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The maximal total range is the maximum distance an aircraft can fly between takeoff and landing, as limited by fuel capacity in powered aircraft, or cross-country speed and environmental conditions in unpowered aircraft. The range can be seen as the cross-country ground speed multiplied by the maximum time in the air. The fuel time limit for powered aircraft is fixed by the fuel load and rate of consumption. When all fuel is consumed, the engines stop and the aircraft will lose its propulsion. Ferry range means the maximum range the aircraft can fly. This usually means maximum fuel load, optionally with extra fuel tanks and minimum equipment. It refers to transport of aircraft without any passengers or cargo. Combat range is the maximum range the aircraft can fly when carrying ordnance. Combat radius is a related measure based on the maximum distance a warplane can travel from its base of operations, accomplish some objective, and return to its original airfield with minimal reserves.

Derivation

For most unpowered aircraft, the maximum flight time is variable, limited by available daylight hours, aircraft design (performance), weather conditions, aircraft potential energy, and pilot endurance. Therefore, the range equation can only be calculated exactly for powered aircraft. It will be derived for both propeller and jet aircraft. If the total mass W of the aircraft at a particular time t is: W = W_0 + W_f, where W_0 is the zero-fuel mass and W_f the mass of the fuel (both in kg), the fuel consumption rate per unit time flow F (in kg/s) is equal to -\frac = -\frac. The rate of change of aircraft mass with distance R (in meters) is \frac=\frac= - \frac, where V is the speed (in m/s), so that \frac=-\frac It follows that the range is obtained from the definite integral below, with t_1 and t_2 the start and finish times respectively and W_1 and W_2 the initial and final aircraft masses R= \int_^ \frac dt = \int_^ -\fracdW =\int_^\fracdW \quad\quad (1)

Specific range

The term \frac, where V is the speed, and F is the fuel consumption rate, is called the specific range (= range per unit mass of fuel; S.I. units: m/kg). The specific range can now be determined as though the airplane is in quasi steady-state flight. Here, a difference between jet and propeller driven aircraft has to be noticed.

Propeller aircraft

With propeller driven propulsion, the level flight speed at a number of airplane weights from the equilibrium condition P_a = P_r has to be noted. To each flight velocity, there corresponds a particular value of propulsive efficiency \eta_j and specific fuel consumption c_p. The successive engine powers can be found: P_=\frac The corresponding fuel weight flow rates can be computed now: F=c_p P_ Thrust power, is the speed multiplied by the drag, is obtained from the lift-to-drag ratio: P_a=V\fracWg ; here ''Wg'' is the weight (force in newtons, if ''W'' is the mass in kilograms); ''g'' is standard gravity (its exact value varies, but it averages 9.81 m/s2). The range integral, assuming flight at constant lift to drag ratio, becomes R=\frac\frac\int_^\frac To obtain an analytic expression for range, it has to be noted that specific range and fuel weight flow rate can be related to the characteristics of the airplane and propulsion system; if these are constant: R=\frac \frac \ln \frac

Electric aircraft

An electric aircraft with battery power only will have the same mass at takeoff and landing. The logarithmic term with weight ratios is replaced by the direct ratio between W_/W_ R=E^* \frac \eta_ \frac \frac where E^* is the energy per mass of the battery (e.g. 150-200 Wh/kg for Li-ion batteries), \eta_ the total efficiency (typically 0.7-0.8 for batteries, motor, gearbox and propeller), L/D lift over drag (typically around 18), and the weight ratio \frac typically around 0.3.https://www.mh-aerotools.de/company/paper_14/09%20-%20Electric%20Flight%20-%20Hepperle%20-%20DLR.pdf

Jet propulsion

The range of jet aircraft can be derived likewise. Now, quasi-steady level flight is assumed. The relationship D=\fracW is used. The thrust can now be written as: T=D=\fracW ; here ''W'' is a force in newtons Jet engines are characterized by a thrust specific fuel consumption, so that rate of fuel flow is proportional to drag, rather than power. F=c_TT=c_T\fracW Using the lift equation, \frac\rho V^2 S C_L = W where \rho is the air density, and S the wing area. the specific range is found equal to: \frac=\frac \sqrt Inserting this into (1) and assuming only W is varying, the range (in meters) becomes: R=\frac \sqrt\int_^\frac dW ; here W is again mass. When cruising at a fixed height, a fixed angle of attack and a constant specific fuel consumption, the range becomes: R=\frac \sqrt \left(\sqrt-\sqrt \right) where the compressibility on the aerodynamic characteristics of the airplane are neglected as the flight speed reduces during the flight.

Cruise/climb

For long range jet operating in the stratosphere (altitude approximately between 11 and 20 km), the speed of sound is constant, hence flying at fixed angle of attack and constant Mach number causes the aircraft to climb, without changing the value of the local speed of sound. In this case: V=aM where M is the cruise Mach number and a the speed of sound. W is the weight in kilograms (kg). The range equation reduces to: R=\frac\frac\int_^\frac where a= \sqrt ; here R_sis the specific heat constant of air 287.16 \frac (based on aviation standards) and \gamma = 7/5 = 1.4 (derived from \gamma=\frac and c_p=c_v+R_s). c_p and c_v are the specific heat capacities of air at a constant pressure and constant volume respectively. Or R=\frac\fracln\frac, also known as the ''Breguet range equation'' after the French aviation pioneer, Breguet.

See also

* Flight length * Flight distance record * Endurance

References

* G. J. J. Ruijgrok. ''Elements of Airplane Performance''. Delft University Press. {{ISBN|9789065622044.
Prof. Z. S. Spakovszky


' MIT turbines, 2002 * Martinez, Isidoro.
Aircraft propulsion. Range and endurance: Breguet's equation
' page 25. Category:Aeronautics