15 units AOA V 15 deg AOA

[bonesvf103]

There's alot of talk in the Tomcat about 15 units AOA. But since the indicator is an ANGLE of attack indicator, why do they say 15 UNITS of AOA?  Wouldn't 1 unit=1 degree?

 

What is the importance of 15 units of AOA to the Tomcat?  Is that where you have the best balance between G and speed for your best and tightest energy sustaining turn?

v6,

boNes

[draconus]

http://www.heatblur.se/F-14Manual/cockpit.html#angle-of-attack-indicator

Tape indicating angle of attack (AOA) on a scale of 0 to 30 units. (Equivalent to -10° to +40° rotation of the AoA probe.)

The indicator has markers on the right for climb (5), cruise (8.5), and stall (29), and a reference bar for on-speed approach (15).

[Spurts]

but the answer to your second part is Yes.  15 units is the best balance of speed and turning. It's also where lateral stick for roll is still effective but so is rudder use.

[BreaKKer]

TLDR:

the wings are 5 degrees up in relation to the nose of the aircraft. -5 units of AOA to get to degrees

Edited February 21, 2023 by BreaKKer

[bonesvf103]

1 hour ago, draconus said:

http://www.heatblur.se/F-14Manual/cockpit.html#angle-of-attack-indicator

Tape indicating angle of attack (AOA) on a scale of 0 to 30 units. (Equivalent to -10° to +40° rotation of the AoA probe.)

The indicator has markers on the right for climb (5), cruise (8.5), and stall (29), and a reference bar for on-speed approach (15).

Yes, I already read that.  But a unit is a measure of an amount. ie, a unit of length could be an inch, a unit of volume could be a liter...what is a unit of AOA equal to?  A degree?  If so why don't they just say 15 deg AOA instead of 15 units?  Or is it something else?  The manual does not state that.

v6,

boNes

 

[RustBelt]

Units AoA are equivalent to degrees in spacing. But are not meant to indicate the ACTUAL alpha. It’s an abstracted scale for ease of use compared to dealing with negative numbers due to the wings angle of incidence compared to the AoA sensor on the nose.

Think Kelvin vs Celsius.  

[draconus]

1 hour ago, bonesvf103 said:

what is a unit of AOA equal to?  A degree?  If so why don't they just say 15 deg AOA instead of 15 units?  Or is it something else?

The unit of AoA is obviously a unit of angle and is a bit bigger than degrees - about 1.3 but it's not easily converted. They are not equal and their range is different. It's common among US military aircraft but not transferable between them either.

[r4y30n]

From what I’ve seen, 15 units typically represents “on speed” for US aircraft and 30 seems to be stall. Peak maneuvering performance varies, in the F-14 it just happens to coincide with on speed. I believe the Phantom is more like 10-12 units. The purpose of units, though, is to ease transition between aircraft; the AoA gauge is always used the same way regardless of aerodynamic differences.

[bonesvf103]

15 hours ago, RustBelt said:

Units AoA are equivalent to degrees in spacing. But are not meant to indicate the ACTUAL alpha. It’s an abstracted scale for ease of use compared to dealing with negative numbers due to the wings angle of incidence compared to the AoA sensor on the nose.

Think Kelvin vs Celsius.  

Kelvin V Celsius.  Now THAT is a great analogy (at least for those of us familiar with that scale).  Thanks!

v6,

boNes

[draconus]

32 minutes ago, bonesvf103 said:

Kelvin V Celsius.  Now THAT is a great analogy (at least for those of us familiar with that scale).

That is not great analogy as K vs C is only the shift of 272,15 degrees, while the single unit size is equal. It's more like Fahrenheit.

Anyway, here's the formula I got somewhere from DCS forum: (15 AoA Units - 3.715) / 1.089 = 10.36 AoA degrees

@r4y30n It's 21-22 units for landing in the Eagle, 17 for A-4/T-45 so not really transferable.

[bonesvf103]

It is a good analogy to me, and why I think it is a good analogy is primarily because of the "ease of use compared to dealing with negative numbers" that RustBelt explained.  It is exactly why I think the Kelvin V Celsius analogy is so great.  You get -C deg but the Kelvin version will never be negative and it helps me have the mindset of the shift of scale in what is being measured.  I'm not talking about it being an equivalent converted unit for unit thing.  The analogy gives me a better sense about how to look at units of AOA v degrees of AOA.

That formula you found is also kind of thing I was looking for because it is not in the HB F-14 manual that I could find, hence why I went here asking around to begin with.  The manual only says what the instrument indicates, but it says nothing about what a unit of AOA is.  That formula answers my original question greatly but it had to be found in the forums to do so.

Thanks everyone for the info.

v6,

boNes

 

Edited February 22, 2023 by bonesvf103

[Naquaii]

53 minutes ago, bonesvf103 said:

It is a good analogy to me, and why I think it is a good analogy is primarily because of the "ease of use compared to dealing with negative numbers" that RustBelt explained.  It is exactly why I think the Kelvin V Celsius analogy is so great.  You get -C deg but the Kelvin version will never be negative and it helps me have the mindset of the shift of scale in what is being measured.  I'm not talking about it being an equivalent converted unit for unit thing.  The analogy gives me a better sense about how to look at units of AOA v degrees of AOA.

That formula you found is also kind of thing I was looking for because it is not in the HB F-14 manual that I could find, hence why I went here asking around to begin with.  The manual only says what the instrument indicates, but it says nothing about what a unit of AOA is.  That formula answers my original question greatly but it had to be found in the forums to do so.

Thanks everyone for the info.

v6,

boNes

 

 

The problem is that there's no definition of what a unit actually is in the F-14 anywhere. They only list what amount of units are preferred in which situations. That formula might be correct but it might also not be the same for every aircraft using units.

The conversion from units to degrees AoA might not even be linear so it might be impossible to do correct conversions to and from units in some cases.

The real question is if it matters outside of those set reference points?

[RustBelt]

19 hours ago, draconus said:

That is not great analogy as K vs C is only the shift of 272,15 degrees, while the single unit size is equal. It's more like Fahrenheit.

Anyway, here's the formula I got somewhere from DCS forum: (15 AoA Units - 3.715) / 1.089 = 10.36 AoA degrees

@r4y30n It's 21-22 units for landing in the Eagle, 17 for A-4/T-45 so not really transferable.

Rankine to Celsius Maybe? But how many people know about Rankine?

[draconus]

1 hour ago, RustBelt said:

But how many people know about Rankine?

One more, now.

15 hours ago, Naquaii said:

That formula might be correct but it might also not be the same for every aircraft using units.

Yes, it's only "correct" for the Tomcat. I know of other formula for the Eagle and I agree it can be non-linear thus not exactly correct, and also convertion is not needed for the operation of aircraft.