Glad someone raised this topic. Too lazy to do it myself. Assuming
a LSA gross wt. aircraft (1320 lbs.) with a wing that weighs 200 lbs.
and you want to test the wing for 4 g's. 4 possible
scenarios.....The first three I have seen in "reputable"
publications...you know...the ones you have to PAY for. The 4th one
is the only other one I could think of. I think we've decided #1 is
wrong. Turning the plane upside down and supporting the frame on the
fuselage. How many bags of manure do you pile on the wing to test.
Assumptions: each bag of manure weighs 1 lb.

Scenario #1 1320 x 4 ( 5280 )
Scenario #2 1320 - 200 x 4 ( 4480 )
Scenario #3 1320 - 200 x 4 + 200 ( 4680 )
Scenario #4 1320 x 4 - 200 ( 5080 )
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OR....

1320 -200 =1120 x 4 = 4480 -200 = 4280

AC weight - wing weight cause wing is supported by the air in real flying so
G's will not load the spar, then multiply by G's _then_;
subtract the weight of the wing, since gravity is pulling on the wing in
the load test, so you can take that many bags bags off.
(since gravity is doing 200 pounds of the work for you)

One fact that should be mentioned is the location of the bags. They should
be placed outwards along the wing in the approximate distribution of lift.
Also, place them centered front to back along the ribs to represent the
center of lift for your airfoil at about an angle of attack that would be
necessary to pull that many G's. When in doubt, rearward would the way to
go. My reason for wanting to do this is to see if the wing takes on extra
twist trailing edge which could lead to a very nasty early tip stall.

Now, how about the fact that conventional airplanes have a tail that is
pushing down to achieve stable flight. That "weight" has to be "lifted" by
something, and that would have to be the wing. Better get some more bags.
How many? Up close to 10% ? That is only a guess; anyone know? So 10% of
4480 is 480 more bags, right?

That puts our wing load test up to 4760.

Wait !!! Did you take into account that the fuselage contributes a
substantial percentage of lift depending on the design? If you knew how
much, you could subtract that calculated factor from the weight you are
going to have to put on the wing for the test.

There are other factors you should think about, such as extra loads placed
on the rear spar due to aerodynamic forces created by the flaps and
ailerons. Somewhere about now my head starts to hurt, so I add bit more
for the wife and kids and let it go at that

Whew! There ARE reasons why people go to school to get Aerodynamic
Engineering degrees.

More food for thought?
--
Jim in NC