Radar ranging for AKAN/ARAK

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?

The HUD only does the jittering for me when the impulse/series selector is set to impulse, at least for a specific distance. If its further or closer it gives a steady calculation. I can't tell any difference in functionality though.

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.

Does the diagram show anything like this? That the system bypasses the QFE input depending on whether radar ranging is on?

Does the diagram show anything like this? That the system bypasses the QFE input depending on whether radar ranging is on?

Anything I've seen in SFI just says that the CK uses aircraft altitude relative to the target, and doesn't mention from which source this information is gleaned. If someone else has found something more specific, please share.

It does say, however, on Del 3, Flik 2, s. 13 that

För att datorn ska beordra avståndsmätning med radar måste följande villkor uppfyllas:

 

* Skedesväljaren ska stå i läge ANF

 

* [...]

which means what I wrote, that the radar is only commanded to measure target range in ANF.

...

Gentleman, you just won internet today :megalol: and actually nailed the main point , so everybody should have a clear view of what's being discussed in this post

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).

Sorry renhanxue I quoted your comment on mistake as I intended to respond to bones :) anyway great tips there which thanks to my mistake won't be unnoticed :thumbup:

Regards

This is an interesting discussion and all, but is anyone able to actually hit something with guns by following these instructions?

I have a shooting range set up on a flat airfield by the sea, dive more than 5 degrees, have radar ranging indicator on the HUD, stable aim, trigger unsafe, wait few seconds for the blinking firing cue and still, the bullets consistently fall short before the target.

This is an interesting discussion and all, but is anyone able to actually hit something with guns by following these instructions?

 

I have a shooting range set up on a flat airfield by the sea, dive more than 5 degrees, have radar ranging indicator on the HUD, stable aim, trigger unsafe, wait few seconds for the blinking firing cue and still, the bullets consistently fall short before the target.

I wonder if the same problem is being experienced here as in the Mirage 2000. The 30mm shells all land short. I think the reason is that the air resistance is too high for those shells, and seeing this one uses the same ones it could be the for the same reason.

I have a shooting range set up on a flat airfield by the sea, dive more than 5 degrees, have radar ranging indicator on the HUD, stable aim, trigger unsafe, wait few seconds for the blinking firing cue and still, the bullets consistently fall short before the target.

Ooops, I just discovered that the AKAN (guns) fireing cue was displayed exactly 1 second too early. If you wait an additional 1 second before firing your solution should be accurate. This bug doesnt affect the rockets. Also, for reference, the firing cue is not the flashing line but the "wings" that are displayed around the sight dot. It is more important to fire at exactly this cue (or rather 0.5 second after this cue) when using the guns, when using the rockets you can fire a little earlier and still somewhat hit the target. You are also supposed to hold the trigger for 1 second and the gun strafe will be centered around your aim point.

I think it is worthwhile to explain the standard ("short") sight for the ARAK/AKAN in Viggen since it is quite difficult to figure out (I know I had trouble understanding how it worked at first). First of all, it is important to know that it is not a CCIP-sight which shows where the rockets/bullets will hit if you fire right now (the ARAK long-range mode is like this however). It is a little piece of SAAB-oddity that has the following design-goals if you will:

1) Provide a sight solution that is as accurate as possible. This also includes limiting the amount of ammunition dispersal so the rockets will be as concentrated as possible. I think the idea was maybe that it would be used against armored ships. The solution to this is firing the rockets/guns at the latest possible point in time (when closest to the target) while still have time to pull out and not being caught in the explosion from the rockets.

2) Provide a steady aim point on the ground. If you notice the sight stays pretty much at one point relative to the ground unless you move your stick or throttle. This allows the velocity measurement function where you can track the target and measure its speed and then the sight will compensate and show where to fire to hit a moving target. This would not have been possible with a regular CCIP-sight.

It works like this (a little simplified): it takes the indicated vertical velocity (barometric - hence you should still set the QFE even though using radar measurement, the sight would spaz out if using the radar height), indicated height (barometric or from the radar) and indicated forward speed and calculates the time it will take for the plane to reach the minimum selected safe height. It subtracts the time it would take for the plane to pull up into level-flight and also a little margin for the pilot to react. Now we have the last firing time. The computer then calculates the height the plane will have when this point in time is reached. The ballistics calculations is then done using the speed, height and orientation that the plane will have when it is at this point in time and displays to the pilot an aim point that shows where the rockets/bullets will hit if the trigger is pulled at that point in time. The pilot then waits for the timer to reach last firing timepoint (wings shown) and pulls the trigger and then immediately pulls up at 5G, and if everything is correct the rockets will hit with very high accuracy while the plane just avoids getting hit by shrapnel from the explosion.

Another way to think about the sight is that it is like a velocity vector indicator that shows where you will hit once you reach the safe altitude (plus time to level out).

Viggen, gentlemen. It does what it needs to, just usually not in the way you expect it.

You Swedish are weird people :D I wonder how many of these oddities are hidden in this incredible piece of technology.

Regards

How do you decide if you want to use baro or radar alt?

If you do "fast selection" (master mode NAV + trigger unsafe) the radar measurement will not be used.

If you set the master mode to ANF and also make sure the radar ranging is on (it is on by default, but you could enter 250 in TAKT to make sure) it will be used. You'll notice it is being used by the "tail fin" appearing above the sight dot when you are getting close.

Thanks for the explanation. I don't know how often you had to deal with stuff like this, but this must have added quite some time to developing its systems.

Ragnar is a warrior. For those that didn't know, Viggen has been in development since way before LNS was a company.