1621

Item 1621

DESIGN: AeroVantage ~ PropRotor - Outside Information - Sikorsky's Variable Diameter Tiltrotor (VDTR)

Notes:

Sikorsky's 'Variable Diameter Rotor' is a proposal to reduce this limitation. However, the mechanisms for varying the length of the blades during flight create their own set of problems. It reduces the disk area in cruise to 70 % of what it is in hover, where as the 2x4 Proprotor's reduction of disk area is 50%.

Related Articles Etc:

The Attributes of a Variable-Diameter Rotor System Applied to a Civil Tiltrotor Aircraft. Have copy on E-drive & hard copy up to page 72.

A Variable Diameter Short Haul Civil Tiltrotor - An overview of the concept - Have hard copy.

Design and Development of a Tabletop Variable Diameter Tiltrotor Demonstrator - This was a video of a university project. The rotor used a spring to assist in the varying of the blade length. I was unable to figure out how it could actually work.

Variable Diameter Rotor ~ Sikorsky's Proposed Method to Reduce this Problem:

Patent search on "AN/Sikorsky AND ABST/"Variable diameter"

6,655,915 Drive system for the retraction/extension of variable diameter rotor systems ~ cable (harmonic drive)

6,578,793 Method and apparatus for fiber strap termination ~ cable/strap (harmonic drive)

6,454,532 Harmonic drive system for the retraction/extension of variable diameter rotor systems ~ cable/strap (harmonic drive)

6,030,177 Drive system for a variable diameter tilt rotor.

6,019,578 Sikorsky's Variable diameter rotor blade actuation system.

5,735,670 Rotor system having alternating length rotor blades and positioning means therefor for reducing blade-vortex interaction (BVI) noise

5,655,879 Mounting arrangement for variable diameter rotor blade assemblies ~ jackscrew assembly

5,642,982 Retraction/extension mechanism for variable diameter rotors

5,636,969 Torque tube/spar assembly for variable diameter helicopter rotors ~ jackscrew assembly

5,620,304 Rotor system having alternating length rotor blades and positioning means therefor for reducing blade-vortex interaction (BVI) noise

5,620,303 Rotor system having alternating length rotor blades for reducing blade-vortex interaction (BVI) noise

Concerns:

IMO the rotor blades must have a very large amount of rigidity to deliver the cyclic moments. Will the variable diameter mechanism be able to handle these demands?

Comparison between; Variable Diameter Tiltrotor, V22 or V44 Tiltrotor, and AeroVantage 1x2 or 2x4:

	(VDTR)	V-22 Osprey	AeroVantage 1x2	AeroVantage 2x4
Gross Weight: (lbs)	50,000	52,600 max.
Cruise Speed: (kts)	350
Range: (nm)	600
Rotor Diameter: (ft)	35.5 - 53.0	38.0	46 ⁽¹⁾	⁽¹⁾
Disk Area: (ft) per rotor	990 - 2,207.0	1,135.0	(2,207+1,135)/2 = 1,671 ⁽¹⁾	⁽¹⁾
Rotor Cutout (ft) & (%R)	8.75 \| 33%	insignificant	insignificant	insignificant
Number of Blades:	4
Blade Area: (ft²)	x	261.5
Disk Loading - Hover: (lb/ft²)	11.33	23.2
Rotor Speed - Hover: (rpm)	216
Rotor Speed - Cruise: (rpm)	216
Tip Speed - Hover: (ft/sec)	600	780
Tip Speed - Cruise: (ft/sec)	402	662
Wing Area: (ft²)		382 ? 301.4?

(1) This is the size of the Effective Aerodynamic Disk Area. The front PropRotor(s) will be approximately 10% larger and the rear PropRotor(s) will be approximately 10% smaller.

The V-22 wing area has to be clarified.

Hover:


Tiltrotor ~ Osprey V-22	Comperable ~ Variable Diameter Tiltrotor	Comperable PropRotor 2x4

Cruise:

Not done

Last Revised: May 19, 2010