airdrop troops

[Aleci]

using the ranger which has the airdrop icon. I have tried a few different planes so far fw-200b Condor and ju-352, none of them have worked.
Is is it only specific planes which can transport troops?
I have tried it with minister control on and off with both the planes and the ranger, and still not working, what is it that i might be missing?
I had it working in a different game, but now i would like to know for sure how this works.

[SGTscuba]

Its based on cargo capacity vs weight of the unit. You can check via the units stats