COBRA Hydraulic Jack

[[email protected]]

Has anyone replaced the scissors jack on a late 90s vintage COBRA trailer with a COBRA Hydraulic Jack. If so I would appreciate it if you would share any details about the switch.

Thanks,

Bill

[Papa3[_2_]]

On Friday, November 20, 2020 at 2:42:35 PM UTC-5, wrote:
> Has anyone replaced the scissors jack on a late 90s vintage COBRA trailer with a COBRA Hydraulic Jack. If so I would appreciate it if you would share any details about the switch.
>
> Thanks,
>
> Bill

Hi Bill,

Not what you asked, but this is R.A.S. after all...

If the reason you are replacing is frustration with the cheap scissors jack and ungainly handle, consider a ratchet-driven scissors jack like this one. https://modernspare.com/product/3000-lb-trulift-ratcheting-scissor-jack-w-secure-pinch-weld-contact-point/

I got one of these in a spare tire kit for my tow vehicle, and it's a pretty slick piece of kit. It still suffers from the geometry issue inherent with the scissors design, but this one is very easy to to crank and could easily be made with a clip to hold the handle on the frame of the ramp.

Otherwise, I'd just write Spindelberger. They're super responsive and helpful and deal just fine in English.

P3

[Heinz Gehlhaar]

On Friday, November 20, 2020 at 11:42:35 AM UTC-8, wrote:
> Has anyone replaced the scissors jack on a late 90s vintage COBRA trailer with a COBRA Hydraulic Jack. If so I would appreciate it if you would share any details about the switch.
>
> Thanks,
>
> Bill
Ours came installed with a Hydraulic Jack, I suspect it is Cobra. We have no problem with it. Not much help to your question but this is R.A.S. after all...
Heinz

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

This is an aside (but this is RAS after all) but I had to replace my (original?) leaky hydraulic jack and found that the bottle in the small floor jack from Harbor Freight is IDENTICAL. Wonders never cease.

[Jay Campbell]

On Saturday, November 21, 2020 at 12:53:27 AM UTC-5, John DeRosa OHM Ω http://aviation.derosaweb.net wrote:
> This is an aside (but this is RAS after all) but I had to replace my (original?) leaky hydraulic jack and found that the bottle in the small floor jack from Harbor Freight is IDENTICAL. Wonders never cease.
I made a complete hydraulic system for my Cobra from off-the-shelf parts from McMaster Carr. If interested, I can send a parts list and photos to your e mail address. Mine is listed above. You will need a drill press and other aluminum metal-working tools (I have a band saw, but a hack saw will do the work too) and some mechanical building experience. If you have those, the total cost will be about $200 and a day's worth of labor. But then you will have a hydraulic jack for your Cobra trailer.

[John Sinclair[_5_]]

On Friday, November 20, 2020 at 11:42:35 AM UTC-8, wrote:
> Has anyone replaced the scissors jack on a late 90s vintage COBRA trailer with a COBRA Hydraulic Jack. If so I would appreciate it if you would share any details about the switch.
>
> Thanks,
>
> Bill



To answer Bill’s question................it’s a snap, :30 minutes wrench time! I propped up the rails, pulled two bolts, out with the old, in with the new. They seem to go out when the ship reaches about 1000 hours which equates to the life limit of the cheap pump!
JJ

[carbonprop[_2_]]

http://glidersource.com/cgi-bin/post.cgi?id=1624

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

On Saturday, November 21, 2020 at 8:37:40 AM UTC-6, wrote:
> I made a complete hydraulic system for my Cobra from off-the-shelf parts from McMaster Carr. If interested, I can send a parts list and photos to your e mail address. Mine is listed above. You will need a drill press and other aluminum metal-working tools (I have a band saw, but a hack saw will do the work too) and some mechanical building experience. If you have those, the total cost will be about $200 and a day's worth of labor. But then you will have a hydraulic jack for your Cobra trailer.

I would very much like to see this parts list. Thanks.

PS - I cannot see your email address "above" in Google Groups version of RAS.

[Chip Bearden[_2_]]

On Saturday, November 21, 2020 at 6:36:14 PM UTC-5, John DeRosa OHM Ω
> On Saturday, November 21, 2020 at 8:37:40 AM UTC-6, Jay Campbell wrote:
> > I made a complete hydraulic system for my Cobra from off-the-shelf parts from McMaster Carr. If interested, I can send a parts list and photos to your e mail address. Mine is listed above. You will need a drill press and other aluminum metal-working tools (I have a band saw, but a hack saw will do the work too) and some mechanical building experience. If you have those, the total cost will be about $200 and a day's worth of labor. But then you will have a hydraulic jack for your Cobra trailer.
> I would very much like to see this parts list. Thanks.

I've already tried to post this once so apologies if this is a duplicate. With Jay Campbell's permission, I've put the photos and BOM for his intriguing DIY hyraulic fuselage jack up on a shared drive.

https://drive.google.com/drive/folders/1LGzSGgSIjY3DRdumSehHUamtx9sABjOn?usp=sharing

Chip Bearden
JB

[Steve Leonard[_2_]]

I think Cobra has now changed to a vertical acting jack like what John has. On at least some trailers.

Steve Leonard

[2G]

On Saturday, November 21, 2020 at 8:16:14 PM UTC-8, Steve Leonard wrote:
> I think Cobra has now changed to a vertical acting jack like what John has. On at least some trailers.
>
> Steve Leonard
I once built a dual scissors jack for my DG400 using two electric car jacks similar to this one:
https://www.amazon.com/Trihelper-Car-Jack-Electric-Emergencies/dp/B08BKSW19Z/ref=sr_1_9?dchild=1&gclid=Cj0KCQiAkuP9BRCkARIsAKGLE8VOJXIBRSbg4kWfdGL-lXwEe8Cc3CHZ4dojjokVrirTNDWydalsxwgaAkxoEALw_wcB&hvadid=410002065743&hvdev=c&hvlocphy=9033822&hvnetw=g&hvqmt=e&hvrand=11518223723253578813&hvtargid=kwd-568753255&hydadcr=24658_11410762&keywords=electric+car+jack&qid=1606020061&sr=8-9&tag=googhydr-20
I replaced their cheap controller with heavy-duty (10A min) switches. The neat part was that I had one jack on a reversing switch. This allowed me to tilt the fuselage which is very useful in getting the correct dihedral angle during assembly. I powered the jacks from the glider's battery.

Tom

[Chip Bearden[_2_]]

On Saturday, November 21, 2020 at 11:16:14 PM UTC-5, Steve Leonard wrote:
> I think Cobra has now changed to a vertical acting jack like what John has. On at least some trailers.

Responses/comments from Jay Campbell re my questions:

On photo 0992 and others, there's a return spring that's not connected to anything. Ignore it; it's a relic of a failed experiment. Also note the tubing spacer that slides over the bolts at the ends of the X to keep the arms aligned. In photo 0995, nuts on the inner sides of the arms do the same thing on the rolling ends of the X.

On photo 0993, there's a retaining strap/angle on the lower channel. Not visible is a similar retaining strap on the underside of the upper channel. These keep the mechanism locked together even when picking it up by the upper channel to slide back into the trailer.

The jack is retained at the top by a 1/4-20 bolt (drilled and tapped into the top of the jack post). At the bottom, the two outer clips retain it. This allows the jack to be removed/replaced (note the two jacks--one a spare--in the BOM) when/if it fails even if the fuselage is resting in the cradle (not that this would ever happen).

The range of motion is limited by the compressed/extended height of the jack and appears to be less than on my factory double-scissors jack (factory hydraulic jack may be different). Jay says it's workable but something to keep in mind. I already do that--I don't lower my scissors jack completely so sometimes roll the mainwheel up on a piece of 2x6 to get it in the cradle if the tail is a little high. In the fully extended position, you may have to adjust wingstand height to align the main pins on uneven ground when solo rigging/derigging, as I do. This will also depend on the glider. Those with a lot of ground clearance won't need this (e.g., IIRC, the Slingsby Vega). Those with a lot less clearance will (e.g., older LS3s with weak rubber shock mounts)

Make certain there's room for the jack on the left side in the stowed-in-trailer position. Clearances could be tight so Jay pop-riveted two small pieces of channel to the fold-down door of the trailer to prevent the assembly from sliding into the wing.

Jay mentioned that several other examples of his design are in use by other pilots. Perhaps they could comment on their experiences. Also, if Cobra has moved to a vertical jack design, could someone post photos of that? Thanks.

Finally, a general question for those with hydraulic jacks: I solo rig exclusively so frequently use the fuselage jack to raise/lower the fuselage to align the main pin bores. How difficult is it to make fine adjustments when opening the valve to lower the hydraulic jack? Do you often end up overshooting and then having to raise the jack back up into the right position? In the past, some Komet trailers used a similar design incorporating a worm-drive-Acme-thread jack, similar to what some vehicles use for a spare tire change. This would involve a lot of cranking vs. a few strokes of the jack handle but might be better for fine adjustments in the "down" direction. Thoughts?

Chip Bearden
JB

[Craig Reinholt]

If it were me, I'd be painting a whole lot of exposed metal on that DIY scissor jack with Plasti-Dip or some other similar rubberized paint. That and some serious shaping of edges, etc.
Craig

[Richard Pfiffner[_2_]]

I build one with Jay's jacks with his help about 10 years ago.

It works great and is very robust.

Richard
www.craggyaero.com

[Richard Pfiffner[_2_]]

I built one of Jay's jacks many years ago with his parts list, pictures and prints.

It works great and is very robust.

Richard
www.craggyaero.com

[2G]

On Sunday, November 22, 2020 at 9:01:16 AM UTC-8, Richard Pfiffner wrote:
> I built one of Jay's jacks many years ago with his parts list, pictures and prints.
>
> It works great and is very robust.
>
> Richard
> www.craggyaero.com

If you need more clearance in the lowered position a double-acting bottle jack is the answer:
https://www.northerntool.com/shop/tools/product_200641735_200641735?cm_mmc=Google-pla&utm_source=Google_PLA&utm_medium=Automotive%20%3E%20Jacks&utm_campaign=Strongway&utm_content=46195&&ds_e_ad_type=pla&gclid=CjwKCAiAtej9BRAvEiwA0UAWXkBPd35LteNjZwQd6aTA u3uRtPS28Ncni2sQfZoZVoNu1fppADxpGxoChUwQAvD_BwE&gclsrc=aw.ds

Tom

[AS]

On Sunday, November 22, 2020 at 6:08:23 PM UTC-5, 2G wrote:
> On Sunday, November 22, 2020 at 9:01:16 AM UTC-8, Richard Pfiffner wrote:
> > I built one of Jay's jacks many years ago with his parts list, pictures and prints.
> >
> > It works great and is very robust.
> >
> > Richard
> > www.craggyaero.com
> If you need more clearance in the lowered position a double-acting bottle jack is the answer:
> https://www.northerntool.com/shop/tools/product_200641735_200641735?cm_mmc=Google-pla&utm_source=Google_PLA&utm_medium=Automotive%20%3E%20Jacks&utm_campaign=Strongway&utm_content=46195&&ds_e_ad_type=pla&gclid=CjwKCAiAtej9BRAvEiwA0UAWXkBPd35LteNjZwQd6aTA u3uRtPS28Ncni2sQfZoZVoNu1fppADxpGxoChUwQAvD_BwE&gclsrc=aw.ds
>
> Tom

Just to keep the nomenclature straight: the link shows a two-stage telescopic cylinder and it is still only single acting, i.e. one can power it up but either a spring inside or the load will have to bring it back down. This is NOT a double acting cylinder which could be extended and retracted hydraulically.
This one will most likely only lift the designated 2t on the first stage, which is still way more than needed in this application here.

Uli
'AS'

[2G]

On Sunday, November 22, 2020 at 7:09:45 PM UTC-8, AS wrote:
> On Sunday, November 22, 2020 at 6:08:23 PM UTC-5, 2G wrote:
> > On Sunday, November 22, 2020 at 9:01:16 AM UTC-8, Richard Pfiffner wrote:
> > > I built one of Jay's jacks many years ago with his parts list, pictures and prints.
> > >
> > > It works great and is very robust.
> > >
> > > Richard
> > > www.craggyaero.com
> > If you need more clearance in the lowered position a double-acting bottle jack is the answer:
> > https://www.northerntool.com/shop/tools/product_200641735_200641735?cm_mmc=Google-pla&utm_source=Google_PLA&utm_medium=Automotive%20%3E%20Jacks&utm_campaign=Strongway&utm_content=46195&&ds_e_ad_type=pla&gclid=CjwKCAiAtej9BRAvEiwA0UAWXkBPd35LteNjZwQd6aTA u3uRtPS28Ncni2sQfZoZVoNu1fppADxpGxoChUwQAvD_BwE&gclsrc=aw.ds
> >
> > Tom
> Just to keep the nomenclature straight: the link shows a two-stage telescopic cylinder and it is still only single acting, i.e. one can power it up but either a spring inside or the load will have to bring it back down. This is NOT a double acting cylinder which could be extended and retracted hydraulically.
> This one will most likely only lift the designated 2t on the first stage, which is still way more than needed in this application here.
>
> Uli
> 'AS'
The lift height you will need depends upon what is needed to extend the gear fully and still clear the ground. This is glider dependent, but will likely be more than what the first stage can produce. And, more importantly, it has a lower profile to allow the fuselage dolly to be well below the glider's nose. This is critical for positioning the glider to be jacked up. Again, this depends upon the individual glider's ground clearance.

Tom

[Lynn Alley]

Which small floor jack at Harbor Freight? There are a whole bunch of them. I would love to replace the bottle on mine.

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

On Tuesday, November 24, 2020 at 12:00:24 AM UTC-6, wrote:
> Which small floor jack at Harbor Freight? There are a whole bunch of them. I would love to replace the bottle on mine.

I believe that it is the $30 cheapest 2 Ton floor jack that I used the bottle from. Lots of spare parts now left over in the junk bin.
https://www.harborfreight.com/2-ton-compact-trolley-jack-64874.html

I have seen the same bottle in cheap jacks at Walmart and other big box stores.

That being said it is always best to take your old bottle with you, plus a ruler, to compare old with new before purchase.

My $0.02,
John (OHM)

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

I should add a couple of things on this topic.

- While the bottle jack approach is just as good as the scissors jack's when making fine UPWARD rigging adjustments (and great for fast coarse raising the fuselage), but is very much inferior when trying to make fine DOWNWARD rigging adjustments. IMHO.
- The foot actuator on the original "Cobra" hydaulic jack fits nicely onto the replacement bottle.
- The original jack has a cleverly bent lever attached to the release valve so that you can use your fingers to open and close it. The replacement bottle's valve is basically a short bolt with the head cut off and a slot cut into the end. You then use the pipe (used to pump the jack up/down) to open/close the valve by rotating the bolt. I use a large screwdriver instead.. Not quite as easy to use as the original bent lever. I was unsure about moving the original lever to the replacement bottle. Same threads? Same ability to close the release valve properly? That all comes down to the machining in the factory which, I fear, is pretty "iffy". Anyone re-invent this?

My $0.02,
John (OHM)

[BG[_4_]]

For those considering replacing their leaky Cobra hydraulic jack, better to replace the seal than deal with the cheap replacement that does not really fit. At least that is what I found with the Harbor Freight solution. I think it does not have the same stroke as I recall. I replaced mine about 8 years ago on now a 20 year old bottle and still working fine today.

Cost $5.42

http://www.mcmaster.com/#mechanical-seals/=ekh96p

part number 9505K82

Buzz Graves

[AS]

On Wednesday, November 25, 2020 at 12:32:05 PM UTC-5, BG wrote:
> For those considering replacing their leaky Cobra hydraulic jack, better to replace the seal than deal with the cheap replacement that does not really fit. At least that is what I found with the Harbor Freight solution. I think it does not have the same stroke as I recall. I replaced mine about 8 years ago on now a 20 year old bottle and still working fine today.
>
> Cost $5.42
>
> http://www.mcmaster.com/#mechanical-seals/=ekh96p
>
> part number 9505K82
>
> Buzz Graves

That's a good choice, Buzz! The key with all Polyurethane seals is to keep the fluid as dry as possible, meaning to keep the water content as low as possible. Polyurethane suffers from hydrolyses, the process by which water slowly penetrates and then dissolves the material from the inside out. The higher the pressure and the higher the water contents the faster the process progresses. Pressure is low in this application but the amount of water that accumulates in fluid may be high, so draining and replacing the oil in the jack may not be a bad idea to keep the seal happy.

Uli
'AS'