It won't but it will make it easier when doing the testing.

Are you doing these offline or online?

If online, have someone take up an airplane with an OAT gauge and record the temperature.

If off line, try a plane with an OAT at the same location as you test. Record the temperature at various altitudes. To make sure the temps are consistant, I would re-enter the same location/mission a few times to make sure the sea level OAT remains the same.

One thought, has anyone checked to make sure the weathering slider does not effect performance? Aircraft will lose performance over time as the engine/propeller wears as well as the finish.

klem,
Don't waste your time with a charlatan, generally you are doing just fine with the tests.

There is plenty of good testing manuals available freely in the net, IMHO the best one is the USAF Flight Test Engineering Handbook, available from Scribd:

http://www.scribd.com/doc/19204672/U...ering-Handbook

It's a large file, over 700 pages but worth to read. As example the correct way to test the critical altitude can found from the section 2.5 (p. 382->).

Its no harder. The data is collected and the TAS calculated, all automatically, as described.

I am doing the tests 'online' through my own server in Multiplayer... Server
Its possible that this may produce different results to a separately connected online server, all I can do is, say, fly a few level speed tests under the same settings on ATAG and see what that does.

Temps at Altitudes (same mB setting) are consistent across the various aircraft tests. These represent several exits and entries to the sim.

The Temperature I am using is generated from the game parameter:
/// [Misc.: Ambient Temperature]
/// <para>Indicates air temperature around machine's location, in K.</para>
/// </summary>
Z_AmbientAirTemperature
There is another available which is
/// [Inst: Ambient Temperature]
/// <para>Returns ambient temperature gauge reading.</para>
/// </summary>
I_AmbientTemp
.... but that appears to be the instrument drive value so I use Z_AmbientAirTemperature

According to the manual the Weathering Slider has no effect on performance.

For my full data set see and run my Performance mission linked in my previous post.

The Weathering slider is labelled "Visual weathering" it doesn't affect performance. Historical performance degradation (wear and tear) was a feature that CLOD was going to have but has at present been dropped or not yet implemented.

it's difficult to tell if the game models density altitude well, to be honest we would need the game to give us more control over atmospheric variables, we know they have used a standard adiabatic lapse rate and the atmosphere is more or less ISA + 10, so we know that the density altitude should be approx 1200 feet more than pressure altitude.
so the tests should be done using 1013 on the altimeter to give pressure altitude and then for each altitude band you test at you know that ISA + 10 means your density altitude is 1200 feet more
i.e 2000 foot pressure altitude at ISA + 10 = 3200 density altitude

the density altitude is what the game test data should be being compared against real life data, if things start to match up then we have an indication of wether the FM's and atmosphere modelling is correct.

Klem,

That assumes that everything is correct in the atmosphere model.

You can cross check it by setting pressure altitude on the altimeter. If the values are different, they you know something is up.

Thanks for that info bongodriver, I believe I have made the mistake of plotting my Hurricane results against indicated altitude instead of bringing them to a common playing field of Density Alltitude.

Apologies to you Felipe for diverting your Thread onto "Principles of Performance Measurement" but it may prove useful to you for gathering data for the Spitfire IIa once I have straightened out the script in my Performance.mis.

So, bongodiver, just to be sure I have got this:

1. I believe my TAS calculations (formulas in earlier post) will still be correct as they use indicated altitude and altimeter setting to arrive at Pressure Altitude and then OAT to arrive at Density Altitude?
2. I the take calculated Density Altitudes and plot TAS against those?

If Yes to both that actually makes the performance figures worse because on my Hurricane chart with DA being higher than Indicated Altitude (SL temp was 16.9C) the results get pushed to the right. Again apologies to Felipe but I'm attaching those Hurricane results (Indicated Alt and DA) as an excercise in my understanding of performance measurement.

I will re-run the tests using 1013mB setting and see how that turns out but I think the results should be the same as the DA chart attached. Then I'll correct my Hurricane Thread post.

In a nutshell Klem yes I think you got it.

as long as your calculations arrive at a density altitude, I prefer 'rule of thumb' calculations over the boffins pages of calculations personally, they may be very slightly less accurate but for the effort it takes.........

heres another one that might be usefull......

TAS increases by 2% over IAS per 1000' and this is also affected by density altitude, this has the surprising effect of increasing the TAS when temparatures are high, we normally associate hight temps with a degradation in performance.

eg.

lets say cruising at pressure alt of 10,000' at 300kts with ISA +10

2% 300kts per 1000' = 60 kts so TAS@ 10,000' = 360 kts in standard conditions.

ISA +10 = 1200' higher density altitude so 10,000' pressure alt = 11,200' density altitude which in turn means another 2% TAS increase = 366kts TAS

OK, well the calculations take place in the script so its not a problem but I'll run those "2%" estimates alongside them just for the hell of it. Hopefully find time this coming weekend.

btw I'm assuming those old A&AEE TAS charts used density altitude as well otherwise the whole measurement process is pointless. They do say 'on a standard day'.

The data in flight manuals is almost certainly always going to be based on standard conditions (ISA) it basically sets the benchmark.
when conditions are exactly ISA then assume density and pressure altitude are the same, density altitude increases with deviations from ISA in the positive temparature range and likewise reduces in colder temps.

bottom line is when you test in actual conditions then assume the density altitude and compare against the charted data.