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

[AeriaGloria]

2 hours ago, DSplayer said:

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

 

I couldn’t find anything about the nozzle there. But what you’re basically saying is that the larger the nozzle exit area value in LUA, the more that performance of the rocket engine increases with altitude? 
 

 

Edited August 22, 2022 by AeriaGloria

[J20Stronk]

1 hour ago, AeriaGloria said:

I couldn’t find anything about the nozzle there. But what you’re basically saying is that the larger the nozzle exit area value in LUA, the more that performance of the rocket engine increases with altitude? 
 

 

 

I did a brief test using the SD-10 we currently have (NEA = 0.0250) and the "new" one (NEA = 0.0122).

At 36,000 ft., Mach 1.1, 0^o pitch: the current missile caps at 2524kts True, while the new one capped at 2409kts True, a 4%-5% difference.

I don't have graphs to compare as I do not own Tacview Advanced, but you can see for yourself by editing the missile entry and modding a payload on the F-15.

Edited August 22, 2022 by J20Stronk

[AeriaGloria]

19 minutes ago, J20Stronk said:

I did a brief test using the SD-10 we currently have (NEA = 0.0250) and the "new" one (NEA = 0.0122).

At 36,000 ft., Mach 1.1, 0^o pitch: the current missile caps at 2524kts True, while the new one capped at 2409kts True, a 4%-5% difference.

I don't have graphs to compare as I do not own Tacview Advanced, but you can see for yourself by editing the missile entry and modding a payload on the F-15.

 

Thank you for the test! And I’m sure that difference impacts range less the more the missile glides. If it’s nozzle exit area is truly about how a rocket changes power with altitude, I wonder what the difference is on the deck 

Anyways, thank you very much for doing the test!

[Napillo]

Well, as I said, it's not true rocket motor physics, just a rough approximation of it. I'd love to see them actually do the calculations.

[DSplayer]

7 hours ago, AeriaGloria said:

I couldn’t find anything about the nozzle there. But what you’re basically saying is that the larger the nozzle exit area value in LUA, the more that performance of the rocket engine increases with altitude? 

5 hours ago, AeriaGloria said:

Thank you for the test! And I’m sure that difference impacts range less the more the missile glides. If it’s nozzle exit area is truly about how a rocket changes power with altitude, I wonder what the difference is on the deck 

Anyways, thank you very much for doing the test!

All of my reports so far relating to this topic have included charts/graphs that demonstrate a performance difference btw.

[AeriaGloria]

1 hour ago, DSplayer said:

All of my reports so far relating to this topic have included charts/graphs that demonstrate a performance difference btw.

I went over them again thank you for pointing it out. To be honest I had a bit trouble reading them at first but that has more do to with a reading comprehension disability of mine

After going over them again and comprehending properly yes I do see, at low altitude there is essentially no difference and as altitude increases the nozzle exit area increases performance the larger it is. So you just be right about the base drag being part of the missile API, as it would show a decrease in kinetic performance but in the opposite altitude correlation. 
 

So interesting, as long as this makes it more realistic I’m all for it. I know there were likely still some things where SD-10 wasn’t able to hit certain performance marks, hopefully this helps. Thank you for your patience. 

[tavarish palkovnik]

 

 

 

 

 

 

 

 

 

 

 

 

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Edited May 16, 2024 by tavarish palkovnik

[tavarish palkovnik]

Shortly to explain these graphs, because I don’t believe that slight differences in form of rocket’s rear and generally slight differences in drag coefficients can change velocity in active time (motor ON) much.

This program of mine is for ballistic flight, it’s true, but that shouldn’t change things much. I will explain later. Program is for single thrust models so I had to improvise a bit, four slides is one shot, two inputs and two outputs respectively. So first slide is start, 12km, 1,1M and ballistic shot with 10deg. Fourth is end and only velocity is what is subject to watch. So final velocity is 1207m/s or 4,09M.

Program is based on law of Cx58, I don’t know how much you are familiar with it. Coefficients i58 active and passive are what should be relative to Cx58. So if I assume i58 as 1,3 and 1,45 and if and it is Cx58 at for example 1,1M 0,628 that means Cx (or Cd who likes more) is 0,8164 in active and 0,9106 in passive respectively (at 1,1M)

Next 4 slides are simulation what if drag in active would be exactly same as in passive, no assist of flame whatsoever, base pressure drag is maximal whatever is exit diameter of nozzle. And such final velocity is 1195m/s or 4,05M. Difference of just 0,04M, just 1% !

Last 4 slides is next simulation, what if drag force would be somehow doubled, i58 2,6 instead of 1,3. Final velocity is 1103m/s or 3,74M or difference of 0,35M or decrease of 8,6% 

However, i58 2,6 means that rocket fly continuously overloaded with angle of attack roughly 10deg. Example, Cx58 at 4M is 0,302 and let’s assume Cy (lift coefficient) at 4M is 0,25. 
Cx=1,3*0,302=0,393 (zero AoA)

Cx ind=10^2/57,3*0,25=0,436

Cx total=0,829 or roughly double more then unloaded Cx.

Forgot to say, reference area is always cross section of rocket. 
So, all together, Cx in active does not influence a lot, it is insignificant in the matter of fact. 
 

Weight of fuel and impulse of fuel primarily and thrust force distribution in time secondary are the ones that change things significantly !

 

Edited August 23, 2022 by tavarish palkovnik

[AeriaGloria]

6 hours ago, tavarish palkovnik said:

Shortly to explain these graphs, because I don’t believe that slight differences in form of rocket’s rear and generally slight differences in drag coefficients can change velocity in active time (motor ON) much.

This program of mine is for ballistic flight, it’s true, but that shouldn’t change things much. I will explain later. Program is for single thrust models so I had to improvise a bit, four slides is one shot, two inputs and two outputs respectively. So first slide is start, 12km, 1,1M and ballistic shot with 10deg. Fourth is end and only velocity is what is subject to watch. So final velocity is 1207m/s or 4,09M.

Program is based on law of Cx58, I don’t know how much you are familiar with it. Coefficients i58 active and passive are what should be relative to Cx58. So if I assume i58 as 1,3 and 1,45 and if and it is Cx58 at for example 1,1M 0,628 that means Cx (or Cd who likes more) is 0,8164 in active and 0,9106 in passive respectively (at 1,1M)

Next 4 slides are simulation what if drag in active would be exactly same as in passive, no assist of flame whatsoever, base pressure drag is maximal whatever is exit diameter of nozzle. And such final velocity is 1195m/s or 4,05M. Difference of just 0,04M, just 1% !

Last 4 slides is next simulation, what if drag force would be somehow doubled, i58 2,6 instead of 1,3. Final velocity is 1103m/s or 3,74M or difference of 0,35M or decrease of 8,6% 

However, i58 2,6 means that rocket fly continuously overloaded with angle of attack roughly 10deg. Example, Cx58 at 4M is 0,302 and let’s assume Cy (lift coefficient) at 4M is 0,25. 
Cx=1,3*0,302=0,393 (zero AoA)

Cx ind=10^2/57,3*0,25=0,436

Cx total=0,829 or roughly double more then unloaded Cx.

Forgot to say, reference area is always cross section of rocket. 
So, all together, Cx in active does not influence a lot, it is insignificant in the matter of fact. 
 

Weight of fuel and impulse of fuel primarily and thrust force distribution in time secondary are the ones that change things significantly !

 

 

IASGATG CFD did say that base drag rapidly disappears with AOA, I believe at 0 AOA you had nearly 20% increase in drag. At 15 degree AOA it was basically 5%, and 2% at 30 degree AOA

[Napillo]

2 hours ago, Бойовий Сокіл said:

real time computational fluid dynamics and gas motor physics

no, but I would hope they would simulate that on their development systems and code the missiles to behave similarly.

[tavarish palkovnik]

On 8/24/2022 at 12:34 AM, AeriaGloria said:

I believe at 0 AOA you had nearly 20% increase in drag

Based on my calculations for this missile and if nozzle exit is 125mm, average difference between active and passive is 8,5%

 

 

 

Here is two samples, one rocket with widely opened nozzle (5V55 of S-300) and one with significant difference between body cross section and nozzle exit cross section (5V27 of S-125 ; 170mm vs 381mm)

 

 

 

 

 

While in first case body cross section is refferent area, in second it is wings (0,96m2) so roughly pick in passive would be 0,67 if cross section (dia 381mm) is refference 

Edited May 16, 2024 by tavarish palkovnik

[tavarish palkovnik]

Now when have some Cx f(M) why not to make some shot to see how far it could fly. 

There is one nice iteration method, rough but nice, not very suitable for long active time and altitudes over 10km but I will turn a blind eye this time

 

So 12km, horizontal flight, same velocity of fighter and target (325m/s), I want of rocket to have velocity of 600m/s when come to target, density of air is 0,3118, average chamber pressure let's say 70 bars, let's say gases will expand fully to ambient pressure of 0,02Mpa, average calculating impulse 240s, average drag coefficient 0,65 and iteration is that rocket will fly all together 37480 m and that distance will reach in 45 seconds. It means 52km is fireing distance

 

And now method with integration...

 

 

 

Or Mach number if more suitable

 

 

 

And finally distance

 

 

 

Iteration is very close to integration, or opposite, 38900m

Edited May 16, 2024 by tavarish palkovnik

[Маэстро]

7 hours ago, tavarish palkovnik said:

Based on my calculations for this missile and if nozzle exit is 125mm, average difference between active and passive is 8,5%

 

 

Here is two samples, one rocket with widely opened nozzle (5V55 of S-300) and one with significant difference between body cross section and nozzle exit cross section (5V27 of S-125 ; 170mm vs 381mm)

 

 

 

While in first case body cross section is refferent area, in second it is wings (0,96m2) so roughly pick in passive would be 0,67 if cross section (dia 381mm) is refference 

Very useful drag charts, thanks. Do you have the same for 5v28?

[tavarish palkovnik]

Only for 5V21 but that should fits to 5V28 with no doubts

 

 

 

 

I guess you are Russian speaking so you will not have problems with these graphs.

Only I need to check what is reference area and I will share it as soon as got it. Something with wings because in that time wings were usually base

Edited May 16, 2024 by tavarish palkovnik

[tavarish palkovnik]

…Ref.area is 8,8m2

[AeriaGloria]

8 hours ago, tavarish palkovnik said:

Now when have some Cx f(M) why not to make some shot to see how far it could fly. 

There is one nice iteration method, rough but nice, not very suitable for long active time and altitudes over 10km but I will turn a blind eye this time

So 12km, horizontal flight, same velocity of fighter and target (325m/s), I want of rocket to have velocity of 600m/s when come to target, density of air is 0,3118, average chamber pressure let's say 70 bars, let's say gases will expand fully to ambient pressure of 0,02Mpa, average calculating impulse 240s, average drag coefficient 0,65 and iteration is that rocket will fly all together 37480 m and that distance will reach in 45 seconds. It means 52km is fireing distance

 

And now method with integration...

 

 

Or Mach number if more suitable

 

 

And finally distance

 

 

Iteration is very close to integration, or opposite, 38900m

 

Boost impulse is 242, sustain is 236. Great work! 

[Маэстро]

17 hours ago, tavarish palkovnik said:

…Ref.area is 8,8m2

Many thanks indeed!

[tavarish palkovnik]

 

...

Edited April 23 by tavarish palkovnik

[tavarish palkovnik]

Forgot to say...this method is appliacable only for velocities >0,8M !