Do most/all piston pressurized aircraft require power on descent to maintain pressurization?

[FORANE]

I read the lancair 4p requires at least a partial power on descent to maintain pressurization. This will make for a high airspeed in low drag aircraft like a lancair. Do all or most piston pressurized aircraft require power on descent to maintain pressurization?

 

[stratobee]

Yes they normally do. At least that was the case on the Aerostar. Below 20" MP it normally couldn't sustain a cabin at altitude. But during a descent the demand for pressurization goes down about as fast as you're descending, so... And in conjunction with the MP naturally climbing as you descend, so it normally never was a problem.

 

[Doggtyred]

I read the lancair 4p requires at least a partial power on descent to maintain pressurization. This will make for a high airspeed in low drag aircraft like a lancair. Do all or most piston pressurized aircraft require power on descent to maintain pressurization?

So pull an inch or two off. You will descend while maintaining speed. Or pop speed brakes

 

[Theboys]

That's when you make up for the gas used to get to the flight levels.

 

[KFD]

That's when you make up for the gas used to get to the flight levels.

Yep. In a piston powered aircraft in the flight levels you don't have excess power so when you descend that is the only time you can realistically approach Vno. You can descend at Vno or higher if the air is smooth so no need to pull the power back to where the pressurization no longer is maintained.

 

[Ted]

Piston pressurized aircraft require power to maintain pressurization. If you think about it, let's say your cabin pressure is 6,000 ft. That's roughly 24". That means that you need to have 24" ahead of the throttle butterfly (really a bit more than with losses/leakages) in order to maintain 24" in the cabin. If you pull the throttles to idle, you won't have that - usually the throttle butterfly is responsible for a couple inches of loss, so you'd still need to have somewhere in the low to mid 20s manifold pressure minimum to maintain that cabin. If you pulled back below that, you'd lose some (but not all) pressurization.

Turbine powered aircraft (at least the ones I've flown) have enough bleed air even at flight idle to maintain pressurization. So you can pull the power back.

The impacts of this depend on the specific airplane. In the 414, I can maintain cruise power, do a 1,500 FPM descent, and still be around Vno. If I pull a little power out, it's easy to do 2,000-2,500 FPM down. I actually end up spending less time in descent than I did in the 310 since the 310 hit Vno very quickly.

I would ask IV-P pilots how they plan their descents. I would think on that plane you'd want speed brakes and a well planned descent.