Help understanding incedence

[zbrubaker]

What effect does the incedence of the wing/airfoil have on flight characteristics/performance? How do you determine the incedence of the wing/airfoil? Are there any 'rules-of-thumb' for deciding on the incedence when designing a model?

[Ollie]

No effect does the incedence of the wing/airfoil have on flight characteristics/performance. Are no any 'rules-of-thumb' for deciding on the incedence.

[zbrubaker]

I guess I should clarify this a bit, my fault for being vague. Wing incedence relative to the tail (horizontal) incedence and visa-versa. Also wing incedence relative to the thrust line.

[Ollie]

Three Contributions to Angle of Attack
As mentioned earlier, it is difficult to directly perceive angle of attack. Fortunately, there are three other quantities that can be perceived, and together they determine the angle of attack. They are:

Pitch attitude, which is defined4 to be the angle that the fuselage makes relative to the horizontal.
Angle of climb, which is just the angle between the flight path and the horizontal.
Angle of incidence, which is the angle at which the wings are attached to the fuselage.
These quantities are related to the angle of attack by a very simple formula:



Pitch Attitude + Incidence = Angle of Climb + Angle of Attack


This relationship is illustrated in figure 2.2. Perhaps the simplest case is straight and level flight at cruise airspeed. In this case, the pitch attitude is zero, the angle of climb is zero, and the angle of attack is equal to the angle of incidence. Some more examples, with specific numbers for a typical airplane, are included in table 2.1.



Figure 2.2: Pitch + Incidence = Climb + Attack

Extending the flaps has the effect of increasing the incidence5 by several degrees. You need to be always aware of what flap setting you are using, and to recognize the distinction between “pitch attitude” and “pitch attitude plus incidence”. For any given flap setting, you can take the incidence to be constant, whereupon angle of attack depends only on pitch attitude and direction of flight.

The table mentions VX and VY, which denote the airspeeds for best angle of climb and best rate of climb, respectively, as discussed in section 7.5. The relationship of airspeed to angle of attack will be discussed in section 2.12.