Cabin Pressure Indicator (in fact a delta-pressure indicator) > change of manual suggested

[TOViper]

Hey folks!

According to RC2, the cabin pressure indicator shows "the current cabin pressure".
Actually in DCS, the pointer behaves like a "delta pressure indicator" and shows the pressure difference between cockpit and atmosphere:
.) It shows 0 on ground (no pressure difference) > seems fine
.) From 0 to ~2440m the pointer stays at zero, which means the pressure in the cockpit is the same as outside > seems fine
.) At ~2440m it starts increasing until finally resting at some ~0.22kp/cm² (which is 0.22 bar) , and stays there during the continued climb (e.g. climb to 6000m) > OK, since SFI says above 5000m it should read ~ 0.20 - 024 ... so seems fine
.) When removing the canopy from the aircraft in 6000m, the indicator jumps back to 0 > seems fine

Assuming the indicator is modeled correctly as a "delta pressure indicator" (which the SFI also doesn't mention in the "non-hemlig" sections ), the RC2 manual on page 40 should be changed accordingly saying something like "Indicates the current cabin differential pressure.".
This issue is currently not listed in the AJS-37 Viggen RC2 manual review 2018-01-29.xlsx, which collects all currently known issues of the RC2.

 

[Machalot]

I'm not an expert on this topic, but I haven't heard the term delta pressure in this context before.  I have heard gauge pressure to describe this measurement, rather than absolute pressure. 

[TOViper]

According to information from widen76's SFI, the following text could be used:

"On the cabin manometer, which is connected to the cabin pressure regulator, the pressure difference between the cabin pressure and the pressure of the surrounding atmosphere can be read. At flight altitudes above approx. 5000 m, the pressure difference must be 0.20 — 0.24 kp/cm².
Note: If the cabin pressure is too low, the CABIN HÖJD caution is triggered."

Edited September 29, 2022 by TOViper