Method and system for alerting aircrew to unsafe vibration levels

• US 7,839,304 B2
• Filed: 05/01/2008
• Issued: 11/23/2010
• Est. Priority Date: 05/01/2008
• Status: Expired due to Fees

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Stepura, Matthew Joseph, Riser, Robert Michael, Long, Mark Andrew, Landers, Allen James
• Primary Examiner(s): Bugg; George A
• Assistant Examiner(s): LAU, HOI CHING
• Application Number:
  US12/113,387
• Publication Number:
  US 20090273488A1
• Time in Patent Office: 936 Days
• Field of Search: 340/963, 340/971, 340/946, 73/66, 244/195, 244/99.1, 244/17.19, 244/17.15, 244/17.13, 244/17.21, 244/208, 244/204, 244/207, 701/3, 701/8
• US Class Current: 340/963
• CPC Class Codes: B64C 27/001 Vibration damping devices

Abstract

An onboard system for a rotary wing aircraft detects a limit cycle oscillation in the tail mast and provides a timely indication of the limit cycle oscillation to an aircrew before serious damage to the airframe is likely to occur.

Claims

1. A system to detect a limit cycle oscillation event in a rotary wing aircraft, comprising:

a vibration sensor that outputs a signal to indicate vibration in a tail mast of the aircraft;

a filter to limit the signal output from the sensor to a predetermined frequency range in which they limit cycle oscillation occurs; and

a first switch to provide a first signal when the filtered signal output from the sensor exceeds a first predetermined amplitude for a predetermined duration;

further comprising, a second switch to provide a second signal after the first switch has provided the first signal and the filtered signal output from the sensor has exceeded a second predetermined amplitude greater than the first predetermined amplitude.

2. The system according to claim 1 further comprising, a third switch to provide a third signal after the second switch has provided the second signal and the filtered signal output from the sensor has exceeded a third predetermined amplitude greater than the second predetermined amplitude.

3. The system according to claim 1 wherein the second predetermined amplitude is about 2.0 g'"'"'s.

4. The system according to claim 2 wherein the third predetermined amplitude is about 3.5 g'"'"'s.

5. The system according to claim 2 wherein each of the first, second and third signals activate an indicator in the cockpit.

6. The system according to claim 2 wherein each of the first, second and third signals are configured to persist until the aircraft is powered down.

7. The system according to claim 1 wherein the filter to limit the signal output from the sensor to a predetermined frequency range comprises attenuating vibratory interference from main rotor and tail rotor blade passing frequencies wherein the filter to limit the signal output from the sensor to a predetermined frequency range comprises attenuating vibratory interference from main rotor and tail rotor blade passing frequencies, wherein the filter comprises a low pass element having a 3 dB frequency of about 21 Hz and a high pass element having a 3 dB frequency of about 7 Hz.

8. The system according to claim 7 wherein the predetermined frequency range of the filter is between about 10 and 15 Hz with less than approximately −

0.9 dB reduction in gain.

9. A system to detect a limit cycle oscillation in a rotary wing aircraft, comprising:

a vibration sensor that outputs a signal to indicate vibration in a tail mast of the aircraft;

a filter to limit the signal output from the sensor to a predetermined frequency range;

a first switch to provide a first signal when the filtered signal output from the sensor exceeds a first predetermined amplitude for a predetermined duration;

a second switch to provide a second signal after the first switch has provided the first signal and the filtered signal output from the sensor has exceeded a second predetermined amplitude greater than the first predetermined amplitude; and

a third switch to provide a third signal after the second switch has provided the second signal and the filtered signal output from the sensor has exceeded a third predetermined amplitude greater than the second predetermined amplitude; and

each of the first, second, and third signals activate an indicator in a cockpit area of the aircraft to provide a warning to an aircrew to indicate detection of a limit cycle oscillation event.

10. The system according to claim 9 wherein the first predetermined amplitude is about 0.7 g'"'"'s, the predetermined duration is about 0.5 seconds, the second predetermined amplitude is about 2.0 g'"'"'s, the third predetermined amplitude is about 3.5 g'"'"'s, the predetermined frequency range of the filter is between about 10 and 15 Hz with less than approximately −

0.9 dB reduction in gain.

11. The system according to claim 9 wherein the warning indicates severity of the limit cycle oscillation event.