Measures for Progress: A History of the National Bureau of Standards

The Bureau's second wind tunnel as set up in Northwest building late in 1919. The
honeycomb at the entrance of the 3-foot wind tunnel steadied the incoming flow of air.
The maximum wind speed that could be established was about 150 miles per hour,
more than enough to determine the air resistance of bombs, projectiles, airplane
models, and for calibrating instruments.
The 12-cylinder Liberty engine mounted for testing in the Bureau's altitude chamber.
When both concrete side doors (one open here) were closed, the air pressure and
temperature inside could be lowered to correspond to any desired altitude, making it
possible to test the engine under simulated flying conditions.
The exhaust from the engine and the air in the chamber were withdrawn by an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 as low
as one-third of an atmosphere, corresponding to an altitude of approximately 35,000
feet.
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