Air-to-Air Missile Discussion

[Pyroflash]

Again with the missiles.. Well, at least they aren't useless right now.

[Mandrake5]

Again with the missiles.. Well, at least they aren't useless right now.

 

 

Really..?

 

I understand the technical difficulties, it's the approach which baffles me: I mean, why keep releasing broken updates, why not keep the old flawed-but-playable missile code we had in 1.2.2 until such time as a real improvement has been achieved?

 

I know the aim-9s were useless in 1.2.2 but everything else at least had a chance of hitting a manoeuvring target, and you never got blown up flying into the back of your own Aim-120B....

[AFAlinebacker42]

The approach will be laid out soon. Basically rather than estimating parameters and using game trial and error as most players are, we are looking up all missile data which is publically available from the suppliers, all applicable milspecs, and then we are producing performance curves for every relavent parameter from 0 to 60,000ft.

 

Question our knowledge or credibility? That's fine. We'll be providing a reference to every text used, and an appendix of every spec and piece of manufacturer data we utilize.

 

We are using CAD to produce 1:1scale models with attached material dendity and strength data, and we will be performing iterative CFD to validate our drag force, range, thrust, etc.

 

About defining maximum range, Rmax is not the same as max range. These are clearly defined, and we'll be showing this as well.

 

Prepare for accurate missile performance, both Russian and American

[Angel101]

how long you can do it all?

[HiJack]

... why keep releasing broken updates, why not keep the old flawed-but-playable missile code we had in 1.2.2 until such time as a real improvement has been achieved?...

Because we wanted to hack open the Huey and enjoy the flap flap flap flap .... :pilotfly:

[159th_Viper]

....we are looking up all missile data which is publically available from the suppliers, all applicable milspecs...

 

I'd be very interested in all that documentation and corroborative sources. Would appreciate it if you could make it publically available and if not, via PM :)

[TZeer]

I'm no air jockey or math guru. But the missiles performance looks anemic at best.

 

Just had a quick test for fun.

 

- Total boost time: 12-13 sec What??

- This is divided roughly 50/50 when looking at animation and behavior in game. So ~6 sec boost and ~6 sec sustained boost?

 

And this:

 

http://forum.keypublishing.com/showthread.php?97983-AIM-120-range-questions

 

 

Gives a good explanation on how missiles behaves in a simplistic way. And some rules of thumb..

 

One that struck out is this one:

 

Remember though that the rate of deceleration actually DECREASES as the

missile's velocity decreases.

 

Another rough rule of thumb:-

 

The time it takes for a missile to lose 25% of its velocity after burn out at supersonic speeds.

 

Never @ > 100,000 m (~300,000 ft) ; in space

~150 seconds @ 24,000 m (~80,000 ft)

~70 seconds @ 18,000 m (~ 60,000 ft)

~25 seconds @ 12,000 m (~ 40,000 ft)

~10 seconds @ 6,000 ft (~20,000 ft)

~5 seconds @ Sea Level

 

Remember, fractions over time are not additive.

In otherwords, if a missile loses about 25% of its velocity in 10 seconds,

in the 10 subsequent seconds (t =20s) the missile loses approximately another 25% of

the remaining 75% not a 100%. Total velocity loss is ~43.75% not 50%.

 

This is highly collated to the fall in air density.

Drag = 0.5 x P x V^2 x Cd x A.

Holding everything else constant Drag falls proportionally to density.

Drag also falls exponentially with Velocity which accounts for the loss in velocity

in the given time slices being about 25% instead of closer to 40%.

 

 

Quick test I did with the AIM-120C

 

@ 40000 feet: Max speed at the end of boost ~ 2600 km/h

After 25 sec, ~ 1500 km/h

 

Lost roughly 43% of it speed.

 

@ 6000 feets: Max speed at the end of boost ~ 1800 km/h

After 10 sec. ~800 km/h

 

Lost rougly 50% of it speed.

Edited May 4, 2013 by TZeer

[Exorcet]

And this is how we see that you guys do it;

I will admit that some of the patch results make me wonder, but the missile flight model isn't necessarily going to be an easy thing. There might be a bit of trial and error going on, but to some degree it's probably necessary.

 

It also might be true that even if the missiles achieve perfect flight model performance, the in game capability of the missiles will still be too low due to guidance or other factors.

 

The test we're doing as player are (often, and including mine) simplistic as they tend to focus on one or maybe two conditions when missile performance must be mapped across a wide range of conditions.

 

In any case, I hope that more people working on the problem brings more solutions.

 

Holding everything else constant Drag falls proportionally to density.

That is a bit of a problem as has been discussed though. CD as a constant thing more often happens at really low speeds (Mach .3 or less). The missiles are primarily supersonic and probably have some specific Mach for lowest CD. As a result drag won't fall with V^2, though it may still be close. You can have things like constant drag across a range of speeds though.

Edited May 4, 2013 by Exorcet

[GGTharos]

These 'rules of thumb' may help you get an idea about missiles, but they don't help you model missiles. Missiles can vary quite significantly in their drag profiles and can and will violate these 'rules of thumb' at will.

 

And this:

 

http://forum.keypublishing.com/showthread.php?97983-AIM-120-range-questions

 

 

Gives a good explanation on how missiles behaves in a simplistic way. And some rules of thumb..

[GGTharos]

No, it isn't.

 

is it safe to say at a 65km shot the r-27er would reach the target first compared to the aim-120c5? Because of lofting. Note: this is a non maneuvering target

[TZeer]

These 'rules of thumb' may help you get an idea about missiles, but they don't help you model missiles. Missiles can vary quite significantly in their drag profiles and can and will violate these 'rules of thumb' at will.

 

 

That's why it says:

 

 

Another rough rule of thumb:-

 

:)

 

So even if it's rough, it gives a guideline. And 25% versus 43% is quite a leap and gives an indication that it bleeds speed to fast.

 

But the boost times seems way of. ~6 sec initial boost and ~6 sec sustained boost?

 

Question: How much sustainer thrust is needed in an AAM like the AMRAAM?

 

Drag force (Newtons) = 0.5 x P x V^2 x Cd x A

 

P = Density of Air (kg/m^3) ; ~1.29 kg/m^3 @ sea level; ~0.232 kg/m^3 @ 12,000 m

V = Velocity (m/s) ; Mach 1 = 340 m/s @ sea level; ~295 m/s @ 12,000 m

Cd = Co-efficient of Drag ; ~ 0.6 to 0.95 for rockets depending mostly on finnage, nose and tail profile. For model rockets we typically use 0.75 Cd as a rough rule of thumb.

A = Sectional Area (m^2) ; ~ 0.025 m^2 for a 7" diameter missile.

 

Therefor, for an AMRAAM like AAM going at high altitudes (40,000 ft)

 

Drag Force @ Mach 4 = 0.5 x 0.232 x (295x4)^2 x 0.70 x 0.025 = 2827 Newtons = 636 lbs

Drag Force @ Mach 3 = 0.5 x 0.232 x (295x3)^2 x 0.70 x 0.025 = 1590 Newtons = 357 lbs

Drag Force @ Mach 2 = 0.5 x 0.232 x (295x2)^2 x 0.70 x 0.025 = 707 Newtons = 159 lbs

Drag Force @ Mach 1 = 0.5 x 0.232 x 295^2 x 0.70 x 0.025 = 177 Newtons = 39.8 lbs

 

It'll take approximately 500 lbs of thrust to sustain a velocity of Mach 3.5+ at high altitudes.

 

For a 335 lbs missile with a 40% fuel fraction and a 245 second specific impulse (about right for missile grade HTPB solid propellant). It can for instance use about 2/3 of its fuel on a 5 second boost @ ~4400 lbs of thrust 1/3 of that fuel for sustain burn @ 500 lbs thrust, it'll be able to sustain the requisite level of thrust for ~22 seconds. Using the classic Delta V equation:-

 

Delta V = 9.8 x IpSec x LN (Initial Mass / Final Mass) = 9.8 x 245 x LN (335/(335-90)) = 751 m/s = Mach 2.55

 

We'll correct it by a factor of ~0.9 to counter the fact that at Mach 4 about 16% of the thrust is simply to overcome drag, whereas at Mach 3 only 8% of the thrust is to over come drag and it falls to rather insignificant levels below that.

 

Mach 2.55 x 0.9 = Mach 2.3

 

Hence, the missile will attain about Mach 2.3 over launch speed or approximately Mach 4.1 on a Mach 1.8 dash release. It will then cruise at that speed for about 22 additional seconds on the sustainer before burning out. At 27 seconds after launch it'll become a gliding dart. At this point it'll be going about Mach 3.6 and about 30 km from the launch point. It'll be decelerating at a rate of about Mach 0.085 per second at Mach 3.6. This will decrease to a rate of Mach 0.059 per second as it crosses Mach 3 and further to Mach 0.026 per second as it passes through Mach 2. It'll take more than 40 seconds more to slow to Mach 2. At this point the missile is about 60~65km from the launch point.

 

 

http://www.f-16.net/index.php?name=PNphpBB2&file=viewtopic&p=123182

[IASGATG]

The problem you have is that the Cd is a complete guess. Moreover, the Cd changes as the missile flies. It's not as simple as that makes it out to be. The maths you're currently looking at is the first instant of the missile in flight. As soon as you change instant, you have to redo all your equations. Don't worry, we're working it out.

Edited May 4, 2013 by IASGATG

[TZeer]

The problem you have is that the Cd is a complete guess. Moreover, the Cd changes as the missile flies. It's not as simple as that makes it out to be. The maths you're currently looking at is the first instant of the missile in flight. As soon as you change instant, you have to redo all your equations. Don't worry, we're working it out.

 

I know :)

 

I have some basic knowledge about it due to my work as a automation technician. Laminar flow, turbulent flow, Reynolds number, higher the flow = higher pressure loss +++ fiscal metering systems.

 

But not enough I think to contribute in any meaningful way, apart from stating, "that looks strange" :D

 

Appreciate the time and work you guys put into this. :thumbup:

[theChris]

No, it isn't.

 

so the 70km range is without loft?

[Shein]

i cant wait for these to be fixed. though its going to be a real eye opener when we're used to missiles being effective at 15 miles, and suddenly they cant kill at 57 miles

[aussieboy]

Hi,

 

The Cdo would be something like:

0.25 @ Mach 1 with thrust off

0.15 @ Mach 1 thrust on

 

0.33 @ Mach 2 with thrust off

0.19 @ Mach 2 thrust on

 

0.24 @ Mach 3 with thrust off

0.14 @ Mach 3 thrust on

 

Reference: Figure 2.6. http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA384590

[IASGATG]

i cant wait for these to be fixed. though its going to be a real eye opener when we're used to missiles being effective at 15 miles, and suddenly they cant kill at 57 miles

 

You have to remember that there is a huge number of things that come into play, biggest of which is obviously have the defender reacts. Next is how the aggressor/defender are positioned and acting in space. Your AIM-120 might kill things at 50nmi, but at sea level it's range will be MUCH smaller.

[IASGATG]

Question - Is there a way of altering the missile's homing behaviour beyond when the targeting computer activates?

[GGTharos]

No, there is not. Missiles use PN, save for the few beam riders/SACLOS. The algorithms are not exposed, and all of that stuff is known and 'on the list'.

[IASGATG]

Okay, thanks. :)

[71st_Mastiff]

is this a bug? 120c? 8nm?

 

so if the 120c are porked what about the r77's?

[Mandrake5]

From a brief test sortie it seems the 120C now has the same effective range against a non-manoeuvring target as the R27ER, i.e 5-7nm.

 

Cant speak for the R77 but would like to know this also.

[IASGATG]

For those of us having trouble with the Russian short-hand comments. What does the Cx_pil variable do? No rush.

[GGTharos]

The amount of drag added to the carrier aircraft when the missile is mounted on a (any) pylon. It has nothing to do with the missile in-flight.

[IASGATG]

Thank you.