Normal Cruise - Mohsen Hamedi

Specific Air Range (SAR)

The air distance travelled per unit of mass of fuel during steady state and level flight cruise condition, and is independent of wind speed.

(1) $\begin{equation*}SAR = \frac{TAS~[knots]}{fuel~flow~[lb/hr]},\end{equation*}$

where $TAS$ is the true air speed.

Specific Range (SR)

The SR is similar to SAR, but in terms of ground speed. Thus,

(2) $\begin{equation*}SR = \frac{ground~speed}{fuel~flow}.\end{equation*}$

Cruise Range (CR)

Cruise range is defined as the air distance traveled while burning a given quantity of fuel.

(3) $\begin{equation*}CR = SAR_{avg} (W_1 - W_2) ,\end{equation*}$

where $W_1$ is the weight at the beginning of cruise segment in $lb$ , and $W_2$ is that at the end of cruise segment. In other words, $W_1-W_2$ is equal to the amount of fuel burnt during the cruise segment.

Maximum Range Cruise (MRC)

During flight at constant altitude, range can be maximized (or fuel burn minimized for a given range) by flying at a Mach number for maximum SAR, referred to as maximum range cruise Mach number. MRC speed, is the speed that will provide the furthest distance traveled for a given amount of fuel burned and the minimum amount of fuel burned for a given cruise distance.

Long Range Cruise (LRC)

Long range cruise speed is defined as the speed above maximum range that will result in a $1%$ decrease in fuel mileage in terms of $nm/kg$ or $nm/lb$ . LRC speed provides $2-3%$ faster cruise speed with sacrificing $1%$ of the range.

Endurance

The maximum length of time that an aircraft can spend in cruising flight. Or, the amount of time an aircraft can stay in the air with one load of fuel. Hence, the maximum endurance flight condition of a jet is at the minimum drag condition.