Combined power main engine start system

The invention relates to engine starting systems for aircraft, and more particularly to engine starting systems for starting gas turbine propulsion engines aboard aircraft.

Modern aircraft secondary power systems are becoming large with increasing demands for electric power and large power for starting the prime propulsion engines. These aircraft have a gas turbine powered auxiliary power unit (APU) on board to provide electrical, hydraulic and pneumatic power for operating systems aboard the aircraft when the propulsion engines are shut down as well as to provide power for starting the propulsion engines. Typically, pneumatic power, provided by a load compressor within the APU, has been used to start the propulsion engines. The load compressor has also been used to provide compressed air for the environmental control system (ECS) aboard the aircraft before and after the propulsion engines are started.

The main engine start (MES) requires much more compressed air from the APU than the ECS load. Since the load compressor is used for both the MES mode and the ECS mode, the APU is sized well above the needs by the MES requirement. The APU is thus oversized for the ECS mode and it is heavier, more costly and less efficient than if it were sized to match the ECS load alone. The heavier APU and its support structure detract from the aircraft fuel load or payload. The excess APU weight therefore shortens the range of the aircraft or reduces its payload.

Although increasing power demands that are due to factors other than MES requirements, such as more electric power cabin services, added avionics functions and large radar load for some military aircraft are also driving up the size and weight of APUs for modern aircraft, by far the most significant factor is the MES requirements.

The invention maximises power delivered by the APU for starting propulsion engines by combining power sources delivered by the APU so that essentially then entire power delivered by the APU for pneumatic, hydraulic and electric power is applied to MES. This is accomplished by employing a combination of pneumatic, hydraulic and electric starters for each propulsion engine that the APU drives simultaneously.

In a preferred embodiment, the invention comprises a starting system for starting the propulsion engines of gas turbine powered aircraft comprising: an auxiliary power unit (APU) with a pneumatic supply source and an auxiliary supply source; at least one gas turbine propulsion engine with a pneumatic starter and an auxiliary starter; a pneumatic supply path for controlling and distributing pneumatic power from the pneumatic supply source to the pneumatic starter upon main engine start; and an auxiliary supply path for controlling and distributing auxiliary power from the auxiliary supply source to the auxiliary starter upon main engine start.

FIG. 1 is a block diagram of a combined power main engine start system for aircraft according to the invention.

FIG. 1 is a block diagram of a combined power main engine start system 2 for aircraft according to the invention. A gas turbine propulsion engine 4 for an aircraft has an associated pneumatic starter 6 and an auxiliary starter 8 . The pneumatic starter 6 is typically a pneumatic motor. The auxiliary starter 8 may be a dynamoelectric machine, such as an electric motor or starter/generator, a hydraulic motor or motor/pump, or a combination of such electric and hydraulic devices.

An auxiliary pump unit (APU) 10 aboard the aircraft has a pneumatic supply source 12 . The pneumatic supply source 12 typically comprises a load compressor or powerhead bleed air source that is part of the APU 10 . The APU 10 also has an auxiliary supply source 16 that supplies auxiliary power. The auxiliary supply source 16 may comprise a dynamoelectric machine, such as an electric generator or starter/generator, a hydraulic pump or motor/pump, or a combination of such electric and hydraulic devices. The pneumatic supply source 12 is coupled to the pneumatic starter 8 through a pneumatic supply path 18 that controls and distributes the flow of pneumatic power from the pneumatic supply source 12 to the pneumatic starter 8 . The auxiliary supply source 16 is coupled to the auxiliary starter 8 through an auxiliary supply path 20 that controls and distributes the flow of auxiliary power from the auxiliary supply source 16 to the auxiliary starter 8 .

The pneumatic supply path 18 comprises pneumatic ductwork and valving to control the flow of pneumatic power from the pneumatic supply source 12 to the pneumatic starter 6 . When the auxiliary starter 8 and the auxiliary supply source 16 are both electric, the auxiliary supply path 20 comprises electrical wiring and switching to control and distribute the electrical current flow from the auxiliary supply source 16 to the auxiliary starter 8 . When the auxiliary starter 8 and the auxiliary supply source 16 are both hydraulic, the auxiliary supply path 20 comprises hydraulic tubing and valving to control and distribute the hydraulic fluid flow from the auxiliary supply source 16 to the auxiliary starter 8 . When the auxiliary starter 8 and the auxiliary supply source 16 comprise both electric and hydraulic devices, the auxiliary supply path 20 comprises a combination of such electric current and hydraulic fluid flow control and distribution components.

During MES, the pneumatic supply path 18 regulates the flow of pneumatic power from the pneumatic supply source 12 to the pneumatic starter 6 . Simultaneously, the auxiliary supply path 20 regulates the flow of auxiliary power from the auxiliary supply source 16 to the auxiliary starter 8 . Preferably, during MES remaining electric and hydraulic loads aboard the aircraft are minimised or removed so that most of the power of the APU 10 is applied to starting the engine 4 during MES.

Since most of the power of the APU 10 is directed or redirected to starting the engine 4 during MES, the APU 10 may be downsized to a capacity wherein the combination of the pneumatic supply source 12 and the auxiliary supply source 16 matches the power needed by the engine 4 for MES, instead of requiring the pneumatic supply source 12 to meet the power requirements of the engine 4 for MES alone. The size, weight and cost of the APU 10 , the pneumatic starter 6 , the pneumatic supply 18 and associated supply structure are thereby reduced.

Described above is a starting system for starting the propulsion engines of gas turbine powered aircraft that combines power sources delivered by the APU so that essentially then entire power delivered by the APU for pneumatic, hydraulic and electric power is applied to corresponding starters on each propulsion engine during MES simultaneously. It should be understood that these embodiments of the invention are only illustrative implementations of the invention, that the various parts and arrangement thereof may be changed or substituted, and that the invention is only limited by the scope of the attached claims.