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Grayhawk … your idea of wheels is
fine. Just make them retractable under a load exceeding the weight of the jack
assembly.
Jim
From: Lancair Mailing
List [mailto:lml@lancaironline.net] On Behalf
Of Sky2high@aol.com
Sent: Tuesday, September 25, 2007
3:43 PM
To: lml@lancaironline.net
Subject: [LML] Re: Lancair 320
aircraft jacks
In a message dated 9/25/2007 12:25:39
P.M. Central Daylight Time, Christopher.Zavatson@baesystems.com writes:
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.
Egads, I have constructed a similar jack,
but a little bit different. I used 2 inch square steel tubing and
1.5 inch square tubing for the sliders in the vertical tubing pieces
(overbuilt, just like my Lancair). There is an area washer welded to the
top of the slider for a bigger base that the wing rests upon with the jack
locating "knob" fitting in the washer hole. Also, there is a
thin steel plate welded between the feet on each side and electric
scissor screw jacks (12 VDC, $50 each) are machine screwed to those
sheets. Since I only use the jack for my plane, the cross piece,
connecting the two sides, is bolted in place. This jack is rigid in
every direction. I still have the jigs for the cutting and welding
up such a jack (already used by another to construct one of their own. I
searched my computer for pix, but could not find them so I will take a
few and send them out along with a parts list. Each side is
infinitely adjustable thus allowing for lateral leveling - all done with push
button ease. BTW, it is painted with old out-of-date two-part tank
sealer.
I considered putting the jack on wheels,
but the smarter side of my brain said, "No!"
Scott
Krueger AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL (KARR)
Darwinian culling phrase: Watch This!
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