The tail was split down the centre on the underside (except for the last 2'). Two strips of 3mm thick polypropelene sheet were then glued into the split. The strips are bolted together at regular intervals. As the tail is curved it is assumed that the strips were first bent to the required shape and then drilled and bolted, creating tension between them and therefore retaining the curvature. The strips extend beyond the front of the tail to fit around the performer's waist. Attached to these (padded) extensions are two leather belts. A triangular aluminium reinforcement piece measuring 20 x 3.5" (55.4 x 89mm) is inserted at the thick end of the tail to aid in its support. A piece of ribbed plastic pipe 15mm in diameter and halved down its length has been glued along underside of the tail to hide the split line.
Behind the Mask - the Secrets of Hollywood's Monster Makers (Mark Salisbury & Alan Hedgecock) page 89 includes a photograph of a performer undertaking tests of the alien warrior costume wearing such a tail.
View showing harness and belts
Bottom view showing plastic pipe to hide split
View showing portion of tail lifted away from inner support
Close up view showing inner support mechanism (polypropelene strips)
See also Alien War reproduction tail