GB2094740A - Helicopter slip indicator - Google Patents

Abstract

A helicopter slip indicator comprising a wind direction transducer attached to the helicopter in such a location as to sense wind direction, and a slip visual display unit 13 mounted in a helicopter cockpit and connected to the wind direction transducer to receive a wind direction signal therefrom and indicate helicopter slip. Signals from the transducer may be employed in automatic stabilisation apparatus. The transducer may comprise a vane 10 mounted clear of the rotor downwards and coupled to a pick-off 11 supplying signals to the indicator 13 and optionally to a stability augmentation system (S A S).The indicator is operative only above a predetermined minimum forward speed of the helicopter. <IMAGE>

Description

SPECIFICATION Improvements in helicopter instrumentation The present invention relates to helicopter instrumentation. It provides a helicopter with a slip indicator.

According to the present invention a helicopter slip indicator comprises: a wind direction transducer attached to the helicopter in such a location as to sense wind direction, and a slip visual display unit mounted in the helicopter cockpit and connected to the wind direction transducer to receive a wind direction signal therefrom and indicate helicopter slip.

The wind direction transducer may be a mechanically rotatable weathercock or vane device having for example a pick-off arranged to emit an electrical signal the magnitude whereof is in accordance with the weathercock or vane configuration. Alternatively the wind direction transducer may have a plurality of air pressure sensors in different locations and a computerfor determining wind direction give readings from each sensor. The transducer is preferably sited at a location unaffected by irrelevant airflows such as rotor blade downwash and engine intake and exhaust flow fields, and is typically mounted beneath the fuselage. It may incorporate a heater or other de-icing means.

The visual display unit is preferably arranged to present slip information visually, in a manner similar to traditional balance indicators. They have a laterally elongated window and a ball therein the diameter whereof approximately equals the depth of the window, so that the display resembles that of a spirit level. While the ball is centrally located it is indicating zero slip; off-centre location indicates direction and magnitude of slip. This indication may alternatively be realised in the present invention in a series of lights, a magnetic indicator or a liquid crystal display (LCD) or light emitting diode (LED) display. It may have a nonlinear scale in the sense of being more sensitive near the centre of the range.

The restoration of a state of zero slip flight to a side slipping helicopter requires movement of the helicopter yaw pedals. Restoration of zero slip flight while maintaining a specific heading requires movement of the pedals and lateral movement of the helicopter cyclic stick. A slip indicator in accordance with the present invention may provide an additional feed into a helicopter automatic stabilisation apparatus whether or not the system has a heading-hold facility. For the purposes of the present patent specification an automatic stabilisation apparatus includes an autopilot.

In a typical stabilisation augmentation system, SAS, having only a rudimentary heading facility, there are three subsystems or channels: pitch and roll channels associated with the helicopter cyclic stick and a yaw channel associated with the yaw pedals. The yaw channel, which may for example comprise a yaw channel servo, a manual servo isolating switch and a yaw pedal operated SAS release switch, is used to maintain heading in the hover and at low speeds. It is made redundant above a certain airspeed by means of a cut-out switch operated by an airspeed signal. The thus redundant yaw channel may be employed for automatic slip control by feeding in the electrical signals from the wind direction transducer. These signals cause the yaw channel servo to move the tail rotor until the transducer is in a neutral position and the aircraft is in zero slip flight.The SAS release switch is operated automatically when the yaw pedals are moved by the pilot, to prevent the system opposing pilot input and to attenuate risks of a runaway.

In a typical auto-stabilisation equipment ASE which has a full heading-hold facility there are four functions: pitch and roll channels associated wih the cyclic stick, a barometric hold channel associated with the helicopter collective lever, and a yaw control through the yaw pedals, with this last channel providing heading hold at any speed. This may include the direct use of the yaw channel for automatic slip control. The channel can, however, be used indirectly if the slip indicator is connected into the roll channel of the ASE. This concept can best be understood by considering the method a pilot would use to restore zero slip flight if the heading-hold was in operation and the aircraft was side slipping.

Suppose that the helicopter has been in zero slip flight on a heading of 360" and has been yawed to 350 by the pilot, who has then engaged the heading-hold facility. In order to restore zero slip flight, while retaining the heading of 350 , the pilot would have to move the cyclic stick to the left to roll the aircraft through 10 to port; as he did this the ASE yaw channel would slowly feed in the equivalent of right yaw pedal until the aircraft was in zero slip flight. A lateral cyclic stick movement has thus been used to restore zero slip flight. Lateral cyclic can correspondingly be generated by the cyclic roll channel of the ASE and this permits an input from the wind direction transducer to restore zero slip flight through the cyclic roll channel.

Apparatus in accordance with the invention will now be described by way of example, with reference to the accompanying drawings, of which: Figure 1 is a block circuit diagram of a slipindicator facility, Figure2 is a schematic diagram of a helicopter fitted with a slip indicator, Figure 3 is a block circuit diagram of part of a SAS incorporating a slip indicator facility, and Figure 4 is a block circuit diagram of an ASE incorporating a slip indicator facility.

Figure 1 illustrates a simple slip indicator facility, which comprises a wind direction transducer in the form of a wind vane 10 and a pick-off 11 and a slip indicator having a signal processor 12 and a visual display 13 of the ball-in-laterally-elongate-slot type.

In Figure 2, which is a diagram of a helicopter cockpit, the facility is shown mounted in a helicopter.

The vane 10 is at a forward location below the fuselage, and the visual display unit 13 is located close to the gravity operated balance indicator which is associated with an artificial horizon 20a mounted in an instrument panel 20. Also shown in the cockpit are yaw pedals 21, a cyclic stick 22, a collective pitch lever 23, and a SAS panel 24.

In a simple embodiment of the invention in which the facility in the helicopter of Figure 2 is just as shown in Figure 1, in the event of the helicopter assuming a yawed attitude, or slipping, the change in airflow direction is sensed by the vane 10 and indicated by an apparent deviation by the ball to the appropriate side of the slot in the display unit 13. To recentralisethe ball - and restore the helicopterto zero slip flight - the pilot will push the appropriate yaw pedal, that is ball to the right, apply right pedal.

He may also need to adjust the cyclic lever 22 to counteract any associated roll.

Figure 3 illustrates the yaw channel of a stabilisation augmentation system (SAS) incorporating a slip facility, and its association with the yaw control of a helicopter. The basic yaw control of the helicopter comprises a yaw pedal 25 attached to a yaw control rod 26 and damped by a damper 27. The rod 26 is connected via an actuator 28 to a servo jack 29 which controls the tail rotor (not shown).

In the SAS yaw channel signals from a rate gyro 30 are passed via a two-way relay 31 and a SAS engage switch and relay 32, 32a, to both a rate amplifier 33 and a rate integration amplifier 34. The outputs of the amplifiers 33 and 34 are passed, the latter via a damper cut-out switch and relay 35, 35a, to a summing amplifier 36 the output from which is influenced by a positional feedback 37 from the actuator 28. The output of the amplifier 36 is passed via a servo power switch and relay 38, 38a, to the actuator 28. By virtue ofthetwo-way relay 31 the wind vane pick-off 11 provides an alternative input to the yaw channel, the relay 31 being controlled by an airspeed switch 39. Avisual display unit 13 is associated with the pick-off 11.

A description of the operation of the yaw system shown in Figure 3 now follows.

When the SAS is switched off via the switch and relay 32, 32a, or 38, 38a helicopter yaw is controlled by the aircrew only, mainly via the yaw pedal 25 controlling the tail rotor via the rod 26, the actuator 28 and the servo 29. Artificial feel is provided to the pedal by the damper 27. In the event of a yaw attitude developing this is sensed by the vane 10 and indicated on the display unit 13. To correct it the pilot has to 'kick the ball back into the middle' by pushing that yaw pedal on the side into which the ball has moved.

While the SAS is switched on at both the engage switch and relay 32, 32a, and the power switch and relay 38, 38a, and at hover or airspeeds below a certain threshold, typically about 50 knots, when due to the switch 39 the relay 31 is set for the SAS yaw channel to take its input from the gyro 30, then the latter is responsible for maintaining the yaw attitude of the helicopter. Signals from the gyro 30 are processed in the amplifiers 33,34,36, and the resultant fed to the actuator 28 when the tail rotor is controlled. Any unwanted yaw attitude indicated by the display 13, as sensed by the vane 10, is not fed into the SAS, but if the pilot wishes to take action due to that or to change the aircraft attitude, he has merely to operate the yaw pedals 25.Any significant pedal deviation operates the cut-out switch and relay 35, 35a, and annuls SAS activity.

Above the threshold airspeed the switch 39 and relay 31 substitutes the pick-off 11 for the gyro 30 as the input to the SAS yaw channel. Unwanted deviations in yaw attitude are thereby automatically corrected, while once again movement of the yaw pedals 25 operates the cut-out switch 35.

The apparatus illustrated in Figure 4 will now be described. The cyclic stick 22 provides, via a control position transmitter 22a, one of three inputs to the roll channel of an automatic stabilisation equipment (ASE). Another input is provided by a vertical gyro 40 and an associated roll synchro 40a, while the third is provided by the pick-off 11 associated with the vane 10. An engage switch 41 determines whether any signal will pass to the ASE, while an airspeed switch 42 and associated relay 42a determines whether a pick-off signal will pass to the ASE. A display unit 13 is associated with the pick-off 11 as before.

In the ASE the input signal is processed by a pre-amp 43 and a rate sensor amplifier 44 whence respectively an error and an error rate signal is passed to an output stage 45. The resultant signal is passed via a servo motor switch unit 46 to a magnetic amplifier 47 which controls a stepping motor generator couple 48, 48a. The mechanical output of the motor 48 controls a pilot valve 49 and the pick-off to a positional feedback transducer 50.

Transducer 50 and generator 48a signals are fed back to the input of the pre-amp 43, the former also providing, via a selector switch 51 in the unit 46, an input to a null indicator 52.

The pilot valve 49 controls a secondary servo 53 and hence a primary servo 54 which in turn controls the roll mechanism of the main rotor head, shewn at 55. An aerodynamic coupling 56 provides a feedback from the rotor head.

The ASE also comprises, now shewn, yaw and pitch channels, with the yaw channel including a heading-hold facility.

In operation of the aparatus shewn in Figure 4, with the airspeed switch 42 off and the engage switch 41 on signals from both the roll synchro 40a and the cyclic stick position transmitter 22a result in the motor 48 operating the pilot valve 49 and via the servos 53 and 54 adjusting the rotor head 55. The feedbacks from the generator 48a, the transducer 50 and via the aerodynamic couple 56 attenuate the primary input when the required roll has been achieved.

At airspeeds above a certain threshold, typically 50 knots, the airspeed switch and relay 42, 42a, permit a yaw imbalance signal from the pick-off 11 to provide a third input to the ASE and adjust the roll attitude of the rotor 55 accordingly. This will create a heading error in the helicoptor flight path which will then be corrected automatically in the ASE yaw channel.

Athreshold airspeed of 50 knots has been selected to ensure a valid signal from the pick-off 11.

However, a valid signal may be obtainable at lower speeds, making it possible to set the threshold lower.

Claims (9)

1. A helicopter slip indicator comprising: a wind direction transducer attached to the heli copter in such a location as to sense wind direction, and a slip visual display unit mounted in the helicopter cockpit and connected to the wind direction trans ducerto receive a wind direction signal therefrom and indicate helicopter slip.

2. An indicator as claimed in claim 1 and wherein the wind direction transducer is a mechanically rotatable vane device having a pick-off arranged to emit an electrical signal the magnitude whereof is in accordance with the vane configuration.

3. An indicator as claimed in claim 1 and wherein the wind direction transducer has a plurality of air pressure sensors in different locations and a compu ter for determining wind direction given readings from each sensor.

4. An indicator as claimed any one of claims 1 to 3 and wherein the wind direction transducer incor porates de-icing means.

5. An indicator as claimed in any one of claims 1 to 4 and wherein the visual display unit has the appearance of a laterally elongated window and a ball therein the diameter whereof approximately equals the depth of the window, so that the display resembles that of a spirit level.

6. An indicator as claimed in any one of the preceding claims and arranged to provide a signal for a helicopter automatic stabilisation apparatus.

7. An indicator as claimed in any one of the preceding claims and connected to the yaw channel of a stabilisation augmentation apparatus for opera tions above a predetermined airspeed.

8. An indicator as claimed in any one of claims 1 to 6 and connected to the roll channel of an auto-stabilisation equipment.

9. A helicopter slip indicator substantially as hereinbefore described with reference to the accom panying drawings.