Performance evaluation of an OH-58A+ with Dimpletape installed

This flight test investigates the performance benefits of a recently developed vortex generator, called Dimpletape®, on an OH-58A+ helicopter rotor blade. This product employs the aerodynamic concepts that are used to reduce the drag on a golf ball. The manufacturer claims significant performance benefits with the product applied to airplane wings and propellers; however, no flight-testing has been conducted on commercial helicopter rotor blades. Four different Dimpletape® lengths where flight-tested on an OH-58A+ to determine the optimum Dimpletape® length and cordwise placement on the main rotor blades for the greatest performance gain. The flight-testing consisted of a quantitative performance evaluation including hover performance (free hover method), level flight performance (W/δ, weight over density ratio test method), and autorotative performance flight tests. The flight test results show that there is an insignificant reduction in power when Dimpletape® is applied to the outboard 10% (19.5 inches) of the rotor blade at the maximum camber point (optimum Dimpletape® length and position tested). In most of the tests Dimpletape® increased the power requirements of the rotor system. Within the scope of these tests the author has concluded that for the given aircraft main rotor blade airfoil there is no significant performance gain with the use of Dimpletape®. The author makes the following recommendations: 1. Do not consider Dimpletape® for operational use on rotary wing aircraft. 2. Do not perform any further testing of Dimpletape® on rotary wing aircraft.