DCS: F-14 Development Update - AIM-54 Phoenix Improvements & Overhaul - Guided Discussion

[captain_dalan]

On 9/5/2024 at 6:13 AM, Flapjacks said:

Hey, how does one tell when a Phoenix goes active while in STT? I read the first post and saw that it said it will go active when it should remain semi-active the whole time, I'm just not sure how to tell when it does this.

The old versions (the A's in this case) don't go active at all if fired in PD-STT at distances over 10 nautical miles, unless fired with the ACM cover up, in which case i think they are active right off the rail (mad dog) and will just fly to the first thing they see. If fired at 10 miles or closer, the missile goes active right after launch at the target that was locked. 

The newer versions (C) follow the above behavior with the exception that if the lock is broken at any given point, the missile goes active immediately and tries to acquire the first thing it sees along radar cone. Also in DCS specifically, the missile goes active at 10 miles from the target, but i don't thing the TDI displays it like it does with TWS shots.

[Karon]

I wonder whether this thread should be closed and a new one opened, with a nice introductory post recapping the status quo of the AIM-54 and its main features. This would help everyone understand where we are now and remove some recurring questions.

_{No, I'm not volunteering.}

[draconus]

42 minutes ago, Karon said:

I wonder whether this thread should be closed and a new one opened, with a nice introductory post recapping the status quo of the AIM-54 and its main features. This would help everyone understand where we are now and remove some recurring questions.

_{No, I'm not volunteering.}

Yeah, a FAQ would be great with first candidates:

Q: Why can't my Phoenix go even near Mach 5?

Q: Why can't my Phoenix go even beyond 10nm?

New thread will probably be created with next iteration ("API").

[MAXsenna]

I wonder whether this thread should be closed and a new one opened, with a nice introductory post recapping the status quo of the AIM-54 and its main features. This would help everyone understand where we are now and remove some recurring questions.
_{No, I'm not volunteering.}

That's actually a great idea!

Sent from my SM-A536B using Tapatalk

[Despayre]

7 hours ago, draconus said:

Yeah, a FAQ would be great with first candidates:

Q: Why can't my Phoenix go even beyond 10nm?

I haven't seen that one, is that really something ppl claim? (and seriously, if it is, how ridiculous)

[Karon]

8 hours ago, draconus said:

Yeah, a FAQ would be great with first candidates:

Q: Why can't my Phoenix go even near Mach 5?

Q: Why can't my Phoenix go even beyond 10nm?

New thread will probably be created with next iteration ("API").

#1 It can technically go to M5. The highest I got is M5.12, IIRC.

#2 because your ordies messed up.

[draconus]

1 hour ago, Despayre said:

I haven't seen that one, is that really something ppl claim? (and seriously, if it is, how ridiculous)

Don't know how much exactly but it won't go far in chase shot at sea level, esp. when shooting at slow dogfight speed.

[Despayre]

14 minutes ago, draconus said:

Don't know how much exactly but it won't go far in chase shot at sea level, esp. when shooting at slow dogfight speed.

Ah, yes, ok, there are some circumstances where you can do something outside of it's design, or where you can force that situation I guess. And I can see ppl whining about that, but, ya, that's just dumb. 

[captain_dalan]

19 hours ago, draconus said:

Don't know how much exactly but it won't go far in chase shot at sea level, esp. when shooting at slow dogfight speed.

It will go relatively far, but the main issue is, the bandit will most likely go further 

[Katsu]

On 5/13/2024 at 6:19 AM, tavarish palkovnik said:

A little bit more of mathematic ...

 

AIM-54 motor.pdf 38.14 kB · 37 downloads

 

I don't know what public available data were used, either by NASA or here. All I know NASA in their own handbook (Solid Rocket Motor Nozzles, page 10) gave characteristics of this motor, in very much details. Together with configuration of grain these numbers are precisely confirmed as you could find on previous page

 

 

 

Depending of temperature motor works from 20 to 30 seconds  √

Maximal chamber pressure from 1000 to 700 psi (from 69 to 48 bar)  √

Average thrust from 5000 to 1000 lbf (from 22269 to 4454 N)  √

 

Only maximal pressure of 69 bar I've got a bit higher, all right, maybe it is not +70degC but +60degC or +65degC as upper limit. When have all this, and when have basic theory about rocket propulsion everything can be calculated, it means easily and indisputably we can have thrust values of this motor in function of altitude. 

Of course, this is one pair of aces, the other pair of aces is that drag coefficient significantly increase with altitude because of friction, but this motor compared to some others gives up there quite much then friction takes.   

 

 

 

 

Hey @tavarish palkovnik
 

As there has been practically no response from HB about all this study you've done, I decided to "implement" your missile calculation in the game by myself for my personal use.

I changed the Thrust of the missile to the average thrust of 10KM (which is usually where the shots occur). 

Unfortunately I don't know much about aerodynamics, but I also lightened the missile's loft factor a bit in an attempt to conserve more energy (I kept all the drag parameters)

 

As you may have noticed, DCS simulation uses a number of shortcuts and simplifications, so i decided to keep this numbers on Mk-47 engine (since seems to be the engine that you provide the data), I believe that the biggest problem with the DCS not being able to reproduce this missile with any fidelity is apparently there is no way of modeling the differences in thrust that the engine undergoes in the atmosphere just a static thrust, burn time and drag.

I got those results: 

the difference doesn't seem to be much from what we already have in the game today, since the drag holds the missile's speed (which is interesting since the missile is heavy and large and it's physically understandable that it can't accelerate). 


From a deck launch : 


And from a 10km Mach 1.5 launch:

Here the missile seems to behave completely differently from the missile we have in the game today, with the air less dense even with the drag unchanged it manages to accelerate much more with extra thrust.




My “implementation” may be faulty in many aspects but seems to be much more closer from according public data mach 5 capable missile than what is implemented in game now.

Your calculations seems to be closer from the discarded CFD data that HB discarded: 

null


Really wish that HB see your work like ED did on HARM.

Thanks!

Edited September 13, 2024 by Katsu

[Machalot]

6 hours ago, Katsu said:

the biggest problem with the DCS not being able to reproduce this missile with any fidelity is apparently there is no way of modeling the differences in thrust that the engine undergoes in the atmosphere just a static thrust, burn time and drag.

The thrust variation with altitude is caused by the ambient atmospheric pressure acting on the nozzle exit area.  If I remember correctly, the AIM-54 is modeled in DCS as having zero nozzle exit area, so the the pressure variation doesn't affect the delivered thrust at all.  I believe if you were to change the nozzle exit area you would see a change in thrust as shown in the figure.

Edited September 14, 2024 by Machalot

[tavarish palkovnik]

Hey @Katsu

Nice to see you're using these numbers. You can even change data for your self...that's surprising to me. Then change active time, take off 3 seconds you gave extra using this average thrust value, although seems as just 3 seconds, that is extra 21 kilograms of non-existing propellant.

This motor although seems as relatively simple is actually very tricky and it's quite difficult to make flight model which will be general for all cases. It's not difficult to the measure that it is impossible, everything is possible, however not in case how this program and model is organized, like you said it is simplified and it is understandable. Make it realistic would be such a hard work that anyone normal would gave up right in the start. Eventually one model but how many motors you have in game, that would be finished in next century.

Tricky motor-tricky case...this launch which you called deck flight, take off non-existing 3 seconds, change thrust used for 10km altitude with average trust for 1km ( 15532 N ; Isp=223,4s) and you will get completely different picture  probably nothing close to what you have in game now.

So you saw HARM numbers as well, that one is different on it's way, there are others issues but at least this altitude issues are not so dramatic like in case of Phoenix. Phoenix is in that real pain and from all tactical motors I know, the worst for modelling because of it's widely open nozzle and nonlinear thrust.

This deck flight, to show what all can happen, how many variables can appear ...

 

     

 

One launch from level flight on 1km at 0,8M, and then after 2 seconds 6G overload for 10 seconds pushing missile upper in rear atmosphere. And with every second drag is in variable of course but thrust is also changing  

 

 

 

Just with lifting to this final altitude and because of lower ambiental pressure 7% of extra total impulse is achieved compared to what would be in level flight at 1km and missile goes over 1,9M while by using thrust from 1km missile barely reach 1,75M. Complicated motor indeed, not easy to work with, special in many points

 

 

 

 

[Katsu]

1 hour ago, tavarish palkovnik said:

Hey @Katsu

Nice to see you're using these numbers. You can even change data for your self...that's surprising to me. Then change active time, take off 3 seconds you gave extra using this average thrust value, although seems as just 3 seconds, that is extra 21 kilograms of non-existing propellant.

This motor although seems as relatively simple is actually very tricky and it's quite difficult to make flight model which will be general for all cases. It's not difficult to the measure that it is impossible, everything is possible, however not in case how this program and model is organized, like you said it is simplified and it is understandable. Make it realistic would be such a hard work that anyone normal would gave up right in the start. Eventually one model but how many motors you have in game, that would be finished in next century.

Tricky motor-tricky case...this launch which you called deck flight, take off non-existing 3 seconds, change thrust used for 10km altitude with average trust for 1km ( 15532 N ; Isp=223,4s) and you will get completely different picture  probably nothing close to what you have in game now.

So you saw HARM numbers as well, that one is different on it's way, there are others issues but at least this altitude issues are not so dramatic like in case of Phoenix. Phoenix is in that real pain and from all tactical motors I know, the worst for modelling because of it's widely open nozzle and nonlinear thrust.

This deck flight, to show what all can happen, how many variables can appear ...

 

     

 

One launch from level flight on 1km at 0,8M, and then after 2 seconds 6G overload for 10 seconds pushing missile upper in rear atmosphere. And with every second drag is in variable of course but thrust is also changing  

 

 

Just with lifting to this final altitude and because of lower ambiental pressure 7% of extra total impulse is achieved compared to what would be in level flight at 1km and missile goes over 1,9M while by using thrust from 1km missile barely reach 1,75M. Complicated motor indeed, not easy to work with, special in many points

 

 

 

 

I've made the corrections you suggested:

 

 

I've come up with some interesting results, but as I'm using the game's own modification to carry out the tests, I can't be too precise.

With this new data, the missile is similar or close to what we have modeled with the mk-60 engine today, but with 4 seconds more burn than it currently has in the game.

With a 10km Shoot lofted trajectory at  +/- mach 1.2, now i got very close to mach 4 (3 seconds less of burner make a lot of difference at this point!) 

And here a leveled shoot on a straight course (or an attempt at it) 

The missile seems to remain very good at the high altitudes where it was designed to work.

what bothers me about the missile today the way it is modeled in the game is that it is very slow even at high altitudes and suffers a lot to break mach 3 due to the lack of thrust, currently the game assumes that the missile has 13595N of thrust in a burn of 27 seconds at any altitudes, which makes it a slow missile both high and low.

Even with the changes, your solution seems to have achieved a good result given what is known about the missile and doesn't “break” it mechanically speaking as a game.

Then I'll do the tests by changing the properties for low altitudes and share results here.

I can only thank you for your time and your work.

It has made me very interested in this type of application of mathematics and physics. 

[tavarish palkovnik]

But @Katsu don’t change propellant mass, it is always 168kg no matter what thrust is. Altitude change specify impulse and specific impulse multiplied with propellant mass gives thrust 

[Katsu]

3 minutes ago, tavarish palkovnik said:

But @Katsu don’t change propellant mass, it is always 168kg no matter what thrust is. Altitude change specify impulse and specific impulse multiplied with propellant mass gives thrust 

Okay! i'll change it back.

Again many thanks Tavarish!

[tavarish palkovnik]

16 hours ago, Katsu said:

I can only thank you for your time and your work.

It has made me very interested in this type of application of mathematics and physics. 

You are welcome, actually it’s so nice seeing someone’s interest in this for me such a fun field of technic. As an engineer working for decades, something what is not boring but I’m kind of saturated with that, and bang, several years ago, also on forum (one other, not this one) , my interest in rocket motors was born. Luckily there was a man who worked all his life with rocket motors, willing to share all he knows, with patience at the beginning…and step by step, book by book, my interest just grew, some knowledge is accumulated of course but because this is indeed specific field of technic and just hobby to me, there are still so many things to learn. There were some good points I believe, there were some completely missed ones which I will always admit, either figured out alone with time or pointed by others *

So, interesting hobby made boring living work easier 

That’s why it’s nice to see someone’s interest, and @Katsu what ever you wish to hear about, if available time and my knowledge allow will be done.

Unless forum sheriffs don’t erase and expel us 

* - this freak of motor is I’m very sure well pointed

Edited September 15, 2024 by tavarish palkovnik

[Gareth Barry]

So for us non-rocket scientists, let me see if i am at least in right ball-park;

The nozzle exit area of the aim54 is relatively large. This, combined with relatively low exhaust pressure, means that at low altitude, the thrust from mass flow of the rocket is being degraded significantly by (Pe-Pa)*A where Pe-Pa is the difference in pressure between ambient and exhaust, and A is the nozzle exit area. This adds to the large and draggy cross section to hurt it badly down here. At high altitudes, where Pa is very much lower, Pe-Pa becomes a much larger positive term, which when mulitplied by A gives a large increase in thrust. In short, this means that the aim54 is very much tuned to high altitudes.

I am not one to question NASA, ED or even for that matter Heatblur- that would be insane and laughably arrogant. It does however seem strange to me that nozzle exit area is and its affect on rocket performance at different altitudes isnt taken into account? Or perhaps i am wrong and it is in fact accounted for? Is the current aim54 in game a sort of 'average' across likely operational altitudes? I ask this not for any changes to be made, but rather to educate myself.

Edited September 15, 2024 by Gareth Barry

[tavarish palkovnik]

You are very right @Gareth Barry with this equation and while with some other motors having small nozzles that simply can be ignored, here with all specificities this can’t be excluded.

However these numbers (plus or minus, increase or decrease of thrust force) are not going to come without involving pressures in calculations and your model as much as I know doesn’t include pressure rates when describing some motor. Actually understandable from one perspective and from other, why not to include it if it is on the table.

I’m not much about computer-ing but this for sure would be very easy to include. From chamber pressure and nozzle expansion ratio to find what is pressure at nozzle exit. That will be pressure in range of ambient pressure at some 10km so I would put thrust on this altitude as nominal one. That thrust would be so called thrust with full expansion, no loss and no gain of ambient conditions.

And from that point this nominal thrust would be changed with (pe-pa)*A where only “pa” is variable and that is piece of cake to make. Ambient pressures are well known and altitude of missile in every second is of course known.

There are no linearity here with Phoenix motor so percentages are not precise enough, some other motors can handle percentages easily but here to have as closest to reality, something more have to be done. Average chamber pressure let’s say 45 bar  -> nozzle expansion ratio 18,5 -> heat ratio 1,2 -> pressure at nozzle exit 0,256 bar 

Let’s say it is close to 10km ambient pressure of 0,26491 bar or 26491 Pa, so nominal thrust to be that one or 18318 N. What would be at 2km where ambient pressure is 79497 Pa … 18318+(26491-79497)*0,238^2*PI/4=15961 N

[Machalot]

2 hours ago, Gareth Barry said:

I am not one to question NASA, ED or even for that matter Heatblur- that would be insane and laughably arrogant. It does however seem strange to me that nozzle exit area is and its affect on rocket performance at different altitudes isnt taken into account?

For some reason, somebody at HB or ED decided to simplify the thrust model by setting the nozzle exit area to 1 square millimeter, effectively zero.  Here's the readout from Quaggles' DCS LUA datamine, with a little searching:

./_G/rockets/AIM_54C_Mk47.lua:  nozzle_exit_area = 1e-06,
./_G/rockets/AIM_54A_Mk47.lua:  nozzle_exit_area = 1e-06,
./_G/rockets/AIM_54A_Mk60.lua:  nozzle_exit_area = 1e-06,
./_G/rockets/AIM_54C_Mk60.lua:  nozzle_exit_area = 1e-06,
./_G/rockets/AIM_54.lua:        nozzle_exit_area = 1e-06,

 

[Gareth Barry]

Hmmm, have to chew on this a bit. Thanks Tavarish for all your input. It does make me wonder what nasa actually modelled, how the Heatblur one matches it etc. From an engineering point of view, considering the history and time period in which the aim54 was developed and what it was designed to kill, this 'tuning' to long range and high altitudes makes sense, as well as the compromises that were needed and considered acceptable to achieve this goal.

[Machalot]

3 minutes ago, Gareth Barry said:

It does make me wonder what nasa actually modelled

NASA used publicly available data.

[Gareth Barry]

I guess let me be a bit more frank-

I wonder what range of conditions and altitudes the nasa model was calculated for? And if it is a wide range of altitudes, what are we missing, as in, why does the nasa model not gel? How is it that a current model without nozzle exit area and and pressure that changes with altitude, 'correct'? What are we missing? Or has the time come to humbly ask Heatblur to reconsider their model? I know that this is has been covered in this thread, but the thread is looooong and i'm lazy....

I only play single player and get plenty of kills with the missile- i know it isnt really a 'mach 5' missile, but the high speed missile at altitude that i thought the thing was famous for is currently a bit more like a long, slow train a comin'.

Edited September 15, 2024 by Gareth Barry

[draconus]

5 hours ago, Gareth Barry said:

I only play single player and get plenty of kills with the missile- i know it isnt really a 'mach 5' missile, but the high speed missile at altitude that i thought the thing was famous for is currently a bit more like a long, slow train a comin'.

HB made the model to match and recreate real life test shots. There's not much more data on the performance so everything else is theory but it also matches that. You also don't know the model fully, not all is in lua files. So what are you looking for? What makes you think it's wrong? You have to base it on something more than feeling.

[tavarish palkovnik]

10 hours ago, tavarish palkovnik said:

However these numbers (plus or minus, increase or decrease of thrust force) are not going to come without involving pressures in calculations and your model as much as I know doesn’t include pressure rates when describing some motor. Actually understandable from one perspective and from other, why not to include it if it is on the table.

It is not academic to quote yourself but what the hech, it is really on the table

 

AIM-54 altitude.pdf

 

Edited September 15, 2024 by tavarish palkovnik

[Raven (Elysian Angel)]

5 hours ago, draconus said:

more than feeling

Or we could ask these guys: