... well maybe not quite supersonic, but very fast .
The forward velocities of today's helicopters are limited to approximately 200 knots. This is due to the combination of compression on the tip of the advancing blades and stall of the tip of the retreating blades. There have been various attempts to minimize this limitation, but the successes have been marginal.
A logical way to overcome this problem is to slow the rotors down. Unfortunately, the combination of fast forward velocity and slow rotor rpm means that the retreating blades are experiencing reverse airflow. Of course, air that is flowing over an airfoil in the reverse direction causes a lot of drag, plus other undesirable features.
A couple of years ago Sikorsky proposed a Reverse Velocity Rotorcraft and gave the blades an elliptical profile. Unfortunately, an elliptical airfoil may reduce the drag on the retreating side, but it will increase the drag on the advancing side. This concept was apparently withdrawn.
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Optimal Reverse Velocity Usage
IMHO, for rotorcraft to achieve significantly faster forward speeds the rotor must have conventional airfoil profiles. In addition, the air must flow from the leading edge to the trailing edge at all times. A means of achieving this is to cause the blades to oscillate about their pitch axii as they pass in and out of the region of reverse velocity.
The
Reverse Pitch Rotor Concept is intended to achieve this.
An objective of this thread is to place the Reverse Pitch Rotor Concept into the public domain.