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[FIXED] The wind moves away the BK90


SspectrumM

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At 1 m/s wind I did not notice any drift, but at 4 m/s cross wind it started to get bad enough to miss the target. Not sure if this is a bug or a feature :huh:

As the BK90 is equipped with an INS (sort of), it should be able to correct for wind by itself, so it sounds like a bug to me.


Edited by QuiGon

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As the BK90 is equipped with an INS (sort of), it should not be able to correct for wind by itself, so it sounds like a bug to me.

 

Why shouldn't the INS be able to correct the wind. It's a lateral movement, so inertia is effected.

Cbu-103 and 105 are also INS guieded and are called WCMD - wind corrected munition dispenser.

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Why shouldn't the INS be able to correct the wind. It's a lateral movement, so inertia is effected.

It should be able to correct, but INS always introduces errors. Being limited in space and weight, the BK90 probably does not have an INS as good as the Viggen. So some drift is to be expected. Now I don't know if the currently experienced drift is due to a modeled INS error (which would be awesome), or that the drift is really due to an faulty implementation.

 

In any case, it is probably best not to plan your attack cross-wind ;)

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Why shouldn't the INS be able to correct the wind. It's a lateral movement, so inertia is effected.

Cbu-103 and 105 are also INS guieded and are called WCMD - wind corrected munition dispenser.

Sorry, that "not" was not supposed to be there. I fixed it now. :music_whistling:

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I've also been noticing this, and helping myself by ofsetting my target waypoint into the wind. Also, i think to implement such a function to the BK90 automatically shouldn't be too hard, correct me if i'm wrong.

 

My idea is as follows: Take a readout of the wind as calculated by the CK37 when the trigger is pulled, and offset the BK90s target position by a set distance into the wind.

 

I've done this mostly on Kirks Hangar with a 5m/s wind on the deck. 150m of offset seems to be working quite good for this. That offset happening automatically would be super sweet!

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Same problem for me too. Also I found that the missile flies perfectly before it starts to dispense the munitions, however after that, everything goes wrong. So I think maybe there is no any kind of wind correction on this weapon? Because when it flies, it is just desgined to go to the point, after the explosion, hb doesnt care how munitions act.

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  • 2 weeks later...
As the BK90 is equipped with an INS (sort of), it should be able to correct for wind by itself, so it sounds like a bug to me.

 

What source could you find (I've not been able to find anything on it not/having an INS)?

 

Similarly - is the drift issue being noted at higher or lower release points?

 

Logically approaching this - INS benefits from having a motor, which the BK90 lacks. Thus just like SAM/AAM corrections post-motor phase the higher/further/longer the munition has to adjust the more "accurate" it would have potential to be.

 

I typically release my BK90s at 80-120M AGL so while there's not a whole lot of time for wind to mess them up, there's also little time to make major course corrections with tiny little fins. In higher winds it might make more sense for a high altitude (400-450M AGL) release and see if correctional guidance from the CK37 helps more?

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What source could you find (I've not been able to find anything on it not/having an INS)?

 

Similarly - is the drift issue being noted at higher or lower release points?

 

Logically approaching this - INS benefits from having a motor, which the BK90 lacks. Thus just like SAM/AAM corrections post-motor phase the higher/further/longer the munition has to adjust the more "accurate" it would have potential to be.

 

I typically release my BK90s at 80-120M AGL so while there's not a whole lot of time for wind to mess them up, there's also little time to make major course corrections with tiny little fins. In higher winds it might make more sense for a high altitude (400-450M AGL) release and see if correctional guidance from the CK37 helps more?

Well, how does it navigate to the target waypoint then, if it does not have some kind of INS?

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:unsure: Can you explain this?

I wonder about this as well. A battery (which the BK90 has) would be sufficent.

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I wonder about this as well. A battery (which the BK90 has) would be sufficent.

 

The BK90 has no rocket or other motor to propel it - it relies entirely on the inertia generated from the host aircraft to reach it's destination. It is a glider. In this case then it would be more like a guided gliding bomb than a missile.

 

Look at the difference between gliders and conventional aircraft in wingspan - gliders typically have massive wings to take advantage of lift which then allow them the ability to maneuver. Gliders are also as light as possible. The BK90 has small control wings and isn't light.

 

As a result guidance is more limited, especially during later phases of it's "glide." This also means that it generally starts with less inertia than say a Maverick which does have a rocket motor and thus has less ability to correct than the Maverick.

 

Greater corrections also result in drag, so too much correction can lead to a glide trajectory that doesn't reach the destination - so it may even be programmed for less correction.

 

The BK90 also suffers from the fact that the overall design is one that allows for aided lift (the boxier flat bottom) vs most missiles which are cylindrical. Lateral wind will play a larger effect on that surface, which combined with less control availability, makes for a weapon that doesn't like wind.

 

Yes the battery on board would operate the control surfaces but that has nothing to do with it.


Edited by Leadnap

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The BK90 has no rocket or other motor to propel it - it relies entirely on the inertia generated from the host aircraft to reach it's destination. It is a glider. In this case then it would be more like a guided gliding bomb than a missile.

 

Look at the difference between gliders and conventional aircraft in wingspan - gliders typically have massive wings to take advantage of lift which then allow them the ability to maneuver. Gliders are also as light as possible. The BK90 has small control wings and isn't light.

 

As a result guidance is more limited, especially during later phases of it's "glide." This also means that it generally starts with less inertia than say a Maverick which does have a rocket motor and thus has less ability to correct than the Maverick.

 

Greater corrections also result in drag, so too much correction can lead to a glide trajectory that doesn't reach the destination - so it may even be programmed for less correction.

 

The BK90 also suffers from the fact that the overall design is one that allows for aided lift (the boxier flat bottom) vs most missiles which are cylindrical. Lateral wind will play a larger effect on that surface, which combined with less control availability, makes for a weapon that doesn't like wind.

 

Yes the battery on board would operate the control surfaces but that has nothing to do with it.

 

You are talking about the inertia BK90, i.e. the fact that a heavy object require more force to push it off course. So basically you are saying that due to the heavy weight and small control surfaces the BK90 is not capable to make the necessary adjustments to compensate for the wind? Sounds plausible to me ...

 

The discussion before was whether or not a BK90 had an INS (inertial navigation system, which is basically a gyro and has nothing to do with the mass of the BK90) or not. It should have one, and it should be able to tell the BK90 it is off course. Whether or not it is able to reach the destination depends entirely on the specific parameters of the wind and BK90 (and how these are modeled in DCS).

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BK90 has inertial system (IMU on attached photo) and it also has radar alt meter and digital computer which uses kalman filtering to keep it on course as best as possible.

From my experience, BK90 underperforms (in sense how wind and terrain can influence it) in DCS...

bk90imu.thumb.jpg.8b3c11df48db7578acce46ed43852648.jpg

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You are talking about the inertia BK90, i.e. the fact that a heavy object require more force to push it off course. So basically you are saying that due to the heavy weight and small control surfaces the BK90 is not capable to make the necessary adjustments to compensate for the wind? Sounds plausible to me ...

 

The discussion before was whether or not a BK90 had an INS (inertial navigation system, which is basically a gyro and has nothing to do with the mass of the BK90) or not. It should have one, and it should be able to tell the BK90 it is off course. Whether or not it is able to reach the destination depends entirely on the specific parameters of the wind and BK90 (and how these are modeled in DCS).

 

Right - the BK90 has an INS. However what I originally was saying is that I don't know that the poor performance of the BK90 in simulation in wind is necessarily a "bug" but rather relative to the fact that as a "guided" munition it would have greater potential for poor performance in wind - thus the simulation may not be far off. Is the accuracy poor in wind vs no wind - yes, is that intentional, possibly.

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  • 9 months later...

*bump*

 

I've noticed the dispensed munitions still dispense off target if there is any wind.

 

It's been shown earlier that the Bk90 has an INS and the manual seems to indicate that the Viggen can account for wind. In this, I suspect the munition (or the CK37) would adjust it's dispense point to compensate for known wind.

 

So, is the lack of automatic offset for the BK90 dispense point to account for wind a bug, modelling shortfall or a limitation of the real system?

 

Devs:

- If it's a bug or a modelling issue, can it be fixed?

- If it's a real world limitation, can a table be provided so we can offset target points appropriately?

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Since they introduced weather on the Blue Flag server I noticed this erroneous behaviour now as well. It would be nice to hear from HB if this is going to be fixed...

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  • 1 month later...
Looks like a bug. Thanks for reporting. Should be easy to fix I hope. Meanwhile there is a workaround.

Thanks, without knowing the code it sounds to me like there just needs a '-' to be replaced with a '+' or vice versa and that's a good example for the frustration that some here (including myself) currently have. While HB has a great Community Manager for the Tomcat now, who has the time to go through all those reports and hand them to the team, you Ragnar apparently have to do do it all by yourself for the Viggen. With that workload on a single person it's hardly a suprise that reports like this here, that only require a quick and minor fix stay unnoticed for so long, while it could have been fixed for quite some time and that can get quite frustrating for us users.

 

Given the fact that HB has its own community manager, just for the Tomcat and also several coders for it as well, while for the Viggen that all is done by a single person, doesn't really fit the statements made by Cobra that the Viggen is all but forgotten.

 

 

Sorry for the rant, but I needed to get this out. I'm very happy that this bug report (and other pending bug reports) has caught your attention now and that you're on it. :thumbup:


Edited by QuiGon

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I've checked and Viggen in DCS doesnt account for the wind drift of the submunitions. It may or may not do this IRL, the docs doesnt say. I anyway added this feature now, but it's impossible to make it perfectly accurate since the submunitions will be dispensed on different altitudes. Inputting incorrect wind-data into CK37 as suggested in this thread may not be a good workaround until the patch since it probably just introduces a error in the INS that just happens sometimes to coincide with the offset for the submunitions.

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There will always be bugs. If everything is a priority nothing is.

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