Veeduber wrote:
Hi Guys.

Does that title tickle any memory-bones?

Well, let's see if I can tickle them again. First-off come the ground
rules: The data came from "Handbook of Instruction for Airplane
Designers, Structures Tests" Air Corps, U.S.Army (Not available to
the public)

...and apparently not available to many Airplane Designers, too. :-)
(Because nobody could remember seeing the thing.)

Okay, start with the outline of whatever airfoil you're working
with... which tells you right off that this isn't going to be good for
ALL airfoils. The airfoil used in the Army manual looks suspicious
like the USA-35B, which was used in the Piper Cub... and was the first
thing C.G.Taylor tossed on the rubbish heap when he designed the
Taylorcraft. However, the Army's test wing was tapered and of
aluminum construction. It would be interesting to know the history of
this manual since, from all appearances it didn't do the Army Air
Corps much good.

Using whatever outline you're using, starting at the trailing edge,
come forward 10% of the airfoil's chord. The next section takes 43.8%
of your airfoil's length. Next comes the main load-bearing section:
27.1% of your airfoil's chord, and finally the leading edge section --
19.1% of the airfoil's chord.

The weight is distributed as follows: 20% is suspended on the leading
edge section, 40% is suspended on the mid-wing section, and 40% is
suspended on the aft-wing section. You will note that NO LOAD is
placed on the trailing edge of the wing.

The method is a bit unusual (in my opinion) but it matches the


This is where your note stops. I expect you wanted to continue by asking
for comments. Coupla thoughts:
There's a freebee 2-D airfoil calculator from an MIT instructor which
shows the shape of the low pressure on the upper surface, and the high
pressure on the lower surface for a whole bunch of airfoils. If you
cut these two shapes out of - lets say - lead sheet
and weighed vertical strips from top and bottom, you would have a
representative load for a particular airfoil station.

But the last time I had that code was two or three computers ago....

So, getting down and dirty:
Say a wing balances at 30% chord, then if you evenly loaded the front
30% with 70% of the load, and the back 70% with 30% of the load,
you balance the turning moment (roughly!)

Your USAAC cite puts roughly that proportion before and after the 30% point.
So it seems to make sense. True, load distribution varies with AoA
yada-yada.....

Brian W