2
$\begingroup$

The Angle of Incidence (AoI) of most GA planes is 6°. During takeoff, the Angle of Attack (AoA) is often 11° or more; does the 11° AoA include the initial 6° AoI in it i.e, 11 - 6 = 5 ? Meaning the deflection for takeoff will be 5° (plus 6° of incidence)?

What I am asking is, when I say my plane is climbing with an AoA of 11°, does this 11° include the wings' AoI?

$\endgroup$
1
$\begingroup$

Speaking of an aircraft, the AOA is simply the angle between the airflow and the aircraft fuselage, in the vertical plane.

The incidence is only required to calculate the wing AOA. The wing AOA is the sum of AOI and AOA_aircraft.

When talking to some aerodynamicist or another engineer, it’s a good practice to state your conventions the first time you use a term, to avoid miscommunication.

$\endgroup$
3
$\begingroup$

Not really.

The angle of incidence is the angle between the chord of the wing and the longitudinal axis of the airplane. But the plane is mostly free to pitch as necessary. So if the best thing is for the wing to have an AOA of 11°, then it can pitch to that point.

Now if the angle of incidence were too different, it could increase drag on the climb-out, or the thrust angle might be less than optimal. But there's no direct relationship.

The angle of incidence is a figure about the geometry of the plane. The angle of attack is how the wing is oriented to the wind. They don't "add" together.

If you did the math the other way (AOA - AOI), you'd find the angle the wind is making with respect to the airplane axis, not a figure that you tend to need.

$\endgroup$
  • $\begingroup$ So if I understand correctly,aoa is totally independent of the angle of incidence? $\endgroup$ – David Teahay May 18 '18 at 8:36
  • $\begingroup$ Simpler question: what is the angle between chord of wing and the ground when the plane has AOA of 11°? 11° or 17°? $\endgroup$ – SF. May 18 '18 at 13:07
  • $\begingroup$ @SF Not a simple relation. Angle to ground depends only on attitude (pitch). AOA depends on path through the air. It would be different for a climbing vs descending plane. $\endgroup$ – BowlOfRed May 18 '18 at 15:23
  • $\begingroup$ @DavidTeahay I hate to say "totally independent", but yes that's right. The angle of incidence is completely fixed while you're flying. The AOA is quite variable as you adjust attitude and path through the air. $\endgroup$ – BowlOfRed May 18 '18 at 15:27
  • $\begingroup$ @SF But if the plane is flying level and the air is still, then the AOA and the wing angle to ground are identical. $\endgroup$ – BowlOfRed May 18 '18 at 15:49
1
$\begingroup$

What they all said, just basically Angle of Attack is created by the pilot pitching the airplane, Angle of Incidence is set by the manufacturer, cannot be adjusted.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.