When most people think of Rolls-Royce, they think of ultra-luxury cars, not airplanes. But a separate Rolls-Royce, spun off of the automaker in 1971, makes aircraft engines. And that company plans to go electric in tackling the world speed record for electric airplanes. To borrow a famous phrase from the automaker, if "horsepower is sufficient." The company has built an all new airplane called ACCEL—"accelerating electrification of flight"—to tackle the speed record attempt sometime in 2020. The ACCEL project is part of a European Commission effort to clean up emissions from air...