A Preliminary Theoretical Study of Aerodynamic Instability of a Two-Blade Helicopter Rotor
Abstract
A theory has been developed in preliminary form which seems capable of predicting the aerodynamic instability phenomena of a two-blade see-saw-type helicopter rotor. In particular, the theory indicates the possibility of unstable vibrations even with the chordwise center of mass at or ahead of the 25-percent-chord position. The stability condition for oscillatory motion is expressed in terms of a small number of composite parameters that are evaluated from the moments of inertia, angle settings, and aerodynamic parameters of a blade. Computed stability results for different coning angle settings, center-of-mass positions, and control-system stiffnesses for one value of blade density and aspect ratio are presented in a chart. It is found that, in addition to parameters analogous to those occurring in wing-flutter theory, the present theory contains a parameter that represents an unstabilizing effect due to the difference between the moments of inertia in flapping and in rotation.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 18, 1947
- Accession Number
- ADA801430
Entities
People
- Carl W. Stempin
- Robert P. Coleman
Organizations
- National Advisory Committee for Aeronautics