PASSIVE LOCAL WIND ESTIMATOR

• US 20140129057A1
• Filed: 04/02/2013
• Published: 05/08/2014
• Est. Priority Date: 04/02/2012
• Status: Active Grant

• Current Assignee: Flir Unmanned Aerial Systems AS (Teledyne Technologies Incorporated)
• Original Assignee: Prox Dynamics AS (Teledyne Technologies Incorporated)
• Inventors: Marton, Trygve Frederik, Muren, Petter, Hall, Alexander Philip
• Granted Patent: US 9,031,719 B2
• Time in Patent Office: Days
• US Class Current: 701/7
• CPC Class Codes: G01P 5/02 by measuring forces exerted by the fluid on solid bodies, e.g. anemometer
• CPC Class Codes: G05D 1/0202 specially adapted to aircraft
• CPC Class Codes: G05D 1/0204 to counteract a sudden perturbation, e.g. cross-wind, gust

Abstract

Local wind fields can be predicted if both the airspeed and the ground speed of the helicopter are known. An aircraft that uses an inertial navigation unit, autopilot and estimator allows a measure of ground speed to be known with good certainty. The embodiments herein extends this system to allow an estimate of the local wind field to be found without actively using an airspeed sensor, but instead combining the measurements of an accelerometer and a drag force model and a model of controlled aerodynamics of the aircraft to estimate the airspeed, which again can be used to estimate the local wind speed.

Claims

1. A method in a device for navigating an aircraft, comprising:

measuring a ground speed associated with the aircraft;

estimating an airspeed of the aircraft based on an acceleration a_B of the aircraft and controlled aerodynamic forces applied to the aircraft;

estimating a wind field experienced by the aircraft based on the ground speed and the airspeed; and

navigating the aircraft based on the estimated wind field.

2. The method of claim 1, wherein the device comprises an accelerometer configured to measure the acceleration a_B of the aircraft, wherein the aircraft comprises a mass m, and wherein the estimating the airspeed of the aircraft further comprises:

multiplying the acceleration a_B, with a mass m resulting in a required aircraft force for experienced motion ;

calculating a controlled aerodynamics _A by a model of the controlled aerodynamics _A having at least a rotation rate and a control state of the aircraft as input in addition to a current estimate for the airspeed _A;

subtracting the controlled aerodynamics _A from the required aircraft force for experienced motion resulting in a calculated drag force _D; and

calculating an unfiltered air speed _A from the calculated drag force _D by reverse calculation of a model of the drag force _D being dependent on the unfiltered air speed _A.

3. The method of claim 2, wherein the estimating the wind field experienced by the aircraft further comprises:

subtracting the calculated unfiltered air speed _A from a measured ground speed of the aircraft resulting in a calculated unfiltered wind speed _W.

4. The method of claim 3, wherein the estimating the wind field experienced by the aircraft further comprises:

filtering the calculated unfiltered wind speed _W with a low pass filter resulting in a calculated filtered wind speed _W.

5. The method of claim 4, wherein the estimating the airspeed of the aircraft further comprises:

subtracting the calculated filtered wind speed _W from the measured ground speed _C resulting in the current estimate for the airspeed _A.

6. The method of claim 2, wherein the drag force _D is calculated by:

7. The method of claim 4, wherein the estimating the wind field experienced by the aircraft further comprises:

calculating at least one of wind magnitude and wind direction from the calculated filtered wind speed _W; and

displaying an indication of the at least one of wind magnitude and wind direction on a screen comprised in the aircraft.

8. The method of claim 7, wherein the indication is represented by an arrow which direction corresponds to the wind direction.

9. The method of claim 8, further comprising:

coloring the arrow so that one certain color indicates a wind magnitude within a certain wind magnitude interval.

10. The method of claim 1, wherein the airspeed is a local airspeed and wherein the wind field is a local wind field located in proximity of the aircraft.

11. The method of claim 1, wherein aerodynamics responsive to control state impacts are defined by the model of controlled aerodynamics _A.

12. The method of claim 1, wherein the aircraft is an Unmanned Aerial Vehicle, UAV.

13. A device adjusted to navigate an aircraft, the device comprising:

means for measuring a ground speed associated with the aircraft;

means for estimating an airspeed of the aircraft based on an acceleration a_B of the aircraft and controlled aerodynamic forces applied to the aircraft;

means for estimating a wind field experienced by the aircraft based on the ground speed and the airspeed; and

means for navigating the aircraft based on the estimated wind field.

14. The device of claim 13, wherein the aircraft comprises a mass m, and wherein the device further comprises:

an accelerator configured to measure the acceleration a_B of the aircraft;

a multiplier adjusted to multiply the acceleration a_B with the mass m resulting in a required aircraft force for experienced motion ;

means for calculating a controlled aerodynamics _A by a model of the controlled aerodynamics _A having at least a rotation rate and a control state of the aircraft as input in addition to a current estimate for the airspeed _A;

a first subtractor adjusted to subtract the controlled aerodynamics _A from the required aircraft force for experienced motion resulting in a calculated drag force _D; and

means for calculating an unfiltered airspeed _A from the calculated drag force _D by reverse calculation of a model of the drag force _D being dependent on the unfiltered airspeed _A.

15. The device of claim 14, further comprising:

a second subtractor adjusted to subtract the calculated unfiltered airspeed _A from the measured ground speed _G of the aircraft resulting in a calculated unfiltered wind speed _W.

16. The device according to claim 15, further comprising:

a low pass filter adjusted to filter the calculated unfiltered wind speed _W resulting in a calculated filtered wind speed _W.

17. The device of claim 16, further comprising:

a third subtractor adjusted to subtract the calculated filtered wind speed _W from the measured ground speed _G resulting in the current estimate for the airspeed _A.

18. A device according to claim 14, further comprising:

means for calculating the drag force _D by;

19. The device of claim 18, comprising:

means for calculating at least one of wind magnitude and wind direction from the calculated filtered wind speed _W; and

means for displaying an indication of the at least one of wind magnitude and wind direction on a screen comprised in the aircraft.

20. The device of claim 19, wherein the indication is represented by an arrow which direction corresponds to the wind direction.

21. The device of claim 20, further comprising:

means for coloring the arrow so that one certain color indicates a wind magnitude within a certain wind magnitude interval.

22. The device of claim 13, wherein the airspeed is a local airspeed and wherein the wind field is a local wind field located in the proximity of the aircraft.

23. The device of claim 13, wherein aerodynamics responsive to control state impacts are defined by the model of controlled aerodynamics _A.

24. The device of claim 13, wherein the aircraft is an Unmanned Aerial Vehicle, UAV.

25. The device of claim 13, wherein the means for measuring the ground speed is at least one of an inertial navigation unit, a Global Positioning System (GPS) unit and an autopilot.