Radar ranging for AKAN/ARAK

[iLOVEwindmills]

So I understand the deal with setting the QFE, but against targets of opportunity I don't really see it as viable to get a sufficiently accurate setting in the short time you have to engage these in a combat zone

 

Now I assumed that radar ranging is the solution for this, as this is what the manual says about it.

 

'Radar ranging is indicated by the “fin” appearing in the HUD. The radar will range to the spot that the sight reticule (dot) is aiming at. As the radar will determine the more or less the exact distance to the aiming point, far more accurate sight calculations (particularly against inclined ground) are yielded. Radar ranging is thereby preferable than triangulation due to this increased accuracy.'

 

Though still my rockets/guns end up significantly off target when I, as far as I can tell, am using this mode.

 

I guess the question is, does targeting still rely on QFE despite using radar ranging? Shouldn't it have all the information it needs from solely the radar data in order to make a fully accurate aiming fix?

 

Or, quite likely, am I not setting things properly?

Edited January 29, 2017 by iLOVEwindmills

[some1]

I have similar observations, quite like the sight is bugged (surprise, surprise).

 

Both in A2A and A2G I have to aim higher than indicated to actually hit something.

[iLOVEwindmills]

I have similar observations, quite like the sight is bugged (surprise, surprise).

 

Both in A2A and A2G I have to aim higher than indicated to actually hit something.

 

 

Well, it seems to be accurate without changing anything about QFE at sea level.

[addde]

You Always need an accurate QFE if u want an accurate shot

[iLOVEwindmills]

You Always need an accurate QFE if u want an accurate shot

 

Is there a particular reason it is not be able to range properly with just the radar?

[Kelevra9987]

The CK37 calculates the Aimpoint by using pretty much everything it can get. QFE is one of them. Is the QFE not set right, the Aimpoint won't be set right either.

[nomdeplume]

The manual also says radar ranging begins when the calculated range is less than 7 KM. So if the target elevation is wildly wrong then it might not think you're close enough to switch to it. It also requires you to have a certain minimum dive-angle, which might be steeper than you think.

 

But: the AJS-37 just isn't designed for engaging 'targets of opportunity'. It doesn't have the fuel capacity to loiter waiting for a target to show up, and even if it encountered something on the way to its target it's unlikely it would just change its mission right there and then. If you've sent strikers to an area you probably want them to hit the planned target...

 

So, it probably just wasn't much of an issue in the real world or a design goal. I would guess if it came up, it would be handled either by switching to the backup (fixed) sight and conducting a "standard" attack (see e.g. the F-5E rocket delivery) using gut feel more or less; or they'd* use a map to work out the terrain elevation and derive the QFE from that.

 

* - they might get the QFE setting from someone else, e.g. ground units in the area, or someone back at base could do the calculation or reference weather charts for them, etc.

[some1]

The CK37 calculates the Aimpoint by using pretty much everything it can get. QFE is one of them. Is the QFE not set right, the Aimpoint won't be set right either.

 

Especially against airborne targets :doh:

 

My understanding is that QFE is needed in A2G before radar ranging is available. Makes no sense otherwise, the ballistic computer doesn't need it for anything if it already has accurate range to the target from the radar and aircraft pitch.

 

Anyway, I've been trying with correct QFE, so that's not it. I'll test more today.

[Rlaxoxo]

Mode to ANF

Selector to ATTACK

Weapon USAFE

 

Look at your gun sight change

 

Aim towards the ground, wait for horizontal line to reach the 2 lines and stop blinking

 

Fire

 

Pretty accurate for me when it comes down to rockets

[mattebubben]

This is my understanding of how the Ranging works so i might be wrong.

 

Even when using a Radar to range (or Laser on some aircraft) you

still need to take Aircraft altitude into account in order to calculate the proper firing solution

(or atleast so i assume).

 

Then you have the option of either Using the Radar Altimeter to get that altitude or using Barometric altitude etc.

 

Either choice have some advantages and disadvantages.

 

The Advantage with using the Radar Altimeter is that the Altitude can be automatically be updated at all times so no need to consider the QFE settings of the target etc.

 

But the disadvantage with this is that unless you are over level terrain (where the ground you fly over is at the same altitude as the Ground the Target is on) the target calculation might give you faulty calculations (Causing the weapons to fall long or short).

 

Where as with relying on a Barometric altimiter for that info you rely on having the correct setting for the Target altitude but the advantage about this is it does not matter if the terrain is level or not you will get an accurate target Solution either way.

 

And since the AJ 37 Viggen was only really planned to be used against targets where the location where known before the aircraft left the ground

(Since With Soviet Sams and Soviet Fighters were bound to be covering any target area limiting exposure time was of primary concern)

having the correct QFE setting was easy enough and gave a more reliable target calculation not dependant on terrain being flat etc.

 

Atleast this is my understanding on how the entire thing works =P

could be wrong though.

 

I find the rockets are accurate enough as long as you have the Correct QFE setting with the rockets impacts covering the target area,

Though i am finding that the Cannons seem to fall short when shooting at the fire command

so might be some problem there or maby im just doing something wrong at the pilot.

Edited January 30, 2017 by mattebubben

[Retrofly]

Quick hi-jack while we are talking about targeting. Is the boresight on the when using the maverick correct, it seems too high to me? Actually when using any sight in ANF mode I have to duck right down in my chair to get anything on the HUD (yes its in the up position).

 

Its making Mav shots difficult as I have to fly below the target, meaning i have less time to line up shots and pull out.

[some1]

Even when using a Radar to range (or Laser on some aircraft) you

still need to take Aircraft altitude into account in order to calculate the proper firing solution

(or atleast so i assume).

 

You just need slant range to target provided by radar, and pitch information from internal aircraft systems. Then you can calculate relative altitude to the target through basic trigonometry. That's why I said that QFE is needed only before radar ranging is available, otherwise it would be very weird to use unreliable information from the pressure altimeter over accurate radar/internal measurements for obtaining firing solution.

 

But my observations are similar to yours. Rockets are pretty accurate, but the gun shells fall short.

[iLOVEwindmills]

You just need slant range to target provided by radar, and pitch information from internal aircraft systems. Then you can calculate relative altitude to the target through basic trigonometry. That's why I said that QFE is needed only before radar ranging is available, otherwise it would be very weird to use unreliable information from the pressure altimeter over accurate radar/internal measurements for obtaining firing solution.

 

But my observations are similar to yours. Rockets are pretty accurate, but the gun shells fall short.

 

Yeah that's the main thing. If it has all the data it needs to produce an accurate firing solution from the radar and other internal systems, why would it insist on taking into account the manual QFE as well?

Especially when that can easily make for obviously wrong firing solutions when the QFE gives information that is clearly incorrect based on information from the aircrafts own measurements.

 

 

I suppose that the only way to use these weapons without accurate QFE is to disable the system entirely and use the fixed sight then. Makes sense in real life I'm sure, but its a bit of a problem for accurate targeting in DCS MP.

 

Maybe we need to get all mission makes to provide QFE information for all targets in the briefing.

[bones1014]

What is the radar altimeter doing while this is all going on?

[renhanxue]

Nothing special. Knowing your current altitude isn't interesting, what you want to know is the target's altitude and there's nothing that says it's got any relation to yours.

[amalahama]

Nothing special. Knowing your current altitude isn't interesting, what you want to know is the target's altitude and there's nothing that says it's got any relation to yours.

 

That's true for the radar altimeter, but it's not for radar-ranging. I totally align with some1, with a/c attitude and radar azimuth-elevation-range data, you can absolutely locate the target point in reference to your position, QFE data is redundant and actually, less accurate than the rest.

 

Regards

[xxJohnxx]

That's true for the radar altimeter, but it's not for radar-ranging. I totally align with some1, with a/c attitude and radar azimuth-elevation-range data, you can absolutely locate the target point in reference to your position, QFE data is redundant and actually, less accurate than the rest.

 

From a mathematical standpoint this is very true. I have had my professional artist draw a picture to have a common reference point we can use for some advanced maths done by my on-site mathematician.

 

 

 

 

Now let's do an analysis of this:

 

The only thing that setting the QFE does is giving us the height h.

 

Without setting the correct QFE we would have the following:

 

The angle a is known thanks to the gyros.

The distance d can be meassured by radar.

 

Now we can calculate both, the lenght l and the height h by using maths.

 

[b]h[/b] = sin([b]a[/b])*[b]d[/b]

and

 

[b]l[/b] = cos([b]a[/b])*[b]d[/b]

So, theoretically, as long as the radar is running and meassuring slant range, there should be no need for setting QFE because there is nothing you can't determin otherwise.

 

However, I am pretty sure LNS did some proper reasearch into the whole target point calculation, so we can safely assume that the real one needed that as well. Now I guess there is a good reason Saab decided to use the altimeter set to QFE. I am just wondering for what?

[renhanxue]

That's true for the radar altimeter, but it's not for radar-ranging. I totally align with some1, with a/c attitude and radar azimuth-elevation-range data, you can absolutely locate the target point in reference to your position, QFE data is redundant and actually, less accurate than the rest.

I'm not sure why you're re-stating the obvious...? bones1014 asked about what the radar altimeter was doing and I explained why it's not used for this - it's doesn't provide the data you want, except in special cases (flat ground). I said nothing about the main radar.

 

Either way, if you're missing ground targets while using radar ranging for rockets/gun pods, keep the following things in mind:

 

1. Is lead calculation active? If it's active it's vital to not unsafe before you have a stable aim point on the target, or any aim point movement will be interpreted as target movement that the computer will attempt to compensate for. TAKT/IN/221000 to disable this, enter with LS/SKU.

 

2. Are you locking before or after trigger unsafe? If you're going for targets of opportunity you might want to try the latter, TAKT/IN/252000 to select that, again enter with LS/SKU.

 

3. Air pressure is still taken into account for rocket ballistics calculations (drag/velocity loss) so having it set in the right neighborhood is still important.

 

4. The ballistic calculations are not CCIP - that is, they are not continuously correct. The aim point is "close to" correct (scientifically accurate term, used in the SFI) at the longest permitted firing range and actually correct when the firing signal in the HUD is given ("wings" on the flight path marker blinking).

Edited January 30, 2017 by renhanxue

[grunf]

The only reason for needing the QFE that comes to my mind is that the computer does not take pitch angle into account. But I find this very unlikely.

[renhanxue]

From a mathematical standpoint this is very true. I have had my professional artist draw a picture to have a common reference point we can use for some advanced maths done by my on-site mathematician.

 

 

 

 

Now let's do an analysis of this:

 

The only thing that setting the QFE does is giving us the height h.

 

Without setting the correct QFE we would have the following:

 

The angle a is known thanks to the gyros.

The distance d can be meassured by radar.

 

Now we can calculate both, the lenght l and the height h by using maths.

 

[b]h[/b] = sin([b]a[/b])*[b]d[/b]

and

 

[b]l[/b] = cos([b]a[/b])*[b]d[/b]

So, theoretically, as long as the radar is running and meassuring slant range, there should be no need for setting QFE because there is nothing you can't determin otherwise.

 

However, I am pretty sure LNS did some proper reasearch into the whole target point calculation, so we can safely assume that the real one needed that as well. Now I guess there is a good reason Saab decided to use the altimeter set to QFE. I am just wondering for what?

Great minds think alike; I find your drawing to have eerie similarities to this bit of the SFI:

 

 

As for how the slant range and aim point are actually calculated, please refer to fig. 14 and 15 respectively:

 

 

 

I'm not serious; I'm pretty sure Alexander the Great couldn't unravel that...

 

[xxJohnxx]

3. Air pressure is still taken into account for rocket ballistics calculations (drag/velocity loss) so having it set in the right neighborhood is still important.

 

This one is not making any sense though. Setting the QFE doesn't input something new into the system that the aircraft can't meassure locally at the given altitude. The altimeter is making an aproximation (1hpa = 10m) and so could the computer. This shouldn't affect ballicstics calculations in regards to drag/velocity at all.

 

Actually, regarding drag/valocity calculations density altitude would be a much more important factor. And for that QNH would be necessary.

[xxJohnxx]

Great minds think alike; I find your drawing to have eerie similarities to this bit of the SFI:

 

 

 

As for how the slant range and aim point are actually calculated, please refer to fig. 14 and 15 respectively:

 

 

 

I'm not serious; I'm pretty sure Alexander the Great couldn't unravel that...

 

Didn't know those diagramms where available to public. Very cool! :thumbup:

 

Now it would just be nice to understand Swedish. :cry:

[Krinje]

Just a stab here, but I'm fairly certain the QFE is just used for the HUD target designation circle so that you can visually identify the target. After radar takes over (you flip the switch and put the piper on the poor sod in a jeep.) QFE is irrelevant. But that's just one dudes opinion on how it could be working.

 

I offer more evidence: because of an artifact we've all experienced. When you unsafe and your HUD jumps/falls like crazy. That's the radar information ranging.

 

The above documents have the exact answer, but I can't read Swedish well enough. I can tell you that Radar ranging overrides QFE if the target is in the air "luftmal" and that there are some filters on QFE and possibly some triangulation blending too?

[renhanxue]

This one is not making any sense though. Setting the QFE doesn't input something new into the system that the aircraft can't meassure locally at the given altitude. The altimeter is making an aproximation (1hpa = 10m) and so could the computer. This shouldn't affect ballicstics calculations in regards to drag/velocity at all.

 

Actually, regarding drag/valocity calculations density altitude would be a much more important factor. And for that QNH would be necessary.

I can't tell you exactly what is going on, but as far as I understand the SFI, the computer calculates average projectile velocity (for both gun pods and rockets) using the aircraft's velocity vector, altitude relative to the target and a constant specific to the weapon type. Then it calculates projectile travel time to target using that, measured or triangulated slant range to the target, and air temperature (at takeoff, as I understand it).

 

If you know the slant range and the pitch angle you also know the altitude relative to the target though, as previously discussed, so QFE may be irrelevant after all.

 

Didn't know those diagramms where available to public. Very cool!

 

Now it would just be nice to understand Swedish.

 

https://forums.eagle.ru/showthread.php?t=168144

 

SFI AJS 37 del 3, page 58 and 59 in the PDF.

[Corrigan]

I have also read the relevant part of the SFI and I don't understand why the QFE would be needed either (nor have I actually seen it explicitly stated that it even is needed).

 

EDIT: Wait, in NAV the radar isn't available for ranging, right? Could that be it? If in NAV, the CK needs QFE since the radar is only commanded to measure target range in ANF.

Edited January 30, 2017 by Corrigan