[FIXED INTERNAL] The R-3R missile in DCS: Too fast and too much drag?

Note that this post is in no way a critique of the Leatherneck simulations Mig-21. I love it and the Mig-21 is IMHO the most impressive module yet in DCS.:thumbup:

However, there is a fundamental issue in the DCS missile flight modeling which seems to plague the Mig-21 R-3R missile as well:

Attached is a track showing a chase intercept scenario with a Mig-21 launching an R-3R missile at 6 Km altitude at 12.5 Km range with a launch speed of 789 Km/h at a target moving at 600 Km/h. As the track shows, in this scenario the R-3R fails to connect and falls out of the sky 21 s into flight.

Also attached, are two figures from a C++ missile simulation program I have developed and been tuning over the last two years. In the C++ simulation, the intercept figure attached shows that the missile launch results in a kill. Of course this is a very marginal case since the missile is basically out of energy, flying at 1013 Km/h with an angle of attack of 4.2 degrees when connecting so any maneuver on the part of the target would probably result in a miss. But given that the target keeps it course, the missile will hit it and result in a kill.

In DCS however, the missile falls out of the sky already 21 seconds after launch and at a relatively high speed of around 1400 Km/h. In fact the whole R-3R flight in DCS is very strange: The missile accelerates to almost 4300 Km/h which is way too fast given the modest engine/ missile weight factor (circa 19%) of this missile. In fact 4300 Km/h is what the AIM-120 C would do under these conditions but this missile has a huge advantage in engine/ missile weight factor (circa 34%) so 4300 Km/h for the R-3R under these conditions is IMHO way to fast.

Now attached is also a page from a book by Russian author Fedosov who has published data on Russian missiles that to the best of my knowledge is pretty good. This data contains both missile engine impulse and speed imparted to missile. Looking at the R-3R, we can see that this missile gets a speed boost of around 1800 km/h. So in the track scenario this should result in around 789 + 1800 = 2589 Km/h. Note that this I quite close to the attached C++ simulation fly-out figure but is quite far from the 4300 km/h in DCS.

I cannot of course say I’m 100% sure I’m right but when it comes to the DCS missile FM there is a user (IASGATG) who has done a really good job of analyzing the AM-120 C using CFD and the results can be seen here:

http://forums.eagle.ru/showpost.php?p=2197925&postcount=1

While IASGATG used CFD to do his analysis, I have used a completely different approach but we still get results that are pretty close:

http://forums.eagle.ru/showpost.php?p=2232007&postcount=186

Now this may not be watertight evidence, but since two fundamentally different approaches yield results so close and since the C++ model predicts results close to the IRL performance data for the Sparrow III (see post #190 in the DCS missile mod thread), I think we are on the right track.

So basically, it looks like that in the DCS model, the R-3R missile has too much drag but gets a higher impulse than IRL.

Don’t know if Leatherneck can do something about this on their own or if it’s all in the hands of DCS. I certainly would be glad if Leatherneck took an interest in this because the DCS developers have unfortunately so far shown very limited interest in the IASGATG mod which I personally think is simply great and deserves a better fate.

Mig21 P51 miss at 12 Km launch at 6 Km alt.trk

DCS in general has some pretty serious issues with missile FM's. The R-27ER has an absolute max range relative to the ground of maybe 20km, in real life it's 80km+. I'm just guessing here, but I bet LNS decided to do whatever they could to make the R-3R missile range as accurate as they could, even if it meant altering other performance attributes.

DCS in general has some pretty serious issues with missile FM's. The R-27ER has an absolute max range relative to the ground of maybe 20km, in real life it's 80km+. I'm just guessing here, but I bet LNS decided to do whatever they could to make the R-3R missile range as accurate as they could, even if it meant altering other performance attributes.

Yep, that may be so. Given that the current R-3R in DCS is so draggy, giving the missile more impulse and speeding it up to a high velocity compensates is a way to go about it but it would be better to lower drag and impulse I think.

If you have not tried IASGATG missile mod the I can recommend that for the R-27ER. Gives much better performance, closer to IRL performance IMHO.

Noticed that the thread has been tagged [FIXED INTERNAL] now so I figured this issue had been addressed but this does not seem to be the case: I still get around 4300 km/h missile top speed from a +800 km/h launch at 6 km altitude so it's still too high and the missile still behaves as if it has the speed-brakes deployed after motor burnout.

FIXED sounds like past tense to me but does [FIXED INTERNAL] mean problem acknowledged and fix is under way? OTOH there is also the [FIX UNDERWAY] classification so I'm just trying to make sense of what does [FIXED INTERNAL] mean and what are the plans?

Well "Fixed Internal" clearly means that developers have fixed this in their version, which is not released to public yet, hence the "Internal" tag, so just now you need to wait for the fix to become public :)

the key word is internal, i.e. a development build that we don't have access to.

Edit: sniped :p

Allright! Now that sounds promising! :thumbup:

BTW: Anybody know if this is limited to the Leatherneck missiles or can we look forward also to fixes for the other missiles like AIM-120 and the R-27-series etc?

@kuky -

would you really go so far as to say....... "fixed"

?

remember, "their version" will be not necessary the "next version".

Also: When you say "fixed" does that mean missile kinematics only or does that include guidance as well? I mean, I would be happy if they started with the kinematics because that would go a long way but to also get guidance improvements would be awesome! :beer:

@kuky -

 

would you really go so far as to say....... "fixed"

 

?

Well yeah... the developer(s) have set this thread as [Fixed Internal] so they are noting that they fixed it... how, I don't know :)

Well yeah... the developer(s) have set this thread as [Fixed Internal] so they are noting that they fixed it... how, I don't know :)

Excellent news. Thanks for the info Kuky!