[sokoloff]

Fixed spark timing is not that big an engineering deficit for an engine that runs at a fairly constant power setting.

Road-going cars need variable spark timing because they are called upon to efficiently make wildly varying amounts of power. (Idle, cruise, accelerate are all part of the normal drive cycle.) Airplane engines, many racecars, and other similar applications that need to produce fixed, high power for prolonged periods of time often use fixed timing mechanisms.