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AFM bug (Angle of attack)


Dembizkit
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The plane is some how indicating a climb when he is pitched down?

I honestly can barely see anything in the image, and there's no context. I think we need more information. Or at least a better picture and a description of what it's showing.

 

F-15 is PFM, could be one of the sensors became damaged or something and is producing non sense output.

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I downloaded the image (what an unbelievably shitty way to host a pic), and he's pulling +1 g at 11 deg alpha, about 650 kIAS, in level flight according to the ADI but 1000 ft/min climb according to the VSI.

 

Testing it myself, it does seem weird. No matter how level I fly, I can't get below 10 deg AoA. Is that how the F-15 flies?

 

EDIT: The AoA instrument is in units, not degrees. Also, I found that apparently 12 units of alpha is fine for cruising.

 

attachment.php?attachmentid=81558&d=1368473763

 

Unless I'm misunderstanding the point of the OP, (which would be forgiveable based on its content), there is no issue.


Edited by Corrigan

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No, units = AoA + 10.

 

The reason is that back then, they didn't want to, or couldn't cleanly deal with negative values in the flight computer, so they got around that in this manner.


Edited by GGTharos
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  • 2 weeks later...
No, units = AoA + 10.

 

The reason is that back then, they didn't want to, or couldn't cleanly deal with negative values in the flight computer, so they got around that in this manner.

 

Good. At least someone told about what I was planning to ask. So the AoA indexer on the HUD will always show you 10 degrees more than real and it usually kicks in above 18 (8 real AoA).

When you can't prove something with words, let the maths do the talking.

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You're right, but to keep confusion down it's referred to as 'cockpit units'. It's the same on the gauge and HuD, and so the training material refers to units of AoA, not degrees.

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Good. At least someone told about what I was planning to ask. So the AoA indexer on the HUD will always show you 10 degrees more than real and it usually kicks in above 18 (8 real AoA).

 

Actually I find the opposite, the mechanical AOA indicator is showing units [HUD AOA in degrees + 10], the HUD AOA indicator is showing AOA in degrees only.

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Not here they don't...Take a look.

 

First pic is degrees, second is units. First pic you are -1 (maybe 0) degrees, second pic you are 9 units. As GG already explains degrees + 10 = Units. -1 (or 0) + 10 = 9 (or 10) units.

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The Hud scale is not an AoA indicator (Although you can derive AoA from it). The 'AoA' indicator is an AoA indicator. Looks at my screenshot, I think you'll figure it out pretty quickly.

 

The HuD AoA indicator doesn't come on until 18uAoA.

 

Not true...Earlier I was at 5000 ft showing 3 degrees on the HUD and 13 units on the mechanical AOA.

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First pic is degrees, second is units. First pic you are -1 (maybe 0) degrees, second pic you are 9 units. As GG already explains degrees + 10 = Units. -1 (or 0) + 10 = 9 (or 10) units.

 

I understand GG's formula but he says "HuD indication doesn't show up until 18uAoA" I'm saying it shows up constantly as you are flying even below 18uAoA.

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I understand GG's formula but he says "HuD indication doesn't show up until 18uAoA" I'm saying it shows up constantly as you are flying even below 18uAoA.

 

Yes. HUD indication is what he has circled in his picture (which does not show up until 18 AoA), it replaces the normal G load indicator....not the bracket you're referencing.

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Yes. HUD indication is what he has circled in his picture (which does not show up until 18 AoA), it replaces the normal G load indicator....not the bracket you're referencing.

 

Yes I understand what you are referring to now. Can't the bracket be used for landing as well...12 degrees on the bracket = 22 uAoA?

Thank you.


Edited by fitness88
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