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Marv,
This design has an unstable mode that folks should be aware
of. Fortunately, it isn't very difficult to eliminate. To
be stable you always want the load to be distributed to the two feet on each end
of the stand. With the current design, this indeed occurs while the
telescoping section is pinned. The load is distributed out the four legs
(upper right sketch). However, while bottle jacks are used to raise
the plane, the load path is no longer through the legs but instead from the
plane straight down through the bottle jack to the floor (upper left
sketch). This isn't too bad if only one side at a time is jacked
up. Some fore/aft stability is provided by the other side and/or the wheels
still on the ground. It gets a little dicey when both left and
right side are being hoisted at the same time, the plane could fall forward or
aft because none of the four jack stand legs are supporting the
plane. One could theoretically crawl under the plane and lift the stand
right off the floor. To be stable while hoisting the plane, the
forces need a path through the structure of the stand (lower center
sketch). Placing the bottle jack on an additional beam between
the two legs provides this path.
Chris
Chris Zavatson
N91CZ
360std
www.N91CZ.com
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