F-14AM - The Iranian Tomcat - History, Performance, and Discussion

Machinery of War Discussion Aircraft
329

I did not say anything about the sustainer thrust.

The peak acceleration claimed in this source is 20G.
In this source it is 19.4G.

Interestingly I was mistaken to believe the 19.4 or 20G figure was for the HAWK motor. The I-HAWK motor is the second stage, and this shows a peak acceleration of approximately 15G with the motor being unable to maintain the peak thrust for a smooth climb. This is likely due to propellant degradation over time in my opinion. The start pattern should hold a better neutral plateau at the top than that.

Although we can more carefully re-create the thrust over time chart if you’d like because the acceleration is given for the rocket over the entire duration of the flight. We know the propellant mass fractions.

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When I read this chart it is showing a total burn time from motor start to minimum thrust value of 7.11 seconds peaking at 15G and from there the thrust picks up for a total of 18.96 seconds peaking at 5G. Since the booster struggled to burn efficiently at the top end - it took longer to burn. The propellant didn’t just disappear. We can expect slightly higher peak figures, a shorter burn time, and thus a smoother plateau at the top of the burn on a “fresh” motor.

The mass of the rocket is 514kg. 15 * 9.81 = 147.15 m/s² acceleration.
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Force is equal to mass times acceleration, a simple calculator will tell you that the resultant force of this acceleration and mass is approximately 75635.1 Newtons.

When I input this mass and adjust the fuel fractions I can find the reasonable ~255-260 ISP expected of this type of propellant (which is the same type and make as the AIM-7F/M’s… even produced in the same building)… I find the fuel fraction used in the booster to be close to ~212kg for this burn time and thrust. Although the thrust is likely lower and the acceleration increase is caused by the loss of mass over time which is why the booster goes from ~12.5 to 15G peak but I’m not taking that into consideration yet.

Thus, the sustainer starts at ~2G and with a remaining mass of ~301kg for the sounding rocket.
Again, F = MA. I’m going to use the nice round number of 3.75G average acceleration arbitrarily. (2 + 5 / 2 = 3.5, add a bit for benefit of the doubt).

We find a thrust average of 5905.62 Newtons over 18.96 seconds.

Using the correct values for mass and propellant mass specifically I’ll share my data;
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Left is the real world expected performance based on my thrust calculations and the proper mass… the right one is the in-game missile.

We know from the grain pattern and acceleration chart that it should have a progressive burn. The available surface area increases as it burns since it is a simple circle pattern. I did the math earlier to determine it should have ~15% more surface area than the start of the burn by the time it ends.
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Source

330

@David_Bowie You can go ahead and forward this chart so the devs can ascertain the proper burn time and thrust for the rocket motor. This is far more comprehensive than any other source we have at the moment.

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The mass of the rocket is given in this source;

Not only does it have acceleration over time, but also the altitude over time which gives us the necessary information to determine thrust changes by air pressure and temperature. All of the necessary information is in these two sources. They both claim 5s boost, 21 seconds sustain contrary to the data which shows it always differs slightly from that. This is actually the case with all rocket motors of the era.

334

@MiG_23M

I’m sorry, But your calculations are useless, because they don’t even take drag into account.

Acceleration is the result of not just thrust on the mass of the vehicle, but rather the result of the net force, which is the vector sum of thrust, drag and vehicle’s weight.

Perhaps you should leave the calculation of the thrust to actual scientists at NASA and just use their reference rockets handbook?! :)

So even your own source essentially confirms the revised values in the 2023 NASA rockets handbook, but you go through some mental gymnastics to claims that “it’s because it wasn’t a fresh motor” :)

335

@David_Bowie
No we don’t need that, because we don’t know the drag values for the orbital vehicle in order to subtract the drag from the net force, to be able to calculate the thrust of the rocket motor.

Plus the M112 motor is used as “second stage” motor of this orbital vehicle, meaning it is burning essentially in space, not at sea level …

So it’s useless …

Plus, this is JUST A SINGLE LAUNCH!

So you think the value that you are (incorrectly) calculating from a single launch, is more accurate and representative than NASA’s reference rockets handbook that is most likely taking many many launches into account?!

336

Atmospheric drag at 20km+ is near zero, you’re looking at fractions of a percent difference. Next slide.

Air pressure at sea level is 14.7 psi… at 10km around 3.84 psi given temperature is the same (it is not). At 20,000m it is even less at 0.79psi.

The aerodynamic drag accounts for a very very small percentage of the missiles’ overall net force here.

Seeing as the missile is being implemented as an air launched missile with lofting in-game and will be operating at practically the exact same altitudes outlined by the charts I shared, it is absolutely the exact source material we need to ascertain burn time and thrust. They know the fuel fractions, and now also the burn time. If they want accurate thrust they can simply adjust until the ISP is around 255-260 and well… there you have it. The missile is accurately modeled.

Surprise surprise, the accurate thrust is around 80kN for the booster and the sustainer is overperforming IMO.

337

Not when you are flying at several times the speed of sound.

You do realize that drag scales with the velocity squared, right?

338

Again, these are variables we can ascertain based on the Phoenix layout. Gaijin has all the tools necessary to model the thrust thanks to these sources and there is far more information available than what is in your sources. The math is NOT difficult here.

Please stop being obtuse and just adjust your report to reflect the best data available. I know it isn’t a “buff” like you wanted.

340

@MiG_23M

What is that even supposed to mean.
We are not talking about missile’s drag in the game.

We are talking about your calculation of thrust based on the acceleration chart of the orbital vehicle. Your calculations ignore drag, which is significant when you are flying at several times the speed of sound.

You are calculating not the thrust, but rather the net force on the vehicle.
Which is the vector sum of thrust, drag and vehicle’s weight.

And then to top it all off, in your ultimate wisdom, you are using the acceleration chart of the ROTEX-T vehicle, but take the weight of the vehicle from the REXUS 2 vehicle’s study!!!

I’m speechless!

It’s like taking the thrust value of the F-15 and calculating its thrust to weight ratio by dividing it by F-16’s weight.

Spoiler

https://i.imgur.com/0fiC3Qv.png

341

The booster before the M112 motor and payload increases the mass, but the weight of the rocket at the expulsion of that would be of the motor + payload.

We have a motor weight of 416kg + payload of 190kg… total mass of 606kg. This bodes well for the thrust value being a bit higher but we already knew the claimed peaks. My calculations are not without flaws but you are blatantly dismissing useful data in a vain attempt to buff the missile rather than bring it to realistic values.

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It even shows here a burn time of approximately 25 seconds and again (but less visible because it is kind of squashed) the acceleration.

There is also velocity and pressure data over time for the launch. The first stage burns out at 768 m/s and then slows down for about 14s before the second stage ignites. Velocity dips to approximately ~550 m/s and then it ignites again, bringing the missile to a peak of almost 1,650 m/s.

1,650 - 550 = 1,100 m/s deltaV without considering drag. This would suggest the in-game model’s additional ~323 m/s is lost to drag? I don’t think so. I think it is slightly overperforming as I stated.

342

You don’t know what you are even doing …

Your calculations are still useless, because they don’t take the drag (which is significant when traveling at several times the speed of sound) into account.

Secondly, this is JUST A SINGLE LAUNCH!

So you think the value that you are (incorrectly) calculating from a single launch, is more accurate and representative than NASA’s reference rockets handbook that is most likely taking many many launches into account?!

343

I don’t think their handbook has any actual data besides peak thrust values and my math is 100% useful and valid. Why are you bent on being wrong?

344

@MiG_23M

Yeah, considering that you were: using the acceleration chart of one launch vehicle with the mass of another launch vehicle, and assuming the drag to be zero at several times the speed of sound, and thinking the data from just a single launch is more representative than NASA’s rockets handbook …

I think we really should have you calculate the thrust values for us …

1 Like
346

Nice off-topic ad hominem … As if my stats even remotely play into the argument at hand …

348

What business of yours is it if I want to keep my nickname and stats private? Feel free to report me …

Again, all you post is off-topic ad hominem … Your comments have absolutely nothing with this thread nor the argument at hand.

350

The information he’s brought into the conversation is useful, most of the things he’s said are pretty handy and are interesting to read. He is just having a debate with MiG_23M rather than a emotional argument.

Like how the Fatter missile should actually be called Fater, how the weight and such are incorrect and more

351

My bad, but again it isn’t totally irrelevant. It shows us that you can find the correct data with the variables provided by those two sources. The NASA sources are also useful, but the data is less conclusive because less is shown.

Regardless, correcting for the actual vehicle mass shows it is still less performance than in-game. The in-game model is overperforming no matter what way you look at it. You continuously refuse to acknowledge that what you are doing is pushing for a buff when the reality is that it is overperforming in-game. This is the only reason you’re so bent on dismissing the sources I’ve shared.

At such high altitudes drag is almost a non-factor. The energy lost from drag is miniscule. Regardless, as I have shown the necessary variables to properly calculate the true thrust are there. More thorough examination and math will need to be done by Gaijin to extrapolate it, but it is there. The NASA sources provide good information on peak thrust but lack the graphs of the other two.

Technically, two. Also they have more known variables and data presented than the NASA source. Combined they provide a REALLY good picture of what the performance should look like and guess what… it is less than what is in-game.

I already showed you the thrust curve and the peak values are known. Using simple % decrease from peak based on the acceleration chart could give you the correct thrust curve. The more datapoints the better when looking at the spikes from the boost stage in the one source.

There are many ways to skin the cat, but you’ve chosen to cut yourself over it instead. Quit being so obtuse about things and tell us… is the in-game missile overperforming? What do you think? Why should the sources I’ve presented be dismissed entire in favor of less detailed information? Just because it is from NASA?

352

@MiG_23M

1- My main point in that bug report was that the values in the 2023 revision of the NASA rockets handbook have been revised compared to the 2005 version.
And this is not meaningless.
It means the previous calculations / estimations of the motor’s thrust and burn time were incorrect / less accurate.

2- You simply cannot calculate the thrust from the data that you have available in those studies, because the drag value is unknown.
You are using the acceleration of the vehicle to calculate the net force exerted on the vehicle.
I.e. by ignoring that portion of the thrust which is being used to compensate / nullify the drag force, you are underestimating the thrust.

3- This is the data from a singular launch, and therefor is not as representative as something like NASA’s rockets handbook which:

A- Relies on the much larger data set (number of launches) that NASA has access to.
B- Is evidently getting revised every several years, to make it even more accurate and representative.

353

@MiG_23M

How?

Only the ROTEX-T study provides an acceleration chart.

The Rexus-2 study does not provide one. It only states that the peak acceleration was 20G.

354

I already told you that is not the only thing that can be ASSUMED from that change. It very well could have been difference in atmospheric conditions and motor quality / propellant degradation of one compared to the other. It doesn’t mean with absolute certainty that the “calculation” (which you swore previously was actual flight or test data) is wrong.

You absolutely can, the drag value is not unknown.

It is two separate studies, with one launch having more available data. Combined with the NASA data (something you’re also pretending isn’t possible)… creates quite a good picture.

It states the 5s, 21s booster-sustainer burn times and 20G acceleration is for the M112 rocket motor only - which again is one of the reasons the math isn’t invalid.

It gives the flight trajectory and altitude achieved over time. The energy loss based on the 26 to 55 second mark at between 20 and 60km altitude (almost none, evident by there being almost no excess deceleration beyond the force of gravity)… tells us what we need to know about the drag at that altitude. They even eject the nosecone making it incredibly non-aerodynamic so that they can deploy the payloads. Earlier in the flight the drag would be noteworthy… but later… not so much. It still gives us an incredibly close ball-park figure that matches the other datapoints such as the claimed 19,000 lbs of thrust.

Now please answer the questions? Is the in-game model over or underperforming in deltaV, top speed, thrust? Why aren’t the three studies more useful than just the NASA one again?

Is it possibly because you want to a-historically buff the missile?

355

No
Because the NASA source at least directly specifies the thrust values.

Whereas your source does not. You are trying to guesstimate the thrust value by assuming the drag (at speeds ~ Mach 2 to Mach 4.5) is zero and assuming this single launch in Sweden is representative of the typical thrust of this motor.

Plus the NASA source is the most recent, and the fact that they have revised their values in the 2023 revision as compared to the 2005 revision of the handbook, is very telling.