Cabin Pressurization

[arb65912]

Thank you for the response , Intrance but I still have a question.

 

The upper two gauges are cabin pressure gauges and just show cabin rate of climb/descend, cabin altitude and differential pressure with exterior.

 

My question is about the CABIN PRESSURE CONTROL gauge.

With CABIN ALT know we can adjust cabin pressure from 1000 to 10,000 FEET

 

Question 1: On the gauge we can see AIRPLANE ALT. AT MAX DIFF.   What that means and how it relates to what we see on the gauge display?

 

Question 2: I want to fly at 20,000'  what number do I set on CABIN PRESSURE CONTROL gouge using CABIN ALT knob?

 

I have to admit that the whole subject is still confusing to me, sorry.

 

Cheers, AJ 

[Intrance]

Question 1: On the gauge we can see AIRPLANE ALT. AT MAX DIFF.   What that means and how it relates to what we see on the gauge display?

 

Question 2: I want to fly at 20,000'  what number do I set on CABIN PRESSURE CONTROL gouge using CABIN ALT knob?

 

I have to admit that the whole subject is still confusing to me, sorry.

 

Cheers, AJ 

 

That's the point where the addon stops being true to the real deal. The "Airplane alt. at max diff." is meant for the small subdial at the bottom. With the addon, it is non-functional.

 

The normal range for cabin altitude is from sea level or 1000ft above field elevation to about 8000ft at FL250. With 8000ft at FL250, you will be near maximum differential pressure. For FL200, a cabin altitude of 5500ft will give you a differential pressure that's very close to the maximum differential pressure. So take a safety margin and set it to 6000ft or 6500ft. Maybe this will help:

 

[woweezowee]

Thank you Intrance. Your posts clarify a lot.

 

However one question remains: What magic button did I miss to turn on in the Jetstream? I'll give it another try asap.

[arb65912]

Hi Intrance, 

 

I think, I am finally getting the idea, I think....

 

This is how I understand it, please let me know if I am wrong.

 

1.Pressure decreases with altitude and a particular altitude has corresponding pressure as on the chart you attached.

 

2. There is a number not be be exceeded as far as maximum differential pressure which is 5.5 psi.

 

3. Since while climbing , the outside pressure will decrease ,we need to adjust the cabin pressure so the maximum differential pressure stays  in 0.0 - 5.5 psi.

 

Assuming that above statement are correct, I would do following steps to set my cabin altitude:

 

 

 

I will be flying at FL250:

A. I would take the level I will be flying at , for this example 25,000 which would give outside pressure of 5.45 psi.

B. Since the range of the cabin altitude is 1000-8000, if I set cabin pressure to 8000 , corresponding  pressure is 10.91 and resulting differential pressure is 10.91-5.45 = 5.46 psi which is still in the allowed maximum differential pressure range 0.0 - 5.5 psi.

 

Now I want to fly at 15,000'

A. I would take the level I will be flying at , for this example 15,000  which would give outside pressure of 8.29 psi.

B . If I set cabin pressure to 8000 with corresponding pressure of 10.91, resulting differential pressure is 10.91-8.29 = 2.62 psi  which is  in the allowed maximum differential pressure range 0.0 - 5.5 psi.

C. If I set cabin pressure to 2000 ( the minimum pressure to keep the allowed maximum differential pressure range 0.0 - 5.5 psi.) , similar calculations will give me 13.66-8.29 = 5.37 psi.

 

Now question for a $1,000,000....    

 

I know now that for the example with 15,000' I can set my cabin pressure between 2000 -8000.

 

How do I know what number between 2000 and 8000 to pick?

 

It is getting much  more clear now. 

 

Thank you, Intrance, will be waiting for that last answer and leave the subject alone.

 

Cheers, AJ 

[Intrance]

I know now that for the example with 15,000' I can set my cabin pressure between 2000 -8000.

 

How do I know what number between 2000 and 8000 to pick?

 

It is getting much  more clear now. 

 

Well, generally speaking you would go for the lowest option. Not much sense in having a really high cabin altitude if it's not needed. So I would say just go for 2000ft or 2500ft.

[arb65912]

Thank you very much, Intrance, I think I pretty much understand now what is going on.

 

One last question ( I know, it supposed to be the last one in previous reply, sorry   )

 

Picking the lowest option for cabin altitude is dictated by passenger comfort?

The higher the cabin altitude, the lower the pressure so we just do not want the passengers to experience like they were hiking in the mountains, correct?

 

Cheers, AJ 

[Intrance]

Thank you very much, Intrance, I think I pretty much understand now what is going on.

 

One last question ( I know, it supposed to be the last one in previous reply, sorry   )

 

Picking the lowest option for cabin altitude is dictated by passenger comfort?

The higher the cabin altitude, the lower the pressure so we just do not want the passengers to experience like they were hiking in the mountains, correct?

 

Cheers, AJ 

 

Yes, mostly passenger comfort. Even though 8000ft cabin altitude should be no problem for passengers (it's a common cabin altitude for larger airliners for instance), there's no real benefit to setting a higher cabin altitude, at least not that I'm aware of. You might reduce stress on the airframe, but those are rated for a number of pressurisation cycles anyway, whether those are to max differential or not.

 

One thing might be if you want to make your passengers a bit easier to handle...    .

Edited January 30, 2013 by Intrance

[arb65912]

Thank you very much, Intrance.     I think , NOW I am good as far as pressure in JS32. Cheers, AJ 

[woweezowee]

Tried again. Did all steps alongside James Gillies checklister video. "cabin" warning yet again. It does not work.

[cruster]

Weird. I just was flying from Germany to somewhere a couple hours northeast. Set the Cabin Alt to 2000 and climbed to FL150. The differential settled right about 5. Never got a warning.

 

I did have a different problem, though. The plane stopped responding to joystick inputs and I couldn't command the autopilot using the pitch wheel at all (used up all the "up" travel and was still pitched down into a 3k FPM descent). Shortly after that, XSB decided to disconnect me from the network with an "unauthorized client (16)" error. Grrr. I've about had it with X-Plane 10 (and this is 10.11!).

[woweezowee]

Sounds like the Stall avoidance system took over?!

[JimboG]

Tried again. Did all steps alongside James Gillies checklister video. "cabin" warning yet again. It does not work.

Hi,

I don't know the exact procedures behind how best to use the cabin pressurisation system, other than what general rule of thumb I have used before.

So for example, I'll set 2000 during pre-flight procedures to get me underway, and then once airborne as part of the Climb checklist I'll increase the cabin pressure to about 4000 - knowing that I am going to go up to about FL150-160 - this seems to work quite well.

I've done Jersey Gatwick (about 90 miles) at this altitude with no warnings, and then of course brought it back down to 2000 during descent (as part of the Descent checklist!) and this seems to do the trick.

I haven't yet been sucked out through the back door of the plane with my brain coming out my nose after landing so I must be doing something right!

Cheers

James

[JimboG]

I haven't yet been sucked out through the back door of the plane with my brain coming out my nose after landing so I must be doing something right!

Sorry guys, don't flame me. It's only 11:19 here and I've had a LOT of Sunday morning coffee.

[woweezowee]

At this point I'd love to have a tutorial by Javier

[Neurus]

I think I read somewhere in the manual that you're supposed to takeoff and land with the Dump (no pressurization).

[cruster]

I think I read somewhere in the manual that you're supposed to takeoff and land with the Dump (no pressurization).

Really? Unless i forget (which happens more than I would care to admit), I general have it on Pressurization from take off to landing. Maybe something is broken on my system.