The BMW X was a small five-cylinder radial engine for sport and training aircraft. Although this engine proved successful at several large-scale events in 1930, including that year's round-Europe flight, only a few were built.
The successor model to the BMW X five-cylinder radial engine, the BMW Xa, was introduced in 1931, with the swept volume increased from 2.2 to 2.9 liters. Power output went up from 50 to 68 hp. The Xa was also not built in any quantity either, and was mainly installed in training and sports aircraft.