The L.A. Comp Subsonic Wind Tunnel
The L. A. Comp wind tunnel is a closed loop, closed throat, subsonic wind tunnel with an atmospheric pressure test section. The tunnel is made of steel, reinforced concrete, and brick construction. Vanes are located at the four corners of the tunnel, where the air is turned through 90 degrees. The tunnel is driven by a 400-hp constant speed electric motor. The motor drives a three-blade seven-foot propeller through an extension shaft. The wind speed is changed by varying the pitch of the propeller blades. This adjustment is made by a hydraulic piston, which is controlled by a stepper-motor driven pilot valve.
The test section of the tunnel is elliptical, 1.22 m (4 ft) by 1.83 m (6 ft), and 3.4 m (11 ft) long. The wind speed can be increased up to 70 m/s (155 miles per hour) approximately. The freestream turbulence is small, estimated to be around 1 percent. The tunnel is equipped with a pyramidal balance for force and moment measurement. The balance is used to measure the lift, drag, and side forces, and the pitching, rolling, and yawing moments. The sensors of the balance are temperature-compensated strain gages. The outputs of the strain gages are available either as voltages or in appropriate physical units through the calibration coefficients. The angle of attack and the yaw angle can be set using stepper motors attached to the balance. These angles are sensed by potentiometers and are available for monitoring.
The data acquisition is accomplished using LABVIEW (National Instruments) on a personal computer. The pressure difference across the contraction is measured using an electronic manometer and serves as a reference for the flow in the test section. The tunnel temperature is monitored using a thermocouple mounted on the south wall. Since there is no provision for cooling, the tunnel must be allowed to come to thermal equilibrium before data acquisition. This is not a serious concern at low speeds; however, the temperature rise in the tunnel can be as high as 15 degrees Celsius above the ambient at high speeds.
In 1936, the wind tunnel was constructed as a WPA project with an initial air speed of 250 mph. It was a recirculating design with water-cooled straightening vanes and powered with a natural gas two-cylinder oil field engine. After WW II, this was replaced with a surplus Allison V-1710 engine from a P-38. In the 1960s, an electric motor and a variable pitch propeller replaced the internal combustion engine.
The original WPA project provided a brick building constructed as part of the tunnel. This included a room for the power source, a room for the test section and instrumentation, and a second story classroom used for lectures and data reduction. The initial design of the tunnel was done as a master's thesis by P. O. Tauson under the direction of Professor L. A. "Doc" Comp.
Professor Comp also later designed the balance system, providing measurements of lift, drag, and moments of pitch, roll, and yaw. In addition to its primary role as an instructional tool, this wind tunnel has been used in support of several industry contracts. All of the original aerodynamic studies for the Aero Commander series of twin-engine propeller-driven executive aircraft were conducted in this tunnel. Later it was used for low-speed aerodynamic studies of lifting body vehicles for the Martin Company.
The tunnel, with an updated digital data acquisition system, was officially named the L. A. Comp Wind Tunnel in 1978.