Mast Dampener and Collective Pitch for a Rotocraft

1 . A method of operating an aircraft having a rotor, comprising:

(a) determining a true airspeed of the aircraft;

(b) determining a rotational speed of the rotor;

(c) varying a collective pitch relative to the rotational speed; and

wherein step (c) comprises determining a rotational speed vs collective pitch curve, programming a controller with the curve, then with the controller, varying the collective pitch in accordance with at least a portion of the curve.

2 . The method according to claim 1 , wherein step (c) further comprises:

at take-off of the aircraft, maintaining the collective pitch at a substantially constant take-off level collective pitch; and

when the rotational speed of the rotor falls below the take-off level collective pitch corresponding to the rotational speed vs collective pitch curve, decreasing the collective pitch in a selected relationship with rotational speed as the rotational speed continues to decrease; then

at a selected lower level of rotational speed, maintaining the collective pitch substantially constant as rotational speed decrease more than said lower level.

3 . The method according to claim 1 , wherein step (c) further comprises tilting a mast of the rotor in fore and aft directions to maintain a desired rotational speed of the rotor.

4 . The method according to claim 1 , wherein step (c) further comprises:

at take-off of the aircraft, maintaining the collective pitch at a substantially constant take-off collective pitch;

comparing the take-off collective pitch to the decrease in actual rotational speed as the aircraft leaves the ground; then

when the actual rotational speed crosses below the rotational speed that corresponds to the take-off collective pitch as observed on the curve, decreasing the collective pitch in accordance with at least a portion of the curve.

5 . The method according to claim 1 , wherein step (c) further comprises decreasing the collective pitch as the rotational speed decreases down to a selected lower level of rotational speed, then maintaining the collective pitch substantially constant as rotational speed decreases beyond the selected lower level.

6 . The method according to claim 5 , further comprising:

below the selected lower level, tilting the rotor fore and aft to maintain a selected minimum rotor RPM level, whereby tilting the rotor aft increases the rotor RPM and tilting the rotor forward decreases the rotor RPM.

7 . The method according to claim 1 , wherein the aircraft has wings that provide substantially all of the lift required for the aircraft when reaching cruise conditions, and wherein the method further comprises:

prior to reaching cruise conditions and when the rotor is still providing a significant portion of lift for the aircraft, automatically tilting a mast of the rotor to maintain a desired angle of attack for the wings; and

when at cruise conditions, automatically tilting a mast of the rotor in fore and aft directions to slow the rotor and maintain the rotor at a selected RPM.

8 . A method of operating an aircraft having a rotor, comprising:

measuring the true airspeed of the aircraft;

measuring a rotational speed of the rotor; and

varying a collective pitch relative to the rotational speed, wherein varying the collective pitch in relation to the rotation speed comprises determining a rotational speed vs collective pitch curve that limits flapping to a selected range for each airspeed, programming a controller with the curve, and selecting a desired take-off level collective pitch.

9 . The method according to claim 8 , wherein varying the collective pitch in relation to the rotation speed further comprises:

determining, using the controller, a lower rotational speed level on the curve that corresponds to the take-off level collective pitch; and

at take-off of the aircraft, maintaining the collective pitch at a substantially constant take-off level collective pitch until reaching this lower rotational speed level.

10 . The method according to claim 9 , further comprising:

responsive to maintaining the collective pitch at a substantially constant take-off level collective pitch until reaching this lower rotational speed level, decreasing the collective pitch in accordance with the curve as the rotation speed decrease beyond this lower rotation speed level to a selected even lower rotational speed level; and

then maintaining the collective pitch substantially constant as rotational speed decreases more than the even lower rotational speed level.

11 . The method according to claim 8 , controlling the tilt of the rotor fore and aft to maintain a desired minimum rotational speed of the rotor.

12 . A method of operating an aircraft having a rotor, a set of wings, and a propulsion source, comprising:

(a) determining a rotational speed vs collective pitch curve for the aircraft and programming a controller with the rotational speed vs collective pitch curve;

(b) pre-rotating the rotor, operating the propulsion source, and increasing a collective pitch of the rotor to cause the aircraft to lift off and commence forward flight;

(c) during the forward flight, tilting the rotor aft to cause the rotor to auto-rotate;

(d) measuring a true airspeed of the aircraft;

(e) measuring a rotational speed of the rotor;

(f) varying the collective pitch, using the controller, according to at least part of the rotational speed vs collective pitch curve.

13 . The method according to claim 12 , wherein the curve of step (a) reaches a substantially constant level of collective pitch after which the controller maintains the collective pitch substantially constant as the rotational speed decreases.

14 . The method according to claim 12 , wherein:

the rotational speed vs collective pitch curve of step (a) has a maximum collective pitch at take-off;

step (b) comprises at take-off selecting a take-off collective pitch less than the maximum collective pitch defined by the rotational speed vs pitch curve, the take-off collective pitch corresponding to a particular rotational speed on the rotational speed vs collective pitch curve; and

step (f) comprises maintaining the selected take-off collective pitch until the actual rotational speed reaches the particular rotational speed on the rotational speed vs collective pitch curve, then varying the collective pitch according to at least a portion of the curve as the rotational speed decreases beyond the particular rotational speed.

15 . The method according to claim 12 , wherein step (c) comprises controlling the amount of tilt of the rotor with the controller to maintain a selected minimum auto-rotational speed of the rotor.

16 . The method according to claim 12 , wherein the curve of step (a) is based on adjusting the collective pitch at a level versus rotational speed that limits flapping of the rotor to a selected range.

17 . The method according to claim 12 , further comprising disabling step (g) during forward flight and manually controlling the collective pitch.

18 . The method according to claim 12 , wherein steps (c) and (g) are coordinated to substantially unload the rotor.

19 . The method according to claim 12 , wherein:

the rotational speed vs. collective pitch curve of step (a) has a maximum collective pitch at take-off and a substantially constant minimum collective pitch that occurs at and beyond a lower level rotational speed;

step (b) comprises at take-off selecting a take-off collective pitch less than the maximum collective pitch defined by the rotational speed vs pitch curve, the take-off collective pitch having a corresponding lower level rotational speed on the rotational speed vs. collective pitch curve;

step (f) comprises maintaining the selected take-off collective pitch until the actual rotational speed reaches this lower level rotational speed, then varying the collective pitch according to the curve as the actual rotational speed falls below this lower level rotational speed; and

step (f) comprises maintaining the collective pitch at the minimum collective pitch after the actual rotational speed reaches and falls below an even lower level rotational speed.

20 . The method according to claim 12 , further comprising, during a short roll or zero airspeed landing, the controller controlling an increase in collective pitch in order to maintain the required lift for the aircraft.