Aircraft tailstrike avoidance system

• US 6,422,517 B1
• Filed: 03/07/2000
• Issued: 07/23/2002
• Est. Priority Date: 12/02/1999
• Status: Expired due to Term

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Sankrithi, Mithra M. K. V., Evans, Monte R., Wells, Stephen L., DeWitt, Wendi M., Eggold, David P.
• Primary Examiner(s): Poon, Peter M.
• Assistant Examiner(s): COLLINS, TIMOTHY D
• Application Number:
  US09/520,329
• Time in Patent Office: 868 Days
• Field of Search: 244/183, 244/181, 244/179, 244/180, 244/221, 244/76.R, 244/75.R, 244/175, 244/187, 244/196, 701/15, 701/16
• US Class Current: 244/181
• CPC Class Codes: B64D 45/04 Landing aids; Safety measures to prevent collision with earth's surface
• CPC Class Codes: G05D 1/0653 during a phase of take-off or landing
• CPC Class Codes: G05D 1/0808 specially adapted for aircraft

Abstract

An improvement to an aircraft flight control system is provided for reducing the likelihood of an aircraft tailstrike. The flight control system includes a pitch command provided to a pitch control device for altering the aircraft'"'"'s pitch attitude. The improvement is a system of altering the pitch command to avoid an aircraft tailstrike. The improvement includes determining a current tailskid closure rate and a current tail height; comparing the current tailskid closure rate with a threshold closure rate to determine an excess closure rate amount; and adding an incremental nose-down pitch command with the pitch command to avoid a potential aircraft tailstrike. The threshold closure rate is dependent upon the current tailskid height. The incremental nose-down pitch command is calculated as a function of the excess closure rate amount. An alternative embodiment is provided in which the current height is compared with a threshold height (that is a function of the current tailskid closure rate) to determine an excess height amount. The excess height is then used to form an incremental nose-down pitch command. Another embodiment is described using both height and rate thresholds to calculate the incremental nose-down pitch command. Alternative arrangements may be used in which other non-derivative and derivative values are used, e.g., pitch angle margin and pitch rate.

Claims

1. In an aircraft flight control system having a normal pitch command signal provided to a pitch control device for altering the aircraft'"'"'s pitch attitude, an improvement for reducing the likelihood of an aircraft tailstrike, the improvement comprising:

(a) determining a current pitch angle margin to tailstrike and a current pitch rate;

(b) comparing the current pitch angle margin with a threshold pitch angle margin to determine an angular margin shortfall amount, the threshold pitch angle margin being dependent upon the current pitch rate; and

(c) adding an incremental nose-down pitch command signal to the normal pitch command signal to avoid a potential aircraft tailstrike, the incremental nose-down pitch command signal being calculated as a function of the angular margin shortfall amount.

2. In an aircraft flight control system having a normal pitch command provided to a pitch control device for altering the aircraft'"'"'s pitch attitude, an improvement for reducing the likelihood of an aircraft tailstrike, the improvement comprising:

(a) determining a current pitch angle margin and a current pitch rate;

(b) comparing the current pitch angle margin with a threshold pitch angle margin and the current pitch rate with a threshold pitch rate to determine an angular margin shortfall amount and an excess rate amount, respectively;

the threshold pitch angle margin being dependent upon the current pitch rate;

the threshold pitch rate being dependent upon the current pitch angle margin amount; and

(c) adding an incremental nose-down pitch command to the normal pitch command to avoid a potential aircraft tailstrike, the incremental nose-down pitch command being calculated as the sum of a function of the angular margin shortfall amount and a function of the excess pitch rate amount.

3. In an aircraft flight control system having a normal pitch command signal provided to a pitch control device for altering the aircraft'"'"'s pitch attitude, an improvement for reducing the likelihood of an aircraft tailstrike, the improvement comprising:

(a) determining a current tailskid height and a current tailskid closure rate, wherein determining the current tailskid closure rate and the current tailskid height includes using at least one sensor to directly measure the values, and wherein determining the current tailskid closure rate and tailskid height includes calculating these values based on a plurality of sensor measurements;

(b) comparing the current tailskid closure rate with a threshold closure rate to determine an excess closure rate amount, the threshold closure rate being dependent upon the current tailskid height; and

(c) adding an incremental nose-down pitch command signal to the normal pitch command signal to avoid a potential aircraft tailstrike, the incremental nose-down pitch command signal being calculated as a function of the excess closure rate amount.

4. The improvement according to claim 3, wherein the plurality of sensor measurements includes at least one of a radio altimeter measurement, an air data measurement, a radar sensor measurement, an inertial reference unit measurement, a laser range finder measurement, a sonar measurement, a wheel speed measurement, a landing gear oleo extension measurement, a landing gear load measurement, a landing gear truck tilt measurement, a physical tailskid compression measurement, and a physical tailskid load measurement.

5. In an aircraft flight control system having a normal pitch command signal provided to a pitch control device for altering the aircraft'"'"'s pitch attitude, an improvement for reducing the likelihood of an aircraft tailstrike, the improvement comprising:

(a) determining a current tailskid height and a current tailskid closure rate;

(b) comparing the current tailskid closure rate with a threshold closure rate to determine an excess closure rate amount, the threshold closure rate being dependent upon the current tailskid height, wherein comparing the current tailskid closure rate to the threshold closure rate includes accessing a lookup table to determine the threshold closure rate, the threshold closure rate having been predetermined as a function of tailskid height; and

(c) adding an incremental nose-down pitch command signal to the normal pitch command signal to avoid a potential aircraft tailstrike, the incremental nose-down pitch command signal being calculated as a function of the excess closure rate amount.

6. The improvement according to claims 5, wherein comparing the current tailskid closure rate to the threshold closure rate includes calculating their difference, the incremental nose-down pitch command being a proportion of the difference.

7. In an aircraft flight control system having a normal pitch command signal provided to a pitch control device for altering the aircraft'"'"'s pitch attitude, an improvement for reducing the likelihood of an aircraft tailstrike, the improvement comprising:

(a) determining a current tailskid height and a current tailskid closure rate;

(b) comparing the current tailskid height with a threshold height to determine an excess height amount, the threshold height being dependent upon the current tailskid closure rate, wherein comparing the current tailskid height to the threshold height includes calculating their difference, the incremental nose-down pitch command being a proportion of the difference; and

(c) adding an incremental nose-down pitch command signal to the normal pitch command signal to avoid a potential aircraft tailstrike, the incremental nose-down pitch command signal being calculated as a function of the excess height amount.

8. In an aircraft flight control system having a normal pitch command signal provided to a pitch control device for altering the aircraft'"'"'s pitch attitude, an improvement for reducing the likelihood of an aircraft tailstrike, the improvement comprising:

(a) determining a current tailskid height and a current tailskid closure rate;

(b) comparing the current tailskid closure rate with a threshold closure rate to determine an excess closure rate amount, the threshold closure rate being dependent upon the current tailskid height, wherein comparing the current tailskid closure rate to the threshold closure rate includes calculating their difference, the incremental nose-down pitch command being a time integral of the difference; and

(c) adding an incremental nose-down pitch command signal to the normal pitch command signal to avoid a potential aircraft tailstrike, the incremental nose-down pitch command signal being calculated as a function of the excess closure rate amount.

9. In an aircraft flight control system having a normal pitch command signal provided to a pitch control device for altering the aircraft'"'"'s pitch attitude, an improvement for reducing the likelihood of an aircraft tailstrike, the improvement comprising:

(a) determining a current tailskid height and a current tailskid closure rate;

(b) comparing the current tailskid height with a threshold height to determine an excess height amount, the threshold height being dependent upon the current tailskid closure rate, wherein the threshold height includes a take-off threshold height and a landing threshold height, the applicable threshold height being selected on the basis of the aircraft'"'"'s current flap configuration; and

(c) adding an incremental nose-down pitch command signal to the normal pitch command signal to avoid a potential aircraft tailstrike, the incremental nose-down pitch command signal being calculated as a function of the excess height amount.