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Cabin Pressure and Temperature Question...

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Hello all...I'm curious if Cabin Altitude Pressure and Cabin Temperature can be realistically simulated, and if so, what .XML math formulas would be required to do this.I would like to include:Cabin Pressure,Cabin Altitude,and Cabin Altitude Rate, + or -Any ideas as to how to program this?Also, I'm unable to find the variable to find Airport Landing Altitude. Is there a way to display the landing altitude of the selected airport in a flight plan?Any help here would be greatly appreciated.Regards,Kevin

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Bump...Again, not looking to create a gauge here... just to simulate numerical readings. Is it possible, given the variables at hand and if so, what example in an .xml equation or formula would be needed to do so?Also, is an Airport altitude reading a possibility?Regards,Kevin

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Hi Kevin,ABout Cabin pressure/temperature: to my knowledge (but of course I can be wrong) this isn't modelled in FS, so I couldn't think of any way to display or derive relevant info.About the Airport Altitude: I don't understand what it exactly is you want. Read the altitude of an airport which is specified in a flightplan ?? (i.o.w. read the flightplan info or FS database in an xml gauge)Cheers< Rob

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I wonder if you can combine this...%GND ALT %((A:GROUND ALTITUDE, feet) )%!d!'...with the latitude/longtitude "stuff"? (*grin*)

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Kevin,I think several of us have a "fake" cab. press. sys. etc.Mathias Lieberecht's planes and an Airbus panel here on Avsim do.I have such a thing in the 767-300.It is just a matter of some combinations between L:Var's and A:Var's like Indicated- and Pressure Altitude, Ambient pressure, Bleed Air pressure etc.These combs can give you values to translate to needles or dig. readouts for cabin alt, cabin diff and cabin rate and the outflow valves etc.Several Modes Auto and Manual are possible.You can build in, simulate some failures with sound alarms and even depressurization with "Blow out"(Crash) or Blackout caused by lack of oxygen. Imagination is the limit....May be you can do something with the GPS Var's for WPT ALT.Also there some mysterious GPS VAR's like:WaypointAirportRunwayElevation WaypointAirportElevation But i never tried to implement them.Have a look at Matthias panels!Jan"Beatus Ille Procul Negotiis"

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Try this thought process:If we know the ambient pressure, and we know the pressure differential of the aircraft pressurisation system, its easy to do the math.Cabin pressure = ambient pressure PLUS the cabin pressurisation differential. For example, a KingAir has a cabin pressurisation differential of about 4.6 psi. In otherwords, it can pump an additional 4.6 psi of pressure into the cabin when compared with ambient pressure.So, at 18000 feet ASL, where ambient pressure is half of that at sea level we have the following:Ambient = 14.7 psi at sea level.Ambient = 18000 feet ASL = 14.7/2 = 7.35 psi.Cabin Pressurisation of 4.6 psiCabin altitude at 18,000 feet in a king air is then 7.35 + 4.6 = 11.95 psi.Obviously the cabin pressure decreases linear to ambient based on the pressure differential the higher we go.Some simple math to convert to other units (mmHg)is all that is requiredHope that mmakes sense?Steve

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Here is a simplified formula for calculating "pressure altitude" for any given altitude up to 65,617' (Above 65,617' the forumula changes again, but for FS I don't think that's really an issue):h = altitude in feetPressSL = 2116.224 (lb/sqft)if h < 26089then delta = pow((1 - 1 / 135442), 5.255876)if h > 36089 & < 65617then delta = 0.22336 * exp((35089 - h / 20806)pressure = (PressSL * delta) / 144This will give you an accurate pressure altitude from which you can easily determine the pressure differential between cabin pressure and ambient pressure altitude.

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Wow...Thanks guys for pointing me in the right direction here!Bill... will try your "easy" formula in the morning. Sounds easy enough for you, but I'm still learning when it comes to more advanced .xml equations. How would I apply this to .xml? The eyes are getting fuzzy right now and sleep is calling. (what's sleep?)Jan... Tried the string example for the airport altitude and it's not working. Even entered a numerical value of "5" befor the "d" to see if that would work... to no avail. It'd be cool to include the airport altitude as it's included in the Secondary Page of the EICAS.Here's a screenshot of the current state of the EICAS... still a couple more pages left to do.Thanks again!

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Kevin,The string works only in the GPS.So i think may be you need to copy a lot of macro's from the GPS gauge to your eicas.Jan"Beatus Ille Procul Negotiis"

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>Bill... will try your "easy" formula in the morning. Sounds>easy enough for you, but I'm still learning when it comes to>more advanced .xml equations. How would I apply this to .xml?> The eyes are getting fuzzy right now and sleep is calling. >(what's sleep?)Honestly, I don't have a clue. I gave up on XML math as being incomprehensible to my 56 year old, fossilized brain. C may be terse, but at least it doesn't suffer from Reverse Polish Notation... :)Here is the complete code segment in C, perhaps someone would be kind enough to translate it to XML for you. Note that even though the cabin is pressurized, there is still a delta factor due to the increased altitude of the aircraft, hence we have to apply the delta correction to the cabin pressure, just as we do the outside ambient pressure altitude. This is designated as "delta_2..."The variables are declared as:ac_alt = 0 ; presssl = 2116.224 ; //pressure at Sea Levelalt_pressure = 0 ; delta_1 = 0 ; delta_2 = 0 ; cab_pressure = 0 ;//ac_alt = ALT_FROM_BAROMETRIC_PRESSUREvar.var_value.n ; if ( ac_alt < 36089 ) { delta_1 = pow ( ( 1 - ac_alt / 135442 ) , 5.255876 ) ; } if ( ac_alt > 36089 ) { delta_1 = .22336 * exp ( ( 36089 - ac_alt ) / 20806 ) ; } alt_pressure = ( presssl * delta_1 ) / 144 ; delta_2 = pow ( ( 1 - cabaltl / 135442 ) , 5.255876 ) ; cab_pressure = ( presssl * delta_2 ) / 144 ; pressure_diff = cab_pressure - alt_pressure ; // end code segmentI hope this is helpful! Perhaps someone will be kind enough to 'translate' this into XML for you... :)

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Jan...Don't have a clue as to what I'm doing wrong with the airport altitude. I imported ALL the GPS macros into the gauge, and I still get a big, fat zero for APT altitude. I have a flight-plan loaded, and yet nothing... I'm about to give up on this one unless someone else might have a bright idea.Also, not being very familiar with more complex .xml string equations, can you make heads or tails with applying Bill's math to an .xml string?Regards,

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Kevin,Go in the GPS to NRST, then APTS, then cursor, then select an airport and press ENT button.Then you get the airport info with ICAO code, name, city, region, position and...ELEVATION!Once you have selected that airport the next code will show you the elevation:%((@c:WaypointAirportElevation, feet))%!d!If you didn't select, this code shows: 0So if you want the landing altitude of the destination in her window, you must first go to the GPS to look wether the destination airport shows up and if so, to select that airport.Still you need an awful lot of GPS macro's!!May be their is an easier way, but i did't tested.Hope it helps,Jan"Beatus Ille Procul Negotiis"

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Hmm, sounds interresting. Maybe some day I'll dig more into this. Thanks."You can build in, simulate some failures with sound alarms and even depressurization with "Blow out"(Crash) or Blackout caused by lack of oxygen. Imagination is the limit...."Can you cause red and black outs with xml events?

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Karl,I "modelled" that in the 767; with A:G forces and a custom L:Oxysys you can trigger an event which calls for a black(+) or red(-) bitmap, full screen, so the rest becomes invisible and also uncontrollable and finally, when you are not able to correct the forces or to descend to an altitude with enough oxygen, you will endup with a crash.Kind off childish, but it works.Jan"Beatus Ille Procul Negotiis"

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