Rotorcraft Center    of Excellence
Tiltrotor aircraft are essentially hybrids of conventional helicopters and turbo-prop airplanes.  Utilizing two turbine powered rotors that can rotate 90°, tiltrotor aircraft combine the vertical takeoff and hovering capabilities of helicopters with the higher cruising speeds and longer ranges associated with turbo-prop airplanes.  Current tiltrotor designs implement blades with fixed diameters, which compromise performance in either tiltrotor configuration.
Industry and university researchers are currently developing tiltrotor blades that simultaneously change diameter in flight as the rotors rotate, termed variable diameter tiltrotors (VDTR), in order to improve efficiency.   With fully extended rotors during hover and rotors that are retracted by 30% or more for cruising, both modes of flight offer significant improvements in performance.  Larger diameter rotors during hovering not only create maximum lift for greater load carrying but also reduce rotor downwash.  Smaller diameter rotors for cruising allow the engine to operate at 100% rpm, which in turn maximizes engine performance and reduces prop rotor-whirl flutter, wing stiffness, and weight requirements.
Background
•Minimum operating speed of 250 RPM
•Rotor diameter approximately 24” with
 35% diameter reduction capability
•Jackscrew / bevel gear design
•Compatible with previously   constructed tiltrotor mechanism
•
Specifications
Bell-Boeing V-22 Osprey
Bell-Boeing V-22 Osprey
VDTR Mechanism   Solid Model
The PENN STATE CHOPPERS, under the supervision of Dr. Ed Smith and Joshua Schatz, are continuing with the design, construction, and testing of a model scale demonstrator of a variable diameter tiltrotor for the Boeing Defense and Space Group.  The primary focus of this project deals with designing a new and secure platform for mounting the existing variable diameter rotor with jackscrew mechanism to the drive shaft, refining and modifying existing parts of the existing rotor, and attaching the variable diameter rotor to the drive shaft on the tiltrotor assembly in order to attain full functionality with regard to the current design specifications.
The project deliverables include a fully functional variable diameter rotor mounted on the tiltrotor demonstrator, detailed CAD design drawings documenting the geometric design, a final report outlining the entire project, video documentation, a web page, and a poster display at the project showcase on May 2, 2003.
Preliminary designs using CAD software were created and finalized before the machining of the individual parts.  Upon completion of the machining and the appropriate wiring the variable diameter tiltrotor demonstrator was capable of altering rotor diameter by up to 35% while both rotating and tilting on its base.  Connectors were used on wires between certain components to allow the variable diameter rotors to be powered and displayed independently from the larger tiltrotor base for showcase purposes.
Team: The Penn State Choppers
                      Brian Hoffman
                      Duane Kessler
                      Michael Kachmar
                      Harold Bolich
Contacts:     Dr. Edward Smith, PSU
                     Joshua Shatz, Boeing
4 / 28 / 2003