This Caloric hot air engine was built by Roger Butzen of Texas, and loaned to the Miniature Engineering Craftsmanship Museum as part of the Engine Collection of Paul and Paula Knapp. Mr. Butzen’s Caloric hot air engine is 10”-long, 10”-wide, 19”-high, and weighs 22 lbs. Hot air engines use the expansion and contraction of air under the influence of a temperature change to convert thermal energy into mechanical work.