Conceptual Design of a Submersible Airplane

The Defense Advanced Research Projects Agency recently outlined a challenging set of requirements for a submersible aircraft that would be used for covert insertion of a team of operators in some coastal region around the world. The submersible airplane would combine the rapid deployment possible using air transport with the lower probability of detection of a submarine. The canonical mission DARPA specified for such an airplane included an 1,000 nautical mile cruise at altitude followed by a 100 nautical mile traverse either on or just above the surface, and then 12 nautical miles traveled below the surface. A total time of 8 hours was specified for this insertion portion of the mission. The airplane must carry 8 operators and their equipment for a total of 2,000 pounds of payload. The airplane must be able to traverse those distances, deploy the team of 8 operators, loiter for 3 days awaiting their return, and then retrace the underwater and surface portions of the mission before refueling. This paper presents the results of a conceptual design study undertaken to create a design capable of meeting or exceeding the requirements specified by DARPA. Methods for sizing the aircraft and evaluating its performance are presented along with trade studies to evaluate different design options. A baseline design configuration is presented that meets or exceeds each of the specified requirements.