DE3522662A1 - METHOD AND DEVICE FOR REDUCING VIBRATION OF A HELICOPTER FUSELAGE - Google Patents

Description

PATENT LAWYERS

Dipl.-Ing. A. Wasmeier

Dipl.-Ing. H. Graf

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W / o 11,941

Day Date

June 20, 1985 W / He

Applicant: Westland plc

Yeovil, Somerset, England

'"' itel:" Procedure and device for reducing Vibrations of a helicopter fuselage "

Priority: UK -? 7r. 84 IS 679 of June 29, 1984

Inventor: 1. Stephen Peter King - engineer 2. Christopher Lan Hughes - engineer

Accounts: Bayerische Vereinsbank (BLZ 75020073) 5839 300 Postal check Mönchen (BLZ 70010080) 89369-801

Place of jurisdiction is Regensburg

Method and device for reducing vibrations of a helicopter fuselage.

The invention relates to a method and a device for reducing or eliminating vibrations, that occur on helicopter fuselages.

There are many sources of vibration in a helicopter, but the most important component in forward flight is generated by the main rotor at the blade passing frequency. The blade passing frequency is equal to the product of the number of main rotor blades and the rotor rotation speed, and forces and Torques usually transmitted through the gear case and the gear case / fuselage mountings that carry vibrations of the fuselage.

If local moments are neglected, every gear housing / fuselage attachment transfers Regardless of whether it is rigid or flexible, three mutually perpendicular drawers (shears), each of which triggers a forced response of the trunk, which has a particularly complex dynamic structure Has. There is therefore a multitude of load paths through which an exciting vibration frequency is applied to the hull is transmitted. For example, in an arrangement with four gear case / fuselage mounts, there are at least twelve Load paths effective.

There has been a tendency to increase travel speeds this problem is exacerbated as the vibratory rotor loads increase rapidly with the forward flight speed of the Helicopter increase.

There are a number of previous suggestions for solving this Problem. These proposals concern vibration absorbers, the best known of which are those in the immediate vicinity of the Vibration source are attached to the rotor head itself. For this

reference is made to GB-A-1264637 and GB-A-1528057. All Vibration absorbers and especially absorbers attached to the rotor head cause considerable weight problems and lead to increased aerodynamic resistance. Such passive absorbers can at best only be viewed as makeshift means v / ground, and they cannot generate total expansion hull values low enough to keep the ever higher To satisfy manufacturer requirements.

Hull insulation based on complicated anti-resonance principles are based, for example, as described and illustrated in GB-A-2004976, GB-A-2043574, EP-A-006Q38 and EP-A-034092, have been used with varying degrees of success. Such systems are usually at the interface fixed between the gear housing and the fuselage and, as passive systems, result in loads that only affect the displacements are related to the fastening points. This of course implies that any non-isolated path, e.g. the twelve Paths noted above that connect the rotor to the fuselage have a significant impact on performance can. Simple soft fastening systems do not have this problem, but on the other hand it is extraordinary difficult to achieve adequate cushioning without using unacceptably soft springs. Another The difficulty with anti-resonance systems is the disadvantageous one Influence on the resulting vibration damping when the rotor speed changes.

GB-A-1182339 describes an active vibration reduction system, the one accelerometer for measuring the vibrations at a selected point of the trunk, an electronic one Arrangement for converting a signal obtained therefrom into hydraulic pressure changes, and a device for Transmission of these signals to a double-acting working cylinder, which is between a rotor support and the Hull is inserted and generates pulses that count the measured vibrations. This only becomes the case of reduction a measured vibration at a selected point on the trunk and does not take into account vibrations that

occur elsewhere. Furthermore, the method and the device according to this older document use one fixed gain factor and and a fixed phase setting the electrical signals to generate the cylinder commands, meaning that the system only deals with body-fixed dynamic properties and rotor-fixed force properties. Lots of facts including the The type of load taken by the helicopter or the changing fuel load can change the dynamic behavior of a helicopter fuselage significantly change what the effectiveness of this proposed system is significant is reduced, since this system cannot guarantee that the Forces generated by the working cylinder actually correspond to the predetermined force based on the signal from the accelerometer correspond.

The object of the invention is to overcome the disadvantages of the known Proposals to Avoid and a Method and Apparatus for Reducing Vibration of a Helicopter Fuselage indicate, with which these disadvantages are eliminated and the vibrations occurring in helicopters are effectively countered can be.

According to the invention, in a method for reducing the vibrations of a helicopter fuselage proposed a variety of actuators between parts of the Turn on helicopter superstructures that are able to perform a relative movement with an excitation frequency, continuously vibrating the plurality of actuators at a frequency substantially equal to correspond to the excitation frequency to generate signals, which correspond to the dynamic accelerations at a variety of points on the fuselage, and these signals one at On-board processing device to supply the output signals to control the phase position and extent of the To generate operation of the actuating devices, the Overall torso vibration is reduced.

⁸ ■ ·· "- ■■ 3522562

A device for reducing the vibrations of a helicopter fuselage induced by the rotor is characterized by a plurality of actuating devices which connect parts of the helicopter structure to one another and which are able to carry out a relative movement at an excitation frequency, a source of energy which continuously drives the actuating devices at a frequency in Displaces vibrations substantially equal to the excitation frequency, a plurality of accelerometers attached to the hull for generating signals representative of hull dynamic accelerations, and processing means for processing these signals and producing output signals for controlling phasing and magnitude the operation of the actuators.

In a further embodiment of the invention, a helicopter proposed with a main support rotor which is connected to a fuselage, which is characterized by a plurality of Actuating devices attached between parts of the structure and capable of relative movement a frequency corresponding approximately to the frequency with which the trunk is vibrated, an energy source that continuously vibrating the actuators at a frequency which is substantially corresponds to an excitation frequency, a plurality of Accelerometers that are attached to the fuselage for generating signals relevant to the fuselage dynamics Accelerations are representative, and an on-board processing device to process the Signals and to generate output signals for controlling the phase position and magnitude of the vibrations Variety of actuators.

In the simplest embodiment of the invention, the excitation frequency can be a preselected dominant frequency, e.g., the rotor passing frequency; at Another embodiment can be the excitation frequency

Instantaneous value from a preselected range of excitation frequencies, the term "excitation frequency" being used here is to be interpreted accordingly.

One of the relatively movable parts has a support plate assembly, the gear housing and the Receives drive motors and which are connected to the fuselage via a resilient connection is attached near each of the four corners. The resilient connection consists for example of elastomeric units and there is conveniently an actuator in the vicinity of each unit intended.

The present invention thus becomes an active system created, which does not isolate the fuselage from forces induced by the rotor, but instead additional ones Forces on the hull relinquishes such that the forced response generated is the response from the rotor cancels induced forces as far as possible. In contrast to the known system according to GB-A-1182339 are according to the present Invention uses a variety of actuating devices, each of which is capable of forces with a To generate excitation frequency, e.g. the blade passing frequency, the force is applied to the trunk and it is an on On-board processing apparatus is provided which consists of one of a variety (e.g. 10 or 12) accelerometers Originating signals output signals are calculated to the phase position and the size of the actuators To control generated forces, the vibrations at the plurality of locations of the accelerometer in the fuselage can be reduced at the same time.

Furthermore, the system according to the invention is adaptable to the extent that than it's own gain and phase shift properties to automatically change the hull dynamics and the rotor impact properties changes.

Ira contrasts with the aforementioned well-known system, which is only at a selected point is effective and that is only able to reduce vibrations at this point as long as a there is a very precisely controlled set of preconditions With the present invention, the vibration is reduced at a plurality of locations at the same time and it is automatic Compensated for changes in operating conditions. This is achieved in that a plurality of actuating devices switched on, each of which introduces a force at an excitation frequency, e.g. the rotor passing frequency, and that the phase position and magnitude of the force signals as a function of the measured inputs at the plurality of Accelerometers is changed.

The control forces from the actuators can be at any point and in any direction are given up, but must be able to move relative to one another between parts of the helicopter structure the excitation frequency. In one embodiment According to the invention, the actuating devices between the fuselage and the transmission housing are parallel to the existing resilient ones Fixings set so that the gear case itself represents a mass capable of responding to the force applied by the actuators. the Rigidity of the fastening system is not critical, so that static deflection problems learn to be avoided, but must There should be little relative movement between the parts, e.g. is possible.

The invention is described below in conjunction with the drawing using an exemplary embodiment. the The single figure shows a partial side view of a helicopter with a device which reduces vibrations is equipped according to one embodiment of the invention.

A helicopter 10 has a main support rotor 11 and a Helicopter fuselage 12, which has a rearwardly extending tail portion 13 on which an anti-torque rotor

14 is included.

The support rotor 11 is driven via a gear housing 15 with the aid of one or more motors; the gearbox

15 and the motor or motors are on a support plate assembly 17, which is attached to the fuselage via four spring connections, each of which is an elastomeric Unit 18 (shown schematically) has, via which forces occurring during operation from the support rotor 11 to the fuselage 12 are transmitted.

Body 12 and support plate 17 represent corresponding parts of the Overall arrangement represent a relative movement with a Can perform frequency that is essentially a vibration excitation frequency is equivalent to.

A vertical electro-hydraulic actuator 19 is arranged between the body 12 and the support plate 17 in the vicinity of each of the four elastomeric units and can apply a vertical force to the fuselage 12 during operation, which by an equal and opposite directed force on the support plate 17 is counteracted.

A pressure fluid source 20 is connected to each of the four actuating devices 19.

Twelve accelerometers 21 (only four of which are shown) are in various locations with the bottom of the Cockpits and the cabin of the fuselage 12 attached, of which ten measure the vertical vibrations and one each measure the lateral and longitudinal vibrations.

13 "'■ ■■■ .-.

The accelerometers 21 are connected to a computer 22 which in turn communicates with each of the four actuators 19 is connected.

During operation, the main support rotor 11 generates vibration forces which, for example, are caused by asymmetrical air flow in the Forward flight are conditional. Since a helicopter fuselage is dynamically complex and subject to many types of vibration, vibratory or oscillatory forces acting on the hull 12 create forced responses in all modes of operation. These forces and associated moments occur mainly at the blade passing frequency and harmonics of this frequency? the blade passing frequency is a product of the rotational speed of the Rotor and the number of rotor blades.

For example, in the four-blade helicopter described above, the blade passing frequency is about 21 Hz.

In the illustrated embodiment, the vibration exciting frequency through the resilient elastomeric units 18 on the body 12 via three mutually perpendicular Transferring shear forces at each of the four mountings. In addition, every fastening creates a vibration, again in three mutually perpendicular directions transfer.

The four electro-hydraulic actuators 19 are continuous with a preselected excitation frequency vibrated so that a set of controllable forces are released that cause the trunk to respond 12 result in a similar way to the response to the rotor forces and moments. As a force against indolence must counteracted v / grounding, it is expedient in the illustrated embodiment, the support plate 17 and the assembled components as an inertial mass

use and to attach the electro-hydraulic actuators 19 so that they have the necessary controllable Generate force between the body 12 and the support plate 17.

In the described embodiment of the invention, the frequency of the vibrations of the actuators becomes so chosen to be substantially equal to the leaf passing frequency, e.g., 21 Hz, and the vibration levels at the corresponding places in the fuselage, which result from the special Forced frequency result, reduce considerably. In an alternative embodiment, these will change over time changing forces generated by the actuators and have any combination of excitation frequencies which lie within a preselected range as determined by the instantaneous value of the acceleration in time is defined, taking vibration values resulting from any constrained frequency with the range of frequencies result, can be significantly reduced.

A decisive feature of the present invention is to be seen in the fact that accelerations correspond to the actual Vibration values at each of the respective selected locations of the accelerometer 21 in the fuselage 12 in electrical Signals are converted, which are transmitted to the computer 22. The computer 22 is programmed so that it Signals from the accelerometers 21 processed and generated corresponding output signals to the phase position and the extent of the operation of the four electro-hydraulics Adjusting actuators 19.

Method and device according to the present invention result Changes in the phase position and the magnitude of the oscillations of the excitation frequency of the four electro-hydraulic actuators 19 to simultaneously check the vibration level at each of the corresponding locations of the accelerometer 21 cancel or significantly reduce, thereby creating a fundamental improvement in the overall vibration level of a helicopter fuselage is achieved.

With the invention, the vibrations are considered to be on the fuselage are viewed as measured and give forces based on the measured vibrations rather than a response to Excitation frequencies, which may or may not give a response, and are different from passive devices which make a parasitic mass necessary for their operation and can only generate forces if they respond to a proper motion.

Furthermore, the invention is able to cancel vibrations generated by other mechanisms such as the higher harmonics of the leaf passing frequency and pressure fluctuations on a large tail surface that is not can be treated by conventional isolation precautions. The computer gives an optimal control, the one Allows minimization that is a number of vibration measurements greater than the number of available degrees of freedom of the control.

The vibration measurements can be "rated" according to their relative importance.

The computer automatically requests an oscillation frequency, which is related to the rotational speed of the rotor, so that rotor speed changes according to the present invention can be recorded, which is not possible with passive isolators working with a mass or spring system is. The invention is also able to reduce vibrations of an uncontrolled mass itself, and this can be done at the embodiment described is of particular importance be, in which the mass is represented by the resiliently attached arrangement of gearbox and motor.

Another important feature, especially with regard to airworthiness, is to be seen in the fact that the electrohydraulic Actuating devices 19 are not arranged in the primary load path and therefore do not take flight loads into account . ■ nuts, which in the described embodiment by

resilient elastomeric units are included, which also give the flexibility of mass which is essential to the present invention.

An embodiment of the invention has been described above and shown, but the invention is not limited to this embodiment. For example, result in the described embodiment of the invention, the resiliently mounted gear housing and the motor an appropriate, resiliently mounted mass that reacts to the controlled forces exerted by the electro-hydraulic actuators is introduced; however, the invention is not limited to such an embodiment; other parts of the structure are used that are capable of relative movement at a frequency, which corresponds to the excitation frequency and which on the forces of the actuator reacts. Furthermore, the invention does not necessarily require a parasitic mass. The invention is therefore also applicable to helicopters in which the gear housing is rigidly attached to the fuselage is.

The number of actuators can be varied and oriented in a desired or appropriate direction will. Further, the number of accelerometers can be varied, although preferably the number cannot smaller than that. Number of actuators should be.

In an embodiment of the invention which is similar to that described above, in which the electrohydraulic Actuators located in the vicinity of the resilient units, may be the corresponding resilient elastomeric Unit and the electro-hydraulic actuator can be integrated in a single arrangement.

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Claims (1)

3522682 Patent claims : A method of reducing vibrations of a helicopter fuselage, characterized in that a plurality of actuating devices (19) are switched between parts (12, 17) of the helicopter structure which are able to carry out a relative movement at an excitation frequency that the plurality of actuating devices at a frequency which corresponds approximately to the Krregerfrequen ", continuously.lca vibrated, that signals are generated which correspond to dynamic accelerations at a plurality of points on the hull, and that these signals are fed to a processing device (22) located on board capable of generating output signals that control the phasing and size of the vibrating actuators, reducing the total value of the Ruifipf vibrations. Device for reducing vibrations of a hoof screwdriver's head, induced by the rotor by a plurality of actuating devices (19), the parts (12, 17) of the Kubschrauberaui'rbanes with each other, connect and are able to move relative to each other to perform an excitation frequency, an energy source (20) that continuously operate the actuators at a frequency substantially equal to the excitation frequency corresponds, set in vibration, a plurality of accelerometers (21), which are attached to the Runtpf are to generate signals necessary for dynamic accelerations of the body are representative, and processing means (22) for processing the signals and aum generating output signals for the controller the phase position and magnitude of the operation of the actuators . BAD 0R ₍ '3? MäL / 3522682 3. Helicopter rait a main rotor that has a fuselage receives, characterized by a plurality of actuating devices (19) which between! 'rush (12, 17) of the Structure switched on and are able to produce a relative movement at a frequency which is essentially one Corresponds to the frequency that causes the hull to vibrate, execute, a power source (20) that the actuators with a frequency that im essentially corresponds to the excitation frequency, continuously vibrated, a large number of Accelerometers (21) attached to the fuselage at selected locations to generate signals; representative of the dynamic accelerations of the hull, and an on-board processing facility (22) for processing these signals and for generating output signals for controlling the Phasing and magnitude of the vibrations of the multitude of actuators. 4. Helicopter according to claim 3, characterized in that the excitation frequency is essentially the rotor blade passage frequency (rotor plate passing frequency). 5. Helicopter according to claim 3, characterized in that the excitation frequency is an instantaneous value represents the selected range of excitation frequencies. 6. Helicopter according to one of claims 3-5, characterized in that one of the relatively movable parts a carrier or plate arrangement (17), which the gear housing (15) and motors (16) receives and that with the fuselage via a variety of resilient mountings (13) is connected. 7. Helicopter according to claim 6, characterized in that each resilient attachment (18) is an elastomeric unit having. Ο "" ■ "■ - ■ '3S22662 8- helicopter according to any one of claims 3-7, characterized characterized in that the actuating device (19) is an electro-hydraulic actuating device. 9. Helicopter according to claim 6, characterized in that the resilient fastenings (1-3) and the actuating devices (19) are the same in number.