Extra 400

Despite I like the packaging, I have a question about that:

- an electric compressor means that we no longer need to carry emergency O2.

All pressurized planes have emergency O2, why removing it? I understand that total electric failure is not prone to happen soon, but in case of it, you would be happy to get you mask on and keep some electrons for usefull purpose : descend through a thick layer with a bit of anti-ice.

but electricity to power compressors must also come from the engine

I thought it came from moving through the earth’s magnetic field

additional steps involving the generators and compressor in the end will use more engine power than bleeding air from the engine.

Maybe, maybe not. Maybe the analysis is out there somewhere.

Rotating electricity generation, in the megawatt area, is very efficient, well up in the 90s %. Bleed air manipulation, OTOH, is a mess. You have hot air pipes running around, funny valves turning the stuff on and off, it’s got to be insulated but you still get a lot of loss over distance, whereas electricity is just thick wires, and with a higher voltage you get the I2R loss down almost as much as you want.

GA is different… little or no R&D spend, mostly mediocre designers working in the field who struggle to develop an electronic ignition box over 5-10 years, electrics taken from 1970s vehicles (hopefully American ones which actually worked, not 1970s European ones which back then were mostly flimsy junk), ridiculously low volumes…

Peter wrote:

And I would be amazed if the engine (piston or turbine) is more efficient with some of the air stolen

Certainly not, but electricity to power compressors must also come from the engine. I would expect that the additional steps involving the generators and compressor in the end will use more engine power than bleeding air from the engine.

Physics is physics.

Bleed air costs power.

Electricity costs power.

And I would be amazed if the engine (piston or turbine) is more efficient with some of the air stolen

Think about it; if it really was more efficient with less air, why not just drill some holes in the side and have that extra efficiency the whole time

I am sure Boeing made that calculation too. They aren’t stupid. And electric generation is a great technology, easy to control for output without mechanical valves, etc.

Sebastian_G wrote:

I am not sure this is a good plan for small GA planes.

For small GA this would only be an option if e.g. you have no turbo available, which most of the time makes pressurized cabins obsolete too, but that is what @Flyingfish was musing about. After all, there are also non-turbo planes which can easily reach 20k ft. On the other hand, taking the pressure from elsewhere than the engine directly eliminates the probability of contaminated cabin air as well as makes the pressurisation independent of the engine, other than for power supply.

Sure, the easier way is to go via turbo or bleed air. That is why the airliner industry has been so slow looking at alternatives. The fact that Boeing has chosen to go the way they did with the Dreamliner however makes it pretty clear that they are becoming increasingly aware that bleed air is problematic in connection with contamination.

Mooney_Driver wrote:

2) install an electrical compressor for pressurization

This is probably the future, even in airliners.

I am not sure this is a good plan for small GA planes. In the piston PA46 pressurization was basically free lunch. You would not design the turbos any smaller without it as the power is required for some high altitude take offs, max power climbs etc. The same on the turbine PA46. You would not modify the turbine a bit. Again the engine is designed for extreme conditions and full pressurization is often not required together with full prop power.

So any other solution would just add weight and complexity. A bigger generator/alternator, additional electrical compressor, probably a second one for safety, all kind of control and instrumentation stuff. Or simply make a hole in the engine air flow, add a hose and more or less the job is done.

Flyingfish wrote:

2) install an electrical compressor for pressurization

This is probably the future, even in airliners.

Bleed air pressurisation, be it from turbos or from jets, have the inherent problem that with not too much defects you can get cabin air that is anything but healthy. The solution with bleed air simply was too “easy” and therefore attractive, as it uses existing technology and was looked at as safe for far too long. Only in recent years, the problems of toxic cabin air has reached an awareness which finally has made it out of the “conspiracy theory” realm into reality. And while these incidents are quite rare, they still exist in enough cases to warrant re-thinking the system.

Using an independent pressurisation source, particularly for small GA planes like the Extra, is totally feasible in todays technology. It eliminates quite a few risk factors: Contamination due to leaky bleed air ducts or due to oil, pressurisation will not necessarily get lost that quick with an engine failure and pressurisation control can actually be easier than if you use bleed air or even vaccum pumps.

Coming up with a system which can replace todays usual way of generating cabin pressure which is cost effective (otherwise nobody will buy it) and independent of the main propulsion but for electric energy, may be one big leap in the future. The Dreamliner already uses a bleed air free pressurisation system.

I would think that if you keep the leaks down, pressurisation could be electric.

But maybe there is a minimum air mass flow required, dictated by ventilation requirements.