A radial flow turbine heat engine comprising: a shaft; a compressor coupled to said shaft to compress intake gas to form compressed gas; a recuperator to heat said compressed gas to form heated compressed gas; a combustor to mix said heated compressed gas with fuel and to combust said fuel and said heated compressed gas to form combustion gas; a turbine coupled to said shaft to expand said combustion gas to form exhaust gas; a compressor outlet manifold to collect said compressed gas from said compressor through a plurality of compressor outlets; and a turbine inlet manifold to supply said combustion gas to said turbine through a plurality of turbine inlets; wherein said compressor outlet manifold comprises a plurality of compressor outlet manifold ducts connected to said plurality of compressor outlets; said turbine inlet manifold comprises a plurality of turbine inlet manifold ducts connected to said plurality of turbine inlets; and said plurality of compressor outlet manifold ducts are circumferentially interdigitated with said plurality of turbine inlet manifold ducts around said shaft to provide: (i) flow paths for said compressed gas through said recuperator located radially inward with respect to a rotation axis of said shaft relative to flow paths for said combustion gas in a portion of said radial flow turbine proximal to said turbine; and (ii) flow paths for said combustion gas to said plurality of turbine inlets located radially inward with respect to said rotation axis relative to flow paths for said compressed gas proximal to said plurality of turbine inlets; comprising a turbine diffuser to receive said exhaust gas from said turbine and to expand said exhaust gas; and wherein said combustor is annular and surrounds said turbine diffuser, or comprises a plurality of separate combustor portions disposed around a circumference of said turbine diffuser. a shaft; a compressor coupled to said shaft to compress intake gas to form compressed gas; a recuperator to heat said compressed gas to form heated compressed gas; a combustor to mix said heated compressed gas with fuel and to combust said fuel and said heated compressed gas to form combustion gas; a turbine coupled to said shaft to expand said combustion gas to form exhaust gas; a compressor outlet manifold to collect said compressed gas from said compressor through a plurality of compressor outlets; and a turbine inlet manifold to supply said combustion gas to said turbine through a plurality of turbine inlets; wherein said compressor outlet manifold comprises a plurality of compressor outlet manifold ducts connected to said plurality of compressor outlets; said turbine inlet manifold comprises a plurality of turbine inlet manifold ducts connected to said plurality of turbine inlets; and said plurality of compressor outlet manifold ducts are circumferentially interdigitated with said plurality of turbine inlet manifold ducts around said shaft to provide: (i) flow paths for said compressed gas through said recuperator located radially inward with respect to a rotation axis of said shaft relative to flow paths for said combustion gas in a portion of said radial flow turbine proximal to said turbine; and (ii) flow paths for said combustion gas to said plurality of turbine inlets located radially inward with respect to said rotation axis relative to flow paths for said compressed gas proximal to said plurality of turbine inlets; (i) flow paths for said compressed gas through said recuperator located radially inward with respect to a rotation axis of said shaft relative to flow paths for said combustion gas in a portion of said radial flow turbine proximal to said turbine; and (ii) flow paths for said combustion gas to said plurality of turbine inlets located radially inward with respect to said rotation axis relative to flow paths for said compressed gas proximal to said plurality of turbine inlets; comprising a turbine diffuser to receive said exhaust gas from said turbine and to expand said exhaust gas; and wherein said combustor is annular and surrounds said turbine diffuser, or comprises a plurality of separate combustor portions disposed around a circumference of said turbine diffuser.