Cabin Pressurization

A place for technical help setting up your Stratocruiser with FSX
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Cliff Wimberly
Airman
Posts: 42
Joined: 10 Jul 2015, 16:56

Cabin Pressurization

Post by Cliff Wimberly »

How do I keep cabin pressurization under control during descent.
The ECS should be able to keep up pressurization as long as the descent is below 1000 fpm but it does not when I am descending from altitudes above 25000msl . If I start my descent at 25000ft or below there is usually no problem as long as I keep the descent below 1000fpm.
I have tried taking over control of pressurization and increasing rate of change from the default level to about 500fpm. The default pressure goal is ok at 8500ft so I usually leave it alone.

TreeTops
Master Sergeant
Posts: 1086
Joined: 07 Apr 2010, 06:13

Re: Cabin Pressurization

Post by TreeTops »

Maintain cabin airflow above 2" to maintain cabin pressure. Use the turbos.
COTS manual pg 57-59
Cheers
Trev

flapman
Staff Sergeant
Posts: 457
Joined: 10 Oct 2013, 21:35

Re: Cabin Pressurization

Post by flapman »

Yes it's quite entertaining juggling turbosupercharger bleed output vs carburetor temperature vs descent rate vs maximum mach vs maximum airspeed in the descent :D
Woohoo!

Cliff Wimberly
Airman
Posts: 42
Joined: 10 Jul 2015, 16:56

Re: Cabin Pressurization

Post by Cliff Wimberly »

Thanx Tree, that makes sense. What descent rate can you maintain by manually controlling the turbos? I don't believe I have a COTS manual. I will check my COTS folder and see if it might be in there. If so I will shake the dust off and do some reading.

TreeTops
Master Sergeant
Posts: 1086
Joined: 07 Apr 2010, 06:13

Re: Cabin Pressurization

Post by TreeTops »

I normally descend at about 1000 fpm with cabin pressure set at 300 fpm. Every 1000 ft I adjust turbos/throttles for minimum power but maintaining 2" cabin air flow pressure. I tend to bring most of the turbos off first and then follow with reducing throttles. CHT will be affected by the turbo/throttle combination. If CHT is getting low use more turbo and less throttle.
Speed can increase provided weather allows. Turbulent air will dictate a slower airspeed and therefore flatter descent.
Turbos should be at 0 for landing/go around. Turbo switches set to takeoff in the event of a go around.
Cheers
Trev

Cliff Wimberly
Airman
Posts: 42
Joined: 10 Jul 2015, 16:56

Re: Cabin Pressurization

Post by Cliff Wimberly »

Your info is right on. Made a long test flight last night (Barrow-KLAX). So as to duplicate the malfunction I cruised at 30k. On approach Ikept the descent around 1000fpm +/_ 200ft. When cabin pressure started to creep up I increased the Turbo Boost Selector to 65% and that stopped the creeping and good cabin pressure was maintained. When I descended thru 10k I turned the turbos over to Larry the Flt Engineer and landed the plane. It turned out to be a simple fix. I appreciate you pointing me in the right direction.
Fly Safe Fly Well
Cliff

TreeTops
Master Sergeant
Posts: 1086
Joined: 07 Apr 2010, 06:13

Re: Cabin Pressurization

Post by TreeTops »

Good to hear you had success. Now is a good time to go through both manuals and see if you can find things that help clarify your operation of this mighty beast of a plane.
Cheers
Trev

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