METHOD FOR ASSISTING A TURBOSHAFT ENGINE IN STANDBY OF A
MULTIPLE-ENGINE HELICOPTER, AND ARCHITECTURE OF A
PROPULSION SYSTEM OF A HELICOPTER COMPRISING AT LEAST ONE
TURBOSHAFT ENGINE THAT CAN BE IN STANDBY
1. Technical field of the invention
The invention relates to a method for assisting a turboshaft engine in standby
mode of a multiple-engine, in particular twin-engine, helicopter. The invention
10 also relates to an architecture of a propulsion system of a multiple-engine
helicopter comprising ·at least one turboshaft engine that is capable of being
placed in a specific standby mode.
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2. Technological background
A helicopter is generally provided with at least two turboshaft engines which
operate at similar modes that depend on the flight conditions of the helicopter.
Throughout the following text, a helicopter is said to be in a cruise flight situation
when it is progressing in normal conditions during all the flight phases apart from
20 transitional phases of take-off, ascent, landing or hovering flight. Throughout the
following text, a helicopter is said to be in a critical flight situation when it is
necessary for it to have available the total installed capacity, i.e. during the
transitional phases of take-off, ascent, landing and the mode in which one of the
turboshaft engines malfunctions, referred to by the abbreviation OEI (One Engine
25 Inoperative).
It is known that, when the helicopter is in a cruise flight situation, the turboshaft
engines operate at low power levels, below their maximum continuous thrust.
These low power levels result in a specific consumption (hereinafter SC), which
30 is defined as the relationship between the hourly fuel consumption by the
combustion chamber of the turbos haft engine, and the mechanical power
provided by said turbos haft engine, which is approximately 30 % greater than the
SC of the maximum take-off thrust, and thus an overconsumption of fuel during
cruise flight.
2
Moreover, the turboshaft engines of a helicopter are designed so as to be
oversized in order to be able to keep the helicopter in flight in the event of failure
of one of the engines. This flight situation corresponds to the OEI mode
5 described above. This flight situation occurs following the loss of an engine, and
results in the fact that each functioning engine provides a power that is
significantly greater than its rated power in order to allow the helicopter to
overcome a dangerous situation, and to then continue its flight.
10 At the same time, the turbos haft engines are also oversized so as to be able to
ensure flight in the entire flight range specified by the aircraft manufacturer, and
in particular flight at high altitudes and during hot weather. These flight points,
which are very restrictive, in particular when the helicopter has a mass that is
close to its maximum take-off mass, are only encountered in specific use cases.
15
These oversized turboshaft engines have an adverse effect in terms of mass and
in terms of fuel consumption. In order to reduce this consumption during cruise
flight it is envisaged to stop one of the turboshaft engines during flight and to
place it in a mode referred to as standby. The active engine or engines then
20 operate at higher power levels in order to provide all the necessary power, and
therefore at more favourable SC levels.
In FR1151717 and FR1359766, the applicants have proposed methods for
optimising the specific consumption of the turbos haft engines of a helicopter by
25 means of the possibility of putting at least one turboshaft engine into a stable
power mode, known as continuous, and at least oneturboshaft engine into a
particular standby mode that it can leave in an urgent or normal manner,
according to need. Leaving the standby mode is said to have occurred normally
when a change in the flight situation requires the turboshaft engine in standby to
30 be activated, for example when the helicopter is going to transition from a cruise
flight situation to a landing phase. Leaving standby mode normally in this manner
occurs over a period of between 10 seconds and 1 minute. Leaving the standby
mode is said to have occurred urgently when a failure of or a power deficit in the
active engine occurs, or when the flight conditions suddenly become difficult.
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3
Leaving standby mode urgently in this manner occurs over a period of less than
10 seconds.
The applicants have thus proposed in particular the following two standby modes:
a standby mode known as assisted super-idling, in which the combustion
chamber is ignited and the shaft of the gas generator rotates, in a
mechanically assisted manner, at a speed of between 20 and 60 % of the
nominal speed. A mode of this kind makes it possible for the gas
generator to be at the lowest possible rotational speed in order to
minimise the fuel consumption. In order to improve the performance of the
gas generator at this low speed, it is proposed to inject mechanical
energy into the gas generator by means of an external source.
a standby mode known as banking, in which the combustion chamber is
extinguished and the shaft of the gas generator rotates, in a mechanically
assisted manner, at a speed of between 5 and 20 % of the nominal
speed. A mode of this kind makes it possible to keep a rotation of the gas
generator in a speed range that permits more rapid ignition of the
combustion chamber if necessary.
These two standby modes thus require the gas generator to be continuously
assisted. The duration of the assistance can be several hours during the
helicopter mission. The technical problem is therefore that of providing a method
for mechanically assisting a turboshaft engine in standby mode. A further
25 technical problem is that of providing an architecture of a propulsion system that
makes it possible to ensure the mechanical assistance of the gas generator of a
turbos haft engine in standby mode during the mission.
30
3. Objects of the invention
The invention aims to provide a method for mechanically assisting the gas
generator of a turboshaft engine in standby mode.
The invention also aims to provide an architecture of a propulsion system that
4
makes it possible to ensure the mechanical assistance of the gas generator of a
turboshaft engine in standby mode during the mission.
The invention also aims to provide, in at least one embodiment, an architecture of
5 this kind that does not require a specific electrical machine.
4. Description of the invention
In order to achieve this, the invention relates to an architecture of a propulsion
10 system of a multiple-engine helicopter comprising turboshaft engines, each
turboshaft engine comprising a gas generator and a free turbine that is rotated by
the gases from said gas generator.
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20
25
An architepture according to the invention is characterised in that it comprises:
at least one turbos haft engine from among said turboshaft engines,
referred to as the hybrid turboshaft engine, that is capable of operating in
at least one standby mode during a stable flight of the helicopter, the
other turboshaft engines, referred to as running turboshaft engines,
operating alone during this stable flight,
an air turbine that is mechanically connected to said gas generator,
means for withdrawing pressurised air from the gas generator of a running
turboshaft engine,
a duct for routing this withdrawn air to said air turbine such that the air
turbine can transform the energy from said pressurised air into
mechanical energy that drives said gas generator of said hybrid
turboshaft engine.
An architecture according to the invention thus makes it possible to provide
30 mechanical power to the gas generator of the hybrid turboshaft engine by means
of an air turbine. This air turbine is powered by the pressurised air withdrawn
from a running turboshaft engine. The architecture according to the invention
thus makes it possible to mechanically assist the gas generator of the hybrid
turboshaft engine when said engine is put into an "assisted super-idling" standby
5
mode or a "banking" standby mode.
This mechanical assistance is possible without, however, needing to use an
external electrical machine. The invention thus permits savings in mass, cost and
5 service life compared with electrical assistance. Furthermore, the invention does
not require electrical energy to be withdrawn from the on-board network of the
helicopter.
An architecture according to the invention uses a primary energy source that is
10 already available in a propulsion system, in the form of pressurised air provided
by a running turboshaft engine. The architecture according to the invention can
therefore be obtained from an already existing architecture of a propulsion
system, without the need for significant modifications to be made to the
architecture.
15
A hybrid turboshaft engine is a turboshaft engine that is configured so as to be
able to be placed, on demand and voluntarily, in at least one predetermined
standby mode that it can leave in a rapid (also referred to as urgent) or normal
manner. A turboshaft engine can only be in standby mode during a stable flight of
20 the helicopter, i.e. when a turboshaft engine of the helicopter has not failed,
during a cruise flight situation when it is progressing in normal conditions.
Leaving the standby mode consists in changing the turboshaft engine to an
acceleration mode of the gas generator by means of driving in a manner that is
compatible with the leaving mode required by the conditions (normal standby-
25 leaving mode or rapid standby-leaving mode, also referred to as urgent).
Advantageously and according to the invention, the means for withdrawing air
from the gas generator of a running turboshaft engine comprise at least one
withdrawal port that is integrated on a compressor of this running turboshaft
30 engine.
According to this variant, the pressurised air is withdrawn directly from a
compressor of the running turbos haft engine. Air withdrawal of this kind makes it
possible to respond to the pressurised air requirements for powering the air
6
turbine without, however, having an impact on the performance of the running
turboshaft engine from which the air is withdrawn.
Advantageously and according to the invention, the air withdrawal means
5 comprise a discharge jet that makes it possible tci meter the flow of air withdrawn
from said running turboshaft engine.
The presence of a discharge jet, preferably arranged directly on the air
withdrawal port, makes it possible to limit the maximum airflow delivered to the
10 air turbine in the event of breakage of the duct for routing air to the air turbine or
in the event of a failure in the assistance circuit.
15
Advantageously and according to the invention, said air turbine is mechanically
connected to said gas generator by means of an accessory gearbox.
An accessory gearbox makes it possible to drive ancillaries necessary for the
operation of the gas generator of the hybrid turboshaft engine, and helicopter
equipment, such as air conditioning devices. According to this variant, the air
turbine is directly integrated on said accessory gearbox, making it possible to
20 both simplify the installation thereof and the interconnection thereof with the gas
generator of the hybrid turboshaft engine, and to provide a portion of the power
that is necessary for driving ancillaries and/or for supplying power to helicopter
equipment.
25 Advantageously, an architecture according to the invention comprises means for
adjusting the mechanical power delivered by said air turbine to said gas
generator of said hybrid turboshaft engine.
The adjustment means make it possible to adapt the mechanical power delivered
30 to the gas generator of the hybrid turboshaft engine according to need. In
particular, for a hybrid turboshaft engine that can operate on demand in a
plurality of distinct standby modes, in particular an assisted super-idling mode,
and a banking mode, the adjustment means make it possible to adapt the power
to each mode.
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7
Advantageously and according to this variant, said adjustment means comprise
means for controlling the flow and/or the pressure of air provided to said air
turbine.
According to this variant, the power adjustment is obtained by means of
controlling the flow and/or the pressure of the air that powers the air turbine.
These control means can be of any kind. For example, according to a first
10 variant, these control means comprise a controlled valve that is arranged on the
air-routing duct. This valve can be a two-state shutoff valve having a passthrough
state in which the air circulates freely in the routing duct, and a blocked
state in which the air cannot power the air turbine. According to another variant,
these control means comprise a variable-pitch distributor that is integrated in the
15 air turbine and is capable of determining the flow and/or the pressure of air of the
air turbine. According to another variant, the control means comprise a plurality of
points for injecting air into the air turbine that are controlled by valves or by a
single distributor.
20 Advantageously, an architecture according to the invention comprises means for
reading information representative of the operation of said hybrid turboshaft
engine, and said control means are dependent on this information.
According to this variant, the information representative of the operation of the
25 hybrid turboshaft engine is used to determine the flow and/or the pressure of air
to be delivered to the air turbine, making it possible to adapt the power delivered
to the gas generator of the hybrid turboshaft engine depending on the operating
state of the hybrid turboshaft engine. For example, this information is measures
of parameters such as the rotational speed of the gas generator or the
30 temperature at the outlet of the high-pressure turbine of the gas generator. This
information furthermore makes it possible to adapt the delivered power to the
conditions observed, to cut off the power supply if an event necessitates this, or
to cause the hybrid turboshaft engine to leave its standby mode in the event of a
malfunction of the mechanical assistance provided to the gas generator by the air
5
8
turbine. This information can also comprise a measure of the rotational speed of
the air turbine, in order to prevent an overs peed that is related to a malfunction of
the kinematic chain connecting the air turbine to the gas generator of the hybrid
turboshaft engine.
Advantageously, an architecture according to the invention comprises a
controlled mechanical disconnection device that is arranged between the air
turbine and said gas generator of said hybrid turboshaft engine and that is
capable of disconnecting said air turbine from said gas generator if there is no
10 supply of air to the air turbine.
This disconnection device makes it possible to mechanically separate the air
turbine from the gas generator of the hybrid turboshaft engine when the air
withdrawal from the running turboshaft engine has been cut or does not exist. A
15 device of this kind can be of any type. According to a variant, said device
comprises a free wheel that is arranged between the output shaft of the air
turbine and the shaft of the gas generator of the hybrid turboshaft engine.
According to another variant, said device comprises a clutch mechanism.
According to another variant, said device comprises a pawl.
20
Advantageously and according to the invention, the hybrid turboshaft engine
comprises an engine compartment in which in particular the gas generator is
arranged, and the air turbine comprises an air outlet which opens into said
engine compartment of said hybrid turboshaft engine so as to limit the drop in
25 temperature in this compartment and to facilitate restarting the turbos haft engine.
According to another variant, the air outlet opens to the outside of the engine
compartment.
30 According to another variant, the air outlet is used to keep the temperature of the
engine oil at a specific level, with the aim of facilitating restarting said engine.
According to another variant, the air outlet opens in an air inlet of the hybrid
turboshaft engine in order to limit the drop in temperature of the parts inside the
9
turbos haft engine, with the aim of facilitating restarting said engine.
The invention applies both to a twin-engine helicopter and to a three-engine
helicopter. In the case of a three-engine helicopter, and according to a first
5 variant, the three turbos haft engines are identical in size. One of the three
turboshaft engines is a hybrid turboshaft engine capable of operating in at least
one standby mode during a stable flight of the helicopter, the two other engines
then being running engines and operating alone during this stable flight. In this
case, the air turbine is arranged between one of the running turboshaft engines
10 and the hybrid turbos haft engine.
According to another variant, the hybrid turboshaft engine is smaller than the two
running turboshaft engines. It is the smaller engine that is capable of operating in
a standby mode. In this case, the air turbine is arranged between one of the two
15 large turboshaft engines and the hybrid turboshaft engine.
According to another variant, the three turboshaft engines are of different sizes.
The smallest turboshaft engine can be switched off during stable flight, and one
of the two larger engines is a hybrid turboshaft engine that is capable of being put
20 into standby mode if necessary, the other turboshaft engine then being the
running turboshaft engine. In this case, the air turbine is arranged between the
two larger turboshaft engines, i.e. the hybrid turboshaft engine and the running
turboshaft engine.
25 The invention also relates to a helicopter comprising a propulsion system,
characterised in that said propulsion system has an architecture according to the
invention.
The invention also relates to a method for mechanically assisting a turboshaft
30 engine, referred to as the turboshaft engine in standby mode, that operates in a
standby mode during a stable flight of a helicopter comprising turboshaft engines,
each turboshaft engine comprising a gas generator and a free turbine, the other
turboshaft engines, referred to as running turboshaft engines, operating alone
during this stable flight.
5
10
10
A method according to the invention is characterised in that it comprises:
a step of withdrawing pressurised air from the gas generator of a running
turbos haft engine,
a step of routing the withdrawn air to an air turbine that is mechanically
connected to said gas generator of said turboshaft engine in standby
mode,
a step of transforming, by means of said air turbine, the energy from the
air provided by said routing step into mechanical energy for driving said
gas generator.
A method according to the invention is advantageously implemented by an
architecture according to the invention. An architecture according to the invention
15 advantageously implements a method according to the invention.
20
Advantageously and according to the invention, said air withdrawal step consists
in withdrawing the air from a compressor of said gas generator of a running
turbos haft engine.
Advantageously, a method according to the invention comprises a step of
adjusting the mechanical power provided by said air turbine to said turboshaft
engine in standby mode.
25 Advantageously and according to this variant, said step of adjusting the power
comprises a step of controlling the flow and/or the pressure of air delivered to
said air turbine.
The invention also relates to an assistance method, to a propulsion system
30 architecture and to a helicopter, characterised in combination by all or some of
the features mentioned above or below.
5. List of drawings
5
10
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Other aims, features and advantages of the invention will emerge from reading
the following description, which is given purely by way of non-limiting example
and relates to the accompanying drawings, in which:
Fig. 1 is a schematic view of an architecture of a propulsion system of a
twin-engine helicopter according to an embodiment of the invention,
Fig. 2 is a schematic view of an architecture of a propulsion system of a
twin-engine helicopter according to a further embodiment of the invention,
Fig. 3 is a schematic view of an architecture of a propulsion system of a
twin-engine helicopter according to a further embodiment of the invention,
a schematic view of a control device according to an embodiment of the
invention,
Fig. 4 is a schematic view of an architecture of a propulsion system of a
twin-engine helicopter according to a further embodiment of the invention.
6. Detailed description of an embodiment of the invention
The embodiments described below relate to an architecture of a propulsion
system of a twin-engine helicopter. This being the case, a person skilled in the art
20 will easily understand how to adapt the described embodiments to a multipleengine,
in particular three-engine, propulsion system.
This architecture comprises two turboshaft engines 5, 6. Each turboshaft engine
5, 6 is controlled by its own inspection-control device, which is not shown in the
25 drawings for reasons of clarity.
Each turbos haft engine 5, 6 respectively, and as shown in Fig. 1, comprises a
gas generator 17, 27 and a free turbine 10, 20 that is powered by the generator
17, 27. The gas generator 17, 27 comprises an air compressor 14, 24 to which
30 air is supplied by an air inlet 18, 28. The compressor 14, 24 supplies a fuel, in the
compressed air, to a combustion chamber 13, 23, which fuel delivers burned gas
that provides kinetic energy. A turbine 12, 22 for partially expanding the burned
gas is coupled to the compressor 14, 24 by means of a drive shaft 15, 25 so as to
be able to rotate the compressor 14, 24 and the equipment necessary for the
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operation of the gas generator or the helicopter. This equipment is arranged in an
accessory gearbox 32, 33. The resultant portion of the burned gas drives the free
power transmission turbine 10, 20 in connection with the power transmission
case of the helicopter, and is then discharged through the exhaust 19, 29.
In all of the following, it is assumed that the turboshaft engine 5 is a hybrid
turboshaft engine that is capable of operating in at least one standby mode
during a stable flight of the helicopter, the running turbos haft engine 6 then
operating alone during this stable flight.
The architecture further comprises an air turbine 30 that is mechanically
connected to the gas generator 17 of the hybrid turboshaft engine 5 by means of
the accessory gearbox 32. Air is supplied to this turbine 30 by means of an airrouting
duct 31. The air-routing duct 31 is connected to an air withdrawal port on
15 the compressor 24 of the running turboshaft engine 6 so as to be able to convey
the compressed air originating from the compressor 24 to the air turbine 30. The
routing duct 31 is thus arranged between the air withdrawal port on the gas
generator 27 of the running turboshaft engine 6 and an air intake inlet mouth of
the air turbine 30. The air turbine 30 thus makes it possible to transform the
20 energy that is available in the compressed air delivered by the air-routing duct 31
into mechanical energy that is available at the output shaft thereof.
According to an embodiment, this air turbine 30 is a reaction turbine of the axial
or centripetal type. According to a further .embodiment, the air turbine 30 is a
25 partial-admission or full-admission impulse turbine.
30
According to an embodiment that is not shown in the drawings, the architecture
further comprises a discharge jet that makes it possible to meter the flow of air
withdrawn from the compressor 24 of the running turboshaft engine 6.
According to the embodiment of Fig. 2, the architecture comprises a controlled
shutoff valve 33 that is a means for controlling the flow and the pressure of air
delivered to the air turbine 30. According to this embodiment, the valve is suitable
for being placed in two states: a first pass-through state in which all of the air
13
withdrawn from the compressor 24 is delivered to the air turbine 30, and a
second blocked state in which the air can no longer be delivered to the air turbine
30.
5 According to a further embodiment as shown in Fig. 3, the architecture further
comprises a module 35 for controlling a variable-pitch distributer 34 of an air
turbine 30 of the axial or centripetal type. This assembly forms the means for
controlling the flow and the pressure of air delivered to the air turbine 30 and, by
extension, forms the means for adjusting the mechanical power delivered to the
10 gas generator 17 of the hybrid turboshaft engine 5.
According to the embodiment of Fig. 4, the architecture further comprises a free
wheel 40 that is arranged between the air turbine 30 and the accessory gearbox
32. This free wheel 40 forms a controlled mechanical disconnection device for
15 the air turbine 30 and the gas generator 17. This free wheel 40 thus makes it
possible to ensure that the air turbine 30 is no longer mechanically connected to
the gas generator 17 when air is no longer being supplied to said turbine by the
air-routing duct 31.
20 The air outlet from the air turbine 30 may be arranged in various ways (not shown
in the drawings).
F?r example, according to a first arrangement, the air at the outlet of the air
turbine 30 is discharged into the engine compartment in order to limit the drop in
25 temperature, with the aim of facilitating restarting the turboshaft engine in
standby mode.
30
According to a further arrang~ment, the air at the outlet of the air turbine 30 is
discharged to the outside of the engine compartment.
According to a further arrangement, the air is injected into the air inlet 18 of the
turboshaft engine in standby mode in order to limit the drop in temperature of the
parts inside the turboshaft engine, with the aim of facilitating restarting said
engine.
14
According to a further arrangement, the air is used to keep the oil of the
turbos haft engine at a temperature that is compatible with limiting the resisting
torque when restarting the turboshaft engine, and so as to be able to rapidly have
5 available all of the power necessary for this restart.
The invention also relates to a method for mechanically assisting the hybrid
turboshaft engine 5 when it is in a standby mode.
10 The method comprises a step of withdrawing pressurised air from the gas
generator of a running turboshaft engine, a step of routing the withdrawn air to an
air turbine that is mechanically connected to said gas generator of said turboshaft
engine in standby mode, and a step of transforming the energy available in the
pressurised air into mechanical energy that is available at the shaft at the outlet
15 of the accessory gearbox.
20
A method according to the invention is advantageously implemented by an
architecture of a propulsion system according to the invention.

CLAIMS
1. Architecture of a propulsion system of a multiple-engine helicopter
comprising turboshaft engines (5, 6), each turboshaft engine (5, 6) comprising a
5 gas generator (17, 27) and a free turbine (10, 20) that is rotated by the gases
from said gas generator,
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15
20
characterised in that it comprises:
- at least one turboshaft engine from among said turboshaft engines,
referred to as the hybrid turboshaft engine (5), that is capable of operating
in at least one standby mode during a stable flight of the helicopter, the
other turboshaft engines, referred to as running turboshaft engines (6),
operating alone during this stable flight,
- an air turbine (30) that is mechanically connected to said gas generator
(17) of said hybrid turboshaft engine (5),
- means for withdrawing pressurised air from the gas generator (27) of a
running turboshaft engine (6),
-a duct (31) for routing this withdrawn air to said air turbine (30) such that
the air turbine (30) can transform the energy from said pressurised air into
mechanical energy that drives said gas generator (17) of said hybrid
turboshaft engine (5).
2. Architecture according to claim 1, characterised in that said means for
withdrawing air from the gas generator (27) of a running turboshaft engine
comprise a withdrawal port that is arranged on a compressor (24) of this running
25 turboshaft engine (6).
30
3. Architecture according to either claim 1 or claim 2, characterised in that
said air withdrawal means comprise a discharge jet that makes it possible to
meter the flow of air withdrawn from said running turboshaft engine (6).
4. Architecture according to any of claims 1 to 3, characterised in that said
air turbine (30) is connected to said gas generator (17) by means of an accessory
gearbox (32).
5
16
5. Architecture according to any of claims 1 to 4, characterised in that it
comprises means (33; 34, 35) for adjusting the mechanical power delivered by
said air turbine (30) to said gas generator of said hybrid turboshaft engine.
6. Architecture according to any of claims 1 to 5, characterised in that said
adjustment means comprise means (33; 34, 35) for controlling the flow and/or the
pressure of air provided to said air turbine (30).
7. Architecture according to claim 6, characterised in that it comprises
1 0 means for reading information representative of the operation of said hybrid
turboshaft engine (5), and in that said control means (35, 34) are dependent on
this information.
8. Architecture according to any of claims 1 to 7, characterised in that it
15 comprises a controlled mechanical disconnection device (40) that is arranged
between the air turbine (30) and said gas generator (17) of said hybrid turboshaft
engine (5) and that is capable of disconnecting said air turbine (30) from said gas
generator (17) if there is no supply of air to the air turbine (30).
20 9. Architecture according to any of claims 1 to 8, characterised in that said
25
air turbine (30) comprises an air outlet which opens into an engine compartment
of said hybrid turboshaft engine so as to limit the drop in temperature in this
compartment and to facilitate restarting the turboshaft engine.
10. Helicopter comprising a propulsion system, characterised in that said
propulsion system has an architecture according to any of claims 1 to 9.
11. Method for mechanically assisting a turboshaft engine, referred to as the
turboshaft engine (5) in standby mode, that operates in a standby mode during a
30 stable flight of a helicopter comprising turboshaft engines (5, 6), each turboshaft
engine comprising a gas generator (17, 27) and a free turbine, the other
turboshaft engines, referred to as running turboshaft engines (6), operating alone
during this stable flight, characterised in that it comprises:
- a step of withdrawing pressurised air from the gas generator (27) of a
5
17
running turboshaft engine (6),
- a step of routing the withdrawn air to an air turbine (30) that is
mechanically connected to said gas generator (17) of said turboshaft
engine (5) in standby mode,
- a step of transforming, by means of said air turbine (30), the energy from
the air provided by said routing step into mechanical energy for driving
said gas generator (17) of said turboshaft engine (5) in standby mode.
12. Method according to claim 11, characterised in that said air withdrawal
10 , step consists in withdrawing the air from a compressor (24) of said gas generator
(27) of a running turboshaft engine (6).
13. Method according to either claim 11 or claim ·12, characterised in that it
comprises a step of adjusting the mechanical power provided by said air turbine
15 (30) to said turboshaft engine (5) in standby mode.
20
14. Method according to claim 13, characterised in that said step of adjusting
the power comprises a step of controlling the flow and/or the pressure of air
delivered to said air turbine (30).