AIM-120 Chaff Resistance

[Dancer]

Hello there,

 

Just testing the F/A-18 A/A weapons and radar. Problems with TWS have already been surfaced so I will only say I've had the same issues with AMRAAM guidance.

 

It also looks like the AIM-120 has become extremely susceptible to chaff. I'm not sure If this has always been the case. Attached is screenshots from Tacview of one of many examples I've encountered on Hoggit's PGAW server with relevant data moments before. The points of interest involve these factors:

 

• The Missile is within 10 nautical miles (Pitbull) when it loses lock
  
• The target is not flying above mach 1 (not LOS rate evasion)
  
• The difference in aspect is roughly 100 degrees.
  

 

If this was intentional I apologies for wasting your time. However I consider your attention to be drawn to this issue when able.

[Airhunter]

Yep, they are beyond broken.

[Breakshot]

Lol, 120 has best resistance to chaff in DCS. Its broken in many other ways but not this.

 

Better to be asking questions of ED how 120C can climb and track at 300km/h (well beyond its stall speed).

 

 

Отправлено с моего STV100-2 через Tapatalk

[85th_Maverick]

On 5/29/2020 at 8:35 AM, Breakshot said:

Lol, 120 has best resistance to chaff in DCS. Its broken in many other ways but not this.

 

Better to be asking questions of ED how 120C can climb and track at 300km/h (well beyond its stall speed).

 

 

 

Отправлено с моего STV100-2 через Tapatalk

I've also told them (being an ex-aerodynamicist) that the AIM-120s have an incredibly high lift, when their stall speeds at 30AoA (zero propellant left) should be about 430-450km/h, not 270 is it was in 2.5 version. Now they've put their mind together a bit and realized that it should be higher, but still not high enough to be normal/realistic. The stall speed of the AIM-120's in version 2.7+ is still around 350km/h or so. It should be 100km/h more than that. Not everyone understands and masters aerodynamics correctly, and it seems like the FM devs at ED are mostly doing that and don't want to listen to those who have studied the problem with better understanding and more correct approaches for finding the more accurate numbers!

[Cmptohocah]

On 5/28/2021 at 7:56 PM, 85th_Maverick said:

I've also told them (being an ex-aerodynamicist) that the AIM-120s have an incredibly high lift, when their stall speeds at 30AoA (zero propellant left) should be about 430-450km/h, not 270 is it was in 2.5 version. Now they've put their mind together a bit and realized that it should be higher, but still not high enough to be normal/realistic. The stall speed of the AIM-120's in version 2.7+ is still around 350km/h or so. It should be 100km/h more than that. 

Would be great of you cold share how these numbers are calculated.

I am no expert, but how can something produce lift at 30 deg AoA? This is a genuine question and I would love to know more about it.

 

[GGTharos]

Kites do it.

[Cmptohocah]

5 hours ago, GGTharos said:

Kites do it.

Did a quick search about kites. Got this, among other results:

Quote

An aircraft could not maintain such a steep angle but kites can because they are tethered to hold the kite stable against the forces of wind pushing against it and the effects of the turbulence created behind.

 

[85th_Maverick]

6 hours ago, GGTharos said:

Kites do it.

Sorry for the bit off-topic reply, but now, no matter how much I believe to know about aerodynamics, there's always room for rather curious new stuff that tends to contradict my view about airflow in general and if true about what it's claimed, I'm only looking forward to comprehend and eventually accept it! As far as I see it, the kite is nothing more than a wing that has an almost elliptical plane projection (seen from the top), has a distribution of cambered airfoils from root to tip and their relative numbers affects lift/drag and critical AoA, and being shaped (grossly) as a circle segment from a front projection (otherwise known as a "C" design), it generates similar beneficial and detrimental effects to that of a negative dihedral and downwards winglets wing. Of course, being of almost a constant radius under load, it has better lift/drag performances than a negative dihedral and downwards winglets wing which would generate additional interference drag between the wing and winglet, but the gross effects are similar, and one of them is that it stalls at regularly lower angles of attack (some 13..14 degrees maximum), compared to most planes and that happens due to both the "stretched" (not under load) aspect ratio of the kite as well as it's relatively high camber. So no..., you'll never see a kite go even beyond 17..18 AoA unless you either bleed off some of the pressure differential between the upper and lower sides of the wing or have some sorts of useful vortices generated along the chords. So, correct me if I'm wrong, but I personally consider that the stall AoA for kites is around 13..14, say 15 AoA, but without any afferent enhancements, that can't be any higher!

[85th_Maverick]

2 hours ago, Cmptohocah said:

Did a quick search about kites. Got this, among other results:

 

"An aircraft could not maintain such a steep angle but kites can because they are tethered to hold the kite stable against the forces of wind pushing against it and the effects of the turbulence created behind."

Don't want to sound absurd or anything, but...I personally don't find that explanation as from someone with a correct understanding of it if he mentions the "steep angle" as angle of attack and that it is great due to being tethered. First of all, being tethered is mandatory if you want it stable under the right pressure differential loads and loads variations within a given range (only above a given positive allowed) as it may happen through a turbulence that won't bring the AoA close to null lift, cause if it passes through turbulence that even for a 0.5 seconds (the material of the kite has very little inertia in order to maintain it's shape for long) the kite would wrap on itself and eventually won't come back to the correct shape under load again, which is hazardous. The angle of attack critical value has nothing whatsoever to do with how the straps and controls and anything else is being tethered on the actual wing, cause that's what it is in the end, a flying wing. The crit./stall AoA has to do only with how the kite (this wing) meets the airflow (be it streamlined, with vortices and their distribution or turbulence) and how that airflow reacts with it according to it's geometries (aspect ratio, sweep, airfoil shapes, taper ratio, flow augmentation devices, etc.). From my opinion, a kite won't go more than 13..15 AoA without stalling and tumbling. I may be wrong if I don't know about some effect that is far from my knowledge, but of what I know, neither kites, neither ship sails can't pass beyond 11..14 degrees (the lower the relative sweep angle and the higher both the aspect ratio and airfoil cambers, the lower the stall AoA, as a global law).

 

The AIM-120 has a very very low aspect ratio for it's fins (around 2 or below, mostly for the C model) and as I've discussed about it before (when I tried in different ways to explain that it has way too much lift in DCS for the correct critical AoA), the nose cone generates a system of vortices that grows in intensity with AoA, thus still maintaining what we call "an attached airflow" almost along it's entire length, increasing the critical AoA on the fins by quite a lot of degrees. The fins alone, at least for the B model (look like MIG-21 wings to me) will stall at around 21..22 deg. AoA, but the vortexes delay the separations of airflow between the high and low pressure areas on the fins up to about 27...28 AoA. The C model, due to having an even lower aspect ratio than the B, will further increase this crit AoA advantage by at least a 1 or 2 degrees.

[GGTharos]

10 hours ago, Cmptohocah said:

Did a quick search about kites. Got this, among other results:

 

 

 

Aircraft should not maintain but many are quite capable.  It's at the limits of controllability and beyond that for some.   For missiles, I don't know.  They have tiny wings but they're also small and light and they tend to implement some interesting aerodynamic designs in some cases (R-73 and Python comes to mind).   The R-77 is quoted as being able to achieve an AoA of 150 but I have some doubts.  Sometimes strakes that don't seem like they'd be very useful can provide airflow control or just lift that could help a lot.

 

There are some rule of thumb for allowable AoA when designing missiles but I don't have them handy.   Older missiles are fairly limited to something around 20 degrees or so.  Tail controlled missiles allow for more, though again going off of memory.

Edited June 5, 2021 by GGTharos

[BIGNEWY]

if you want to report a bug add a short track replay showing the problem, replying to old threads isnt going to help. 

 

thanks

[85th_Maverick]

On 6/5/2021 at 9:34 PM, GGTharos said:

Sometimes strakes that don't seem like they'd be very useful can provide airflow control or just lift that could help a lot.

 

There are some rule of thumb for allowable AoA when designing missiles but I don't have them handy.   Older missiles are fairly limited to something around 20 degrees or so.  Tail controlled missiles allow for more, though again going off of memory.

 

Yes man, the strakes will not only sometimes, but always (but only in varying amounts depending on geometry and positioning) increase the boundary layer's kinetic energy through the induced vortex/vortices over a portion of the surfaces down the flow. Thus, the lift slope, not only that it continues to extend versus AoA, but if the vortex's energy increases with AoA, the slope also becomes exponential by some power. The aerodynamics is a domain for which I'm happy to live, it's wonderful! It would be interesting (for me, at least) to know why would the tail controlled missiles be able to increase the airflow separation AoA.

Edited June 7, 2021 by 85th_Maverick

[Hobel]

On 5/29/2020 at 7:35 AM, Breakshot said:

Lol, 120 has best resistance to chaff in DCS. Its broken in many other ways but not this.

 

Better to be asking questions of ED how 120C can climb and track at 300km/h (well beyond its stall speed).

 

 

 

Отправлено с моего STV100-2 через Tapatalk

It depends, the f14 can work wonders with its chaff.

 

3 Aim12C 

 

[Csgo GE oh yeah]

Just Meme-14 things. 
Was the ECM blinking thing ever sorted ? Probably not. 

Just meme-14 things. 

Edited October 21, 2021 by Csgo GE oh yeah

[Cmptohocah]

On 10/17/2021 at 3:01 PM, Hobel said:

It depends, the f14 can work wonders with its chaff.

 

3 Aim12C 

 

Was this in MP?

[Hobel]

6 hours ago, Cmptohocah said:

Was this in MP?

yes

[Cmptohocah]

4 hours ago, Hobel said:

yes

It could be a case of connection issues or rather syncing issues. Strange things can happen in multiplayer.

Edited October 22, 2021 by Cmptohocah

[Hobel]

8 hours ago, Cmptohocah said:

It could be a case of connection issues or rather syncing issues. Strange things can happen in multiplayer.

 

I will test it again, but it doesn't look like it.

 The rockets track perfectly and then, for whatever reason, just go on the chaff.

 

this happens especially with the F14 + Chaff