ARCHITECTURE FOR A PROPULSION SYSTEM OF A HELICOPTER
INCLUDING A HYBRID TURBOSHAFT ENGINE AND A SYSTEM FOR
REACTIVATING SAID HYBRID TURBOSHAFT ENGINE
1. Technical field of the invention
The invention relates to an architecture of a propulsion system of a multiengine
helicopter, in particular a twin-engine or three-engine helicopter, and to a
helicopter comprising a propulsion system that has such an architecture.
2. Technological background
As is known, a twin-engine or three-engine helicopter has a propulsion
system comprising two or three turboshaft engines, each turboshaft engine
comprising a gas generator and a free turbine which is rotated by the gas
generator and is rigidly connected to an output shaft. The output shaft of each
free turbine is suitable for inducing the movement of a power transmission
15 gearbox, which itself drives the rotor of the helicopter.
It is known that, when the helicopter is in a cruise flight situation (that is,
when it is progressing in normal conditions, during all flight phases, except for
transitional phases of take-off, ascent, landing or hovering flight), the turboshaft
20 engines develop low levels of power that are below the maximum continuous
output thereof. These low levels of power lead to a specific consumption
(hereinafter SC), defined as the ratio between the hourly fuel consumption of the
combustion chamber of the turboshaft engine and the mechanical power supplied
by this turboshaft engine, of approximately 30 % greater than the SC of the
25 maximum take-off power, and they therefore lead to an overconsumption of fuel
during cruise flight.
Furthermore, 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 that
30 one of the engines fails. This flight situation arises after the loss of an engine and
results in the fact that each operating engine supplies a power level much
beyond its nominal power so that the helicopter can cope with a dangerous
situation, and then continue its flight.
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The turboshaft engines are also oversized in order to be able to ensure
flight over the entire flight range specified by the aircraft manufacturer and in
particular flight at high altitudes and in hot weather. These flight points, which are
highly demanding, particularly when the weight of the helicopter is close to its
5 maximum take-off weight, are encountered only in certain circumstances of use.
These oversized turboshaft engines are disadvantageous in terms of
weight and fuel consumption. In order to reduce this consumption during cruise
flight, it is envisaged to put at least one of the turboshaft engines on standby
10 during flight. The active engine or engines then operate at higher power levels in
order to provide all the necessary power, and therefore at more favourable SC
levels.
In applications · FR1151717 and FR1359766, the applicants have
15 proposed methods for optimising the specific consumption of the turboshaft
engines of a helicopter through the option of putting at least one turboshaft
engine into a stable flight mode, known as a continuous flight mode, and at least
one turboshaft engine into a particular standby mode from which it can exit in a
rapid or normal manner, as required.
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An exit from standby mode is described as "normal" when a change in
flight situation requires the activation of the turboshaft engine that is on standby,
for example when the helicopter is going to transition from a cruise flight situation
to a landing phase. A normal exit from standby of this kind occurs over a period
25 of time between 10 seconds and 1 minute. An exit from standby mode is
described as "rapid" when a failure or deficit of power in the active engine occurs
or when the flight conditions suddenly become difficult. An emergency exit from
standby of this kind occurs over a period of less than 10 seconds.
30 The applicant has already proposed a system for reactivating the
turboshaft engine on standby allowing an exit from standby mode (in a normal or
rapid manner) that uses an electric machine. This electric machine can be
supplied with power by the onboard network of the helicopter (hereinafter OBN),
which is a DC voltage 28-volt network and/or a network of which the voltage is
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provided by an appropriate power electronics unit connected to a compatible AC
voltage of the aircraft. It has also been proposed to use an electric machine to
mechanically assist the turboshaft engine during a specific standby mode.
The inventors have therefore sought to improve the performance of the
architectures of propulsion systems comprising at least one turboshaft engine
suitable for being put in standby mode and a system for reactivating the
turboshaft engine comprising an electric machine.
In particular, the inventors have sought to propose a new propulsion
system architecture that allows a very good level of availability of the reactivation
system to be obtained. The inventors have also sought to propose a new
architecture that allows any failures in the system for reactivating the turboshaft
engine on standby to be detected.
3. Aims of the invention
The invention aims to provide a new architecture of the propulsion system
of a multi-engine helicopter.
The invention also aims to provide, at least in one embodiment, an
architecture of a propulsion system of a multi-engine helicopter comprising a
turboshaft engine configured to be capable of being put on standby and a
reactivation system that has an improved availability in comparison with the
systems from the prior art.
The invention also aims to proVide, at least in one embodiment, an
architecture that allows any failures in the reactivation system to be detected.
The invention also aims to provide a helicopter comprising a propulsion
30 system that has an architecture according to the invention.
4. Disclosure of the invention
In order to achieve this, the invention relates to an architecture of a
propulsion system of a multi-engine helicopter comprising turboshaft engines
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connected to a power transmission gearbox, characterised in that it comprises:
- at least one turboshaft engine among said turboshaft engines,
referred to as a hybrid turboshaft engine, capable of operating in at
least one standby mode during a stable flight of the helicopter, the
other turbos haft engines operating alone during this stable flight,
- at least two systems for controlling each hybrid turboshaft engine,
referred to as reactivation systems, each system comprising an
electric machine connected to the hybrid turboshaft engine and
designed to be capable of rotating said hybrid turboshaft engine,
and at least one source of electrical power for said electric
machine, each reactivation system being configured such that it
can drive said turboshaft engine in at least one operating mode
among a plurality of predetermined-modes.
An architecture according to the invention therefore makes it possible to at
least duplicate the systems for reactivating a hybrid turboshaft engine capable of
operating in a standby mode. The reactivation system of an architecture
according to the invention therefore comprises at least two separate electric
machines, each machine being connected to the hybrid turboshaft engine so as
20 to form at least two separate reactivation systems configured to be capable of
driving the turboshaft engine towards at least one operating mode selected from
a plurality of predetermined modes.
A hybrid turboshaft engine within the meaning of the invention is a
25 turboshaft engine configured to be capable of being put, on demand and
deliberately, in at least one predetermined standby mode, from which it can exit
in a normal or rapid (also referred to as emergency) manner. A turboshaft engine
can be in standby mode only during a stable flight of the helicopter, i.e. when no
turboshaft engine of the helicopter has failed, during a cruise flight situation,
30 when it is progressing in normal conditions. The exit from standby mode consists
in changing the turboshaft engine into a gas generator acceleration mode by
means of driving in a manner that is compatible with the exit mode required by
the conditions (normal standby-exiting mode or rapid standby-exiting mode, also
referred to as emergency exit).
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Advantageously and according to the invention, given that the turboshaft
engine comprising a gas generator, said plurality of predetermined modes
comprises:
5 - a mode, referred to as the rapid reactivation mode, in which said
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turboshaft engine is rotated from the standby mode up to a speed
in the range of between 80 and 105 % of the nominal speed of said
gas generator of said turboshaft engine in a period of less than 10
seconds;
- a mode, referred to as the normal reactivation mode, in which said
turboshaft engine is rotated from the standby mode up to a speed
in the range of between 80 and 105 % of the nominal speed of said
gas generator of said turboshaft engine in a period in the range of
between 10 seconds and 60 seconds;
a standby mode, referred to as the assisted super-idle mode, in
which the turboshaft engine is continuously rotated at a speed in
the range of between 20 and 60 % of the nominal speed of said
gas generator of said turboshaft engine;
- a standby mode, referred to as the turning rnode, in which the
turboshaft engine is continuously rotated at a speed in the range of
between 5 and 20 % of the nominal speed of said gas generator of
said turboshaft engine.
Advantageously and according to the invention, given that said helicopter
25 comprising at least one onboard network, each reactivation system configured to
drive said turboshaft engine in said rapid reactivation mode comprises a source
of electrical power formed by an energy storage unit; and each reactivation
system configured to drive said turboshaft engine in said normal reactivation
mode or a standby mode comprises a source of electrical power formed by an
30 on board network of the helicopter.
An energy storage unit makes it possible to supply a significant amount of
power compatible with the energy required for the turboshaft engine to exit its
standby mode rapidly. The storage unit is therefore very suitable for the
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reactivation system intended for the rapid reactivation of the turboshaft engine.
The onboard network allows the corresponding reactivation system to be
tested, both on the ground before takeoff and during flight, for example before the
5 turboshaft engine is put on standby. In addition, such a source of energy is
sufficient to supply power to an electric machine intended to restart the hybrid
turboshaft engine under normal reactivation conditions.
Advantageously and according to the invention, said onboard network is a
10 network configured to supply a compatible AC voltage of the aircraft.
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According to a first advantageous variant of the invention, the architecture
comprises:
- at least one first reactivation system configured to be capable of
driving said turboshaft engine in the rapid reactivation mode, the
normal reactivation mode and at least one standby mode;
- at least one second reactivation system configured to be capable of
driving said turboshaft engine solely in said normal reactivation
mode.
In order to do this, in practice, the first system is connected to two
separate sources of electrical energy, namely an energy storage unit and the
onboard network of the helicopter. The second system is also connected to the
onboard network.
According to this variant, the first and the second reactivation systems are
both compatible with a normal reactivation of the turboshaft engine. They can
therefore be called upon alternately at each start-up in order to check their
availability.
The first reactivation system is in addition configured for both a rapid
reactivation and a standby mode. Therefore, during the standby mode, the
system is called upon, which acts as a test of the system, in readiness for any
rapid reactivation. The absence of any malfunction in the system is thus checked
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during the standby mode.
In the event that the first system is unavailable, the second system is
called upon for a normal reactivation of the hybrid turboshaft engine.
During a rapid reactivation of the hybrid turboshaft engine, the first system
is called upon and the second system is able to provide additional power if
necessary.
In combination with the first variant, the second system can also be
configured to be capable of driving the turboshaft engine in said rapid reactivation
mode. In order to do this, the second system is, in practice, connected to a
second electrical energy storage unit.
An architecture according to this particular variant therefore has available
two separate reactivation systems allowing the turboshaft engine to be restarted
rapidly. Thus, in the event of a failure of one rapid reactivation system, the other
system can compensate for the failure.
According to a second advantageous variant of the invention, the
architecture comprises:
- at least one first reactivation system configured to be capable of
driving said turboshaft engine in both the rapid reactivation mode
and the normal reactivation mode;
- at least one second reactivation system configured to be capable of
driving said turboshaft engine solely in said standby mode.
In order to do this, in practice, the first reactivation system comprises two
sources of electrical power, namely an energy storage unit and the onboard
30 network of the helicopter, and the second reactivation system is connected
directly to the onboard network.
The first system is called upon at start-up in order to check the availability
of the system. In standby mode, the second system is called upon in order to
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avoid producing wear in the system allocated to rapid reactivation. Any
unavailability of the second system results in a switchover to the first system and
in the reactivation ofthe turboshaft engine.
In combination with this second variant, the second system can also be
configured to be capable of driving the turboshaft engine in said normal
reactivation mode. In order to do this, the second system is connected to the
onboard network.
This variant is advantageous particularly in that in the event of a failure of
the first system, the second system can provide normal reactivation of the
turboshaft engine.
In addition, the two systems can be tested at any moment.
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 an architecture of a propulsion system of a
multi-engine helicopter and to a helicopter provided with a propulsion system
having such an architecture, these being characterised in combination by all or
some of the features mentioned above or below.
5. List of figures
Other aims, features and advantages of the invention will become
apparent upon reading the description that follows, which is given purely by way
of non-limiting example and relates to the accompanying figures, in which:
Fig. 1 is a schematic view of an architecture from the prior art
comprising a turboshaft engine controlled by a single control
system;
- Fig. 2 is a schematic view of another architecture from the prior art;
- Fig. 3 is a schematic view of an architecture according to an
embodiment of the invention;
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Fig. 4 is a schematic view of an architecture according to another
embodiment of the invention;
- Fig. 5 is a schematic view of an architecture according to another
embodiment of the invention;
- Fig. 6 is a schematic view of an architecture according to another
embodiment of the invention;
Fig. 7 is a schematic view of an architecture according to another
embodiment of the invention.
6. Detailed description of some embodiments of the invention
The embodiments described below are some examples for carrying out
the invention. Although the detailed description refers to one or more
embodiments, this does not necessarily mean that each reference relates to the
same embodiment, or that the features apply only to a single ·embodiment.
15 Individual features of different embodiments can also be combined in order to
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provide other embodiments. In addition, in the figures, for the purposes of
illustration and clarity, the scales and the proportions are not necessarily
accurate.
Fig. 1 is a schematic view of an architecture of a known helicopter
propulsion system comprising a turboshaft engine 10 and a system for controlling
said turboshaft engine. The control system comprises an electric machine 11
suitable for rotating the turbos haft engine 10 on demand so as to ensure the
start-up thereof. The electric machine 11 draws its power directly from a low-
25 voltage onboard network 12 of the helicopter, which is typically a network that
supplies a 28-volt DC voltage.
Fig. 2 is a schematic view of an architecture of a known helicopter
propulsion system comprising the turboshaft engine 10 and another system for
30 controlling said turboshaft engine. The control system comprises an electric
machine 11 suitable for rotating the turboshaft engine 10 on demand so as to
ensure the start-up thereof. The electric machine 11 draws its power from a
compatible high AC-voltage onboard network 14 of the aircraft. The control
system also comprises a power conversion module 13 designed to convert the
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high AC voltage supplied by the on board network 14 into a voltage for controlling
the electric machine 11.
The turboshaft engine 10 having the architectures from Fig. 1 and 2 is
5 generally started on the ground. An in-flight restart of a turboshaft engine
according to this architecture is an exceptional event.
Fig. 3 to 7 show architectures according to the invention that allow at least
one turboshaft engine to be put on standby and to be reactivated during flight. In
I 0 addition, the proposed architectures make the reactivation operations reliable
and allow the different reactivation systems to be tested regularly .
.In Fig. 3 to 7, only the hybrid turboshaft engine is shown, it being
understood· that in a multi-engine architecture., in particular. a twin-engine or
15 three-engine architecture, the architecture comprises a plurality of turboshaft
engines of which at least one is a hybrid turboshaft engine.
An architecture according to the invention comprises a plurality of
turboshaft engines connected to a power transmission gearbox (not shown in the
20 figures).
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Among the plurality of turboshaft engines, at least one turboshaft engine,
referred to as a hybrid turboshaft engine 20, is capable of operating in at least
one standby mode during a cruise flight of the helicopter.
According to the embodiments shown in Fig. 3 to 7, the architecture
comprises two systems 30, 40 for reactivating the hybrid turboshaft engine 20. In
the whole of the following, the reactivation system denoted by reference numeral
30 will be referred to as the first reactivation system and the reactivation system
30 denoted by reference numeral 40 will be referred to as the second reactivation
system.
It is also hereby specified that the same reference numerals 30 and 40
are used to indicate the first and second reactivation systems in Fig. 3 to 7, even
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though the reactivation systems may not be the same from one embodiment to
another.
Each reactivation system 30, 40 is configured to be capable of driving the
5 turboshaft engine 20 in at least one operating mode among a plurality of
predetermined modes.
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In light of the turboshaft engine comprising a gas generator, the
predetermined modes comprise at least the following modes:
- a mode, referred to as the rapid reactivation mode, in which the
turboshaft engine 20 is rotated from the standby mode up to a
speed in the range of between 80 and 105 % of the nominal speed
of the gas generator of the turboshaft engine within a period of less
than 10 seconds;
- a mode, referred to as the normal reactivation mode, in which the
turboshaft engine 20 is rotated from the standby mode up to a
speed in the range of between 80 and 1 05 % of the nominal speed
of the gas generator of the turboshaft engine within a period in the
range of between 1 0 seconds and 60 seconds;
a standby mode, referred to as the assisted super-idle mode, in
which the turboshaft engine 20 is continuously rotated at a speed in
the range of between 20 and 60 % of the nominal speed of the gas
generator of the turboshaft engine;
- a standby mode, referred to as the turning mode, in which the
turboshaft engine 20 is continuously rotated at a speed in the range
of between 5 and 20 % of said nominal speed.
In Fig. 3, the first reactivation system 30 comprises an electric machine
31, a power conversion device 32, an electrical energy storage unit 33, and an
30 onboard network 51. The second reactivation system 40 comprises an electric
machine 41, a power conversion device 42 and an on board network 51, which is
shared with the first reactivation system 30.
This embodiment allows the first reactivation system 30 to drive the
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turboshaft engine 20 in any of the rapid reactivation mode (by the use of the
energy from the storage unit 33), the normal reactivation mode (by the use of the
energy from the on board network 51 or from the storage unit 33), or at least one
standby mode (by the use of the energy from the onboard network 51). It also
5 allows the second reactivation system 40 to be capable of driving the turboshaft
engine 20 in said normal reactivation mode (by the use of the energy from the
on board network 51).
According to this embodiment, the first and second systems can be called
10 upon alternately at each start-up to check their availability.
Since the first system is also configured for a rapid reactivation and a
standby mode, the transition of the turboshaft. engine 20 into standby mode
.· allows the integrity of the system 30 to be tested and therefore any malfunction
15 then preventing rapid reactivation of the turboshaft engine 20 by the system 30 to
be detected. In the event of a malfunction being detected, the second system 40
is then called upon for a normal reactivation of the hybrid turboshaft engine 20.
During a rapid reactivation of the hybrid turboshaft engine 20 by the first
20 reactivation system 30, the second system 40 can also potentially provide
additional power if necessary.
The architecture shown in Fig. 4 is a variant of that shown in Fig. 3. This
architecture comprises, in addition to the elements described in relation to Fig. 3,
25 a second storage unit 43 arranged in the second reactivation system 40.
30
This embodiment therefore allows the second reactivation system 40 to
also drive the turboshaft engine 20 in the rapid reactivation mode (by the use of
the energy from the storage unit 43).
This architecture is therefore redundant and has a high degree of
availability.
In Fig. 5, the first reactivation system 30 comprises an electric machine
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31, a power conversion device 32, an electrical energy storage unit 33, and an
onboard network 51 that is, for example, an onboard network supplying an AC
voltage of 115 volts. The second reactivation system 40 comprises an electric
machine 41, a power conversion device 42, an on board network 52 that is, for
5 example, a network supplying a DC voltage of 28 volts, the onboard network 51
shared with the first reactivation system 30, and optionally an electrical energy
storage unit 53.
In this embodiment, the first reactivation system 30 allows the turboshaft
10 engine 20 to be driven in the rapid reactivation mode (by the use of the energy
from the storage unit 33), in the normal reactivation mode (by the use of the
energy from the onboard network 51 or from the storage unit 33) or in a standby
mode. It also allows the second reactivation system 40 to be capable of driving
·the turboshaft engine 20·in a normal reactivation· mode (by tHe use of the energy
15 from the onboard network 52 or from the optional storage unit 53 or by the
energy from the onboard network 51). In particular, this particular configuration
allows the second system 40 for reactivating the turboshaft engine 20 to use the
onboard network 51 for high power levels, for example levels greater than 10 kW,
and to use the onboard network 52 for lower power levels, for example levels
20 below 10 kW.
In Fig. 6, the first reactivation system 30 comprises an electric machine
31, a power conversion device 32 and an electrical energy storage unit 33. The
second reactivation system 40 comprises an electric machine 41, a power
25 conversion device 42 and an onboard network 51.
In this embodiment, the first reactivation system 30 allows the turboshaft
engine 20 to be driven in the rapid reactivation mode (by the use of the energy
from the storage unit 33). It also allows the second reactivation system 40 to be
30 capable of driving the turboshaft engine 20 in a standby mode (by the use of the
energy from the on board network 51) or in a normal reactivation mode.
In Fig. 7, the first reactivation system 30 comprises an electric machine
31, a power conversion device 32, an electrical energy storage unit 33, and an
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onboard network 51. The second reactivation system 40 comprises an electric
machine 41, a power conversion device 42 and the on board network 51, shared
with the first system 30.
In this embodiment, the first reactivation system 30 allows the turboshaft
engine 20 to be driven in the rapid reactivation mode (by the use of the energy
from the storage unit 33) and in the normal reactivation mode (by the use of the
energy from the onboard network 51 or from the storage unit 33). It also allows
the second reactivation system 40 to be capable of driving the turboshaft engine
10 20 in a standby mode or in a normal reactivation mode (by the use of the energy
from the onboard network 51).
In a variant, the second system can be configured to drive the turboshaft
engine 20 solely in a standby mode (by the use of the energy from thif on board
15 network 51).
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The advantage of this architecture is the ability to use power-optimised
electric machines, in particular for the electric machine 41, the only function of
which is to provide the standby mode.
For each mode, the control of the reactivation systems is governed by the
turboshaft engine control system known by the acronym FADEC, for Full
Authority Digital Engine Control.
The invention is not limited solely to the embodiments described. In
particular, the invention may comprise a plurality of hybrid turboshaft engines,
each turboshaft engine being provided with at least two reactivation systems of
its own as described.

CLAIMS
1. Architecture of a propulsion system of a multi-engine helicopter
5 comprising turboshaft engines connected to a power transmission gearbox,
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characterised in that it comprises:
at least one turboshaft engine among said turboshaft engines,
referred to as a hybrid turboshaft engine (20), capable of operating
in at least one standby mode during a stable cruise flight of the
helicopter, the other turboshaft engines operating alone during this
stable flight;
- at least two systems (30; 40) for controlling each hybrid turboshaft
engine (20), referred to as reactivation systems, each system (30;
40) comprising an electric machine (31; 41)conriected td·ttie hybrid
turboshaft engine (20) and suitable for rotating said hybrid
turboshaft engine, and at least one source (33; 43; 51) of electrical
power for said electric machine (31; 41), each reactivation system
(30; 40) being configured such that it can drive said turboshaft
engine (20) in at least one operating mode among a plurality of
predetermined modes.
2. Architecture according to claim 1, each hybrid turboshaft engine
comprising a gas generator, characterised in that said plurality of predetermined
modes comprises:
a mode, referred to as the rapid reactivation mode, in which said
turboshaft engine (20) is rotated up to a speed in the range of
between 80 and 105% of a nominal speed of said gas generator
of said turboshaft engine in a period of less than 10 seconds;
a mode, referred to as the normal reactivation mode, in which said
turboshaft engine (20) is rotated up to a speed in the range of
between 80 and 105 % of said nominal speed of said gas
generator of said turboshaft engine in a period in the range of
between 10 seconds and 60 seconds;
a standby mode, referred to as the assisted super-idle mode, in
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which the turboshaft engine (20) is rotated continuously at a speed
in the range of between 20 and 60 % of said nominal speed of said
gas generator of said turboshaft engine;
a standby mode, referred to as the turning mode, in which said gas
generator of said turboshaft engine (20) is rotated continuously at
a speed in the range of between 5 and 20 % of said nominal
speed.
Architecture according to claim 2, chara~terised in that:
each reactivation system (30; 40) configured to drive said gas
generator of said turboshaft engine (20) in said rapid reactivation
mode comprises a source of electrical power formed by an energy
storage unit (33; 43);
each reactivation system (30; 40) configured to drive s·aid gas
generator of said turboshaft engine(20) in said normal reactivation
mode or a standby mode comprises a source of electrical power
formed by an onboard network (51) of the helicopter.
4. Architecture according to claim 3, characterised in that said onboard
20 network (51) is a network configured to supply a compatible AC voltage of the
aircraft.
5. Architecture according to any of claims 1 to 4, characterised in that it
comprises:
25 - at least one first reactivation system (30) configured to be capable
30
6.
of driving said turboshaft engine in the rapid reactivation mode and
the normal reactivation mode and at least one standby mode;
- at least one second reactivation system ( 40) configured to be
capable of driving said turboshaft engine solely in said normal
reactivation mode.
Architecture according to claim 5, characterised in that said second
reactivation system (40) is also configured to be capable of driving the turboshaft
engine in said rapid reactivation mode.
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7. Architecture according to any of claims 1 to 4, characterised in that it
comprises:
- at least one first reactivation system (30) configured to be capable
of driving said turboshaft engine in both the rapid reactivation mode
and the normal reactivation mode;
- at least one second reactivation system ( 40) configured to be
capable of driving said turboshaft engine solely in said standby
mode.
8. Architecture according to claim 7, characterised in that said second
reactivation system (40) is also configured to be capable of driving the turboshaft
engine (20) in said normal reactivation mode.
15 9. Helicopter comprising a propulsion system characterised in that said
propulsion system has an architecture according to any of claims 1 to 8.