Chapter 4: The High-Speed Propeller Program
[129] Both the 200-hp emergency propeller dynamometer and the 2000-hp dynamometer were underpowered for many of the desired high-speed testing conditions. It was for this reason that the bulk of the testing was carried out with two-blade propellers. It occurred to me in 1945 that we could double the power loading of our test blades if a one-blade propeller could be made to work; that is, we could obtain the same blade operating conditions as for a two-blade 10-foot propeller absorbing 4000 hp. As time permitted, I analyzed the balancing problems of articulated counter-balanced one-blade propellers in sufficient depth to convince myself that they were feasible and practical and they were added to our program. Tests with the one-blade propellers showed more vibration than the two-blade propellers because of their unbalanced aero-dynamic loads but these were not excessive and did not affect the propeller data (ref. 151). The one-blade propellers (fig. 32) were used principally in the pressure-distribution programs (ref. 149), and in a few cases, additional force tests were made after the tubes had been removed and the grooves filled.
The measurement of blade deflections in these tests, and in general....

photo of 1 blade propeller
[130] FIGURE 32.-The one-blade, 10-foot-diameter propeller.
....the measurement of torsional deflections of thin-bladed propellers, is often required. An optical system for such measurements, developed by Corson in the PRT in 1940, was used in the 16-foot tunnel program (ref. 152). Torsional deflections were applied in the angle of attack determinations needed for the analysis of pressure distribution and other propeller test results.