Radial engines have several advantages for airplanes:
- They can produce a lot of power. A typical radial engine in a B-17 has nine cylinders, displaces 1,800 cubic inches (29.5 liters) and produces 1,200 horsepower.
- Radial engines have a relatively low maximum rpm (rotations per minute) rate, so they can often drive propellers without any sort of reduction gearing.
- Because all of the pistons are in the same plane, they all get even cooling and normally can be air-cooled. That saves the weight of water-cooling.
Radial engines reached their zenith during WWII. There are some radial engines around today, but they are not that common. Most propeller-driven planes today use more traditional engine configurations (like a flat four-cylinder) or modern gas turbine engines. Gas turbines are much lighter than radial engines for the power they produce.
One place where you can still see the influence of the radial engine concept is in the two-cylinder engine of a Harley Davidson motorcycle.
It can be thought of, in a way, as two pistons from a radial engine. In a Harley, both pistons share a single connection point to the crankshaft, like in a radial engine.
For more information on radial engines and related topics, check out the links on the next page.