Spitfire Mk IIa performance tests - Patch 1.07.18301

[klem]

Originally Posted by bongodriver

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.

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.

[bongodriver]

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

[klem]

Originally Posted by bongodriver

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'.

[bongodriver]

Originally Posted by klem

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.

[Crumpp]

"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.

Yes it will be a great help in any future testing. It is silly to even discuss airplane performance without knowing the atmospheric conditions.

You can tell if the game is modeling denisty altitude by looking at the FTH. If the FTH matches standard day conditions, the atmospheric model is not correct.

[Crumpp]

http://books.google.com/books?id=m5V...arging&f=false

[Peril]

Originally Posted by Crumpp

Yes it will be a great help in any future testing. It is silly to even discuss airplane performance without knowing the atmospheric conditions.

You can tell if the game is modeling denisty altitude by looking at the FTH. If the FTH matches standard day conditions, the atmospheric model is not correct.

Hi crumpp.

If the terrain is to scale in ClOD, you could try 'time vs distance' over varying alts to confirm atmospheric change effects on TAS.

[Crumpp]

Hi crumpp.

If the terrain is to scale in ClOD, you could try 'time vs distance' over varying alts to confirm atmospheric change effects on TAS.

Hi Peril,

Good to see you. Hope they get the P-40 in the game soon, LOL.

That is a really good idea. You could even do T vs D in cardinal directions to check wind modeling, confirm the PEC, and TAS.