"The steam comes out of the boiler at high pressure and strikes blades inside the casing, setting the shaft to spinning. As the steam expands, the blades grow larger, thus the shape of the case. With this system, we can drive the shaft at speeds not achievable by traditional steam engines. In addition, the high pressure can spin up the shaft very quickly, reaching top speed almost instantly."
The man at the valve cranked it open. As steam roared out of the boiler, the familiar howl of the fan engine filled Cal's ears.
"Cover your ears, Your Highness," she shouted as she covered her own. Under the howl, a whining grew. She heard at least one blade scrape the inside of the casing. The screw jumped from a dead stop to a blur in the blink of an eye. Thumping shook the table, showing the thing was further out of true than she'd thought.