low fuselage trailer ramps

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When my Crown trailer ramp is fully lowered my ASW-20 fuselage does not
clear the dolly cradle. Furthermore the scissors jacks require
excessive torque from the fully lowered position. Currently I roll the
main wheel up a small wooden ramp to raise everything a few inches. I'm
interested in other solutions. In particular does anyone have
experience with the screw jack ramp arrangement described on the Cobra
web site? Since a Cobra or Komet ramp won't directly apply to my
trailer I'm considering building my own such ramp. Does anyone have a
source for this type of screw jack in the USA? I have seen similar
jacks used in some older European cars. My web searches on "screw jack"
only return very large capacity equipment.

http://www.cobratrailer.de/english/index.html
The illustration opposite shows different versions of lift ramps for
the fuselage: ...a version with screw jacks, especially useful for
gliders with low fuselage...

[Papa3]

wrote:
Does anyone have a
> source for this type of screw jack in the USA? I have seen similar
> jacks used in some older European cars. My web searches on "screw jack"
> only return very large capacity equipment.
>
> http://www.cobratrailer.de/english/index.html
> The illustration opposite shows different versions of lift ramps for
> the fuselage: ...a version with screw jacks, especially useful for
> gliders with low fuselage..

Mark,

In my opinion, the screw jack is definitely the best design. A
scissors jack suffers from the fact that the lift vector is at a
miniumum when fully compressed - ie. just when we need it most in
gliding. Hydraulic jacks are always requiring maintenance and run the
risk of a "rapid decompression" if you accidentally flip the valve,
leading to a nasty fuselage tip over. The screw jack provides
linear lifting, so the amount of lifting is always directly
proportional to the amount of turning you do on the handle.

I had the screw jack from Anschau Komet, and it was great. I think you
can find the parts you need if you search on "acme threaded jack"
instead of just "screw jack". McMaster Carr sells a line of "light
duty" Acme Threaded Jacks that might be just the ticket. You need a
mechanism to drive both worm gears uniformly, so there is some
engineering involved. It may just be easier to spend the money and buy
one from Cobra or Komet.

http://www.mcmaster-carr.com and type in Acme Screw Jack in the search
window.

Regards,

Erik Mann
LS8-18 (P3)

[Michael Huber]

"Papa3" >wrote

> scissors jack suffers from the fact that the lift vector is at a
> miniumum when fully compressed - ie. just when we need it most in

I use a horizontal hydraulic cylinder and the upper part of a scissors jack.
Erik is still right about the lift vector, but you can gain a little over a
real scissors jack. My ramp cannot tilt, so lifting in the middle only works
well for me.

/\
---> / \

Michael

[[email protected]]

What's so wrong with using the wooden ramp? I use this solution for my
ASW15/Avionic setup and in my club we also have ASW19/Komet,
ASW20/Komet and ASW20/Cobra combinations all using a small wooden ramp.
The Waibel designs (except the ASW12) all seem to combine a fairly low
landing gear with a drooped front fuselage which makes it hard to get
the dolly low enough to clear. I think it's a lot easier just to keep
things the way they are.