I used 0.55 lbs of air per minute per person as specified in Part 23.831. This actually only applies to flight above FL410, but figure its a reasonable criteria regardless.

If you know of any published leak rates for aircraft, I would love to see it. I've searched and haven't seen any data on that. However my guess is leakage rates are below ventilation requirements and thus doesn't set the pressurization flows.

Why do they bother putting those masks on airliners then?

Right, but those can be waived via "equivalent level of safety" procedure. That's how Cirrus got around spin certification for SR series, for example.

To put that number in context, the FJ33 is rated to extract 50 lbs/min of bleed air.

That's 13 times the flow you used (3.85 lbs/min).

In many twins (mine included), cabin pressure can't quite be maintained on one engine. My engines are rated for 46 lbs/min each, so my leak rates are above what one of my engines put out.

On a "well sealed" cabin, I would expect leak rates around 15 lbs/min are the best that can be achieved. There are just so many little places where leaks can develop such as around control cables and electrical connectors.

As the airplane ages, this will climb without any indication the leak rate has gone up until it hits the limit of what the engine can put out. Then the owner will search for and repair leaks until it again makes full diff, but it may be close to 100% of the air flow is out leaks and not the outflow valve.


I believe the tightest cabins are many times the minimum. For certain, the engine bleed air systems put out MANY times the minimum during normal operation. Since that hurts engine performance, one expects they wouldn't do that unless they needed to.

Mike C.

That's why they have second source of pressurization requirements, to keep from exposing those pax to the full altitude of complete decompression. Pilot masks have to be pressure masks, etc. Having hypoxic or sick passengers is preferrable to having a hypoxic or sick pilot.

I don't think second source of pressurization will help in explosive decompression scenario.

You have to show "equivalent" safety.

How do you do something that is equivalent to a second engine pressure source?

Whatever that is represents weight and complexity that would have been better as a second engine. Now you get propulsion redundancy as well.

Mike C.

That is not classified as a "probable" failure thus no redundancy is required to deal with this scenario.

Mike C.

With these new jet engines with bypass ratios up to 14:1 and things like variable pitch fan blades if these guys keep going these manufacturers will invent the propeller....

https://www.asme.org/engineering-topics ... ng-a-pitch

Andrew

Every other jet, since none of them are singles, lands at an airport following engine failure.

Mike C.

They have accomplished that goal.

The question is if there is truly a real SEJ market at all once the euphoria of the concept meets reality.

Mike C.

You still don't know what reality is for the SF50. None of us do.

I still say...... Cirrus has a lot of smart people working for them. The things you say won't work about the SF50 are the most basic concepts of designing an airplane. Why would they have come this far if things as basic as what you're pointing out were truly realities of SE Jet design? If what you say is true this thing would have never made it through the first meeting on the concept. So how did it get this far?

Do you believe every new product that hits the market is guaranteed success?

That's besides the point and not applicable to this situation.

Everything you guys poo poo the SF50 over is widely known knowledge. It's not some secret. It's extremely basic stuff.

Let's get away from engineering and look at the big picture. Cirrus created the market for plastic parachute-equipped planes from thin air just like apple created the market for ipods. There was no need for those products until they were introduced, but once available they became ubiquitous.

Is there a market for a SE jet that sits in a currently unserved niche? Who knows, why don't we wait and see. The track record of the people making it is pretty good when it comes to creating new market segments.