GROUND PROXIMITY WARNING SYSTEM UTILIZING RADIO AND BAROMETRIC ALTIMETER COMBINATION

• US 3,715,718 A
• Filed: 08/11/1970
• Issued: 02/06/1973
• Est. Priority Date: 08/11/1970
• Status: Expired due to Term

• Current Assignee: Ralph A. Astengo
• Original Assignee: Ralph A. Astengo
• Inventors: Astengo, Ralph A.
• Primary Examiner(s): Claffy, Kathleen H.
• Assistant Examiner(s): Leaheey, Jon Bradford
• Application Number:
  US05/062,861
• Time in Patent Office: 910 Days
• Field of Search: 340/27R,37NA,26,12A,112A
• US Class Current: 340/970
• CPC Class Codes: G01P 1/103 by comparing the value of the measured signal with one or several reference values in general G01R17/00
• CPC Class Codes: G01P 3/62 Devices characterised by the determination or the variation of atmospheric pressure with height to measure the vertical components of speed measuring pressure in general G01L
• CPC Class Codes: G01S 13/10 using transmission of interrupted, pulse modulated waves determination of distance by phase measurement G01S13/32
• CPC Class Codes: G05D 1/0607 specially adapted for aircraft

Abstract

A ground proximity warning system for an aircraft which produces a warning signal when the rate of descent of the aircraft exceeds a limiting value determined by the aircraft altitude. The rate of descent of the aircraft is calculated from a combination of measurements of the altitude of the aircraft above ground and the barometric altitude of the aircraft. A signal representing the rate of change of the altitude of the aircraft above ground is limited, to minimize false warnings as a result of surface irregularities. The barometric portion of the system is disabled during take-off run and the initial portion of the aircraft climb-out to avoid a false warning resulting from an increased barometric pressure condition during this maneuver. The limits on the aircraft altitude rate signal are modified in accordance with the flight mode of the aircraft, to reduce the sensitivity of the warning system during the final stage of a landing approach. The warning system provides an alarm to the pilot which is an audio tone modulated at a low frequency repetition rate. A soft warning is actuated when the sink rate of the aircraft exceeds a desired level for the altitude at which the aircraft is operating. If the aircraft is also below a limiting altitude, a hard warn signal is provided. The repetition rate of the warning signal, while in a soft warn condition, is a function of the difference between the altitude of the aircraft and the altitude at which the sink rate would be proper. A complementary filter with which the altitude rate signals are combined, includes an operational amplifier connected in an unloading amplifier configuration with a resistive circuit connecting one input signal with the amplifier and a capacitive circuit connecting the other input signal with the amplifier, the resistive and capacitive input circuits forming a low pass filter for the first signal and a high pass filter for the second signal.

Claims

1. An instrument for determining the proximity condition of an aircraft with respect to the ground, comprising:

means for generating a signal representing the altitude of the aircraft with respect to the ground;

means responsive to said altitude signal for generating a signal representing the time rate of change of the aircraft altitude with respect to the ground;

means responsive to said altitude rate signal, limiting the amplitude thereof;

means for generating an aircraft barometric altitude signal;

means responsive to said barometric altitude signal for generating a signal representing the time rate of change of the aircraft barometric altitude;

means for combining long term components of the limited signal representing the time rate of change of the altitude of the aircraft with respect to the ground, and short term components of the signal representing the time rate of change of the barometric altitude of the aircraft, to develop a calculated aircraft altitude rate signal; and

means for combining a function of the calculated altitude rate signal and a function of the signal representing the altitude of the aircraft with respect ground, providing a warning signal when the rate of approach of the aircraft toward the ground is excessive for the altitude of the aircraft with respect to the ground.

2. The instrument of claim 1 in which the amplitude limit of the altitude rate signal is adjustable.

3. The instrument of claim 2 in which said altitude rate limit is adjusted as a function of the flight mode of the aircraft.

4. The instrument of claim 2 including means sensing a characteristic of the aircraft configuration and means for adjusting the limiting amplitude of said aircraft altitude rate signal in accordance with the aircraft configuration.

5. The instrument of claim 1 wherein said altitude rate signal is of one polarity for a climb and of the other polarity for a descent and said limiting means limits signals of each polarity.

6. The instrument of claim 3 having a first altitude rate limit for landing approach and a second altitude rate limit for other flight modes.

7. The instrument of claim 6 in which the first limit for landing approach is selected in accordance with the recovery characteristics of the aircraft and the second limit for other flight modes, is selected in accordance with the maximum climb characteristics of the aircraft.

8. The instrument of claim 1 in which the means for combining the limited altitude rate signal with the barometric altitude rate signal to provide the calculated altitude rate signal is a complementary filter.

9. The instrument of claim 8 in which said complementary filter includes a low pass filter section having the limited altitude rate signal connected therewith, a high pass filter section having the barometric altitude rate signal connected thereto and means combining the outputs of said filter sections.

10. The instrument of claim 9 in which the transfer characteristic of said low pass filter is 1/( Tau c s+1) and in which the transfer characteristic of the high pass filter is Tau cs/( Tau c s+1).

11. The instrument Of claim 10 in which the filter time constant, Tau , is adjustable.

12. The instrument of claim 11 in which the filter time constant, Tau , has a value of the order of 1 to 5 seconds.

13. The instrument of claim 8 wherein said complementary filter comprises:

an operational amplifier having a positive input, a negative input and an output, a feedback circuit connecting the output of the operational amplifier to the negative input thereof for operation of the amplifier as an unloading amplifier with a high input impedance, a resistive circuit connecting said limited altitude rate signal with the positive input of said amplifier, and a capacitive circuit connecting said barometric altitude rate signal with the positive input of said amplifier, the resistive and capacitive circuits forming a low pass filter for the limited altitude rate signal and a high pass filter for the barometric rate signal.

14. The instrument of claim 1, including:

means for disabling said barometric altitude signal generating means during take-off of the aircraft.

15. The instrument of claim 14 including means for maintaining the disabled condition of said barometric altitude signal generating means during the initial portion of a climb-out following take-off.

16. The instrument of claim 14 wherein said means for disabling the barometric altitude signal generating means includes means responsive to the signal representing the altitude of the aircraft with respect to the ground.