Aspect angle

[Hippo]

Sorry if this is the stupidest post ever, but it's dawning on me that I must've been misunderstanding this for years.

This is the mission setup. 

The targets and I are both heading 090 at the same speed.

This is what I see on the radar.

The manual describes, in several places.

"Target Aspect Angle Pointer. Displays relative target heading."

I have always thought that the pointer told me where the tgt's nose was pointing, so shouldn't the "stalks" of the targets to the left be pointing straight up as both the target and I are on parallel headings?  The radar image suggests that the target is flying to a point ahead of me.

Does anyone have a better definition?

 

Edited July 1, 2022 by Hippo

[Scotch75]

I'm thinking the discrepency is because the radar projects out as a cone (3D) from the aircraft, but the image is "unwrapped" onto a 2D square. A bit like the map projections of the globe (Mercator etc). However, I'm sure there are some experts in this field that will have a more accurate and technical explanation.

Cheers!



Sent from my SM-G998B using Tapatalk

[Hippo]

47 minutes ago, Scotch75 said:

I'm thinking the discrepency is because the radar projects out as a cone (3D) from the aircraft, but the image is "unwrapped" onto a 2D square. A bit like the map projections of the globe (Mercator etc). However, I'm sure there are some experts in this field that will have a more accurate and technical explanation.

Cheers!



Sent from my SM-G998B using Tapatalk
 

Thanks.  Thinking about it, it makes perfect sense.  It had never occurred to me that the mapping also rotates the heading.

[=475FG= Dawger]

You are misunderstanding aspect angle, which is what is being displayed.

 

[Phantom711]

vor 5 Stunden schrieb Hippo:

Sorry if this is the stupidest post ever, but it's dawning on me that I must've been misunderstanding this for years.

This is the mission setup. 

The targets and I are both heading 090 at the same speed.

This is what I see on the radar.

The manual describes, in several places.

"Target Aspect Angle Pointer. Displays relative target heading."

I have always thought that the pointer told me where the tgt's nose was pointing, so shouldn't the "stalks" of the targets to the left be pointing straight up as both the target and I are on parallel headings?  The radar image suggests that the target is flying to a point ahead of me.

Does anyone have a better definition?

 

 

It is absolutely not a stupid question.

Aspect angle or target aspect is not the targets heading in relation to your heading, but your position in relation to his nose (in easy terms). If the target is pointing at you, the "dongle" would show straight down. No matter if he is in the center or anywhere else on the radar.

On the map, if you draw a line from you to the targets in question then you see, that their heading is not an extension of that line as you suggest, but that their heading is like 45 deg to the right from that line. This is exactly, what is being reflected in the radar picture.

 

Hope this helps.

[Figaro9]

Check also:

https://tawdcs.org/radar-f15/

 

 

[Frederf]

It's sometimes important to know that radar never knows the target's heading. The velocity tick mark represents target motion, not orientation. To radar all targets are metal spheres with no front or back. The technical name for "heading" here is the track azimuth.

The radar presentation here is known as B-scope (A-scope is the suuper old display of signal intensity vs range, C scope is elevation vs range, D scope similar C, E scope elevation v range, F-P, R scope etc.). In B scope the x-y axes are azimuth and range. The whole bottom edge is zero range so the tip of your nose cone is smeared out along it.

All vertical motion is radial, change of range with no change bearing. The velocity ticks can either be in this B-scope coordinate system or it can change to a non-distorted system where up is always your track az, rightward marks are your track +90, and so on.

Different radars do things differently, some remain in B-scope for both plot and tick and some mix up formats between the two. It looks like F-18 radar is not mixed display. If you and all targets are going north, not all the tick marks will point up.

[Hippo]

9 hours ago, Frederf said:

It's sometimes important to know that radar never knows the target's heading. The velocity tick mark represents target motion, not orientation. To radar all targets are metal spheres with no front or back. The technical name for "heading" here is the track azimuth.

The radar presentation here is known as B-scope (A-scope is the suuper old display of signal intensity vs range, C scope is elevation vs range, D scope similar C, E scope elevation v range, F-P, R scope etc.). In B scope the x-y axes are azimuth and range. The whole bottom edge is zero range so the tip of your nose cone is smeared out along it.

All vertical motion is radial, change of range with no change bearing. The velocity ticks can either be in this B-scope coordinate system or it can change to a non-distorted system where up is always your track az, rightward marks are your track +90, and so on.

Different radars do things differently, some remain in B-scope for both plot and tick and some mix up formats between the two. It looks like F-18 radar is not mixed display. If you and all targets are going north, not all the tick marks will point up.

Thank you for your (as always) interesting and detailed response, and to everyone else who replied.  For years I had never given aspect angle a second thought: as long as the target was on my nose, it was just obvious.  In the case above, the target was not on my nose, which was the cause of my confusion.  My understanding is that the tick marks on the F-18 display are supposed to be aspect angle.  Thank goodness for the SA display.

Edited July 2, 2022 by Hippo

[Frederf]

It is aspect as shown in the screenshot in post 1. You just aren't 180 "tail" (or 0, AA and TAA are 180 apart and who can remember) aspect to the targets to the front left as evidenced by the tick marks not pointing up.

Measure the angle from the tick mark left/right to the down direction and that's your aspect left/right off his nose. For example you're about 140 right aspect off the target's nose (or 40 right off his tail).

[Hippo]

31 minutes ago, Frederf said:

It is...

Whilst you're here...

Same mission.  I find that if I TWS and L&S one of the targets at my 12 o'clock and try to activate RAID (or EXP) it doesn't do anything (issue 1).  If I move the scan over the targets to my left, L&S one of those, then RAID and EXP do work, but RAID stops working after about one second (issue 2);  EXP works as expected .   Do you have any ideas as to why this might be?  I'm thinking it might be because the targets' speeds are (almost) identical to mine?  Also, targets are at the same altitude and heading.

Edited July 2, 2022 by Hippo

[Frederf]

What do you mean "doesn't do"? Is the EXP label not boxed or is the display not changed or what? Does it say SCAN RAID when you turn RAID on?

I see you're at a 10nm range scale so EXP isn't going to expand the display since it picks a 10nm block about the target which is going to be 0-10 min-max without EXP and looks like roughly 5nm centered with your targets which would also be 0-10. I don't know if the display does odd numbers like 1-11, 2-12, 3-13, etc., manual certainly suggests so. Ah yes a 5.1nm EXP goes from -4 to +5 range.

Looks like EXP isn't available below 5.0nm. The box won't highlight. I guess that makes sense that if you close to within 5nm with EXP on it stops being useful and kicks off.

What's really weird is that if you SCAN RAID on a target, the BRA figures at the bottom count down like you're scanning a stationary point in the sky. The L&S target was ~6nm away but SCAN RAID was just scanning where the target was when I started. Since I'm flying forward this range decreases and when it hits 5.0nm SCAN RAID auto quits. I don't know if that's intentional behavior.

All of these quits or no-go's with EXP and RAID seem to occur when the range drops below 5.0nm. With EXP that's the current range. With SCAN RAID it's the static point in space when you started the scan so you run over it pretty quickly.

[Hippo]

2 hours ago, Frederf said:

What do you mean "doesn't do"? Is the EXP label not boxed or is the display not changed or what? Does it say SCAN RAID when you turn RAID on?

I see you're at a 10nm range scale so EXP isn't going to expand the display since it picks a 10nm block about the target which is going to be 0-10 min-max without EXP and looks like roughly 5nm centered with your targets which would also be 0-10. I don't know if the display does odd numbers like 1-11, 2-12, 3-13, etc., manual certainly suggests so. Ah yes a 5.1nm EXP goes from -4 to +5 range.

Looks like EXP isn't available below 5.0nm. The box won't highlight. I guess that makes sense that if you close to within 5nm with EXP on it stops being useful and kicks off.

What's really weird is that if you SCAN RAID on a target, the BRA figures at the bottom count down like you're scanning a stationary point in the sky. The L&S target was ~6nm away but SCAN RAID was just scanning where the target was when I started. Since I'm flying forward this range decreases and when it hits 5.0nm SCAN RAID auto quits. I don't know if that's intentional behavior.

All of these quits or no-go's with EXP and RAID seem to occur when the range drops below 5.0nm. With EXP that's the current range. With SCAN RAID it's the static point in space when you started the scan so you run over it pretty quickly.

Thanks again!  I put myself further away and all now works as expected, so it does seem to be down to my being too close.

[sk000tch]

Some real questionable advice here, and the rest is flat out wrong. Glad to see things haven't changed while I was away

The language ED used in the manual is terrible (relative headings?), but the b-scope display is correct. It’s showing TA as 135 Right which is correct for the map you’ve drawn. I suspect we have some definition issues along with confusion about what its trying to display, but once you’ve got it down its quite intuitive. I'll try to break them down concisely and in a way that's relevant to the questions, but there is a lot of material out there much more thorough and better than anything I can do here. 

TA, or target aspect, is best thought of as your position from the bandit’s perspective. The bandit’s position from your perspective is Antenna Train Angle or ATA. So TA is how Bandit sees  your, and ATA is how you see him - right? ATA is obvious from a B-Scope display, so the information a pilot needs the track file to computer is what? Target aspect right? On the scope its relative to straight down, so if TA is zero, meaning his nose is on you, the line will point straight down.

It might help to consider that Target Aspect is what controls the hot/cold calls you get from AIC. Where TA is 180 - 120ish, AIC will say they are cold. From (I’m guessing here) between 0 and 50-60, AIC will call them as hot. In between the two they’re flanking. And again, this is 100% dependent on the bandit’s heading and how that changes where you are relative to their nose.

Stated differently, target aspect is the angle between BH (bandit heading) and the angle between BR (Bandit Recip) and BB (Bandit Bearing). ATA his the angle b between FH and BB, and its synonymous with Angle Off.

Aspect Angle is complementary to Target Aspect. Aspect Angle will always equal 180-Target Aspect, but it is defined as the degrees from BB to BH, or basically degrees to the bandit’s six. Hence the term high aspect, where nose on fighters are approaching 180 AA. In your picture, for the bandit bearing 045, AA is 45 right, and of course TA is therefore 135 right, as shown on B-scope.

There are a number of other terms that aren't particularly relevant to the question, but very important for employing a fighter effectively. Cut is a good example, whidch is just the angle from FH to BR. It’s particularly useful for plotting intercepts where you wish to arrive with enough turning room. Unfortunately, in DCS the AI is frustrating, greatly favors high aspect engagements and lacks any 2vX sophistication. With a few exceptions, bandits will turn head on and keep you there until the merge. In that situation there’s nothing you can do to create LS, or to move that line from pointing directly down. 

One last thing that might help. I saw some flashcards that looked like the work of a T-45 student. Because its is so important to have all these down to second nature, it really helps to get  fast  with  the definitions and relationships between fighter heading and flightpath, bandit heading, flightpath, recip and bearing. ATA, TA and AA. HCA and Cut, Elevation Angle, slant range and vertical displacement. And of course, lateral separation. Presumably they're still floating around somewhere

Edited July 5, 2022 by sk000tch