The interactive cutaway shows that both the AFT and the FWD baggage spaces are unpressurized

I wonder if it is as simple as an oxygen bottle for pressurization.

What is it?

Mike C.

An oxygen bottle works as a pressure surrogate while you complete an emergency descent. No bottle of anything could maintain pressure in lieu of incoming bleed air because the cabin is going to leak too much.

It’s an interesting thought since twin jets have provisions to get safely down in the event of a rapid decompression, which is more dramatic than losing the engine and having the cabin bleed down. I’m unclear as to the FAA’s distinction there.

As to backup systems, how big of a centrifugal compressor and electric motor would be needed to pressurize that space?

I really like this concept BUT; I can tell you that the JT15D-5 is so rare right now that they are not going to be find enough of these on the market for any sort of serial production. They are going to have to go with a new Williams eventually and that's going to add 1 million to the price.

Depends on a lot of variables, but about 10-20 HP would be my estimate based on providing about 1/4 the usual bleed air from one FJ44-3A.

10 HP would be about 400 amps from a 24 volt battery, which has no generator helping it any more since the engine is dead. You need ~ 5 minutes of power to get from FL410 to 15,000 ft. This completely drains a typical turbine starting battery so you need a dedicated one just for this system so you have the regular one left over afterward.

For the dedicated battery, motor, compressor, plumbing, and controls, figure 200-250 lbs.

A PW610F engine weighs 260 lbs, a pair 520 lbs. A single FJ44-3A weighs 535 lbs and you have to add the backup compressor system to that.

There are so many advantages to having two naturally redundant engines over one with kludgy backup systems.

Mike C.

Perlan high altitude pressurized sailplane might have some answers. https://perlanproject.org/2023/

The JT15D-5 is only being used for the experimental plane and they weren't planning to make very many of them.

My boat has a bunch of Victron lithium iron phosphate batteries. 25.6V w/ 300 Ah of capacity. 127 pounds apiece. Capable of discharging in a controlled manner at 1.5C… 450Ah rate. It could easily power such a motor for 5 minutes and LFP batteries are already certified in GA planes. Not my specific battery but similar batteries This is the “safe” lithium battery chemistry. That’s why we use them in boats. Given this data, I would guess a backup pressurization system could be made for 200 lbs.

I agree with Mike C - there are other benefits to a twin engine design.

I’m just pointing out the current state of LFP batteries.

By the way - we have eight of these batteries on our sailboat, Big electrical system.

Zeke

Not after it cold soaks at FL410 and -60 C.


This chart only goes to -20 C, extend that trend to -60 C and the battery is basically useless. Large solar PV battery banks have heaters in them for this purpose (and fire suppression systems as well).


I'm just pointing out the temperature characteristics of the LFP battery.

They would have to provide a heater to keep it warm. And that will need a thermostat. And that will need an overtemp sensor in case the thermostat fails. And that will need a caution light on the panel. And that will need an entry in the AFM abnormal section of the manual. And that will need to covered in ground school for the type rating. And the electrical system has to be uprated for the additional load. And the system will need to be on an inspection schedule. And the battery will have a cap check every so often. And the battery will have to be replaced periodically probably at great expense. And maybe the battery will need a fire suppression system. And....

The above is just the effects of having this battery, we haven't even started on the backup compression system itself.

Mike C.

Mike,

It’s common to have battery heaters on these batteries. They use their own energy to provide that heat and they have a charger running during cold weather ops. Putting the battery in the bottom of the baggage compartment is one option. Less likely to be super cold.

The over temp sensor is part of the Battery Management System. My boat has 8 of these batteries. And with the BMS I can see the voltage and temp of each individual cell in each battery. The BMS will automatically shut down the battery if it senses a voltage or temp out of limits - well before a catastrophic failure.

I have an EarthX LFP battery in my Pitts Model 12 and it has been a great battery. It has an integrated BMS.

If you need 5 minutes of power at a 400Ah rate to run a pump, that’s only 32A draw down. That would take the battery down to a 89% state of charge. No big deal.

And you’re right about the compression pump. I specifically didn’t mention it because I know nothing about it.

I was simply pointing out that there is a battery out there with the energy density, demonstrated safety, and FAA certificability (not a real word but you get the idea) that meets the energy requirements.

Zeke
Zeke

Not after it cold soaks at FL410 and -60 C.


This chart only goes to -20 C, extend that trend to -60 C and the battery is basically useless. Large solar PV battery banks have heaters in them for this purpose (and fire suppression systems as well).


I'm just pointing out the temperature characteristics of the LFP battery.

They would have to provide a heater to keep it warm. And that will need a thermostat. And that will need an overtemp sensor in case the thermostat fails. And that will need a caution light on the panel. And that will need an entry in the AFM abnormal section of the manual. And that will need to covered in ground school for the type rating. And the electrical system has to be uprated for the additional load. And the system will need to be on an inspection schedule. And the battery will have a cap check every so often. And the battery will have to be replaced periodically probably at great expense. And maybe the battery will need a fire suppression system. And....

The above is just the effects of having this battery, we haven't even started on the backup compression system itself.

Mike C.

For sure. Even though I'm in the twin-is-better camp, single-engine economics are very, very compelling. Especially for new aircraft purchases.

For sure. Even though I'm in the twin-is-better camp, single-engine economics are very, very compelling. Especially for new aircraft purchases.

If that's a barrier for you, you aren't a jet pilot no matter how many engines it has. Two words: "type rating". There will also be yearly recurrent training. This isn't some BFR level exercise, but a multiday intensive training program.

My multi rating cost me two days and $3K back in 2006. It was insignificant on my path to becoming a jet pilot.


Not if the one engine is limited to lower altitudes.

Even if the Stratos achieves FL410, I predict it will not be more efficient than an Eclipse EA500, a roughly equivalent airplane but with two engines.


The Stratos arrangement is high drag. This is not just airframe aerodynamic drag, nut also intake losses from the long and bent intake duct. And then you have to consider intact duct deicing, too.

Pylon mounted engines are low drag and vastly safer than an embedded engine in the fuselage. All sorts of bad things can happen to the engine and the airframe is safe, including the engine falling off entirely, or catching fire. Plus the cabin is a lot quieter than having the engine inside the fuselage.

The Stratos is a "brochure plane". That means all the numbers are at best a guess, at worst a lie. When it is "real", then we can debate what it actually does.

Mike C.