Hood Tech Mechanical developed and maintains a quiet wind tunnel (per MILSTD1474), which is used to measure engine and propeller noise, and the thrust, of small- to medium-sized unmanned aircraft.  The wind tunnel delivers a three- foot-diameter (0.9m-diameter) column of air at up to 100 knots.  Its length (approximately 300 meters), and the flexible tubing which allows over-the-hill separation of blower from tunnel outlet, isolate the propulsion noises of the tunnel from the test area, and its rural setting reduces interference from competing sounds.

The Hood Tech Mechanical quiet wind tunnel employs a long flexible tube to deliver silent airflow from the muffled blower.  Test data confirm that the wind tunnel meets MILSTD1474.

Wind Tunnel Specifications
Power Whisperwatt 100kVA 480VAC 3PH (behind hill)
Fan 100 HP squirrel cage with vernier damper adjust
Duct 6-foot x 1000 ft soft plastic
Nozzle Tapers to 3 ft diameter
Airspeed 0-50m/s (0-97 knots)
Thrust measurement resolution 0.3 Newton

The wind tunnel has also been used to simulate the in-flight effects of rain, proving very useful for rapid design of improved moisture seals for aircraft payload and nose cone.  Finally, a pendulum structure is used to determine the thrust of a UAS by matching with wind speed, providing thrust measurements precise to within 0.3 Newton.

Thrust Measuring Pendulum

The tunnel also functions to test the thrust of aircraft.  The pendulum system shown in the drawing above measures thrust to within 0.3 Newton resolution.