<p>The performance of aircraft engines under the conditions of low pressure and temperature encountered in flight was determined with this equipment. The chambers were of heavy monolithic concrete construction and were equipped with refrigerating machinery and vacuum pumps or large capacity. The dynamometers for the absorption and measurement of the power developed were mounted outside the chamber, as were all other necessary apparatus and engine controls. One of the new chambers (after this photo was taken) would have a planned dynamic capacity sufficient to test engines up to 1000 horsepower. 
</p>
The exhaust from the engine and the air in the chamber were withdrawn by an electric-driven centrifugal exhauster. The pressure could thus be reduced to one-third of an atmosphere, corresponding to an altitude of approximately 35,000 feet.
National Institute of Standards and Technology
National Institute of Standards and Technology