M.Sc Thesis


M.Sc StudentAlon Maayan
SubjectThe Effect of Fineness Ratio on the Pitch Damping Derivative
DepartmentDepartment of Aerospace Engineering
Supervisors Professor Arieli Rimon
Professor Iosilevskii Gil
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Dynamic wind tunnel tests were conducted in order to investigate the effect of fineness ratio on the pitch damping sum. The test apparatus enables a single degree of freedom, unforced oscillatory pitch rotation. The research configurations were composed of a cylindrical body, a conical nose and tail fins, at subsonic Mach number. For fineness ratio of 2, near zero angle of attack, the oscillation amplitude did not decay and limit cycle oscillations appeared. When the oscillation average angle of attack was not zero, the amplitude exhibited an exponential decay. It appears that limit cycle oscillations are generated due to a positive sign of the pitch damping sum, a dynamic behavior that corresponds to the Van Der Pol equation. Comparison between test results of the pitch damping sum and slender body theory expressions shows, as expected, that for a decrease in fineness ratio there is a decrease in the resemblance. For engineering purposes, it seems that even at a low fineness ratio of 3, the slender body theory approximation can still be useful, but it does not predict the sign change of the pitch damping sum at a fineness ratio of 2. Small sensitivity was found to changes in Reynolds number, roll orientation and nose length.