Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Sat, 11 Jan 2003 10:49:55 -0500
Message-ID: <redirect-1980791@logan.com>
From: "Mike Hutchins" <mhutchins@attglobal.net>
Subject: Wing Loading Mysteries
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In-Reply-To: <list-1980709@logan.com>

Brian,

I think you are confusing the aerodynamic characteristics associated with
wing loading and the structural strength of the wing. The two are not
necessarily related.

Wing Loading primarily relates to the stall speed of the aircraft as well as
its relative sensitivity to turbulence. In other words, the higher the wing
loading, the greater the stall speed (assuming the coefficient of lift is
the same for the wings compared). Conversely, the higher the wing loading,
the less turbulence will tend to upset the aircraft. It also effects the top
speed somewhat in that a smaller wing will have less wetted surface area,
and therefore less parasitic drag. This is offset, however, by the slightly
higher angle of attack needed to support the aircraft with a smaller wing,
leading to increased form drag.

The structural limit of 12,000 pounds for the L-IV wing is suspect to me. In
Martin Hollmann's book, "Modern Aircraft Design", he reports that the L-IV
wing failed under a total load of 9,250 lbs. This correlates to an
aerodynamic wing loading of 8.3 G's (Using a Gross Weight of 2900 lbs.),
according to Martin's calculations. Note that this is not simply Load At
Failure / Aircraft Gross Weight.

In regards to a proposed Gross Weight of 4000 lbs, this will derate your
maximum G-Force at wing failure by 42% (you get to subtract the structural
weight of the wing, 310 lbs., but not the fuel and accessories), to a
maximum of 4.8 G's. Backing out the 2x safety factor, this leaves you with a
maximum G-Force of 2.4 G's. In other words, with a bank angle of 65 degrees
in level flight you would be at the rated structural maximum G-Force. And
this is only for the positive G Situation.

Along these same lines, a Gross Weight increase to 4000 would result in a
stall speed of roughly 104 mph. Using 1.3  x Vso, your landing speed would
now be 135 mph. Your brakes, ignoring the effects of aerodynamic braking,
would have to absorb 260% more energy to bring you aircraft to a stop.

I have no idea how long your takeoff and landing distances would be. Thats
for another night.

Disclaimer - I'm not an engineer, nor have I slept at a Holiday Inn.

Best Regards,
Mike Hutchins