Angle of Attack in Warbird's Planes

The Angle of Attack with a plane is the angle that the wings are at relative to the airflow. In general, the higher the Angle-of-Attack, the higher the lift (which increases the G load on the plane), and the higher the drag. There are two aspects to the Angle of Attack, the actual angle of the wings, and the incidence angle. The Incidence angle is the angle the wings are set relative to the fuselage. As all planes need a positive angle of attack to maintain level flight, most planes have the wing tilted slightly so that the weapons of the plane can fire directly forward while flying straight/level at some speed. For most planes this is 200-250mph, fly below this speed, then you will sink if you have the crosshairs of the plane on the horizon. Fly above this speed and you will rise

This study is a study of the Angle of Attack and Incidence angle of Warbirds. It turns out that if you measure the angle-of-attack while right side up and upside down, you can determine the angle-of-attack for a certain speed and the incidence angle of a wing. Fly upside down, you will notice that the nose often needs to be quite high to keep level flight, as the wings have to produce a certain angle-of-attack, and the nose angle has to also counter the incidence angle of the wing.

In order to determine the maximum angle of attack a plane can handle, the method I chose was to measure the crosshair position above the horizon. Now it turns out that the green markers on the "Heads-Up-Display" mark off 10 degrees above/below the horizon each. Now it also happens that the new custom gunsight feature can display lines anywhere on the screen. Using the 1024x768 F6F art exclusively (so as to accurately measure stall speed between different planes), I set up a gunsight as so:

16
-500,0,500,0
-400,85,400,85
-400,170,400,170
-225,43,-175,43
225,43,175,43
-225,128,-175,128
225,128,175,128
-225,8,-200,8
-225,17,-200,17
-225,25,-200,25
-225,34,-200,34
-225,51,-200,51
-225,59,-200,59
-225,68,-200,68
-225,76,-200,76
0,-10,0,10

This sets up a gradient on the screen marking off each of the 10 degrees between the green 10 degree markers, allowing an angle-above-the-horizon to be determined to the nearest degree.

Normally AoA cannot be easily measured. But when flying level it can, and straight/level stall speed occurs at maximum AoA at the slowest possible speed that can maintain level flight. It was this technique which with I measured AoA.

But AoA cannot be measured directly since the wing has an incidence angle. So I measured the stall-speed level flight angle right side up and upside down. Measuring upside-down was rather tricky since the stall horn doesn't work upside down. Once both measurements have been gathered, one can average them both to determine the real angle of attack, and also the incidence angle.

This study makes several assumptions. The first is that the gunsight points directly forward of the plane. I am assuming that ICI used this as a reference point for the rest of the plane, and am hoping that they felt that determining real angles for the guns (and thus the gunsight) would yield little benefit for the effort. If WB models this, then my angles will be off. The second assumption I'm making is that the wing behaves identically right-side-up as up-side-down (including AoA limits). In "Real Life", this isn't the case *especially* with flaps deployed. I'm again assuming that ICI felt that this particular detail was more trouble than it was worth, especially since most planes fly right-side-up, the G tolerance for negative G's is rather low, and the fact that most people testing the "real" planes would probably not record this data as it has so little (normal) use in either combat or design. If ICI did model this then my recordings become suspect.

My method for recording the data was: Set each plane to 10% gas. Maintaining level flight, I reduces speed until the plane could no longer sustain level flight and called that speed the stall speed, recording both the speed and the angle the crosshairs were above the horizon. I then repeated this flying upside down. Once I had these numbers, I deployed full flaps and repeated.

Anyway, here are the results:

Stall Speed, Flaps Up/Flaps Down

Graph:

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