Spit/109 sea level speed comparisons in 1.08 beta patch

[klem]

Originally Posted by MusseMus

Yes it seems the Z value is the only reliable "gaguge" för speed. My point was that it seems like there is quite a big difference between the speed gauge in the spit and 109. Countless posts on this forum complain about the spit is going too slow in level flight and most of them draw this conclution from the speed gauge alone. I'm not saying they are wrong, but reading the speed gauge gives the impression that a 109 is travelling much faster than a spit, even if they are flying side by side.

You may like to know that (deep breath):

Z values for IAS, TAS are given in 'world co-ordinates' units, e.g. 130.5 means 130.5 world co-ordinate units. I did some tests of distances on the CoD map versus Google Earth and to cut a long story short 'world co-ordinates' are effectively in meters, e.g. if you subtract one from another (using pythagoras unless you travelled perfectly east or west) the distance is in metres.

In one set of Spitfire tests I did I registered 249.83mph (402.06kph) on the IAS gauge at 10,000 feet (thats a scripted-out value that is fed to the gauge graphic, the needle can't be read that accurately and the tooltip rounds to whole numbers). Using rough conversion 2% per 000 feet that's 299.79mph TAS or 482.47kph TAS. More accurately using Density altitude that calculates as 290.72mph TAS or 467.87kph TAS.

The Z values were 132.09 IAS and 134.92 TAS. Assuming these to be metres per second (nothing else fits) that's 475.52kph Z_IAS, 485.71kph Z_TAS.

More confusion because I understood the rough conversion to TAS is 2% per thousand feet which should put the Z_TAS at 475.52 * 1.2 = 570.62kph not 485.71. OR... Z_TAS should put Z_IAS at 485.71 / 1.2 = 404.76. If we trust Z_TAS the IAS begins to look right and Z_IAS wrong. If we trust Z_IAS the IAS gauge and Z_TAS are wrong. Conclusion? Who knows but Z_TAS and IAS gauge have more going for it, after all the IAS value has to come from somewhere.

so at 10,000ft
IAS mph....IAS kph.....Z_IAS kph......IAS kph (from Z_TAS) ...Z_TAS(kph).....TAS@D.A.(kph from IAS)
249.83......402.06........475.52.........404.76......................485.71.....................4 67.86 (remember TS@D.A. will be different because its calculated for a standard day)

Now you could argue that according to the Z_IAS value the Spitfire is travelling 18% faster than the IAS gauge says. Alternatively..... Z_TAS converted to IAS says the IAS gauge is near enough correct. If that's right then the small difference between IAS gauge and IAS from Z_TAS could be caused by atmosphere factors (standard day to CoD day).

We have to be sure we're testing these aircraft properly. With respect, "I tested it at 10,000 feet and it isn't as fast as it should be" is very subjective because:
1. It was being tested using the IAS gauge which now falls under suspicion (for ALL aircraft). Or does it?
2. It "isn't the same top speed as the historical" data because it isn't being tested at or converted to a 'standard day' which is how historical data is published. How many of you know that the default SL pressure for CoD on line is 995mb, not 1013.25 as on a standard day? And that doesn't take account of CoD's SL temperature which is never the standard day 15C.
3. We don't really know if/which IAS, Z_data or whatever is truly accurate but I'm more inclined to trust the Z data and particularly Z_TAS.

I have never tested the 109 but I will after the patch although it would be nice to have some other guys help.