We found this concept within the multiple programs instructed by NASA for the development of all types of engines for aerospace use.

-The one presented by inventor Allan McDougal is a Stirling type hot gas engine with two crankshafts interconnected by a common gearbox.

“McDougal's concept”

-This engine has expandable formulas to obtain higher powers.

"Drawing of a quadruple engine"

"Interior diagram of the previous drawing"

-The details of the key numbers are not mentioned since they are essentially those of a multiplied Stirling.