GB1565981A - Aircraft systems - Google Patents

Description

(54) IMPROVEMENTS RELATING TO AIRCRAFT SYSTEMS (71) We, BRInsH AIRCRAFT COR- PORATION LIMITED, a British Company, of 100 Pall Mall, London, S.W.1., do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement.

This invention relates to aircraft having a cabin requiring to be air conditioned. It has for an object a reduced requirement for fresh air for air conditioning purposes supplied from a source, such as an auxiliary power unit or a propulsion engine, and hence improved economy of operation of the aircraft as a whole.

According to the invention an aircraft includes a cabin to be air conditioned, a source of pressurised fresh air, a compressor, a turbine coupled to drive the compressor, fresh air supply means adapted to supply fresh pressunsed air from the source selectively and alternatively to the compressor for further compression or directly to the turbine to provide power required from the turbine, non-fresh air supply means adapted to sup ply non-fresh pressurised air from the cabin to the compressor for further compression when and only when the fresh air is supplied directly to the turbine, transfer means adapted to transfer compressed air from the compressor to the turbine to provide power required from the turbine, and delivery means adapted to deliver air exhausted from the turbine to the cabin.

This arrangement can be operated in two alternative modes, one, being a non recirculatory mode, in which the fresh air is directed to the compressor and not directly to the turbine, and no non-fresh air is recirculated through the compressor and turbine for delivery to the cabin, and the other, being a recirculatory mode, in which the fresh air is directed directly to the turbine instead of the compressor, and non-fresh air is recirculated from the cabin through the compressor and turbine and is returned to the cabin after being mixed with fresh air directed to the turbine.

A preferred embodiment of an aircraft according to the invention is described with reference to the accompanying drawings in which: Figure 1 is a diagram of an aircraft air conditioning system in one mode of operation and, Figure 2 is a similar diagram but with the system in a further mode of operation.

An aircraft has a cabin shown generally at 1 which requires air conditioning. The cabin has a pressure bulkhead 2. The aircraft further has two propulsion engines (not shown) and an auxiliary power unit (not shown) from either or both of which pressurised fresh air can be obtained. The cabin air conditioning is provided by duplicated systems which are independent of one another, each being normally supplied by one propulsion engine, but which share a common duct 3 through which fresh air is delivered from the propulsion engines and/or the auxilliary power unit. The duct 3 has an isolating valve 4 which is normally closed but which can be opened to supply both systems from one propulsion engine should one engine fail. The duplicated systems have a further connecting duct 24.

For ease of description only one system is illustrated; a duct 5 for the delivery of fresh air to the non-described system is shown for reference only.

In the illustrated system a duct 6 supplies fresh air from the propulsion engine and/or the auxiliary power unit through a flow control valve 7 whch adjusts the mass flow of fresh air in accordance with a flow sensor 8. Further reference to this flow sensor will be made. The fresh air is passed by duct 6 through a first heat exchanger 9 housed in a cooling air duct 10. Subsequently the duct 6 divides into two rurther ducts 11 and 12, that - referenced 11 (the said first duct) supplying an inlet of a compressor 16 and that referenced 12 (the said second duct) supplying an inlet nozzle 12a of a turbine 17.

The compressor 16 is driven by the turbine 17 by means of a shaft 18.

Located in- the duct 11 is a shut-off valve 21 (the said first valve), and located in the duct 12 is a non return valve 22 (the said second valve) arranged such that a higher pressure upstream of the valve compared with that downstream of the valve causes it to open.

A duct 13 (the said third duct) connects an outlet of the cabin 1 to the duct 11 downstream of the valve 21 and hence to an inlet of the compressor 16. A further duct 14 connects an outlet of the compressor 16 with an inlet nozzle 14a of the turbine 17 through a second heat exchanger 20 also situated in the cooling air duct 10.

The duct 13 incorporates a non-return valve 23 (the said third valve) arranged such that a relatively higher pressure on its downstream or compressor side compared with its upstream or cabin side causes it to close.

Accordingly when the valve 21 is open, the valve 23 is closed and vice versa.

A duct 15 connects a turbine outlet with an inlet of the cabin 1. This duct includes a water separator 19 to remove any water in the flow, the blow sensor 8, and non-return valves 29 which allow flow into but not out of the cabin 1.

The flow sensor 8 senses the total mass flow being delivered to the cabin by the single system described and operates the flow control valve 7 to regulate the fresh air input accordingly. The non-fresh air input remains unregulated by this valve 7.

A duct 30 interconnects the ducts 12 and 14 just upstream of their respective turbine nozzles 12a and 14a. The duct includes a non-return valve 28 arranged to open when the pressure in the duct 14 is greater than that in the duct 12.

In operation, in the non-recirculatory mode of Figure 2 (code named the Bootstrap Mode) the shut-off valve 21 is opened such that the non-return valves 22 and 23 are closed to positively prevent flow along ducts 12 or 13 respectively. Fresh air from the source, cooled in the heat exchanger 9, is supplied exclusively to the compressor 16 along duct 11, is compressed, passed along duct 14, is cooled in the heat exchanger 20 and is passed into the turbine 17 through nozzle 14a where, in expanding it does work to power the turbine and drive the compressor 16; it is simultaneously cooled.In this mode of operation, the non-return valve 28 is open allowing fresh air from the duct 14 to flow through duct 30 to the nozzle 12a; thus both turbine inlet nozzles 12a and 14a are in use to provide suitably large nozzle area to pass into the turbine the mass flow consistent with this mode of operation.

The cooled air exhausts from the turbine along duct 15 and is delivered to the cabin through the non-return valves 29.

This mode of operation is used in operating cases where maximum fresh air ventilation is necessary, for example, the clearance of smoke from the cabin, or in certain failure cases. The latter include failure of one of the twin air conditioning and pressurisation systems, a failure in that part of the system concerned with recirculation of nonfresh cabin air, and a partial failure of the fresh air supply upstream of the twin systems described.

In operation, in the recirculatory mode of Figure 1, (code named the Shoestring Mode) the valve 21 is closed and the valves 22 and 23 accordingly open so that all the pressurised fresh air after cooling in the heat exchanger 9 directed to the nozzle 12a of the turbine 17 along duct 12.

This fresh air does work in the turbine to provide a proportion of the power required from the turbine. The compressor 16 draws non-fresh air frim the cabin 1 along duct 13, passes it through duct 14, through the heat exchanger 20, to the turbine nozzle 14a. The valve 28 remains closed.

This recirculatory air does work in the turbine to provide the remainder of the power required from the turbine, is mixed with the fresh air from the nozzle 12a and, subsequently, the cooled mixed flow exhaust is delivered through duct 15 to the cabin 1.

This mode of operation is used in normal operation; it is possible to achieve a 1:1 ratio of fresh to recirculated air flow, with the advantage of almost doubling the mass flow to the cabin when the auxiliary power unit is the sole source of fresh air, and of almost halving the mass flow of fresh air required from the propulsion engines when those engines are the sole source of fresh air, for example in cruising flight.

Having described the basic details and functioning of the system, some further features and variations which may be known per se are now described.

In the Figures, a fan 27 is driven by the turbine 17 to supply cooling air during ground running or low speed flight when the flow of ram air is insufficient for cooling.

In med.ium to high speed flight the cooling flow is supplied primarily by ram air.

The temperature of the air leaving the heat exchangers 9 and 20 is controlled by regulating the ram air flow, in the duct 10.

This is achieved by a ramp 31 in the ram air duct intake and by shutters 32 in the ram air exit. Both are controlled by a temperature sensing device 33 in the cabin 1.

A duct 34 with a shut off valve 35 con nects the duct 14 with the turbine 17 so that the nozzle 14a can be partially by-passed in order to maintain the turbine outlet above the frost point.

A shut-off valve 36 is provided in the duct 13 adjacent the cabin bulkhead to prevent cabin de-pressurisation in the event of failure of the ducts 13 or 14. This valve 36 is interconnected with the valve 21 to ensure that it cannot be closed unless valve 21 is open.

As before mentioned, a 1:1 fresh to nonfresh (recirculated) flow ratio is normally achieve able, but in some circumstances, such as a hot day cruise at 35,000 ft. altitude, this might not be possible when a relatively small fixed turbine nozzle 12a is used. Accordingly an alternative larger nozzle with a variable area capability is preferably provided.

Similarly, the turbine nozzle 14a can be too small in certain circumstances during operation in the so-called Bootstrap Mode and as before mentioned the duct 30 is provided to remedy this by allowing the nozzle 12a to be used simultaneously. An alternative embodiment is to delete this duct 30 and instead substitute a larger nozzle for the nozzle 14a having a variable area capability. When the duct 30 is deleted it is found that the non-return valve 22 must be replaced by a shut off valve interconnected with the valve 21 to ensure correct sequencing. In fact it would be perfectly feasible to replace the non-return valve 22 with a shut off valve linked to valve 21 in all the described systems.

finally, the turbine de-frost duct 34 could be eliminated by some other form of turbine de frosting: for example, the duct 14 could deliver its flow into a plenum chamber (not shown) surrounding the turbine casing prior to entering the nozzle 14a In the described example the turbine 17 is a single rotor device onto which the two nozzles 12a and 14a are directed. In an alternative embodiment the single rotor can be replaced by two rotors, one having the nozzle 12a and one having the nozzle 14a.

It is envisaged that the compressor and turbine unit will rotate continuously througout the operating envelope of the system.

WHAT WE CLAIM IS: 1. An aircraft including a cabin to be air conditioned, a source of pressurised fresh air, a compressor, a turbine coupled to drive the compressor, fresh air supply means adapted to supply fresh pressurised air frorn the source selectively and alternatively to the compressor for further compression or directly to the turbine to provide power required from the turbine, non-fresh air supply means adapted to supply non-fresh pressurised air from the cabin to the compressor for further compression when and only when the fresh air is supplied. directly to the turbine, transfer means adapted to transfer compressed air from the compressor to the turbine to provide power required from the turbine, and delivery means adapted to deliver air exhausted from the turbine to the cabin.

2. An aircraft according to claim 1 wherein the fresh air supply means includes a first duct connecting the source with an inlet to the compressor, a second duct connecting the source with an inlet to the turbine, a first valve in the first duct, a second valve in the second duct, said valves being arranged so that when one is open the other is shut, and the non-fresh air supply means includes a third duct connecting an outlet of the cabin with said inlet to the compressor.

a third valve in the third duct, the third valve being arranged so that when the first valve is open the third valve is closed and vice versa.

3. An aircraft according to claim 2 wherein the first valve comprises an on-off valve, and the second and the third valves comprise non-return valves.

4. An aircraft according to claim 4 wherein the delivery means includes a flow sensor and the regulator is operated in accordance with demands from the flow sensor.

5. An aircraft substantially as hereinbefore described with reference to the accompanying Figures.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. nects the duct 14 with the turbine 17 so that the nozzle 14a can be partially by-passed in order to maintain the turbine outlet above the frost point. A shut-off valve 36 is provided in the duct 13 adjacent the cabin bulkhead to prevent cabin de-pressurisation in the event of failure of the ducts 13 or 14. This valve 36 is interconnected with the valve 21 to ensure that it cannot be closed unless valve 21 is open. As before mentioned, a 1:1 fresh to nonfresh (recirculated) flow ratio is normally achieve able, but in some circumstances, such as a hot day cruise at 35,000 ft. altitude, this might not be possible when a relatively small fixed turbine nozzle 12a is used. Accordingly an alternative larger nozzle with a variable area capability is preferably provided. Similarly, the turbine nozzle 14a can be too small in certain circumstances during operation in the so-called Bootstrap Mode and as before mentioned the duct 30 is provided to remedy this by allowing the nozzle 12a to be used simultaneously. An alternative embodiment is to delete this duct 30 and instead substitute a larger nozzle for the nozzle 14a having a variable area capability. When the duct 30 is deleted it is found that the non-return valve 22 must be replaced by a shut off valve interconnected with the valve 21 to ensure correct sequencing. In fact it would be perfectly feasible to replace the non-return valve 22 with a shut off valve linked to valve 21 in all the described systems. finally, the turbine de-frost duct 34 could be eliminated by some other form of turbine de frosting: for example, the duct 14 could deliver its flow into a plenum chamber (not shown) surrounding the turbine casing prior to entering the nozzle 14a In the described example the turbine 17 is a single rotor device onto which the two nozzles 12a and 14a are directed. In an alternative embodiment the single rotor can be replaced by two rotors, one having the nozzle 12a and one having the nozzle 14a. It is envisaged that the compressor and turbine unit will rotate continuously througout the operating envelope of the system. WHAT WE CLAIM IS:

1. An aircraft including a cabin to be air conditioned, a source of pressurised fresh air, a compressor, a turbine coupled to drive the compressor, fresh air supply means adapted to supply fresh pressurised air frorn the source selectively and alternatively to the compressor for further compression or directly to the turbine to provide power required from the turbine, non-fresh air supply means adapted to supply non-fresh pressurised air from the cabin to the compressor for further compression when and only when the fresh air is supplied. directly to the turbine, transfer means adapted to transfer compressed air from the compressor to the turbine to provide power required from the turbine, and delivery means adapted to deliver air exhausted from the turbine to the cabin.

2. An aircraft according to claim 1 wherein the fresh air supply means includes a first duct connecting the source with an inlet to the compressor, a second duct connecting the source with an inlet to the turbine, a first valve in the first duct, a second valve in the second duct, said valves being arranged so that when one is open the other is shut, and the non-fresh air supply means includes a third duct connecting an outlet of the cabin with said inlet to the compressor.

a third valve in the third duct, the third valve being arranged so that when the first valve is open the third valve is closed and vice versa.

3. An aircraft according to claim 2 wherein the first valve comprises an on-off valve, and the second and the third valves comprise non-return valves.

4. An aircraft according to claim 4 wherein the delivery means includes a flow sensor and the regulator is operated in accordance with demands from the flow sensor.

5. An aircraft substantially as hereinbefore described with reference to the accompanying Figures.