[FIXED] [OB 2.7.16.28157] SD-10 nozzle_exit_area value incorrect

[DSplayer]

Since I originally thought it would be better suited in the ED Weapon Bugs section:

 

TLDR Summary: The SD-10's nozzle_exit_area value is too large in comparison to its 3D model and other contemporary missiles. It currently has the same value as the R-33E (0.025 square meters). This is a lot larger than the AIM-120C-5's nozzle_exit_area value (0.0132 square meters) even though the SD-10's nozzle is slightly smaller than the AIM-120C-5's.

Link to Performance Charts (also included in the original post)

Edited August 19, 2022 by uboats

[DSplayer]

To tack onto this bug report, the LD-10 currently has a nozzle_exit_area value of 0.01368 for its march motor stage but not its boost stage as that line doesn't exist for that stage. The value of 0.01368 is closer to what seems reasonable but still is kinda bigger than the value of the AIM-120 even though the SD/LD-10 nozzle is a bit smaller than the AIM-120's (could be a 3D modelling error from either Deka or ED).

 

Screenshot from the mils_ld10.lua file's section where the LD-10 uses the "anti_rad_missile" scheme (the "anti_radiation_missile2" scheme section doesn't have a nozzle_exit_value but this section isn't used):

Spoiler

 

[Napillo]

The diameter of the SD-10 is 20mm larger (about 10%), so it's area should be larger than the AIM-120. 

[DSplayer]

5 hours ago, Napillo said:

The diameter of the SD-10 is 20mm larger (about 10%), so it's area should be larger than the AIM-120. 

It's possible but the nozzle diameter isn't exactly proportional when compared to the diameter of the missile. For example the AIM-7's nozzle is around 3.5 inches in diameter even though the missile has an 8 inch diameter. Plus the external model for the SD/LD-10's nozzle is smaller than the AIM-120's nozzle.

[AeriaGloria]

5 hours ago, Napillo said:

The diameter of the SD-10 is 20mm larger (about 10%), so it's area should be larger than the AIM-120. 

The 3D model in game shows SD/LD-10 having smaller nozzle then AIM-120, you can see the comparison in photos in post linked in OP. This could be true and possible that it has smaller nozzle then AMRAAM, or it could be an in accuracy with the 3D modeling. Either is a possibility 

Edited August 18, 2022 by AeriaGloria

[AeriaGloria]

11 minutes ago, DSplayer said:

It's possible but the nozzle diameter isn't exactly proportional when compared to the diameter of the missile. For example the AIM-7's nozzle is around 3.5 inches in diameter even though the missile has an 8 inch diameter. Plus the external model for the SD/LD-10's nozzle is smaller than the AIM-120's nozzle.

Also since the effect occurs when motor is on, should the boost stage also have a nozzle exit area value? Can’t find many dual stage missiles that might have the value to see if anything else does. 

[DSplayer]

1 minute ago, AeriaGloria said:

Also since the effect occurs when motor is on, should the boost stage also have a nozzle exit area value? Can’t find many dual stage missiles that might have the value to see if anything else does. 

Well all stages should have a nozzle_exit_area value. AIM-120s and AIM-7s all have that value for both of their missile motor stages.

[AeriaGloria]

47 minutes ago, DSplayer said:

Well all stages should have a nozzle_exit_area value. AIM-120s and AIM-7s all have that value for both of their missile motor stages.

Ahh I see. So I’m assuming that, adding a nozzle exit area value to boost stage (and thus decreasing drag), could possibly reduce or outweigh the impact of reduced sustain stage nozzle exit area value (which would increase drag). 
 

Only picture I have seen of LD-10/SD-10 from the back is this, and it’s from an indoor display and could easily be a mock up. But it conforms exactly with 3D model in game 

[DSplayer]

41 minutes ago, AeriaGloria said:

Ahh I see. So I’m assuming that, adding a nozzle exit area value to boost stage (and thus decreasing drag), could possibly reduce or outweigh the impact of reduced sustain stage nozzle exit area value (which would increase drag). 
 

Only picture I have seen of LD-10/SD-10 from the back is this, and it’s from an indoor display and could easily be a mock up. But it conforms exactly with 3D model in game 

I dont think it would decrease drag at all but I know that it would increase the missile’s speed depending on altitude. A missing value would also cause some weird stuff to happen. Either the missile performing at a higher than intended speed or at a lower than intended speed.

 

Drag for missiles is predetermined by other variables within the missile luas.

Edited August 18, 2022 by DSplayer

[AeriaGloria]

1 hour ago, DSplayer said:

I dont think it would decrease drag at all but I know that it would increase the missile’s speed depending on altitude. A missing value would also cause some weird stuff to happen. Either the missile performing at a higher than intended speed or at a lower than intended speed.

 

Drag for missiles is predetermined by other variables within the missile luas.

 

Sorry I do mean over all speed. I meant drag as the whole thing the nozzle exit area does is that size of the rocket exhaust streamlines the rear of the missile to an extent equal to its size. The idea being it’s a coefficient on top of regular drag, that says “if nozzle is xyz big drag will be reduced by xyz amount.”
 

  Which is what I mean, that adding it to a stage where it’s not already there could only decrease drag while that specific stage is on, right? 

[Napillo]

3 hours ago, AeriaGloria said:

Only picture I have seen of LD-10/SD-10 from the back is this, and it’s from an indoor display and could easily be a mock up.

and if it is a mockup, the place where the rocket would go would obviously be filled in with something, thus inaccurate 

[Exorcet]

2 hours ago, AeriaGloria said:

Sorry I do mean over all speed. I meant drag as the whole thing the nozzle exit area does is that size of the rocket exhaust streamlines the rear of the missile to an extent equal to its size. The idea being it’s a coefficient on top of regular drag, that says “if nozzle is xyz big drag will be reduced by xyz amount.”
 

  Which is what I mean, that adding it to a stage where it’s not already there could only decrease drag while that specific stage is on, right? 

The exit area determines how much exhaust gas expands. The ideal is to match the surrounding pressure, but this varies with altitude, so an exit area is picked to give the missile the desired altitude performance. Larger = better high altitude performance (in general).

[DSplayer]

2 hours ago, AeriaGloria said:

Sorry I do mean over all speed. I meant drag as the whole thing the nozzle exit area does is that size of the rocket exhaust streamlines the rear of the missile to an extent equal to its size. The idea being it’s a coefficient on top of regular drag, that says “if nozzle is xyz big drag will be reduced by xyz amount.”
 

  Which is what I mean, that adding it to a stage where it’s not already there could only decrease drag while that specific stage is on, right? 

I mean that the streamlining thing isn't a thing from my limited understanding of rocket dynamics in DCS. It's merely a value that determines the thrust of the rocket since the thrust depends on the propellant mass flow rate, velocity of the exhaust gases, pressure at nozzle exit, ambient pressure, and area of the nozzle.

Like what Exorcet said, more expansion of the exhaust gasses which reduces exhaust pressure as you go up in nozzle exit area value. There is just no drag or streamlining that comes from changing this value.

 

1 hour ago, Napillo said:

and if it is a mockup, the place where the rocket would go would obviously be filled in with something, thus inaccurate 

To be fair, the mockup in that picture does seem to show the basic nozzle shape and placement with probably no live propellant and other explody things. Similar to the National Air and Space Museum's AIM-120A they have. It could be just a captive round they put on display.
 

[uboats]

done for sd10/ld10, using 0.065 as radius -> 0.013273

may not be included in OB update this month, but guaranteed by next month

[DSplayer]

11 minutes ago, uboats said:

done for sd10/ld10, using 0.065 as radius -> 0.013273

may not be included in OB update this month, but guaranteed by next month

Is the 3D models for the AIM-120 and SD/LD-10 just not 100% in sync in terms of dimensions? The nozzles are a bit smaller on the SD/LD-10 when compared to the AIM-120C-5 using the 3D models as a reference.

[Mike_Romeo]

7 hours ago, DSplayer said:

The nozzles are a bit smaller on the SD/LD-10 when compared to the AIM-120C-5 using the 3D models as a reference.

I can confirm that. SD-10 nozzles are arround 0,9655 times smaller than the one of the Aim-120. If you now multiply that with the nozzle_exit_area value for Aim-120 (0.0132), you get 0,0127 instead of 0.01327. @uboats could you please check this as well ?
28649 : 27663 = 0,96558344095779957415616600928479
0,0132 x 0,96558344095779957415616600928479 = 0,01274570142064295437886139132256

[uboats]

6 hours ago, Mike_Romeo said:

I can confirm that. SD-10 nozzles are arround 0,9655 times smaller than the one of the Aim-120. If you now multiply that with the nozzle_exit_area value for Aim-120 (0.0132), you get 0,0127 instead of 0.01327. @uboats could you please check this as well ?
28649 : 27663 = 0,96558344095779957415616600928479
0,0132 x 0,96558344095779957415616600928479 = 0,01274570142064295437886139132256

Then, it’s 0.01219 = aim120_area * scale * scale. updated.

Edited August 19, 2022 by uboats

[tavarish palkovnik]

Good day to all !

Here is one rear view at operating PL-12 missile if it will be helpful 

 

Is there anyone who could translate this, is it written anything about missile this motor is related for?

 

Motors and burning processes are interest of mine and I saw that in DCS this PL-12 or SD-10 has very awkward buster-sustain distribution and ratio. If info I got is not wrong, in buster stage of 6s 57,6kg of fuel is burned, and in sustained stage 11,6kg for 4 seconds. Interesting indeed.

What exactly is length and weight of this rocket, internet gives values in contradiction, 3934mm 3850mm, 199kg, 180kg etc etc

Actually what I’m looking for is origin of this motor

 
I believe it must be somehow related with R-77 in some stages of development and using its motor for other applications (surface to air variant) and these Chinese missiles which have roots from R-77

Edited August 20, 2022 by tavarish palkovnik

[AeriaGloria]

14 hours ago, tavarish palkovnik said:

Good day to all !

Here is one rear view at operating PL-12 missile if it will be helpful 

 

Is there anyone who could translate this, is it written anything about missile this motor is related for?

 

Motors and burning processes are interest of mine and I saw that in DCS this PL-12 or SD-10 has very awkward buster-sustain distribution and ratio. If info I got is not wrong, in buster stage of 6s 57,6kg of fuel is burned, and in sustained stage 11,6kg for 4 seconds. Interesting indeed.

What exactly is length and weight of this rocket, internet gives values in contradiction, 3934mm 3850mm, 199kg, 180kg etc etc

Actually what I’m looking for is origin of this motor

 
I believe it must be somehow related with R-77 in some stages of development and using its motor for other applications (surface to air variant) and these Chinese missiles which have roots from R-77

 

I would bet it’s motor has little correlation to R-77. Word on the street was always that Agat and Vympel collaborated with LETR on design of the fox 3 seeker. Supposedly it did use Russian components somewhere until 2018. 

What’s surprsing is R-77 nozzle exit area is 0.02835, which is over twice of SD-10. Not sure the 3D model backs that up.

Also, while the seeker is likely related to R-77, the actual missile itself is designed from the PL-11, a license produced Aspide (European AIM-7 Sparrow), so the rocket motor itself may have more to do with being a modernized AIM-7 rocket then anything else 

Edited August 21, 2022 by AeriaGloria

[DSplayer]

6 hours ago, AeriaGloria said:

I would bet it’s motor has little correlation to R-77. Word on the street was always that Agat and Vympel collaborated with LETR on design of the fox 3 seeker. Supposedly it did use Russian components somewhere until 2018. 

What’s surprsing is R-77 nozzle exit area is 0.02835, which is over twice of SD-10. Not sure the 3D model backs that up.

Also, while the seeker is likely related to R-77, the actual missile itself is designed from the PL-11, a license produced Aspide (European AIM-7 Sparrow), so the rocket motor itself may have more to do with being a modernized AIM-7 rocket then anything else 

 

Slightly larger diameter than the R-33 and the nozzle almost is the same diameter as the diameter of the missile itself both in real images and the 3D model.

[tavarish palkovnik]

Comparing to photograph, motor indeed could be around 2080mm what makes this very interesting.

 

This is situation with Mk-58 of AIM-7F, two grains burning at the beginning together and then only sustaining one. The one is 23,6kg, other 37,7kg having different burning rates. Roughly speaking in first 4,5 seconds 45 kilos of fuel burn and rest remaining 11 seconds. Not for my taste but it is as it is.

If similar principle will be applied to motor of PL-12…

 

It is about 69 kilograms of fuel in total, exactly what DCS use if I’m not wrong.  

But if this configuration should burn for 6 seconds using 57,6kg of fuel and remaining 11,6kg for next 4 seconds then it should looks something like this…

And it looks horrible, unreal. I don’t know source of this distribution ratio, I don’t know if this perhaps is result of “squaring” thrust curves or something else but simply it doesn’t looks natural.

 

And what influence more, exit diameter of nozzle or perhaps thrust distribution in time. Usually area of exit is around 10 times bigger then cross section area of throat so it can gives some clues about pressure in chamber and respectively burning rates

 

Edited August 21, 2022 by tavarish palkovnik

[AeriaGloria]

8 hours ago, DSplayer said:

Slightly larger diameter than the R-33 and the nozzle almost is the same diameter as the diameter of the missile itself both in real images and the 3D model.

Damn, every rocket exhaust is a snowflake, they’re all different!

[Napillo]

Idk, you change the size of the exhaust, you invoke Saint Robert's Law. I believe the values were picked based on the flight characteristics desired, as the rocket motor modeling of DCS isn't quite great. ex: the explosive being given in units of weight of TNT equivalent, as explosive components in warheads differing in strength not proportional to weight.

[AeriaGloria]

4 hours ago, Napillo said:

Idk, you change the size of the exhaust, you invoke Saint Robert's Law. I believe the values were picked based on the flight characteristics desired, as the rocket motor modeling of DCS isn't quite great. ex: the explosive being given in units of weight of TNT equivalent, as explosive components in warheads differing in strength not proportional to weight.

What would saint roberts law change here? The LUA defines a specific fuel mass, impulse, and burn time, so none of those can change 

 

On 8/18/2022 at 8:11 PM, DSplayer said:

I mean that the streamlining thing isn't a thing from my limited understanding of rocket dynamics in DCS. It's merely a value that determines the thrust of the rocket since the thrust depends on the propellant mass flow rate, velocity of the exhaust gases, pressure at nozzle exit, ambient pressure, and area of the nozzle.

Like what Exorcet said, more expansion of the exhaust gasses which reduces exhaust pressure as you go up in nozzle exit area value. There is just no drag or streamlining that comes from changing this value.

 

To be fair, the mockup in that picture does seem to show the basic nozzle shape and placement with probably no live propellant and other explody things. Similar to the National Air and Space Museum's AIM-120A they have. It could be just a captive round they put on display.
 

Okay I don’t see how Ve or Pe are defined in DCS, so not sure if the nozzle exit area can still change things without those two values unless there are some place holder approximations buried beyond the LUA? 
 

IASGTAGS CFD for the AIM-120 said that the turbulence caused after the motor turns off, increasing drag of the missile, can be approximated as 2-20% difference in drag. Which would make quite a difference at even a middle value of 10%. 
 

So are you aware or have you done any testing in DCS with wildly different nozzle exit areas to see what effect they have? 

Edited August 22, 2022 by AeriaGloria

[DSplayer]

59 minutes ago, AeriaGloria said:

What would saint roberts law change here? The LUA defines a specific fuel mass, impulse, and burn time, so none of those can change 

 

Okay I don’t see how Ve or Pe are defined in DCS, so not sure if the nozzle exit area can still change things without those two values unless there are some place holder approximations buried beyond the LUA? 
 

IASGTAGS CFD for the AIM-120 said that the turbulence caused after the motor turns off, increasing drag of the missile, can be approximated as 2-20% difference in drag. Which would make quite a difference at even a middle value of 10%. 
 

So are you aware or have you done any testing in DCS with wildly different nozzle exit areas to see what effect they have? 

 

I've done testing regarding the AIM-54 and nozzle_exit_areas. Since it currently has a nozzle_exit_area value of 1e-6, its not very desirable and doesn't get a performance boost as the motor is basically launched higher and higher in altitude. That reduction in drag do to the motor being operational is better simplified as motor-on drag and is prevalent with every missile, with or without nozzle_exit_areas, in DCS iirc.

Here's an example of a motor-on drag with the sparrow that a friend got somewhere:



Further reading: http://fullafterburner.weebly.com/next-gen-weapons/missile-aerodynamics

Edited August 22, 2022 by DSplayer