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#1
06-09-2012, 03:42 PM
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And I don't want an arbitrary game balance: do I have to fly in a crap plane? I do it and I'll try to fly it in the historical way. (for example I16 vs 109). The thing I don't want is implementing something that heavily affects the combat simulation over more important things. Because in real life "Good Tactic" >>>>> "Raw Performance"... Anyway I don't think the elevator authority issue was about TAS or IAS: it was modelled like a loss of control surface effectiveness instead of a simple stick heavyness... in the game it was impossible to operate the stick with the strength of 2 arms like the real pilots did... they roughly modelled a pilot's strength related aspect without taking in account the pilot's stamina/fatigue modelling. I hope it will be possible in CloD's future.
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 A whole generation of pilots learned to treasure the Spitfire for its delightful response to aerobatic manoeuvres and its handiness as a dogfighter. Iit is odd that they had continued to esteem these qualities over those of other fighters in spite of the fact that they were of only secondary importance tactically.Thus it is doubly ironic that the Spitfire’s reputation would habitually be established by reference to archaic, non-tactical criteria. Last edited by 6S.Manu; 06-09-2012 at 03:50 PM. 
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#2
06-09-2012, 08:09 PM
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Holtz. I don't know exactly if your saying Airspeed should be limited by compressibility, or if your saying at which Compressibility actually becomes noticeable to causing a runaway dive / increasing speed / decreasing control.
Or are you meaning loss in engine performance? Cause your right, its going to decrease performance, but in a dive, your still going to increasing speed from the simple physics of gravity, only acceleration would be affected. But it won't act like a "Dive Break," that's how I see you trying to explain it. Quote:
The real key to compressibility stall is the atmospheric conditions via what altitude your at. Higher alt= less dense air. I say this from the fact that most stories I've read about WW2 compressibility stalls, they always start out with the pilots typically above 25,000 ft. They get into a dive, and as they go faster the laminar flow of the high alt / less dense air around the wings and control areas is so reduced to the point that the pilot looses control / has a runaway dive. At which point the only thing they can do is chop power, but your speed is still going to increase because your diving. Your only able to regain control of the aircraft when it decreases down to denser air density returning laminar flow to the aerodynamics of the aircraft. However by this time your either A) Going so fast and theres no return of laminar flow that controlability doesnt return. B) The aircraft begins or already has broken up from structure failure of approaching the speed of sound. There is one story I remember reading about Robin Olds, in a P-38. Started a dive at bomber escort alt (think 30,000 range) Got into a compressibility stall and literally didn't pull out of it till a few 100 ft above the ground. The P-38 is one of the most notorious WW2 aircraft with this aerodynamic design problem. But seeing as most aircraft in CLOD at the moment are not modeled correctly above 18,000, I see it as only being a miniscule problem till this is fixed, then worry about compressibility FM problems.
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#3
06-09-2012, 09:27 PM
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The compressibility issue the simulation shows is limited to the speed aspect and controllability is not modelled. The lower curve takes the compressibility drag rise and propeller efficiency loss due to speed and Mach effects into account while the higher curve assumes constant propeller efficiency and a "flat" Cdo which does not start to rise as the speed goes up. The problem is if compressibility is not modellled then any aircraft in the sim will build up too much speed in a dive meaning it will zoom too high in the pullout. This would work to the advantage of so-called BnZ tactics in the sim since energy retention would be higher than IRL.
Mach effects on compressibility are an interesting but complex subject but the C++ simulation posted does not model any impact on controllability due to Mach effects which is beyond the capabilities of the code which is limited to performance comparisons only. As you point out the P-38 was especially susceptible to this phenomena but the Mach "tuck" effect did affect the other types as well and it was more of a question at which Mach the problems started to appear. However, I think modelling this is even more complex and I think it would be a significant step in the right direction just to get the flight performance aspect of compressibility in to begin with. While it was some time ago I looked into it, I still believe that the Me109 elevator control modelling in IL2 was off because it modelled loss of control authority more due to TAS than IAS: At low alt you were OK at certain IAS but at high alt you lost authority at the same IAS even though the Mach number was quite low. Since I have not flown the Me109 here in CloD I have no idea how this is modelled. Hopefully it has improved. Last edited by Holtzauge; 06-09-2012 at 09:35 PM. Reason: Added Me109 elevator control part
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#5
06-09-2012, 09:31 PM
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This is a good thread.
Manu, I don't believe that holtzauge was implying that using BnZ is unfair; only that aircraft whose performance was limited by compressibility effects would see an unfair advantage, I.e more speed and "e retention" than they would have historically had. This is why some 1946 servers banned the 190D9, because it was possible to fly it and a few other aircraft through the sound barrier, since compressibility was not modeled. Holtzauge, it would also be helpful to be able to see the source code for this c++ solver so we can audit it. Otherwise, and no offense intended, from our perspective we have only the word of an anonymous forum poster that the simulation is accurate. Ihope that makes sense. Last edited by CaptainDoggles; 06-09-2012 at 09:43 PM.
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#6
06-09-2012, 09:38 PM
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We do not even know if compressibility is modelled or not. We do not have real world test figures for correct high speed dive behaviour, and a random poster's colored graphs based on cluster of guesswork figures and labeled '109' or 'Spitifre' hardly make a comparison basis.
It makes an interesting theoretical discussion but the whole thread is absolutely useless for checking the FM's validity. Unless someone would suggest the developer's should rely on hobbysts guesstimations of performance.
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Il-2Bugtracker: Feature #200: Missing 100 octane subtypes of Bf 109E and Bf 110C http://www.il2bugtracker.com/issues/200 Il-2Bugtracker: Bug #415: Spitfire Mk I, Ia, and Mk II: Stability and Control http://www.il2bugtracker.com/issues/415 Kurfürst - Your resource site on Bf 109 performance! http://kurfurst.org 
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#7
06-09-2012, 10:33 PM
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#8
06-09-2012, 10:03 PM
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My dream is to dive with the sun at my six and approaching slowly the enemy: in IL2 you need to go so fast since he can see you in 2 second (if the pilot is smart) and so you have almost no time to attack his plane (if you can spot and track it under your plane, of course). With the implementation of a realistic visibility function (realistic scanning time and reviewed dot system) and the abolition of the damned engine radar then the compressibility issue can be limited, since we won't need to dive at high speed. Because of this I said it's not only a issue of low priority, but it can damage the entire combat simulation.
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A whole generation of pilots learned to treasure the Spitfire for its delightful response to aerobatic manoeuvres and its handiness as a dogfighter. Iit is odd that they had continued to esteem these qualities over those of other fighters in spite of the fact that they were of only secondary importance tactically.Thus it is doubly ironic that the Spitfire’s reputation would habitually be established by reference to archaic, non-tactical criteria. Last edited by 6S.Manu; 06-09-2012 at 10:06 PM.
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#9
06-09-2012, 10:04 PM
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As to posting my C++ source code I will be a bit stingy and keep that to myself. I'm actually working on a book project so I need it for my own selfish purposes. I do understand your scepticism though. I would not buy a pig in a poke either. I guess that means you need to apply a healthy dose of scepticism to my posts  Would be nice if you could post some results though. If you have an idea about an alternative dive scenario, either Me109E or Spit Mk1 just let me know and I could model that as well. What I need is boost, weight, dive angle, initial altitude and TAS speed. Based on this I could generate another chart like the one I posted. Last edited by Holtzauge; 06-09-2012 at 10:24 PM. Reason: Added sim input data
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#10
06-09-2012, 10:27 PM
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Perhaps, once we get a good idea of how the atmosphere and aerodynamics are modeled in the sim, we could run some analyses using a free tool like OpenFOAM which I've used in the past. I may PM you in the future to pick your brain about simulating this stuff, Holtzauge Quote:
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