Brian Whatcott wrote:
In responding to the anonymous poster's load test anxiety, I let the
facts run away from me.

Here is the test question:
You have supported a 1000 lb airplane upside down, and wish to apply a
4g load test.

I'm afraid I found the allegedly simple question confusing because it
makes some unstated, but important, assumptions:

Is this a test of the fuselage or the wings?

Is the airplane supported from the ground by way of the fuselage or the
wings (and if the latter, where on the wings)?

And is this supposed to be a positive or negative load test?

How much weight do you add to the wings etc.?

Depends:

If you put it upside down and proceed to add weight to the wings, then if
the plane is supported by way of the fuselage, most of the plane's weight
appears to be directly supported by the ground supports. Only the wing's
weight (rather light) would seem to be stressing/sheering the wing spars.
So 4000 lbs minus wing_weight would seem to be needed to be added for a
_positive_ 4g load on the wings.

But if the plane is supported by way of the wing tips (say), the plane's
full weight is indeed stressing/sheering the spars. Then you'd have to
add only 3000 lb weight to the _fuselage_ - but this would probably be
something like a _negative_ 4g load test. But I believe not a very
accurate one.

Hands up, all who said 3000 lb.
Correct!
The airframe is already
supporting its own (1g) weight. :-)

Just let me know where you think my reasoning is wrong and why yours is
correct. I'm thinking maybe you composed the post a tad too quickly. ;-)