Aspect angle and angle off- confused again!

So, I thought I was comfortable with this topic until I looked at one of Chuck's Guides. (The Mirage, but it's not relevant.)

 

In the attached graphic, I am fine with the Aspect Angle diagram in the bottom middle. That is how I understand aspect angle. However, every other part of that page confuses me.

 

Looking at the image of the 2 planes in the top middle, I would say that the aspect angle was somehing like 40-50 degrees right, yet Chuck (and the radar, apparently) says it is 142. It's the same for the bottom left diagram which I guess is representing the same situation.

 

Now, if the plane in the middle of the diagram was the bandit, then I coiuld believe the 142 degrees, but it's not.

 

In addition, I just can't see how the Angle Off in that case is 35 degrees at all. To me, it looks like it should be around 110-120.

 

Please will someone tell me where I am going wrong here? I would be so grateful!

Aspect angle can be measured of the tail USAF style or of the nose as per the US Navy.

 

Unfortunately you just have to see which one the Aircraft is set for . So your 40 Nose Aspect or NASP is also 140 Tail aspect TASP.

 

 

NASP is actually a little easier to work with and tell you if the bandit can see you on radar. Greater than 70 NASP he can't see you .

 

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Edited November 24, 2019 by WindyTX

Thanks but that doesn't help me, I'm afraid. I'm comfortable with the definition of aspect angle in the document I attached, but, AFAICS, it doesn't match up with the scenario shown, nor can I see where the Angle Off numbers come from.

Ok so the Aircraft is Using Tail Aspect. Draw a line from the aircraft to you, then measure the angle off the tail.

 

Heading straight at you is a 180Tasp. Your heading doesn't matter at all. Heading away from you is a 0 TASP.

 

I think you are trying to use Nose Aspect hence it's 180 - TASP = NASP.

 

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This is how I have understood it, see attached:

Different forces use slightly different terms to mean the same thing. There are concepts of Target Aspect Angle (TAA) and Aspect Angle (AA) but very commonly both are called "aspect" without further clarification. This is an example where the concept is TAA but the term is abbreviated to "aspect angle." TAA is the angle from the target's nose to the LOS from the target to you. AA is the same angle but from astern.

 

I have no idea why the concept of angle off (HCA) or AOT was mentioned since it's not reported by the radar. It seems the author wished to shoe horn in some extra knowledge which is not particularly relevant. AOT (from the target's perspective) is the supplement of TAA. If you are 142 degrees from his nose then you are also 38 degrees AOT. AON + AOT = 180 degrees obviously and always.

 

Angle off (HCA) is yet a third concept. While TAA and AOT are descriptions of relative position. Angle off, a.k.a. heading crossing angle is a description of relative orientation. Your heading, target's heading what's the difference? One can see how HCA can be any value regardless of the relative positioning. In the case where your airplane is pointed directly at the target then your position AOT from target's perspective and HCA must be the same.

 

Long story short the radar spits out a TAA number which is your position angle. Zero is in front, 180 is behind.

Guys, are you saying that Chuck’s Guide is incorrect? He clearly states that the HUD shows ‘angle off tail’. Now, if that is not correct, then my confusion has ended as I can see that there is simply a nose and a tail aspect angle being displayed.

Ah, now I see it. The "35" in the picture is showing AA as opposed to TAA figure on VTB. The "35" is the aspect angle (0 is behind, 180 is in front). The yellow arrow should point to the number, not the box.

 

TAA and AA are the same information (where you are relative to bandit nose) but different conventions of zero reference. The Mirage just happens to use different flavors in different places.

Ah, now I see it. The "35" in the picture is showing AA as opposed to TAA figure on VTB. The "35" is the aspect angle (0 is behind, 180 is in front). The yellow arrow should point to the number, not the box.

 

TAA and AA are the same information (where you are relative to bandit nose) but different conventions of zero reference. The Mirage just happens to use different flavors in different places.

 

Yes, that is how I understand it. My confusion was/is caused by the fact that Chuck states categorically that the HUD figure (of 35 degrees) is Angle Off Tail (AOT), which we are saying is incorrect, I think.

In the OP picture:

 

 

If the target flew right away from you the lower left diagram would tell a target aspect angle of 180. The diagram to the right would say aspect angle is 0.

 

 

Both have nothing to do with angle of tail.

 

 

Confusion is understandable.

Edited November 25, 2019 by Tom Kazansky

I think we are all agreed on what is represented here, i.e. on the radar it is AA using bandit NOSE as 0, and the HUD shows AA using TAIL as 0.

 

The question is, is Chuck's Guide wrong? I would suggest it is, and that is what is causing the confusion. He is stating that the HUD shows the Angle Off Tail, i.e. the angle between flight paths, which is a different concept to the AA using tail as reference, and I don't think that is correct.

 

Can anyone confirm this?

Or does the lower left diagram is simply where the target is from your point of view. So not what I would call an aspect angle. So it would not be 180 as I thought before but independent from the N/TASP?

May be the example plane in the lower left diagram is not chosen too well because it is approximately 135 from your point of view and has an angle of nose aspect of approximately the same. The diagram could have been clearer with an aspect angle of 90 imho.

That doesn't add up at all. In that case, sum of angles would be more than 180 degrees.

 

What? Angle of Tail is based on your vector, to the contacts vector. Target aspect is based on radar lock line and contacts aspect. Why would you sum those up, they are two different things?

But no, doesnt fit. Just went in and grabbed a bunch of shot with various angles, to help.

Well yea, but where did I measure lock line against your own vector? Its vector against vector for Angle off, and contact aspect angle against your radar lock line (LOS in below image).

 

Went looking for a good image showing / explaining angle off, and that fits what I scribbled in that image on previous page. Just doesnt add up in-game (Mirage) in all cases, or am I completely missing something.

 

 

 

 

angle off vs aspect

 

by Art of the Kill, Pete Bonanni

My confusion was/is caused by the fact that Chuck states categorically that the HUD figure (of 35 degrees) is Angle Off Tail (AOT), which we are saying is incorrect, I think.

It's not the usual way of manner of stating it but it isn't wrong. That figure on the VTH does represent the AOT of yourself from target's perspective. It's just not the particular phrasing most would use.

 

What you're discovering is that a neat and tidy world where everyone uses one and only one term for one and only one situation is not the one we live in. All of these geometry terms are based on A-to-B object-to-object and can take on different meanings depending on who is A and who is B. Some abbreviate target aspect angle TAA and some TA and some just call it aspect.

 

TA and AA are supplementary angles. 35 + 142 =/= 180

35+142 does equal 180. You have to remember the value displayed has a resolution less than single integers. If I remember "35" is displayed for all angles between 35 and 40.

 

He is stating that the HUD shows the Angle Off Tail, i.e. the angle between flight paths

Angle off tail is not the angle between the flight paths (angle off, HCA). I know the term angle off tail contains the words angle and off, but they are unrelated. This is one reason why angle off should be called heading crossing angle, to avoid this mix up. AOT and aspect angle are essentially the same thing unless you want to get into the particulars of attitude vector compared to velocity vector. The purple arc in post #19 is angle off, not angle off tail.
Edited November 25, 2019 by Frederf

Oouh, and the penny dropped.. I hope :thumbup:

Its essentially where you are in relation to the enemies tail, or in other words, if Im the enemy and I look over my shoulder, the angle you are off my tail, thats the, well Angle off Tail. If you are bang on my 7 o'clock, that would be 30 AoT.

 

Im sorry for what confusion and complications I might have added to the topic, but atleast I helped establish what Angle off Tail isnt :music_whistling:

Angle off tail is not the angle between the flight paths (angle off, HCA). I know the term angle off tail contains the words angle and off, but they are unrelated. This is one reason why angle off should be called heading crossing angle, to avoid this mix up. AOT and aspect angle are essentially the same thing unless you want to get into the particulars of attitude vector compared to velocity vector. The purple arc in post #19 is angle off, not angle off tail.

 

This is exactly why there is confusion. Chuck's Guide says it is. Look at the attachment. It's a small section from the first one I posted.

 

I'm pretty sure this info is wrong and should be corrected in his guide. I would just like you guys to confirm this is the case.

Strictly speaking the VTB shows the TAA, not AA if you adhere to what I know to be NATO conventions. That's a minor error of not minding conventions.

 

Ah yes, the first statement of the first bullet point, that's incorrect usage. The second part of that first bullet point is consistent with an acceptable usage of AOT but is incompatible with the first statement.

 

The second bullet paragraph is good enough.

 

If given the task to rewrite page 108 of that guide I would describe the concepts in perhaps fewer words and pictures and would avoid the term AOT, TAA, AA, and probably even aspect at all since those are doctrinal terms. Instead I would describe in plain language that the numeral represents the angle between various velocity vectors and line of sight. It's not the time nor place to teach air combat geometry when describing a cockpit display. The pilot will learn such geometry elsewhere and figure out the connection himself.

 

More of interest to me as a student pilot would be details of if the angle displays are of the 2D plane or of 3D space and things like numerical resolution. If target is directly ahead of me in azimuth but elevated 20 degrees above will the angle readout be 20 or 0? Is "35" rounding to nearest 5? 10? Is it floor function, ceiling function? Does VTB show angle to nearest 1 degree? 3? 10?

So, simply put, we have the radar showing AA relative to the nose (TAA), HUD showing AA relative to tail (AA), Angle Off Tail - heading difference - nowhere, and the page in the document needing some correction re what is displayed on HUD.

See the attached graphic

 

Terms & Concepts.

 

Range. The distance between two aircraft.

 

Aspect angle. The relative position of the attacker to the target without regard to the attacker’s heading. It is defined as the angle measured from the tail of the target to the position of the attacker.

 

HCA. HCA is primarily concerned with the relative headings of two aircraft. It is defined as the angular distance between the longitudinal axes of the attacker and the defender. Whenever the attacker is pointing at the defender, the AA and angle off will be the same.

 

Antenna train angle. The number of degrees the defender is off the boresight of the attacker.

In case you missed it :)

 

Edited November 26, 2019 by Kappa

Guys, we are not talking about the definitions. Pretty sure that is clear. The issue was/is how they are presented in Chuck's Guide, and I think we have established that there is a mistake there which led to my original confusion.