Quick Aerostar Question

Tantalum

Tantalum

Final Approach
Joined
Feb 22, 2017
Messages
9,250
Display Name
Display name:
San_Diego_Pilot
So as you know I have a fetish for this aircraft. Was watching this YouTube video and had a question for the crew here, as I believe there are a couple Aerostar pilots

Q: Why do they set the cabin altitude 1,000 ft above cruise altitude and 1,000 ft above the landing field elevation? To quote Spinal Tap, why not just set the knob to account for the 1,000 ft diff needed?

 
Perhaps to avoid an issue with landing with residual cabin pressure? I love those planes, as well. Got to crawl all over one but wasn't available to tag along on a flight.
 
Same reason you set an 150PSI max pressure tank to 140 PSI. There's gonna be some leakdown, and then you aren't running the compressor non stop. Just a guess.

Also I have zero experience in pressurized aircraft.
 
It has nothing to do with the Aerostar specifically, it's done in many pressurized aircraft. And the reasons given above are correct, so that the cabin is completely depressurized on landing.

But if I read the question correctly, I don't think you're asking about that. I "think" you're asking, "why isn't the pressure control system set up so that you just set the field elevation directly, and then it ensures it's completely depressurized 1000 feet above that"? It wouldn't take any great technology, just mark the dial 1000 feet off from where it really is.

And that's a good question I don't have an answer to.
 
Kenny Phillips said:
I love those planes, as well.
Click to expand...
Really bad a$$ and remarkably fast.. I want to say they're the fastest GA piston twin

EdFred said:
There's gonna be some leakdown, and then you aren't running the compressor non stop.
Click to expand...
RussR said:
so that the cabin is completely depressurized on landing
Click to expand...
Thanks, that makes sense, and what I was guessing, but didn't know if it was something other than that.. since the 1K seemed like a specific number and wasn't sure why the valving mechanism wouldn't just automatically account for that.. or if there was some other tribal knowledge reason like "always start with the alternator off" or something

RussR said:
"why isn't the pressure control system set up so that you just set the field elevation directly, and then it ensures it's completely depressurized 1000 feet above that"? It wouldn't take any great technology, just mark the dial 1000 feet off from where it really is.
Click to expand...
YES! thanks.. I wonder how modern systems work

Anyway, thanks guys. Cool!
 
There are a couple active A * pilots on Beechtalk.
 
In a perfect world there’d be one in my hangar... wait... I’m still waiting for a hangar...:confused:
 
I desperately need to find a way to make more money
 
FlySince9 said:
In a perfect world there’d be one in my hangar... wait... I’m still waiting for a hangar...:confused:
Click to expand...

Ditto LOL I was gonna say, what's a hangar....
giphy.gif
 
Tantalum said:
So as you know I have a fetish for this aircraft. Was watching this YouTube video and had a question for the crew here, as I believe there are a couple Aerostar pilots

Q: Why do they set the cabin altitude 1,000 ft above cruise altitude and 1,000 ft above the landing field elevation? To quote Spinal Tap, why not just set the knob to account for the 1,000 ft diff needed?

Click to expand...

Most pressurization systems seem to work very similarly, though I am most current on the King Air 200 system.

Take off is set to cruising altitude plus 500 to 1000'. This allows the controller to positively control the vacuum to the outflow valve throughout the climb and cruise. Also limits the max diff slightly, which ensures that the pressure relief isn't exceeded, which will cause pressure bumps, and can be uncomfortable.

Descent is set to landing field elevation plus 500' to ensure the cabin is fully depressurized prior to landing. Airframes are usually not designed for landing while pressurized. If reset while at cruise, don't delay descent, as the pressure will rise to max diff and the over pressure safety will activate, and cause pressure bumps.

There is also a negative pressure safety incorporated into the valves, so that outside air pressure can never be greater than cabin pressure, such as during an emergency descent.
 
JAWS said:
Most pressurization systems seem to work very similarly, though I am most current on the King Air 200 system.
Click to expand...
Epic response, thank you sir!
 
JAWS said:
There is also a negative pressure safety incorporated into the valves, so that outside air pressure can never be greater than cabin pressure, such as during an emergency descent.
Click to expand...
Is there a risk of malfunction such that the doors become sucked closed due to the pressure differential? How about the other direction?
 
asicer said:
Is there a risk of malfunction such that the doors become sucked closed due to the pressure differential? How about the other direction?
Click to expand...

Doors? No. Outflow Valve? No.

On an aircraft, think beer can. It is designed to withstand higher pressure inside than out. Pop the top to equalize the pressure and then squeeze, bad things happen. The negative relief prevents the bad things from happening. It is something like a fraction of a PSI.
 
Tantalum said:
YES! thanks.. I wonder how modern systems work
Click to expand...

What do you consider a modern system?

My buddy’s Malibu has the pressurization controls integrated into the G1000. You don’t have to set cruising altitude but you still have to manually set the destination airport altitude to insure the cabin depressurizes before landing.
 
mondtster said:
My buddy’s Malibu has the pressurization controls integrated into the G1000. You don’t have to set cruising altitude but you still have to manually set the destination airport altitude to insure the cabin depressurizes before landing.
Click to expand...

Yeah, the latest systems will set the landing altitude as well. Pretty much a completely hands off pressurization system at that point. :)

Still have to set cruise and landing altitudes in my current work bird, though.
 
You should try the 38 pressurization system. I'm pretty sure the Geneva Convention would consider that thing a WOMD. You know it's bad when the student goes idle at the top of the descent and you immediately go:

giphy.gif


:D one engine stays above 70% bud, or you fail for inflight planning. My sinus cavities thank you for your Service.
 
kayoh190 said:
Yeah, the latest systems will set the landing altitude as well. Pretty much a completely hands off pressurization system at that point.
Click to expand...

We were told it was supposed to do that. In practice, it hasn’t ever changed unless we change the elevation manually. Perhaps there is a user selection to do that which we need to set up yet.

The pressurization system in that airplane is indeed pretty much hands off.
 
mondtster said:
My buddy’s Malibu has the pressurization controls integrated into the G1000. You don’t have to set cruising altitude but you still have to manually set the destination airport altitude to insure the cabin depressurizes before landing.
Click to expand...
Hmm, wonder why it doesn't do that for you. Unless you didn't enter an IAP or VNAV profile it should already know that info as well as your intentions.
 
asicer said:
Hmm, wonder why it doesn't do that for you. Unless you didn't enter an IAP or VNAV profile it should already know that info as well as your intentions.
Click to expand...

My best guess is that not entering it automatically allows you the latitude of not setting up a flight plan for a flight. But the times where you wouldn’t set a destination in a plane like this would be pretty rare.
 
I love Aerostars, too. If I was ever fortunate enough to be in the market for a piston twin, they'd be at the top of my list, although to be honest, might get bumped in favor of a plane with more presence in the marketplace, if only for parts and service availability, especially a larger body of mechanics who know how to work on them.

I'm always conscious of parts and service when it comes to things like cars and planes. Too far outside the realm of what I can get serviced easily, and I start to get put off. But assuming I had the money, training, and service wasn't an issue, I'd love to have an Aerostar.
 
Is a Twin Commander and an Aerostar the same thing or derivatives of the same plane?
 
N1120A said:
You could stop throwing money at the Cirrus :p
Click to expand...
Moving out of SoCal would also do it on the net income side of the house. Sunshine gets expensive when every tom dick and harry is trying to do it on the same square mile as you. I couldn't afford my hobby in my hometown. Pains me, but these are the opportunity costs of life.
 
hindsight2020 said:
Moving out of SoCal would also do it on the net income side of the house. Sunshine gets expensive when every tom dick and harry is trying to do it on the same square mile as you. I couldn't afford my hobby in my hometown. Pains me, but these are the opportunity costs of life.
Click to expand...

That depends. Neither Tantalum, nor I, would make the income we do outside where we live.
 
N1120A said:
That depends. Neither Tantalum, nor I, would make the income we do outside where we live.
Click to expand...

I understand that. But if you can't do the things you want, the above is a moot point. I'm being rhetorical, I'm not personally questioning your motivations.
 
hindsight2020 said:
Moving out of SoCal would also do it on the net income side of the house. Sunshine gets expensive when every tom dick and harry is trying to do it on the same square mile as you. I couldn't afford my hobby in my hometown. Pains me, but these are the opportunity costs of life.
Click to expand...
You're doing it wrong. As the price of your house goes up, you take equity out at 4% and put it in the stock market where it earns 10-20%. SoCal house gives you $100k/year in equity the past couple years. How much would that be elsewhere? :)
 
The "elevator" feeling you get when rotating on takeoff in an Aerostar is unique. Pretty tight cockpit, though...
 
You must log in or register to reply here.
Back
Top