I've been doing some work on and off over the last few years on the aerodynamics and dynamics of slung loads, and one thing that no-one is really sure of is why some loads spin on a single strop (in forward flight) and others don't.
There does seem to be a stability boundary for box-like loads, based on the length/height and width/height ratios - so for example the US Army CONEX container spins, but the TRIO doesn't. (
Geometry effects on autorotation of rectangular prisms)
However, most of the available data is from wind tunnel tests (basically boxes on a bit of string), so it would be really useful to know what actually happens in the real world.
I'd therefore appreciate any information on peoples experiences with box-like loads (containers, blade boxes, ACUs etc) on a single strop or longline ... which ones spin, which ones don't?
Thanks