What type of propulsion system did the XB-15 utilize?

The XB-15 was a heavy bomber prototype developed by Boeing during the 1930s. It utilized a propeller-driven propulsion system, which is characteristic of aircraft from that era. The aviation technology of the time primarily focused on piston engines, which powered propellers to generate thrust.

The selection of propeller-driven engines was essential for providing the necessary lift and speed for heavy bombers like the XB-15. This design allowed for more efficient cruising at lower altitudes, which was critical for strategic bombing missions and the operational use of the aircraft.

Jet propulsion was still in its infancy during the time the XB-15 was being developed, making it impractical as a means of propulsion for this specific model. Similarly, rocket propulsion systems, while experimented with in some military applications, were not commonly used in large aircraft like bombers. Electric-powered systems were also not viable for heavy, high-performance aircraft during this time period. Thus, the propeller-driven design was the most fitting choice for the XB-15.