ARCHITECTURE OF A MUL Tl ENGINE HELICOPTER PROPULSION
SYSTEM AND CORRESPONDING HELICOPTER
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 having an architecture of this
kind.
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
gearbox (referred to in the following by the abbreviation PTG), which itself
drives the rotor of the helicopter which is equipped with blades having a
variable pitch.
Furthermore, it is known that, when the helicopter is in a cruise flight situation
(i.e. when it is progressing in normal conditions, in AEO (all engines
operative) mode, during all the flight phases apart from transitional phases of
take-off, landing or hovering flight), the turboshaft engines operate at low
power levels, below their maximum continuous output (hereinafter MCO). In
some arrangements, the power provided by the turboshaft engines during a
cruise flight can be less than 50 % of the maximum take-off output
(hereinafter MTO). These low power levels result in a specific consumption
(hereinafter SC), which is defined as the relationship between the hourly fuel
consumption by the combustion chamber of the turboshaft engine and the
thrust provided by said turboshaft engine, which is approximately 30 %
greater than the SC of the MTO, and thus a reduction in the efficiency of the
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gas turbines (or an increase in the SC).
In order to reduce this consumption during cruise flight (or during holding on
the ground for example), it is possible to stop one of the turboshaft engines
and to put it into a mode known as standby. 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 the following, "economical flight phase" will denote a flight phase during
which at least one turboshaft engine is in standby mode, and "conventional
flight phase" will denote a flight phase during which none of the turboshaft
engines are in standby mode.
In FR1151717 and FR1359766, the applicants proposed methods for
optimising the specific consumption of the turboshaft engines of a helicopter
by the possibility of putting at least one turboshaft engine into a stable flight
mode, referred to as continuous flight mode, and at least one turboshaft
engine into a particular standby mode that it can leave in emergencies or in a
normal manner, according to need. A transition out of the standby mode is
referred to as 'normal' when a change in the flight situation requires the
turboshaft engine in standby to be activated, for example when the helicopter
is going to transition from a cruise flight situation to a landing phase. A normal
transition out of standby mode of this kind occurs over a period of between 1 0
seconds and 1 minute. A transition out of the standby mode is referred to as
an 'emergency' when a there is a power failure or a power deficit in the active
engine, or when the flight conditions suddenly become difficult. An emergency
transition out of standby mode of this kind occurs over a period of less than
10 seconds.
A turboshaft engine leaves a standby mode and transitions from an
economical flight phase to a conventional flight phase for example by means
of a pack for restarting the turboshaft engine, which pack is associated with a
device for storing energy, such as an electrochemical store like a lithium ion
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battery, an electrostatic store like a supercapacitor, or an electromechanical
store like a flywheel, which allows both the turboshaft engine to be provided
with the energy required for restarting and a nominal operation mode to be
reached.
Such a pack for restarting the turboshaft engine in standby has the
disadvantage of sUEistantially increasing the total weight of the turboshaft
engine. The benefit in terms of fuel consumption obtained by placing the
turboshaft engine in standby is thus partly lost by the excess weight brought
about by the restart device, the device for storing energy required for the
restart, in particular when each turboshaft engine is equipped with an
emergency restart device of this type.
The inventors have thus sought to solve problems which are incompatible a
priori, namely the possibility of placing the helicopter in the economical flight
phase, i.e. of placing at least one turboshaft engine in standby, without
increasing the weight of the overall propulsion system too much.
In other words, the inventors have sought to propose a new architecture of
the propulsion system of a twin-engine or three-engine helicopter.
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 an architecture of a propulsion system of a
multi-engine helicopter which allows a turboshaft engine to be placed in
standby and allows the quick restart thereof.
The invention also aims to provide, in at least one embodiment of the
invention, an architecture of a propulsion system which has a mass and a
volume which are acceptable for being installed in a helicopter.
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The invention also aims to provide, in at least one embodiment of the
invention, an architecture of a propulsion system which has a lower cost than
the architectures from the prior art that have the same performance.
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 that are
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, which is capable of operating in at
least one standby mode during a stable flight of the helicopter, the
other turboshaft engines operating alone during this stable flight,
at least one pack for quickly restarting a hybrid turboshaft engine in
order to bririg said engine out of said standby mode and to reach a
nominal operating mode ,
at least one auxiliary power unit that is connected to a restart pack
and is capable of providing this restart pack, on demand, with power
required for bringing said corresponding hybrid turboshaft engine out
of said standby mode.
Therefore, the architecture of the propulsion system of a multi-engine
helicopter according to the invention has at least one hybrid turboshaft
engine, the other turboshaft engines being non-hybrid and each hybrid
turboshaft engine being capable of operating in a standby mode. The
architecture of the invention is therefore asymmetrical because it has at least
one hybrid turboshaft engine and at least one non-hybrid turboshaft engine.
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
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emergency) or normal manner. A turboshaft engine can only be in standby
mode during a stable flight of the helicopter, i.e. when no turboshaft engine of
the helicopter has fail~d!. during a cruise flight situation when it is progressing
in normal conditions. Leaving the standby mode consists in changing the
turboshaft engine into a mode for accelerating the gas generator by means of
driving in a manner that is compatible with the leaving mode required by the
conditions (normal standby-leaving mode or rapid (also referred to as
emergency) standby-leaving mode).
Furthermore, the architecture provides at least one restart pack supplied with
current by an auxiliary power unit, thus making it possible to overcome the
drawbacks of the prior art linked to the use of a battery-like or supercapacitorlike
energy storage source.
An auxiliary power unit (referred to in the following by the abbreviation APU)
of this type ensures that a restart pack of a hybrid turboshaft engine has a
permanent electricity supply, regardless of the atmospheric conditions (in
particular regardless of the temperature), the supply also being constant over
time (no aging effect).
This APU can, for example, comprise a thermal engine (such as a connected
gas power turbine or a two-stroke or four-stroke petrol or diesel engine) and a
starter-generator capable of restarting the combustion of the unit and of
supplying the required electrical power to the electrotechnical pack.
An architecture according to the invention is particularly suitable for
helicopters that already have an auxiliary power unit intended, for example,
for supplying non-propulsive, electrical, mechanical, hydraulic and/or
pneumatic power during all the flight phases in which the turboshaft engines
are not able to do so: on the ground, in the transition phases (take off,
landing), in the approach phases, etc. The use of this APU together with a
restart pack of an architecture according to the invention thus makes it
possible to dispense with an energy storage system for assisting a turboshaft
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engine in standby.
A restart pack of an architecture according to the invention is, for example, an
electrotechnical, pyrotechnic, pneumatic or hydraulic pack. Throughout the
rest of the text, reference will be made in particular to an electrotechnical
restart pack, with the understanding that the invention also covers an
architecture provided with a pyrotechnic, pneumatic or hydraulic restart pack.
Advantageously, an auxiliary power unit has an economical standby function,
with the chamber ignited and at low speed, and a function of quickly leaving
this standby mode in order to quickly provide its maximum power to the
electrotechnical pack to restart the hybrid turboshaft engine. The electrical
power is made available within a time period that is compatible with the flight
safety requirements, in particular in the event of a turboshaft engine in
standby being restarted in an emergency, or in the event of a non-hybrid
turboshaft engine being lost.
Advantageously, an architecture according to the invention comprises:
just one hybrid turboshaft engine capable of operating in at least one
standby mode during a stable flight of the helicopter, the other
turboshaft engines operating alone during this stable flight,
just one pack for quickly restarting said turboshaft engine to bring said
engine out of said standby mode and to reach a nominal operating
mode,
just one auxiliary power unit that is connected to said restart pack and
capable of providing said restart pack, on demand, with power
required for bringing said hybrid turboshaft engine out of said standby
mode.
An architecture that has just one hybrid turboshaft engine, just one restart
pack and just one auxiliary power unit connected to said restart pack means
that the number of components can be reduced. Furthermore, this limits the
total weight of the propulsion system. An architecture of this kind thus
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combines the adviiril"ages of an SC optimisation, owing to the possibility of
placing a turboshaft engine in standby, with reduced size and weight.
Advantageously and according to this variant, the architecture comprises: a
low DC voltage onboard network (referred to in the following by the
abbreviation OBN) for supplying power to helicopter equipment, at least one
source of electric power for said onboard network, and said auxiliary power
unit is connected to said onboard network by means of an AC/DC converter.
Said auxiliary power unit is connected to the electrotechnical pack by means
of an AC/DC converter. A converter of this type enables the use of both an
auxiliary power unit that supplies an AC voltage, and a DC electrotechnical
pack. According to another variant, the auxiliary power unit directly generates
a direct current.
The power unit not only makes it possible to provide the energy required for
restarting the hybrid turboshaft engine, but also to supply power to the
onboard network. The architecture therefore has redundancy in the electrical
power generation (by means of an electrical power source and the auxiliary
power unit) for supplying power to the OBN, meaning that a possible failure of
the first power source for the OBN is compensated for by the second power
source.
According to this variant and advantageously, the architecture comprises a
contact switch that is arranged between said auxiliary unit and said onboard
network and controlled such as to decouple said auxiliary power unit from
said onboard network when said hybrid turboshaft engine is restarted in an
emergency.
According to this variant, the auxiliary power unit can supply all of its power to
the hybrid turboshaft engine in order to restart it. Indeed, the contact switch
makes it possible to decouple the auxiliary unit from the onboard network
such that all the power from the auxiliary unit is intended for the turboshaft
"g 8
engine. The OBN supply is maintained by the power source, which thus
compensates for the auxiliary unit being unavailable.
The contact switch can be arranged upstream or downstream of the AC/DC
converter.
Advantageously and according to this variant, the source of electrical power
for said onboard network is selected from the group comprising:
at least one current generator that is arranged between said power
gearbox and said onboard network and is associated with an AC/DC
converter
a starter-generator that is arranged between a non-hybrid turboshaft
engine and said onboard network.
According to another variant, the auxiliary power unit can be placed into
standby during the cruise flight phases and so can no longer carry out the
generation function. In this case, the architecture has to comprise two
electrical power sources for the OBN. For example, a first electrical power
source is a generator that is arranged between the PTG and the OBN and
associated with an AC-DC converter, and a second electrical power source is
a starter-generator that is arranged between a non-hybrid turboshaft engine
and the OBN.
Advantageously and according to this variant, said generator is capable of
providing an AC voltage of 115 volts and said associated converter is capable
of providing a DC voltage of 28 volts.
Advantageously and according to the invention said quick restart pack
comprises: an electrical machine capable of restarting said hybrid turboshaft
engine when leaving standby in normal conditions, and a device for leaving
standby in an emergency that is capable of restarting said hybrid turboshaft
engine when leaving standby in emergency conditions.
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A turboshaft engine comprises, as is known, a gas generator and a free
turbine that is supplied with the gases from the gas generator. The gas
generator comprises a shaft and a combustion chamber that is supplied with
fuel.
A mode for leaving standby in an emergency is a mode in which the
combustion chamber is ignited and the shaft of the gas generator is brought
to a speed of between 80 and 105 % within a period of less than 10 seconds
following an order to leave standby.
A mode for leaving standby normally is a mode in which the combustion
chamber is ignited and the shaft of the gas generator is brought to a speed of
between 80 and 1 05 % within a period of between 1 0 seconds and 1 minute
following an order to leave standby mode.
The electrical machine can be an electrical machine operating using
alternating or direct current.
Advantageously and according to the invention, said device for leaving
standby in an emergency is an electrotechnical, pyrotechnic, pneumatic or
hydraulic device.
Advantageously and according to the invention, said auxiliary power unit is
connected to the restart pack by means of an AC/DC converter.
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 multiengine
helicopter, and to a helicopter equipped with a propulsion system
having an architecture of this kind, characterised in combination by all or
some of the features mentioned above or in the following.
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5. List of drawings
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 Fig. 1, which is a schematic view of
an architecture of a propulsion system of a twin-engine helicopter according
to an embodiment of the invention.
6. Detailed description of an embodiment of the invention
Fig. 1 is a schematic view of an architecture of a propulsion system of a twinengine
helicopter according to an embodiment of the invention. This
architecture comprises two turboshaft engines 1, 2 that are connected to a
power transmission gearbox 3. Each turboshaft engine 1, 2 is controlled by its
own inspection-control device, which is not shown in the figure for reasons of
clarity.
As is known, each turboshaft engine further comprises a gas generator and a
free turbine that is rigidly connected to an output shaft rotated by the gas
generator. The output shaft of each free turbine is suitable for inducing the
movement of the power transmission gearbox 3 (referred to in the following
by the abbreviation PTG), which itself drives the rotor of the helicopter which
is equipped with blades having a variable pitch.
According to the invention, the turboshaft engine 1 is a hybrid turboshaft
engine that is capable of operating in at least one standby mode during a
stable flight of the helicopter.
This standby mode is preferably selected from the following operating modes:
a standby mode referred to as normal idling, in which the combustion
chamber is ignited and the shaft of the gas generator rotates at a
speed of between 60 and 80 % of the nominal speed,
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a standby mode referred to as normal super-idling mode, in which the
combustion chamber is ignited and the shaft of the gas generator
rotates at a speed of between 20 and pO % of the nominal speed,
a standby mode referred to as assisted super idling, in which the
combustion chamber is ignited and the shaft of the gas generator
rotates, with mechanical assistance, at a speed of between 20 and 60
% of the nominal speed,
a standby mode referred to as turning, in which the combustion
chamber is extinguished and the shaft of the gas generator rotates,
with mechanical assistance, at a speed of between 5 and 20 % of the
nominal speed,
a standby mode referred to as shutdown, in which the combustion
chamber is extinguished and the shaft of the gas generator is at a
complete stop.
The architecture further comprises an electrotechnical pack 5, 6 for quickly
restarting the hybrid turboshaft engine 1 in order to bring it out of the standby
mode and to reach a nominal operating mode.
This restart pack 5, 6 is supplied with electricity by an auxiliary power unit 11
(referred to in the following by the abbreviation APU) by means of an AC/DC
converter 1 0. This auxiliary engine provides non-propulsive power to the
electrotechnical pack 5, 6 on demand to allow said pack to bring the hybrid
turboshaft engine 1 out of its standby mode.
This APU 11 can, for example, comprise a thermal engine (such as a
connected gas power turbine or a two-stroke or four-stroke petrol or diesel
engine) and a starter-generator capable of restarting the combustion of the
APU and of providing the necessary electrical power to the electrotechnical
pack. Preferably, the APU provides an AC voltage of 115 volts.
The AC/DC converter 10 enables the high AC voltage of 115 volts supplied by
the APU 11 to be converted into high DC voltage required for restarting the
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turboshaft engine 1. According to other embodiments, the APU directly
provides a DC voltage, and so there is no need for a voltage converter 10.
The architecture further comprises a low-voltage onboard network 7,
preferably of 28 volts (referred to in the following by the abbreviation OBN),
for supplying power to helicopter equipment during flight.
This OBN 7 is supplied with current by the APU 11 by means of a high
AC/Iow DC voltage converter, and by a starter-generator 4 that is connected
to the turboshaft engine 2 and directly provides low DC voltage. The OBN 7
further supplies power to a battery 8 for storing 28 volt energy. According to
another variant (not shown in the figure), the OBN 7 is supplied with power by
a generator installed on the PTG 3.
To prevent the restart of the turboshaft engine 1 being disrupted, a contact
switch 12 is arranged between the OBN 7 and the APU 11 to decouple the
OBN 7 and the APU 11 when all the electrical power in the APU 11 is
required to bring the turboshaft engine 1 out of the standby mode.
Preferably, the APU provides an AC voltage of 115 volts and the OBN 7 is a
28 DC volt network. This APU 11 can also directly supply power to specific
equipment 9 of the helicopter.
According to the embodiment in Fig. 1, the quick restart pack comprises an
electrical machine 5 that is capable of restarting the hybrid turboshaft engine
1 when leaving standby in normal conditions, and a device 6 for leaving
standby in an emergency that is capable of restarting the turboshaft engine 1
when leaving standby in emergency conditions.
This device 6 for leaving standby in an emergency is, for example, an
electrical, pyrotechnic, pneumatic or hydraulic device.
According to another embodiment of the invention (not shown in the figure),
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the APU is designed to provide a DC voltage and the electrical machine is
designed to operate using alternating current. In this case, an inverter is
arranged between the APU and the electrical machine to rectify the current
and to power the electrical machine by means of the energy produced by the
APU.
The invention is not limited to the described embodiments only. In particular,
the architecture can comprise three turboshaft engines for the equipment of a
three-engine helicopter.

CLAIMS
1. Architecture of a propulsion system of a multi-engine helicopter,
comprising turboshaft engines (1, 2) that are connected to a power
transmission gearbox (3),
characterised in that it comprises:
at least one turboshaft engine among said turboshaft engines, referred
to as a hybrid turboshaft engine (1), which is capable of operating in at
least one standby mode during a stable flight of the helicopter, the
other turboshaft engines (2) operating alone during this stable flight,
at least one pack (5, 6) for quickly restarting a hybrid turboshaft engine
(1) in order bring said engine out of said standby mode and to reach a
nominal operating mode,
at least one auxiliary power unit ( 11) that is connected to a restart
pack (5, 6) and is capable of providing said restart pack (5, 6), on
demand, with power required for bringing said corresponding hybrid
turboshaft engine (1) out of said standby mode.
2. Architecture according to claim 1, characterised in that it comprises:
just one hybrid turbos haft engine (1) capable of operating in at least
one standby mode during a stable flight of the helicopter, the other turboshaft
engines (2) operating alone during this stable flight,
just one pack (5, 6) for quickly restarting said hybrid turboshaft engine
(1) in order to bring said engine out of said standby mode and to reach a
nominal operating mode,
just one auxiliary power unit (11) that is connected to said restart pack
(5, 6) and is capable of providing said restart pack (5, 6), on demand, with
power necessary for bringing said hybrid turboshaft engine (1) out of said
standby mode.
3. Architecture according to claim 2, characterised in that it comprises:
a low DC voltage onboard network (7) for supplying power to
helicopter equipment during flight,
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at least one source (4) of electrical power for said onboard network
(7),
and in that said auxiliary power unit (11) is connected to said onboard
network (7) by means of an AC/DC converter (17).
4. Architecture according to claim 3, characterised in that it comprises a
contact switch (12) that is arranged between said auxiliary unit (11) and said
onboard network (7) and is controlled such as to decouple said auxiliary
power unit (11) from said on board network (7) when said hybrid turboshaft
engine (1) is restarted in an emergency.
5. Architecture according to either claim 3 or claim 4, characterised in
that said electrical power source (4) of said on board network is selected from
the group comprising:
at least one current generator that is arranged between said power
transmission gearbox and said onboard network and is associated
with an AC-DC converter,
a starter-generator (4) that is arranged between a non-hybrid
turboshaft engine and said onboard network.
6. Architecture according to claim 5, characterised in that said generator
is capable of providing an AC voltage of 115 volts and in that said associated
converter is capable of providing a DC voltage of 28 volts.
7. Architecture according to any of claims 1 to 6, characterised in that at
least one quick restart pack (5, 6) comprises an electrical machine (5) that is
capable of restartill!;J ~!_least one hybrid turboshaft engine (1) when leaving
standby in normal conditions, and a device (6) for leaving standby in an
emergency that is capable of restarting said hybrid turboshaft engine ( 1)
when leaving standby in emergency conditions.
8. Architecture according to claim 7, characterised in that said device for
leaving standby in an emergency can be an electrotechnical, pyrotechnic,
pneumatic or hydraulic device.
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9. Architecture according to any of claims 1 to 8, characterised in that at
least one auxiliary power unit (11) is connected to a restart pack by means of
an AC/DC converter ( 1 0).
10. Helicopter comprising a propulsion system, characterised in that said
propulsion system has an architecture according to any of claims 1 to 9.