be 760N.

Mine still work, but on a cold day it's a real heft to get the upper clamshell open. I'd hate to replace the struts and then end up with the same situation if the strength is too low.

[Dennis Cavagnaro]

Hi Dave...I have the same trailer and replaced mine with 1100N from Williams and they work fine. I couldn’t locate the 900Ns . One strut was broken so i couldn’t wait to locate the 900n.

DC

[Dan Marotta]

Or have the opposite condition.

I met Tom Bjork on a typically windy Moriarty day when I noticed him
dangling from the lid of his Cobra.Â* I ran to his aid and, together, we
got the top down.Â* It started a great friendship...

On 12/13/2019 9:30 PM, David Cleveland wrote:
> Mine still work, but on a cold day it's a real heft to get the upper clamshell open. I'd hate to replace the struts and then end up with the same situation if the strength is too low.

--
Dan, 5J

[David Cleveland]

Dennis, you have a trailer with the struts on the outside? And 1100N wasn't too much to pull down? That's good to know. I don't want to get into the situation Dan describes. I've seen that a few times myself.

[Nick Kennedy[_3_]]

On Friday, December 13, 2019 at 5:54:33 AM UTC-7, David Cleveland wrote:
> I have a 1981 Cobra trailer designed for a single seat glider. The trailer design is of the type that has the struts located on the outside of the trailer, with an aluminum top. I am looking to replace the gas struts.
>
> I have contacted Wings and Wheels. They have been very helpful, but they do not carry the struts for this design. They also mentioned that Spindelberger/Cobra do not carry the item.
>
> I am looking for two things. My struts were painted in the past, so I am unable to get the read the strength of the strut. I am also looking for a recommendation for replacement or refurbish.
>
> Thanks
>
> David Cleveland
> Salt Lake City

Dave I've got the same trailer
When my Lift struts failed they were the 900 version
I replaced them with 1100 from Williams and they work great.
No lifting [ or very very little ] and I can pull it down with no problem to close it.
I think would would be happy with the stronger struts.
Be careful when you change them as you know, that top is heavy and if it were to fall on you it could kill you.
Safe Flying
T

[David Cleveland]

Thanks Nick. That's good to hear. Sounds like 1100N gas struts are the way to go. If W/W has no way to get the struts I'll work on some of the second party manufacturers. I had a good talk with Richard yesterday. He gave me a good steer, as well as a few cautions I hadn't thought about.

Yeah, I've had my struts off before and I've worked on the same kind of trailer for friends. Those tops are surprisingly heavy.

DC

[Clay[_5_]]

If all else fails McMaster Carr sells some adjustable force gas springs that I have on my trailer (not a Cobra). They might fit.

[Matt Herron (Sr)]

I have a new pair of Cobra struts that I would be happy to sell, cheap.
These are the stats: N= 850; Art-Nr = 3 500 30; Herst-Dat = 0605
Dont\'t ask me what these figures mean. I have no idea!

[AS]

On Sunday, January 5, 2020 at 10:38:23 PM UTC-5, Matt Herron (Sr) wrote:
> I have a new pair of Cobra struts that I would be happy to sell, cheap.
> These are the stats: N= 850; Art-Nr = 3 500 30; Herst-Dat = 0605
> Dont\'t ask me what these figures mean. I have no idea!

850 Newton force, Manufacturing Date June 2005.
The 3 500 30 is the mfg's article number.

Uli
'AS'

[David Cleveland]

On Sunday, January 5, 2020 at 8:38:23 PM UTC-7, Matt Herron (Sr) wrote:
> I have a new pair of Cobra struts that I would be happy to sell, cheap.
> These are the stats: N= 850; Art-Nr = 3 500 30; Herst-Dat = 0605
> Dont\'t ask me what these figures mean. I have no idea!

Thanks Matt. The strut force is a bit light for what I need. The trailer I have calls for at least 900N, but most input I've received is that 1000N to 1100N works best.

David

[[email protected]]

Re the 2005 manufacturing date: 850 newtons is almost 200 lbs. That's more difficult to measure by hand than an LS landing gear spring or a canopy spring, but it might be advisable to do so. Gas springs don't last forever.

They (and I use that word intentionally) deteriorate on the shelf. The pressure inside the cylinder is still very high even when it's in the extended position. I've seen figures of 1% to 2% loss per annum, which adds up. After they're installed, dust or grit getting into the seal can result in much faster deterioration in force.

When storing a gas spring/strut, hand or position it with the piston rod pointed down. The oil in the cylinder will pool in the bottom of the cylinder and help maintain the seal there. Never store them upside down or laid flat, say, on a workbench or in a toolbox. I learned this the hard way back in my LS-3 landing gear gas strut days when I smugly pulled out the bright, shiny-looking spare I'd carried for several years and was crestfallen to find it was as weak as the one I pulled out of the glider.

This also applies to installation. Given a choice, most of the advice I read is to install in a position where the piston end will be lower than the cylinder end most of the time. It may be (e.g., in my old LS-3, IIRC) that it's positioned one way when the wheel is up but the other way when the wheel is down.

Chip Bearden
JB

[[email protected]]

Guys it's been a while since I followed up on this post. I located a manufacturer in Oregon that will make custom size and force gas struts. The company is called American Gas Springs. They have a website if you want to check it out.

Richard Pfiffner ordered a couple for his Cobra trailer and they worked fine. I am in the process of ordering some as well. I've had some difficulty getting a response, but I thought I'd put it out in case there was anyone else who wanted to add on to the order.

Right now I am ordering standard sized Cobra struts for pre 1984 trailers. These are the trailers with the struts on the outside. I am also ordering the same for a Komet trailer of the same vintage. If you want to PM me I can give you my specs.

David

On Friday, December 13, 2019 at 5:54:33 AM UTC-7, David Cleveland wrote:
> I have a 1981 Cobra trailer designed for a single seat glider. The trailer design is of the type that has the struts located on the outside of the trailer, with an aluminum top. I am looking to replace the gas struts.
>
> I have contacted Wings and Wheels. They have been very helpful, but they do not carry the struts for this design. They also mentioned that Spindelberger/Cobra do not carry the item.
>
> I am looking for two things. My struts were painted in the past, so I am unable to get the read the strength of the strut. I am also looking for a recommendation for replacement or refurbish.
>
> Thanks
>
> David Cleveland
> Salt Lake City

[David Cleveland]

Yeah. Whoops. That last post was from David Cleveland. I was using someone's else's computer.

David

[LOV2AV8]

LS Technologies in Canada is awesome. Our club has ordered multiple sets from them.

Randy "AV8"

[Richard Pfiffner[_2_]]

On Tuesday, March 17, 2020 at 9:11:53 AM UTC-7, David Cleveland wrote:
> Yeah. Whoops. That last post was from David Cleveland. I was using someone's else's computer.
>
> David

I also used American Gas Springs for my Cobra Trailer. I used 1300 newtons.. Measure the extended length and the retracted length and be sure and include the correct fitting lengths in the calculation. I held the top up with a crane and replaced the struts. Be especially specific on the extended length and retracted length. If it is too long the mechanism will go over center too short and the top will not close. I went to the factory 40 miles north of me Medford, Or and picked up the gas springs. The make lots of stuff that involve gas springs.

Richard
www.craggyaero.com

[Mark Bearden]

David - another data point if it helps...several years ago I replaced the struts on my 1978 vintage Komet trailer with off-the-shelf units from Bansbach Easylift. They can do any custom strut you want but lead time (at that time) was 5 weeks. I was able to work with one of their tech support guys and got what I needed with one of their "quick ship" struts. We had to match specific end fittings with one of several base struts available to get required compressed and extended length but they were super helpful, provided engineering drawings to confirm specs, and responded very quickly.

Believe their struts are actually manufactured and stocked in Germany but I had mine in ~2 weeks. I ordered 1600N and they work fine...certainly firm but not objectionable to close. I had the same experience as others...the top of that trailer is crazy heavy so exercise reasonable care.

Mark Bearden

[[email protected]]

On Sunday, January 5, 2020 at 7:38:23 PM UTC-8, Matt Herron (Sr) wrote:
> I have a new pair of Cobra struts that I would be happy to sell, cheap.
> These are the stats: N= 850; Art-Nr = 3 500 30; Herst-Dat = 0605
> Dont\'t ask me what these figures mean. I have no idea!

A reminder: Cobra struts have a small hole in the port strut, the purpose of which is to put a safety pin in when the top is up.

[[email protected]]

> A reminder: Cobra struts have a small hole in the port strut, the purpose of which is to put a safety pin in when the top is up.

Note that the hole is NOT through the gas strut rod itself, but through the square telescoping tube that houses the gas strut.

[John DeRosa OHM Ω http://aviation.derosaweb.net]

David - One comment from someone that has never replaced a Cobra strut (but might have to someday).

Please take lots of pictures of your replacement process and publish them for the benefit of all. Also publish a list of resources and data you found and used. Years ago I did this for installing Wederkind sleeves on L'hotellier fittings and I still get a thank you note from time to time.

Ditto message to anyone replacing internal struts.

Thanks, John OHM Ω

[David Cleveland]

Will do. That's a good idea. I've had mine off several times for various reasons. It's not difficult, but does require caution for some obvious reasons, others no so much.

David

[Tom BravoMike]

On Wednesday, March 18, 2020 at 11:13:23 AM UTC-5, John DeRosa OHM Ω http://aviation.derosaweb.net wrote:
> David - One comment from someone that has never replaced a Cobra strut (but might have to someday).
>
> Please take lots of pictures of your replacement process and publish them for the benefit of all. Also publish a list of resources and data you found and used. Years ago I did this for installing Wederkind sleeves on L'hotellier fittings and I still get a thank you note from time to time.
>
> Ditto message to anyone replacing internal struts.
>
> Thanks, John OHM Ω

BTW, how do I know it's time to replace the struts? I have a 1984 Cobra trailer with the square telescoping tube; with low winter temperatures the top wouldn't stay up, but it does when the temperature rises during the flying season. Should I get new struts right now?

[JS[_5_]]

On Wednesday, March 18, 2020 at 12:41:44 PM UTC-7, Tom BravoMike wrote:
> On Wednesday, March 18, 2020 at 11:13:23 AM UTC-5, John DeRosa OHM Ω http://aviation.derosaweb.net wrote:
> > David - One comment from someone that has never replaced a Cobra strut (but might have to someday).
> >
> > Please take lots of pictures of your replacement process and publish them for the benefit of all. Also publish a list of resources and data you found and used. Years ago I did this for installing Wederkind sleeves on L'hotellier fittings and I still get a thank you note from time to time.
> >
> > Ditto message to anyone replacing internal struts.
> >
> > Thanks, John OHM Ω
>
> BTW, how do I know it's time to replace the struts? I have a 1984 Cobra trailer with the square telescoping tube; with low winter temperatures the top wouldn't stay up, but it does when the temperature rises during the flying season. Should I get new struts right now?

Cold weather failure is often the first sign that its time to replace.
Jim

[Charlie M. (UH & 002 owner/pilot)]

Low ambient temp suggests low strut pressure...don't care if car rear hatch or glider trailer big cover.... works decent when warm, sucks when cold....
Lube pivot points at a minimum....likely replace gas struts.....
What is cost of struts vs. cost of glider when trailer cover crashes on glider????
I have have worked on sailplanes after "stupid stuff"..... gas struts are relatively cheap in that case....and you fly...
Your choice....

[David Cleveland]

Wings and Wheels has the struts for the trailers that are inside. The struts for the single seat measure 45"- 46". Call W/W and they will help once you measure yours. Look to see if there are any markings that indicate the strut force. There are several versions.

Don't wait. Besides not being able to lift the clamshell top to get your glider out as the CUs are popping, the reasons are obvious.


DC

[[email protected]]

Charlie- do you have a neurological problem with your right hand? Your posts indicate a possible case of uncontrollability with your third finger. The "ROL." finger, as it is referred to in typing, seems to jitter on the "period" key, resulting in a shortage of periods available to the rest of the world.

[Dennis Cavagnaro]

Just to accent your point Dave when i bought my Ventus it had a new canopy ...apparently the strut failed on the trailer when the glider was roll out on the ramp and the handle was in the Verticle (open), position when it collapsed.

DC (the other DC)

[Charlie M. (UH & 002 owner/pilot)]

No more issue than "non flying types" asking why I fly an aircraft with no engine...."extra dots" may be similar to a pause while face to face....dots can signify a breath while face to face....

I deleted previous post since limited value to this thread...just answering you....

Previous post had some limited value here.....BTDT.....

[David Cleveland]

I finally was able to get some custom gas springs made and installed. They work very well. The short story is that I used a company in Oregon, American Gas Springs. I know others have had good results getting custom springs made by other sources, but I wasn't able to find any who would make small orders.

I used 1200N for a final gas spring force. A detailed description of the process, as well as the dimensions and install are described in a document available on Google Drive:

https://drive.google.com/file/d/1oEewfk7ERKOLRcJ7Y0Tre0iepV5-pRFN/view?usp=sharing

[Richard Pfiffner[_2_]]

On Thursday, June 18, 2020 at 4:53:33 AM UTC-7, David Cleveland wrote:
> I finally was able to get some custom gas springs made and installed. They work very well. The short story is that I used a company in Oregon, American Gas Springs. I know others have had good results getting custom springs made by other sources, but I wasn't able to find any who would make small orders.
>
> I used 1200N for a final gas spring force. A detailed description of the process, as well as the dimensions and install are described in a document available on Google Drive:
>
> https://drive.google.com/file/d/1oEewfk7ERKOLRcJ7Y0Tre0iepV5-pRFN/view?usp=sharing

I used the same company American Gas Springs but I used 1300N. Easier to life and almost goes up by itself. Pull some to get down.

I picked mine up only 40 miles north of me. They have an extensive product line of gas springs etc. for everything and a really nice manufacturing facility.

Richard
www.craggyaero.com

[[email protected]]

Nice work. I had to do that for an older (1978) Komet many years ago and, like you, was shocked at just how heavy the top is.

Two thoughts:

1. It should be obvious but rod-end-down/body-end-up can be different in the raised and lowered positions. I've seen trailers that way and the LS-3 landing gear is also, forcing you to pick one alternative. I go for the position that the mechanism is in 99% of the time (i.e., top down for a trailer)..

2. The attach bolts are cantilevered out beyond the trailer wall and have been known to fail. I suspect that's more likely if you insert a lot of washers as spacers. Just be careful to monitor that. They apparently bend before they fail so you should see it. I don't know what was there originally but consider sourcing some Grade 8 or other very-high-strength bolts. Maybe even drilling out the holes oversize and going up in size.

Perhaps someone else can comment on bolt failures. It's a known, apparently not-very-common, but potentially disastrous weakness.

It's a greatÂ*feeling to get everything installed and working--even though all you have is what you started out with. :)

Chip Bearden
JB

[Frank Whiteley]

On Friday, June 19, 2020 at 8:46:04 AM UTC-6, wrote:
> Nice work. I had to do that for an older (1978) Komet many years ago and, like you, was shocked at just how heavy the top is.
>
> Two thoughts:
>
> 1. It should be obvious but rod-end-down/body-end-up can be different in the raised and lowered positions. I've seen trailers that way and the LS-3 landing gear is also, forcing you to pick one alternative. I go for the position that the mechanism is in 99% of the time (i.e., top down for a trailer).
>
> 2. The attach bolts are cantilevered out beyond the trailer wall and have been known to fail. I suspect that's more likely if you insert a lot of washers as spacers. Just be careful to monitor that. They apparently bend before they fail so you should see it. I don't know what was there originally but consider sourcing some Grade 8 or other very-high-strength bolts. Maybe even drilling out the holes oversize and going up in size.
>
> Perhaps someone else can comment on bolt failures. It's a known, apparently not-very-common, but potentially disastrous weakness.
>
> It's a greatÂ*feeling to get everything installed and working--even though all you have is what you started out with. :)
>
> Chip Bearden
> JB

I seem to recall that the Komet trailers originally came with 8mm bolts and that because of the failures it was recommended to replace them with 10mm bolts.

Frank Whiteley

[David Cleveland]

Referencing Chips comment about using harder bots. He is absolutely correct.. Many trailers I've seen, mine included, have multiple washers at the mounting point to move the strut and spring arms out away from the trailer. Use caution.

Metric bolts have a different hardness grading system. A metric bolt marked 8.8 is the same hardness as an SAE grade 5. If you want to upgrade the hardness of a metric bolt, use a 10.9 or even 12.9. Frank's comment about using a large diameter bolt would be a good idea as well.

[Richard Pfiffner[_2_]]

On Saturday, June 20, 2020 at 4:59:06 AM UTC-7, David Cleveland wrote:
> Referencing Chips comment about using harder bots. He is absolutely correct. Many trailers I've seen, mine included, have multiple washers at the mounting point to move the strut and spring arms out away from the trailer. Use caution.
>
> Metric bolts have a different hardness grading system. A metric bolt marked 8.8 is the same hardness as an SAE grade 5. If you want to upgrade the hardness of a metric bolt, use a 10.9 or even 12.9. Frank's comment about using a large diameter bolt would be a good idea as well.

If you can't find metric you could use 5/16" grade 8 bolts these are only .0015" smaller than an 8mm basically the same.
McMaster Carr has a selection of grade 8 both the carriage bolt that is used on the bottom end and the hex head used on the upper. Also use the nyloc nuts. Highest grade they offer on the carriage is 8, 10 offered for the upper bolts.

They have the both metric bolts in the 8.8 or Grade 5.

Richard
www.craggyaero.com