The Stability of Portable Bridges Carried on Slings Beneath Helicopters,

The Australian Armed Forces have class 16 airportable bridges in service, and there is a requirement to transport them beneath Chinook helicopters. Before the bridges can be carried as routine, it is necessary to determine the effects they have on the stability and flying qualities of the helicopter. In this report, information available concerning the operation of helicopters carrying airportable bridges is reviewed. In addition, a series of wind tunnel tests have been made with 115 scale models to determine the maximum safe speed for a helicopter carrying two different class 16 bridges, a 16 m 52 ft clear span, and a 22 m 72 ft raft, separately on a single hook. The tests indicated that the 16 m 52 ft bridge could be carried safely at speeds up to 65 knot on a 16 m 53 ft cable, provided it was slung 5 deg nose up in the static condition, and two small flat fins were attached to the aft end. The raft had to be carried in two loads, A and B, because of weight limitations. Load A, which consisted mainly of deck boxes and accessories, could be safely carried without fins at speeds up to 60 knot on a 16 m 53 ft cable provided it was rigged 1 deg to 2 deg nose up. Load B, which consisted of four ramps and four articulators, could also be carried at 60 knot, but small flat fins were required and it had to be slung 5 deg nose up and carried on a 10 m 33 ft cable.