BK-90 Range and HUD symbology

[TLTeo]

So I'm trying to figure out exactly what the BK-90 is capable of, because there's quite the discrepancy between the manual and HUD symbology, and what one can actually do in game.

 

The manual states that allowed release altitudes are between 50 and 500 meters, in which case the range is ~10 km or so depending on our airspeed at release. This also seems to match the HUD symbology. The issue however comes when one tries to release the weapon from higher altitudes, say, a few thousand meters. In this case, the weapon still guides to the target perfectly well and actually has far more range, but the symbology does not reflect this capability.

 

I have attached a Tacview of me hitting some dummy targets from ~16nm away, releasing from ~16000 feet (unfortunately tracks are completely broken for me, so I can't include that). By the time they reach the target, the dispensers are flying at ~300 knots and fairly high (~10 degrees) AoA, so they are at the limit of their range. This is not quite what a JSOW does, but better than a e.g. JDAM or CBU-105 dropped from a similar speed/altitude, which is still impressive. In this case however the HUD range bar is flashing, indicating that a course correction is required. Diving to below 500 meters causes the flashing to disappear and the normal symbology to appear, so the jet does not expect that drop to be succesful.

 

So what I'm getting at is - should the BK-90 be capable of high altitude releases and achieve such a large standoff range? If yes, how come the HUD symbology does not reflect this? If not, how come we can artificially get so much more performance out of the weapon? Personally, my gut feeling says yes, high altitude standoff delivery should be possible - given that it's a modern weapon that is still in service with several air forces, which certainly don't limit themselves to Cold War era low level strikes.

Tacview-20210825-235618-DCS.zip.acmi

Edited August 26, 2021 by TLTeo

[QuiGon]

2 hours ago, TLTeo said:

So I'm trying to figure out exactly what the BK-90 is capable of, because there's quite the discrepancy between the manual and HUD symbology, and what one can actually do in game.

 

The manual states that allowed release altitudes are between 50 and 500 meters, in which case the range is ~10 km or so depending on our airspeed at release. This also seems to match the HUD symbology. The issue however comes when one tries to release the weapon from higher altitudes, say, a few thousand meters. In this case, the weapon still guides to the target perfectly well and actually has far more range, but the symbology does not reflect this capability.

 

I have attached a Tacview of me hitting some dummy targets from ~16nm away, releasing from ~16000 feet (unfortunately tracks are completely broken for me, so I can't include that). By the time they reach the target, the dispensers are flying at ~300 knots and fairly high (~10 degrees) AoA, so they are at the limit of their range. This is not quite what a JSOW does, but better than a e.g. JDAM or CBU-105 dropped from a similar speed/altitude, which is still impressive. In this case however the HUD range bar is flashing, indicating that a course correction is required. Diving to below 500 meters causes the flashing to disappear and the normal symbology to appear, so the jet does not expect that drop to be succesful.

 

So what I'm getting at is - should the BK-90 be capable of high altitude releases and achieve such a large standoff range? If yes, how come the HUD symbology does not reflect this? If not, how come we can artificially get so much more performance out of the weapon? Personally, my gut feeling says yes, high altitude standoff delivery should be possible - given that it's a modern weapon that is still in service with several air forces, which certainly don't limit themselves to Cold War era low level strikes.

Tacview-20210825-235618-DCS.zip.acmi 74.97 kB · 1 download

 

 

Interesting question. Maybe the Swedes just had no use for releases at 500+ m and thus it has never been evaluated and the HUD doesn't reflect it?

 

On a side note: What other countries use the BK90?

[TLTeo]

Yeah I shouldn't have used the plural, I convinced myself that Gulf Air Forces used it but I must have confused it with some other cluster weapon. From what I can find, the Hellenic Air Force are the only users.

[QuiGon]

4 hours ago, TLTeo said:

From what I can find, the Hellenic Air Force are the only users.

 

On which aircraft? Never heard of them using the BK90.

 

https://www.haf.gr/en/equipment/ 

Edited August 26, 2021 by QuiGon

[TLTeo]

17 minutes ago, QuiGon said:

 

On which aircraft? Never heard of them using the BK90.

 

https://www.haf.gr/en/equipment/ 

 

According to Wikipedia, the Phantom https://en.wikipedia.org/wiki/Hellenic_Air_Force#Air-to-ground

Could be that it's either retired because cluster munitions (even though Greece did not sign on the Cluster Munitions Convention), or standard Wikipedia bullcrap though.

 

I think my point stands though. I don't think you introduce a supposedly standoff weapon in the 90s, post Desert Storm, that can only be launched at treetop level. That's just weird, the RB-15 which was introduced at the same time on the same aircraft does not have that limitation to name one.

Edited August 26, 2021 by TLTeo

[MYSE1234]

13 minutes ago, QuiGon said:

 

On which aircraft? Never heard of them using the BK90.

 

https://www.haf.gr/en/equipment/ 

 

Fairly sure I've seen an image of an F-4 with Bk90s mounted on the wings.

[Snappy]

Well,

 

of course I'm not qualified to say whether or not the real weapon would be capable of such a feat in theory. I would think heatblur modelled the HUD symbology correctly.

I could imagine though , one possible reason for why they (the swedes) didn't implement or didn't want to do high alt & long range stand off releases with that  weapon:

The higher and farther away you release, the greater the possible navigational error of the weapon enroute to target is going to be. Plus , at higher altitudes  in reality you get usually/often significantly stronger winds than down low , so those might either further degrade the accuracy or worse push the weapon out of its envelope, make it impossible to reach the intended target. Plus the winds might change a lot on the way down in direction and intensity.

Consider the development background time  too, the early 90s, that means GPS was either still exclusive US military use  or even if it was  after it was made publicly available,  that was initially in its less accurate mode. So you don't get that accuracy.  So I'd guess the weapon guides on inertial only. I don't know how good or accurate the system in it was and how accurate the data it was fed from the aircraft was on average under actual  battlefield conditions.

So given all of the above, and also the general political /ethical image of cluster ammunition, I can easily imagine  the swedes wanting to keep the possibility of their submunitions landing somewhere else and not on target  as low as possible, even if it was deemed a necessary weapon for them.

Could be totally wrong though,

 

As for DCS, at lot of things there are modelled too perfect  , so I'm not surprised that the weapon functions well from further away, but many factors are probaby not simulated that affect the real weapons, as well as a lacking weather / wind simulation.
 

Snappy

Edited August 26, 2021 by Snappy

[TLTeo]

I'm not sure whether that's the reason. The CBU-105 is also guided exclusively by an INS, rather than GPS, and it can do high altitude perfectly fine. In fact, correcting for the wind is the whole point of the WCMD kit, it's in the name. Both are area weapons anyway, so a bit of drift is probably perfectly fine. They don't need the accuracy of a JDAM to do their thing. 

 

On the ethics side, the BK-90 supposedly has all sorts of in-built ways to avoid leaving submunitions behind, so I think that's factored in already.

[Snappy]

50 minutes ago, TLTeo said:

I'm not sure whether that's the reason. The CBU-105 is also guided exclusively by an INS, rather than GPS, and it can do high altitude perfectly fine. In fact, correcting for the wind is the whole point of the WCMD kit, it's in the name. Both are area weapons anyway, so a bit of drift is probably perfectly fine. They don't need the accuracy of a JDAM to do their thing. 

 

On the ethics side, the BK-90 supposedly has all sorts of in-built ways to avoid leaving submunitions behind, so I think that's factored in already.

Not so sure about that. 

 

It actually seems that the very point of upgrading from CBU 97 to CBU-105 was to significantly  increase its accuracy and bringing it to precision guided munitions status by adding the WCMD and GPS guidance.

The weapon itself may not have it, the GPS for it apparently was planned but dropped, but only because the delivery aircraft are fitted with GPS and it gets a final accurate position from that aircraft GPS just before launch.

I don't think the VIggen would get anywhere near that GPS accuracy for release , because a) its ADR system is accumulating much larger errors over time and b) the TERNAV system that's used to update it/reduce errors would not work at the release altitudes that you proposed, because it is based on radar altimeter data  and that becomes unusable at such altitudes, radar alt normally works reliably only until up to approx 2500-3000 ft  . So in order to get a decent base accuracy for the BK-90 release the Viggen most likely has to stay low . 

 

Plus the CBU-105 entered service quite a bit later (in 98 I think) so its onboard processors for the flight path computation in the WCMD kit  are probably more capable in regards to navigational calculations and drift compensation.

----
Yea, I read that part too about the supposed fail-proof  - leave behind submunition in the Bk-90, which supposedly can't explode later.

Not sure how much of that is marketing and whether I buy into that . Even if its true, it didn't make it significantly more political / ethical acceptable  in reality.
 

 

 

Edited August 26, 2021 by Snappy

[renhanxue]

I don't know how well the BK90 anti-UXO measures actually did work (that's almost certainly still classified) but I do know that a great deal of effort was put into it and for good reasons. Remember the weapon system came out of the Cold War, and as such the Swedish doctrine at the time meant that it would have been designed for almost exclusive use on Swedish territory. Leaving behind significant amounts of UXO would have been a big headache for the Swedish authorities afterwards and a highly undesirable property of the weapon.

Edited August 26, 2021 by renhanxue

[QuiGon]

13 hours ago, MYSE1234 said:

Fairly sure I've seen an image of an F-4 with Bk90s mounted on the wings.

 

I would love to see that, as I have not seen any good evidence of other countries using the BK90

 

Edit:

Nvm, I found it: https://www.haf.gr/en/equipment/afds-autonomous-free-flight-dispenser-system/

They use it on the A-7 and F-4:

http://www.defense-aerospace.com/article-view/release/3592/greek-af-tests-gliding-dispenser-(nov.-15).html

http://www.defense-aerospace.com/articles-view/release/3/4107/free-flight-of-new-greek-af-dispenser-(jan.-11).html

 

In regards to the actual topic the last link also says:

Quote

AFDS, developed and manufactured by LFK, is an unpowered, gliding, intelligent submunition dispenser system. Its flight is controlled by a computer, digital guidance equipment, an inertial navigation system with integrated GPS, and aerodynamic rudders. Flying at low level, pilots can "fire-and-forget" the AFDS up to ten kilometres from target. Over 20 kilometres stand-off can be achieved from higher altitudes.

 

Edited August 27, 2021 by QuiGon

[Bananabrai]

I was curiouse and testet that as well, so from 1250m AGL and M0,90 I am able to achieve 15km.
But then from 2000m and same speed I am not able to achieve 20km.

 

Seems like you have to get exponentialy higher to reach twice the distance or something...

 

 

 

[IDontLikeBigbrother]

Yes, even launching at the low altitude with 500m, bk90 is capable of double range as the manual or the hud symbol claimed. If the launching speed is 0.8mach, you can get a guaranteed hit 10km away.

[TLTeo]

11 hours ago, Bananabrai said:

I was curiouse and testet that as well, so from 1250m AGL and M0,90 I am able to achieve 15km.
But then from 2000m and same speed I am not able to achieve 20km.

 

Seems like you have to get exponentialy higher to reach twice the distance or something...

One thing I noticed is that the BK90s don't really glide horizontally like a JDAM or JSOW, instead they fly a shallow dive until they reach low altitude, so it makes sense that they wouldn't benefit as much from high alt launches.

  

9 hours ago, IDontLikeBigbrother said:

Yes, even launching at the low altitude with 500m, bk90 is capable of double range as the manual or the hud symbol claimed. If the launching speed is 0.8mach, you can get a guaranteed hit 10km away.

Hmm, so we're back to "either the flight model or HUD symbology are wrong", except it applies to low altitude as well. Interesting.

[MYSE1234]

1 hour ago, TLTeo said:

...

 

Hmm, so we're back to "either the flight model or HUD symbology are wrong", except it applies to low altitude as well. Interesting.

Why not both? 

I know for a fact that the release cue is not shown at the (assumed correct) distance shown in a diagram in one of the manuals, but only at high speeds.
We've got two diagrams showing the release envelope at:
"100m and mach 0.9", the max range shown there is 7km, directly in front
"100m and mach 0.7", there the max range in front is 3,2km, +-50 or so

The cue I got when testing this some time ago at "100m and mach 0.9" was at 5,1km, so about 73% of what it should be, according to the manual. The slower mach 0.7 is very accurate to what is shown in the manual, with a distance of 3,16km. Well within the margin of error.

To have the cue at the correct mach 0.9 distance is impossible, from my testing.

NOTE: I only tested up to 550m, so it might be possible to get the 0.9 cue accurate at higher up, but from 450-550m it's a constant distance of 6,6km.
            Image below is probably ONLY, accurate in distance directly in front of the aircraft. I did not test drops to the side, as that should have take too much time to do.

[TLTeo]

4 minutes ago, MYSE1234 said:

it might be possible to get the 0.9 cue accurate at higher up

From what I can tell, higher up makes the cue less accurate, not more, so that's unlikely. Good reminder though, I forgot your thread!

[Bananabrai]

Well, the question for me is: Does the system wants to have the Bk90 over the target at a certain speed?

I noticed, although with 1250m AGL and M0.90 I reached 15km, but barely, and the canisters were not flying very fast any more.

 

I think it stalls around or just somewhere below 300 kts (F2 external view reading.)

On my shot is was not much above that. Maybe IRL there is a requierement that the thing only is guaranteed to work properly if it's dispensing at a certain speed?

 

As the Bk90 is also seen and fired upon by AAA etc., speed is also an advantage for it.

A greater range of course would then be a nice advantage for the releasing aircraft...

[MYSE1234]

21 minutes ago, Bananabrai said:

Does the system wants to have the Bk90 over the target at a certain speed?

...

That's what I was thinking too, but from my testing I see nothing pointing to that in DCS, it might be the case irl.

[IDontLikeBigbrother]

On 9/1/2021 at 4:53 PM, MYSE1234 said:

"100m and mach 0.9", the max range shown there is 7km, directly in front

 

On 9/1/2021 at 4:53 PM, MYSE1234 said:

The cue I got when testing this some time ago at "100m and mach 0.9" was at 5,1km, so about 73% of what it should be, according to the manual.

I know it's from the manual, so I'm not doubting about the accuracy. But even the range of 7km is really a dangerous number, it's just on the max range of sa19 Tunguska. If I launch at 7km, due to the 0.9mach high speed, the closest distance between me and the tunguska maybe 6km or even closer. It's highly possible to take a shot from tunguska. As the imgs shown below:

Launch at 7km

pull a 7g turn, the closest distance is 6km

still take a shot(the missile didnt have enough energy though)

7km is pretty safe to the stings or manpads, but it's dangerous to the Tunguska. While tunguska is in service since 1982, bk90 is designed since 1986 and in service since 1992. It's a pretty strange short range design.

[renhanxue]

5 hours ago, IDontLikeBigbrother said:

 

It's a pretty strange short range design.

It really is and ever since that manual page was declassified I've always wondered why it has that weird and seemingly completely arbitrary low release altitude restriction. I assume there must be some reason for it, but I doubt we'll get any reasonable explanation in the near future because the development documentation is probably not going to be declassified for a while yet.

[QuiGon]

13 hours ago, renhanxue said:

It really is and ever since that manual page was declassified I've always wondered why it has that weird and seemingly completely arbitrary low release altitude restriction. I assume there must be some reason for it, but I doubt we'll get any reasonable explanation in the near future because the development documentation is probably not going to be declassified for a while yet.

 

I still believe it's just because of the doctrine: There was no need for higher releases, as the doctrin for the Viggen was low altitude, so they probably never evaluated the performance of the BK90 at highter altitudes and thus restricted the launch altitude to levels that were tested.

But that's also just speculation on my side

[TLTeo]

@IronMike bump/ping to get some attention on this behaviour, per your request in the EA discussion thread.

[IronMike]

13 minutes ago, TLTeo said:

@IronMike bump/ping to get some attention on this behaviour, per your request in the EA discussion thread.

 

Thank you, I saw the thread earlier, but will deal with it tmrw, need to finish cutting Jester Lantirn stuff today... Need to read myself a bit into the thematic, too. Thanks for the ping!

[IronMike]

On 8/26/2021 at 5:15 AM, TLTeo said:

So I'm trying to figure out exactly what the BK-90 is capable of, because there's quite the discrepancy between the manual and HUD symbology, and what one can actually do in game.

 

The manual states that allowed release altitudes are between 50 and 500 meters, in which case the range is ~10 km or so depending on our airspeed at release. This also seems to match the HUD symbology. The issue however comes when one tries to release the weapon from higher altitudes, say, a few thousand meters. In this case, the weapon still guides to the target perfectly well and actually has far more range, but the symbology does not reflect this capability.

 

I have attached a Tacview of me hitting some dummy targets from ~16nm away, releasing from ~16000 feet (unfortunately tracks are completely broken for me, so I can't include that). By the time they reach the target, the dispensers are flying at ~300 knots and fairly high (~10 degrees) AoA, so they are at the limit of their range. This is not quite what a JSOW does, but better than a e.g. JDAM or CBU-105 dropped from a similar speed/altitude, which is still impressive. In this case however the HUD range bar is flashing, indicating that a course correction is required. Diving to below 500 meters causes the flashing to disappear and the normal symbology to appear, so the jet does not expect that drop to be succesful.

 

So what I'm getting at is - should the BK-90 be capable of high altitude releases and achieve such a large standoff range? If yes, how come the HUD symbology does not reflect this? If not, how come we can artificially get so much more performance out of the weapon? Personally, my gut feeling says yes, high altitude standoff delivery should be possible - given that it's a modern weapon that is still in service with several air forces, which certainly don't limit themselves to Cold War era low level strikes.

Tacview-20210825-235618-DCS.zip.acmi 74.97 kB · 5 downloads

 

 

 

Ok, finally got to reading through it. This does not strike me as odd, since a) the delivery parameters are not meant to be for such a high release and b), like a TALD or similar not self propelled weapon, ofc the higher and faster you go, the further it will fly. But as you seen yourself, when it reaches the release point, it is already at its low energy envelope. While yes, today one would want to adjust the HUD for such deliveries, back then the doctrine simply may have been "no". There is of course a difference sometimes in between what a weapon can do, and how a certain military wanted to use it. The delivery parameters being adjusted for the latter would not surprise me at all.

Maybe @Jediteo can shed more light on that, too. Maybe also @Naquaii could shed some additional light on this. (Thanks!) 

[IronMike]

On 9/1/2021 at 9:53 PM, MYSE1234 said:

Why not both? 

I know for a fact that the release cue is not shown at the (assumed correct) distance shown in a diagram in one of the manuals, but only at high speeds.
We've got two diagrams showing the release envelope at:
"100m and mach 0.9", the max range shown there is 7km, directly in front
"100m and mach 0.7", there the max range in front is 3,2km, +-50 or so

The cue I got when testing this some time ago at "100m and mach 0.9" was at 5,1km, so about 73% of what it should be, according to the manual. The slower mach 0.7 is very accurate to what is shown in the manual, with a distance of 3,16km. Well within the margin of error.

To have the cue at the correct mach 0.9 distance is impossible, from my testing.

NOTE: I only tested up to 550m, so it might be possible to get the 0.9 cue accurate at higher up, but from 450-550m it's a constant distance of 6,6km.
            Image below is probably ONLY, accurate in distance directly in front of the aircraft. I did not test drops to the side, as that should have take too much time to do.

 

I tracked this issue for further investigation, thanks.