Wind Bug Found in DCS: World 1.2.7

[Habu23]

After practicing CCIP and CCRP attacks with dumb bombs, I was becoming increasingly frustrated when my bombs were flying very far off course. Over the past half year, many people were convinced that the A-10C's LASTE system was to blame for bomb inaccuracy. After 1.2.6, I was only able to hit targets when I turned the wind completely off. Whenever I set a consistent wind speed and direction on the ground, 2,000m, and 8,000m, I could not hit anything. It turns out that this was not LASTE's fault at all.

 

In fact, the wind speed that you set at 10m is multiplied by two in the game regardless of the value set in the editor. It is entirely believable that there is an accidental (x2) in the code that is making this occur. LASTE and calculating systems of other aircraft are indeed computing a good solution, but an unexpected and incredibly strong wind layer in the last few thousands of feet are causing bombs to fly off course. Let me demonstrate:

 

Editor Settings:

 

 

CDU wind readouts and bomb results:

 

 

 

Bombs hit way off the mark downwind of the target:

 

 

Now ground level wind speed is set to half the desired value:

 

Editor Settings:

 

 

CDU wind readouts and bomb results:

 

 

 

Bombs hit right on the mark!

 

 

In each test three bombs were dropped with 30 feet dispersion via level CCRP release at 6,500 feet to minimize error margin in experiment. Results are consistent with any wind speed inputted in the editor.

 

Conclusion: There is definitely an issue with ground level wind speeds being multiplied by two while in the game. This problem does not occur when dynamic weather is used.

Hopefully this will be fixed in the next patch.

 

Habu

Edited April 12, 2014 by Habu23

[chaos]

That's interesting. Might possibly be due to converting metric (m/s) to imperial (knots) or vice-versa. Good catch if that is indeed the problem...

[Flagrum]

In fact, the ME uses meters per second and the CDU uses knots. 1 m/s = 0.514 knots. So it is at least absolutely plausible that the CDU shows only half of the value in the ME.

 

The CDU works with an algorithm with a certain wind model. This model corresponds to the DCS "reality" only if you set the 10 m wind layer in the ME. Iirc, the wind speeds dimishes, the higher you are. If you now use several wind layers in the ME, the IFFCC does not take that into account automatically - you would have to edit the CDU wind page for that.

 

That being said, there were some intense discussion a few months ago about all this. In the end, the consent was - or at least the result I took from it was - that IFFCC wind correction works, that also additional wind layers in the CDU are taken into account correctly, but that you still have to expect sub-perfect results as dropping dumb bombs is inherently unprecise and difficult and that there is no real magic bullet for that.

Edited April 12, 2014 by Flagrum

[Justin Case]

Yep. Editor is in M/S and the A-10C uses knots.

[ZaltysZ]

Units are not the issue. 6 m/s = 12kts. However, A10C shows 24 kts near the ground, when wind is just 12kts there. If you go higher, it shows the wind correctly.

 

I have done a simple test: created a mission with Ka-50 near the water with 2 waypoints, then flew the mission with different winds at 10m altitude. ABRIS shows cross-track error and flight time, so I divided the former by the later and evaluated the wind. Every time it was like in mission editor. Wind isn't doubled near the ground in game world.

 

I don't think this is a game world bug as OP suggested. I think it is just A10C problem.

[Flagrum]

Units are not the issue. 6 m/s = 12kts. However, A10C shows 24 kts near the ground, when wind is just 12kts there. If you go higher, it shows the wind correctly.

 

I have done a simple test: created a mission with Ka-50 near the water with 2 waypoints, then flew the mission with different winds at 10m altitude. ABRIS shows cross-track error and flight time, so I divided the former by the later and evaluated the wind. Every time it was like in mission editor. Wind isn't doubled near the ground in game world.

 

I don't think this is a game world bug as OP suggested. I think it is just A10C problem.

Multipe wind layers in the ME - as the OP configured - makes things very complex. Especially if those wind layers are not entered in the CDU ...

[ZaltysZ]

Multipe wind layers in the ME - as the OP configured - makes things very complex. Especially if those wind layers are not entered in the CDU ...

 

Things are complex for bombing solution and etc. However, the "glitch" is far simpler here. In fact, we can simply forget bombing for now, and concentrate just on calculation of wind near the ground.

 

Most aircraft with advanced NAV systems can calculate wind by itself while using data from INS, GPS and so on. A10C does the same. The "glitch" is that it doubles the wind speed near the ground.

[Flagrum]

Things are complex for bombing solution and etc. However, the "glitch" is far simpler here. In fact, we can simply forget bombing for now, and concentrate just on calculation of wind near the ground.

 

Most aircraft with advanced NAV systems can calculate wind by itself while using data from INS, GPS and so on. A10C does the same. The "glitch" is that it doubles the wind speed near the ground.

No. I am not talking about the complexities of bombing alone. I am talking about the complexity of the wind and how much of that the IFFCC is able to determine/calculate. The A-10C calculates the wind according an algorithm that is based on a specific model of how the wind changes for different altitudes. I believe, the standard model is a somewhat linear function that is based on 0m/s at -4000 ft MSL up to the measured speed at your current altitude. If you now have several wind layers (as the OP did), that model does not fit anymore - unless you enter the wind layer data in the CDU (which the OP did not, I assume).

 

edit:

the wind model that is actually used in DCS is even more complex than described above as it also takes altitude/density into account. So if you have set 10m/s at 10m and the program assumes 0m/s at -4000ft, it will NOT give you 20m/s at +4000 ft. Instead, if only the first layer is configured in the ME and the other remain at 0m/s, the wind at higher altitudes begins to dimish. So in fact, it is not a linear function ...

 

Maybe there is some kind of "glitch" in the way the wind is modelled ... or it is just a lack of understanding real weather and configuring the layers in the ME accordingly to get "good" overall results...

 

But all I am saying is, my experience is, that with one wind layer the IFFCC does a decent job in predicting the impact point ... and thus something seems to be not totally off there. But with several wind layers things might be hard to understand how and why it is simulated as it is.

 

edit2:

some sample data - you can see, the wind is never really exact as configured in the ME, instead it is a smoothed curve

http://forums.eagle.ru/showpost.php?p=1857309&postcount=4

Edited April 12, 2014 by Flagrum

[Flagrum]

There's no several wind layers at OP's test. He set the same wind at all levels.

Technically, that ARE different layers. It is a difference if you have 10m/s at 10m and 10m/s at 2000m or if you set 10m/s @ 10m and 0m/s @ 2000m.

 

In the latter case, the wind starts earlier to dimish and to converge towards 0m/s.

[Flagrum]

I really don't know how the DCS wx engine works, but if you set all layers to one value, there's nothing to dimish and to converge because delta speed is 0.

Look at the charts in the posting I liked to earlier ("edit2").

I am not claiming I fully understand how the weather works, but I know that it is more complex that it looks at first glance.

 

edit2:

this here: http://forums.eagle.ru/showpost.php?p=1857309&postcount=4

[ZaltysZ]

the wind model that is actually used in DCS is even more complex than described above as it also takes altitude/density into account. So if you have set 10m/s at 10m and the program assumes 0m/s at -4000ft, it will NOT give you 20m/s at +4000 ft. Instead, if only the first layer is configured in the ME and the other remain at 0m/s, the wind at higher altitudes begins to dimish. So in fact, it is not a linear function ...

 

Yes, but this is not the issue :) The issue is: if you set wind to 12kts (6m/s) at 10m layer and you fly your A10C exactly 10m above sea level, its NAV system will show 24kts (12m/s) wind. I have tested and wind at 10m altitude is 6m/s if ME shows 6m/s at 10m, however A10C thinks wind is double than that.

[Flagrum]

Great, look at the second image. You set wind speed 40kts, but until you reach 5000ft, the wind is higher than set in ME. Why the algorithm works like that? If i set ground wind to 10knots, I want 10 knots at the ground.

 

Can you do the graph for wind direction? I would like to see if there's any drift if you set all layers at the same direction and speed.

I think it has to do that it is not a linear function, but a curve to gradually match the set speed. Otherwise you would have sudden jumps when you enter an other wind layer. Something like this:

 

And no, sorry, I neither have the data anymore nor would I have any clue of how to illustrate the different directions (disclaimer: I am a total math layman :o)

[Flagrum]

Yes, but this is not the issue :) The issue is: if you set wind to 12kts (6m/s) at 10m layer and you fly your A10C exactly 10m above sea level, its NAV system will show 24kts (12m/s) wind. I have tested and wind at 10m altitude is 6m/s if ME shows 6m/s at 10m, however A10C thinks wind is double than that.

I can not replicate this. Post a .trk please?

And/or maybe I misunderstood you there - what exactly did you enter where and what did you read where? "In the ME, you set ____ m/s and CDU showed ____ kts"?

[Yo-Yo]

PLEASE KEEP IN MIND.

 

The wind has gradient approx from 500 m and down to the ground. In highlands it's slightly different.

The wind set in ME is the wind MEASURED at 10 m at the lowland airdrome weather service.

 

The actual wind IS DIFFERENT. As in RL.

[Habu23]

Interesting discussion by all, but please understand that this is not an issue of the IFFCC computing accurate results or if wind is realistically implemented, because as you all have mentioned it is so. Instead, there is a disconnect between the value entered by a mission maker for ground level wind speed and the actual wind speed seen in game (multiplied by two).

 

Habu

[Flagrum]

Interesting discussion by all, but please understand that this is not an issue of the IFFCC computing accurate results or if wind is realistically implemented, because as you all have mentioned it is so. Instead, there is a disconnect between the value entered by a mission maker for ground level wind speed and the actual wind speed seen in game (multiplied by two).

 

Habu

This is not observable with your screen shots imo as you don't read the wind speed at 10 m AGL, but 400 ft AGL. I bet, if you fly over the ocean at 30 ft you will get the value you set in the ME.

 

... and/or post a .TRK :o)

[ZaltysZ]

I can not replicate this. Post a .trk please?

And/or maybe I misunderstood you there - what exactly did you enter where and what did you read where? "In the ME, you set ____ m/s and CDU showed ____ kts"?

 

I have done more vigorous testing and everything is fine. I was seeing 24kts in CDU when wind was 6m/s in ME and I was flying at 30-50ft ASL/AGL. The reason why it was showing higher wind was probably due to not stable enough flying. CDU lags a bit and steep wind gradient does not help it too.

[ZaltysZ]

Interesting discussion by all, but please understand that this is not an issue of the IFFCC computing accurate results or if wind is realistically implemented, because as you all have mentioned it is so. Instead, there is a disconnect between the value entered by a mission maker for ground level wind speed and the actual wind speed seen in game (multiplied by two).

 

Habu

 

Wind in real life dimishes rapidly near the ground, because terrain, trees, buildings and etc. obstruct air flow. In ME you enter that dimished wind as wind at 10m (AGL). 500m or so higher it doubles and then transits into next wind layer.

[Habu23]

With my tests I was able to get the speed down to about 14 knots at 10 meters above the ocean. If I went just a 100 feet higher, the wind speed increases drastically to double the speed set in the editor, 24 knots. I understand that a gradient needs to be modeled to correctly and realistically progress through the various wind gradients, but the way it is now is more of a multiplier effect than a gradual, normally distributed gradient.

 

If I set wind speed at 6 m/s on the ground in the mission editor, as a mission maker I would expect that the wind will blow at 6 m/s (+ or - a few knots, not double its wind speed) on the ground up to at least 4,000 feet, simply because I wanted it so. With the current system, I am forced to put in a value half of what is desired in order for the wind to be consistently 6 m/s from 10m to 2000m above the ground. This isn't entirely obvious, and may lead to unintended consequences for mission designers not fully aware of how wind is implemented. I hope you all understand what I am saying.

[Boris]

Running 1.2.8 now...

 

I can definitely confirm that wind speeds are far too high at the ground level. By 2x, just as the OP said.

 

I came across this today practicing CCIP bombing with wind adjustment.

 

I set the wind speed at ground level for 7m/s in the editor, which should give me an expected wind speed of 14 Kts in the pit of my A-10c.

Instead, it was consistently showing 28 to 29 Kts near the ground!

 

I climbed to 6000ft to confirm my setting for 2000m, which was 5 m/s, and the speed shown in cockpit was 10 Kts, which is spot on and to be expected.

 

I highly doubt that the high wind speeds on the ground are some sort of complex effect caused by different layers. All higher layers had slower wind speeds.

Edited May 14, 2014 by Boris

[Boris]

I've looked a little further into this...

 

I set up a mission with one wind layer only at 10 meters, at 0 degrees for 4m/s.

 

All higher wind layers were set to 0m/s.

 

What one logically should expect to see in the CDU is 173/008. That is, the wind is coming from the magnetic bearing of 173 degrees at 8 knots, as knots are roughly twice m/s. We should not expect the wind to be any higher than 8 knots anywhere, since no higher wind, turbulence or weather system was set up in the editor.

 

However, this reading of 8 knots wind can only be obtained when skimming the ground very closely near sea level. At only a few hundred feet the wind speed increases greatly, culminating in 17 knots (around 8m/s) at around 1300 feet.

From there, the wind speed drops again and reaches 0 as the 2000m layer is reached at around 5000 feet.

 

Something is definitely wrong here. There is absolutely no reason I can see, why the wind speed should double within the first layer. What we would expect to see in this scenario is a gradual drop in windspeed from 8m/s at sea level to zero at around 6000 feet.

No other wind layer shows this eratic behaviour.

 

Can someone confirm this please?

Edited May 14, 2014 by Boris

[ФрогФут]

The wind slows down near the ground. The start of the slow down is somewhere at the 200 meters altitude, so you will surely need much higher wind at 200 meters to get the wind to desired 8 knots at 10 m.

[Boris]

The wind slows down near the ground. The start of the slow down is somewhere at the 200 meters altitude, so you will surely need much higher wind at 200 meters to get the wind to desired 8 knots at 10 m.

 

Hi ФрогФут, thanks for your reply!

 

But that is the problem. The wind down at sea level (0m) IS the setting set in the mission editor. The increase in windspeed above this go far above the levels set.

 

To break it down...

 

Mission editor: The wind is set to 4m/s at the 10m layer.

 

In game (A-10C): When flying right near the ground the CDU will display 8 Knots (4m/s)

When rising above 200m, as you say, the wind picks up dramatically.

At around 1300 feet ASL the wind is at it's highest (around 17 knots in this scenario) - Twice as high as any wind speed set in the mission editor!

 

Wind speeds above this altitude are lower again, since in the test I had them set to 0, with 0m/s windspeed at around 5000 feet.

 

So basically, the windspeed of the bottom layer is twice as fast as it should be.

Edited May 14, 2014 by Boris

[ФрогФут]

When rising above 200m, as you say, the wind picks up dramatically.

That is what i said. The wind MUST be higher, so that after slowing near the ground give you what you set for 10 m. 10 m - is the altitude of measurement equipment.

[howie87]

That is what i said. The wind MUST be higher, so that after slowing near the ground give you what you set for 10 m. 10 m - is the altitude of measurement equipment.

 

What I think people want is to be able to set a 'maximum' value for wind speed.

 

The altitudes you can set wind speeds for should be the altitudes where wind speeds peak.

 

For exanple if you got rid of the 10m setting and made it 200m instead, people would know that the wind speed between 0-200m will be not be higher than what they set in the editor.

Edited May 15, 2014 by howie87