Design and Testing of a Small, Semi-span, Prop-rotor Model for Whirl Flutter Stability

Open Access
Johnson, Samuel Craig
Graduate Program:
Aerospace Engineering
Master of Science
Document Type:
Master Thesis
Date of Defense:
Committee Members:
  • Edward Smith, Thesis Advisor
  • tiltrotor
  • wind tunnel
  • testing
  • whirl
  • flutter
  • stability
Modern tiltrotor aircraft are capable of ecient hover as well as high-speed forward ight. The large, exible rotors required for good hover performance make this type of aircraft susceptible to an aeroelastic instability in high speed forward ight known as whirl utter. High rotor in ow may result in negative aerodynamic damping that is great enough to cause the coupled wing, pylon, and rotor system to be unstable. Traditionally, thick, sti wings have been used to avoid such situations; however, if eciency and top speed are to be improved, new methods must be employed. Wind-tunnel testing is a crucial part of understanding the phenomenon and testing new concepts. The current study has focused on developing a test platform that can be used to inexpensively and quickly test whirl utter stability. A small, wind-milling model was designed, fabricated and dynamically tested in the Penn State 2-foot by 3-foot wind-tunnel facility. Several con gurations were tested for beam-wise modal damping variations with wind speed. Changes due to aerodynamic e ects were clearly visible and one con guration exhibited whirl utter at 110 ft/s. In-house computer codes were used to generate theoretical predictions and compared with the experimental results. Good correlation was achieved for stable con gurations; however, the unstable con guration proved dicult to match. This is perhaps due to sections of the untwisted blades encountering high angles of attack and thus deviating from the linearized theory used in the computational code. The equipment, procedures, and computational tools are in place and have proven that whirl utter tests at very small scale are indeed possible. Future models should focus on more accurate scaling of full-size vehicles and avoid nonlinear aerodynamic e ects on the rotor.