Double scissor jack for trailer ramp?

[Bullwinkle]

All,

I have a new (to me) glider and trailer. Good rig, but like most things,
capable of improvement.

The ramp that extends from the back of the trailer for assembly has a
single, car style scissor (spare tire) jack for raising and lowering the
fuselage. It rocks back and forth a bit too much, and that makes it a bit
too unstable for my taste.

I see other trailers with a double scissor jack that are clearly more
stable, and would like to go that direction. Can't find any info on Our
Friend the Internet about how to do that, though.

Can anyone point me in the right direction?

Are there any of these, new or used, available? (Yes, I know I could order
one from Cobra or Komet, but would like to save that for a last resort.
Looking for something here in USA, if possible.)

Any spares from trailers no longer in use?

Making one of these is acceptable, but would like some advice on types of
jacks to get, how to connect them, etc.

Thanks in advance for your advice,
Bullwinkle

[Martin Gregorie]

Bullwinkle wrote:
>
> I have a new (to me) glider and trailer. Good rig, but like most things,
> capable of improvement.
>
> The ramp that extends from the back of the trailer for assembly has a
> single, car style scissor (spare tire) jack for raising and lowering the
> fuselage. It rocks back and forth a bit too much, and that makes it a bit
> too unstable for my taste.
>
One of our club trailers had a pair of scissor jacks, but they were old
and one eventually stripped its thread. We replaced it with a single
jack that was already at the club. That works OK but, as you say, its
less stable.

The problem is to find a (pair of) jacks with narrow enough spans to fit
side by side within the width of the tail ramp. None of the screw jacks
I could find in car places were narrow enough and the hydraulic jacks
were all too tall. However, I did do some research and found a source of
suitably small screw jacks, though not until after the ramp had been
repaired.

The jacks you need were made for British sports cars. They are narrow
because they were kept inside the spare wheel. They are still made: find
one of the specialists who supply parts for Triumph or MG sports cars
should be able to sell you suitable jacks for a reasonable price.

The jacks are set to the same height and welded into the ramp's rear U
channel and ground support after lining them up the same way and using a
sleeve to join the screws together.

--
martin@ | Martin Gregorie
gregorie. |
org | Zappa fan & glider pilot

[Udo Rumpf]

I used a couple of Honda Civic scissor jacks.
They are light weight and compact.
When collapsed the jack ideally should have the screw stick out of
the threaded thrust bearing just a bit (as oppose to being flush).
This allows a fork to be welded on to connect a shaft, without interfering
with the threaded portion of the jack. If the welding interferes with the
thread you will not be able to collapse the jack completely.
In any case, if you get a couple of jacks you will see what is needed
and what needs to be done.
Udo




> Friend the Internet about how to do that, though.
>
> Can anyone point me in the right direction?
>
> Are there any of these, new or used, available? (Yes, I know I could order
> one from Cobra or Komet, but would like to save that for a last resort.
> Looking for something here in USA, if possible.)
>
> Any spares from trailers no longer in use?
>
> Making one of these is acceptable, but would like some advice on types of
> jacks to get, how to connect them, etc.
>
> Thanks in advance for your advice,
> Bullwinkle
>

[[email protected]]

Make certain the jack lifting pad moves in a straight vertical motion.
Some scissor jacks let the lift pad translate as it moves vertically.

Gale Winnett

[Bob Salvo]

When you say "back and forth", I think of "side to side". If that is right,
attach small chains at each end (side) so that when the ramp is raised high
enough to allow lowering the main wheel, these chains become taught. Cheap
and easy!

Bob (RS)

"Bullwinkle" > wrote in message
...
> All,
>
> I have a new (to me) glider and trailer. Good rig, but like most things,
> capable of improvement.
>
> The ramp that extends from the back of the trailer for assembly has a
> single, car style scissor (spare tire) jack for raising and lowering the
> fuselage. It rocks back and forth a bit too much, and that makes it a bit
> too unstable for my taste.

[Bullwinkle]

Thanks to all for your suggestions (including Todd, who I am sure was joking
about the procedure below ;) ).

I think I know how to proceed now.

Bullwinkle

On 1/16/06 8:59 AM, in article ,
"T o d d P a t t i s t" > wrote:

> Bullwinkle > wrote:
>
>> I see other trailers with a double scissor jack ...
>> Are there any of these, new or used, available?
>
> Some people like the Cobra hydraulic jack enough that
> they've retrofitted one to their trailer and then have an
> old double scissor to get rid of.
>
> I suggest the following - Find a likely prospect with glider
> and trailer. Wait until his attention is elsewhere, then
> with glider supported in his fuselage dolly and wings on,
> retract his gear, put his tail dolly on and lower the double
> scissors fuselage dolly jack as far as you can. When he
> returns, point out that his gear is up. He will be unable
> to extend it until he lifts his fuselage. The double
> scissors has very little mechanical advantage from the low
> retracted position and raising wings plus fuselage from very
> low, particularly with the tail dolly holding the tail high
> is extremely difficult. As the pilot struggles, make a few
> judicious comments about the improved hydraulic jack system.
>
> Leaning on the wing while he cranks, adding water ballast to
> his wings, lead ballast under his seat cushion or putting
> sand in the jack bearings may improve results.

[[email protected]]

I've dealt with single and double scissors jacks on Cobra/Komet
trailers for about 25 years. As Todd points out, they have nearly zero
mechanical advantage when fully lowered. The hydraulic jack alternative
eliminates this problem but, based on all the complaints I've heard,
introduces others (e.g., leaks).

The most intriguing solution I've seen is replacing the scissors jacks
with vertical screw jacks with Acme (square shouldered) threads. The
mechanical advantage is the same no matter the height of the jack. I
know Komet offers this as an alternative because I actually trial
fitted one to my Cobra trailer before deciding not to pay the cost to
upgrade. Cobra may offer it as well.

I haven't checked into U.S. sources (new or used) but if I were
undertaking a rebuilding project, I'd definitely consider this
alternative. The biggest obstacles would appear to be (1) that the
jacks are vertical so they have to be set on either side of the
fuselage and (2) it may be more difficult to drive them simultaneously
than with the two-scissors-jack approach where one jack drives the
other.

Chip Bearden
ASW 24 "JB"

[TTaylor at cc.usu.edu]

I purchased two regular scissor jacks for mine and slaved them
together. About $10 each at:

http://www.toolshopusa.com

I have been intrigued with trying a leveling jack:

http://www.pplmotorhomes.com/parts/rv-jacks/rv-leveling-jacks.htm

Tim

[01-- Zero One]

I saw an interesting jack yesterday at Harbor Freight.. It was a
hydraulic scissor jack. Looked like it might be stable enough that you
could use just one in the middle. I tried to find it online just now
and can't locate it. When I go back out there, I will look at it
closer..



Larry

"01" USA

[01-- Zero One]

Here is a link to one that looks like the one I saw at Harbor Freight.



http://www.autobarn.net/mvp22lbhydsc.html



YMMV,



Larry





"01-- Zero One" > wrote in message
>:

I saw an interesting jack yesterday at Harbor Freight.. It was a
hydraulic scissor jack. Looked like it might be stable enough that you
could use just one in the middle. I tried to find it online just now
and can't locate it. When I go back out there, I will look at it
closer..



Larry

"01" USA

[[email protected]]

<<Chip, since you've seen one with this design, how did they drive them
simultaneously? >>

Todd, can't recall how they drove both vertical screw jacks
simultaneously. Obviously there had to be some kind of shaft extending
to the opposite-side jack but not sure whether it was driven by the
screw in the first jack or what. I suspect you've already checked the
Anschau and Entec sites like I have and discovered there's no photo. I
recall seeing one somewhere a while ago, though, so maybe someone can
point to it.

I was intrigued because it seemed like the best of all worlds: like
having two hydraulic bottle jacks without the leaks. I can't recall the
details but it was a spare and I could have bought it from Entec on the
spot saving freight, etc. And knew for sure it would bolt/weld right up
to my fuselage track. But the price for the jack assembly was pretty
steep ($500?) and I decided to pass.

Not sure why more of them aren't done that way. The biggest
disadvantage I can see apart from possible cost is that, like the
twin-hydraulic-jack approach, the jack towers have to be far enough
apart to avoid scraping the sides of the fuselage/cradle (with some
room to spare for misalignment coming in). But it looked like it would
have worked fine for my ship.

Chip Bearden
ASW 24 "JB"

[Udo Rumpf]

> Todd, can't recall how they drove both vertical screw jacks
> simultaneously. Obviously there had to be some kind of shaft extending
> to the opposite-side jack but not sure whether it was driven by the
> screw in the first jack or what. I suspect you've already checked the
> Anschau and Entec sites like I have and discovered there's no photo.

Chip,
since I use this type of jack with the wing assembly dollies,
I can give you my view on it the jack arrangement for a ramp.
The jacks are modified screw jacks as used with Mercedes Cars.
The jacks would be used up side down in the ramp application.
The thrust bearings are reversed. The gear that is driven normally
by the hand crank shaft is replaced by a short straight shaft. with an
adaptor for inserting a hand crank and on the other side of the shaft
stub is the connection for the drive shaft to drive the other jack.
the drive shaft is protected by a channel.

Udo

[Papa3]

wrote:
> <<Chip, since you've seen one with this design, how did they drive them
> simultaneously? >>

> I recall seeing one somewhere a while ago, though, so maybe someone can
> point to it.
>
I had one shipped mistakenly with my new Anschau trailer about 5 years
back (I had ordered the one with the foot-pump scissors jack). I used
it for a year while waiting for the "right" one to come in. I wish
I had kept the Acme Screw Jack! It's far-and-away the best (simplest,
most robust, constant mechanical advantage) design out there.

IIRC, there was a simple, robust linkage (solid rod) connecting the
drive mechanisms on the two jacks, so they were synchronized. I think
they just extended the drive bar from the "master" cyclinder to the
"slave" (where master is the one that is closest to the handle).

The two slight drawbacks are:

1. You have to stoop get down to the actuator handle.
2. The jack towers take up some room, so the whoe unit is slighltly
bulkier than the scissors jack.

I did look into this about a year back (I think I actually posted
something - check the archives). I found a screw jack with a two-sided
drive pickup (ie. you could attach the handle on either side), which
took care of the master cylinder problem. Welding up the appropriate
cradle would not have a been a big deal. Unfortunately, I found this
only after some pretty random Googling, and I never wrote down the
manufacturer. I think some combination of Acme screw jack and
reversible finally did the trick.

P3

[bumper]

The main argument for not using a hydraulic jack for the ramp, is that they
leak. Leakage is a problem that seem common with the cheap jacks that Cobra,
and probably other trailer manufactures, use.

Using hydraulics has several advantages over mechanical jacks; lower
friction, compactness, ease of incorporating into a given lift design, and
lower maintenance (assuming a good quality jack is used).

My 3 year old Cobra trailer has a hydraulic jack. It started leaking after
just one season. Disassembly found the oil gray in color, contaminated with
metal particulate. Internal machining was crude and course. I drained,
flushed and refilled the jack, putting it back in service. The leaking has
stopped for now.

Being in a "jack servicing mood" I inspected a 30+ year old, US made
Craftsman bottle jack my wife bought me as a gift. The oil was clean, honey
colored, and the cylinder walls were smooth and shiney. This jack has not
leaked so much as a drop of oil. Despite use and abuse, it's original build
quality shows.

Cobra tailers aren't cheap . . . they, and the other manufactures, should be
ashamed of themselves for using such a crappy jack!

Using a mechanical jack is one solution, but I think a better one is to use
a good quality hydraulic jack to begin with. Until then, it's probably a
good idea to drain and refil newer jacks, at least annualy, until the oil
shows clear.

bumper

[[email protected]]

schrieb:

> <<Chip, since you've seen one with this design, how did they drive them
> simultaneously? >>
>
> Todd, can't recall how they drove both vertical screw jacks
> simultaneously. Obviously there had to be some kind of shaft extending
> to the opposite-side jack but not sure whether it was driven by the
> screw in the first jack or what. I suspect you've already checked the
> Anschau and Entec sites like I have and discovered there's no photo. I
> recall seeing one somewhere a while ago, though, so maybe someone can
> point to it.
>
> I was intrigued because it seemed like the best of all worlds: like
> having two hydraulic bottle jacks without the leaks. I can't recall the
> details but it was a spare and I could have bought it from Entec on the
> spot saving freight, etc. And knew for sure it would bolt/weld right up
> to my fuselage track. But the price for the jack assembly was pretty
> steep ($500?) and I decided to pass.
>
> Not sure why more of them aren't done that way. The biggest
> disadvantage I can see apart from possible cost is that, like the
> twin-hydraulic-jack approach, the jack towers have to be far enough
> apart to avoid scraping the sides of the fuselage/cradle (with some
> room to spare for misalignment coming in). But it looked like it would
> have worked fine for my ship.
>
> Chip Bearden
> ASW 24 "JB"

For a lifting unit with vertical spindles there are spindles with a
90° drive gear and a strong, but very little axial ball bearing
needed. The axles from the gear have to be long enough to weld a
spindle between the two units to connect them. The distance must be
outside the rails to make space for the fuselage. With some gliders
this will give difficulties with the space to the wings and this will
make it impossible to use this system on certain gliders.
One spindle needs a left hand drive, the other a right hand drive (
They are working mirror-like because one is left of the rail, the other
is right of the ramps rail ). And this spindles should not exceed 300
mm in height because of the danger of scratching your wings leading
edge.
Where to buy?
We make them.( In little numbers)
Only 4 and a half manhours each, you need two spindles.
And than you need to connect them and to weld them on a base.
This may explain the price.......
AS
cobratrailers

[[email protected]]

As you write: a 30+ year old US made hydraulic...
Had you tryed to find a new one US or European made hydraulic jack what
fits in size to a lifting unit?
If you find one, please, please send me the adress of the manufacturer.
Sorry, but all the hydraulic jacks in this days are made in China (
Also these showing an US or European brand ). As I know , there is no
US or European manufacturer left.
But hydraulic is the only way to lift a motorglider or a open glass
ship with relatively little force.
To avoid leaking, please take a eye to the little sticker on the left
hand ramp rail:
OPEN VALVE SLOOOOOOOWLY.
This will hold the sealings and valves in a good shape and avoid
leaking.
Since last autumn we found a manufacturer what uses a significant
better sealing system. So, there should be some of the problem solved.
AS