Su27 vertical&horizontal scan - Help needed

[holimoli]

Hi,

 

I did a couple of tests/calculations the last days about the radar of the Su27...and I really got stuck with something...I hope somebody can help me out here and find my mistake.:helpsmilie:

 

Here is what I've tested.

 

I tried the same test at different distances like 20,50,70 away too - So far similar results...I'm still testing.

 

Here are some HUD pictures I've taken: http://imgur.com/a/JgsFe

 

Vertical scan:

- I put myself (Su-27) at 5000m, about 650kmh.

- I put 3 contacts ( Su-27) 10km in front of me with same speed an 1000m altitude separation. 1st at 6000m, 2nd contact at 5000m and 3rd 4000m respectively.

- I put my radar on with default expected range 10km and started to scan with 1+,0,-1 elevation. I tried all PRF settings.

 

 

 

At elevation +1 I only see contact 1. I had to dive about 700m to see contact 2 as well on the radar.

At elevation 0 I only see contact 1,2.

At elevation -1 I only see contact 2,3.

 

So can anyone tell me why I don't see all 3 contacts at elevation 0? Or why I do see contact 3...I should either see all three contacts or only contact 2 at elevation 0. AFAIK my scan zone 10km away from me is about 1750m in total (875m up, 875m down) - If this is right I should only see contact 2 then. Also I shouldn't see contact 2 at elevation -1.

 

Does anybody know how the radar cone is implemented/calculated in the game? It's a 10° degree beam going 5° up and 5° down from your nose in initial position, right? And manipulating the elevation will change the radar angle in relation to the expected range !?

 

 

Horizontal scan:

-Again I put myself (Su27) at 5000m,650kmh

-I put 1 contact (Su27) heading towards me 25km away and 12,5km to my right at same altitude.

 

If I scan in initial position without manipulating the radar I'll see the contact on the right limit of my HUD. If I increase my separation to him >12,5km he will disappear on my HUD. So why is the limit at 25km away 12,5km? That's not 30°, isn't it?

 

Thanks for any help! I'll keep testing in the meantime ;)

[DrDetroit]

The radar seem odd in the SU-27. Seems I can hardly pickup anything outside of 30nm or so, while my wing can see contacts much farther out and more quickly - more like 50nm or so.

 

So I use his data link to find my targets alot, unless I'm within 10-15nm, then it's DF mode.

 

I think your test confirm the 'strangeness' of the SU-27 radar.

 

Good day,

 

DrDetroit

[Weta43]

From the photos it looks like they might just be too widely spaced to all fit in the scan cone at the same time.

Move the zone left & see if L & C appear, then right and see if C & R appear.

[Santi871]

I can tell you the radar is working 100% correctly from what you've described. I'm a little busy and on mobile right now but I will do all the math for you later, but if you want a heads up, check the radar diagram on my guide.

[apocom]

At 10km you scan 1763m vertical.

 

So at elevation 1 you scan the area 6000-7763m, so you can see 1 contact (6000m).

At elevation 0 you scan the area between 5000-6763m so you see 2 contacts (5000m and 6000m).

At elevation -1 you scan the area between 4000-5763m so you see 2 contacts (4000m and 5000m)

 

For your horizontal scan problem I'm not excaclty sure what you mean. Your contact is like 26° away from you. Do you use elevation at this point?

[holimoli]

wow thanks for all the fast replies.. ill get more into detail now :)

 

From the photos it looks like they might just be too widely spaced to all fit in the scan cone at the same time.

Move the zone left & see if L & C appear, then right and see if C & R appear.

 

No I can pick up all 3 contacts without changing my heading..the screenshots are about vertical only. But thanks for the hint!

 

I can tell you the radar is working 100% correctly from what you've described. I'm a little busy and on mobile right now but I will do all the math for you later, but if you want a heads up, check the radar diagram on my guide.

 

Yes already read your guide! I got the same numbers as u. Thanks! Nice guide btw. :)

 

 

 

 

At 10km you scan 1763m vertical.

 

So at elevation 1 you scan the area 6000-7763m, so you can see 1 contact (6000m).

At elevation 0 you scan the area between 5000-6763m so you see 2 contacts (5000m and 6000m).

At elevation -1 you scan the area between 4000-5763m so you see 2 contacts (4000m and 5000m)

 

For your horizontal scan problem I'm not excaclty sure what you mean. Your contact is like 26° away from you. Do you use elevation at this point?

 

 

So this means the radar looks basically 10° up in its initial position!? I thought it goes 5° up/down. At least thats what the right side of the HUD shows.

 

 

yes, excatly he is 26° to the right. Manual states the radar can scan 30° right/left!? And the contact will fade if he is >12,5km left/right

[apocom]

So this means the radar looks basically 10° up in its initial position!? I thought it goes 5° up/down. At least thats what the right side of the HUD shows.

 

yes, excatly he is 26° to the right. Manual states the radar can scan 30° right/left!? And the contact will fade if he is >12,5km left/right

 

I can't find any hard evidence that the radar looks up, but your problem and Santis guide descripes it that way.

 

The contact should fade at 14434m left/right at 25km, because thats 30°. I have to test it if its exactly so precise, I can imagine that its harder for the radar to find targets at its edge.

[Santi871]

I can't find any hard evidence that the radar looks up, but your problem and Santis guide descripes it that way.

 

The contact should fade at 14434m left/right at 25km, because thats 30°. I have to test it if its exactly so precise, I can imagine that its harder for the radar to find targets at its edge.

 

The radar does look up 10°. It took a while to find but it was somewhere in this forum.

 

And you are right, 30° gives 14.4km, and my diagram is wrong, I think I accidentally wrote sine instead of tangent in wolfram alpha.

 

So in that case I'm not sure why it fades at 12.5, its possible the cone has some sort of diffusion, as it would in real life.

[holimoli]

The radar does look up 10°. It took a while to find but it was somewhere in this forum.

 

And you are right, 30° gives 14.4km, and my diagram is wrong, I think I accidentally wrote sine instead of tangent in wolfram alpha.

 

So in that case I'm not sure why it fades at 12.5, its possible the cone has some sort of diffusion, as it would in real life.

 

 

yea it really seems the radar is 10° up. My +/-5° was solely based on the HUD markers. So what are the HUD markers on the right then? I thought the notch is representing your nose (0°) and the bar letft to the elevation number is your radar cone (10°)...:/

 

 

But its a really big gap 12.5 to 14.4...hmmm.

[Ironhand]

So what are the HUD markers on the right then?...

The HUD markers represent the vertical piece of sky you can see through the HUD. They're there as a reference so that you know how far above or below the HUD you are scanning.

 

EDIT: The line in the image that you label as "Nose 0*!?" is the level line or horizon line (I believe). If you pitch your nose up or down, I think you'll see the HUD reference lines move up or down in relation to it.

Edited November 6, 2015 by Ironhand

[Frostie]

Holimoli are you sure the radar doesn't see +/- 5.5deg. This would put the contacts at the very edge of the radar cone at 962m meaning a slight variation in range can make a huge difference in seeing the contacts and not.

[apocom]

Ok, I've done different tests now. Mostly because I wanted to find out if the radar really sees 30° (it does).

 

But I found another thing I can't explain with the radar looks 10° up.

I put 2 test rows in front of me, one at 10km the other at 25km. Lets ignore the 2nd.

Every aircraft was set to 3000m altitude and 900km/h.

 

I changed my starting altitude a bit, because doing this manually means I changed the distance too much to the other aircrafts. I could see the targets on my radar from ~1800m to ~3400m. That would mean that the radar fov is not +10°, but more like +7.5° and -2.5° or +7° and -3°.

[ShuRugal]

I don't know the exact scan height of the N001 in degrees, but it has a vertical FOV approximately equal to what you can see through the HUD.

 

If you look at the HUD scale for the radar vertical setting, you will notice that there are two bars sticking out the right of the scale, which move vertically as you pitch up and down: these bars represent the vertical FOV of the HUD in relation to the horizon. The short vertical bar to the left of the scan elevation number represents the vertical FOV of the radar scan zone.

 

You will notice that these are approximately the same height, and it is because the radar scan zone and the HUD are the same vertical height, as viewed from the pilot's seat. At a range of 10km, the scan zone is less than 1km high (you will notice that the bar moves more than its own height between each number of vertical displacement when range is set to 10km).

 

Thus your experience that targets separated by 1km altitude are not simultaneously visible at 10km or less is exactly correct: The radar scan zone is not high enough to see them both at the same time in a horizontal plane.

[Santi871]

To be fair, the radar fov is tiny within 20km. It wasn't designed to search at such close ranges, so its a better idea to use the vertical scan mode.

[DarkFire]

To be fair, the radar fov is tiny within 20km. It wasn't designed to search at such close ranges, so its a better idea to use the vertical scan mode.

 

That, or the longitudinal aiming mode (4 key) which is also useful when you're just entering WVR combat.

[Santi871]

That, or the longitudinal aiming mode (4 key) which is also useful when you're just entering WVR combat.

 

I find it to be redundant, I don't see how it's better than VS.

[DarkFire]

I find it to be redundant, I don't see how it's better than VS.

 

It can be useful, but only in that you don't have to roll to get your lift vector lined up with a target so you can make offset passes if you really want to. Otherwise I agree that vertical scan is generally more useful in most WVR fights.

[holimoli]

The HUD markers represent the vertical piece of sky you can see through the HUD. They're there as a reference so that you know how far above or below the HUD you are scanning.

 

EDIT: The line in the image that you label as "Nose 0*!?" is the level line or horizon line (I believe). If you pitch your nose up or down, I think you'll see the HUD reference lines move up or down in relation to it.

 

Thanks for clarifaction! Just read it up again in the manual :). Dunno where i picked that "notch=nose" thing up...-.-

 

 

Ok, I've done different tests now. Mostly because I wanted to find out if the radar really sees 30° (it does).

 

But I found another thing I can't explain with the radar looks 10° up.

I put 2 test rows in front of me, one at 10km the other at 25km. Lets ignore the 2nd.

Every aircraft was set to 3000m altitude and 900km/h.

 

I changed my starting altitude a bit, because doing this manually means I changed the distance too much to the other aircrafts. I could see the targets on my radar from ~1800m to ~3400m. That would mean that the radar fov is not +10°, but more like +7.5° and -2.5° or +7° and -3°.

 

Didn't double check the 30° azimuth yet but yeah so far i get up values of 6,3°...Dunno, the value seems really odd to me.I did a couple of runs with contacts@different alt - I'm a little bit tired and confused after getting these values :S....Need to think about it and have a look at my test conditions again;).

 

 

Btw im doing all of this in DCS 1.5b I haven't tried it in 1.2.6 yet.

[apocom]

So I've done a test multiple times, everytime with the same result.

 

I've put 7 targets in front of me (15km away), 1 reference target, then from left to right

 

-3.6° | -3.1° | -2.6° | +/-0° | -2.4° | -2.9° | -3.4°

 

I can resolve every target but the target -3.6°, thats why I believe the radar looks 3.5° down.

 

EDIT: That's also close to Holimolis finding that the radar looks 6.3° up (6.5° for my calculation)

Edited November 7, 2015 by apocom

[Santi871]

So I've done a test multiple times, everytime with the same result.

 

I've put 7 targets in front of me (15km away), 1 reference target, then from left to right

 

-3.6° | -3.1° | -2.6° | +/-0° | -2.4° | -2.9° | -3.4°

 

I can resolve every target but the target -3.6°, thats why I believe the radar looks 3.5° down.

 

EDIT: That's also close to Holimolis finding that the radar looks 6.3° up (6.5° for my calculation)

 

Interesting findings. It's a shame there's so hard to find official data for this radar.

[apocom]

Ok, I've checked my findings with tacview if I've done any mistakes, and I have.

 

I've locked the target at 5000m (the radar told me it flies at 4999, so an ok error) and adjusted my own altitude accordingly. But my own altitude is displayed false. I have no idea why, it's neither ASL nor AGL (according to tacview). There is an error of 100m so my previous findings are false.

 

I retested everything so that in tacview the maximum error is 7m.

 

With this I can find a target that is -3.8° below, but not a target that is -3.9° below.

[Frostie]

I've tested and also and come to the same conclusion of +6.5/-3.5.

Same for the MiG-29.

The F-15 is +5/-5.

In testing you also have to account for radar memory so getting an accurate figure may not be possible.

 

To get close +/-5 degree with the Russian radars then the target range needs to be set at 60km and elevation -1.

[holimoli]

really interesting.yes.. Here is in detail what i did to get the 6,3° up.

 

I began from the beginning. I put my contacts at 3 different altitudes again based on an assumption the the radar cone is either 10°,7° or 5° up in its initial position.

 

I put myself at 2000m alt.

I put again 3 contacts 40km ( It was a little bit more..like ~46km) away, heading towards me.

The contacts had altitutdes of :

-Contact1: 7053m (= tan(10°)*40000)

-Contact2:6906m (=tan(7°)*40000)

-Contact3: 5300m (=tan(5°)*40000)

All 3 contacts had 500TAS

 

I started the mission hit the active pause key and waited. So i have 3 contacts at 3 different altitude flying towards me. All I had to do is wait until one of those contact fades from the radar, then hit the pause key go into f10 measure the distance and read the alt.

 

These are the results:

Contact1(10°) : Is not visible at all... This means the radar doesn't look 10° up.

Contact2(7°): The contacted faded @44240m from me. Since the radar does take 1-3 secs to update and myself needs like 0,3-0,5s to react. I did it twice and added some meters due to the radar update delay and took the average of it.

1st run: Contact2 fades@44240m, Contact3 fades@29670m

2nd run: Contact2 fades@44450m, Contact3 fades@29680m

 

I took these values and added some "radar update delay", calculated the angles and took the average.

 

500TAS leads to 138,89m/s

Contact2-1st run: 44240+(1*138,89), 44240+(2*138,89),44240+(3*138,89)

Contact2-2nd run: 44450+(1*138,89), 44450+(2*138,89),44450+(3*138,89)

 

Contact3-1st run: 29670+(1*138,89), 29670+(2*138,89),29670+(3*138,89)

Contact3-2nd run: 29680+(1*138,89), 29680+(2*138,89),29680+(3*138,89)

 

I calculate every angle with arctan((contact alt - my alt)/(contact distance))

For example..Contacts 1st run values:

0sec delay: arctan((6906-2000)/(44240)=6,33°

1sec delay: arctan((6906-2000)/(44240+138,89)= 6,31°

2sec delay: arctan((6906-2000)/(44240+2*138,89)=6,29°

3sec delay: arctan((6906-2000)/(44240+3*138,89)=6,26°

 

and so on....

 

I couldn't find any mistake yet..so I assume the 6,3° is right..but again this value seems really odd to me and I'm gonna do some more tests... :)

Edited November 7, 2015 by holimoli
wrong number

[apocom]

I've tested and also and come to the same conclusion of +6.5/-3.5.

 

Have you checked your flight with tacview? That's where my problems occurs. I have no idea what more correct is, tacview or the ingame display.

 

The aircrafts are set to

 

-3.7° | -3.8° | -3.9° | +/-0° | +6.4° | +6.3° | +6.2° | +6.1°

 

According to tacview my overall error is 3m.

 

As you can see -3.8° ,-3.9° and +6.4° are missing.

 

First of all, I have no idea if I've done everything correct. Mostly because the values ingame differ. I belive tacview is right, just because if I put my plane at 5000m ASL, tacview tells me it's 5000m ASL but ingame its 4890m.

 

I couldn't find any mistake yet..so I assume the 6,3° is right..but again this value seems really odd to me and I'm gonna do some more tests...

Second, these values seems strange at first sight, but they have their own beauty. For every 10km your radar looks 1km up (more like 1.1) and for every 15km your radar looks 1km down.

[holimoli]

Have you checked your flight with tacview? That's where my problems occurs. I have no idea what more correct is, tacview or the ingame display.

 

The aircrafts are set to

 

-3.7° | -3.8° | -3.9° | +/-0° | +6.4° | +6.3° | +6.2° | +6.1°

 

According to tacview my overall error is 3m.

 

As you can see -3.8° ,-3.9° and +6.4° are missing.

 

First of all, I have no idea if I've done everything correct. Mostly because the values ingame differ. I belive tacview is right, just because if I put my plane at 5000m ASL, tacview tells me it's 5000m ASL but ingame its 4890m.

 

 

Second, these values seems strange at first sight, but they have their own beauty. For every 10km your radar looks 1km up (more like 1.1) and for every 15km your radar looks 1km down.

 

I think the pressure isn't set when u enter your aircraft. That's where the discrepancy comes from...Might be wrong though... I'dont have much experience with this.

 

So basically u are getting the same values as I am..hmhmhm..So if the radar is 6,3°-3,7° it should look like this: