[quote="Adam S Frisch"]Now these are Schiff Aero figures, so obviously take them for what they are, but on the Commander 690 the Sundstrand system (original) took 100psi air pressure at 600 degrees F to pressurise the cabin. That was then cooled and reduced to 5-6psi and 80 degrees. You can see the waste. They're robbing the engines of 70 hp when only 17hp are needed.quote]

Adam, FWIW, I've read the brochure and love the concept of removing bleed air from the cabin. However, I don't think those representations are anywhere close to reality. I can barely see the needles move in a stock 331 powered airplane if I shut off the bleed air. Now I might get a head rush, but the plane won't go a significant amount faster nor become more substantially more fuel efficient in my experience. Reliability is a much bigger concern to me. Even with bleed air from the compressor, the 331 is substantially more fuel efficient than any other turbine.

There are 53 PC12's flying right this second according to FA. Someone better write the pilots and tell them it's all over.

No one is saying the pc12 is unsafe. Just that you couldn't certify it (or another SETP) over 250 today without an exception.

No one's saying the type cert for the PC12 is going to be yanked, or even that they'll be operationally restricted to FL250.

The rule change was to the "seeking new certification for flight above FL250" rules and consistent with past practice, the FAA doesn't go back and make every flying machine amend their type certificate and re-certify every time a rule changes...

That's saying "it's unsafe".

This is true. But how much does piping, heat exchange, old and big valves, outflow systems weigh? Probably a lot more than we think. I can get a BLDC motor straight off the RC shelf that will deliver 20hp and weigh 2kg. That's a power to weight ratio of 10 to 1. Add a compressor wheel and a housing and it seems to me you could make an electrical pressurisation pump that weighs 4kg or less than 10lbs in total. Sure you'd need some sort of PWM driver for it and cooling, maybe add another 2lbs? What would the bigger alternators and the cabling weigh? I'm nots sure, but a BLDC motor can also act as generator with rectification. Add another 20lbs? It seems that for around 30-40lbs you could have a system that could provide electric pressurisation (battery is not part of this example).

How much is the weight of the current bleed air systems? Anybody's guess. Maybe an electric system would be heavier, but what price do you put on a system that will never pop your ears, rob less power and not have any aerotoxicity problems and allow you to cruise at reduced power settings?

I'd pay extra for that even if it was 10lbs heavier. Without a doubt.



Problem is you'd be back at a system that's 'oversupplying' pressure and the relying on dump valves to regulate i.e. overflow. That's a waste. It's much more efficient to have fast acting input regulation. And the best way to do that would be electric. Plus, with such a system you still couldn't pull back to idle at altitude and expect to keep the cabin up.

Nobody interpreted it as that.

But to say SETP is now "unsafe" above FL250 but at the same time you have more PC12's flying than any other GA plane on the planet is pretty moronic.

All the more reason PC12's will continue to increase in value I guess. Now they can't have any competition.

25 Kg of air is 736 SCF of air at 14.7 PSI, 1 atm.

I couldn't find a cylinder big enough to hold that.

Closest thing I found was a 510 CF cylinder, operating at 6000 PSI (!), and the cylinder weighed 195 pounds empty, 233 pounds with air. It was 10" diameter and 55" long, which would be non trivial to locate in the airframe.

Feels like a bomb.

How are you going to charge the cylinder? When?

Also, when you let all that air out, the adiabatic cooling could cause some sort of freeze up problem.

Scaled to 25 kG of air, it weighs as much as a PW610F engine.

Just put a second engine on the plane and then you can go to FL410! Why is everyone so frightened of a second engine? It actually costs LESS to operate than ONE!

Mike C.

Nobody called them unsafe either. Only pointed out a recent high profile event that will make regulators unlikely to bend.

You should write a letter to Pilatus and TBM and tell them. You'd be a hero. Oh yeah, don't forget to send a letter to Beechcraft 1985 and tell them too.

Nobody interpreted it as that.

But to say SETP is now "unsafe" above FL250 but at the same time you have more PC12's flying than any other GA plane on the planet is pretty moronic.

All the more reason PC12's will continue to increase in value I guess. Now they can't have any competition.

They're all gonna die!!!

I never even considered losing my engine at FL270 may cause depressurization. It also means I'm gonna descend. Nooooooooooo. I'll have to put my O2 mask on and find a place to land.

Of course, how many times has this happened? I dunno.

Hey, tell me about the Phenom 100 with the pro pilot flying that crashed into that house last month and killed 6 people. I'll bet that accident really changes the rules for twin engine airplanes.

You need most of that for an electric compressor system. Compression generates heat.

The bleed air systems don't weigh much. It is a 1 inch pipe from each engine, through a check valve, into the cabin.

All the outflow and regulators remain on an electric system.

Most of the weight is in whatever you do for cooling the air be it vapor cycle or air cycle machine, and that also remains for an electric compression system.


Uh, no, you are REQUIRED to have a sufficient amount of flow into the cabin so people can BREATHE.

It is not sufficient to just make the cabin have PRESSURE. That would be like putting people in a tank with no air exchange.

So the way systems are designed is that they provide that required IN flow, and then use OUTFLOW valves to keep the pressure up.

So your electric system would have to have the same flow rate or nearly so.

Mike C.