So what's the real performance of AIM-120C

[D-Scythe]

He also said the range continues to increase beyond the transonic regime, e.g. by 50% instead of 40% if you launch at M1.5 instead of M1.3. So, independent of transonics, faster still equals more range. What role does transonic drag really play, then? Even the way Rhen describes it, you're still getting 40% extra range ("or more") for 44% extra speed - i.e. by going faster, you get less out than what you put in.

 

There's not much a difference between 40% and 44% is there?

 

How much flight time does the missile spend in the transonic regime after subsonic launch anyway? miniZAP says 1 second. If a missile's range could be increased by 40% by carrying 1 more second of propellant burn, why don't they carry 1 more second of propellant burn? I think something quite different is the explanation here.

 

Hmm maybe the "missing" range increased is explained by the faster missile achieving a greater loft altitude during missile fly out? Even a 200 kmph increase in speed can result in a >2000 m (over 6500 ft) increase in loft altitude, where missiles aren't penalized as severely by drag induced by the greater air densities at lower altitudes.

 

Transonic drag is a bigger factor in the missile flight end-game, as I see it. Especially for the R-77, whose potato mashers induce a ton of drag in this speed regime.

[HubMan]

He also said the range continues to increase beyond the transonic regime, e.g. by 50% instead of 40% if you launch at M1.5 instead of M1.3. So, independent of transonics, faster still equals more range. What role does transonic drag really play, then? Even the way Rhen describes it, you're still getting 40% extra range ("or more") for 44% extra speed - i.e. by going faster, you get less out than what you put in.

44% more of speed at launch for 40% of total range is very, very nice :) As it's not 44% of maximum top speed at the end of the boost phase, but merely mach 0.4 more for a missile that can reach mach 3 / mach 4... The "44%" are actually only a bit more that 10% of the top speed of the missile, it is not the same :) You get a lot more than what you put in... :)

 

How much flight time does the missile spend in the transonic regime after subsonic launch anyway? miniZAP says 1 second. If a missile's range could be increased by 40% by carrying 1 more second of propellant burn, why don't they carry 1 more second of propellant burn?

As minizap does not correctly modelize to my opinion what happens when the missile goes through the transonic regime, there is no surprise that going through it is so little energy consuming :)

 

I think something quite different is the explanation here.

Maybe :) It's also maybe just something more to add to what I understood :D

 

 

Hub.

[SwingKid]

Transonic drag is a bigger factor in the missile flight end-game, as I see it.

 

Agreed - and a max-range missile spends the same amount of time decelerating through transonic, no matter what speed it was launched at. Take a look at the Vm charts here:

http://www.ecf.utoronto.ca/~pavacic/lomac/betaforum/aim9lperf.jpg

 

Except a little at sea level, there is not a very strong discontinuity in the deceleration of the missile as it decelerates (Mach 1 is about 1000 FPS at 10 Kft)

If what's affecting the range of the missile is transonics, that's where we'd expect to see the effects - in the deceleration tail, not from the launch speed.

[GGTharos]

Cool; it's too bad you don't have a guidance model with moving fins in there :)

 

Only if you set "Gravity Factor" to 0.0 G.

With default 1 G gravity, the missile must generate 1 G lift to run straight, and miniZAP calculates some induced drag based on wing area and AOA.

[nscode]

Yes, since angle of attack has an effect on the reference area and Cd

[Pilotasso]

Missile range increase with speed can only be taken advantage on very few fighters. For example the F-16, the increase of the range will probably exceed that of the radar, or at the very least exeed the range for wich the radar can maintain a stable lock.

[GGTharos]

Or, the increased range doesn't give you any advantage because it's barely shorter than detection range.

[tflash]

One of the main claimed advantages of the APG-79 over the APG-73 in the Super Hornet is that with this radar the Superbug can use the Amraam to its full potential and full range.

 

And they are talking about the AIM-120C, not the coming D model. This is tell-taling about the Amraam, no?

 

An Aesa-equipped Superbug with current Amraam is a quantum leap better than a Phoenix-sporting Tomcat, whatever nostalgics might claim. And I'm a nostalgic:D

[GGTharos]

Actually, it's more telling about radars :)

The difference here is that an AESA radar can easily track and scan for targets in a WIDE azimuth, while providing RAPID updates to missiles via datalink, as opposed to a mechanically scanned radar which under the same circumstances, might provide one update every 8 sec.

 

The idea is that while with the APG-73 you had to engage multiple targets along a narrow azimuth to get the most reliable tracking, with the APG-79 you can do so across your entire radar FOV. This means you can significantly overlap another superbug's attack pattern, allowing you to better cover each other, on in general, it permits you to engage targets outside of parameters that were possible with the APG-73 (ie. very widely separated by altitude and azimuth).

 

One of the main claimed advantages of the APG-79 over the APG-73 in the Super Hornet is that with this radar the Superbug can use the Amraam to its full potential and full range.

 

And they are talking about the AIM-120C, not the coming D model. This is tell-taling about the Amraam, no?

 

An Aesa-equipped Superbug with current Amraam is a quantum leap better than a Phoenix-sporting Tomcat, whatever nostalgics might claim. And I'm a nostalgic:D

[HubMan]

Agreed - and a max-range missile spends the same amount of time decelerating through transonic, no matter what speed it was launched at. Take a look at the Vm charts here:

http://www.ecf.utoronto.ca/~pavacic/lomac/betaforum/aim9lperf.jpg

 

Except a little at sea level, there is not a very strong discontinuity in the deceleration of the missile as it decelerates (Mach 1 is about 1000 FPS at 10 Kft)

If what's affecting the range of the missile is transonics, that's where we'd expect to see the effects - in the deceleration tail, not from the launch speed.

On the other hand, if you look carefully (see you schema edited below), you will see that -there is- a deceleration around 1200FPS ie right at the beginning of the transonic ;)

I'm not especially suprised, as I don't think a missile slowing down through the transonic area is experiencing the same troubles than one trying to push through, especially if it is and unguided one... :)

 

 

 

Anyway, the more I think about your Sidewinder example, the more I think that the geometry of the missiles and way they are launched ie rail vs ejector is related :

- the AIM-9 is launched straight from a rail

- the AIM-120 can be fired as well from a rail, but you will find it mostly used on downward ejectors for the F-15, the F-22... And that's what Rhen was refering to :) I'm curious about what happens will the missile is violently going down and then fire it's engine, going through the transonic regime, either with a downward momentum or trying to manoeuver to get into an horizontal or lofted trajectory.... :D

 

And I may be wrong of course, but I think that the Sidewinder model is not really applicable to the AMRAAM :D

 

Cheers :)

 

 

Hub.

[SwingKid]

Note:

In order to give it a top speed of Mach 4.5, other researchers give the AIM-120 a Specific Impulse of 287 s. The default value in miniZAP is 230 s. miniZAP users may adjust this value as desired.

[Pilotasso]

6 seconds of propelant...in videos I can count at least 7, and they are probably AIM-120A or B

[RvEYoda]

very nice charts for the aim9 there. Clearly shows how incredibly important the original speed of the launching aircraft is ;)

From what I can read in the 20.000 ft diagram it accellerates approx 2100-2200/5 ~ 440 kph/s^2..... This is around 12 G accelleration. The deceleration is less than this, 6-8 G so the missile keeps it speed very nice!

 

Where did you say you got these charts from?

The "variant" here could be r73?

 

Imo also like Hubman said it is reasonable to assume different results for the aim120, certainly more optimized for long range/time flight ;)

 

Ah crap that was feet per second.

This makes the missile EVEN BETTER :D

1 (foot per second) = 1.09728 kph

real life aim9 kicks lo 120 ^^

[GGTharos]

How did you measure this deceleration?

[RvEYoda]

How did you measure this deceleration?

 

i just took the peak dec from the graphs above. add 9-10% since i missed the fps not kph.

If you mean for lockon I have made graphs of the missiles there. Should be possible to find these.

[GGTharos]

Alright, maybe my physics is way off whack, and correct me if it is, but my calculation was as follows:

 

In one second, the AIM-120 in LO lost 100kts (from 1529, to 1429). The fact that I may have fractions of a second hanging off here and there is immaterial.

 

So I convert this to kph ... 185kph lost in that one second, which is 51mps or so, which is what ... just over 5g.

 

So am I cracked, or are you? :D

[SwingKid]

6 seconds of propelant...in videos I can count at least 7, and they are probably AIM-120A or B

 

6 seconds of boost-only thrust.

The real AIM-120 is about 11 seconds, but most of that is reduced sustain thrust.

The total impulse of the two models may still be similar.

 

Where did you say you got these charts from?

The "variant" here could be r73?

 

http://forums.eagle.ru/showthread.php?p=328375#post328375

The "variant" is a hypothetical, Sidewinder-sized radar missile that sounds like an early AMRAAM proposal (note date of article).

[Pilotasso]

real AMRAAM is much faster than the one in LOMAC (mach 2.5 VS 4+)so if the drag decceleration in the game is in the order of that IRL we still have a problem here.

[RvEYoda]

Alright, maybe my physics is way off whack, and correct me if it is, but my calculation was as follows:

 

In one second, the AIM-120 in LO lost 100kts (from 1529, to 1429). The fact that I may have fractions of a second hanging off here and there is immaterial.

 

So I convert this to kph ... 185kph lost in that one second, which is 51mps or so, which is what ... just over 5g.

 

So am I cracked, or are you? :D

 

hmm...i think my Lo test was at 10.000 ft.

let me see what my graph showed.

 

please don't mind the in-graph decelleration comments, they are not accurate ^^

where it says something about "20g break" should say more like 2-3g :P

(lines are ~correct though)

 

 

 

Cool : I got the same numbers as you GG for high speeds :) at 10.000 ft. 5-6 G deceleration at the 2900-3000 kph TAS range.

Don't know where I got the 25G numbers from.....sry ^^. However this is ofc course still comparing RL aim9 vs Lo amraam ^^

I guess it's a top speed+AoA issue we have in game for high speeds, for low I'm not sure.

 

However an interesting thing to note is that the real aim9 (if the source is reliable) only seems to acc around 10-15G, compared to lo 30+

If this is comparable to Amraam, it should also be one of the reasons why shots fired with high launch speed currently don't really give any advantage in Lo

 

So compared to the rest of missiles :

 

[GGTharos]

As you know, AoA effects are not modeled for missiles. It's just a point mass with acceleration, drag, and g-loading effects on speed, as far as I can tell.

[RvEYoda]

As you know, AoA effects are not modeled for missiles. It's just a point mass with acceleration, drag, and g-loading effects on speed, as far as I can tell.

 

This does look to be the case

[GGTharos]

I will also note that the R-77 and AIM-120 lines nicely demonstrate how the launch speed of an aircraft would make a difference ... if you changed those into speed v range or range v time as well ...

[RvEYoda]

I will also note that the R-77 and AIM-120 lines nicely demonstrate how the launch speed of an aircraft would make a difference ... if you changed those into speed v range or range v time as well ...

 

 

as long as we have 30+ G acc ,

the diff will be minimal, and the gain would be lost by

the extra space required to run from the enemy's missile =(,

much bigger turn radius, so currently no gains.

 

talking lockon numbers changing launch speed might give you 0.5 km at best when comparing

400 kph v 1600 kph launch.

(this excluding the need for earlier break of since you will have a massive turn radius)

[GGTharos]

I don't think you follow. ;)

The R-77 line is basically an in-accurate, but reasonable simulator of an AIM-120 launched at higher initial velosity ;)

[RvEYoda]

I don't think you follow. ;)

The R-77 line is basically an in-accurate, but reasonable simulator of an AIM-120 launched at higher initial velosity ;)

 

well, maybe at least a slight improvement :P.

 

I'm still totally against a speed cap and would enjoy a more reasonable acc.

however if we remove it right now we end up with missiles flying mach10....

 

id like, cut acc to 13 G and remove cap, to see what happens. Maybe we'll have some fun :)

However, loft holds prio over anything else