ATTN: F-15 Drivers: Aspect Angle ?

[Ironhand]

I had added this to my "New Tutorial" thread this morning but thought it might get more visibility here:

 

To anyone familiar with my simming history, it's no secret that I'm fairly new to the F-15 cockpit. So I have a question. When in STT lock or TWS with a PDT, the 2nd number in the top left corner of the VSD is supposedly the Aspect Angle (AA). I say "supposedly" because everything I've seen about this sim's rendition of the F-15 VSD has indicated that to be true. In my recent tutorial, I parrotted that misinformation even though the number wasn't behaving like an AA.

 

I've been puzzling over it, since the tutorial. This morning came the dawn. That number is actually the DTG (Degrees-To-Go) in xx*10 form. 15R=150 degrees Right. Everytime I run the angles for varying intercepts, the number I get for DTG is the number of degrees displayed in that position on the VSD. In the intercept lexicon, degrees-to-go (DTG) is the fewest number of degrees you have to turn to make your heading identical to the bogie's. The implications are fairly obvious, especially if you are in lag pursuit.

 

So my question is: Does the real VSD show DTG or AA in that position? Anyone know for sure? My assumption would be the latter, since AA is the angle that drives the Air Force computations. But I don't really know. As I understand it, the Navy and Marines use Target Aspect (TA), a completely different angle. Both derive DTG from those primary angles, though.

 

Rich

[GGTharos]

Unfortunately I don't have any docs on the VSD to be able to tell you :/

[Ironhand]

Unfortunately I don't have any docs on the VSD to be able to tell you :/

I was hoping you might. Not that it matters, I suppose. We have what we have. This is an intellectual exercise more than anything else. OTOH, I won't be calling that number the Aspect Angle in future tutorials.

 

Rich

[GGTharos]

Good call :)

[RvEYoda]

Well.....Whats funny is that the aspect number is actually

displayed wrong

 

I believe what it calculates is actually not AA but some wierd angle off.

Try it by putting target 50 nm in front of you, going straight towards you.

 

Then if you have it on your 10 oclock it should still show head on aspect...

However it does not. Put him on 2 oclock and yet again it shows something different.

Remember that target nose is still straight on you, while your nose is moving around.

 

 

 

MSPAINT!!!

 

Edited September 26, 2008 by =RvE=Yoda

[Ironhand]

Well.....Whats funny is that the aspect number is actually

displayed wrong

 

I believe what it calculates is actually not AA but some wierd angle off...

No. It's not some weird number. It's a valid number but definitely not the AO or AA. What is being displayed is the DTG. It's the number you get when you subtract the cut from 180 degrees. Or put another way, the degrees you get when you subtract the bogie's heading from yours. (Doing it the 2nd way, though, is harder to calculate if his heading has more degees than yours and it's easier to make a mistake.) That's why, for instance, the number displayed remains 9R (90 Right) if you set up a flight to pass your nose at a 90 degree angle left to right. All other angles (AA, TA, AO, etc) change except the cut and DTG.

 

EDIT: BTW, Yoda, I'm at work and whatever image you have displayed isn't displaying in my decrepid work browser. It simply says: MSPaint.

 

EDIT II: Yoda, I just had time to look at your example again (I'm still at work). If I understand you correctly, you will first see the DTG as "H" (180 degrees)--I'm assuming that, in your example, the bogie's heading is your reciprocal and he's starting at your 12 o' clock. (Otherwise, the following will not be correct.) Then you turn 60 degrees to the right to put the bogie at 10 o' clock. The DTG should now show 12R (120 Right). You then turn 120 degrees to the left to put the bogie at your 2 o' clock. The number you now see will be 12L (assuming the day hasn't left me completely brain dead).

 

Rich

Edited September 27, 2008 by Ironhand

[RvEYoda]

The above example in the picture shows 13R in VSD

That is in the instantaneous moment of the picture above.

 

The bogey's heading is straight towards me. (pure)

 

Which is consistent with what you said :).

Edited September 27, 2008 by =RvE=Yoda

[3Sqn_Sven]

I've never heard of the DTG concept but the figure should be aspect angle in the top left. Of note is that USAF and USN are 180` out when they talk about aspect angle, ie one calls nose on 0 aspect the other calls it 180. Also of note is that in lock on the aspect is incorrectly shown when you turn away from the target, as the target aspect changes on the display while the number does not.

[Ironhand]

I've never heard of the DTG concept but the figure should be aspect angle in the top left.

Unfortunately it's not. The formula the sim uses to provide that number yields the DTG. And does it perfectly the entire time.

 

...Also of note is that in lock on the aspect is incorrectly shown when you turn away from the target, as the target aspect changes on the display while the number does not.

Again, unfortunately, that's because that number is never an aspect angle of any sort in the sim. Set up any scenario you'd like in the Editor and run the numbers. Then jump into the cockpit. What you got for the DTG will be what you see reported as aspect angle on the VSD.

 

Rich

[IvanK]

The USN term is specfic and called "Target Aspect"

[3Sqn_Sven]

Ahh I see what you mean. I always knew they'd just stuffed up the representation of AA, and judging by the manual which says that it should be aspect angle in the top left, this is how they have done it. Weird.

[Ironhand]

The USN term is specfic and called "Target Aspect"

Yes. As I understand it, US Naval and Marine aviation uses the Target Aspect as the number to base the other numbers on. And the USAF uses the Aspect Angle. TA and AA are the two aspect angles that make up the 180 degree hemisphere. Here's a quick graphic I made to show the angles we're talking about:

 

 

The number displayed is supposed to be the AA but, rather, it's the DTG that's displayed. In the scenario above, 9R (90 degrees Right) will be the number displayed for the bogie's entire flight across your nose. If his pass were right-to-left, instead of left-to-right, the number would be 9L.

 

Rich

[UWBuRn]

Despite what the manual says about that number (and if i recall correctly it says is AA), i always treated it as an Angle Off mesuared starting from the tail of the target, but i'm not 100% sure if it's correct. :)

[Ironhand]

Despite what the manual says about that number (and if i recall correctly it says is AA), i always treated it as an Angle Off mesuared starting from the tail of the target, but i'm not 100% sure if it's correct. :)

I was puzzled, too, and spent a number of hours trying to figure it out. I realized what we were looking at yesterday morning when I ran the numbers in a variety of situations and always got the number I saw in the cockpit, when I solved for the DTG. Give me your heading and the bogie's heading at the time you want to check the VSD and I'll tell you the number you'll see there.

 

Rich

[IvanK]

May be better calling it Heading Crossing Angle HCA. Back in the 60/70's Intercept profiles were based on Specific HCA's . Intercepts were known as "150 Front", or "130 Front", or "90 Stern", "130 Stern" etc.

[A.S]

Back to groundschool and basics

 

Angle Off

Angle-Off is the difference, measured in degrees, between your heading and the bandit's. This

angle provides information about the relative fuselage alignment between the pilot's jet and the

bandit's. For example, if the Angle-Off between you and a bandit were 0°, you would be on a

parallel heading with the bandit, and the two fuselages would be aligned. If the angle-off were

90°, your fuselage would be perpendicular to the bandit.

 

 

 

Aspect Angle

Aspect angle is the number of degrees measured from the tail of a target to your aircraft.

Aspect angle is important because it indicates how far away your aircraft is from the target's 6

o'clock position. Aspect angle has nothing to do with your heading. Note that the aspect angle

stays the same, regardless of which way your aircraft is heading. Along with a measure in

degrees from the target's tail. In order to determine if the angle is left or right aspect, start at the

target's 6 o'clock facing the target. If your aircraft is in the right hemisphere, you have right

aspect; in the left hemisphere, you have left target aspect. Aspect angle is important because, if

you know the aspect angle and range to the target, you then know his lateral displacement or

turning room from the target-and lateral displacement is very important in BFM.

 

 

 

just a reminder cuz it causes often confusion :book:

 

 

THAT 13 L / 13 R THING :huh: ??

 

The Intercept

Now we have to complete the intercept, get a VID and shoot this guy. Since we need to get a VID to shoot these bandits, the best intercept to fly is a stern conversion. By rolling out the bandit's 6 o'clock, we will have time to pick up a tally on the bandit and get a shot. If we go in at high aspect, we may not see the bandit until we are inside Rmin for a missile shot.

What is a stern conversion, you ask? A stern conversion is shown in the next image

 

 

There are several steps to flying a stern conversion intercept.

 

1.

Switch to SAM (Situation Awareness Mode) or STT (Single Target Track) radar mode to get the aspect angle of the bandit formation. The next image shows a radar display with the aspect angle of the target marked.

 

 

 

2.

Turn opposite the aspect angle to get turning room on the targets. ( personal quick note from me (AS) here: there are reasons why you dont go the shortest way - headon- to target. either gun nor missiles...cuz you want to survive by keeping options open... may it be a 50/50 gunshot or the ability to dodge misisles ...thx Yoda for LRM hihi..)

In other words, if the aspect is 160° left aspect, then you need to turn right to move the targets to the left side of the scope. Do not turn so far that you take them off the scope. Just turn far enough to put them about 40° on the scope. The below image shows how you make this turn. Notice the figure has a god's-eye view and a radar view. All you are going to get in the jet is a radar view. It is up to you to use your gray matter to convert a radar display to a god's-eye view of the intercept.

 

 

Now is a good time to show what happens if you don't analyze the aspect properly and turn the wrong way for offset. Let's say the aspect was 160° left and you turned left for offset. Would this work? The answer is no, and below shows why. If you turn the wrong way, you will actually be taking away your turning room rather than increasing it. This will not be obvious by just looking at the target's position on the radar scope.

 

 

3.

The next step is to hold the targets at 40° on the scope and drive in. In order to hold the targets at 40°, you may have to check turn into them occasionally. The explanation for this is a little outside the scope of this book, but put simply, a target that is not on a collision course will always drift away from you. Think about this statement in driving terms. If you are driving on a two lane highway, you will notice that the oncoming traffic moves across your windshield and then suddenly flashes by. The oncoming traffic never just stays in the exact same spot on the windshield unless you are about to end up with chrome between your teeth. The same thing applies in air combat. During an intercept, you are driving the target away from a collision angle in order to get turning room. That means that the target will keep drifting farther away from you unless you turn to hold it at a particular angle

 

 

Edited September 28, 2008 by A.S

[A.S]

4.

In order to perform an intercept, all you have to do is follow the procedures. It's just like baking a cake. You don't have to understand the chemical process, you just have to follow the steps.

When you get to 10 miles from the bandits, go to STT and turn to put the target you are locked to in the HUD. This is the part of the intercept where things get serious. There are two reasons that we put the target on the nose at 10 miles. The first reason is so we can get a tally on the target. In the HUD, we have a Target Designator box with a target in it. The next image shows a HUD with the TD box labeled

 

 

The other reason we turn to put the target on the nose at 10 miles is to get small. It is much harder to see a jet that is pointing at you because there is less surface area to look at.

When we get a tally on the target, the intercept is over and it is time to use BFM. Remember in this fight that we only have a TD box on one of the two targets. As soon as we get a tally on the bandit in the HUD, we need to look for the other guy. Don't make the mistake of putting your eyes into the "random flail" mode. If the bandits have stayed in a visual formation (which is about 90% of the time), then the other bandit will be just outside the HUD when you get a tally on the guy in the TD box.

[A.S]

you read this above and you are even more confused now? read this

 

To understand the real maning of this 13L/13R display "Thing" i suggest reading

Multi-Command Handbook

 

http://www.fas.org/man/dod-101/sys/ac/docs/16v5.pdf

 

page 109 ....

 

It has to do with Intercept Terminolgies such as:

 

Forward Quarter

Stern Conversion

Single Side Offset

Trail

Sweep

Pincer

Drag

Lead-Around

Hook

Option

Break Away

Cross Block

 

...these are just examples..... but it has alot to do with entering from BVR to WVR in ACM ( Tajectory Optimization )

 

 

(not everything is a 40km dot in the skies :PPP )

Edited September 28, 2008 by A.S

[Vekkinho]

Thanks AS!

[Ironhand]

AS's post saves me making that tutorial. That was about 2 or 3 tutorials away. :) Good post. The only problem I have with it is the discussion--or, rather, the diagram--for Aspect Angle. The diagram indicates that the "Right" or "Left" is determined by which side of your aircraft the bogie is on. I've seen this diagram before and it is incorrect. The "Right" or "Left" orientation is determined by the side of the bogie which is facing you. It is HIS orientation, not yours, that determines it. The angle remains the same, in the diagram above, but the orientation does not.

 

Rich

[RvEYoda]

Ironhand, i think you should look at the AA diagram again....

It shows the same aspect regardless of your heading ;)

(i refer to the circle shaped one)

[Ironhand]

Ironhand, i think you should look at the AA diagram again....

It shows the same aspect regardless of your heading ;)

(i refer to the circle shaped one)

Yes, that's correct and I agree with that. But look at the diagram. It states that, if the bogie is to your right, the aspect angle remains "Right" regardless of the bogie's heading. That is incorrect. The aspect is the bogie's, not yours.

 

In the diagram, there are two bogies to the right of the fighter. The bogie whose heading is the fighter's reciprocal is 45R. The bogie whose heading is parallel to yours is 45L. The diagram states that they are both 45R. That is incorrect.

 

Rich

[Ironhand]

May be better calling it Heading Crossing Angle HCA. Back in the 60/70's Intercept profiles were based on Specific HCA's . Intercepts were known as "150 Front", or "130 Front", or "90 Stern", "130 Stern" etc.

Sorry. I missed this when I blew through earlier. Not sure if that would be the same angle. Also not sure how the USAF refers to it. Naval aviation referred to it as the DTG as recently as 2002. Not sure if the nomenclature has changed since then.

 

Rich

[RvEYoda]

Yes, that's correct and I agree with that. But look at the diagram. It states that, if the bogie is to your right, the aspect angle remains "Right" regardless of the bogie's heading. That is incorrect. The aspect is the bogie's, not yours.

 

In the diagram, there are two bogies to the right of the fighter. The bogie whose heading is the fighter's reciprocal is 45R. The bogie whose heading is parallel to yours is 45L. The diagram states that they are both 45R. That is incorrect.

 

Rich

 

Am i looking at the wrong picture?

In the one i refer to, there is only one bogey, but

it displays two different situations where you are.

 

You are the black plane.

The bogey is the red plane

[A.S]

I think i understand your confusion:

 

Aspect Angle and Aspect Angle

 

both times we speak bout the same Term but ..

 

Aspect Angle generally in flight geometry:

Aspect angle describes 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.

 

***********************

 

Aspect Angle in VSD:

 

indications like 14 L 14 R DO NOT only describe a full geometrical readout like you would have to understand on paper...... It is an interception guide or/and indicator !!! and as such to understand if shown in VSD.

 

In TWS you have the aircrafts symbolized with an arrow. That alone is an indication for you to see how to maneuver.

In STT you just see a blank symbol with no grafical attitude indication BUT you see 0-18 L/R.

That provides you enough information to "crank" to the right side in order to engage, keep bandit on the angle limits, reduce closure and to have enough seperation for turning room - be it into the bandit or having right tragectory for defensives.

 

 

by defintion in Interception Terminilogy:

 

 

read Book (above) page 106 4.13.2 down to page 109

 

Both times we read or speak bout Ascpect Angle but with different meaning

 

PS:

there is no 45L or 45 R - it goes from 0 to 18 ...

Angle Off is also known as HCA (Heading Crossing Angle). This is the basic, root form of other, more specific geometry’s (Angle Off Tail - AOT, and Angle Off Nose - AON).

Edited September 28, 2008 by A.S