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KSATRoadWarrior

Altimeter/Barometric Pressure question

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Is it possible or "normal" for the barometric pressure (thus altimeter) to change (300 to 500 ft) when crossing through a series of mountain ranges?

I was flying across some mountains between OPPG and OP12 in the CS C-130 and experienced that today with "real" weather.

Or could there be a "bug" in the altimeter? After leaving the series of mountains (which did change in elevation) the problem seemed to go away as I was heading to OABT. Any info appreciated, thanks in advance.

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Yes, it is possible. What is possible is for local altimeter setting to change so much that would result in a few hundred ft of error.

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An inch error in the altimeter setting equals 1,000 feet of altitude.

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it's not uncommon to hear different altimeter settings given in a area when with approach. All depends on the local altimeter settings at airports in that area

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How timely or accurately is the "real" weather from parts of the world like Pakistan being updated in the wx program you are using? Therein probably lies the reason for seeing unbelievable changes in wx sometimes in this game.

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Your AGL / MSL works on the atmospheric pressure . There is a pitot tube which inflates the balloon or something.  Remember the Standard Pressure is 29.92 hmmm I think above 1000 or 10000 ft I FORGOT LOL.

 

 Depending on the local weather conditions the pressure changes the altitude changes.

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What do you mean by "real weather"? Which FS are you using? FS 9; FSX?; P3D? Are you using an addon weather program?

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500ft change would be about 33hpa difference. It's not possible to have such a change instantly. It's highly unlikely to have such a change even within few hours. For a reference, today in Europe, there is 44hpa difference, between cyclone and anticyclone, but it's spread over 1500nm with gradual change.

 

It's not normal, and it's probably due wrong wx data imported in FSX

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I've seen barometric pressure bounces with Active Sky 2012.  The bounce lasts for about one second and I expect it is due to AS2012 downloading fresh data or a data interruptions.

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500ft change would be about 33hpa difference.

:ph34r:

I'm not sure how I came up with this number it's about 19hpa difference, not 33. 

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Each hpa is about 29.54545 feet's worth. That is the calculation made in the sim. An instant 300/500ft change is not possible in real life.

Let's take standard pressure of 1013.2mb and an airport elevation say of LIMF which is 989ft. Asume 1013.2 is the QNH. Divide 989 by 29.54545=33.47. Subtract 33.47 from 1013.2 then the QFE at LIMF is 979.73.

So in the above case of a change of 300ft the pressure chage would be about 10mbars. So it's a glitch or bug in the weather generating programme.

 

Just look at this chart and observe the spacing of the isobars. you can see the pressures written on them.

http://www.eurometeo.com/english/display/image_ASXX

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Thank you all for your responses!! I believe what I was seeing was real since it did gradually reduce in the amount of change as I flew away from the mountain ranges. I also believe that my weather data may have been a little scewed as well. I will probably fly the route again in a few days, and control the weather from within FSX to confirm it is not an CS altimete issue. Thanks again, information was very helpful and informative!!

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