In Fig. 4.6 a schematic diagram of the entire airplane in steady level flight is shown. The lift balances the weight of the plane, while the thrust balances the drag.
Figure 4.6: Forces acting upon the entire airplane.
We see that
Modern commercial jets have 
; the precise value depends
on the wing design and the specific performance criteria.
What about stability? The resultant aerodynamic force, usually denoted 
, engages the plane at the center of pressure . Gravity acts at the center of gravity (or the center
of mass) of the plane. The relative positions of these two points
determines the stability of the plane. Having the center of pressure
ahead of the center of gravity leads to stable flight, while putting the
center of gravity ahead produces unstable flight.
Propellers and jets
Please read Section 7.5 of Melissinos. See also Sections 9.1-9.7 in Introduction to Flight by J. D. Anderson, which is on reserve.
