Cockpit pressure schedule

[AH_Sid]

I've been running a few test comparing the 'cockpit pressure schedule' against what we have simulated for our F86F-35, it looks like there's a bug here.

 

For reference here's the relevant pages from the F-86F Flight Manual.

 

click for larger versions

 

 

 

 

 

I ran a some of test at Batumi (Altitude 37 Feet, Standard Temperature +15°c, Standard Pressure 29.92), using V1.5.2.48162.126 of DCS.

 

With each test I trimmed the aircraft out to climb at full (100%) power, pressurization set to 'Press', and took a screen shot of the instruments as each 1000' point was passed. I did this first using the using the 2.75 psi schedule, then with the 5.0 psi schedule.

 

 

I then plotted the results using the screen shots on to the Cockpit pressure schedule graph from the manual. With both the 2.75 psi schedule, and the 5.0 psi schedule, they follow the manuals graph fairly well until around 29000 to 30000 feet, then it's as if a seal fails and the cabin will jump massively instantly.

 

 

2.75 psi cockpit pressure schedule

 

 

 

As you can see all starts out well, the cabin climbs to 12,500' and maintains this as per the manual. At 21,000' a/c altitude, the cabin altitude starts to maintain the 2.75 psi pressure differential and slowly climb with aircraft to maintain the differential. It should do this all the way to maximum a/c altitude. As we get higher though and the outside pressure goes down, and the pressure difference between each 1000' of altitude decreases as well, meaning the cabin altitude should slowly curve away from the actual a/c altitude, while maintaining the 2.75 psi pressure differential.

 

But what I'm seeing in game, is the a/c gets to around 29,000' to 30,000' (the exact altitude varies each time I test it, but always around that range), and then something 'pops' and the cabin altitude suddenly jumps to 2,000' below the a/c altitude, then maintains this 2,000' altitude difference until the top of climb.

 

 

 

 

5.0 psi cockpit pressure schedule

 

The results using the 5.0 psi schedule are very similar, the graph from the manual (it's a that very pale line), is followed correctly until around 30,000'. Then incorrectly climbs rapidly to maintain an incorrect 2,000' difference in cabin/aircraft attitude. Again we should get a curved line as 5.0 psi pressure differential is maintained, giving a cabin altitude of around 22,000' at an a/c altitude of 50,000'. Instead we are seeing the cabin altitude reach 48,000' here.

 

 

 

Edited December 20, 2015 by =AH=_Sid

[AH_Sid]

As we get higher though and the outside pressure goes down, and the pressure difference between each 1000' of altitude decreases as well, meaning the cabin altitude should slowly curve away from the actual a/c altitude, while maintaining the 2.75 psi pressure differential.

I found a nice graphic which perhaps sums it better than I managed to in words. :smilewink:

 

[AH_Sid]

Many thanks again, I see the 'cockpit pressure schedule' is now correctly following the pressure schedule from the manual in the latest public build (V2.0.1.49921)

 

Just one small nitpick, if you’re at altitude and you move the 'cockpit pressure schedule switch selector' from 5 to 2.75 psi the cabin alt now jumps instantaneously from 22,000ft ish to 30,000ft ish, the rate of change should be limited a bit more, the same applies if you change to ram. In other words, if you change from a high pressurisation setting to a lower one, the pressure would slowly dissipate (between ¼ and 1 psi a second), not dump instantly.

 

Edited February 8, 2016 by =AH=_Sid