cabin won't pressurize

[KenG 492]

Well part of the problem is the CABIN PRESSURE switch is modeled as only a two way switch where as in the actual airplane it is a three way switch.

 

In Carenado's 1900 you can either DUMP or TEST the cabin, we are missing the important PRESS position.

 

In the DUMP position the system applies vacuum to the outflow valves to force them open and it opens the fresh air door.

 

In the PRESS position the system allows the cabin controller to modulate vacuum to the outflow valves to give you scheduled pressurization.

 

In the TEST position the system removes vacuum (overriding the WOW switch) causing both valves to close completely. The TEST position is suppose to be a momentary position, as soon as you let go of the switch it is spring loaded to the PRESS position. 

 

So flying around with the pressurization in the TEST position you would eventually see the cabin reach it maximum PSID, but the copilot's finger would be tired from holding it in that position.

 

You would almost never see anything above 5.1 PSID as the outflow valves have a positive pressure relief that kicks in at 5.0 +- .01 PSID where static air from outside the cabin will cause a schrader valve to open on top of the outflow valve which will act as a vacuum on the top chamber of the valve which will force it to open due to differential pressure in the two chambers. The valve will then chatter between full open and full closed and the cabin PSID will have a slight twitch. In order to have a cabin PSID above 5.1 PSID both outflow valves would have to be stuck closed. In private airplanes where the owner smokes every now and then you will get a case of sticking valves. It takes allot of cigarette smoke to equal enough tar on the valves for them to stick, this is a very rare event.

 

It also looks like Carenado has the wrong pressurization controller in the airplane. To me it looks like it is from the King Air 300/350 which can reach FL350 with a cabin altitude of around 10,000' at that altitude with a maximum PSID of 6.5 +-0.1.

[mlovetto 6]

Plane still starts at a negative cabin altitude for me... even after SP1

[KenG 492]

Plane still starts at a negative cabin altitude for me... even after SP1

 

Concur pressurization is still broke in the 1900. All they seem to have done was add a white chevron to the knob to show where the controller is pointing. All of the controllers I have used has a small clear piece of plastic in the window with a black lubber line. Regardless the DUMO-PRESS-TEST switch is still a two position switch as opposed to a three position and the controller is still the wrong controller.

[vonmar 122]

As far as I can tell, Carenado, in this simulation, wants you to just rotate the the large dial to the altitude goal you want, for your cruise altitude "cabin altitude".

Then during climb, like after 1000 feet, dial the cabin climb rate you want (small knob) .. like 500 or 1000 ft/min.

 

I will estimate what I actually did on a test flight today ... I will look back at some screenshots a see if I can get exact numbers.

I wanted to cruise at 16000 feet.

I set a cabin goal of 6000 feet.

Cabin climb of 800 ft/min e.g.

And it looked good to me.

The screenshots were taken just as I reached cruise altitude.

Lastly, I dialed a climb rate of 0 ft/min ( I think it was like 5ft/min).

[Joe L 62]

As far as I can tell, Carenado, in this simulation, wants you to just rotate the the large dial to the altitude goal you want, for your cruise altitude "cabin altitude".

Then during climb, like after 1000 feet, dial the cabin climb rate you want (small knob) .. like 500 or 1000 ft/min.

 

I will estimate what I actually did on a test flight today ... I will look back at some screenshots a see if I can get exact numbers.

I wanted to cruise at 16000 feet.

I set a cabin goal of 6000 feet.

Cabin climb of 800 ft/min e.g.

And it looked good to me.

The screenshots were taken just as I reached cruise altitude.

Lastly, I dialed a climb rate of 0 ft/min ( I think it was like 5ft/min).

The issue for me though is where are you getting 6,000'?  Your picture clearly shows the issue - 6,000' is shown to equate to AC altitude of 25,000 (plus 500), not 22,000.  I am also doing a flight at 22,000, and the controller indicates the cabin altitude is about 4,200 - of course resulting in CABIN DIFF warning.

 

At least if there is a chart somewhere the clearly indicates what cabin altitude to set we could ignore the cabin controller ACFT ALT and set the cabin pressure as you are doing.

[vonmar 122]

Joe,

 

Do not look at the aircraft altitudes (like AFCT 25) ... just look at the numbers on the outside (desired cabin alt) and you will be good to go.

 

Here is an ISA Chart for you to look up upper level PSI's

 

 

[JRBarrett 3,050]

Joe,

 

Do not look at the aircraft altitudes (like AFCT 25) ... just look at the numbers on the outside (desired cabin alt) and you will be good to go.

 

Here is an ISA Chart for you to look up upper level PSI's

In practice, it should be just the opposite. Most of the posters here are focusing on the wrong parameter. You set the controller per aircraft altitude, NOT cabin altitude.

 

I don't (yet) own the Carenado 1900, so I can't address if their pressurization emulation is buggy or not, but here is an explanation of how the system should work in actual operation. (I maintain these in my r/w job).

 

In a real aircraft using this kind of controller, the pilot does NOT concern himself with setting a specific cabin altitude. The only setting he needs to adjust is the aircraft's expected cruise altitude + 1000 feet, which is normally set before takeoff.

 

Prior to takeoff, the weight-on-wheels switch causes the controller to apply maximum vacuum to the outflow valves, driving them full open, so the aircraft will not pressurize on the ground. At this point, the differential pressure is zero, and the cabin altitude will be the same as the actual ambient altitude of the aircraft.

 

Once airborne, the outflow valves will slowly modulate to a partially closed position. As the aircraft starts to climb, the controller will hold a constant cabin altitude for the first several thousand feet of climb. So, if you took off from an airport at 1000 feet MSL, the cabin altitude will remain pretty close to 1000 feet for quite some time.

 

With the cabin altitude held constant, the differential pressure will start to increase as the aircraft climbs. To accomplish this, the controller positions the outflow valves more and more closed with increasing altitude.

 

Once the differential pressure is close to the maximum allowed for the specific airframe, then, and ONLY then, will the cabin altitude start to climb, to maintain the cabin differential at a fixed pressure.

 

The "goal" of the pressurization controller (in a manner of speaking), is NOT to maintain a fixed cabin altitude, but to maintain a FIXED DIFFERENTIAL PRESSURE (close to, but not exceeding, the aircraft's rated max diff). The cabin altitude will rise to whatever level it has to, in order to maintain that constant differential.

 

An aircraft like a Gulfstream IV, which is rated for a differential pressure of almost 9 psi, will maintain a cabin altitude of near sea level, until almost 20,000 feet, before the cabin altitude finally begins

to rise. (Reaching an altitude of about 7500 feet at an aircraft altitude of 45,000 feet.)

 

The 1900, with a max diff of only 5 PSI, will obviously start climbing the cabin earlier... more like 10,000 feet aircraft altitude.

 

In descent, the opposite events unfold. Prior to descent, the pilot will dial in pressure altitude of the airport + 500 feet. As descent proceeds, the cabin altitude will descend at the selected rate (500 fpm) with the fixed cabin differential pressure of just under 5 psi. By the time the aircraft reaches about 10,000 feet, the cabin altitude will have descended to the selected airport pressure. From this point forward, as the aircraft continues to descend, the cabin altitude will remain constant, and the differential pressure will begin to decrease, reaching zero diff (or close to it) just before landing.

 

The "cabin altitude" markings on the rotary controller in the 1900 are basically only for reference. They show the relationship between aircraft altitude and the expected cabin altitude at that altitude - but the pilot only is concerned with dialing in the expected cruise altitude. The cabin altitude essentially "takes care of itself".

 

Also, on this type of controller, the pilot would typically NOT adjust the "rate" knob. He would set it for a cabin climb or descent rate of (typically) about 500 fpm (for passenger comfort), and then leave it strictly alone from then on. One thing he would NEVER do is to turn it all the way counter-clockwise to a rate of "zero", as this would essentially disable the controller's ability to modulate the position of the outflow valves.

 

As another user pointed out, the toggle switch next to the dial SHOULD be a three-position switch, with the center position, being the "normal" setting. Moving it to "dump" will drive the outflow valves fully open, and holding it in "test" will drive the valves fully closed. If it doesn't work this way in the Carenado 1900, that would indeed be a bug.

[vonmar 122]

 

 

In practice, it should be just the opposite.

 

We know that.

So, for now, the workaround I mentioned in previous post will get us flying.

[KenG 492]

Basically the things Jim has stated is correct. Again I teach pilots how to fly King Air 200s, 300s, and 1900s for a living and have flown these airplanes.

 

The rate knob does seem way off for the Carenado 1900. I don't have the tool tips on but at about the 9 to 12 O'clock position should be about 500 to 1000 fpm rate of climb/descent. The knob generally only moves about 3/4 of the way around, the Carenado version seems to continue to turn (I don't know how far as I got board watching it spin around.) Finally the rate of climb and descent is only controllable between 200 to 2000 fpm. Believe me this is a maintenance check I have had to perform in flight and no it is not any fun.

 

The other problem with the Carenado 1900 controller is the controller is wrong. The cabin altitude and aircraft altitude should coincide so that at FL250 the aircraft is approaching 5.0 PSID or just about 9,100' cabin altitude.

 

Here is the chart that Beechcraft gives me in the AFM for checking this.

 

  With a Cabin Altitude of 5,500 at FL250 this tells me the PSID is 6.6. This is the controller you would find in a late model B200 or a B300, not a B190. No wonder you are getting over-pressurization warnings. Now I do not know how the actual gauge works as 1s and 0s but this would be the first thing I'd check.

 

 So knowing this I can use my handy chart  and set the Cabin side of the altimeter correctly so I get something slightly less than 5.0 PSID. i.e. At FL250 I would set the cabin to 10,000' and ignore what is on the inside of the scale. For landing I would set the field pressure altitude +500' so that when I cross that datum the cabin will be depressurized.

 

 Actually we do move the rate knob much to maintenance's displeasure. Normally it is set to 500 fpm and we leave it that way. However, if we are getting slam dunked by ATC (say it doesn't happen :huh: ) then if I leave the rate knob alone and I am descending the aircraft between 2,000 to 2,500 fpm then the aircraft will fly through the cabin altitude earlier then I want. In the back you get this nice hissing sound as negative pressure relief is doing its thing. So I increase my cabin rate of descent so as to arrive at my pressure datum and the cabin depressurizes normally. (It's the professional thing to do.)

 

 Yes I have stated it two or three times, the Pressurization Switch is broke. We do not fly around with it in test.

 

Bottom line is this is a bug and Carenado did not fix it in SP1. I have not had time to submit another bug report, but if someone else wants to and reference this posting be my guest. Otherwise I'll get around to it when I have time.

[vonmar 122]

I sent Carenado a ticket before SP1 showing the dialed .. indication was wrong.

 

I also included their Carenado P46T gauge ...indicating ok.

 

 

 

 

 

 

[vonmar 122]

"The rate knob does seem way off for the Carenado 1900. I don't have the tool tips on but at about the 9 to 12 O'clock position should be about 500 to 1000 fpm rate of climb/descent."

 

Well, turn on the tool tips and take a look ..it works ... for setting the climb rate.

 

Also according to your pressurization graph ... the post I did #84 with the screenshots at 16000 feet and information on my settings... are the gauges reading correctyl?

[vonmar 122]

I did a test flight video the other day.

 

Today I re-recorded (edited) the portion checking cabin altitude gauges at cruise altitude (the cabin goal 6K feet was set during initial departure climb out).
Then changing the goal cabin altitude to a new value (7K feet) to further check gauges operation and set cabin climb rate to zero ft/min at the end of the cabin climb.

 

 

[JimG 0]

You guys are on to it now.  I was reading that 21,000 aircraft altitude should be 6,500 cabin altitude.  The controller should read these numbers opposite each other, but they are way off.  Until a fix, I would recommend using Ken's chart above and setting the Cabin Altitude on the controller using the 5 PSI line to 1000' above the altitude you will be flying.

 

Jim

[mike2060 4]

Here is what the real gauge looks like:

[vonmar 122]

Here is what the real gauge looks like:

 

Have you opened a support trouble ticket with Carenado and given them the real world photo of what they should be using.