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A gas turbine engine comprises a fan drive gear system, a low spool connected to the fan drive gear system, and a high spool disposed aft of the low spool. The low spool comprises a rearward-flow low pressure compressor disposed aft of the fan drive gear system, and a forward-flow low pressure turbi

A gas turbine engine comprises a fan drive gear system, a low spool connected to the fan drive gear system, and a high spool disposed aft of the low spool. The low spool comprises a rearward-flow low pressure compressor disposed aft of the fan drive gear system, and a forward-flow low pressure turbine disposed aft of the low pressure compressor. The high spool comprises a forward-flow high pressure turbine disposed aft of the low pressure turbine, a combustor disposed aft of the high pressure turbine, and a forward-flow high pressure compressor disposed aft of the combustor.

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1. A gas turbine engine comprising: a fan drive gear system comprising: a turbofan;a fan shaft connected to an inner diameter of the turbofan; andan epicyclic gear system connected to a downstream end of the fan shaft;a low spool connected to the fan drive gear system, the low spool comprising: a re

1. A gas turbine engine comprising: a fan drive gear system comprising: a turbofan;a fan shaft connected to an inner diameter of the turbofan; andan epicyclic gear system connected to a downstream end of the fan shaft;a low spool connected to the fan drive gear system, the low spool comprising: a rearward-flow low pressure compressor disposed aft of the fan drive gear system; anda forward-flow low pressure turbine disposed aft of the rearward-flow low pressure compressor;a high spool disposed aft of the low spool, the high spool comprising: a forward-flow high pressure turbine disposed aft of the forward-flow low pressure turbine;a combustor disposed aft of the forward-flow high pressure turbine; anda forward-flow high pressure compressor disposed aft of the combustor;a reverse ducting disposed radially outward of the high spool for directing output of the rearward-flow low pressure compressor to the forward-flow high pressure compressor such that the output reverses flow to pass through the high spool;exhaust ducting disposed radially outward of the reverse ducting for receiving exhaust gas from the forward-flow low pressure turbine and fan air from the turbofan: andan intercooling and recuperating heat exchanger mounted adjacent the reverse ducting between the rearward-flow low pressure compressor and the forward-flow high pressure compressor;wherein flow through the engine extends sequentially through the rearward-flow low pressure compressor in a downstream direction, and through the forward-flow high pressure compressor, the combustor, the forward-flow high pressure turbine and the forward-flow low pressure turbine in a forward direction. 2. The gas turbine engine of claim 1 and further comprising: a low pressure shaft comprising: a forward portion connected to the epicyclic gear system;a mid portion connected to the rearward-flow low pressure compressor; andan aft portion connected to the forward-flow low pressure turbine; anda high pressure shaft disposed axially downstream of the low pressure shaft, the high pressure shaft comprising: a forward portion connected to the forward-flow high pressure turbine;a mid portion extending concentrically through the combustor; andan aft portion connected to the forward-flow high pressure compressor. 3. The gas turbine engine of claim 2 and further comprising an accessory gearbox extending axially from a downstream end of the high pressure shaft. 4. The gas turbine engine of claim 3 and further comprising an accessory gearbox extending radially from the low pressure shaft using a tower shaft. 5. The gas turbine engine of claim 2 and further comprising a balance piston and a tapered roller bearing connected to the low pressure shaft to react axially forward directed thrust on the low pressure spool. 6. The gas turbine engine of claim 1 and further comprising: an intermediate pressure turbine disposed between the forward-flow low pressure turbine and the forward-flow high pressure turbine;a gear shaft connecting the epicyclic gear system to the intermediate pressure turbine;a low pressure shaft comprising: a forward portion connected to the rearward-flow low pressure compressor; andan aft portion connected to the forward-flow low pressure turbine; anda high pressure shaft disposed axially downstream of the low pressure shaft, the high pressure shaft comprising: a forward portion connected to the forward-flow high pressure turbine;a mid portion extending concentrically through the combustor; andan aft portion connected to the forward-flow high pressure compressor. 7. The gas turbine engine of claim 1 and further comprising: an annular exhaust duct for guiding fan air from the turbofan;a flow splitter disposed within the exhaust duct to divert a portion of the fan air to the rearward-flow low pressure compressor to produce a downstream flow of low pressure air;a core engine case surrounding the high spool;a reverse flow duct disposed concentrically between the exhaust duct and the core engine case, the reverse flow duct comprising: an inlet end configured to receive downstream flow of the low pressure air from the rearward-flow low pressure compressor;an elbow connected to the inlet end and configured to redirect downstream flow of the low pressure air into upstream flow; andan outlet end connected to the elbow and configured to direct upstream flow of the low pressure air into the forward-flow high pressure compressor; andan exhaust vent comprising: an inlet configured to receive gas from the core engine case; andan outlet configured to discharge gas into the annular exhaust duct. 8. The gas turbine engine of claim 1 wherein the forward-flow high pressure compressor comprises an axial flow compressor. 9. A turbofan engine comprising: a turbofan propulsor for producing downstream flowing bypass gas and core gas;a low pressure spool comprising: a low pressure compressor for receiving downstream flowing core gas from the turbofan propulsor; anda low pressure turbine having upstream flow;a gear reduction system for coupling the turbofan propulsor to an input rotation;a reverse air duct for turning downstream flowing core gas from the low pressure compressor radially inward for upstream flow;a reversed-flow core with upstream flow configured to receive upstream flowing core gas from the air duct and to deliver upstream flowing core gas to the low pressure turbine;an exhaust pipe for turning upstream flow of core gas from the low pressure turbine radially outward for discharge into the downstream flow of bypass gas; andan intercooling and recuperating heat exchanger mounted adjacent the reverse air duct between the low pressure compressor and the reversed-flow core. 10. The turbofan engine of claim 9 wherein the reversed-flow core includes an axial flow high pressure turbine and an axial flow high pressure compressor. 11. The turbofan engine of claim 10 and further comprising: a fan shaft for connecting the turbofan propulsor to the gear reduction system;a low pressure shaft for connecting the low pressure compressor to the low pressure turbine; anda high pressure shaft for connecting the high pressure compressor to the high pressure turbine. 12. The turbofan engine of claim 11 and further comprising a gear shaft for connecting the gear reduction system to the cross-flow low pressure spool, the gear shaft providing the input rotation. 13. The turbofan engine of claim 11 and further comprising: an intermediate pressure turbine disposed between the low pressure turbine and the high pressure turbine; anda gear shaft for connecting the gear reduction system to the intermediate pressure turbine, the gear shaft providing the input rotation. 14. A gas turbine engine comprising: a fan drive gear system comprising: a turbofan;a fan shaft connected to an inner diameter of the turbofan; andan epicyclic gear system connected to a downstream end of the fan shaft;a low spool connected to the fan drive gear system, the low spool comprising: a low pressure shaft;a rearward-flow low pressure compressor disposed aft of the fan drive gear system; anda forward-flow low pressure turbine disposed aft of the rearward-flow low pressure compressor;a high spool disposed aft of the low spool, the high spool comprising: a forward-flow high pressure turbine disposed aft of the forward-flow low pressure turbine;a combustor disposed aft of the forward-flow high pressure turbine; anda forward-flow high pressure compressor disposed aft of the combustor;reverse ducting disposed radially outward of the high spool for directing output of the rearward-flow low pressure compressor to the forward-flow high pressure compressor such that the output reverses flow to pass through the high spool;exhaust ducting disposed radially outward of the reverse ducting for receiving exhaust gas from the forward-flow low pressure turbine and fan air from the turbofan; and an augmenter mounted within the exhaust ducting radially outward of the high pressure spool;wherein flow through the engine extends sequentially through the rearward-flow low pressure compressor in a downstream direction, and through the forward-flow high pressure compressor, the combustor, the forward-flow high pressure turbine and the forward-flow low pressure turbine in a forward direction; andwherein an accessory gearbox extending radially from the low pressure shaft using a tower shaft. 15. The gas turbine engine of claim 14 and further comprising: the low pressure shaft comprising: a forward portion connected to the epicyclic gear system;a mid portion connected to the rearward-flow low pressure compressor;and an aft portion connected to the forward-flow low pressure turbine; anda high pressure shaft disposed axially downstream of the low pressure shaft, the high pressure shaft comprising: a forward portion connected to the forward-flow high pressure turbine;a mid portion extending concentrically through the combustor; andan aft portion connected to the forward-flow high pressure compressor. 16. The gas turbine engine of claim 15 and further comprising an accessory gearbox extending axially from a downstream end of the high pressure shaft. 17. The gas turbine engine of claim 15 and further comprising a balance piston and a tapered roller bearing connected to the low pressure shaft to react axially forward directed thrust on the low pressure spool. 18. The gas turbine engine of claim 14 and further comprising: an intermediate pressure turbine disposed between the forward-flow low pressure turbine and the rearward-flow high pressure turbine;a gear shaft connecting the epicyclic gear system to the intermediate pressure turbine;a low pressure shaft comprising: a forward portion connected to the rearward-flow low pressure compressor; andan aft portion connected to the forward-flow low pressure turbine; anda high pressure shaft disposed axially downstream of the low pressure shaft, the high pressure shaft comprising: a forward portion connected to the forward-flow high pressure turbine;a mid portion extending concentrically through the combustor; andan aft portion connected to the forward-flow high pressure compressor. 19. The gas turbine engine of claim 14 and further comprising: an annular exhaust duct for guiding fan air from the turbofan;a flow splitter disposed within the exhaust duct to divert a portion of the fan air to the rearward-flow low pressure compressor to produce a downstream flow of low pressure air;a core engine case surrounding the high spool;a reverse flow duct disposed concentrically between the exhaust duct and the core engine case, the reverse flow duct comprising: an inlet end configured to receive downstream flow of the low pressure air from the rearward-flow low pressure compressor;an elbow connected to the inlet end and configured to redirect downstream flow of the low pressure air into upstream flow; andan outlet end connected to the elbow and configured to direct upstream flow of the low pressure air into the forward-flow high pressure compressor; andan exhaust vent comprising: an inlet configured to receive gas from the core engine case; andan outlet configured to discharge gas into the annular exhaust duct. 20. A turbofan engine comprising: a turbofan propulsor for producing downstream flowing bypass gas and core gas;a low pressure spool comprising: a low pressure shaft;a low pressure compressor for receiving downstream flowing core gas from the turbofan propulsor; anda low pressure turbine having upstream flow;a gear reduction system for coupling the turbofan propulsor to an input rotation;an air duct for turning downstream flowing core gas from the low pressure compressor radially inward for upstream flow;a reversed-flow core with upstream flow configured to receive upstream flowing core gas from the air duct and to deliver upstream flowing core gas to the low pressure turbine;an exhaust pipe for turning upstream flow of core gas from the low pressure turbine radially outward for discharge into the downstream flow of bypass gas; and an augmenter mounted within an exhaust ductradially outward of the reversed-flow core;wherein an accessory gearbox extending radially from the low pressure shaft using a tower shaft.