Capt Stubbing .
In your reply you state that you are seeing the effects start at 300mph but don't state at what altitude. Well that could be the case depending on altitude. Its not an IAS but a Mach number problem. In the chart you post note that at 30,000feet the limit is in fact 290Kias this equating to 0.68Mach. The limit of onset values (at 1G) is solely Dependant on Mach number. This is exactly what is happening in Il2. I have the luxury of real time Mach number display in the tests I perform. So far in what I see the onset of compressibility in the P38 is almost exactly on the documented numbers.
As to why the other aircraft don't have the same issue. Well many of them didn't in real life suffer quite the same problem as the P38. The design of the P38 resulted in a fairly low (by comparison with the other types) Critical Mach number (Mcrit). Further complicating this was the design of its tailplane, a large surface immediately behind and in the combined downwash of the inner wing cockpit cuploa area. So the P38 had an inherently lower Mcrit than the others types. There is for example documented cases of late model Spitfires achieving Mach 0.92.... a speed no P38 would ever approach.
You also state:
"The flaps we have in the game are nothing more than a Speed Brake which slows the plane down and causes some sort of lifting action. "
I disagree, again the documentation on the P38 describes the effects of the Dive flaps resulted in up to a 4G pitch up raising the nose and assisting the pilots recovery. Sure the increase in Drag will assist in deceleration but the prime function of the P38 Dive brakes was to get the nose pitching up. It does exactly that in IL2 as well. (BTW don't forget that dive flaps of almost exactly the same design were fitted to late model P47D's and other types). To test in Il2 get yourself to Vmax at sea level and activate the Dive brakes what happens ? just a decel or decel + pitch up ?
I do agree with you that some types P47,D9 and Tempest do end up at huge Mach numbers (1.15 in my tests) which are unrealistic. Rest assured this is being looked at. The Il2 FM was never really designed to model compressibility to the nth degree. The DT team is aware of this and is discussing this and other things.
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