Performance Factors (continued)
Another way that designers help you out is by carefully selecting wing camber. I can’t get into too much detail here because I’m not an aeronautical engineer, but I can give you a general idea of how the camber affects lift.
For a VERY basic understanding, lets compare the wings of a trainer, with those of a supersonic jet.
The wing on the left is that of a F104 Starfighter, capable of reaching speeds of Mach 2, and on the right is a run-of-the-mill Cessna (it’s a 177), capable of 140 knots on a good day. Notice the chord difference. The Starfighter’s wing is EXTREMELY thin in comparison – the air has a shorter distance to travel around the wing and less of a pressure drop is created.
To keep from stalling, the Starfighter has to be flown very quickly – it’s stall speed is roughly 200 knots, while the Cessna will stall at around 50 knots.
So why don’t all airplanes have big fat wings? When a wing generates lift, it also generates Induced Drag (remember that article?). If the wing is too good at producing lift then at higher speeds it will create so much drag (drag quadruples when you double your speed) that the shape becomes problematic.
Dihedral affects lateral stability (roll). The more dihedral you have (to a point, obviously), the more of a tendency the airplane is going to have toward rolling wings level. The opposite is true as well – except that negative dihedral is called anhedral. An unstable airframe is favored in situations where agility is required (this is also why fighters have an aft CG).
In the next section we’ll look at wing shapes.