OTHER: Rotor Concept - Traversing Ideal Twist - Overview

• The following is research and development of a rotorcraft blade that should provide very fast forward speeds and efficient hover. In addition, it should provide a significantly improved L/D ratio during high-speed forward flight.

• The hovering rotor experiences zero velocity and its center.
• The blades of a rotor with ideal twist will have a positive pitch of 90º (vertical chord) at the center of the rotor; if it were possible to extend the blade to the very center of the mast.
• A theoretical 90º blade pitch at the center of the mast is not a problem on a hovering rotor, since there is no velocity at this location. Of course, ideal twist reduces logarithmically (inverse exponential) when moving outward from the mast toward the tip.

• A rotor with forward velocity has a circular 'reverse velocity region' on its retreating side. The spanwise location on the blade that intersects the circumference of this reverse velocity region will experience zero forward velocity airflow. This is identical to the zero in-plane airflow at the center of the hovering rotor.
• At the circumference of this reverse velocity region there will be a lateral airflow on the blade due to the lateral component of its movement.
• This circumference will increase as the reverse velocity region increases, which will result in the intersection location on the blade moving out toward the tip where the lateral airflow on the blade is faster. However, the rotor will be slowing down as one of the causes of the reverse velocity region's increase and this will decrease the lateral airflow on the blade at this intersection point.
• The longitudinal airflow will be zero and the lateral airflow will be minimal at this intersection point. Therefore, the pitch of the blade at this location on its span can be vertical with little or no detrimental effect, because there is minimal airflow normal to the surface of the vertical blade segment.
• In other words, this rotor will operate by taking the rotor characteristics, which exist at the center a hovering rotor with ideal twist, and moving these characteristics outward along the span the retreating blade.
• In other words, the center of ideal twist is always concentric with the intersection of the blade's pitch axis and the circumference of the circle of reverse velocity. 
• The retreating blade has positive twist inboard of this intersection and negative twist outboard of this intersection. I.e. the blade has negative pitch inboard of this intersection and positive pitch outboard of this intersection.

• The blades always have positive angles of attack and the airfoils' leading edges are always the 'leading edge' in respect to the airflow.
• The blades are pointing straight up at the location on their span (or theoretical span when mu > 1) where the airflow is zero.
• The drawing above shows the azimuth of the blades where the tip is experiencing zero airflow at various forward velocities.
• The blades will have a very large twist on either side of the location of zero airspeed, where the blade element is oriented vertically. This is comparable to 'ideal twist'

• Taking this concept to the extreme ~
• Consider the ability slow the rotors to the point of having 'stopped rotors'.
• Then consider the possibility of intentionally stopping the rotors upon the loss of power and gliding to a landing. This being an option, along with autorotation.
• Then consider the option of landing and taking of using a runway and not even starting the rotors.

• The tip speed of the rotor will slow as the forward velocity of the craft increases.
• The average speed of the twist as it moves back and forth alone the span of the retreating blade will be 0.63 * tip speed ratio (μ) * tip speed of rotor at cruise (ΩR).
• The speed (should be? / may be?) 174 fps (118 mph) for all sizes of craft.

• The segments are only out of rotational alignment with the adjacent segment when they are rotating about the feathering axis and this rotation only takes place at the location of zero airflow.
• There is the possibility of neutralizing rotor induced vibration at the source. This ability exists because there are many independent segments on all blades.
• The blades could be made slightly asymmetrical to improve their lift during stopped rotor cruise. This may result in vibration during hover since half the blades will have an inverted asymmetrical profile, but perhaps this vibration could be substantially removed.
• It looks like the lateral component of airflow passing the blade will be attempting to resist the rotation about the spare, in both the 3rd and the 4th quadrants.

• US 5,405,104 ~ Stopped rotor aircraft utilizing a flipped airfoil X-wing

1. See OTHER: Rotor Concept - Rotor X Wing - Traversing Twist - Simplistic Method
2. See OTHER: Rotor Concept - Rotor X Wing - Traversing Twist - Advanced Method

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