This method prevents any movement which might cause the propeller to strike the wall. The driven pully on the shaft is carried between the two outside bearings. The end bearing is used to carry the propeller thrust as well as part of the radial load from the belt and pulley, the other bearings being free to move axially. The speed range of the tunnel is from 0 to 150 miles per hour, but for most routine work a speed of 100 miles per hour is the maximum used. A vibration point occurs at 36 miles per hour.
Air speed is measured by two methods.
A pitot-static tube was used first to explore the test section to determine the quality of the air flow. Leads from the static and dynamic tubes are connected to an inclined differential manometer graduated to read to 0.01 inch of water. The calibration of the tube and manometer includes a correction for compressibility of air. Readings of the manometer are taken directly and referred to a curve which gives the corrected air velocity in feet per second. Instrumentation Pressures are measured in the tunnel are measured using a traditional manometer board.