Compressibility modelling

[41Sqn_Banks]

Originally Posted by Crumpp

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.

Your point?

[Crumpp]

Your point?

It is written in english. Is that not your language?

[CaptainDoggles]

Originally Posted by Crumpp

The relative performance is intact and all aircraft gain equally

All aircraft will see a reduction in drag in the transsonic realm, true. But not all aircraft can get to that realm, and so see no benefit.

In 1946 it was possible to fly a handful of planes fast enough to just break Mach 1 or so, if you dove just right. I am sure that a guy working with a group that would restore Fw 190s would agree that D-9s were not capable of supersonic flight.

The simple fact is that all aircraft respond to the atmospheric model the same way, or at least we hope so, but not all aircraft can exploit flaws in said atmosphere.

The faster aircraft, whose performance was severely limited by wave drag, etc. in reality, gain a significant speed advantage over others.

It should be plain to see that the relative performance is not intact in this case.

[Crumpp]

In 1946 it was possible to fly a handful of planes fast enough to just break Mach 1 or so, if you dove just right.

Wow....that is not a good simultaion at all, LOL. I did not play IL2 1946 except on very rare occasion with a few of our members.

I do play some of IL2:COD. It is not the same game.

[CaptainDoggles]

Originally Posted by Crumpp

Wow....that is not a good simultaion at all, LOL. I did not play IL2 1946 except on very rare occasion with a few of our members.

I do play some of IL2:COD. It is not the same game.

Given that the original sim was designed only to simulate the Sturmovik, I think it has held up quite well over the years. Looking at the engine in that light, their choice not to include some kind of linearized compressibility correction (Prandtl-Glauert or otherwise) is justified in my opinion.

Designing a game engine is just like engineering anything else. You select the use cases you want to have, and make simplifications without worrying too much about how they affect your outside cases.

[Holtzauge]

Yes, getting at least some modelling of subsonic compressibility based on the Prandtl factor could have been a way to go to get at least something in there even though that would have affect all airplanes the same but if you look at wind tunnel data and results from flight tests then the different aircraft have significantly different drag characteristics in the M=0.5-0.85 range with some like the P-51 and Spitfire being better than others like the late war Me109's which suffered from an earlier onset of drag creep.

This report has some nice info on the P-51 and was one of the sources I used as input to the drag modelling.

http://ntrs.nasa.gov/search.jsp?R=19...20the%2520drag

In the IL2/C++ P-51 20 degree dive comparison the Cdo goes up from the low Mach Cdo of around 0.018 to about 0.034 at M=0.75 which is hardly negligible and explains the truncating effect on speed and why the Mach never goes higher in the C++ simulation. Since this increase in Cdo seems not to have been present in IL2 the speed increases unabated to 960 Km/h which seems a bit on the high side

Pity that this was not included in CloD when a lot of work seems to have been done in other areas such as damage modelling and improved graphics etc. Being familiar with IL2 I was hoping that CloD would also take a significant step towards better FM as well. If I had to choose between better graphics and better flight models then it would have been the latter no contest. On the other hand from a commercial perspective I guess better graphics wins the day over hard core simmers fancies so I can understand the priorities taken from that perspective.

[6S.Tamat]

Originally Posted by Holtzauge

... If I had to choose between better graphics and better flight models then it would have been the latter no contest. On the other hand from a commercial perspective I guess better graphics wins the day over hard core simmers fancies so I can understand the priorities taken from that perspective.

I agree with the fm choice, but the problem is that u need a better physic management in general and then a good environment management (seeing the contacts, the clouds, tree collision etc etc), then the graphic. About the commercial perspective, seeing the results they had until now i would not guess so much .
About the compressibility, despite the interest of the argument, the list of the important stuff to correct or implement is so long that now it is a "not a problem". to give u an example less used of the wrong simulation of the atmosphere, the "amazing" Cem if you check the engineswith the megnetos, does not change the rpm, and for me this is a bigger feeling killer (an trust killer, as they pushed alot on the new total sim engine management).

[robtek]

Originally Posted by 6S.Tamat

......., the "amazing" Cem if you check the engineswith the megnetos, does not change the rpm, and for me this is a bigger feeling killer (an trust killer, as they pushed alot on the new total sim engine management).

I am strongly disagreeing with you, last time i checked the magnetos on a Bf110 the engine lost waaay too much rpm's when switching one off, - 500 instead of - 35 rpm's!!!

[6S.Tamat]

Originally Posted by robtek

I am strongly disagreeing with you, last time i checked the magnetos on a Bf110 the engine lost waaay too much rpm's when switching one off, - 500 instead of - 35 rpm's!!!

well if they fixed in all the airplanes (i tried on the bf109 and wasn't working at all), also if really late (it is something that I could not understand how they didn't notice at the start) it is a good news in a drab landscape.

[Crumpp]

About the compressibility, despite the interest of the argument, the list of the important stuff to correct or implement is so long that now it is a "not a problem".

Right and the point I was making.

When it comes time though, the community will have to be very careful in its selection of theory.

The agreement between theory and flight is not always very good. Some are worse than others.