Spit/109 sea level speed comparisons in 1.08 beta patch

[TomcatViP]

Originally Posted by Holtzauge

There are a number of issues with the outlyer 109E 500 km/h sea level top speed:

First of all the Baubeschribung 500/570 Km/h speed curve does not map any known engine power/alt curve: These either have the characteristic bulge associated with the hydralic clutch or the notch type with two speed superchargers where as the curve showing 500 Km/h at SL and 570 Km/h at altitude in the Baubeschribung has a straight line between these points. So which DB601 in a series Me109E had this power/altitude characteristic? None that I have seen published.In addition the date of the the Baubeschribung is stated as "circa 1939"and reference made to the Yugoslavian manual. So this looks more like some early marketing material supporting Messerschmitts export activities which also predictably for marketing material includes a caveat of plus minus 5% which would then place the more realistic speed performance of around 475 Km/h within the guaranteed range.So to conclude, the data supporting 500 Km/h SL speed either references prototype data or refers to some early marketing material. In addition, it looks like estimate for the "guaranteed" engine data coming close to 500 Km/h for the V15 prototype is for 1,35 not 1,3 ata.

Moving then to some more realistic speed estimates based on what could be expected of a series type aircraft at 1.3 ata: Note that the C++ simulation data for the high and low altitude speed of the +6.25 and +12 boost Spitfire is quite consistent with historic data. Using the same principles for calculating the Me109E low level speed the result also yields around 570 Km/ at altitide but at low level the result is around 475 Km/h not 500 Km/h. These curves were calculated using the actual historic series type engine data and consequently show the effects of the hydraulic clutch, something missing from the 500/570 Km/h chart. I'm sure the usual suspects will question the validity of the C++ simulations but as an answer to that we have the Me109E figures posted by HoHun on the All About Warfare forum (www.allaboutwarfare.com) and as can be seen the calculations agree remarkably well. In addition one can conclude that both calculations agree quite well with the actual measured top speed posted earlier by Al Schlageter.

Finaly, it's interesting to note the type of evidence evaluation practiced by some in this forum: There was a mountain of evidence supporting 100 octane that was dismissed as inconclusive and now we are expected to swallow a molehill of evidence for 500 Km/h sea level top speed when most data, calculated and test measurements point to something around 475 Km/h.

Talk about double standards....

I will be delighted to hve a look at your C++ "simulation". Pls show us the core engine instead of hijacking any scientific credits. Let me guess... inviscid, incompressible and lift line theo with linear curve discretisation? lol

[Holtzauge]

Originally Posted by TomcatViP

I will be delighted to hve a look at your C++ "simulation". Pls show us the core engine instead of hijacking any scientific credits. Let me guess... inviscid, incompressible and lift line theo with linear curve discretisation? lol

Well you guessed wrong! I actually did a post a while back arguing for the introduction of subsonic drag rise which is missing in CloD but modelled in the C++ simulation. Modelled a Spitfire Mk1 and showed that the speed build up in CloD in quicker than it should be because compressibility effects are missing.

Seeing you seem to be such an expert perhaps you would be so kind to point out what is wrong in my Me109E speed/alt chart and how it really should look like?

[TomcatViP]

Originally Posted by Holtzauge

Well you guessed wrong! I actually did a post a while back arguing for the introduction of subsonic drag rise which is missing in CloD but modelled in the C++ simulation. Modelled a Spitfire Mk1 and showed that the speed build up in CloD in quicker than it should be because compressibility effects are missing.

Seeing you seem to be such an expert perhaps you would be so kind to point out what is wrong in my Me109E speed/alt chart and how it really should look like?

The core.. That's not too much to ask.

[Holtzauge]

Originally Posted by TomcatViP

The core.. That's not too much to ask.

Actually it is. I'm going to use the C++ results in a book project so I'm not going to sink my own project by posting my code before that

[TomcatViP]

Originally Posted by Holtzauge

Actually it is. I'm going to use the C++ results in a book project so I'm not going to sink my own project by posting my code before that

Well... and naming the eq. that you use is that so much classified that you can't even do it?

[Holtzauge]

Originally Posted by TomcatViP

Well... and naming the eq. that you use is that so much classified that you can't even do it?

There is no single equation behind it and it's not a FEM program if that is what you mean. The C++ code is an extension of the code I wrote for my masters thesis (In Simula!) which was to access the influence of external stores like missiles etc on the performance of jet fighters. This meant I had to convert it to C++ and add some functions to handle prop performance and ram effect on engine. The prop function is dependant not only on advance ratio and density effects but also includes Mach effects due to prop tip speed. The same goes for the drag which rises steeply at typical dive Mach like 0.7 and upwards. Not much use in simulating dive performance otherwize. This shortcoming not to model compressibility effects is a major flaw in both IL2 and CloD IMHO.