The stability of a helicopter rotor in forward flight depends on several factors such as aerodynamics, blade structural
parameters, and control inputs. In high speed forward flight, most of the blade sections encounter three-dimensional
effects due to the radial component of relative air velocity. These three-dimensional effects can have a significant
influence on the airfoil aerodynamic characteristics depending on the angle of attack of the blade section and hence
can affect the stability of rotorcraft. The effect of yawed flow on lead-lag mode damping of an isolated rotor in
forward flight is investigated in this work. The damping results are also correlated with existing experimental data.
Correlation results improve at high advance ratio when yawed flow effects are included in the aerodynamic model.
When linearized, the forward flight system is periodic corresponding to rotation frequency of the blades, and stability
computations hence rely on Floquet theory. Floquet transition matrix (FTM) is usually estimated by integrating
the linearized system of equations using n (number of states) independent initial conditions. The stability of the
rotor is then evaluated from the eigenvalues of FTM. The limitation of this classical approach are 1) Integrating

with an optimization problem, 2) Using time-varying control inputs, 3) Huge computational cost to estimate Flo-
quet eigenvector for mode identification as well as a periodic control application. Stability and trim analysis based

on the pseudospectral method are demonstrated for rotorcraft analysis to address above limitations. Further, the
framework is adapted to include concept of fast-Floquet which relies on blade-to-blade symmetry to further improve
the computational efficiency. For rotors operating in low air density (like that of Mars), the aerodynamic damping
experienced by blades is significantly reduced. Hence it becomes important to estimate the operating forward speed
of rotorcraft with stability as a constraint during design stage. The pseudospectral framework described above is
utilized for solving the above optimization problem. Experimental work is also carried out on a rotor fixed to a test
stand inside a low-density chamber to simulate hover condition. The purpose of the experimental work is to validate
the basic blade aerodynamic model in hover, which is used for rotorcraft forward flight stability studies.