Dave_Jackson
22nd Aug 2008, 22:31
The Preamble:
An objective of the new Sikorsky ~ X2 ABC (http://www.unicopter.com/1465.html)is to increase the forward speed over that of the previous Sikorsky ~ S-69 ABC (http://www.unicopter.com/0891.html) by 30 to 40 knots. Much of this is to be done by reducing the profile and induced drag of the blades. Specifically, to reduce the drag and downward thrust resulting from the negative angle-of-attack airflow over the blade roots on the retreating side.
However, significantly higher forward speeds cannot be achieved by drag reduction alone. Lift must be produced from this Reverse Velocity Region. Extracting more lift from the rotors means that they can be smaller, and this in turn, means that they will generate less total drag.
The Concept:
The X2 is using blade roots that have rounded profiles at both the leading and the trailing edges. This limits the increase in its maximum forward speed.
The concept on this thread is based upon the very opposite. Essentially, this concept has blade roots that have sharp profiles at both the leading and the trailing edges. The aerodynamic advantage of sharp trailing edges is obvious. The problem with sharp leading edges is that they are subject to leading edge stall at small angle of attacks.
However, if the roots of the blades are not subjected to angles of attack that exceed a specific amount, they should not stall.
The Method:
The rotors have Independent Root and Tip Control (http://www.unicopter.com/B436.html). The blade tips are controlled directly by the pilot, perhaps without the need for power assist. However, G-forces, forward airspeed, plus the pilot's collective and cyclic actions etc. are input to a computer. This computer then controls the pitch of the blade roots through actuators, perhaps at rates greater than 1/P.
The rotors have Blades, with Sharp Leading & Trailing Edges Near the Blade Root (http://www.unicopter.com/1613.html).
All of this will allow for additional reductions in the RPM of the rotors, and this allows for greater forward velocities without experiencing excessive compression at the tips of the advancing blades.
_________
Tear the idea apart; or line up for the initial share offering. :)
Dave
An objective of the new Sikorsky ~ X2 ABC (http://www.unicopter.com/1465.html)is to increase the forward speed over that of the previous Sikorsky ~ S-69 ABC (http://www.unicopter.com/0891.html) by 30 to 40 knots. Much of this is to be done by reducing the profile and induced drag of the blades. Specifically, to reduce the drag and downward thrust resulting from the negative angle-of-attack airflow over the blade roots on the retreating side.
However, significantly higher forward speeds cannot be achieved by drag reduction alone. Lift must be produced from this Reverse Velocity Region. Extracting more lift from the rotors means that they can be smaller, and this in turn, means that they will generate less total drag.
The Concept:
The X2 is using blade roots that have rounded profiles at both the leading and the trailing edges. This limits the increase in its maximum forward speed.
The concept on this thread is based upon the very opposite. Essentially, this concept has blade roots that have sharp profiles at both the leading and the trailing edges. The aerodynamic advantage of sharp trailing edges is obvious. The problem with sharp leading edges is that they are subject to leading edge stall at small angle of attacks.
However, if the roots of the blades are not subjected to angles of attack that exceed a specific amount, they should not stall.
The Method:
The rotors have Independent Root and Tip Control (http://www.unicopter.com/B436.html). The blade tips are controlled directly by the pilot, perhaps without the need for power assist. However, G-forces, forward airspeed, plus the pilot's collective and cyclic actions etc. are input to a computer. This computer then controls the pitch of the blade roots through actuators, perhaps at rates greater than 1/P.
The rotors have Blades, with Sharp Leading & Trailing Edges Near the Blade Root (http://www.unicopter.com/1613.html).
All of this will allow for additional reductions in the RPM of the rotors, and this allows for greater forward velocities without experiencing excessive compression at the tips of the advancing blades.
_________
Tear the idea apart; or line up for the initial share offering. :)
Dave