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Posted for Greg Nelson <gregsays@swbell.net>:
Many thanks to all of you for your helpful comments regarding what I
suspect is an aft CG problem on my Lancair 360 small-tail plane. Soon I
will address those questions and comments in another message but first I
have a proposal which I should like to see discussed in this forum--and
here it is.
Maybe there is a quick, simple and sure double check of aircraft cg
available to all of us (or perhaps we should say a quick, non-flying check
of inadequate cg). The position of the main gears is absolutely fixed on
each airplane as is the position on the rear tie down similarly fixed. By
hanging a carefully-measured weight on the tie down until the nose wheel
lifts off the ground slightly (1/2 in.), we should know (within a percent
or two) whether the scale-measured W/B data is corroborated.
This procedure can get around a lot of problems including sticking,
uncalibrated scales, inaccurate measurements, bad arithmetic,
misunderstanding of W/B logic and procedures, and any important post-weight
and balance changes made to the airplane after the FAA inspection (and any
formal updates). It will definitely not serve as a replacement for a
proper W/B determination because FAA regulations require a thorough W/B
spreadsheet and, clearly, a formal W/B does give more useful information.
Instead, this tiedown test should be used as a quick check to assure
Lancair builders and pilots that W/B numbers are within a safe zone.
To be done accurately, the airplane should be loaded exactly as it flies,
i.e., fire extinguisher, thermos, tool kit, oxygen, flight bag, headsets,
etc., all installed in the airplane (again, "exactly as it flies"). To
further standardize, we should ensure that the wheels (only) are exactly
level in both the roll and pitch axes and each plane should have full fuel,
canopy closed, cowling installed and no baggage. The only difference from
its flying configuration would be that no passenger or pilot should be in
the airplane at the time the measurement is taken (this because it will
standardize our numbers and comparisons).
Lancair test pilot, Doug Weeldreyer, says that he can determine by pushing
down on the horizontal stab whether an airplane has an adequate forward cg.
The harder he pushes, the more forward the cg. Our efforts to assemble
hard data on this phenomenon will assist us in flying more safely. My
airplane requires 123 pounds of downward force on the tiedown to lift the
nose wheel inch. I would sincerely appreciate if others would test their
airplanes for comparisons.
Greg Nelson
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LML homepage: http://www.olsusa.com/Users/Mkaye/maillist.html
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