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Old 12-06-2018, 08:18 AM   #11
QuiGon
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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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Old 12-06-2018, 09:39 AM   #12
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Logically approaching this - INS benefits from having a motor, which the BK90 lacks.
Can you explain this?
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Old 12-06-2018, 09:39 AM   #13
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Can you explain this?
I wonder about this as well. A battery (which the BK90 has) would be sufficent.
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Old 12-06-2018, 04:05 PM   #14
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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.

Last edited by Leadnap; 12-06-2018 at 04:07 PM.
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Old 12-06-2018, 04:25 PM   #15
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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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Old 12-06-2018, 04:57 PM   #16
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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...
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Old 12-06-2018, 05:33 PM   #17
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Thanks for the info!
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Old 12-06-2018, 06:22 PM   #18
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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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