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I like Scott's idea of using channel attached to the spar as an
intermediate solution to the jacking dilemma, and if I had the room I would
probably have done something similar. Unfortunately my fuselage sits in a
corner with the outboard end of the left stub wing just inches from a wall,
so space limitations constrain me from incorporating that sort of solution.
Additionally, sooner or later the jacks which will ultimately be used to
get the aircraft off its gear need to be dealt with anyway, so I figured
the best thing to do was attack that problem right off and save a step
along the way. Little did I know that I'd be building that system twice
anyway (no grins here). 8-(
In response to Bob's question, your system and my original failed system
seem only to share building materials... yours sounds much more stable that
my original one turned out to be, as yours has the jacks on the floor
raising a pipe which is ultimately supported by your tripods. On my
original stand, the overall footprint was about 44" long (left to right)
and about a foot deep (front to rear). On top of this base-board was
constructed a pair of pedestals to hold a pair of bottle jacks... the
pedestals shared a common board which was mounted upside-down-T fashion to
the base to keep them from shifting side to side, and the framework which
ultimately held the platforms that the bottle jacks sat on used
particle-board trapezoids all glued and stapled to provide fore-and-aft
stability to the platforms. The platforms finished out about 14" tall,
were just slightly larger than the jack base, and were situated so when the
bottle jack was set on top the extended jack shaft would align with the
lift points in the bottom wing skin, just inside the inboard gear doors.
Each jack was provided a plywood disk with a hollow in the bottom to accept
the jack shaft which had a 1/4" screw sticking out of the top to go into
the lift point locating hole, and a piece of carpet over the disk provided
the protection to the bottom of the fuselage. This all would have worked
fine had the jacks been firmly attached to their pedestals, as that would
have necessitated that entire assembly to rock, and that 12" fore-aft
footprint of the stand's base-board just wouldn't do that. What did
happen was the jacks rocked on top of the pedestals, so the pedestal
assembly stayed where it was supposed to, but the jacks hinged backwards on
their own bases, and that's where the catastrophe came from.
My new unit has an 18" fore-aft footprint, is just as wide as the lift
points (they're 36.5" OC) so now the jack sits on the floor, under the
assembly, and raises a square tube which slides inside a larger tube
segment and which can be pinned into position once the desired lift height
is achieved. When I drilled the lift tubes and their sockets for the pins
I set it up so I could adjust either side in increments of 1/8" for
levelling purposes, which would mean that I'd never need anything more than
a 1/8" shim one side or the other to achieve level. I am pleased to report
that the new unit is very stable, plenty strong, and seems to be doing the
job nicely. I just wish I'd done it this way in the first place.
<Marv>
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