Method of regulating a three-engined power plant for a rotary wing aircraft

Abstract

A power plant comprising two engine groups and a main power transmission gearbox. Each engine group drives the main gearbox mechanically in order to rotate a main rotor of an aircraft at a frequency of rotation NR. A first engine group comprising two main engines is regulated on a first setpoint NR* for the frequency of rotation NR, while a second engine group comprising a secondary engine is regulated on a second setpoint W.sub.2* for power of the second engine group. In addition, each engine operates with margins relative to operating limits. The second setpoint W.sub.2* for power is determined so that each secondary engine operates with a lowest second margin that is equal to the lowest first margin of the first engine group.

Claims

1. A method of regulating a power plant of a rotary wing aircraft, the power plant comprising a first engine group, a second engine group, and a main power transmission gearbox, the two engine groups mechanically driving the main gearbox in order to rotate a main outlet shaft of the main gearbox, the main outlet shaft being constrained to rotate with a main rotor of the aircraft having a frequency of rotation NR, the first engine group having at least two main engines, the second engine group having at least one secondary engine, each main engine having a plurality of main operating limits and operating with first margins respectively relative to each of the main operating limits, each secondary engine having a plurality of secondary operating limits and operating with second margins respectively relative to each of the secondary operating limits, the method comprising the following steps: determining a first setpoint NR* for the frequency of rotation NR of the main rotor; regulating the operation of each main engine on the first setpoint NR* for the frequency of rotation NR; determining a second setpoint W.sub.2* for power to be delivered by the second engine group, so that each secondary engine operates with the lowest second margin that is equal to the lowest first margin of the first engine group; and regulating the operation of each secondary engine on the second setpoint W.sub.2* for power.

2. The method of regulating a power plant according to claim 1, comprising the following steps: determining a flight anticipation power Ws* needed for the flight of the aircraft and to be delivered jointly by the first engine group and the second engine group; determining a third setpoint Wi* for power to be delivered by the first engine group, such that:
Ws* =W.sub.1* +W.sub.2* using the third setpoint W.sub.1* for power so that the first engine groups and the second engine group anticipate a power need of the aircraft and act jointly to deliver the flight anticipation power Ws*.

3. The method of regulating a power plant according to claim 1, wherein, the main gearbox having a plurality of tertiary operating limits having a limit power that it can transmit to the outlet shaft, each main engine being capable of delivering a maximum power, when the most critical operating limit of the power plant is a tertiary limit of the main gearbox, the second setpoint W.sub.2* is determined so that it is equal to the limit power of the main gearbox minus the sum of the maximum powers of each main engine.

4. The method of regulating a power plant according to claim 3, wherein the maximum power for each main engine is determined depending on the stage of flight of the aircraft.

5. The method of regulating a power plant according to claim 4, wherein a selection algorithm is used for determining the stage of flight of the aircraft using the values for a horizontal speed Vh and a vertical speed Vz of the aircraft.

6. The method of regulating a power plant according to claim 1, wherein in the event of a failure of at least one main engine, the operation of each secondary engine is regulated on the first setpoint NR* for the frequency of rotation NR of the main rotor.

7. The method of regulating a power plant according to claim 1, wherein in the event of a failure of at least one main engine, the operation of each secondary engine is regulated on the second setpoint W.sub.2* for power.

8. The method of regulating a power plant according to claim 1, wherein in the event of a failure of at least one main engine, the operation of each secondary engine is regulated so that it delivers its maximum power.

9. The method of regulating a power plant according to claim 1, wherein the first engine group comprises two identical main engines, and the second engine group comprises one secondary engine.

10. A power plant for an aircraft, the power plant comprising a first engine group, a second engine group, and a main power transmission gearbox, the two engine groups mechanically driving the main gearbox in order to rotate at least one main outlet shaft of the main gearbox, the main outlet shaft being constrained to rotate with a main rotor of the aircraft having a frequency of rotation NR, the first engine group having at least two main engines and a first regulator device, the first regulator device being configured to regulate the operation of each main engine on a first setpoint NR* for the frequency of rotation NR of the main rotor, the second engine group comprising at least one secondary engine and a second regulator device, the second regulator device being configured to regulate the operation of each secondary engine on a second setpoint W.sub.2* for power from the second engine group, each main engine having a plurality of main operating limits and operating with first margins relative to each of the main operating limits, each secondary engine having a plurality of secondary operating limits and operating with second margins relative to the secondary operating limits, the power plant including calculation means configured to determine the second setpoint W.sub.2* so that each secondary engine operates with the lowest second margin that is equal to the lowest first margin of the first engine group.

11. The power plant according to claim 10, wherein the calculation means comprise anticipation means configured to determine a flight anticipation power Ws* necessary for the flight of the aircraft and that needs to be delivered jointly by the first engine group and the second engine group, a third setpoint W.sub.1* to be delivered by the first engine group and defined such that:
Ws* =W.sub.1* +W.sub.2* being used so that the first engine group (10) and the second engine group (20) anticipate a power need of the aircraft (30) and deliver jointly the flight anticipation power Ws*.

12. The power plant according to claim 10, wherein the main gearbox having a plurality of tertiary operating limits having a limit power, each main engine being capable of delivering a maximum power, when the most critical operating limit of the power plant is a limit of the main gearbox, the calculation means determine the second setpoint W.sub.2* to be equal to the limit power of the main gearbox minus the sum of the maximum powers of each main engine.

13. The power plant according to claim 12, wherein the maximum power for each main engine is defined depending on the stage of flight of the aircraft.

14. The power plant according to claim 10, wherein the first engine group comprises two identical main engines, and the second engine group comprises one secondary engine.

15. The power plant according to claim 10, wherein in the event of a failure of at least one main engine, the second regulation device is configured to regulate the operation of each secondary engine on the first setpoint NR* for the frequency of rotation NR of the main rotor.

16. The rotary wing aircraft having at least a main rotor, a power plant, and an avionics installation, the power plant driving the main rotor in rotation, and the aircraft including the power plant that is a power plant according to claim 10.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention and its advantages appear in greater detail from the context of the following description of implementations given by way of illustration and described with reference to the accompanying figures, in which:

(2) FIG. 1 shows a rotary wing aircraft fitted with a device of the invention for regulating a power plant;

(3) FIG. 2 is a block diagram summarizing the method of the invention for regulating a power plant; and

(4) FIG. 3 is a plot representing the operating limit zones of the power plant of the invention.

(5) Elements present in more than one of the figures are given the same references in each of them.

DETAILED DESCRIPTION OF THE INVENTION

(6) FIG. 1 shows a rotary wing aircraft 30 having a main rotor 31, a tail rotor 32, a power plant 1, and an avionics installation 5. The power plant 1 has a first engine group 10, a second engine group 20, and a main power transmission gearbox 2. The two engine groups 10 and 20 drive the main gearbox 2 mechanically in order to drive rotation of a main outlet shaft 3 of the main gearbox 2. The main outlet shaft 3 is constrained to rotate with the main rotor 31, which rotates at a frequency of rotation NR in order to provide the aircraft 30 with lift and possibly also propulsion.

(7) The tail rotor 32 may also be driven in rotation by the main gearbox 2 via a secondary outlet shaft from the main gearbox 2.

(8) The first engine group 10 comprises two identical main engines 11 and 12 and a first regulator device 15. The first regulator device 15 has two main computers 13 and 14, each main computer 13, 14 being connected to a single main engine 11, 12. The main computers 13 and 14 are also connected to each other.

(9) The second engine group 20 comprises a secondary engine 21 and a second regulator device 25. The second regulator device 25 comprises a secondary computer 22 connected to the secondary engine 21. The secondary engine 21 is different from the main engines 11 and 12. The secondary engine 21 is lighter in weight and of smaller dimensions than the main engines 11 and 12, and it delivers a maximum power that is less than that of the main engines 11, 12.

(10) The main engines 11 and 12 and the secondary engine 21 are turboshaft engines, each comprising a gas generator and a free turbine driving the main gearbox 2.

(11) The main engines 11 and 12 and the secondary engine 21 can deliver maximum powers M.sub.1, M.sub.2, and M.sub.s respectively that differ depending on the stage of flight and the operating conditions of the engines, in particular a maximum continuous power MCP, a maximum takeoff power TOP, and OEI contingency mechanical powers. It is then possible to use a selection algorithm A.sub.1 for determining the stage of flight of the aircraft automatically, for example, using the values for the horizontal speed Vh and the vertical speed Vz of the aircraft.

(12) In addition, each main engine 11, 12 operates with first margins relative to main operating limits and the secondary engine 21 operates with second margins relative to secondary operating limits. These main or secondary operating limits are, for example, the frequency of rotation NG of the gas generator, the temperature T4 of the gas leaving said generator, and the torque of the free turbine.

(13) The main gearbox 2 also has a plurality of its own tertiary operating limits 4 such as a limit torque and a limit operating temperature.

(14) The main gearbox 2 also has a plurality of its own tertiary operating limits such as a limit torque and a limit operating temperature.

(15) The avionics installation 5 has calculation means 6 and anticipation means 7.

(16) FIG. 2 is a block diagram summarizing the method of the invention for regulating a power plant. This method of regulating a power plant comprises four main steps.

(17) During a first step 51, a first setpoint NR* is determined for the frequency of rotation NR of the main rotor 31. This first setpoint NR* may be a fixed value as determined during development of the aircraft 30, or it may be a variable value that is then determined continuously while the aircraft 30 is in flight by the calculation means 6.

(18) During a second step 52, the operation of each main engine 11, 12 is regulated on the first setpoint NR* for the frequency of rotation NR of the main rotor 31 by means of the first regulator device 15.

(19) Thus, by means of the first regulator device 15, the first engine group 10 serves to control the frequency of rotation NR of the main rotor 31, this frequency of rotation NR being substantially equal to the first setpoint NR*.

(20) The first regulator device 15 serves, by way of example, to regulate both main engines 11, 12 using a proportional integral regulation loop. Since these two main engines 11, 12 are identical, their operation is then symmetrical, each main engine 11, 12 contributing an equal share to driving the main rotor 31 via the main outlet shaft 3.

(21) During a third step 53, a second setpoint W.sub.2* is determined for the power to be delivered by the second engine group 20.

(22) In a first implementation of the method, the second setpoint W.sub.2* is determined in identical manner for the entire flight envelope of the aircraft 30. The second setpoint W.sub.2* is determined by means of the calculation means 6 depending on the main operating limits of the main engines 11, 12 of the first engine group 10 so that the secondary engine 21 operates with the lowest second margin that is equal to the lowest first margin from among the first margins of the main engines 11, 12.

(23) In a second implementation of the invention, the second setpoint W.sub.2* is determined in different manner depending on the most critical operating limit of the power plant 1 from among the main operating limits of the main engines 11, 12 and the tertiary operating limits of the main gearbox 2.

(24) Two scenarios are possible, shown in the graph in FIG. 3, depending on the flight envelope of the aircraft 30, and in particular depending on the atmospheric pressure Zp around the aircraft 30 associated with its altitude and the temperature T of the air outside the aircraft 30.

(25) Thus, when the most critical operating limit of the power plant 1 is a main operating limit of the main engines 11, 12, corresponding to the zone A in FIG. 3, the second setpoint W.sub.2* is determined, as for the first implementation of the invention, i.e. so that each secondary engine 21 operates with the lowest second margin that is equal to the lowest first margin of the first engine group 10.

(26) However, when the most critical operating limit of the power plant 1 is a tertiary limit of the main gearbox 2, corresponding to the zone B in FIG. 3, the second setpoint W.sub.2* is determined so that said second setpoint W.sub.2* is equal to the limit power of the main gearbox 2 minus the sum of the maximum powers of each main engine 11, 12. This limit torque that the main gearbox is capable of providing is determined as a function of its limit torque or of its limit operating temperature and current operating conditions.

(27) By way of example, and as shown in FIG. 3, the portion of the flight envelope in which the most critical operating limit of the power plant 1 is a tertiary limit of the main gearbox 2 occurs at an atmospheric pressure corresponding to an altitude lying in the range 500 feet (ft) to 10000 ft and a temperature of the air outside the aircraft 30 lying in the range ?40 degrees Celsius (? C.) to 15? C.

(28) However, these values vary greatly from one aircraft to another and they also depend on the power delivered by its main engines, as a function, for example, of their state of aging. Furthermore, for a given aircraft, the greater the power delivered by the main engines is, the greater the size of the zone B of FIG. 3 is.

(29) During a fourth step 54, the operation of the secondary engine 21 is regulated on the second setpoint W.sub.2* for power by the second regulator device 25. The second engine group 21 thus delivers second power W.sub.2 that is substantially equal to the second setpoint W.sub.2*.

(30) The operation of the secondary engine 21 is thus optimized as a function of power requirements from the main engines 11, 12. The secondary engine 21 is in particular heavily loaded when the main engines 11, 12 are themselves heavily loaded. The second power W.sub.2 of said secondary engine 21 thus makes it possible to reduce the load on said main engines 11, 12.

(31) The method of regulating a power plant may also include three additional steps.

(32) During a fifth step 55, a flight anticipation power Ws* is determined by the anticipation means 7. This flight anticipation power Ws* corresponds to power that is necessary for the flight of the aircraft 30 and that needs to be delivered jointly by the main engines 11 and 12 and the secondary engine 21.

(33) During a sixth step 56, the calculation means 6 determine a third setpoint W.sub.1* for the power that the first engine group 10 is to deliver, such that:
Ws*=W.sub.1*+W.sub.2*

(34) During a seventh step 57, the third setpoint W.sub.1* for power is used so that the first engine group 10 and the second engine group 20 anticipate a power need of the aircraft 30 and jointly deliver the flight anticipation power Ws*.

(35) The first engine group 10 and the second engine group 20 then jointly deliver an output power Ws that is equal to the sum of the second output power W.sub.2 delivered by the second engine group 20 plus a first power W.sub.1 delivered by the first engine group 10, such that:
Ws=W.sub.1+W.sub.2

(36) The first power W.sub.1 is then substantially equal to the third setpoint W.sub.1* and the output power Ws is substantially equal to the flight anticipation power Ws*.

(37) Furthermore, in the event of failure of a main engine 11, 12, it is possible to regulate the operation of the secondary engine 21 on the second setpoint W.sub.2* for power in a manner that is identical to the first implementation. Thus, the secondary engine 21 operates with the lowest second margin that is equal to the lowest first margin of the first engine group 10.

(38) In the event of failure of a main engine 11, 12, it is also possible to regulate the operation of the secondary engine 21 on the second setpoint W.sub.2* for power in a manner that is identical to the second implementation.

(39) Nevertheless, in the event of a failure of a main engine 11, 12, the regulation of the secondary engine 21 may also be different so as to have a different distribution of power delivery by the power plant 1 between the main engine 11, 12 that has not failed and the secondary engine 21.

(40) For example, it is possible to use the secondary engine 21 delivering its available maximum power. The second engine group 20 then delivers a second maximum power W.sub.2 in order to limit the first power W.sub.1 delivered by the first engine group 10. It is thus possible to reduce or even avoid use of the OEI contingency modes of each of the main engines 11 and 12 and the associated contingency mechanical powers.

(41) It is also possible to regulate the operation of the secondary engine 21 on the first setpoint NR* for the frequency of rotation NR of the main rotor 31, in order to guarantee that this first setpoint NR* is complied with. This regulation may be performed in proportional mode or in proportional integral mode.

(42) Naturally, the present invention may be subjected to numerous variations as to its implementation. Although several implementations are described, it should readily be understood that it is not conceivable to identify exhaustively all possible implementations. It is naturally possible to envisage replacing any of the means described by equivalent means without going beyond the ambit of the present invention.