warren,
I apologize if you know all of this.
This is what correct data will show.
From:
Aerodynamic Design Of Transport Aircraft
Angle of attack. The acute angle formed between the chord line of an airfoil and the direction of the air striking the airfoil.
Angle of attack for 757 type wing (asymmetric)
This is a generic chart. The 757 wing is asymmetric.
Note that, at 0° AoA, you are still generating lift (Cl = 0.2), and according to this curve, the zero lift AoA is -2°.
Again, the curves above are generic (not precise for the 757), but they are gonna be darn close. I've seen the data for the 757 wing in which the zero lift AoA is -4°. The principles & trends are still applicable.
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Angle of incidence. The angle formed by the chord line of the wing and a line parallel to the longitudinal axis of the airplane.
Angle of incidence for the 757
You can see that the "average" Angle of Incidence is approximately 6°. When the plane is on take off roll, the pitch angle is 0°, the AoA is about PLUS 6°. The wings are generating lift (as proven by the fact that they flex upwards during the take off roll), just not nearly enough to unstick the plane from the ground.
One thing to note is that, whenever the plane is in level flight (and this includes on take-off roll), the AoA is equal to the Pitch Angle plus the Angle of Incidence. (This ignores the irrelevant-to-this-conversation situation of microbursts, significant vertical wind speeds.)
Here I've plotted the data for the take off roll.
"Indicated AoA": according to Celestrin(
http://www.internationalskeptics.com/forums/showthread.php?postid=2819232#post2819232 ), this is the "Pitch Limit Indicator". Which can be thought of as "angular margin to stall warning", the difference between the current AoA minus the stall warning AoA. As Celetrin notes, you always want to keep this number less than zero.
You can see the pitch angle = 0° (implies that the AoA = +6°) during take off. At transition, the pilot gradually brings the nose up. The plane generates enough lift to unstick at a pitch = 8° (AoA = 14°), and he continues to raise the nose to about 17° pitch. You'll note that, for all the numbers before this point, the AoA is simply 6° (the Angle of Incidence) greater than the pitch angle.
But in the climb, the apparent wind is not coming horizontally anymore, so the AoA is less than 6° greater than the pitch angle. So, at a pitch angle of, say, 15°, the AoA may be as low as, say 18°.
And it appears that, on climb out, they bring the AoA right up to this limit (Ind AoA stops just below 0°), probably for a max performance take-off, to get as high as possible as quickly as possible for noise abatement. The decrease in "indicated AoA" during the climb out (even tho pitch angle increases to about 19°) is probably due to reconfiguring the wings (retracting flaps).
Everything makes sense, except for the decision to call this parameter "indicated AoA". That's completely weird.
As to cruise performance, in level flight, the AoA is going to be about 6° greater than the pitch angle.
I BELIEVE that I read that the pitch at level cruise was 2.5°, which would make the AoA be about +8.5°.
It is possible that the reference that I saw said that the AoA in level cruise was 2.5°, which would make the pitch be -3.5°.
Any of you pilots know which of these situations is right for 757 cruise flight?
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BTW, Warren, here is the vertical velocity data (based on differential "PA as per 757-3b"). You can see the abnormal spikes in the data. You can also see it in the tabulated "PA as per 757-3b" data, just not as obviously.
Tom