Space Metal Fabricators of Columbia, South Carolina, and Mitutoyo America Corporation have jointly developed a tool to help helicopters fly smoother.
While flying, helicopters generally experience a low frequency vibration in the main rotor blades. This is due, in part, to slight differences in each blade’s aerodynamics. These vibrations are not likely to cause structural damage but may adversely affect electronics; they also absorb power.
To dampen vibration, some main rotors incorporate trim tabs located on the blades’ trailing edges which can be adjusted to keep blades rotating smoothly. Some systems incorporate electronic, in-flight rotor track-and-balance systems that provide information used to adjust the pitch of the tabs. Specialized tools then are used to physically bend the tabs.
Besides in-flight indication, tab adjustment may result from preventive maintenance routines. Due to the frequency of these adjustments, a helicopter operator asked Space Metals to develop a tool to improve productivity of the procedure. According to Keith Berry, Senior Engineer, Space Metal Fabricators, “We developed a trim tab bender tool consisting of three components: a measuring device utilizing a custom-built Mitutoyo dial indicator, a tab bender and a gage plate. In operation, the device is mounted to the gage plate for calibration to zero. Next the zeroed-out tool is mounted to the rotor blade. (See Fig. 1) Then, the tab bender is used to set the correct trim as expressed by the dial indicator measuring displacement in degrees.”
Commenting on the indicator design, Pat Harkness, Product Specialist, Mitutoyo America, said, “The indicator’s zero-setting needed to be the mid-point from which the tab would be displaced in either a positive or negative direction. So we designed a gear ratio to match expected displacement – in either direction – plus an indicator face marked in ± degrees. (See Fig. 2)
Fig. 1
Fig. 2