The rotorblades are retained by a tension-torsion pack, a multiturn loop of small diameter music wire, encapsulated, I suppose, in polyurethane or some other elastometer. Small diameter music wire has a tensile strength of upwards from 350 kips and a multiturn pack is very soft in torsion, resulting in low cyclic control force. Nothing new here, just a good way of doing things. Music wire packs have been used for quite a while in certificated helicopters and also in the UltraSport series of home built helicopters, another professional design.

A 'tension-torsion strap' concept was next developed. This was based on an idea commonly used in helicopter main blade retention and most notably in the variable-pitch fans used in the NOTAR (no tail rotor) helicopter [6]. Tension-torsion straps are made by potting tows of uni-directional strong fibres within an elastomeric resin. Some kind of termination arrangement is provided for transferring the external loads to the fibres. The straps are very strong and stiff axially, but have low torsional stiffness. The NOTAR tension-torsion straps are made by looping many turns of Kevlar yarn around a pair of circular spools and then potting within a polyurethane elastomer. One spool is attached to the blade end and the other to the rotor. The strap transmits the centrifugal load to the hub but the blade can twist freely.