I think thats why its important to show the devs what we find. This is a beta test after all and we don't know how far they have gone in testing the FMs or how far they intend to go with FM development and what their target data is.

Felipe, it would be nice if you could include the historical data alongside the test data for an immediate comparison. And the source reference of course to fend off any arguments. What do you set yout altimeter to? I adjust mine for "true height" as pos.z from for Point3d pos = me.Place().Pos(); (converted to feet for the Hurri). Default 1000mb is something like 100 ft out at SL and around 200ft at 20,000 ft, not a lot but...

Sure Klem, ill use the real tests too in comparasion. So the altimeter was setted to 985mb 0ft at manston airfield, then i start to run the tests, so its about -400ft if we do by your technics, no winds and other things, if you are talking about that i do this way :D

thx klem

Hi Felipe,

Manston elevation is around 144 ft and Tangmere ~40 feet. I checked the Altimeter error two ways. I deliberately ditched in the sea and checked the output file for ditched altitude reading I_Altitude (when it hit the water) and also the 'True Height' or PosHeight from this:
Point3d pos = me.Place().Pos();
PosLongitudinal = pos.x;
PosLateral = pos.y;
PosHeight_m = pos.z
PosHeight_ft = PosHeight_m * 3.2808399
That indicated that the altimeter should be set to 992Mb.

Of course for low flying its the Sea level you want which in theory can change with the tides but I don't think that's modelled.

I also use HudLog to display some parameters on screen all the time including Altimeter Altitude and True Height so I can easily set the Altimeter. The frustrating thing is that I just loaded the mission again and found that it has changed to 995mb and I don't know why! Anyway its only something like 100 ft difference so no big deal with the FMs being as far off as they are. Funny thing is that if I ignore that and set it to 992 I seem to be about right over the sea low level.

Why dont you guys set altimeter to 1013? this is what will give you standard pressure altitude which is what most charted data is based on, theres not much need to actualy test at sea level, simply start the testing at 1000ft and the data can be projected for the last 1000ft to sea level.

Manstons surveyed elevation was 150ft during wartime and tides are never factored, an elevation is based on mean sea level i.e. the average of all tide heights.

are you guys using the density altitude conversion for the tests?

?????!!!!???

Don't pull tht hairs too much... You'll need it when getting older !

Because the CoD environment doesn't seem to be set to 1013. In any case the True Airspeeds are calculated in the script using IAS, Altitude and the CoD environment data (apparent pressures and temperatures) including Density Altitude:

//calculate TrueAirspeeds and MACH
//Pressure Altitude P_alt=Ind_Alt+145442.2*(1- (alt_set/1013.25)^0.190261)
Pressure_Alt = I_Altitude+145442.2*(1- Math.Pow((C_AltimeterPinion/1013.25),0.190261));
//Density altitude (D_Alt) = P_Alt +(StdTemp0/.0019812)*(1-(StdTemp0/OAT)^0.2349690) ; = P_Alt +(273.15/.0019812)*(1-(273.15/OAT)^0.2349690)
Density_Alt = Pressure_Alt + 137870.9872804361 * (1 - Math.Pow((273.15 / Z_AmbientAirTemperature),0.2349690));
//TrueAirspeed_mph = CS/(1-6.8755856*10^-6 * ''DA'')^2.12794 (NB assume IAS = CS)
TrueAirspeed_mph = I_VelocityIAS / Math.Pow((1 - 6.8755856 * Math.Pow(10, -6) * Density_Alt), 2.12794);
TrueAirspeed_kph = TrueAirspeed_mph / 0.621371192;
TrueAirspeed_kt = TrueAirspeed_mph / 0.868976242;
//Mach Number (M) = TAS/CS; CS = sound speed= 38.967854*sqrt(T+273.15) where T is the OAT in celsius; TAS is true airspeed in knots.
MACH = TrueAirspeed_kt / (38.967854 * Math.Sqrt(Z_AmbientAirTemperature + 273.15));

There is no CoD C# parameter for Pressure to set the Altimeter by so I have to measure it and/or set it by reference to True Height. I am assuming 'True Height' is from Mean Sea Level. Can't think what else it would be. I set the Altimeter to read as near as possible to True Height when on the runway so I won't hit the sea on low level tests and I'll have near-correct Altitude reading on he Altimeter. Having said that, at a setting of 992mb its about 4 feet out at sea level but its about 2,000 feet out at 20,000 ft. something wrong somewhere. I don't thionk it matters at the moment as he performance is so far off but I'll include some mB vs Altitude error checks after the next patch.

EDIT: Did some tests.
Max Alt setting available is 1045mB. At True Height 20,000 ft, Alt reading ~19,900. Closest I could get.
Alt setting 1045mB at TH 15,000ft, Alt reading ~15,500. Alt setting for correct TH reading 1027mB
Alt setting 1027mB at TH 10,000ft, Alt reading ~10,500. Alt setting for correct TH reading 1007mB
Alt setting 1007mB at TH 5,000ft, Alt reading ~5,800. Alt setting for correct TH reading 998mB

Am I missing something?

At 992mb at 19C, the density altitude at sea level is 1194 feet.

If the atmosphere is correct, then standing at sea level is the same as being at 1200 feet altitude on a standard day to the airplane.

Your altimeter is just a barometer and measures pressure. It will only show some 554 feet!!!

All the altimeter sees is pressure while the aircraft sees density. Test flying is done at pressure altitude and performance calculated according to density altitude.

Set the ALTIMETER to 29.92inHg or 1013Mb. That is your altitude for starting your performance calculations.

Well that would skip the first calculation of Pressure Altitude from indicated altitude and altimeter setting and I might try that but I don't see how that would change the resulting TAS.

I'm not a test pilot, I'm just doing the Maths and it took me a while to get my head around how to do these tests. I did it that way so I could fly at/very near sea level on the altimeter although as bongodriver says I could just project the 0ft value.

I'm not sure what your trying to say other than to collect the readings in a different way that skips one calculation step.

Do you think my results will be incorrect for some reason? See above fornulae drawn from
http://williams.best.vwh.net/avform.htm#Mach
and my Hurricane results
http://forum.1cpublishing.eu/showthread.php?t=33135

Problem?

Hello .. know you are a pilot in real life, as I also am .... I wonder CLOD simulated the density of air?

When we tested only noted the IAS and TAS data calculated by default by this site http://www.csgnetwork.com/tasinfocalc.html

We are open to good tips please!

Thanks