System and method for controlling rotorcraft

1. A method comprising:

receiving a first sensor signal from a pitot tube of a rotorcraft, the first sensor signal including raw airspeed values of the rotorcraft;

receiving a second sensor signal from an accelerometer of the rotorcraft;

measuring a first speed of the rotorcraft, the first speed being groundspeed of the rotorcraft or raw airspeed of the rotorcraft;

determining airspeed values of the rotorcraft, the determining comprising:

using the raw airspeed values in the first sensor signal as the determined airspeed values in response to the first speed of the rotorcraft being less than or equal to a predetermined value; and

estimating the determined airspeed values in response to the first speed of the rotorcraft being greater than the predetermined value, the estimating comprising:

combining the first sensor signal and the second sensor signal with a complementary filter to determine estimated airspeed values; and

using the estimated airspeed values as the determined airspeed values; and

adjusting flight control devices of the rotorcraft according to the determined airspeed values.

2. The method of claim 1 , wherein combining the first sensor signal and the second sensor signal comprises:

integrating the second sensor signal with respect to time to obtain a first filtered signal; and

adding the first filtered signal and the first sensor signal to obtain a second filtered signal, the second filtered signal including the estimated airspeed values of the rotorcraft.

3. The method of claim 1 , wherein the predetermined value is a first threshold when the rotorcraft is accelerating, and the predetermined value is a second threshold when the rotorcraft is decelerating, the second threshold being less than the first threshold.

4. The method of claim 3 , wherein the first threshold is 40 knots, and the second threshold is 25 knots.

5. A rotorcraft comprising:

a pitot tube;

an accelerometer;

a plurality of flight control devices; and

a flight control computer coupled to the pitot tube, the accelerometer, and the flight control devices, the flight control computer being configured to:

receive raw airspeed values of the rotorcraft from the pitot tube;

receive raw forward acceleration values of the rotorcraft from the accelerometer;

measure a first speed of the rotorcraft, the first speed being groundspeed of the rotorcraft or raw airspeed of the rotorcraft;

determine airspeed values of the rotorcraft by:

using the raw airspeed values as the determined airspeed values in response to the first speed of the rotorcraft being less than or equal to a predetermined value; and

estimating the determined airspeed values by combining the raw airspeed values and the raw forward acceleration values in response to the first speed of the rotorcraft being greater than the predetermined value; and

adjusting flight control devices of the rotorcraft according to the determined airspeed values.

6. The rotorcraft of claim 5 , wherein the flight control computer is configured to estimate the determined airspeed values by:

combining the raw airspeed values and the raw forward acceleration values with a complementary filter to determine estimated airspeed values; and

using the estimated airspeed values as the determined airspeed values.

7. The rotorcraft of claim 6 , wherein the flight control computer is configured to combine the raw airspeed values and the raw forward acceleration values by:

integrating the raw forward acceleration values with respect to time to obtain integrated forward acceleration values; and

adding the integrated forward acceleration values and the raw airspeed values to obtain the estimated airspeed values.

8. The rotorcraft of claim 5 , wherein the predetermined value is a first threshold when the first speed of the rotorcraft is less than or equal to the predetermined value, and the predetermined value is a second threshold when the first speed of the rotorcraft is greater than the predetermined value, the second threshold being less than the first threshold.

9. A method comprising:

receiving a first sensor signal from an accelerometer of a rotorcraft;

receiving a second sensor signal from a pitot tube of the rotorcraft;

combining the first sensor signal and the second sensor signal with a complementary filter to determine an estimated speed of the rotorcraft;

adjusting flight control devices of the rotorcraft according to the estimated speed of the rotorcraft;

measuring a groundspeed of the rotorcraft; and

resetting the complementary filter in response to the groundspeed of the rotorcraft being less than a predetermined threshold.

10. The method of claim 9 , wherein the estimated speed of the rotorcraft is an estimate of vertical speed of the rotorcraft.

11. The method of claim 9 , wherein the estimated speed of the rotorcraft is an estimate of airspeed of the rotorcraft.

12. The method of claim 9 , wherein the combining the first sensor signal and the second sensor signal with the complementary filter comprises:

filtering the first sensor signal with a first filter to obtain a first filtered signal;

filtering the second sensor signal with a second filter to obtain a second filtered signal, the second filter and the first filter complementing one another; and

adding the first filtered signal and the second filtered signal to determine the estimated speed of the rotorcraft.

13. The method of claim 9 , wherein the combining the first sensor signal and the second sensor signal with the complementary filter comprises:

subtracting the first sensor signal from the second sensor signal to obtain a noise difference signal;

filtering the noise difference signal to obtain a filtered difference signal; and

adding the first sensor signal and the filtered difference signal to determine the estimated speed of the rotorcraft.

14. The method of claim 9 , wherein the receiving the first sensor signal comprises:

receiving an acceleration signal from the accelerometer; and

integrating the acceleration signal to obtain the first sensor signal.

15. The method of claim 9 , wherein the receiving the second sensor signal comprises:

receiving a velocity signal from the pitot tube; and

using the velocity signal as the second sensor signal.

16. The method of claim 9 , wherein the adjusting the flight control devices of the rotorcraft comprises:

decoupling pilot flight controls of the rotorcraft from the flight control devices according to the estimated speed.