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DCS Aim-7 Sparrow Potentially Underperforming


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Please see, https://www.designation-systems.net/dusrm/m-7.html

As one can see in the table towards the end of the page, according to the article, the Aim-7A and B have a maximum speed of around Mach 2.5 while the Aim-7C, E, F, and M/P have a top speed of around Mach 4. Clearly, these are just brochure figures and that the actual top speed of the missiles is most certainly lower during most (non-ideal) engagements. However, when testing the Aim-7's in DCS, one finds that their top speeds during "ideal engagements" are much lower than expected (according to the article). As one can see in the first image below, the top speed of a lofting Aim-7MH when fired at 35000ft and Mach 1.2 under standard atmospheric conditions is around 1530 knots TAS or Mach 2.67, slightly higher than the top speed of the A and B (according to the article). In the second image, under very similar launching conditions and parameters, the top speed of an Aim-7E is around 1515 knots TAS or Mach 2.64, similar to the MH. According to the article, the similarities in top speeds are to be expected however the value of them are at least a Mach number lower than one would expect. 

 

 

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Aim-7MH Launch .trk Aim-7E Launch .trk


Edited by DCS FIGHTER PILOT
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Additionally, I would also like to add that when launching an Aim-MH and E in game at 35,000ft and Mach 2 under standard atmospheric conditions, the top speed of both missiles is only around 1950 knots TAS or Mach 3.4, still quite below the brochure number. 

If I was to guess, it seems as if the initial burn of the motors in both missiles is far too short, only allowing the missile to get up to mediocre speeds before it cuts out completely (like the E), or transitions to the sustain burn (like the MH). For reference, the total burn time for the Aim-7E and initial burn for the Aim-7MH in game is currently, around 3-3.5 seconds. 

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Fast Aim-7E Launch .trk Fast Aim-7MH Launch .trk

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The motor burn times, and thrusts of all the sparrows in game are correct; there's plenty of IRL documentation on the topic. I think the problem is the speed and altitude you are launching from; 35kft is far from "extreme". Try more like, M2 at 50kft in an F-15 to get a better sense of what kind of reference brochure speeds are using. I would also avoid adding loft into it, as that reduces top speed. Also, the website you listed isnt exactly a "source" by any stretch of the imagination (though the M4 figure for top speed is listed in more reputable sources as well)

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4 minutes ago, dundun92 said:

I would also avoid adding loft into it, as that reduces top speed.

Not necessarily. The reduced density of higher air can allow for much greater speed even if the missile has to climb.

On the missile itself, the AIM-7 does feel rather weak compared to almost any other contemporary. It has low drag, but nothing else to write home about. However I don't have data myself to say conclusively that it's undermodeled.


Edited by Exorcet

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15 minutes ago, Exorcet said:

Not necessarily. The reduced density of higher air can allow for much greater speed even if the missile has to climb.

At 40kft the air is so thin it doesn't gain much. The nozzle isn't vacuum-optimized, and the drag is already low. It'll still gain range from lofting, but max speed will be lower than if it didn't convert most of its kinetic energy into altitude. Mach 4 claims are probably something like "launched from a Tomcat at Mach 2 and 50kft", since that's how marketers roll.

AIM-7 was, IRL, a crap missile, with poor kinematics and poor reliability. You could score kills with it, but it wasn't easy. Russian Fox 1s of the time were better. 

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37 minutes ago, Dragon1-1 said:

At 40kft the air is so thin it doesn't gain much. The nozzle isn't vacuum-optimized, and the drag is already low. It'll still gain range from lofting, but max speed will be lower than if it didn't convert most of its kinetic energy into altitude. Mach 4 claims are probably something like "launched from a Tomcat at Mach 2 and 50kft", since that's how marketers roll.

AIM-7 was, IRL, a crap missile, with poor kinematics and poor reliability. You could score kills with it, but it wasn't easy. Russian Fox 1s of the time were better. 

I wouldn't exactly say that, AIM-7F/M use APN while the R24/R27 still use raw PN.  They also outrange both missiles as well.  Even the AIM-7D uses TPN.

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1 hour ago, dundun92 said:

The motor burn times, and thrusts of all the sparrows in game are correct; there's plenty of IRL documentation on the topic. I think the problem is the speed and altitude you are launching from; 35kft is far from "extreme". Try more like, M2 at 50kft in an F-15 to get a better sense of what kind of reference brochure speeds are using. I would also avoid adding loft into it, as that reduces top speed. Also, the website you listed isnt exactly a "source" by any stretch of the imagination (though the M4 figure for top speed is listed in more reputable sources as well)

The thrust values aren't exactly the same as the AIM-7 SMC their a bit lower thrust and not quite as long burning.  Honestly imho I think most of the updated missiles motors in the game are under-performing a little.   I wish we had a thrust vs time chart to verify but we don't.

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1 hour ago, Dragon1-1 said:

At 40kft the air is so thin it doesn't gain much. The nozzle isn't vacuum-optimized, and the drag is already low. It'll still gain range from lofting, but max speed will be lower than if it didn't convert most of its kinetic energy into altitude. Mach 4 claims are probably something like "launched from a Tomcat at Mach 2 and 50kft", since that's how marketers roll.

AIM-7 was, IRL, a crap missile, with poor kinematics and poor reliability. You could score kills with it, but it wasn't easy. Russian Fox 1s of the time were better. 

 

I don't believe any of that is really correct.  More likely the rocket motor configuration in game is incorrect.   The documents they are sourced from are fraught with errors (easy to see if you do some basic math) and ED has settled on an acceptable solution.

The AIM-7 was never a 'crap missile' ... like all missiles, major challenges were faced during the Vietnam and Korea era in terms of reliability mostly, and even AIM-7F still had a good old con-scan system.   The AIM-7M however proved to be a reliable missile and oddly enough reasonable competitor to the R-27R, which is why the R-27RE was produced.

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Sorry, but no. In Vietnam, it had plethora of problems, including randomly exploding halfway to the target, erratic flight paths and so on. PK of about 13%, according to Wikipedia. They were used in ODS and they still kind of sucked, even against targets that weren't particularly challenging, although they had better results then (still, just 19 were BVR shots, the rest was WVR). ED has modeled the missile performance correctly, according to the available data. Said performance just isn't very good. It was certainly not well regarded by the pilots.

Yeah, the AIM-7M managed to match R-27R, but the Soviets countered with the vastly superior R-27ER (and even before then, I think the Russian missile was faster). I was referring more to the fact R-23 was faster and had more range than the E variant, among other things. In fact, when the Soviets got their hands on a Sparrow, they started a project to copy it, which they promptly canceled when they realized their own missile was better. The later model Sparrows were usable, but they were never really good. 

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16 minutes ago, Dragon1-1 said:

Sorry, but no. In Vietnam, it had plethora of problems, including randomly exploding halfway to the target, erratic flight paths and so on. PK of about 13%, according to Wikipedia. They were used in ODS and they still kind of sucked, even against targets that weren't particularly challenging, although they had better results then (still, just 19 were BVR shots, the rest was WVR). ED has modeled the missile performance correctly, according to the available data. Said performance just isn't very good. It was certainly not well regarded by the pilots.

A big part of this problem was extremely poor maintenance and loaders.  The reliability of the missiles climbed dramatically in the navy after programs to train crews were implemented.  Ontop of all of that you had pilots who had no to very little knowledge about the limitations of the missiles.  I think something like 60-80% of misses were due to out of parameter shots.  With most of the rest being maintenance related.   The sparrow did have the issue you mentioned which was caused by mutual interference if you had two F4's supporting missiles within extremely close range to each other.  However this stopped being a problem in the navy when they dropped the super rigid right on your leads wingtip formations developed by the likes of bode and started using more modern tactics and started flying with greater separations between jets.

16 minutes ago, Dragon1-1 said:

Yeah, ''the AIM-7M managed to match R-27R, but the Soviets countered with the vastly superior R-27ER (and even before then, I think the Russian missile was faster). I was referring more to the fact R-23 was faster and had more range than the E variant, among other things. In fact, when the Soviets got their hands on a Sparrow, they started a project to copy it, which they promptly canceled when they realized their own missile was better. The later model Sparrows were usable, but they were never really good. 

I thought that the 7E had superior kinematic performance, not to mention a better guidance law with TPN.

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Problems with the early sparrows and their causes were well documented, nothing random about them.  It was a byproduct of the technologies used, maintenance, and the shooting aircraft's radar characteristics of the time.   The average Pk of 7Ms was ~0.34, and it has higher for the well stored and well maintained samples, though the sampling was low.

The R-27 hasn't got a good combat example to its name for the shots taken.

 

And none of this really has anything to do with the rocket motor anyway.


Edited by GGTharos

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20 hours ago, Dragon1-1 said:

At 40kft the air is so thin it doesn't gain much. The nozzle isn't vacuum-optimized, and the drag is already low. It'll still gain range from lofting, but max speed will be lower than if it didn't convert most of its kinetic energy into altitude. Mach 4 claims are probably something like "launched from a Tomcat at Mach 2 and 50kft", since that's how marketers roll.

AIM-7 was, IRL, a crap missile, with poor kinematics and poor reliability. You could score kills with it, but it wasn't easy. Russian Fox 1s of the time were better. 

I have heard somewhere on here (I will not quote anyone as it may very well be wrong), that the PL-12/SD-10 was based off of the sparrow (and likely the AMRAAM). If the Aim-7 was such a "crappy missile" why would anyone want to base their tech off of it? 


Edited by DCS FIGHTER PILOT
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Honestly, this looks more like a Chinese R-77/AMRAAM than the Sparrow. The Russians had a chance to base their tech on it and gave it a pass, which is saying something given how much they liked to copy Western designs. If the Chinese worked off the Sparrow, this would mean they didn't have anything better, but Russians were involved in PL-12 design, so I don't think there's a whole lot of AIM-7 in it.

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The Russians didn't really copy western designs ... yes, they copied the 9B and learned something new about how to arrange the missile internally, but the rest is all them.

The PL-10 probably started with Aspide (a foreign AIM-7 modification) but it's hard to tell what of it is in there.  The Russians likely contributed ARH seeker technology or knowledge.   The SD-10/PL-10 isn't exactly a great missile, but it's not a missile that should be ignored either.


Edited by GGTharos

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20 hours ago, nighthawk2174 said:

The thrust values aren't exactly the same as the AIM-7 SMC their a bit lower thrust and not quite as long burning.  Honestly imho I think most of the updated missiles motors in the game are under-performing a little.   I wish we had a thrust vs time chart to verify but we don't.

So for the 7F/M, the problem is that there seems to be multiple sources that give different boost times; the SMC/SAC puts it at 4.5s w/ 5700 lbs of thrust. The 1984 weapons file puts it at 5750 lbs thrust for 4s. Theres also this source, im unsure of the origin, but it puts it at 3.5s boost, which I think is the correct one:

nullAIM-7F_Characteristics.jpg

The reason the SMC's 4.5 sec burn time seems suspect is that when you do the math on the thrust per the SMC (25.5 kN) and mass flow rate (38 kg of boost fuel, accounting for the flipped boost/sustain prop mass in the SMC), you get an ISP of ~312s for the boost, which is very much out of whack. if you reduce the burn time to 3.5s, the ISP drops to 241s; which is a much more sane value.

For reference, ED's sparrow has a 3.7s boost, 38.48kg fuel mass, 25.1 kN thrust, and 247s of ISP, which lines up with the SMC boost motor mass and a reasonable ISP. So at least IMO, the AIM-7 motor is pretty good RN compared to what we know about it IRL.

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The SMCs are full or 'errors' and there's not reason to regard the boost/sustain weights are correct.  Put for 4.5s for the boost, 6.5 for sustain, give boost 105lbs and susain 30, you get something really reasonable and that matches up really well to other qualitative information.

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19 hours ago, GGTharos said:

The SMCs are full or 'errors' and there's not reason to regard the boost/sustain weights are correct.  Put for 4.5s for the boost, 6.5 for sustain, give boost 105lbs and susain 30, you get something really reasonable and that matches up really well to other qualitative information.

Yeah i did the math that would line up as a possibility.  It’d help if we had more info, boost sustain motors are highly variable in how they can be set up.

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Sorry Maestro but my opinion is that:

It is most certainly under-performing.  It is a mach 4 missile (you can see this 'up to mach 4' in a lot of literature) and you cannot get it there even if you launch it at mach 2 in DCS.  You also cannot easily get that speed by altering the aerodynamics, so working with the motor arrangement is the only thing that's left.

You circled mach 2.9 but if I had sent you this document you'd be asking the same questions I'll ask now 'At what launch speed and altitude'?

And I also have a very strong suspicion that if you asked the SMEs and they were willing to comment on this at all, they might not be averse to adding 0.2-0.3M to that missile's top speed in game.

I'm fairly certain that I've seen almost all the same sources that you have for this motor, and there is always something that does not add up.

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On 5/31/2022 at 1:37 PM, dundun92 said:

So for the 7F/M, the problem is that there seems to be multiple sources that give different boost times; the SMC/SAC puts it at 4.5s w/ 5700 lbs of thrust. The 1984 weapons file puts it at 5750 lbs thrust for 4s. Theres also this source, im unsure of the origin, but it puts it at 3.5s boost, which I think is the correct one:

Unless I'm tripping, the 1976 SMC, the 1977 SMC, and the 1984 Weapons file all agree on a boost of 4.5s at 5750 lbs and a sustainer for 11s at 1018

nullimage.pngimage.pngimage.png

 

I doubt I have anything that hasn't already been referenced in this thread, but I am curious why one figure (Missile Mach #) that only appears to be referenced in the least mature version of a document is taken as absolute truth over a figure that shows up across multiple documents (burn times). 

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17 hours ago, GGTharos said:

Sorry Maestro but my opinion is that:

It is most certainly under-performing.  It is a mach 4 missile (you can see this 'up to mach 4' in a lot of literature) and you cannot get it there even if you launch it at mach 2 in DCS.  You also cannot easily get that speed by altering the aerodynamics, so working with the motor arrangement is the only thing that's left.

You circled mach 2.9 but if I had sent you this document you'd be asking the same questions I'll ask now 'At what launch speed and altitude'?

Of course 🙂 What parameters you suppose to launch missile at to reach Mach 4? Right now launched at 60Kft and Mach 2 missile speeds up to Mach 4. To make missile able to achive Mach 4 at 40Kft altitude (launched Mach 2) you should spent all fuel for boost. 

And there is no issue with drag. See attached. Three different sources(Tactical missile design by E. Fleeman, raytheon wind tunnel test data - denoted by triangles, our CFD validation - denoted by x'es) give almost the same values. Also see motor data from Feelman's book.

 

17 hours ago, GGTharos said:

And I also have a very strong suspicion that if you asked the SMEs and they were willing to comment on this at all, they might not be averse to adding 0.2-0.3M to that missile's top speed in game.

I'm fairly certain that I've seen almost all the same sources that you have for this motor, and there is always something that does not add up.

Who is SME in that case? Pilots do not need to know such things. Raytheon engineers? Not an option.

Guys, all this sounds like you think we do not analyse data we have, do not see mistakes, do not do research. But we do. We try our best.

aim-7cd0.jpg

flee.jpg

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3 hours ago, Маэстро said:

Of course 🙂 What parameters you suppose to launch missile at to reach Mach 4? Right now launched at 60Kft and Mach 2 missile speeds up to Mach 4. To make missile able to achive Mach 4 at 40Kft altitude (launched Mach 2) you should spent all fuel for boost. 

Hi Maestro, normally I like to run tests before I present anything but ... I don't have access to anything until August - certainly I failed to do at least my back-of-the-envelope calculations this time, but also I'm not concerned with Mach 4 in practice , it's just a reference point 🙂

Thanks for responding.

3 hours ago, Маэстро said:

And there is no issue with drag. See attached. Three different sources(Tactical missile design by E. Fleeman, raytheon wind tunnel test data - denoted by triangles, our CFD validation - denoted by x'es) give almost the same values. Also see motor data from Feelman's book.

I have seen the same sources then.  I don't know that Fleeman has the right numbers for the motor, I'm inclined to trust that source but on the other hand there are no guarantees.

3 hours ago, Маэстро said:

Who is SME in that case? Pilots do not need to know such things. Raytheon engineers? Not an option.

Guys, all this sounds like you think we do not analyse data we have, do not see mistakes, do not do research. But we do. We try our best.

Pilots do know, they have resources for this sort of thing ... but they may not be able to talk about it:  Vault documents and also debriefs from real and simulated combat make a lot of data available, data from instrumented shots is likely available.

I have no doubt with respect to your skills and knowledge, just FYI - I am bringing this to your attention as IMHO the missile is running a little slower than I believe it should; not my much, mach 0.2 or so.  It's also possible that this is caused by guidance issues, wasting speed in unnecessary maneuvers in the boost stage.


Edited by GGTharos

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8 hours ago, near_blind said:

I doubt I have anything that hasn't already been referenced in this thread, but I am curious why one figure (Missile Mach #) that only appears to be referenced in the least mature version of a document is taken as absolute truth over a figure that shows up across multiple documents (burn times). 

The 4.5 sec figure is an issue mathematically vs the weight of propellant they list - it blows up the ISP.    The only way to fix this is to adjust the propelland mass for boost/sustain and also cut the sustainer time down.

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14 minutes ago, GGTharos said:

The 4.5 sec figure is an issue mathematically vs the weight of propellant they list - it blows up the ISP.    The only way to fix this is to adjust the propelland mass for boost/sustain and also cut the sustainer time down.

Yup which is really the big issue here, to really know for sure were going to need an actual motor thrustvtime graph.  Until we get one though the fleeman numbers are the best we got.  I don't disagree with your conclusion though GG I'm also of the opinion it may be a little slow.

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