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

Abstract

Flight and aerodynamics laboratory experiences have supported the aeronautical engineering courses in the United States Military Academy’s mechanical engineering program for over 50 years. Whirl stands are the rotary-wing equivalent of wind tunnels; they are used to generate experimental data on small- or full-scale rotor systems. The helicopter whirl stand laboratory is a cornerstone event in the program’s Helicopter Aeronautics course, used to reinforce students’ understanding for predicting and calculating hover performance data. The experimental apparatus includes a remote control (RC) helicopter mounted to a static test stand, instrumented with load cells to measure lift and torque. The helicopter is capable of varied revolutions per minute (RPM) and collective blade pitch. Control of the apparatus and measurement readings occur from behind a protective wall with an observation window. The objective of the laboratory is to compare the results of predictive analyses, conducted using Blade Element Theory (BET) and Blade Element Momentum Theory (BEMT), to experimental data. Students calculate the coefficient of thrust based on collective pitch angles and atmospheric conditions using an iterative approach in numerical analysis software. A recent effort appreciably improved the lab by adding two experimental twisted-blade cases in addition to the original untwisted blades. The ability to change between the original and updated (twisted) blades offers insight into the advantages and disadvantages of each in hover. The upgraded blades were designed internally by students to match the original rotor diameter, outsourced for precision manufacturing, and tested for incorporation into the laboratory. Overall, the upgraded laboratory offers a relevant, comprehensive application to deepen students’ conceptual understanding of rotorcraft aerodynamics, laboratory procedures, and modeling principles taught in the course.