<p>Flight and aerodynamics laboratory experiences have supported the United States Military Academy’s aeronautical engineering program for nearly 50 years. Whirl stands are the rotary-wing equivalent of wind tunnels and are used to generate experimental data on small scale or full-scale rotor systems. They may be used in conjunction with wind tunnels to simulate forward flight, or, as in our case, they may stand alone to simulate hover conditions. A recent effort revitalized and significantly improved the helicopter whirl stand laboratory, a system originally used for predicting and calculating hover performance data in the program’s Helicopter Aeronautics course. The experimental apparatus includes a remote control (RC) helicopter with two 24.5-inch untwisted rotor blades giving the disk a 53-inch diameter. The blades have a 4-inch root cut out and a 2.1-inch rectangular chord. The RC helicopter is mounted to a static test stand placing the rotor 85 inches vertically from the floor and is instrumented with load cells to measure lift and torque. Control of the apparatus and measurement readings occur from a control station on the opposite side of a protective wall with an observation window. The helicopter is capable of varied RPM (operating at a nominal 1000 RPM) and collective blade pitch (with measurements taken from zero to 15 degrees in three-degree increments). Additional equipment includes a thermometer and barometer to characterize the air density. The objective of the laboratory is to compare the results of predictive analysis conducted using blade element theory (BET) and blade element momentum theory (BEMT) with experimental data. Students calculate the coefficient of thrust based on collective pitch angles and atmospheric conditions using an iterative approach in MATLAB. In the prediction, students assume uniform inflow and model the blades as if they had an ideal twist. Students further modify their code to account for non-uniform inflow using blade element momentum theory (BEMT) to calculate theoretical thrust and coefficient of thrust, iterating to converge on a solution. In calculating the BET prediction and comparing to the results, students often encounter discrepancies between the actual lab apparatus with untwisted blades and the assumption of an ideal twist in calculating the predicted performance metrics. The improved laboratory offers a comparison between newly designed and manufactured RC blades that incorporate an ideal twist. The new blades were designed in-house by students, laser cut from foam, and carbon fiber wrapped to match the original blade dimensions with the addition of the ideal twist. The ability to change between original untwisted blades and those with an ideal twist offers insight into the advantages and disadvantages of each in hovering flight while minimizing sources of discrepancies with students’ calculations using BET. Demonstrating the ability to change the rotor blade dimensions on apparatus further offers the possibility for more in-depth independent studies of unique airfoil shapes and designs in hovering flight. Overall, the upgraded laboratory offers a relevant, comprehensive application to deepen students’ conceptual understanding of rotorcraft aerodynamics, laboratory procedures, and modeling and similarity principles.</p>

Incorporation of Blade Twist and Non-Uniform Inflow Effects In Undergraduate Helicopter Aeronautics Whirl Stand Laboratory

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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