DART: Development of an advanced rotor for tilt-rotor

This paper presents the overall development status of the European Tilt-rotor hub program. This hub, which is now entering the manufacturing phase, provides unique innovative features induced by the selected concept of a small radius gimballed and homokinetic 4-bladed rotor. This activity is organised within a consortium of 10 companies led by EUROCOPTER and including major helicopter manufacturers (ECD, AGUSTA/WESTLAND), engineering and research centres (SENER, NLR, ONERA, CIRA), major elastomeric components supplier (PAULSTRA) and a manufacturing company (SPASA). The design activity is supported by the General Engineering calculations that will be presented briefly with emphasis on rotor performance, loads calculations and dynamics studies. A detailed presentation of the selected rotor configuration is presented with a focus on the constant velocity joint, the cuff, the pitch control system, the yoke, and the elastomeric components. The completion of the hub characterisation and fatigue tests is expected on March 2006. Background The DART rotor development is somewhat the legacy of several research activities: the first independent European efforts (before the EUROFAR studies) the recent Integrated European efforts (EUROFAR, ERICA) --------------------------------------------------------------------[1] Rotors design – DART technical manager. Before the EUROFAR program, several European companies had imagined, designed and sometimes tested S/VTOL aircrafts (Ref [1] ,[2] and [3] ). Among them, the ducted propeller concept seemed promising enough to NORD to launch the prototype 500. Flight testing in the late 60’s proved the aircraft was unstable and difficult to control. Since then, the concept of tilting ducted rotor was abandoned in Europe and elsewhere, and paved the way to the tiltrotor concept, as demonstrated by Bell with the XV3 and XV15. Shortly after Nord abandoned the ducted propeller concept, Aerospatiale started a paper study on the tilt-rotor concept (X 910). The EUROFAR (European Future Advanced Rotorcraft) was the first integrated European effort to develop a convertible tilt-rotor. As for DART, European helicopter manufacturers and research centres joined their forces to acquire the knowledge to build a successful tilt-rotor. Emphasis was put in the aerodynamic development of the rotor (Ref [4] ) but extensive work was also performed in the architecture, aircraft performance, aerodynamics, dynamics, handling quality fields (Ref [5] ). It should be noted that the EUROFAR team already selected a 4-bladed rotor to bring significant improvements in terms of noise and vibrations. Several very innovative concepts were proposed to achieve the aeromechanics requirements such as the constant velocity joint, the virtual hinge offset and pitch-flap coupling, but because very little hardware was manufactured within EUROFAR, it was not possible to test full-scale these innovations. In the past, several examples of new rotorcraft configurations were tested. Among them, we find the tilt-wing, the tilt-rotor, the ducted fan as well as several examples of compound aircraft. The only concept, which proved successful, was the Bell tiltrotor. The development of the tilt-rotor in the U.S. was heavily sponsored by the NASA which helped gather a good understanding of the complex aeromechanics features of this aircraft.