Method for predicting vibrations of an aircraft

Abstract

A method for predicting vibrations in an aircraft comprising an active vibration reduction system includes estimating a first vibration amplitude or frequency resulting from adjustments by the active vibration reduction system and the respective sensitivities of the aircraft depending on the flying state using a statistical mathematical process, recording a second vibration amplitude or frequency by a sensor, generating a pseudo-vibration profile by combining the first and second vibration amplitudes or frequencies, comparing the pseudo-vibration profile with a predefined target vibration profile, and outputting a signal when a specific threshold value has been exceeded.

Claims

1. A method for predicting vibrations in an aircraft, wherein the aircraft comprises an active vibration reduction system for reducing vibrations in at least one of a main rotor or a tail rotor, wherein the method comprises: at a first point in time t1, determining a current adjustment by the active vibration reduction system and a respective flying state-dependent sensitivity of the aircraft, and estimating a first vibration amplitude or frequency by executing a statistical mathematical process, wherein the first vibration amplitude or frequency comprises an estimated delta vibration that is reduced as a result of the current adjustment by the active vibration reduction system and the respective flying state-dependent sensitivity of the aircraft; recording a second vibration amplitude or frequency by means of at least one sensor at a second point in time t2; generating a pseudo vibration profile by combining the first vibration amplitude or frequency and the second vibration amplitude or frequency at a third point in time t3 occurring after t2, wherein the pseudo vibration profile comprises an estimation of a vibration profile that would exist if the active vibration reduction system was inactive; comparing the pseudo vibration profile with a predefined target vibration profile of the aircraft at a fourth point in time t4 occurring after t3; and outputting a signal when a specific threshold value of the target vibration profile has been exceeded by the pseudo vibration profile at a fifth point in time t5 occurring after t4.

2. The method according to claim 1, wherein in that the output signal comprises at least one of an acoustic, haptic, or visual signal.

Description

(1) The present invention shall be explained in greater detail based on the following figures. Therein:

(2) FIG. 1 shows a profile of the 1/rev main rotor vibrations of an undamaged aircraft in various flying states, without active vibration reduction;

(3) FIG. 2 shows a profile of the 1/rev main rotor vibrations of a damaged main rotor in accordance with FIG. 1;

(4) FIG. 3 shows a profile of the 1/rev main rotor vibrations of an undamaged aircraft in various flying states, with active vibration reduction; and

(5) FIG. 4 shows a method according to the invention in a preferred embodiment.

(6) FIGS. 1 to 3 describe the prior art, and are provided for a better understanding of the present invention.

(7) As such, FIG. 1 shows a characteristic vibration profile, in the form of a polar diagram, of the 1/rev main rotor vibrations of an undamaged, i.e. an intact rotorcraft in the form of a conventional helicopter with main and tail rotors without an active vibration reduction system. The points 1, 2, 3 and H represent reference measurements of the vibrations in various flying states, wherein the transitions between the individual measurement points is interpolated linearly. Thus, point H represents a hovering, point 1 represents forward flight at 90 knots, point 2 represents forward flight at 110 knots, and point 3 represents forward flight at 130 knots. The crosshatched region indicates a corridor representing a “normal” operating range of the undamaged aircraft in hover and forward flight, but not in flying maneuvers.

(8) FIG. 2 shows, by way of example, the resulting vibrations 3′ of a damaged main rotor in level flight at 130 knots for an aircraft without active vibration reduction. These malfunctions can be detected by current Health and Usage Monitoring Systems (HUMS).

(9) A vibration profile for a helicopter with an active system is shown in FIG. 3. When an active system is used for vibration reduction, the amplitudes of the rotor-harmonic vibrations are normally low in all flying states. Moreover, the vibrations of the undamaged aircraft no longer display a characteristic phase, as is the case with rotocraft that have no active system for vibration reduction.

(10) Active systems for vibration reduction are normally also capable of minimizing the vibrations in damaged main or tail rotors, such that no difference can be detected between undamaged and damaged rotocraft with regard to vibrations.

(11) FIG. 4 shows the method according to the invention for solving this problem.

(12) In a first step 110, the first vibrations, i.e. the first amplitudes or frequencies, are determined or estimated by means of a statistical mathematical procedure at a first point in time t1. These vibrations result from adjustments by the active system for active vibration reduction and the sensitivities of the rotocraft depending on flying states. The flying state-dependent sensitivities are determined by means of model calculations and flight tests.

(13) In a second step 120, at a second point in time t2, second vibrations, i.e. second amplitudes or second frequencies are recorded by sensors.

(14) Both vibrations, i.e. the estimated first vibrations and the second measured vibrations are combined to form a pseudo vibration profile in a third step 130 at a third point in time t3, and compared with a target vibration profile in a fourth step 140 at a fourth point in time t4.

(15) The target vibration profile is determined by means of model calculations and flight tests.

(16) When a specific threshold of the vibration profile has been reached and/or exceeded, a signal is generated and output in a fifth step 150 at a fifth point in time. The signal can be output acoustically or visually, for example.