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

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.

What is claimed is: 
     
         1 . An apparatus, comprising:
 an instrument for characterizing the flight of an aircraft during a turn 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 gyro that is supported by the aircraft and provides gyro outputs that are intended to be responsive to an Earth gravity axis; and   a processor configured for determining a centripetal acceleration of the aircraft responsive to said turn based on the Earth-based reference system data for the first and second positions in conjunction with the time increment and for applying compensation to said gyro based on the centripetal acceleration such that the gyro more accurately responds to the Earth gravity axis.   
     
     
         2 . The apparatus of  claim 1  further comprising:
 a GPS system that is carried by the aircraft to produce the Earth-based reference system data as GPS data and the processor uses the GPS data and the time increment to determine the centripetal acceleration. 
 
     
     
         3 . The apparatus 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 apparatus of  claim 2  wherein the processor determines the centripetal acceleration using no more than the GPS data and the time increment. 
     
     
         5 . The apparatus 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 apparatus 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 apparatus of  claim 1 , further comprising:
 said processor further configured to resolve 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 to determine 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 apparatus of  claim 7  wherein said processor is further configured to represent the northing component change as ΔV N , the easting component change as ΔV E , the time difference as Δt, and to determine the centripetal acceleration, α, as 
       
         
           
             
               
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         9 . The apparatus of  claim 1  wherein the centripetal acceleration combines with the Earth's gravitational acceleration to produce an apparent acceleration and the compensation shifts the axis of reference of the accelerometer from the apparent acceleration toward the Earth gravity axis. 
     
     
         10 . The apparatus of  claim 1 , further comprising:
 a GPS system that is carried by the aircraft to serve as said instrument, 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.   
     
     
         11 . The apparatus of  claim 10  wherein said processor saves 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. 
     
     
         12 . The apparatus of  claim 10  wherein said processor is further configured to apply 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. 
     
     
         13 . The apparatus of  claim 10  wherein said processor is further configured to apply 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. 
     
     
         14 . The apparatus of  claim 10  wherein said processor is further configured to apply 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. 
     
     
         15 . A method, comprising:
 characterizing the flight of an aircraft during a turn 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 responsive to said turn based on the Earth-based reference system data for the first and second positions in conjunction with the time increment; and   applying compensation to a gyro that is intended to slave to the Earth gravity axis based on the centripetal acceleration such that the gyro more accurately responds to the Earth gravity axis.   
     
     
         16 . The method of  claim 15  wherein the Earth-based reference system data includes GPS data comprising a first GPS packet for the first position and a second GPS packet for the second position and the centripetal acceleration is determined using no more than the GPS data and the time increment. 
     
     
         17 . The method of  claim 16  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 and determining the centripetal acceleration includes 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 establishing 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. 
     
     
         18 . The method of  claim 17  including representing the northing component change as ΔV N , the easting component change as ΔV E , the time difference as Δt, and determining the centripetal acceleration, α, as 
       
         
           
             
               
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         19 . The method of  claim 15  wherein the centripetal acceleration combines with the Earth's gravitational acceleration to produce an apparent acceleration and applying the compensation shifts the axis of reference of the accelerometer from the apparent acceleration toward the Earth gravity axis.