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Unformatted text preview: AA 311 Lecture 16: Range and Endurance Reading:  Chapter 6.12-6.13. Two important concepts in aircraft performance are range and endurance. Roughly speaking, range of an airplane is the distance it can cover on a tank of fuel, and endurance is the time it can stay in the air on a tank of fuel. Cruise flight begins at the end of the climb phase when the airplane has reached the desired altitude, and cruise flight ends when the descent phase begins. For a given amount of fuel load, the horizontal distance covered with respect to the ground during the cruise flight is called cruise range and does not include any distance covered during the climb or descent. Here, the term range refers to the cruise range. Range is an important performance measure for commercial transport airplanes like the Boeing 747 or Airbus 320. Range is also important for military bombers like the B-52 or the B-1. From physical considerations, the range will be maximum when the airplane cruises at that velocity when the ratio of velocity to fuel consumed per unit time is maximum. Endurance is the total time that an airplane can remain in the air for a given fuel load and is usually expressed in hours. The endurance is an important performance measure for reconnaissance or surveillance airplanes. It is also of interest to all aircraft during the loiter, which is defined as that phase of flight where the primary aim is to remain airborne and not worry about the ground distance covered. Long-range bombers like the B-52 or the B-1 may loiter while on an airborne alert. A fighter aircraft on a combat air patrol mission loiters while guarding the airspace from intruding aircraft. When the primary aim is to be airborne, the aircraft is essentially in level flight, and it will fly at that speed when the fuel consumed per unit time is a minimum. Recall that the two most commonly used propulsion systems (reciprocating engine - propeller configuration; and jet engine) usually have different specifications. For propeller airplanes the available power stays roughly constant, hence they are rated in terms of power, usually Watts (W) or horsepower (hp). Jet engines are rated in terms of available thrust, usually in Newtons (N) or pounds (lbs). Another important specification relating to engines is the fuel consumption, which is generally specified in weight of fuel used per unit time. For a constant power aircraft the power-specific fuel consumption (PSFC) is weight of fuel consumed per unit time per unit power: c p =- W P , where W is the weight of the aircraft, W = dW/dt is the time rate of change of weight, and P is the power developed by the reciprocating engine. Usually the power available for propulsion is less than the power developed by the engine due to dissipation and inefficiencies of the propeller. Hence P A = P, (1) where is the propeller efficiency, < 1, and the power developed by the reciprocating engine is sometimes called the shaft brake power (see Figure 1). Note that specific fuel consumption is usually specified as(see Figure 1)....
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This document was uploaded on 02/05/2012.
- Fall '09