I think electric engines could also fill this gap in the future (when batteries are good enough), since they should produce basically the same power regardless of altitude.
In a very long run maybe but today in a high flying turbine aircraft the turbine does a lot of things. First, obviously, it produces thrust for the prop or the fan. But then it also produces a lot of heated pressurized air for the cabin and other tasks (deicing on some models etc.). Further it produces a lot of eletricity for all kinds of system. In a typical small plane this can easily be 3 kW just for electric stuff. Then further it poweres the aircon if required.
So in a real world battery powered application it would not only have to make the thing fly, which is hard enough, but beyond that power all those other things. So this is not impossible but way down the line. All those electric eVTOL toys ignore this completely. They claim to make it fly a certain distance, which is already a lie, but then no word about cabin comfort, deice and other requirements.
In fact a propeller version fo the GT50 engine could do the trick at least for experimentals. As the entire helicopter is supposed to be priced less than an Alsion engine alone, the GT50 engine alone can not be that expensive and it has good spec for a small pressurized plane. I am just not sure about high altitude performance as they do not need that for the helicopter.
https://www.hillhelicopters.com/gt50-engine
Also at high altitudes OAT drops significantly, which further eats into battery performance…
For below FL200, there are loads of solutions. The TB20, SR22, loads of old types, etc, etc.
To address this properly, you need a FL250+ plane. That gets you above most warm fronts; these tend to have FL200-250 tops. One can do FL250 with a mask but that is impractical for routine enroute, especially with passengers, and totally so with kids. So you need pressurisation. The whole thing then gets a bit heavier.
Now we are into this thread.
Forget electric. The charging points at airports come with a free petrol grass strimmer 
A used TBM is a great aircraft but suffers from
Why are there so few small pressurised aircraft?
Complexity and price. But the idea behind them was also clear: Stop the nagging of wifes who resent to need canulas or masks. And if done right, this is a good thing. Pressurized flying is a far cry from sitting there for hours with canulas or masks, which will make passengers uncomfortable.
The first pressurized GA single as some may remember was the M22 Mustang, followed by the Cessna P210. The Mustang, which still flies in some exemplars, was quite an airplane for it´s day and I somehow regret not knowing about one next door to me going for a song a few years back, I´d have picked it up immediately. It was built between 1966 and 1970 and bancrupted Mooney for the first time, as they lost money on every airframe. Only 36 were built.
The numbers were not too shabby though: 190-200 kts, 24000 ft ceiling, 1200 NM range and capable to operate out of tiny runways. It had a TIO521 with 310 HP as it´s engine. A CFI friend of mine recently found himself tasked to introduce a new owner to one of the few remaining ones and loved the airplane once he realized what it could do. Nowadays you can pick up a M22 for a song if you find one and have a good idea on how to work on it.
The next incarnation was the Mooney 301, which, had it progressed to serial production, would have given the Malibu a run for it´s money. But actually it did reach production albeit as a very different airplane in the end: The TBM. And that type is of course a huge success story.
The first successful pressurized single was the P210. It came 8 years after the demise of the M22, a 6 seater featuring a similar size powerplant (TSIO520 at 310 hp). It was the single engine version of the Cessna 337P and most of the pressurisation e.t.c came from it. The initial version was about 20-30 kts slower than the M22, had a realistic service ceiling of around 20000 ft even though the book sais you can do 23000 ft. With an almost identical fuel load (90USG unmodified) the range of the P210 is also considerably smaller, which is why most feature auxiliary fuel tanks, some of them several including baggage tanks. Some 900 were built, some of which by now have received a turboprop conversion called Silver Eagle featuring an Allison turbine.
I suppose the first real high performance pressurized single would have been the Malibu, which, along with the TBM, are the most common these days. Exotic hotrods like the Lancair 4P, a ferocious hotrod which also formed the base for the Columbia design excluded.
I do recall the attempt to change the way those airplanes are pressurized by using an electric compressor, such as it´s done by the Dreamliner today. This has the distinct advantage that no leaks of rather unhealty engine gasses would enter the cabin, even if an engine blows, as it happened with fatal consequences near Graz recently with an A220. The question is however, whether such a compressor could source enough electric power and what it´s failure mode would be. It does not appear for now that a lot of manufacturers follow the 787 principle. For GA however, it might solve one problem all pressurized piston planes have which has to do with heat management in the engine. This might actually help future pressurized designs if there are any.
To address this properly, you need a FL250+ plane. That gets you above most warm fronts; these tend to have FL200-250 tops.
Not even FL310 helps much when there is any convection around. My experience is 250-300 is the worst level band in that regard. A small airliner turboprop at FL250 is an all weather plane, due to the proper diameter size of the wx radar antenna.
To be above weather FL400+ is needed.
Why are there so few small pressurised aircraft?
Easy one, market size and costs. Or the other way round.
Pressure cabin places the category a step higher than most pistons, and just a minute step below TPs.
Now TPs themselves, wade thru the jet waters, again another step on the infinite ladder of prestige, intromittent organ size and/or length, comfort, and exponentially rising costs.
My experience is 250-300 is the worst level band in that regard
Same here. 310 was a level of choice (and max for the RJ85 IIRC), but once up there we cruised in the clear most of times.
Now European weather is quite benign compared to what one can expect on other continents… CB tops for instance seldom exceed 350 here (my humble observations), but easily reach 500 in the Caribbean for instance.
Snoopy wrote:
Not even FL310 helps much when there is any convection around.
With convection things can go much higher even. Over the Black Sea Coast, I´ve seen cumulubumpus up to FL450 approx (we went past one at FL410 and it was still much higher.) Convective stuff is there to be avoided, not flown above, as the Sibir TU154 who tried found out.
Most of those pressurized SEP have ceilings at around 230-250, some are more comfortable down between 180 and 240. Particularly if you fly over the Alps regularly however, this is a game changer. Most airways over the alps, where there are any left, are FL170 or higher, so you need oxygen. Many flying spouses resent it, most kids will eventually pull the stuff of and forget flying with babies if they need O2.
Also most times I did consider (and eventually fly) across the Alps on top, We were talking 160-180. While this is still canula territory, it is oxygen territory for sure. In my old days I used to do a couple of short crossings via the Gotthard at FL140-160 without them, but it is not something you should do.
For me, pressurisation is a simple spouse/family pacifier rather than the license to end up in IMC all the time, rather to go above when possible and to negotiate the often ridiculously high MEA´s in European airspace.
If I had the cash I´d go for a pressurized 210 I think… plenty of charge and plenty of range too if it has all the tanks and it can do 240 if it needs. And frankly, I´d have loved to get my hands on that M22, but seeing what became of it, maybe better not. (It suffered a nose gear collapse shortly after being purchased… that plane was based in Wangen LAchen before.)
However, if you can do FL250-270 (below RVSM) you can still get ~99% despatch rate, in wx where you can avoid convective wx visually. This has been proven by many owners of such machines, over many years, because that capability is quite old (e.g. a 421C).
Airliners want > 99% but they have better hardware And CAT3 makes a huge difference.
Snoopy wrote:
A small airliner turboprop at FL250 is an all weather plane, due to the proper diameter size of the wx radar antenna.
I was wondering if the new GWX75 with volumetric scanning offer any improvement over the older models from Garmin, which were no good.
I now have a 12 inch Collins and it’s so much better than the 10 and 12 inch radars from Garmin I used earlier.
