A couple of times a year somebody gives me a new undercarriage to certify, where obviously the landing shock is important to know. The way I handle it is as follows: -
(1) Slowly load the undercarriage up until we get fed up, measuring how far the top of the undercarriage / aeroplane / something easy to measure goes down with load.
(2) Plot a graph of deflection versus static load.
(3) Integrate (usually graphically, counting squares is quite therapeutic on a bad Friday) this graph to turn it into energy stored versus static load.
(4) Using my magic book of formulae, I work out the speed at which the undercarriage will be hitting the ground. (For aircraft there are standard formulae which are generally a function of wing loading).
(5) From mass of the aircraft and the impact speed I work out the kinetic energy when it hits.
(6) I plot this energy as a line on the graph at (3) to give me mean impact force.
(7) Divide this by weight to give me the g-loading at impact.
There are a few weaknesses in my method. If the u/c uses any kind of fluid-based shock absorbers (as opposed to springs) then their characteristics depend upon the RATE of application, and so I've no choice but to actually drop it. Also, when I use this test to calculate the various static load tests I have to do to certify the undercarriage, I need to remember that much higher shock loads than static loads are needed to break metallic or composite structures. But this is in the safe sense, and so long as it passes static, there's no problem.
If you can find a formula for descent terminal velocity on your airdrop loads and then apply (1) - (4) above, you should get a meaningful answer.
Finally, this test takes a lot of mass, usually sand or gravel bags. I always advise people planning such tests to first find somebody who either wants a kids sandpit or to gravel their drive!
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