Aerodynamics and Design for Ultra-Low Reynolds Number Flight

Chapter 5
The test fixtures for measuring thrust consist of an aluminum bar with a motor-mount on
one end and a contact point for an electronic two milligram-accurate balance on the
other. It is supported at near mid-span by a shaft and ball-bearings, providing a single
axis of rotation. Upward thrust is transferred to a downward force on the balance that
can be read directly, then converted to the thrust value by the ratio of the moment arms.
Two fixtures have been fabricated to cover a wider range of rotor sizes.
The smaller set of test equipment, configured for thrust measurement, is pictured in
Figure 5.5. Rotor torque for larger rotors may be measured by mounting the rotor and
motor to the shaft of the balance bar with the rotor axis of rotation parallel to the shaft.
The registered force on the balance is converted to a torque across the moment arm from
the balance contact point to the aluminum bar’s axis of rotation. This configuration is
shown in Figure 5.6.
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