Flight Testing in CoD

[Viper2000]

Originally Posted by Osprey

I don't know if this ever started or how serious Viper is but I am willing to help with the testing but ONLY if there is some assurance from the development team that it is being taken seriously.

From what I am seeing wider Europe is undertaking a Public Beta test which is adhoc and incredibly disorganised.

So, if we are given genuine co-operation from Luthier & friends, and that we supply genuine reliable information to them to use, then I'm signed up.

I haven't started any work on this yet because, as you point out, we're effectively in a public beta at the moment, and with major code changes taking place so regularly the chances are that a lot of the work we put in would be wasted.

I've also got a PhD to finish.

Originally Posted by heloguy

I would think that the 1976 standard day wouldn't be the best choice as that's not what testing data from the 30's and 40's was based on. Maybe the earlier two would be the best to use.

As far as ambient conditions, either use the gauges in game and hope they are calibrated correctly, or just e-mail the developers to find out what the stock standard atmospheric conditions are.

If there's a way to adjust atmospheric conditions in the FMB (I would look, but will not have my computer with COD for awhile as I'm in the States), then you could create a mission in the FMB that all testers would be compelled to use that are a part of this project.

Really, the best historical data (if it exists) would be that which has variable test data, such as a curve that represents the difference in performance compared to altitude and temperature on the graph axes in order to adjust for density altitude. If this sim has variable weather as it says, then it will be hard to see if the aircraft performs correctly over a range of temps and pressures if it's only tested on a standard day.

Using a 1930s or 1940s atmosphere standard is likely to cause confusion, because all sorts of things were different in those days (eg the definition of the Kelvin).

It's also inherently more likely to produce flame wars because if we pick a NACA atmosphere then people will see American aeroplanes with data which looks like primary source data and potentially German or British aeroplanes with corrected data which disagrees with primary sources. We would then find ourselves having to explain the concept of standard atmospheres and correction factors in the face of vociferous accusations of bias from the large population of trolls that inhabit the forum.

Whatever we do, we're going to end up picking a single standard atmosphere so that we can compare the performance of all the aeroplanes in the sim on the same chart. Apart from anything else, if we don't do this, the chances are the somebody else will do so in a biased way with the intention of forwarding their own agenda, since quite a lot of forum trolls seem more interested in being able to say "my aeroplane is better than yours" than in historical accuracy.

Ideally, I'd use the ISO standard atmosphere, because it's neutral and current. However, I don't think that it's freely available, and that would both interfere with testing and lead to accusations that the process was not transparent.

The 1976 US standard atmosphere is freely available on the internet, and avoids most of the risk of accusations of bias it's post-war*, and it is relatively modern (so we get basically modern SI units, though it uses its own private value of the gas constant, presumably for historical reasons).

*Therefore all of the aeroplanes we test will see correction factors.

[CaptainDoggles]

I've got some of my old university textbooks still, one of them has a standard atmosphere in the appendix; I'll check to see which version it is. The textbook is relatively new so it ought to be a modern ISO atmosphere.

[Skoshi Tiger]

Just done a quick check on the Spitfire II, on the ground at Mansten ( 178 feet) the closest I can get in 1 MB increments is a bout 993mb, at Shoreham (7 feet) on the same map 992 MB.


With the current standard SL pressure at 1013 MB it looks like theres a bit of a Low over the South East of England.

Also, FTIW, from the oil temp it's about 21 Degrees.

Cheers

[CaptainDoggles]

Originally Posted by Viper2000

Ideally, I'd use the ISO standard atmosphere, because it's neutral and current.

Just had a look. The appendix in this particular book gives temperature, pressure, density, and speed of sound in SI units and English units. Data are every 2000m up to 70km for SI, and every 5000 feet up to 175000 feet for English units.

Let me know if that's worth anything to you and I'll see what I can do about scanning it.

[Crumpp]

Using a 1930s or 1940s atmosphere standard is likely to cause confusion, because all sorts of things were different in those days

I remember the same conversation a few years ago.

Good Luck.

[Viper2000]

It's fairly easy to code up the ISO standard atmosphere to 20-30 km in excel. When we get to that stage, we will probably build a test kit of some sort with a various tools for data reduction. Eventually we'll get a load of test data points from different sources and then plot them all onto a single large chart for each set of parameters of interest (e.g. one TAS vs altitude chart, one ROC vs altitude chart etc.).

It would still be useful to have tables from another source for crosschecking, but don't feel under any pressure because:

• There's not much point in testing anything until the sim settles down, which I expect will be a couple of patches after the US release.
  • Obviously until then the sim is in a constant state of flux, so our results would probably be obsolete before we could publish them.
  • The object of the exercise is to make the sim better. That means that it's only worth producing test results if the devs are likely to have time to read them, which they obviously don't at the moment, and won't until the other game engine related bugs are fixed.
  • Additionally, a lot of the effort required comes from the fact that at the moment we don't have a lot of information about the assumptions underlying the model. We also don't have testing tools (like the old devicelink autopilot in IL2). In the longer term, when the devs are under less pressure, they might provide us with some helpful information, and indeed somebody might even come up with a new autopilot.
  • There are therefore very strong arguments for waiting a while before we invest serious effort into this project.
• The way to actually attack the problem will be to code up a model and then interrogate it to derive the correct standard values for our exact test points. We don't want to be interpolating from tables if we can possibly avoid it because this leads to error and argument.

We're still probably going to have issues of course, because you'll generally find that standard atmospheres use geopotential altitude (it makes the maths easier; there's a nice discussion in the document which sets out the 1976 US standard atmosphere), whereas I somehow suspect that this sim might just use geometric altitude.

Indicated altitude will almost certainly come out as geopotential, because it's referenced to ambient pressure (if the model doesn't differentiate between geometric and geopotential altitude then the most likely fudge would be to just use the geometric altitude as input to a standard, geopotential atmosphere model, which is a small source of error), but "wonder woman" altitude will probably be geometric (WW alt was effectively radar alt in IL2, and thus geometric, but indicated altitude was true altitude above MSL because the altimeter pressure setting was fixed at QNH for the map - but this was probably also geometric because IL2's model was quite simple and it doesn't make much difference at low altitude anyway).

Converting between geopotential and geometric altitude isn't a problem, but explaining the differences to certain sections of the community could be a pain (it's only a tiny difference at the sort of altitudes we're going to be working at, but if a job's worth doing then it's worth doing properly... and also, if people see a difference they're likely to make accusations of error and/or bias, because that's how the cookie crumbles - spot the jaded realist...).

[CaptainDoggles]

Originally Posted by Viper2000

[*]We don't want to be interpolating from tables if we can possibly avoid it because this leads to error and argument.[/list]

I agree, which is why I held off posting it.