Evaluation of High-Angle-of-Attack Aerodynamic-Derivative Data and Stall-Flutter Prediction Techniques
Abstract
The problem of stall flutter is approached in two ways. First, using the M.I.T.-NACA airfoil oscillator, the aerodynamic reactions on wings oscillating harmonically in pitch and translation in the stall range have been measured, evaluated, and correlated where possible with available published data, with the purpose of providing empirical information where no aerodynamic theory exists. The major effects of Reynolds number, airfoil shape, and reduced frequency on the aerodynamic reactions have been reaffirmed. No instances of negative damping were observed in pure translatory motion and the ranges of negative damping occurring in pure pitch had the same general trends noted by other experimenters. Data on the time-average values in the stall range of both lift and moment are presented for the first time. Second, the results of numerous experimental observations of stall flutter have been reviewed and the various known attempts at its prediction have been examined, compared, and extended. The sharp drop in critical speed and change to a predominantly torsional oscillation usually associated with the transition from classical to stall flutter is apparently primarily but not entirely caused by the marked changes in moment due to pitch. Fairly good stall-flutter predictions%have been reported only when adequate empirical data for this aerodynamic reaction happened to be available for the desired airfoil shape, Reynolds number range, and reduced-frequency range. A semiempirical method of predicting the variations of moment in pitch with airfoil shape, reduced frequency, initial angle of attack, and amplitude of oscillation has been presented.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 1951
- Accession Number
- ADA380217
Entities
People
- H. C. Johnson
- Robert L. Halfman
- S. M. Haley
Organizations
- National Aeronautics and Space Administration