stefasaki

I understand that this airport is very far from important areas and it's not even easily shown in the F10 map, however there's some beautiful terrain around and I love to fly there. Well, since the last update, there's trees in the middle of the runway and what used to be a river just before the runway is now a river colored hill. Aerodromo O'Higgins has a similar issue, albeit less serious: some trees are very close to the runway and I am pretty sure that's not the case in real life. I don't think these issues have already been reported but I do apologize in case they have. Keep improving the map and happy new year! below two screenshots for reference

It’s most likely at ISA +5 which is the standard dcs day. However temperature does not have an effect on the eagle in the game and its performance is mostly consistent with a -10 day on the charts. This also explains the mach 2.606 max speed that we have on a clean eagle in the game. The eagle’s flight envelope is accurate enough I think, there are much bigger differences for other airframes. It would just need a dependency on temperature (which has a huge influence)

Please turn down the passive aggressiveness, I was not attacking you in any way. I just gave an example about fatigue in aluminum, the main material for fighter jets. I just stated the fact that if something breaks at X force after about 10^5 cycles then it should break at 2X at the first cycle (18 is the double of 9 and forces on the airframe scale linearly with g's if the weight and configuration is the same). @Spurts Yes I was implying 10 cycles per hour, seemed reasonable for a fighter jet... I guess it depends on what we agree a cycle is. My comment was merely there to put numbers about fatigue stresses, it is not directly related to any aircraft but it applies well to a wing spar for instance. If we were to consider 10^4 cycles then the ultimate strength should be about 30% lower than the original.

The fatigue limit is always lower than the static limit. For aluminum it is halved after around 10^5 cycles, which is typical for an airframe life. This means that if an aircraft breaks up at 9 g's after 10^5 cycles then it is should be able to withstand 18 g's when it's new. This is an over-simplification of the problem but it should give you an insight.

We were comparing missiles with similar aerodynamic configurations, for which wing loading becomes the main difference. Comparing the standard case and the "variant" is pointless since their nose cone is very much different and as such this assumption cannot be made. also the "variant" is lighter and the geometrical wing loading (considering the body) is not that different

Any end of the year news about this? Things got horribly quiet lately and I am definitely looking forward to fly this mod...

There’s another thing though which could limit the AMRAAM performance compared to the AIM-9 aside from the higher wing loading (I’ll try to do rough calculations to get some numbers about this as soon as I can): that is trim control. On the AIM-9 both surfaces are producing positive lift when in a turn, due to the CG being in the middle, while on an AMRAAM the rear wings most likely just provide trim control (likely a downforce as the CG is forward of the main wing but could also be a small positive lift if the nose cone develops a strong enough force). This further decreases the effective lifting surface of the missile. It’s true that the max AOA of the AMRAAM is likely much higher than that of an AIM-9 but in my opinion it should not be enough to compensate for the difference in effective wing loading between the two missiles (at very high AOA the lift coefficient curve is almost flat for low aspect ratio lifting bodies). I stand by my opinion that the max lift coefficient seems overestimated in the game by at least 15% (up to 50% for worst case scenario). Of course we should have a real manual with experimental data to confirm this, as at the moment CFD’s for highly separated flows are definitely not reliable, even with industrial level resources (read this as “do not try to do this CFD at home”) @nighthawk2174 Just checked the geometrical wing loading (considering the area of the whole planform) : the aim-9 "variant" has a 26% lower wing loading compared to the aim-120C. If you account for the fact that the rear surfaces likely just provide trim on the AMRAAM, the difference in effective wing loading reaches at least 40%. This also means that for a specified lift coefficient and velocity the resulting g loading of the AIM-120C should be at least 40% less than that of the aim-9 "variant". Even agreeing that the AIM-120 is certainly capable of a higher max lift coefficient, this difference cannot be in the order of 40%.

Ok, first thing first: a missile doesn't reach 40 g's at 1100 kph as you stated before, that wasn't logical at all. The true value at 1100 kph and 10 kft according to your graph is between 10 and 12 G's which is definitely a more reasonable number. Then there's the original case: mach 1.3 at 3000 ft. Let's do a simple correction about the air density and your graph should still be useful. Rho at 3000 ft is 1.11 kg/m3 while at 10000 it becomes 0.9; therefore we can assume that your graph times ~1.23 should yield a somewhat correct value. The "variant" stands at roughly 25 (the line is closer to 30 but the graph is logarithmic) which is therefore corrected to 31. Now, since this value is around 15% less than what happens in the game, we can say that the model is in fact overestimating a bit. Then there's the fact that your graph is not about an AMRAAM but refers to an unspecified AIM-9. To believe that this graph is somehow valid for both, we'd need at least their wing loadings, which for most Sidewinder variants it should be lower than that of an AMRAAM. This in turn would mean that the expected max G at a specified Mach of an AMRAAM should also be lower than that of such AIM-9, i.e. less than 31 g's at mach 1.3 and much less than what happens in the game. Let me know if you have an actual wing loading number, we can only keep speculating otherwise. If that graph happened to be for an AIM-9M (surely not an -X) we can expect a wing loading which is about 30% lower than that of an AMRAAM, a value which would linearly correct the max G to 22 G's for my original test case. This is the value I'd actually expect from an aim-120c at 3000 ft and mach 1.3.

@nighthawk2174 Interesting, would you care to show such g loading charts? My guess is that for those charts they were accounting for motor thrust which would significantly increase the turning capability of such missiles, while my reasoning accounts just for the aerodynamic platform. A missile has a thrust to weight ratio that is so high that its thrust makes up for most of the centripetal force needed in a turn at low speed (at 30 deg of AOA half of the thrust is actually making you turn). That means that you just need 1100 kph in order for the fins to provide trim, but the actual turn is done by the rocket motor. 40 G’s at 1100 kph sound otherwise not believable, at least not without a thorough explanation.

Hi everyone! Even though this has been an issue for quite some time (since the last flight model update of the AMRAAM) I have now decided to ask about some clarifications over the behaviour of the AIM-120. My concerns are mainly about the maximum lift coefficient of the missile. At the moment the AIM-120 is capable of pulling 35.1 G's at 1558 km/h TAS (as the picture below shows), which is a value that makes me raise my eyebrows a little bit. In fact, this value would imply (considering an empty weight of the missile of 75 kg) that the value of S*Cl is 0.25. This also means that the lowest speed at which the missile can sustain flight would be lower than 69 m/s (249 km/h or 155 mph). And I say lower than because the maximum lift coefficient at the fast edge of the transonic regime is quite substantially lower than the incompressible value. Now, I appreciate the hard work that you put in to come close to a high fidelity missile, but there has to be some kind of error in your CFD. The error may be subtle but is certainly a possibility, especially since CFD is not an exact tool and requires careful analysis to be trusted (I know this for a fact, having worked on CFD's myself). Instead of being just pedantic, I'd like to ask you to give me, or the community in general, the opportunity to look into the details of your calculations, as there may be someone capable of quickly identifying the culprit (I'd be looking at the mesh, most problems are there) and hopefully leading to a more trustworthy model. Pulling 35 g's while still in the transonic regime is a bit silly as a number, I am sure that if there are any aeronautical engineers in your team they would agree with this straight away. After all, if this were possible, the next supersonic transport would look exactly like an AIM-120.....

I don’t think that the current discrepancy is enough to start a rework... afterall it is within 5% in most circumstances. Also experience tells us that not much has been done even in cases of obvious and ridiculous differences in acceleration for FC3 aircraft (su-27.....there’s already a thread on this) so I am afraid that nothing will come out of this... the only difference here is that the performance charts are public domain and it’s easy to point out various errors, as opposed to the flanker. Actually I appreciate the level of detail in the fulcrum’s flight model, it’s one of the most detailed (and accurate) ones and actually depends on temperature, which has a huge impact on acceleration and top speed (at the moment a lot of modules, like the f-15 for example, are not influenced at all by this).

Yeah I have just now read that it is already being discussed elsewhere, but I don't think it will hurt if this gets its own separate thread. It's an important issue afterall...

Yesterday I took the Eagle for a ride and I noticed that with a full load of missiles the aircraft was accelerating way more than before. So I did a top speed test with a full payload and I reached Mach 2.606, which is exactly the value that you can reach without any stores. This is obviously a bug that should be corrected I think... I don't want to get used to a spacecraft, it'll be hard to go back afterwards In the picture you can see that you can factually reach mach 2.606 in level flight with 6 AMRAAM's on board, firing all the missiles will not decrease the aircraft's drag as it will not accelerate further.

Hi there! just tried this mod out, it's a great addition I have to say! I have a few concerns about its new missiles though, each and everyone of them has some kind of issues. I used this mod mainly as an adversary and these are the problems I found about its missiles : The MICA IR is hardly a threat since a single maneuver will make it stop. Its drag while maneuvering is considerably overestimated. The MICA NG and the METEOR have similar problems: their speed is too high (both reach Mach 16... haven't you noticed that?!?) and this also means that they won't hit anything if they loft because the missile goes pitbull just a couple of seconds before intercept and it does not have the time to maneuver towards the enemy (the missile will fly over the target at mach ~12 while pulling max G's). If the missile does not loft it becomes unavoidable due to its ludicrous speed. I hope you can sort these things out. Best regards

There’s also another minor nuance that should be easy to correct: at 710 JPT we currently get the 15 seconds warning, which should happen at 780 JPT. According to your manual the time limit at 710 JPT should be 15 minutes

After reading part of the su-27sk manual the deep inverted stall looks realistic, it supposedly is very hard to get out of it. It seems however too easy to enter it. Per the manual you need a negative AOA and an airspeed lower than 310 km/h, which is also what happens in DCS, the problem is that often in the game you can enter the inverted stall while recovering from a cobra-like maneuver, as the game thinks for some reason that your AOA becomes negative, while it should always remain positive. Basically any pitch down with the direct control mode (even from 90+ degrees of AOA) will result in an immediate negative AOA, this is why it’s very easy to enter it in the game if you’re not being careful

The last 1-1.5 seconds you are referring to are needed to align with the runway, the turn is already completed. If anything it looks closer to 13 than 14 seconds. You cannot replicate that time in DCS without over g-ing or disabling the FBW. Yeah, I know about the problems in the transonic region, I hope that will get fixed, as it certainly is a bigger problem than the probably slightly underestimated Cl max. edit: actually the Cl max may be correct, it's just that the FBW in the sim fails to keep max AOA as the speed drops below cornering speed and therefore the Cl decreases. if the aircraft were capable of keeping max AOA for the entire circle then we might see a 13 sec full turn even in DCS

Hi! I just wanted to point out that the all time best 360 turn done by a fighter jet at an airshow goes to the su-27 (-PD variant flown by Kvochur) which routinely did it in 13 seconds. That was the last maneuver of Kvochur's demos in the Nineties, the aircraft was very light at the time of that manuever (17500 kg or so) and it wasn't by any means a sustained turn. Still, no other aircraft comes even close to that. In terms of DCS performance the Su-27 can't do better than 14 seconds without disabling the FBW, so there is some room for improvements there, while the MiG-29 is quite accurate, as a 16 seconds full circle (the best done by a Fulcrum at airshows) can be easily replicated. I find the mig-29's flight model to be quite realistic and well done actually. Here's a video of the 13 seconds turn (4:25 -> 4:38) :

@nighthawk2174 I think the point they were trying to make about the f-15 was the fact that accurate drag indexes aren't taken into account, nothing to do with the acceleration of a clean F-15C, for which all kinds of charts are available and we are mostly sure that, at least for a standard day, the in-game performance is correct. There are minor errors anyway, but nothing big enough to be game changing like for the flanker. An example is that the F-15C in DCS reaches a maximum Mach number of 2.606 regardless of temperature, and that's not correct, only at very low temperatures it should be possible to reach that speed. On the other side I have a feeling that the Eagle doesn't perform as it should at very low temperatures in DCS, as its acceleration and climbing ability aren't influenced much. But this again is very marginal and the game is accurate enough for the eagle really. The correct drag indexes for the various pylons would be a nice addition though (if they are really wrong in the game). The problem we are discussing here concerns the acceleration of the su-27, for which no official charts are available. The effect of temperature on acceleration is significant, but it usually is in the order of 15-30 % for every 20 °C of difference (when not close to the maximum speed in that particular condition). The discrepancy we have here at mach 1.1-1.3 is in the order of 150%. An error is clearly present. The video is just there to prove that something is wrong indeed, it's not meant to provide data to be used in modeling.

That's understandable. Is there any high altitude acceleration number that we might crosscheck with DCS?

I did that test with a clean aircraft, meaning that a slighly better result was expected. What we really would need is an official acceleration chart...

@BBCRF I just checked the 1100-1300 (true airspeed, km/h) acceleration at 2000 m of altitude and the su-27 in DCS needs about 12 seconds with a total weight of 20000 kg. However, the su-30mk2 in the video needs about 9~10 seconds to do the same (940 to 1110 indicated airspeed, assuming standard day) at over 3000 m of altitude. Are you sure that your value was for true airspeed and not for indicated airspeed? Anyway, a 20% improvement in acceleration is typical for low temperatures, that could explain the discrepancy between the video and your data, what isn't explained is the enormous difference in the 1100-1300 range (indicated airspeed), suggesting that the biggest modeling error is in the drag coefficient at Mach 1.1-1.3

The aircraft in the video is pointing down slightly in the first part, but it points upwards in the 1100-1300 range, and that's where we have the biggest difference. It never actually goes to 2900m, what you see there is a typical dip in the altimeter reading across Mach 1, it's a known thing. You should just check the vertical speed indicator. Of course that video cannot be taken as reference for further modeling, it is merely there to show that the current su-27 in DCS is, in fact, wrong. Also I don't get your statement about the 430 km/h thing.... I just chose to measure the 600-1100 and 1100-1300 segments.... it's just a choice, we are also sure that the engines are fully spooled up at 600 km/h in this case

I ran a first acceleration test with the su-27 in DCS just to give some numbers on the current situation. This test was run in standard DCS conditions (surely this is a higher temperature than the one in the video, but the purpose of this test was to show the order of magnitude of the discrepancy we currently have) with a lightly fueled Su-27 (which would obviously be lighter than the su-30mk2 in the video). The altitude was 3200 m and all the speeds are indicated airspeeds in km/h, times are in seconds: 600-1100 1100-1300 Su-30mk2 (IRL) 21~22 18~19 Su-27 (DCS) 32 70 The results show clearly that this difference in acceleration cannot be attributed to differences in ambient conditions/airframe but that a modeling error is evidently present. The current difference in acceleration that we have between real life and DCS in the 1100-1300 km/h range is comparable to difference that lies between a Formula 1 car and a sedan car (in the 0-100). That's why I think that a rework would be nice, this is not some minor modeling error.

Subsonic acceleration is mostly correct, I did that test and the result was close to 15 seconds, which should be the correct value. The problem is in the transonic regime.