Baro altitude VS F2 bar altitude

I've been playing with the altimeter's behavior and noticed that the in-cockpit value is different than the one displayed in the F2 view's info bar. There is some kind of ratio between the two, and this ratio is linearly evolving with altitude. Tried with the Mirage 2000 and the F-5E, standard conditions (15°C, no wind, 29.92, above the black sea). At around 25000 ft the ratio is 1, below that altitude the F2 altitude is higher than the cockpit value. Above, reverse the situation.

I'm curious about this. Is it a real altimeter's behavior ? can the F2 altitude value can be considered as true ?

(I think there is a slight instrument reading error about the F-5E :P)

F2 should be direct value from game engine value. the true value.

Under service limitation, the simed instrument/gauge value(speed/atl/aoa etc..) should be slightly different

Did you cal the baro when at ground?

Did they really simulate the sensor and sensor limitation. maybe/ maybe not. at least not under extreme condition( like break service ceiling too much), still remain extreme accuracy, way too accuracy.

F2/F10 GUI is true geometric altitude. The instruments vary based on manufacture (the real one and any differences when simulated). Air data computer like Mirage will likely be the most different since it's not a simple instrument, correcting for Mach, temperature, installation, etc.

There is a genuine error (last I looked) with static weather under otherwise ISA conditions, a double temperature calculation or something. Zero Pascal delta dynamic weather didn't have it.

I think each instrument must be looked at individually. What is the assumed atmosphere that they are designed to? Is it ISA or an earlier 1958 US military model or some other? Are they sampling pressure and making a calculation or are they relying on some default toolkit of dcs.getAltimeter function for example? Is the underlying DCS atmosphere what we expect? How can we check its state variables directly without being doubtful that perhaps it is our particular module which is the source of any differences?

I think for example you find a sea level airport, Batumi I think is 4m or 14m and set pressure delta 0 Pa, 15C and look at pressure altitude. Then you set as low a delta Pascal pressure as you can centered (text edit .miz) exactly over your start with a few pressure centers so it's as static as possible and set the temperature low too all according to an ISA table and see if the altimeter will read the table height given these conditions.

Did you cal the baro when at ground?

Yes

Did they really simulate the sensor and sensor limitation. maybe/ maybe not. at least not under extreme condition( like break service ceiling too much), still remain extreme accuracy, way too accuracy.

What would still be interesting is the investigation of cold weather effect on altimeters within DCS.

https://allaboutairplanes.wordpress.com/2011/08/31/correction-formula-on-altimeters-in-cold-weather/

F2/F10 GUI is true geometric altitude. The instruments vary based on manufacture (the real one and any differences when simulated). Air data computer like Mirage will likely be the most different since it's not a simple instrument, correcting for Mach, temperature, installation, etc.

I've noticed that I've measured the F-5E altitude computed from the CADC, and giving the gauge reading accuracy and difficulty to stabilize the aircraft, I'm quite surprised that the values are very similar to the Mirage 2000's.

After that I tested the classic pneumatic mode, it shifts the altitude values and it's sensitive to Mach number variation as expected.

There is a genuine error (last I looked) with static weather under otherwise ISA conditions, a double temperature calculation or something. Zero Pascal delta dynamic weather didn't have it.

I didn't knew that, so I just made some measurements and I confirm it. The F2/gauge ratio seems to be constant and very close to 1 with the dynamic weather engine, so it looks more reliable to me. I will now ditch the old static weather engine for my studies.

What is the assumed atmosphere that they are designed to? Is it ISA or an earlier 1958 US military model or some other?

Interesting question, I need to perform some calculations based on theory, and my tools use the ISA model only…

Maybe I'll try to find it out later.

My current results:

I've been playing with the altimeter's behavior and noticed that the in-cockpit value is different than the one displayed in the F2 view's info bar. There is some kind of ratio between the two, and this ratio is linearly evolving with altitude. Tried with the Mirage 2000 and the F-5E, standard conditions (15°C, no wind, 29.92, above the black sea). At around 25000 ft the ratio is 1, below that altitude the F2 altitude is higher than the cockpit value. Above, reverse the situation.

 

I'm curious about this. Is it a real altimeter's behavior ? can the F2 altitude value can be considered as true ?

 

 

(I think there is a slight instrument reading error about the F-5E :P)

I'd always noticed the altitude errors as well since way back at A-10 beta. I can't for the life of me find it but someone wrote a similar thread, threw a bunch of math at the problem and determined that there is a slight, consistent error with how DCS itself calculates altitude. I don't know if that ever got fixed but I assume not since I've recently bumped radar altimeters against the baro (adjusting for the differential) and they can never seem to agree, or even disagree consistently. I'll post back if I can ever find that damn original thread.