A RAPID ASSISTANCE DEVICE FOR A FREE TURBINE ENGINE OF AN
AIRCRAFT
Technical field
The invention lies in the field of free turbine
engines, of the kind commonly to be found on helicopters.
It should be recalled that a gas turbine engine (GT)
having a free turbine comprises a power turbine or free
turbine that, in a helicopter, drives the rotors of the
10 helicopter via an overrunning clutch, or "freewheel'', and
a main gearbox (MGB), and that the engine also comprises
15
a gas generator that is constituted mainly by a
compressor, a combustion chamber, and a high pressure
turbine.
Stepdown gearing or an accessory gearbox serves to
connect the shaft of the gas generator to an electrical
machine (abridged EM) constituted by a stator and a rotor
and capable of operating equally well as a motor
(starter) or as a generator. In motor mode, the
20 electrical machine is powered by an electrical energy
source and it develops driving torque so as to drive the
gas generator of the engine in rotation, in particular
for the purpose of starting it, thereby providing
assistance on starting. In generator mode, the
25 electrical machine is driven in rotation by the gas
generator so as to enable mechanical power to be taken
off and then converted into electrical power.
State of the art
30 For a twin-engined aircraft in cruising flight,
Documents FR 2 967 132 and FR 2 967 133 propose putting
one of the two engines in a standby mode so as to
desynchronize its free turbine from the main gearbox,
while increasing the power delivered by the other engine,
35 thereby enabling overall fuel consumption of the system
to be reduced.
2
The invention thus lies in particular in the context
of a helicopter having at least two engines, and of
reducing its fuel consumption while it is performing
cruising flight, i.e. during a stage of flight that is
5 characterized by relatively little power being required
from each engine, thus giving rise to specific
consumption (abridged SC) that is very high. To make
cruising flight economic, one of the engines is put on
standby, so that the other engine operates at high power,
10 thereby making it possible for the helicopter to benefit
from specific consumption that is much lower.
Several variants of this standby mode have been
proposed.
In a first variant, referred to as "super idle'', the
15 gas generator of the desynchronized gas turbine is
regulated at a slow idling speed.
In a second variant, referred to as "assisted super
idle", the gas generator of the gas turbine that is
desynchronized from the MGB is likewise regulated on a
20 low idling speed, and simultaneously assistance drive
torque is applied to the gas generator via the electrical
machine and the accessory gearbox.
In a third variant, the combustion chamber of the
engine is totally extinguished, and it is then proposed
25 to maintain the gas generator in rotation at a speed
suitable for facilitating reignition at the end of the
stage of cruising flight. The range of speeds that are
suitable may be referred to as a preferred ignition
window. This mode of operation, referred to as "turning''
30 mode, requires prolonged assistance to be given to the
gas generator.
In all three of those modes of operation, which are
likely to be maintained throughout the duration of
cruising flight, the amount of power transmitted to the
35 MGB by the engine on standby is generally zero, and it is
generally not possible to take power from its gas
generator.
3
In the three above-mentioned variants, it is
necessary to be able to reactivate the desynchronized
engine rapidly, in particular in an emergency situation,
e.g. in the event of another engine failing, if there are
5 three or more engines in all, - or in the event of the
other engine failing if there are two engines.
Specifically, that is the reason why the gas generator is
kept rotating at a speed for facilitating reignition in
the system where the combustion chamber is extinguished.
10 Maintaining the gas generator rotating in the
preferred ignition window ("turning" mode) and providing
prolonged assistance to the gas generator when it is
regulated to idle ("assisted super idle'' mode) both
require relatively low power, but end up requiring a
15 large amount of energy, since the advantage of the system
lies in using it throughout a long duration of flight.
Among other solutions, Documents FR 2 967 132 and
FR 2 967 133 propose using an electric starter powered by
a starter/generator connected to the gas generator of the
20 other engine, or to a generator driven directly or
indirectly by the free turbine of the other engine.
Emergency restarting from a low speed situation, or
from a combustion chamber extinguished situation requires
high power to be applied to the shaft of the gas
25 generator because of the large amount of inertia of its
rotating assemblies and because of the opposing torque
from the compressor of the engine. That power needs to
be delivered over a duration that is brief, of the order
of a few seconds, in order to enable the engine to be
30 started rapidly.
In Document FR 2 967 133, among other solutions, it
is suggested that electrical energy, in particular from a
supercapacitor, can be used to provide a burst of
assistance to the gas generator.
35 Document EP 2 581 586 also proposes using two
supercapacitors (which are members for storing
electricity), each of which is charged by a respective
5
4
electricity generator driven by the gas generator of one
of the two engines, and each of which can be used briefly
to start the other engine when it is in a shut-down
state.
In this context, a particular object of the present
invention is to provide technical means that are
practical for use on board an aircraft having at least
two engines to provide the ''rapid reactivation'' function
when starting from an economic mode of operation of the
10 turbine, by making use, instead of the conventional
15
electrical starter, of an electrotechnical system that is
powered by the on-board network or by a specific
electrical energy power supply network and that makes the
following various modes of operation possible:
starting a gas turbine on the ground;
economic mode;
reactivating in flight a turbine that was
previously in economic mode; and
· rapidly reactivating in flight a turbine that was
20 previously in economic mode.
Another object of the present invention is to make
it possible on a single-engined aircraft to provide
effectively a function of rapidly reactivating an engine
in the event of an unwanted shut-down mode occurring, by
25 making use, instead of the conventional electrical
starter, of an electrotechnical system that is powered by
the on-board network or by a specific electrical energy
power supply network.
The invention lies in particular in the context of
30 French patent application No. 14/00753 filed on March 27,
2014, and relates more particularly to providing an
electrical system architecture providing means for
performing the rapid reactivation mode on the gas turbine
in flight in improved manner.
35 The architectures of electrical systems that have
been proposed in the past for hybridizing a gas turbine
always make use of a storage element of the "secondary"
5
kind, connected to the high voltage direct current (HVDC)
bus and having the function of storing the amount of
electrical energy that is necessary for the rapid
reactivation mode. The term ''secondary" means that such
5 storage elements are rechargeable. Most of them require
a battery management system (BMS).
Existing solutions thus present several drawbacks,
with the main drawback being as follows:
1/ Independently of the secondary storage technology
10 (Li-ion battery, NiMH, supercapacitor, hybrid capacitors,
... ), a BMS comprises equipment that is said to be
"complex" since it includes power switching devices and
makes use of electronics for monitoring the state of
charge, the operating parameters, and the state of health
15 of the storage member, and is therefore governed by
avionics certification standards, such as the D0-178 and
D0-254 standards of the radio technical commission for
aeronautics (RTCA) .
A BMS increases the weight of the system and its
20 probability of failure.
2/ Known secondary couples have a non-negligible
self-discharge rate, which makes it essential for the
battery to be recharged periodically and thus requires
the presence of a charger, either on board the aircraft,
25 or in ground infrastructures.
3/ Secondary couples degrade little by little even
when they are used rarely (calendar aging). This means
that they must be tested and replaced periodically.
4/ Such secondary storage members also have the
30 drawback of being active at all times, i.e. the system
can provide electrical energy at any moment in unwanted
circumstances such as short circuits, or they can become
discharged prematurely as a result of a leakage current
phenomenon.
35 5/ Such secondary storage members have another
general drawback of poorly withstanding severe
environments, such as high and low temperatures, and also
6
poorly withstanding mechanical stress (vibration,
impacts). In order to accommodate such environmental
constraints, secondary members need to be dimensioned
accordingly, which leads to a regrettable increase in the
5 weight of a system for mounting on board an aircraft and
more particularly on board a helicopter.
6/ Another drawback of certain technologies for
secondary storage members is the danger such elements
present in the event of thermal runaway, where thermal
10 runaway can be caused in particular by short circuits
that are external or internal to the secondary storage
members, by overloading, or by other causes, in
particular environmental causes.
7/ Coupling a secondary storage unit to the on-board
15 network is problematic given the interactions between the
network having a voltage that may vary at any time, and a
secondary battery having a voltage that is a function of
its state of charge. It is therefore necessary to take
precautions (which make the system more complex) in order
20 to avoid any electrical risk, or indeed any risk of the
storage unit not being operationally available.
Summary of the invention
In order to remedy the above-mentioned drawbacks,
25 the invention proposes an aircraft including at least one
first free turbine engine having a gas generator and
associated with an electrical machine capable of
operating both as a starter and as a generator, the first
engine being capable of being put into a standby mode or
30 into an unwanted shut-down mode, the electrical machine
being connected to a specific electrical energy power
supply network, such as an on-board network, the aircraft
further including a rapid assistance device with at least
one electrical energy storage member adapted to be
35 electrically connected to said electrical machine
associated with said first engine in order to provide a
burst of assistance to the gas generator of that engine,
7
the aircraft being characterized in that said electrical
energy storage member constitutes a non-rechargeable
"primary" energy storage member suitable for use once
only after activation, to the exclusion of any
5 "secondary" energy storage member comprising a storage
battery, a supercapacitor, or a hybrid capacitor
configured to be rechargeable and to be activated
permanently, and in that the rapid assistance device
includes means for activating the electrical energy
10 storage member and coupling means for coupling the
electrical energy storage member with an electrical power
supply system of said electrical machine.
In a first possible embodiment, the electrical
energy storage member comprises a ready-for-use device
15 with low self-discharge incorporating an anode and a
cathode in contact with an electrolyte.
In a second possible embodiment, the electrical
energy storage member comprises a device that is inert
prior to activation, incorporating an anode, a cathode,
20 and an electrolyte that does not wet the anode and the
cathode.
Under such circumstances, the electrical energy
storage member may comprise a battery with separate
electrolyte, having a separate tank for storing the
25 electrolyte and means for releasing the electrolyte from
the separate tank in order to enable it to come into
contact with the anode and the cathode on activating the
electrical energy storage member.
As an alternative, the electrical energy storage
30 member may comprise a thermopile adapted to keep the
electrolyte solid at ambient temperature during storage
and to liquefy the electrolyte by heating on activation
of the electrical energy storage member.
The means for activating the electrical energy
35 storage member may comprise pyrotechnic activation means.
8
In another possible embodiment, the means for
activating the electrical energy storage member comprise
electrical activation means.
In a particular embodiment, the electrical energy
5 storage member is connected in parallel with said
specific electrical power supply network, which may be a
direct current (DC) electrical energy power supply
network. A non-return diode may be interposed, where
necessary, between the electrical energy storage member
10 and the DC on-board network. The DC on-board network is
itself normally powered by the alternating current (AC)
on-board electrical energy power supply network via a
rectifier member or an alternating current to direct
current (AC/DC) converter.
15 In another particular embodiment, the electrical
energy storage member is connected in series with the
rectifier member or the AC/DC converter that produces the
voltage of the DC network from the specific electrical
energy power supply network such as an AC on-board
20 network, and in parallel with a diode.
The diodes may be semiconductors or controlled
switches of electromechanical type or of static type.
In general manner, the electrical energy storage
member may comprise one or more elements or sets of
25 elements connected in series, in parallel, or in seriesparallel.
In a particular embodiment, the invention applies to
an aircraft including a plurality of free turbine
engines, each having a gas generator and each associated
30 with an electrical machine capable of operating both as a
starter and as a generator, at least one of the plurality
of engines being capable of being put in a standby mode,
while at least one other one of the plurality of engines
is in a mode of normal operation.
35 Under such circumstances, in a particular
embodiment, the rapid assistance device of the invention
has a single electrical energy storage member adapted to
9
be electrically connected via a switch device to the
electrical machine that is associated with that one of
the plurality of engines that requires a burst of
assistance to the gas generator of the engine previously
5 put on standby.
10
The invention provides an aircraft having at least
one free turbine engine and including an assistance
device as mentioned, which aircraft may in particular be
a helicopter.
Brief description of the figures
Other characteristics and advantages of the
invention appear from the detailed description of
particular embodiments of the invention given with
15 reference to the accompanying drawings, in which:
20
· Figure 1 is a diagram of a rapid assistance device
in a first embodiment of the invention, with a primary
energy member connected in parallel with an on-board
network of an aircraft;
· Figure 2 is a diagram of a rapid assistance device
in a second embodiment of the invention, with a primary
energy member connected in series with an on-board
network of an aircraft;
· Figure 3 is a diagram showing a system of the
25 invention integrated in the propulsion and electrical
systems of an aircraft;
· Figure 4 is a diagram of a rapid assistance device
in a third embodiment of the invention, with a single
primary energy member connected in parallel with an on-
30 board network of an aircraft; and
35
· Figure 5 is a diagram of a rapid assistance device
in a fourth embodiment of the invention, with a single
primary energy member connected in series with an onboard
network of an aircraft.
Detail.ed description
With reference to Figure 3, the general electrical
10
architecture of an example system to which the invention
is applicable is as follows. Electricity is generated on
an aircraft by at least two alternators (abridged ALT1
and ALT2) 18, 19 that are driven by a main gearbox (MGB)
5 20, and typically constituted by "3-stage'' type machines
delivering AC at 115 volts (V) and at a frequency of
400 hertz (Hz), it being possible to envisage other
rotary machines.
This architecture is advantageous in the context of
10 economic cruising flight on one engine, since it
guarantees functional and organic independence between
generating electricity and operating the turboshaft
engines 11, 21, thus making it possible to retain a
sufficient level of availability and of redundancy for
15 generating electricity when in economic cruising flight,
while one of the two engines 11, 21 is kept on standby,
which is not compatible with taking any power from the
gas generator of that engine operating on standby.
In addition, this architecture is less penalizing
20 for the operation of the engines 11, 21 than taking power
from the gas generators of the engines 11, 21, in
particular in terms of impact on their acceleration and
on their specific consumption performance, insofar as the
electrical power consumed by the on-board network 17 of
25 the aircraft is taken mechanically from the free turbine
and not from the gas generator.
The alternators 18, 19 (ALT1 and ALT2) power the
electricity network 17 of the aircraft. Thus, the onboard
network 17 is powered by one or more alternators
30 18, 19 that are driven directly or indirectly via at
least one of the engines 11, 21. When one of the engines
11, 21 is shut down, it is necessarily the other engine
that powers the on-board network 17 in prolonged manner.
Nevertheless, there may be other sources of energy
35 available for powering the network 17 and serving in
particular for powering all of the electrical system 100
associated with the engines 11, 21, which other sources
11
may be constituted by an on-board auxiliary power unit 53
(abridged APU), by one of more storage batteries 51, or
indeed, when on the ground, by a ground power unit 52.
The main gearbox 20 (MGB) is driven by the engines
5 11, 21. In this embodiment they are free turbine
turboshaft engines. Each of them comprises a gas
generator and a power turbine (free turbine) driving the
MGB 20 via an overrunning clutch, or ''freewheel".
Each engine 11, 21 is associated with a respective
10 rotary machine 12, 22 that is suitable for operating both
as a starter and as a generator, and that can be powered
from the on-board network 17 of the aircraft via an
electrical control system 50 that includes the device of
the invention.
15 First and second embodiments of the invention are
described with reference to Figures 1 and 2. In addition
to the engines 11 and 21 and the AC on-board network 17,
Figures 1 and 2 show embodiments of the electrical
assembly 100 of Figure 3 constituting an electrical
20 starter system that can be applied to the engine 11 or to
the engine 21.
In the embodiment of Figure 1, it can be seen that
the engine 11 has an electrical starter system comprising
an alternating current to direct current converter 16,
25 also referred to as an AC/DC converter, which is powered
from the AC on-board network 17, and a direct current to
alternating current converter 13, also referred to as a
DC/AC converter, connected to the AC/DC converter 16 and
serving to power the electrical machine 12, also referred
30 to as the EM. The AC on-board network 17 and the AC/DC
converter 16 define a DC electrical power supply network
(output voltage Vee), however other DC network
embodiments are possible.
In accordance with the invention, a diode 15 may be
35 connected between the DC/AC converter 13 and the AC/DC
converter 16. This diode is useful when the DC network
is used by equipment other than the EM 12. It serves to
12
reserve for the EM 12 all of the power produced by the
storage unit 14 (described below) when the voltage
produced by the storage unit 14 is greater than the
voltage Vee of the DC network. It enables the DC network
5 to contribute to powering the EM 12 when the voltage
produced by the storage unit 14 is less than the voltage
Vee of the DC network. The anode of the diode 15 is
connected to the positive pole of the output from the
AC/DC converter 16, and the cathode of the diode 15 is
10 connected to the positive pole of the DC/AC converter 13.
Naturally, and in equivalent manner, the cathode of the
diode 15 could be connected to the negative pole of the
output from the AC/DC converter 16, with the anode of the
diode 15 being connected to the negative pole of the
15 DC/AC converter 13. The diode 15 may be a semiconductor,
or a controlled switch that may be static or
electromechanical.
Furthermore, a primary storage unit 14, i.e. a nonrechargeable
electrical energy storage member suitable
20 for single use, is connected in parallel with the
converters 13 and 16, the positive pole of the primary
storage unit 14 being connected to the cathode of the
diode 15 and the negative pole of the primary storage
unit being connected to the negative poles of the
25 converters 13 and 16.
The primary storage unit 14 is optimized for power
discharges that are short and intense. By way of
example, it may be a ready-for-use device with low selfdischarge
that incorporates an anode and a cathode in
30 contact with an electrolyte.
Nevertheless, the primary storage unit 14 could be a
device that is inert prior to being activated,
incorporating an anode, a cathode, and an electrolyte
that does not wet the anode and the cathode.
35 Under such circumstances, the electrical energy
storage member 14 may comprise a battery with electrolyte
that is separate, the battery having a separate tank for
5
13
storing the electrolyte together with means for releasing
the electrolyte from the separate tank so as to enable it
to come into contact with the anode and the cathode when
the electrical energy storage member 14 is activated.
Alternatively, for a device that is inert prior to
being activated, the electrical energy storage member 14
may comprise a thermopile adapted to keep an electrolyte
solid at ambient temperature during storage and to
liquefy the electrolyte by heating when the electrical
10 energy storage member 14 is activated.
The primary electrical storage unit 14 is activated
when the engine 11 needs to be restarted in an emergency.
By way of example, the means for activating the
electrical energy storage member 14 may comprise
15 pyrotechnic activation means, or indeed mechanical
activation means, or indeed electrical activation means.
In the embodiment of Figure 1, the electrical energy
storage member 14 is connected in parallel with the onboard
DC electrical power supply network Vee, but because
20 a diode 15 is interposed between the electrical energy
storage member 14 and the AC/DC converter 16 that is
powered by the AC on-board network 17, when the
electrical energy storage member 14 is activated by
activation means (not shown in the drawings) in order to
25 deliver the energy needed for rapidly reactivating the
engine 11 that was previously on standby, the voltage
across the terminals of the storage member 14 may be
greater than the voltage level Vee of the DC network as
delivered by the on-board network 17 associated with the
30 AC/DC converter 16. The diode 15 then has a negative
potential difference between its anode and its cathode
and is in a non-conductive state. The electrical energy
needed for rapidly reactivating the gas turbine of the
engine 11 is thus delivered entirely by the primary
35 energy storage unit 14, which presents the advantages of
delivering all of the power supplied by the storage unit
14
14 to the EM 12, without raising the voltage Vee of the
DC on-board network of the aircraft.
When the voltage delivered by the storage unit 14
loaded by the DC/AC converter 13 and the EM 12 is less
5 than the voltage Vee of the DC network, the diode 15
conducts, thereby enabling the DC network to contribute
to powering the EM 12.
Finally, if it is desired that the DC network does
not participate in powering the EM 12 when the voltage
10 from the storage unit 14 is less than that of the DC
network, and given that the diode 15 may be a controlled
switch, as mentioned above, it is possible to control the
switch 15 so that it does not conduct under such
circumstances.
15 Figure 1 shows elements 23 to 26 co-operating with
the second engine 21 and the second electrical machine
22, which elements correspond respectively to the
elements 13 to 16 co-operating with the first engine 11
and with the first electrical machine 12. The elements
20 23 to 26 are not described again. The elements 23 to 26
perform roles analogous to those of the above-described
elements 13 to 16, when it is the engine 11 that is
operating at a high power rating while the engine 21 is
on standby and might need to be reactivated rapidly.
25 Since it is never necessary to restart both engines
11 and 12 at the same time, it is possible to have only
one on-board storage unit 14 for restarting one or the
other of the two engines 11 and 21. An electrical or
electromechanical switch member 38, 48 connects the
30 single storage unit 14 either to the DC/AC converter 13
(as shown in Figure 4 with the switch 38 in the closed
position and the switch 48 in the open position), or else
to the DC/AC converter 23, depending on requirements.
As shown in Figure 4, it is possible to use not only
35 a single storage unit 14, but also a single diode 15 and
a single AC/DC converter 16, providing switch members 38,
48 are available so that the storage unit 14 sends its
15
energy to the EM 12 or to the EM 22. The embodiment of
Figure 4 thus differs from the embodiment of Figure 1 by
omitting the elements 24 to 26. Furthermore, the
switching function is very simple to implement using
5 contactors 38 and 48, i.e. simple on/off switches for the
DC/AC converters 13 and 23.
In a variant, the DC/AC converter 23 of Figure 4
could also be omitted. Under such circumstances, it is
possible to omit the on/off switches 38 and 48, with
10 on/off switches being arranged not at the DC inputs of
the DC/AC converters 13 and 23, but at the interface
between the EMs 12 and 22 and the AC output from the
DC/AC converter 13.
Thus, the systems of elements 13 to 16 and 23 to 26
15 can be implemented in full or in part by using single
elements, the switching taking place where the systems
duplicate each other.
It is also possible to make provision for only one
of the engines, e.g. the engine 11, to be suitable for
20 being put on standby, while the other engine 21 always
operates at high power, in which case the elements 24 and
25 could be omitted without a switching function being
necessary, since no rapid reactivation needs to be
performed for the second engine 21.
25 Figure 2 shows another embodiment that is analogous
to the embodiment of Figure 1 and includes similar
elements that are given the same reference numbers and
are not described again, but in which the respective
primary storage units 114 and 124 are associated with
30 respective diodes 115 and 125.
Thus, in Figure 2, in the second embodiment of the
invention, there can be seen a primary storage unit 114,
i.e. a non-rechargeable electrical energy storage member
suitable for single use, that is connected in parallel
35 with a diode 115 between the converters 13 and 16, the
negative pole of the primary storage unit 114 being
connected to the anode of the diode 115 and to the
16
positive pole of the AC/DC converter 16, and the positive
pole of the primary storage unit 114 being connected to
the cathode of the diode 115 and to the positive pole of
the DC/AC converter 13.
5 When the primary storage unit 114 is not in
operation, the EM 12 can be powered by the DC on-board
network via the diode 115. If the engine 11 that was
previously on standby needs to be rapidly reactivated,
the diode 115 becomes non-conductive and the primary
10 storage unit 114 is connected in series with the
converters 13 and 16.
Thus, when the primary energy storage unit is
activated, it is in series switch the on-board network 17
associated with the AC/DC converter 16. The electrical
15 energy needed for rapidly reactivating the gas turbine of
the engine 11 is delivered by the primary energy storage
unit 114 and by the on-board network 17, which, in
comparison with the solution of the embodiment shown in
Figure 1, enables the energy storage unit 114 to be
20 underdimensioned in terms of the power and the energy it
is to deliver. Nevertheless, the DC/AC converter 13 then
needs to be dimensioned so as to accommodate the
resulting voltage and be capable of passing all of the
electrical power needed for rapid reactivation.
25 The solution of the embodiment in Figure 2 makes it
possible to optimize the power supply voltage during
rapid reactivation, which voltage is the sum of the
voltage delivered by the primary storage unit 114 plus
the voltage Vee output from the rectifier 16, thereby
30 making it possible to minimize the current flowing in the
overall electrical circuit. The storage unit 114 may be
dimensioned so as to deliver a voltage that is lower than
the voltage level generated in the Figure 1 solution,
thereby presenting the advantage of reducing the weight
35 and the bulk of this member.
Compared with the solution of the embodiment of
Figure 1, the solution of the embodiment of Figure 2 is
17
not independent of the on-board network 17, such that in
certain applications it may be necessary to add filter
elements upstream from the converter 16 in order to
comply with requirements for network stability.
5 In the embodiment of Figure 2, the elements 23, 124,
125, and 26 associated with the second engine 21 and with
the second electrical machine 22 perform the same roles
respectively as the elements 13, 114, 115, and 16
associated with the first engine 11 and with the first
10 electrical machine 12, but are involved when it is the
second engine 21 that is put on standby and might need to
be reactivated rapidly, while the first engine 11 is
operating at high power.
As in the first embodiment, it is nevertheless
15 possible to switch a single storage unit 114 to the
engine 11 or to the engine 21, or else for example to
allocate the role of being in standby mode to the first
engine 11 only, in which case it is possible to omit the
elements 124 and 125.
20 Figure 5 shows a particular embodiment in which a
single storage unit 114, a single diode 115, and a single
AC/DC converter 16 are used. As in Figure 4, it is then
possible to use two on/off switches 38 and 48 or merely
to apply on/off control to the DC/AC converters 13 and
25 23, or to use a changeover member 39 (shown in Figure 5),
which may be a simple switch, for selecting between
having the single storage unit 114 in series with the
DC/AC converter 13 (position shown in Figure 5) or in
series with the DC/AC converter 23. In a variant, as in
30 the embodiment of Figure 4, it is possible to omit the
DC/AC converter 23 and use a single DC/AC converter 13.
Under such circumstances, switching should be performed
not at the DC input of the DC/AC converter 13, but at its
AC output.
35 The nature of the storage member 24, 114, or 124 can
be entirely analogous to that described above with
respect to the storage member 14.
18
In the present invention, the storage member 14 or
114, or 24 or 124 as the case may be, that is integrated
in the electrical system of an engine that might be put
on standby, i.e. the engine 11 or the engine 21 as the
5 case may be, is necessary in order to enable the
corresponding gas turbine that is initially in standby
mode to be reactivated rapidly, e.g. because of a problem
with the gas turbine that was operating previously. The
above-described situation is assumed to be extremely
10 rare, and it necessarily requires a maintenance operation
to be performed subsequently on the gas turbine. It
therefore appears that there is no major drawback in the
storage member 14 or 114, or 24 or 124 as the case may
be, being a storage unit that can be used once only and
15 that needs to be replaced when performing maintenance on
the engine.
In this concept where the storage member 14 or 114,
or 24 or 124 as the case may be, is a one-shot member, it
becomes possible to use so-called "primary" storage
20 technology, i.e. the storage units are not rechargeable.
As mentioned above, primary couples come in two
families:
1/ Family of primary couples that are ready for use
25 In this situation, the electrolyte wets the anode
and the cathode.
Various high-performance primary couples are in
existence that present very low self-discharge, so they
do not degrade over time, and thus do not require
30 periodic recharging, thereby making it possible to avoid
using a battery management system (EMS) which constitutes
equipment that is complex and also increases both the
weight of the system and its probability of failing.
By way of example, mention may be made of the
35 following couples Li-S02 , Li-Mn02 , LiSOCl2 , Zn-Mn02 (saline
or alkaline), Zn-Ag20, this list not being exhaustive.
19
2/ Family of inert primary couples
Their electrolyte does not wet the anode and the
cathode. This family comprises two sub-families:
2.1/ A battery with a separate electrolyte: the
5 electrolyte is taken from an auxiliary tank, and is
released on activation.
10
By way of example, mention may be made of the
silver-zinc (Zn-Ag20) couple, this list not being
exhaustive.
2.2/ Thermopile: the electrolyte is solid at ambient
temperature and is heated and thus liquefied very quickly
on activation.
By way of example, mention may be made of the
Ca/CaCr04 and Li/FeS2 couples, this list not being
15 exhaustive.
These couples have the advantage of being
electrically and chemically inert so long as they are not
activated.
They provide a solution to all of the prior art
20 drawbacks that make use of electrical energy storage
members of the so-called "secondary" type.
25
a/ They do not require a BMS.
b/ No self-discharge takes place. There is no need
to charge them.
c/ No degradation takes place over time and they can
be guaranteed for a period of 15 or 20 years, for
example.
d/ There is no electrical danger nor any risk of
unwanted discharge, since the energy storage members 14,
30 114, 24, 124 are electrically inert.
e/ Since the energy storage members 14, 114, 24, 124
are chemically inert, they withstand severe environmental
conditions very well.
f/ There ip no risk of thermal runaway in the inert
35 state.
g/ When the energy storage members 14, 114, 24, 124
are in an inactive state, they have the property whereby
20
the insulation resistance between the + and - polarities
of the storage member is very high, thus enabling such a
member to be installed in an electrical architecture
without taking prior precautions, and an electrically
5 inert battery can thus be coupled to the on-board network
17 very simply by means of a parallel connection (the
storage unit 14 is in an insulating state) or a series
connection (the storage unit accommodates the zero
voltage state).
10 Even though the present description states that the
storage unit 14 or 114, 24, or 124 is single in terms of
a functional entity, it should be observed that it need
not be constituted by a single member, but could in fact
comprise one or more couples or sets of couples connected
15 in parallel, or in series, or in series-parallel.
Furthermore, the description above relates to two
engines 11 and 21, however the invention applies in the
same manner to a smaller or greater number of engines
that can be used on a single aircraft, with one or more
20 devices of the invention, or with a device of the
invention having switching, being applied to one or more
of the engines.
When a single-engined aircraft has a single engine
11, corresponding to the situation of the embodiments of
25 Figures 1 and 2 in which there exists only the upper
system of elements co-operating with the engine 11, the
storage unit 14 or 114 serves to provide rapid assistance
in order to deliver a burst of rapid assistance to the
gas generator of the engine 11 in the event of the engine
30 11 being shut down in unwanted manner while in flight.
In general manner, the invention is not limited to
the embodiments described, but extends to any variant
within the ambit of the scope of the accompanying claims.

CLAIMS
1. An aircraft including at least one first free turbine
engine (11) having a gas generator and associated with an
electrical machine (12) capable of operating both as a
5 starter and as a generator, the first engine (11) being
capable of being put into a standby mode or into an
unwanted shut-down mode, the electrical machine being
connected to a specific electrical energy power supply
network (17), such as an on-board network, the aircraft
10 further including a rapid assistance device with at least
one electrical energy storage member (14; 114) adapted to
be electrically connected to said electrical machine (12)
associated with said first engine (11) in order to
provide a burst of assistance to the gas generator of
15 that engine (11), the aircraft being characterized in
that said electrical energy storage member (14; 114)
constitutes a non-rechargeable "primary'' energy storage
member suitable for use once only after activation, to
the exclusion of any "secondary" energy storage member
20 comprising a storage battery, a supercapacitor, or a
hybrid capacitor configured to be rechargeable and to be
activated permanently, and in that the rapid assistance
device includes means for activating the electrical
energy storage member (14; 114) and coupling means (15;
25 115) for coupling the electrical energy storage member
with an electrical power supply system (13, 16) of said
electrical machine (12).
2. An aircraft according to claim 1, wherein the
30 electrical energy storage member (14; 114) comprises a
ready-for-use device with low self-discharge
incorporating an anode and a cathode in contact with an
electrolyte.
35 3. An aircraft according to claim 1, wherein the
electrical energy storage member (14; 114) comprises a
device that is inert prior to activation, incorporating
22
an anode, a cathode, and an electrolyte that does not wet
the anode and the cathode.
4. An aircraft according to claim 3, wherein the
5 electrical energy storage member (14; 114) comprises a
battery with separate electrolyte, having a separate tank
for storing the electrolyte and means for releasing the
electrolyte from the separate tank in order to enable it
to come into contact with the anode and the cathode on
10 activating the electrical energy storage member (14;
114).
5. An aircraft according to claim 3, wherein the
electrical energy storage member (14; 114) comprises a
15 thermopile adapted to keep the electrolyte solid at
ambient temperature during storage and to liquefy the
electrolyte by heating on activation of the electrical
energy storage member (14; 114).
20 6. An aircraft according to any one of claims 1 to 5,
wherein said means for activating the electrical energy
storage member (14; 114) comprise pyrotechnic activation
means.
25 7. An aircraft according to any one of claims 1 to 5,
wherein said means for activating the electrical energy
storage member (14; 114) comprise electrical activation
means.
30 8. An aircraft according to any one of claims 1 to 7,
wherein the electrical energy storage member (14) is
connected in parallel with said specific electrical
energy power supply network (17).
35 9. An aircraft according to claim 8, wherein a diode (15)
is interposed between the electrical energy storage
member (14) and a rectifier member or an AC/DC converter
23
(16) powered by said specific electrical energy power
supply network (17).
10. An aircraft according to any one of claims 1 to 7,
5 wherein the electrical energy storage member (114) is
connected in series with a rectifier member or an AC/DC
converter (16) powered by said specific electrical energy
power supply network (17), and in parallel with a diode
(115) .
10
11. An aircraft according to claim 10, wherein said diode
(115) is constituted by a controlled switch of
electromechanical type or of static type.
15 12. An aircraft according to claim 10, wherein said diode
(115) is constituted by a semiconductor element.
13. An aircraft according to any one of claims 1 to 12,
wherein the electrical energy storage member (14; 114)
20 comprises one or more elements or sets of elements
connected in series, in parallel, or in series-parallel.
14. An aircraft according to any one of claims 1 to 12,
including a plurality of free turbine engines (11, 21),
25 each having a gas generator and each associated with an
electrical machine (12, 22) capable of operating both as
a starter and as a generator, at least one of the
plurality of engines (11, 21) being capable of being put
in a standby mode, while at least one other one of the
30 plurality of engines (11, 21) is in a mode of normal
operation.
15. An aircraft according to claim 14, characterized in
that the rapid assistance device has.a single electrical
35 energy storage member (14; 114) adapted to be
electrically connected via a switch device (38, 48; 39)
to said electrical machine (12 or 22) that is associated
24