Method and device for determining the state of a vibrating structure of a rotary wing aircraft

• US 6,176,136 B1
• Filed: 12/03/1998
• Issued: 01/23/2001
• Est. Priority Date: 12/04/1997
• Status: Expired due to Fees

• Current Assignee: Eurocopter
• Original Assignee: Eurocopter
• Inventors: Struzik, Alain, Zoppitelli, Elio
• Primary Examiner(s): NOORI, MAX H
• Application Number:
  US09/204,304
• Time in Patent Office: 782 Days
• Field of Search: 735/93, 736/49, 736/58, 736/60
• US Class Current: 73/660
• CPC Class Codes: B64C 2027/002 mounted between the rotor drive and the fuselage
• CPC Class Codes: B64C 2027/005 using suspended masses
• CPC Class Codes: B64C 27/001 Vibration damping devices
• CPC Class Codes: G01H 1/003 of rotating machines G01H1/10 takes precedence
• CPC Class Codes: G01M 13/028 Acoustic or vibration analysis

Abstract

The present invention relates to a method and to a device for determining the state of a vibrating structure of a rotary wing aircraft, while the latter is operating. The device includes sensors arranged on the vibrating structure and capable of measuring the values of vibrational parameters, and a calculation unit receiving the values measured by the sensors and calculating, from these and from estimated values of the vibrational parameters, a correlation coefficient, comparing the latter with a predefined range of values and deducing from this comparison the state of the vibrating structure.

Claims

1. A method for determining a state of a vibrating structure of a rotary wing aircraft while said aircraft is operating, said method comprising:

(a) defining n main vibrational modes of said vibrating structure, n being an integer greater than or equal to 1;

(b) defining p vibrational parameters to enable a response of said n main vibrational modes defined in step (a) to be estimated, p being an integer greater than or equal to n;

(c) determining estimated values of each of said p vibrational parameters;

(d) measuring values of said p vibrational parameters while said rotary aircraft is operating;

(e) calculating a correlation coefficient from said estimated values and said measured values;

(f) comparing said correlation coefficient with a predefined range of values; and

(g) deducing said state of said vibrating structure from results of the comparison in step (f).

2. The method claimed in claim 1,

wherein steps a) and b) are performed in a preliminary step, as is determining the means needed for determining said estimated values, and the remaining steps are performed in a subsequent step while said rotary wing aircraft is operating.

3. The method claimed in claim 1, wherein at least one of said p vibrational parameters correspond to at least one of a speed, a displacement, a force, an acceleration and a strain.

4. The method claimed in claim 1,

wherein the measured and estimated values of said vibrational parameters are complex values.

5. The method claimed in claim 1,

wherein said estimated values of the vibrational parameters are values measured on the vibrating structure while said rotary wing aircraft is operating, for a normal state of said vibrating structure.

6. The method claimed in claim 1,

wherein said correlation coefficient corresponds to the difference between a first term obtained from said estimated values and a second term obtained from said measured values.

9. The method claimed in claim 1,

wherein said vibrating structure is a suspension system (SP) for a transmission gearbox of said rotary wing aircraft, said transmission gearbox being mounted between propulsion means and a lift rotor of said aircraft and approximately longitudinal to a axis of said rotor, and being suspended with respect to the fuselage of said aircraft, said suspension system comprising:

struts distributed radially around said transmission gearbox, the upper ends of which are connected to the upper part of the transmission gearbox, and the lower ends of which are articulated to suspension leaves;

a suspension means connecting the lower part of the transmission gearbox to the fuselage of the aircraft and comprising said suspension leaves; and

resonator means associated with said struts respectively.

10. The method claimed in claim 9,

wherein at least one of said vibrational parameters is measured on at least one of the following elements of said suspension system:

a strut, a suspension leaf, a mass support and an oscillating mass of a resonator means, said resonator means comprising an oscillating mass connected by a mass support to a suspension leaf.

11. A device for implementing the method specified in claim 1,

which comprises:

sensors arranged on said vibrating structure and capable of measuring the values of said vibrational parameters; and

a calculation unit receiving the values measured by said sensors and determining, from these and from estimated values of the vibrational parameters, the state of said vibrating structure.

12. A device as claimed in claim 11,

which additionally comprises means which filter the values measured by said sensors, relative to a frequency bΩ

, b being the number of blades of the rotary wing aircraft lift rotor and Ω

being its rotational speed.

7. A method for determining a state of a vibrating structure of a rotary wing aircraft while said aircraft is operating, said method comprising:

(a) defining n main vibrational modes of said vibrating structure, n being an integer greater than or equal to 1;

(b) defining p vibrational parameters to enable a response of said n main vibrational modes defined in step (a) to be estimated, p being an integer greater than or equal to n;

(c) determining estimated values of each of said p vibrational parameters;

(d) measuring values of said p vibrational parameters while said rotary aircraft is operating;

(e) calculating a correlation coefficient from said estimated values and said measured values;

(f) comparing said correlation coefficient with a predefined range of values; and

(g) deducing said state of said vibrating structure from the results of the comparison in step (f);

wherein said correlation coefficient Q is calculated from the expression;

$Q=\left(\frac{\sum <br><br>i<br><br>\left(\mathrm{Umi}\times <br><br>\stackrel{\_}{\mathrm{Uei}}\right)}{\sqrt{\left(\sum <br><br>i<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{Umi}\times <br><br>\stackrel{\_}{\mathrm{Umi}}\right)\times <br><br>\left(\sum <br><br>i<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{Uei}\times <br><br>\stackrel{\_}{\mathrm{Uei}}\right)}}\right)$

in which;

the Umi terms, with i varying from 1 to p, represent the measured values of the vibrational parameters;

the Uei terms, with i varying from 1 to p, represent the estimated values of the vibrational parameters; and

{overscore (Umi)} and {overscore (Uei)} are the complex conjugates of Umi and Uei respectively.

8. The method claimed in claim 7,

wherein said predefined range of values is between 0.95 and 1.

13. The method according to claim 7, wherein said vibrating structure is a suspension system for a transmission gearbox of said rotary wing aircraft, said transmission gearbox being mounted (i) between propulsion means and a lift rotor of said aircraft and (ii) longitudinal to an axis of said rotor, and said transmission gearbox is suspended with respect to a fuselage of said aircraft, wherein said suspension system comprises:

struts distributed radially around said transmission gearbox, said struts having upper ends which are connected to an upper part of the transmission gearbox and lower ends which are articulated to suspension leaves of a suspension means, said suspension means connecting the lower part of the transmission gearbox to the fuselage of the aircraft; and

resonator means connected with said struts.

14. The method according to claim 13, wherein said resonator means comprises an oscillating mass connected by a mass support to said suspension leaves and wherein at least one of said vibrational parameters is measured on at least a respective one of said struts, said suspension leaves, said mass support, and the oscillating mass.

15. A device for implementing the method recited in claim 7, said device comprising:

sensors arranged on said vibrating structure for measuring values of said p vibrational parameters;

a calculation unit for receiving the measured values from said sensors and for determining the state of said vibrating structure from both the measured values and estimated values of the vibrational parameters.

16. The device according to claim 15, further comprising filtering means for filtering the measured values from said sensors, relative to a frequency bΩ

, where b is a number of blades of the rotary wing aircraft lift rotor and Ω

is a rotational speed of said rotor.