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The Evolution of the Radial and the Rotary 8:41 Lena: You mentioned radial engines earlier—the ones that look like a circle of cylinders. They always look so "vintage" to me. Was there a specific reason we moved away from those, or do they still have a place in the sky?
8:53 Miles: They are definitely the icons of the "Golden Age," but their design was purely functional. In a radial engine, the cylinders are arranged in a circle around the crankshaft. The big advantage was that they were rugged. Because they were air-cooled and didn't have a complex radiator system, they could take a lot of damage—say, in a military setting—and keep running. But they had a major drawback: they were huge.
9:17 Lena: Right, a giant circle of metal creates a lot of wind resistance.
0:46 Miles: Exactly. It’s like trying to fly a barn door through the air. As planes got faster, that drag became a dealbreaker. But before the standard radial took over, there was an even weirder version called the "Rotating Radial" or "Rotary" engine. This is one of those things in aviation history that sounds like a prank if you don't know it's real.
9:41 Lena: What do you mean "rotating"? Like the whole engine spun?
Miles: Yes! In a normal engine, the engine stays still and the crankshaft spins the propeller. In a rotary engine, the crankshaft is bolted to the airplane and stays perfectly still. The entire engine—the cylinders, the crankcase, everything—spins around it. And the propeller is bolted to the outside of the engine.
10:03 Lena: That sounds terrifying. Why on earth would you do that?
10:06 Miles: It solved a huge problem for 1909: cooling. Back then, they didn't have great metallurgy or high-speed flight. If the engine was stationary, it would overheat almost instantly. But if the entire engine is spinning at 1,200 RPM, it's essentially its own giant fan. It keeps itself cool even when the plane is moving slowly. The Seguin brothers flew the first practical one, the Gnome Omega, in 1909, and it changed everything because it had a great power-to-weight ratio.
10:34 Lena: But I'm guessing having a massive, heavy engine spinning around at high speeds caused some handling issues?
10:41 Miles: Oh, big time. It acted like a giant gyroscope. If you tried to turn the plane one way, the gyroscopic force of the spinning engine would try to push the nose up or down. Pilots had to learn to "fight" the engine just to stay level. Eventually, as we got better at making stationary air-cooled engines, the rotary faded away.
11:00 Lena: It’s such a clever, if slightly crazy, solution to a temporary problem. But what about the Wankel engine? I’ve heard that mentioned as a modern "rotary" engine. Is that the same thing?
11:12 Miles: Not at all, and it’s a really important distinction. The Wankel is a "pistonless" rotary engine. Instead of pistons going up and down, it uses a triangular-shaped rotor that spins inside an oval-shaped housing. It’s incredibly elegant because it has far fewer moving parts. No valves, no connecting rods, no heavy crankshaft.
11:32 Lena: So it’s lighter and smaller?
11:34 Miles: Much smaller. A Wankel engine is about half the weight and size of a traditional piston engine with the same power. And because it's made of an aluminum housing with a steel rotor, it has this amazing safety feature: it almost never seizes if it overheats. Aluminum expands more than steel, so if things get too hot, the clearances actually get wider rather than tighter. In a piston engine, an overheat usually means the piston expands and gets stuck in the cylinder—catastrophic failure.
12:02 Lena: That sounds like a dream for aviation! Why aren't we all flying Wankels?
12:06 Miles: It’s one of those "what if" stories in engineering. After World War II, the industry got distracted by the jet engine. Everyone thought turbines would scale down to even the smallest planes, so research into the Wankel for aircraft stalled. It found a home in Mazda sports cars instead. But today, it’s seeing a huge comeback in motor gliders and UAVs—drones—where that compactness and smooth, vibration-free power are exactly what’s needed.
12:30 Lena: It’s interesting how these "alternative" designs keep circling back. It’s like the industry is constantly rediscovering these ideas when the needs change—like wanting smaller, lighter powerplants for drones.
12:43 Miles: Definitely. It shows that there isn't one "perfect" way to build a mother of flight. Depending on whether you need ruggedness, cooling, or extreme lightness, the internal combustion engine can take some pretty wild forms.