Future tiltrotors

R. Bell and Boeing independently are looking at future tiltrotors and improvements to the current generation. The latter include a variable-geometry rotor with slotted blade providing higher lift in the hover without incurring a power penalty in forward flight. Others address the download issue, and include movable overwing vanes to deflect the rotor downwash and active synthetic jets to delay flow separation over the wing.

S. Bell is studying a larger quad tiltrotor (QTR) with four proprotors. The military version has a C-130-size fuselage, 20t payload and uses V-22-size dynamics. A 120-passenger civil QTR would cruise at 340kt. Boeing’s advanced tiltrotor concept – designed to meet the same NASA runway-independent aircraft needs as Bell’s civil QTR and Sikorsky’s RVR – is a canard configuration with two large-diameter, five-blade proprotors at the tips of a W-planform wing designed to minimize download.

T. Faster rotorcraft have yet to be flight tested even experimentally, but Boeing hopes to fly the unmanned X-50 canard rotor/wing (CRW) demonstrator this year. Previous stoppable rotor/wing rotor/wing designs had problems with conversion between rotor- and wing-borne flights, but CRW is different. Earlier designs used the rotor/wing to provide lift in all modes, whereas the CRW unloads the rotor/wing during conversion, with lift being provided by the foreplane and tailplane.

U. Boeing believes this will ease the transition between the helicopter mode, where the rotor/wing acts as a two-blade reaction-drive rotor, and aeroplane mode, where the rotor/wing is locked perpendicular to the fuselage. The concept simplifies the powerplant design, with warm turbofan exhaust gases ducted to nozzles in the rotor tips for vertical flight, and then redirected rearwards to provide jet propulsion for forward flight.

V. Although it promises to be the first concept to combine the best attributes of rotary- and fixed-wing aircraft, the canard rotor/wing will have to fly successfully to be taken seriously. Until it does, the gap between helicopters and jets will remain.

2. Consult a dictionary and find the meaning of the following words and word combinations:

1. high-thrust blades

2. blade vortex interaction (BVI)

3. the mitigating technologies

4. random noise

5. the airshed

6. windtunnel

7. piezo-electric actuators

8. mechanical swashplate

9. to cancel out noise and vibration

10. the reverse velocity rotor (RVR)

11. tilting forward

12. to enhance safety

13. shed air

14. precursors

15 gearbox struts

16. blade pitch

17. tiltrotor