Burt Rutan's White Knight and SpaceShip One, Photo Courtesy of Scaled Composites
Thermodynamics and Propulsion

13. Aircraft Performance

In this chapter we will make the connections between aircraft performance and propulsion system performance. For a vehicle in steady, level flight, as in Figure 13.1, the thrust force is equal to the drag force, and lift is equal to weight. Any thrust available in excess of that required to overcome the drag can be applied to accelerate the vehicle (increasing kinetic energy) or to cause the vehicle to climb (increasing potential energy).

Figure 13.1: A schematic of the forces on an aircraft in steady level flight
Image fig5BreguetFreeBodyDiagram_web

$\displaystyle T = D, \qquad L = W$    

$\displaystyle W = L = D\frac{L}{D} = T\left(\frac{L}{D}\right)$