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68 PERFORMANCE, STABILITY, DYNAMICS, AND CONTROL
induced- drag term CD, iS primarily the drag due to lift. However, it also includes
those parts of the skin-friction and pressure drag that vary with angle of attack
The induced-drag parameter k in Eq. (2.2) is given by
~
. 1
k - - (2.4)
:rre A
For finite wings, e is the wing planform e:fficiency factor. For elliptical wing
planform, a - 1. In other words, for a given aspect ratio A, the induced drag
is a minimum for an elliptical wing. However, for the complete airplane, the
definition of e is modified to include the variation of skin-friction and pressure
drag coefficients with angle of attack andis called the Oswald's efficiency factor.
Generally, two types of powerplants are commonly used on modern airplanes,
1) the piston engine-propeller combination or the piston-prop and 2) the tur-
bojeL Piston-props are widely used on light general aviation airplanes, whereas
jet engines are used for commercial transport and rrulitar}r aircraft. In view of
this, the performance analyses presented mt'this text will be based on these two
types of powerplants. We will be referring to an airplane with a piston-prop pow-
erplant as a propeller airplane and that with a turbojet powerplant as ajet air-
plane.
v"The propulsive characteristics of the propeller airplane are normally given
in terms of the power developed by the reciprocating (piston) engine ancl the
propulsive efficiency of the engine3ropeller combination. The power available
for propulsion is th:eYproduct of the power developed by the reciprocating (piston)
engine and the propulsive efficiency ofthe engine-propeller combination. Because
of this, it is common practice to analyze the performance problems of a propeller
airplane in terms of the power available and the power required. The power re-
quired is the power necessary to overcome the aerodynamic drag of the airplane.
In this text, we will use kW as the unit of power and denote the power developed
by the engine in kW using the notation P[kW).
The propulsive characteristics of the jet airplane are normally specified in terms
ofthe t~rust produced by thejet engine, which is referred to as the thrust available.
Hence, the performance characteristics of the jet airplane are usually discussed
in terms of the thrust available and the thrust required. The thrust required is the
thrust necessary to balance the aerodynamic drag of the airp.lane.
The specific fuel consumption of a propeller airplane is the weight of fuel
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