The latest bomber to make its debut over Iraq has four engines, no cockpit, and a flight time limited by the length of its battery. ISIS, the radical insurgent group holding territory in both Syria and Iraq, is fighting for its life in Mosul, the large city in Northern Iraq it has held since 2014. Most of the weapons ISIS uses are are familiar, if still horrific: rifles and mortars, artillery and suicidal car bombs. To that arsenal, ISIS recently added commercial drones, converted into tiny bombers.
For the first year and a half of the program, two X-15 aircraft flew with two XLR-11 engines. Designed and built by Reaction Motors, this engine burned ethyl alcohol and liquid oxygen and delivered a maximum thrust of 6,000 pounds. But even with two of these engines boosted to increase their thrust, they couldn't give the small rocket plane the power it needed. These engines also weren't throttleable. The pilot's main control over thrust was to turn each engine's four barrels on and off individually.