main rings, and wire bracing; however, the structural members were of Duralumin tubing, rather than the built-up girders of earlier rigids. The structure was described as "half as heavy and twice as strong as the structural material in the ill-fated Hindenburg." The hulls were enclosed by a double-layer outer cover, comprising an outer Tedlar layer and an inner layer of ripstop nylon treated with dope. The gas cells were also made of Tedlar. The fins were of sheet Duralumin on frames of the same material, joined primarily with epoxy resin rather than by riveting. Landing gear The airship had a tricycle undercarriage with a non-steerable nosewheel beneath the central hull and steerable (via a connection with the rudders) wheels at the tips of the ventral fins at the aft ends of the outer hulls. The nosewheel functioned as an "internal mooring mast," with a telescopic strut that allowed the ship's angle of attack to be varied while moored (e.g. nose down to hug the ground or nose up in preparation for takeoff) and a tie-down fitting at its lower end. Propulsion The AEREON III was powered by a single engine located at the aft end of the central hull. This engine was reported in 1962 as being a Solar Titan gas turbine of , but the engine eventually installed was described as a "four-cylinder McCullough" (sic—presumably McCulloch). The engine drove a diameter, two-bladed pusher propeller (actually a helicopter rotor rotating in the vertical plane). The location of the propeller at the aft end of the hull was stated to assist in boundary layer control and its cyclic pitch feature to facilitate low-speed control. AEREON patented this propulsion and control system in 1966. However, the propeller required shortening before trials commenced because of its "greatly excessive vibration." Buoyancy control Five propane burners in each hull enabled the helium to be heated to increase lift; the ship would be about heavy (i.e. weight greater than static lift) with the gas cells 83 percent filled with helium, but heating the gas would increase the static lift by . The helium could also be cooled by admitting air through vents in the noses of the hulls, with the assistance of blowers. The double-layer outer cover, mentioned above, facilitated thermal insulation of the gas cells. AEREON also patented the pressurization and buoyancy-control system, in 1965. One source states that the AEREON IIIs buoyancy-control capabilities would