Double scissor jack for trailer ramp?

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"

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

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 a

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

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

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

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