the fastest propeller-driven plane ever built is the Grumman F8F Bearcat. It was a carrier-based fighter aircraft developed by the United States during World War II. The Bearcat had a top speed of approximately 421 miles per hour (678 kilometers per hour). It was renowned for its exceptional speed and agility. However, please note that aircraft technology and records may have changed since then, so there might be newer and faster propeller planes in existence.