By Jim Davis    2021-03-12

Helicopter Abbreviations and Symbols

The following abbreviations and symbols are used in articles throughout this website.  These are mostly consistent with other helicopter literature.

 $$\alpha$$ angle of attack of the fuselage, rotor plane or a blade section depending on the context A rotor area AFCS automatic flight control system $$\beta$$ sideslip angle or blade flapping angle $$\beta_C$$ main rotor longitudinal flapping $$\beta_S$$ main rotor lateral flapping $$C_L$$ roll moment coefficient ($$L/\rho AR(\Omega R)^2$$) $$C_M$$ pitch moment coefficient ($$M/\rho A R(\Omega R)^2$$) $$C_T$$ rotor thrust coefficient ($$T/\rho A (\Omega R)^2$$) CCW counterclockwise CW clockwise D drag force F force GW gross weight $$\lambda$$ rotor inflow ratio (($$V\sin \alpha + v)/\Omega R$$) L lift force LZ landing zone $$\mu$$ rotor advance ratio ($$V\cos \alpha /\Omega R$$) $$m$$ mass M pitch moment N yaw moment NR main rotor speed as a percent of nominal speed $$\Omega$$ main rotor speed $$\phi$$ Euler roll angle $$\psi$$ Euler yaw angle $$\Psi$$ main rotor azimuth angle $$p$$ body roll rate $$q$$ body pitch rate $$r$$ body yaw rate $$\rho$$ air density $$r$$ distance of blade section from rotor center R main rotor radius SAS stability augmentation system T rotor thrust TAS true airspeed $$\theta$$ Euler pitch angle $$\theta_0$$ collective control angle $$\theta_C$$ lateral cyclic blade angle $$\theta_S$$ longitudinal cyclic blade angle $$u$$ body axis forward velocity $$v$$ body axis lateral velocity $$V$$ total velocity of air relative to helicopter or rotor $$v_i$$ rotor-induced velocity $$w$$ body axis vertical velocity $$y$$ out-of-plane displacement of a blade section

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