DESIGN:UniCopter ~ Rotor - Disk - Advancing Blade Concept (ABC)
Sikorsky's XH-59A ABC
Retreating Blade Consideration:
The Sikorsky ABC's rotor diameter is 36 ft., it has a -10º nonlinear twist, the rotor speed in auxiliary propulsion is 450 ft/sec. (240 rpm). At 217 knots (250 mph) the location of zero free air velocity on the retreating blade is at 14.5 radius (0.81 R). This is 819 fps (0.75 M up to 0.85 M at altitude) at the advancing tip.
Figures 13 in the report 'Advancing Blade Concept (ABC) High Speed Development' shows;
This is the penalty for the -10º of twist. They said that any future blades would have less twist.
The desired top speed is 300 knots (345 mph). This will be 959-fps (0.88 M up to 0.92 M at altitude) at the advancing tip. The total span of the retreating blade at 270º azimuth will be in reverse velocity.
More information on twist: DESIGN: UniCopter ~ Rotor - Blade - General - Twist
More information on the:Sikorsky's XH-59A ABC
Sikorsky's X2 ABC
Currently under development and testing. .
Stepniewski's Synchropter ABC
This is a 119-page evaluation of three different rotorcraft configurations as contenders for an optimal high-speed rotorcraft. The Synchropter (Intermeshing) ABC is his preference. .
The intent is for the advancing blades to provided a sufficiently higher lift then the retreating blades so as to give the combined rotor disk some dihedral without giving it so much that the vertical and lateral vibrations become too severe.
The application of ABC will also allow for faster forward velocity without retreating blade stall. The airfoil should therefor selected for its high-speed performance and not its stall resistant characteristics.
Note that for the Interleaving configuration the intent is to modify the ABC by removing some thrust from the inboard sides of the disks and adding this thrust to the outboard sides of the disks during hover. This means that outboard side of the disks will produce more thrust during both realms of flight.
Note: The pitch and loading on the advancing blade(s) will be higher then normal since the thrust is not evenly distributed between the advancing and retreating sides.This might be only a difference of + & - 10%.
Amount of ABC:
Initially consider the advancing blade supporting 120% of the load and the retreating side supporting 80% of the load.
This means that the advancing side is supporting 116.67 / 83.33 = 50% more than the retreating side.
The intent is for the thrust from the advancing blades on the outside of the two disks to be reasonably matched by the thrust from twice as many retreating blades on the inside interleaving area.
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Last Revised: July 15, 2008