Here is a copy of any artical that was published back in 1992. It has the
formula to calculate the wing loading of "any" size plane. It is pretty long
so be patient.
Hope this helps everyone.
True wing loading is calculated in weight per cubic foot of wing volume (
justlike the hull displacement in a boat ). Most people discuss it in ounces
per squarefoot. That doesn't work, which is why ppeople usually qualify it by
saying that a big airplane can have a heavier wing loading than a small one.
If you always use pounds per cubic foot, a particular wing loading will have
the same flying characteristics at the same speed, regarless of the airplane
We want our models to fly and land a lot slower than the big ones, so we need
our wing loadings to be much less than those of big airplanes. The big ones
fly smoother, of course.
Here's how to calculate true wing loading in any size airplane, from a
***-band-powered "peanut" to a giant scale model:
Take the wing area given on the plans (560 square inches, for example) and
multiply it by 2/3 the height of the average size rib (technically, the "mean
chord") in the wing (our rib was 1.25 inches high at the spar, so 22/3 is .834
Use 2/3 of the height of the rib because the typical wing rib is 2/3 the area
of a rectangle drawn around it, and the wing volume is thereby reduced from
what you would expect just using the real height of the rib times the wing
area. If the wing is not tapered, you can use any rib, because they are all
the same size.
The result (560 x .834 = 467) is the wolume of the wing in cubic inches, so
divide by 1728 (the number of cubic inches in a cubic foot) to get cubic feet
of wing. This gives you 0.27 cubic feet (467/1728 = .27). Multiply by 25
pounds (per cubic foot) for comfortable loading and you get 6.75 pounds (.27 x
25 = 6.75). That should be the maximum weight of your airplane.
Wasn't that easy? This calculation will tell you a lot about the flying
characteristics of your model before it ever leaves the ground.
This process, by the way, explains why biplanes are usually considered to have
only 75% of theirrr wing area available for use in the "square inch" wing
loading calculations. The wing ribs in a biplane are much smaller than those
in a monoplane of the same wing area. This simply reduces the wing volume/wing
area ratio in a biplane, and consequently makes it a less efficient lifter of
weight. It isn't some arcane "interference"; it's just low wing volume.
A reasonable wing loading is 25 pounds per cubic foot of wing for a scale
fighter of for a model of any powerful airplane. Here are some other general
guidelines to wing loading" 15 pounds per cubic foot is a "floater" in any
size; 20 pounds per cubic foot is a sporty flier; and 30 pounds per cubic foot
I tried 35, several times. It can be done, but it takes a lot out of you, and
a lot out of your wallet. It doesn't do your pride any good, either.
It also takes a lot of really smooth runway, and runways are like money:
there's never enough, and what there is, you've used already.