Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml@lancaironline.net
Date: Sun, 14 Sep 2003 23:03:24 -0400
Message-ID: <redirect-2579548@logan.com>
From: "IIP" <IIP@hawaii.rr.com>
Subject: [LML] Re: Gross Weight & Balance of IV-P, Other considerations for Lancairs
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We had this discussion about a year ago, and I was surprised at the lack
of conclusions I was able to draw. We rated our IV-PT at a GW of 4,000#.
Our empty CG is about 1" forward of the forward CG "limit". With 4,000#
reasonably distributed (4 heavy guys and 150# in the cargo compartment),
we were just forward of aft CG. That was our logic for the GW rating,
and the DAR thought it was fine.

Flying is another matter. We intend to do a lot of flight testing to
draw data curves for increasing GW's from 3,000 to 4,000, and with
several loading configurations. Lancair's comment was that the IV gear
had been landed over 4,000# many times over the years, with no damage. I
believe, as others have stated, that the gear load on touchdown is THE
critical element. I intend to be able to "grease it on" regularly before
I attempt GW's higher than about 3,200#. Someone more qualified than I
will do the stall regimes.

I'm still confused about the applicability of the static test. So,
Lancair put 12,000# on a wing (the story goes that the FAA wouldn't pass
it until it broke, so after they had 12,000# on it then they sawed about
1/3 through the spar to get it to break!). Does that tell us much of
ANYTHING, really? In the first place, the sand bags on a wing can hardly
replicate the distribution of flight forces acting on it. And a wing is
rarely static in flight anyway. It tells us nothing about the negative
strength of the wing. It doesn't tell us much about the strength of 2
wings properly held together by a spar box. Which brings me back to a
question I asked (and got no response to) last time: If one wing is
static tested to +12,000#, won't 2 wings support +24,000#? It seems to
me the weight of the fuselage is supported by the wing spars equally on
both sides. So, if the fuselage is the net weight we are concerned with
(as opposed to the weight of the wings, which is largely equalized by
lift), then wouldn't we ADD the weight of the wings to 24,000# to get
the GW and G limits we should be worrying about in clear air? Hopefully
one of you rocket scientists out there can clear this one up! (or can
tell me I'm an idiot and to read "Aerodynamics for Naval Aviators"
again.)

Brian Barbata
N104PT, 50+ hours