Preheater in the 10-by 10-Foot Supersonic Wind Tunnel

The 10- by 10-Foot Supersonic Wind Tunnel at the NACA Lewis Flight Propulsion Laboratory was built under the Congressional Unitary Plan Act which coordinated wind tunnel construction at the NACA, Air Force, industry, and universities. The 10- by 10, which began operation in 1956, was the largest of the three NACA tunnels built under the act. Researchers could test engines up to five feet in diameter in the 10- by 10-foot test section. A 250,000-horsepower axial-flow compressor fan can generate airflows up to Mach 3.5 through the test section. The incoming air must be dehumidified and cooled so that the proper conditions are present for the test. A large air dryer with 1,890 tons of activated alumina soaks up 1.5 tons of water per minute from the airflow. A cooling apparatus equivalent to 250,000 household air conditioners is used to cool the air. The air heater is located just upstream from the test section. Natural gas is combusted in the tunnel to increase the air temperature. The system could only be employed when the tunnel was run in its closed-circuit propulsion mode.