Centripetal acceleration determination, centripetal acceleration based velocity tracking system and methods

• US 9,309,004 B2
• Filed: 09/20/2013
• Issued: 04/12/2016
• Est. Priority Date: 09/21/2012
• Status: Active Grant

• Current Assignee: Merlin Technologies Incorporated
• Original Assignee: Merlin Technologies Incorporated
• Inventors: Mercer, John E.
• Primary Examiner(s): Algahaim, Helal A
• Assistant Examiner(s): Mott, Genna
• Application Number:
  US14/032,375
• Publication Number:
  US 20140088800A1
• Time in Patent Office: 935 Days
• Field of Search: 701/2, 701/7, 701/10, 701/14, 701/120, 701/121, 701/122
• US Class Current: 1/1
• CPC Class Codes: B64D 43/02 for indicating aircraft speed or stalling conditions
• CPC Class Codes: G01P 15/14 by making use of gyroscopes gyroscopes per se G01C19/00
• CPC Class Codes: G01P 5/00 Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft application of speed-measuring devices for measuring volume of fluid G01F
• CPC Class Codes: G01P 7/00 Measuring speed by integrating acceleration measuring travelled distance by double integration of acceleration G01C21/16
• CPC Class Codes: G01S 19/39 the satellite radio beacon positioning system transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO

Abstract

The flight of an aircraft is characterized in terms of Earth-based reference system data for a first position and a second position of the aircraft that are separated by a time increment. A centripetal acceleration of the aircraft is determined based on the Earth-based reference system data for the positions in conjunction with the time increment. A rate of rotation is established corresponding to the time increment in an aircraft-based reference system. Aircraft airspeed is determined based on the centripetal acceleration and the rate of rotation. A turn can be detected as characterized by a change in track angle from a prior GPS packet compared to a new packet. Aircraft turns can be detected based on a change in track angle in GPS packets. Compensation can be applied to a gyro based on centripetal acceleration such that the gyro more accurately responds to the Earth gravity axis.

Claims

1. A method for determining an airspeed of an aircraft in flight during a turn, said method comprising:

characterizing the flight of the aircraft in terms of Earth-based reference system data for a first position and a second position of the aircraft that are separated by a time increment;

determining a centripetal acceleration of the aircraft based on the Earth-based reference system data for the first and second positions in conjunction with the time increment;

establishing a rate of rotation corresponding to the time increment in an aircraft-based reference system; and

determining the airspeed based on the centripetal acceleration and the rate of rotation.

2. The method of claim 1 wherein characterizing uses the Earth-based reference system data as GPS data that is generated by a GPS system that is carried by the aircraft.

3. The method of claim 2 wherein the GPS data comprises a first GPS packet for the first position and a second GPS packet for the second position.

4. The method of claim 3 wherein determining the airspeed uses no more than the GPS data and the rate of rotation as input values.

5. The method of claim 3 wherein the GPS data for each of the first and second GPS packets is characterized as a groundspeed vector including a magnitude and a track angle.

6. The method of claim 3 wherein the GPS data for each of the first and second GPS packets is characterized by a north component and an east component of groundspeed.

7. The method of claim 1, further comprising:

resolving a difference between the Earth-based reference system data for a first groundspeed vector at the first position and a second groundspeed vector at the second position into northing components and easting components and determining the centripetal acceleration based on a change in the northing component from the first position to the second position, a change in the easting component from the first position to the second position and the time increment.

8. The method of claim 7 further comprising:

representing the northing component change as Δ

V_N, the easting component change as Δ

V_E, the time difference as Δ

t, and determining the centripetal acceleration, α

, as

9. The method of claim 7, further comprising:

determining a vertical velocity acceleration;

comparing the vertical velocity acceleration to a groundspeed-heading change acceleration; and

selecting one of a two dimensional acceleration vector or a three dimensional acceleration vector for the centripetal acceleration based on the comparison.

10. The method of claim 1 wherein determining the airspeed uses the expression:

V=α

/ω

where V is the airspeed, α

is the centripetal acceleration and ω

is the rate of rotation.

11. The method of claim 1 wherein determining the rate of rotation includes monitoring an output of a rate gyro onboard the aircraft which is indicative of changes in a yaw orientation of the aircraft.

12. The method of claim 11 wherein monitoring the output of the rate gyro includes reading a plurality of outputs of the rate gyro during the time increment and averaging the plurality of outputs to serve as the rate of rotation.

13. The method of claim 1 wherein establishing the rate of rotation includes reading a heading gyro to determine a first heading for the first position and a second heading for the second position and determining the rate of rotation based on a difference between the first position heading and the second position heading in conjunction with the time increment.

14. The method of claim 1, further comprising:

prior to said characterizing, providing a GPS system that is carried by the aircraft which GPS system outputs GPS data as a series of GPS packets for selective use as the Earth-based reference system data such that a first packet is selected from the series in association with the first position and a second packet is selected from the series subsequent to the first packet and the second packet is associated with the second position.

15. The method of claim 14, further comprising:

saving at least a portion of the series of GPS packets in a rolling buffer for selection of at least the first packet therefrom based on a comparison to a current packet that terminates the series of GPS packets.

16. The method of claim 14, further comprising:

applying a packet selection interval to the series of GPS packets such that the first selected packet and the second selected packet are spaced apart by a predetermined number of unused packets.

17. The method of claim 14, further comprising:

applying a packet selection interval to the series of GPS packets such that the first selected packet and the second selected packet are spaced apart by at least a predetermined amount of time.

18. The method of claim 14, further comprising:

applying a packet selection interval to the series of GPS packets having a duration that is based on a rounding error in the GPS data such that the first selected packet and the second selected packet are spaced apart in time by at least a predetermined amount of time.

19. The method of claim 1, further comprising:

at least one of (i) displaying the airspeed and (ii) providing the airspeed to a control system of the aircraft.

20. An apparatus for determining an airspeed of an aircraft in flight during a turn, said apparatus comprising:

a GPS receiver for characterizing the flight of the aircraft in terms of Earth-based reference system data for a first position and a second position of the aircraft that are separated by a time increment;

a processor configured for

determining a centripetal acceleration based on the Earth-based reference system data for the first and second positions in conjunction with the time increment,

establishing a rate of rotation corresponding to the time increment in an aircraft-based reference system, and

determining the airspeed based on the centripetal acceleration and the rate of rotation.

21. The apparatus of claim 20, further comprising:

a rate sensor for monitoring a rate of change in a yaw orientation of the aircraft; and

said processor further configured for generating the rate of rotation based on the rate of change in the yaw orientation.

22. The apparatus of claim 20, further comprising:

a heading gyro for producing a first heading for the first position and a second heading for the second position; and

said processor further configured for determining the rate of rotation based on a difference between the first position heading and the second position heading in conjunction with the time increment.

23. A method for monitoring the flight of an aircraft, the aircraft carrying a GPS system which outputs GPS data as a series of GPS packets for selective use as Earth-based reference system data, said method comprising:

periodically monitoring at least selected ones of the series of GPS packets to serve as the Earth-based reference system data for detecting that the aircraft is engaged in a turn based on a track angle that forms part of each GPS packet;

detecting a turn as characterized by a change in the track angle from a prior packet corresponding to a prior position of the aircraft to a new packet corresponding to a new position of the aircraft;

determining a centripetal acceleration based on the prior packet, the new packet and a time increment that separates the prior packet and the new packet;

establishing a rate of rotation corresponding to the time increment in an aircraft-based reference system; and

determining the airspeed based on the centripetal acceleration and the rate of rotation.

24. An instrument, comprising:

a GPS receiver for characterizing the movement of a craft that is supported by a moving ambient in terms of Earth-based reference system data for a first position and a second position of the craft that are separated by a time increment;

at least a selected one of a heading gyro to provide a heading output for tracking a heading of the craft in a craft-based reference system and a rate sensor for monitoring a rate of change of a yaw orientation of the craft in the craft-based reference system;

a processor configured for

determining a centripetal acceleration based on the Earth-based reference system data for the first and second positions in conjunction with the time increment,

establishing a rate of rotation corresponding to the time increment in the craft-based reference system based on the heading output if the heading gyro is selected or based on the rate of change of the yaw orientation if the rate sensor is selected, and

determining a velocity of the craft in a turn relative to the moving ambient based on the centripetal acceleration and the rate of rotation.

25. A method for monitoring the flight of an aircraft, the aircraft carrying a GPS system which outputs GPS data as a series of GPS packets, said method comprising:

a) at least periodically monitoring selected ones of the series of GPS packets for detecting that the aircraft is engaged in a turn based on a track angle that forms part of each GPS packet as characterized by a change in the track angle from a prior packet corresponding to a prior position of the aircraft to a subsequent packet corresponding to a subsequent position of the aircraft;

b) responsive to detecting a turn, determining a centripetal acceleration of the aircraft based on the prior packet, the subsequent packet and a time increment that separates the prior packet and the subsequent packet;

c) establishing a rate of rotation of the aircraft corresponding to the time increment in an aircraft-based reference system; and

d) determining an airspeed of the aircraft based on the centripetal acceleration and the rate of rotation.

26. The method of claim 25, further comprising:

repeating (a)-(d) for at least one additional packet corresponding to at least one additional position of the aircraft wherein the additional packet serves as the aforerecited subsequent packet and the aforerecited subsequent packet serves as the aforerecited prior packet to determine a subsequent airspeed of the aircraft based on the centripetal acceleration and the rate of rotation.

27. The method of claim 25, further comprising:

e) responsive to detecting that a turn is not in progress, performing at least one of displaying an indication to a pilot of the aircraft and initiating an output to an aircraft control system.

28. The method of claim 25 further comprising:

e) responsive to detecting a turn, switching an autopilot from maintaining a GPS groundspeed to maintaining airspeed as determined based on the centripetal acceleration and the rate of rotation.

29. A method for monitoring the flight of an aircraft, said method comprising:

periodically monitoring a change in a yaw orientation of the aircraft;

performing a turn detection procedure based at least in part on a current value of the change in the yaw orientation;

responsive to detecting a turn, characterizing the flight of the aircraft in terms of Earth-based reference system data for a first position and a second position of the aircraft that are separated by a time increment;

determining a centripetal acceleration of the aircraft based on the Earth-based reference system data for the first and second positions in conjunction with the time increment;

establishing a rate of rotation corresponding to the time increment in an aircraft-based reference system; and

determining an airspeed of the aircraft based on the centripetal acceleration and the rate of rotation.

30. The method of claim 29, wherein said turn detection procedure comprises:

comparing a current value of the change in yaw orientation to a yaw window minimum value as a threshold for purposes of detecting that the aircraft is engaged in a turn.

31. The method of claim 30, further comprising:

specifying the window minimum value to include a minimum change in yaw orientation of the aircraft for a specified time period.

32. The method of claim 31 including selecting the minimum change in yaw orientation and the specified time period based, at least in part, on a standard rate turn for the aircraft.

33. The method of claim 29, said turn detection procedure comprising:

specifying a window minimum value to include a minimum change in the yaw orientation of the aircraft for a specified time period;

summing a series of yaw orientation readings obtained during the specified time period to establish a total change in the yaw orientation over the specified time period; and

comparing the total change in the yaw orientation to the yaw window minimum value as a threshold to detect that the aircraft is engaged in a turn.

34. The method of claim 33, said turn detection procedure further comprising:

before said summing, testing an initial yaw orientation reading against a trigger threshold to determine that the initial yaw orientation reading is responsive to an actual turn, as opposed to momentary heading deviations of the aircraft.

35. The method of claim 33 further comprising:

generating the series of yaw orientation readings based on an output of a selected one of a heading gyro and a yaw rate gyro.