METHOD FOR QUICKLY STOPPING THE ROTOR OF A HELICOPTER AFTER LANDING

Abstract

A method for quickly stopping the propulsion rotor of a helicopter after landing, comprising, following a request for quickly stopping the engine by a helicopter pilot, the following steps managed by the control unit of the turbomachine: Detecting the absence of the thermal stabilization phase of the gas generator of at least one turbomachine, controlling an extinction of the combustion chamber of the gas generator of at least one turbomachine, maintaining the rotation of the gas generator of which the combustion chamber is extinguished by means of said at least one electrical machine to ventilate the gas generator and stopping the main rotor of the helicopter by means of a mechanical brake.

Claims

1. A method for quickly stopping the main rotor of a helicopter after landing, the helicopter comprising a main rotor for the propulsion of the helicopter, at least one turbomachine, a main gearbox connected between said at least one turbomachine and the main rotor, a turbomachine control unit, an electric power supply network, and at least one electrical machine coupled to the electrical network, said at least one turbomachine including a gas generator equipped with a mechanical shaft, a free turbine coupled to the main rotor via the main gearbox and mechanically independent of the mechanical shaft of the gas generator, and a system configured to mechanically couple an electrical machine to the gas generator, wherein the method comprises, following a step of requesting the quick stop of the engine by a helicopter pilot, causing the extinction of the combustion chamber of the gas generator of at least one turbomachine, the following steps managed by the control unit of the turbomachine: detecting the absence of the thermal stabilization phase of the gas generator of at least one turbomachine to confirm that the request for stopping the engine is a request for quickly stopping the main rotor, in the event of absence of the thermal stabilization phase, maintaining-the rotation of the gas generator for each turbomachine of which the combustion chamber is extinguished, by means of said at least one electrical machine mechanically coupled to the gas generator and powered by the electrical network, to ventilate the gas generator, and stopping the main rotor of the helicopter by means of a brake.

2. The method according to claim 1, wherein the rotation by said at least electrical machine of the extinguished gas generator is maintained for a predefined ventilation period starting with the extinction of the combustion chamber, and the power supply of the electrical machine is stopped at the end of the ventilation period.

3. The method according to claim 1, wherein the rotation by said at least one electrical machine of the extinguished gas generator is maintained as long as at least one measured temperature of the gas generator is greater than a first threshold and/or the absolute value of a measured temperature gradient is greater than a second threshold, or the power supply of the electrical machine is stopped.

4. The method according to claim 1, wherein the helicopter comprises at least two turbomachines each having a free turbine (13) connected to the main rotor via the main gearbox, and the method also comprises, prior to the step of requesting the quick stop of the engine, a step of requesting operation in auxiliary power unit mode of at least one turbomachine driving the following steps managed by the control unit of the turbomachine: increasing the torque of at least one turbomachine until at least one other turbomachine supplies a zero torque to the main gearbox, disengaging said at least one turbomachine supplying a zero torque, and operating in auxiliary power unit mode said at least one disengaged turbomachine to drive an electrical machine and power supply the electrical network of the helicopter, the step of requesting quick stop of the engine by the helicopter pilot-causing the extinction of the combustion chamber of the gas generator of each turbomachine still engaged to the main gearbox, and the step of detecting the absence of a thermal stabilization phase being applied to the gas generator of each turbomachine still engaged to the main gearbox.

5. The method according to claim 4, wherein the step of requesting operation in auxiliary power unit mode of at least one turbomachine is requested by the helicopter pilot prior to the step of requesting the quick stop of the engine, and information on the actual operation in auxiliary power unit mode of at least one turbomachine is transmitted to the pilot prior to his request for quickly stopping the engine.

6. The method according to claim 1, wherein the electrical network of the helicopter is configured to be power supplied by at least one alternator driven by an auxiliary power unit.

7. The method according to claim 1, wherein the electrical network of the helicopter comprises at least one battery of the electrical network powering said electrical machine.

8. The method according to claim 2, wherein the rotation by said at least one electrical machine of the extinguished gas generator is maintained as long as at least one measured temperature of the gas generator is greater than a first threshold and/or the absolute value of a measured temperature gradient is greater than a second threshold, or the power supply of the electrical machine is stopped.

9. The method according to claim 2, wherein the helicopter comprises at least two turbomachines each having a free turbine connected to the main rotor via the main gearbox, and the method also comprises, prior to the step of requesting the quick stop of the engine, a step of requesting operation in auxiliary power unit mode of at least one turbomachine driving the following steps managed by the control unit of the turbomachine: increasing the torque of at least one turbomachine until at least one other turbomachine supplies a zero torque to the main gearbox, disengaging said at least one turbomachine supplying a zero torque, and operating in auxiliary power unit mode said at least one disengaged turbomachine to drive an electrical machine and power supply the electrical network of the helicopter, the step of requesting quick stop of the engine by the helicopter pilot causing the extinction of the combustion chamber of the gas generator of each turbomachine still engaged to the main gearbox, and the step of detecting the absence of a thermal stabilization phase being applied to the gas generator of each turbomachine still engaged to the main gearbox.

10. The method according to claim 3, wherein the helicopter comprises at least two turbomachines each having a free turbine connected to the main rotor via the main gearbox, and the method also comprises, prior to the step of requesting the quick stop of the engine, a step of requesting operation in auxiliary power unit mode of at least one turbomachine driving the following steps managed by the control unit of the turbomachine: increasing the torque of at least one turbomachine until at least one other turbomachine supplies a zero torque to the main gearbox, disengaging said at least one turbomachine supplying a zero torque, and operating in auxiliary power unit mode said at least one disengaged turbomachine to drive an electrical machine and power supply the electrical network of the helicopter, the step of requesting quick stop of the engine by the helicopter pilot causing the extinction of the combustion chamber of the gas generator of each turbomachine still engaged to the main gearbox, and the step of detecting the absence of a thermal stabilization phase being applied to the gas generator of each turbomachine still engaged to the main gearbox.

11. The method according to claim 2, wherein the electrical network of the helicopter is configured to be power supplied by at least one alternator driven by an auxiliary power unit.

12. The method according to claim 3, wherein the electrical network of the helicopter is configured to be power supplied by at least one alternator driven by an auxiliary power unit.

13. The method according to claim 4, wherein the electrical network of the helicopter is configured to be power supplied by at least one alternator driven by an auxiliary power unit.

14. The method according to claim 5, wherein the electrical network of the helicopter is configured to be power supplied by at least one alternator driven by an auxiliary power unit.

15. The method according to claim 2, wherein the electrical network of the helicopter comprises at least one battery of the electrical network powering said electrical machine.

16. The method according to claim 3, wherein the electrical network of the helicopter comprises at least one battery of the electrical network powering said electrical machine.

17. The method according to claim 4, wherein the electrical network of the helicopter comprises at least one battery of the electrical network powering said electrical machine.

18. The method according to claim 5, wherein the electrical network of the helicopter comprises at least one battery of the electrical network powering said electrical machine.

19. The method according to claim 6, wherein the electrical network of the helicopter comprises at least one battery of the electrical network powering said electrical machine.

20. The method according to claim 9, wherein the step of requesting operation in auxiliary power unit mode of at least one turbomachine is requested by the helicopter pilot prior to the step of requesting the quick stop of the engine, and information on the actual operation in auxiliary power unit mode of at least one turbomachine is transmitted to the pilot prior to his request for quickly stopping the engine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG. 1 is a simplified schematic view of a helicopter propulsion assembly with a main gearbox according to the prior art.

[0036] FIG. 2 is a schematic section view of a turbomachine with a free turbine according to the prior art.

[0037] FIG. 3 shows a flowchart of a method for quickly stopping a main rotor of a helicopter according to a first embodiment.

[0038] FIG. 4 shows a first graph of the evolution over time of the rotation speeds of the rotor and of the gas generator during the application of the stopping method of FIG. 4.

[0039] FIG. 5 shows a flowchart of a method for quickly stopping a main rotor of a helicopter according to a second embodiment.

[0040] FIG. 6 presents a graph of the evolution over time of the rotation speeds of the rotor and of the gas generator during the application of the stopping method of FIG. 5.

DESCRIPTION OF EMBODIMENTS

[0041] A propulsion assembly of a helicopter 1 with a main gearbox according to the prior art is presented schematically in FIG. 1.

[0042] The helicopter 1 is equipped with a main rotor 2, for lift and propulsion, as well as an anti-torque rotor. In the example illustrated in FIG. 1, the anti-torque rotor is a tail rotor 3 but it could be a rotor coaxial with the main rotor. The drive train of the helicopter comprises in particular a turbomachine 4 to supply the power necessary for the flight of the helicopter and a main gearbox 5 the function of which is to transmit the power of the turbomachine 4 to the main rotor 2 and to the tail rotor 3 to set them in motion by mechanisms which are schematically shown in FIG. 1 by a first shaft 6 mechanically coupled to the main rotor 2 and a second shaft 7 mechanically coupled to the tail rotor 3. The turbomachine 4 is shown here with its exhaust 8.

[0043] Generally, the main gearbox 5 includes a mechanical input 9 from which the inner gears are driven which actuate the shafts 6 and 7 respectively coupled to the main rotor 2 and to the tail rotor 3.

[0044] Generally too, the turbomachine includes a mechanical output 10, which can be a first series of gears reducing the number of revolutions, coupled to the mechanical input 9 of the main gearbox 5 by a third shaft 11.

[0045] A section view of a turbomachine 4 with a free turbine according to the prior art is shown schematically in FIG. 2. The turbomachine 4 comprises a gas generator 12 and a free turbine 13 to which the third shaft 11 is mechanically connected. As is known, the free turbine 13 is mechanically independent of the gas generator 12, in other words the third shaft 11 is not coupled to the shaft of the gas generator.

[0046] In FIG. 3 is shown a flowchart of a method for quickly stopping a main rotor of a helicopter according to a first embodiment.

[0047] In this first embodiment, the helicopter 1 can comprise one turbomachine 4 or several turbomachines.

[0048] In a first step 100 of the method, at the conclusion of a landing phase of the helicopter 1, the pilot issues a command to stop the engine in order to quickly accomplish a given mission such as for example disembarking or embarking passengers.

[0049] In a second step 110 of the method, an electronic control unit determines whether the thermal stabilization phase of the gas generator 12 of the turbomachine 4 has already taken place. If it has already taken place, in a step 115 the control unit transmits a signal to control the extinction of the gas generator 12, following which the pilot commands the stop of the main rotor 2 by the application of a brake on the shaft 6 of the main rotor 2.

[0050] If, on the other hand, no thermal stabilization phase is detected, the control unit commands the extinction of the combustion chamber of the gas generator 12 of the turbomachine 4 in a step 120, then the braking of the main rotor 2 in a step 130, and the ventilation of the gas generator 12 of the turbomachine in a step 140. The ventilation of the gas generator 12 is accomplished by the rotation of the gas generator 12 by an electrical machine which is powered by the electrical network of the helicopter. The electrical network of the helicopter can be coupled to one or more battery(ies), and possibly to at least one auxiliary power unit.

[0051] In a following step 150, the control unit verifies whether the ventilation of the gas generator 12 is completed. As long as it is not completed, the method repeats the steps 140 and 150.

[0052] Once the ventilation of the gas generator is completed, the control unit commands, in a step 160, a cut-off of the power supply of the electrical machine rotating the gas generator 12.

[0053] With a method of this type, an evolution over time is thus obtained of the rotation speeds of the rotor and of the free turbine in solid lines, and of the gas generator in dotted lines as shown in the graph illustrated in FIG. 4.

[0054] During a first phase T.sub.1, the helicopter lands and uses the power of the turbomachines. After landing, in a second phase T.sub.2, the pilot lowers the pitch of the rotor, consequently reducing the power delivered by the turbomachines to the minimum needed to maintain the speed of the main rotor 2. Then, in a third phase T.sub.3, following the command to stop the engine actuated by the pilot, the speed of the rotor decreases quickly until it is totally stopped, and the rotation speed of the generator also drops. Following the stop of the rotor, in a fourth phase T.sub.4, the rotation speed of the gas generator 12 is brought to, then maintained at a ventilation speed threshold. Once the ventilation is completed, the electrical machine rotating the gas generator 12 during the ventilation phase is stopped, and the rotation speed of the gas generator 12 decreases very quickly until zero speed is reached.

[0055] Shown in FIG. 5 is a flowchart of a method for quickly stopping a main rotor of a helicopter according to a second embodiment.

[0056] In this second embodiment, the helicopter 1 comprises at least two turbomachines 4.

[0057] In a first step 200 of the method, following a landing phase of the helicopter 1, the pilot issues a request for operation in auxiliary power unit mode of one of the two turbomachines and a command for stopping the other engine to be able to quickly accomplish a given mission such as for example disembarking or embarking passengers.

[0058] In one alternative, the request for transition into the APU mode could be generated by the control unit upon receiving a command for a quick stop without there being any thermal transition.

[0059] In a step 212, the torque of at least one turbomachine is increased until at least one other turbomachine supplies zero torque to the main gearbox 5. Then, in a following step 214, the control unit commands a disengagement of the turbomachine or of the turbomachines supplying a zero torque, and activates in a step 216 an operation of the turbomachine or of the turbomachines thus disengaged in an operation of production of electrical energy, called auxiliary power unit, to power supply the electrical network of the helicopter 1.

[0060] In a second step 210 of the method, an electronic control unit determines whether a thermal stabilization phase has already occurred, i.e. whether the turbomachine is thermally stabilized. If it has already occurred, the control unit commands the stop of the turbomachine and the stop of the rotor by the application of a brake to the shaft 6 off the main rotor in a step 215.

[0061] If, on the contrary, no thermal stabilization phase is detected, the control unit commands, in a step 220, the extinction of the combustion chamber of the gas generator 12 of at least one of the turbomachines 4 that are still engaged, then the braking of the main rotor 2 in a step 230. And, in a step 240, it commands the ventilation of the gas generator 12 of said at least one turbomachine 4 that is still engaged and the combustion chamber of which is extinguished. The ventilation of the gas generator 12 is accomplished by the rotation of the gas generator 12 by an electrical machine which is powered by the electrical network of the helicopter, and therefore by at least one disengaged turbomachine operating in an auxiliary power unit mode.

[0062] In a subsequent step 250, the control unit verifies whether the ventilation of the gas generator 12 is completed. As long as it is not completed, the method repeats the steps 240 and 250.

[0063] Once the ventilation of the gas generator is completed, the control unit commands, in a step 260, a cut-off of the power supply of the electrical machine rotating the gas generator 12.

[0064] With a method of this type, an evolution over time of the rotation speeds of the rotor of the free turbine in solid lines, and of the gas generator in dotted lines is thus obtained, as shown in the graph illustrated in FIG. 6.

[0065] During a first phase t.sub.1, the helicopter lands and uses the power of the turbomachines. After landing, in a second phase t.sub.2, the pilot reduces the pitch of the rotor, consequently reducing the power delivered by the turbomachines to the minimum needed for maintaining the speed of the main rotor 2. Then, in a third phase t.sub.3, the control unit accomplishes the steps 212 to 216 to select at least one of the turbomachines and transition it into an auxiliary power unit mode and command the stop of the engine that is still engaged.

[0066] Then, in a fourth phase, the combustion chamber of at least one of the turbomachines that are still engaged is extinguished and the rotation speed of the generator drops. The main rotor is braked, which causes a drop in the speed of the main rotor 2 until it is totally stopped.

[0067] Following the stop of the rotor, in a fourth phase t.sub.4, the rotation speed of the gas generator 12 is brought to, then maintained at a ventilation speed threshold. Once the ventilation is completed, the electrical machine rotating the gas generator 12 during the ventilation phase is stopped, and the rotation speed of the gas generator 12 decreases very quickly until zero speed is reached.