Helicopter Abbreviations and Symbols

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


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