Engines of Our Ingenuity

No. 795:
HOT-AIR ENGINE

by John H. Lienhard

Click here for audio of Episode 795.

Today, a fable about failure and success. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

John Ericsson was the knight errant of 19th-century inventors. Born in Sweden, he moved to England, then America. His imagination was as fertile as Edison's. Yet his real majesty lay in the way he let his reach exceed his grasp.

Michael Lamm spells that story out in the history of three ships: The Princeton, the Ericsson, and the Monitor. Each one failed one way or another. But each one rewrote history.

Ericsson was 39, and in debtor's prison, when he decided to come to America. He'd spent himself bankrupt trying to sell the British Navy on replacing paddle wheels with screw propellers.

Here, he convinced our Navy to build its first screw-driven warship, the Princeton, in 1844. In a trial run, a Princeton gun exploded. Two cabinet members lay among the dead. The blast had nothing to do with propellers, but it greatly damaged Ericsson's cause. Still, screw propellers drive all our ships today.

The next great fiasco came nine years later. It was the Ericsson, a 250-foot paddle-driven ship powered by a gigantic hot-air engine. The engine was one fourth as long as the ship itself.

Ericsson didn't invent the hot-air engine. It'd been cooked up earlier by a Scottish Presbyterian minister named Stirling. But Ericsson developed it into a fine working perfection.

He used heated air to drive a piston. As the air exhausted, it gave its remaining heat to the incoming air. That could've made it quite efficient. But there are a few catches.

Air is an insulating material. It's hard to heat and hard to cool. To work, the engine had to be large and slow moving. So, on January 11, 1853, reporters went below to see the Ericsson's engine. It was a quiet visual symphony of slow-moving connecting rods -- beautiful to see. The test run seemed to be a complete success. Few people noticed how slowly the ship had moved.

Ericsson's huge engine had put out only 250 HP. An ocean-going steamboat that size typically needed over 2000 HP.

Ericsson saw the problem before the newspapers did. To generate enough power and run efficiently, the engine would have to run at higher pressures than we could yet handle. The engine faded from view in his lifetime. But down through the whole 20th century we've created variants on that same hot-air engine.

Now Civil War clouds gathered, and Ericsson created his third star-crossed ship. In 1862, his Union Monitor could only limp way from a dubious battle with the Confederate Merrimack. Yet it eventually defined the modern iron-clad, steam-driven, turreted warship.

So, again and again, Ericsson reached too far. And, each time he did, he helped to create the engines -- of this century.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)


Lamm, M., The Big Engine That Couldn't. American Heritage of Invention & Technology, Vol. 8, No. 3., Winter, 1993, pp. 40-47.

See also Episodes 151, 695, and 1344 for more on Ericsson, and 743, for more on Stirling and the hot-air engines.


The Engines of Our Ingenuity is Copyright © 1988-1997 by John H. Lienhard.

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