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#11
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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#12
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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#13
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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#14
06-09-2012, 10:33 PM
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#16
06-10-2012, 12:55 AM
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While I disagree with the idea of "energy retention" or as some call it "energy bleed", I seem to recall that he had some WWII era tests that used the same profile. Might be good to use that same profile so we can use any existing historical tests to validate. Here is one of the threads on the topic: http://forums.ubi.com/showthread.php...Status-(BETA)?
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#17
06-10-2012, 12:25 PM
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 Jokes aside: You are welocome to PM me though and I could tell you a bit about how I've gone about it.
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#18
06-10-2012, 12:31 PM
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Concerning the validity of the C++ modelling, I just remembered we did a comparison of the C++ compressibility modelling and what was implemented in IL2 at the time (4.09m). As can be seen there is good agreement in the models as long as the speed does not start to reach into the compressibility range. The figure also shows that the lag between the compressibility and non-compressibility models following the pullout. As can be seen, the non-compressibility model means the P-51 will end up higher than it should. I think the effects should be less here in CloD though, since the Me109E and Spitfire Mk1 were not as fast, not as powerful and had a higher Cdo/weight factor so it took them longer to reach compressibility speeds.
I do not master devicelink so Wurkeri helped me with the IL2 data which he sent me in Excel format so I could get that into the graph. One graph shows the raw data (red) and the other (black) where I translated the data so as to be aligned with the C++ data. I think this figure gives a good illustration of the problem: The aircraft should not in a dive speed up to a "point" but rather have the top truncated by compressibility effetcs. Doggles: If you do run a test in CloD and can get the Spitfire or Me109 data into an Excel sheet then that would be good because then I can include that together with the C++ results. However, If it is difficult to get continuous data out of CloD then I think a simple dive test down to 2.5 Km alt and reading off the speed there ( or a number of dives and averaging the result would be even better) could do to begin with to get a ballpark estimate.
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#19
06-10-2012, 04:02 PM
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You will only be trading one set of assumptions for another set of inaccuracies.
Compressibility effects are accounted for by a tabular velocity correction in subsonic incompressible flow theory. The formulation for that correction is an approximation that is considered valid one up to ~Mach 2.3. Who will determine the onset of compressibility and who will determine what theory we use? Each method accounts for the effects in varying amounts because each one gives different levels of agreement within small sections of the flight realm. Think of them like mathmatical microscopes, each is designed to exam with greater agreement a specific area of flight. Now, that being said, there have been some real advances in this area. Our ability to express compressibility has greatly improved and I believe in our childrens lifetime, it will no longer be an issue. Which area's are we going to trade one unrealistic set of assumptions for another unrealistic set of assumptions in order to be more realistics in say.... Mach .95 to Mach 2.2?? Nothing in WWII flew in this realm.... Or Mach .7 to Mach .9?? Nothing in WWII spent any significant time in this realm...... Or subsonic incompressible flow.... Zero airspeed to ~Mach .65 to .7, where ever you put the onset of compressibilty??? Hey, this is the realm WWII airplanes spend almost all of their time flying in!! IMHO, this is an enviromental issue. The subsonic incompressible flow theory used in the game is considered valid and appropriate. The inaccuracies of it's tabular compressibility corrections still return a valid assumption and equally effects all the FM's. The relative performance is in intact and all aircraft gain equally. In short, you will not be making anything more accurate. You will only be trading one set of assumptions for another set of inaccuracies wrapped in a much more complicated package. Last edited by Crumpp; 06-10-2012 at 04:27 PM.
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#20
06-10-2012, 04:23 PM
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BTW, If you can dive from 7Km to 2.5KM at +6.25lbs in the Spitfire Mk I.....
If you mean you dove the aircraft at Emergency power..... There is much bigger fish to fry in this "sim" than how compressibility is handled in transonic flight. Personally I would like to see more realistic operation of the aircraft, a stability and control model, and atmospheric modeling. If they get the atmospheric model down, nobody will be using high rpms and overboosting at high density alitudes. Last edited by Crumpp; 06-10-2012 at 04:30 PM.
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