Confused on AoA readings and the gun cross

[Lobster]

I must be misunderstanding/doing something wrong, but the AoA bracket, AoA indicator, and gun cross aren’t matching up for some reason. With the FPM on the AoA bracket at 11 degrees the gun cross is showing about 8 degrees and the AoA indicator is showing 10.5 degrees. With the FPM at the bottom of the bracket at 15 degrees the gun cross is showing about 11 degrees and the AoA indicator is showing 12 degrees.

Testing the same in 4.32 I’m mistakenly using the gun cross as an AoA estimator, so scratch that. But in 4.32 when the FPM marker is on 15 degrees AoA bracket the AoA indicator shows 15 degrees, while in 4.33 it shows 12 degrees. What’s going on there?

[Blu3wolf]

Its a little hard to judge from your post, how you are determining AoA.

In general, with no sideslip, and with the DRIFT C/O switch in NORM, the angle between the gun cross and the FPM is the AoA. The gun cross is the direction the nose is pointed, in plain terms; the FPM is the direction the aircraft is going. The difference between the two is called angle of attack and commonly measured in degrees.

The landing bracket, displayed in the HUD when the gear is lowered, allows for an easy display of AOA in the HUD. When the FPM is at the top of the staple, or bracket, there is 11° between the gun cross and the FPM - and also, 11° AOA. At the bottom of the staple, there is 15° between the gun cross and the FPM - and indeed, also 15° AOA.

With the FPM at the top of the staple, the center pedestal AOA indicator should show 11° AOA. Is this not the case for you?

[Dee-Jay]

Hi Lobster!

@Lobster:

I must be misunderstanding/doing something wrong, but the AoA bracket, AoA indicator, and gun cross aren’t matching up for some reason. With the FPM on the AoA bracket at 11 degrees the gun cross is showing about 8 degrees and the AoA indicator is showing 10.5 degrees. With the FPM at the bottom of the bracket at 15 degrees the gun cross is showing about 11 degrees and the AoA indicator is showing 12 degrees.

Testing the same in 4.32 I’m mistakenly using the gun cross as an AoA estimator, so scratch that. But in 4.32 when the FPM marker is on 15 degrees AoA bracket the AoA indicator shows 15 degrees, while in 4.33 it shows 12 degrees. What’s going on there?

Screenshot would be useful.

[Lobster]

In general, with no sideslip, and with the DRIFT C/O switch in NORM, the angle between the gun cross and the FPM is the AoA.

That’s where I’m messing up! I was thinking the AoA was the angle between the gun cross and the horizon line for some odd reason. Now it makes sense.

With the FPM at the top of the staple, the center pedestal AOA indicator should show 11° AOA. Is this not the case for you?

It’s showing close to 11 degrees, right at about 10.5 degrees. But when I put the FPM at the bottom of the staple the indicator shows 12 degrees when the same position in 4.32 reads 15 degrees.

Here’s a screenshot, Dee-Jay.

I know I’m not actually landing, but attempting the same in 4.32 showed 15 degrees on the AoA indicator, so I’m wondering why it isn’t here in 4.33.

[Dee-Jay]

That’s where I’m messing up! I was thinking the AoA was the angle between the gun cross and the horizon line for some odd reason. Now it makes sense.

Angle between the gun cross and the horizon line is your pitch (attitude).
AoA is the angle between the gun cross and the velocity vector.

[Dee-Jay]

On this pic I see:

Pitch about +12°
Path about -2°
AoA about 12 + 2 = 14°

[Dee-Jay]

On this one I read:

Pitch about +11° - 12°
AoA slightly above 12°

[Blu3wolf]

@Dee-Jay:

http://i.imgur.com/rcn94bb.png

On this pic I see:

Pitch about +12°
Path about -2°
AoA about 12 + 2 = 14°

Do note deejay, that this picture could depict 90 degrees angle of attack.

When the FPM is crossed as in the picture above, it indicates that the FPM exists outside the HUD FOV. In this case, that it is too low to be displayed in the HUD. Slope and AoA may be significantly lower than they appear at first glance.

[Dee-Jay]

@Blu3wolf:

Do note deejay, that this picture could depict 90 degrees angle of attack.

Ah yes … you are 100% right I didn’t pay attention enough.

Good catch!

[Blu3wolf]

And it seems I did not pay enough attention, to my own words - slope may be significantly steeper than it appears, and AoA may be much HIGHER than it first appears, not lower as I said. Oops.

[Lobster]

Now I’m even more confused. I’ll see if I can get shots where the FPM is visible in the HUD. In the screenshot I posted I was fairly certain that it was at the bottom of the staple (15 degrees) since it was visible in the HUD while about 1 degree above the bottom of the bracket.

[Dee-Jay]

Look alright here:

Lets say that we might have about 1° of instrumental error (or reading bias). Not that much.

[Blu3wolf]

Looks like 11.1 degrees to me.

[Dee-Jay]

@Blu3wolf:

Looks like 11.1 degrees to me.

yep … about 12° (+/-1°)