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Engineering Engines: What Do Horses, Cars, and Planes Have in Common?

4 minutes

Hundreds of years ago, James Watt decided that my friend, Helga, could lift 550 pounds a foot in the air in one second. That's the definition of a horsepower. This lawn mower has six horsepower. This car has 130 horsepower. This Cessna has 230 horsepower.

(woman) And this jet has 85,000 horsepower. All of these engines produce power by forcing fuel and air into a tight space and then burning it. But they do it in different ways.

(woman) A car uses a piston engine. This piston engine has been cut in half to look inside. A mixture of fuel and air enters this metal cylinder. It's compressed when the piston pushes up onto it. This mixture is burned through a spark plug, causing it to expand, and the piston comes back down. And this happens over and over again. There are multiple pistons in a car that connect through a series of linkages to the wheel, causing it to turn. This is a plane. You might think its closest cousin is a jumbo jet. Actually, it's more closely related to a car, because it uses a piston engine. Here is the piston engine. Instead of it being attached to the wheels, it's attached to the propeller. Small planes weigh about the same as most cars. They need the same amount of horsepower to get airborne. But a Boeing 777, with all its passengers, cargo, and fuel, is about 200 times the weight of a Cessna, so it needs a lot more horsepower.

(man) You could use pistons to provide that horsepower, but you'd need 67 of the most powerful piston engines ever built to fly a 777 at cruising speed. That won't work.

(woman) What you really need is one engine that can produce enough horsepower to fly the plane. A turbine engine produces much more horsepower than a piston engine because it uses giant fans to compress the air. At the front of the engine is a spinning intake fan, which brings a huge amount of air into the engine. As we move backwards through the engine, these compressor blades make that air more and more compressed until we get here, where fuel is introduced and burned. That hot, high-pressure flow gets sent out the back of the engine, making the engine's thrust. At the same time, that flow passes through turbine blades, and those blades are connected to a shaft that runs all the way back to the front and spins the intake fan. That's what keeps the engine running. We've gone from one horsepower to 290,000 horsepower. So, Helga, I guess we don't need you anymore. Run free. Join your herd. That's Brandon. He's domesticated. Accessibility provided by the U.S. Department of Education.

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Ever wondered what horsepower really means, and what horses have to do with other modes of transportation? MIT scientists explain how engines work in various machines, including the surprising ways that they're all related. Part of the "Science Out Loud" series.

Media Details

Runtime: 4 minutes

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Episode 1
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Grade Level: 9 - 12
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Episode 2
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Episode 3
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