Multi-blade propellers

A variable pitch multi-blade propeller of use more particularly as the rear rotor of a rotary-wing aircraft comprising

• an axis of the rotor,
• at least one pair of blades mounted diametrically opposed with respect to said rotor axis,
• a tubular rotor driving shaft bearing a rigid rotor hub rotatably mounted around said rotor axis,
• said at least one pair of blades including
• a single composite spar common to the two said blades secured at its central part to said rotor hub and made of fibers having high mechanical strength and agglomerated by a synthetic resin,
• and two radial shells having an aerodynamic cross-section and secured to said composite spar, one on each side of said rotor hub,
• a pitch control shaft slidingly mounted through said tubular driving shaft, said hub and the central part of each said spar for collectively controlling the pitch angles of all said blades,
• a coupling element substantially perpendicular to and integral with said pitch control shaft,
• a pitch control assembly with the inward end of each said shell secured to said assembly and subjecting said shell to a torque centered on the longitudinal axis of the corresponding said spar,
• each said composite spar being made up of a single elongated strip, the fibers of which are all unidirectional and longitudinal fibers,
• said strip being made up in its central portion, between said two corresponding shells, of two flat bundles each presenting fibers all extending without any interruption from one end of said corresponding bundle to the other end, and having a slot defined in the middle of said strip by the central parts of said two bundles being separated one from the other,
• said pitch control shaft directly and freely slidingly mounted thrugh said slot,
• said shell of each said blade being internally connected along its entire length to the corresponding part of said elongated strip by a mass of adhesive synthetic cellular or foam material.