SubSonex: The Second Coming of the Microjet

Pawing back through the archives, I can confidently declare that 2002 was the summer of the VLJ—the very light jet. Some were practically swooning over the notion of sub-$1 million jets and there was a thundering herd of them, led by the rock star of VLJs, the Eclipse.

During a round of interviewing that year and in 2003, I asked how these companies were going to deliver these breathtakingly low price points. Eclipse's intro price was $837,000; the Safire S-26 was $800,000. We were assured that these prices would be met by a convergence of efficient, automated manufacturing technology similar to that used in auto plants and that would, in turn, instigate automotive volumes, making the price points both realistic and profitable.

Didn't happen. There are a host of reasons why these airplane projects cratered, but one of them is that the companies made flawed assumptions about scale economy and typed in sticker numbers before they had anything beyond the vaguest idea of what the airplanes would actually cost to build. Williams tanked on development of the EJ22 for Eclipse and although Pratt & Whitney had a predictably sane development program for the PW600 series engine borne of years of experience, that yielded simpler and cheaper engines, but that's not the same as simple and cheap in the absolute.

That this history was written in a slurry of blood and charred dollar bills isn't because the people proposing these projects were stupid, dishonest or inexperienced. I think it's because, as I have said before, that when certain people (including me) get within 50 feet of airplanes, their normally functioning brains turn to a mass of quivering mush incapable of anything resembling rational thought. I'm putting this idea upfront as a sort of warning as I segue into the main course of today's blog: microjets.

Nearly 80 years after the turbojet engine first took flight, these remarkably simple engines remain all but inaccessible to light general aviation. This is so because despite their simplicity, the vaunted advent of CNC machinery hasn't made them cheap to build and they aren't especially fuel efficient, either. Not for nothing are Airbus and Siemens looking at electrically driven ducted fans as the powerplant for the future. But since we never give up in aviation, the small jet engine floats out there just within reach and that's what makes the SubSonex JSX-2 such an intriguing project, if you're willing to build it yourself.

Last month, I spent three days in the desert shooting the jet and covering my colleague, KITPLANES editor Paul Dye, learning to fly it. You can see the video on that coverage here and a full report in the August 2015 issue of KITPLANES.Veteran airshow performer Bob Carleton was instrumental in helping John Monnett develop the SubSonex and provided oversight for the flight training, which results in a kind of mashed up type rating, since jets, regardless of size, still require that.

I like to think I retain a small sliver of analytical capability when I'm around airplanes as appealing as the SubSonex and I find the numbers intriguing. The kit with engine costs about $130,000, so by the time you throw in the avionics, paint and other extras, call it $150,000 to $160,000. For a jet, even a single-seat jet, that's not a lot of money in the context of upper strata experimentals or even LSAs. In fact, it strikes me as a decent value for a would-be builder or owner who passionately wants to fly a jet airplane. I could actually afford it myself.

It's also not difficult to fly, but does require the somewhat cumbersome training evolution described in the video. I doubt if that would put many owners off; it certainly wouldn't faze me. How would you use such a thing? I think it's primarily a VFR sport flyer similar to other experimentals or LSAs. Take off of a Saturday morning and burn up 30 gallons of Jet A beating up the local area and the pattern. Great fun. (You'll need a longish runway, however. The SubSonex isn't exactly a STOL airplane and the brakes need improving.)

Sonex gives the still air range as 480 miles at a 240-MPH cruise, so you could use the airplane for light travel, although it would take planning and effort. It burns about 34 GPH during takeoff and typically half that in cruise with a 40-gallon capacity. I wonder if a creative builder might find room for a little more fuel.

The engine is a 40-pound jewel of a creation from PBS Velká Bíteš, a Czech Republic company formerly in the Soviet orbit. The TJ-100's origins are in APU applications, but it finds use in small UAVs today. Rated thrust is 250 pounds, which Carleton says is a perfect match for the airplane. When we were shooting the airplane, he explained how a jet engine's simplicity percolates down through the airplane itself. With no heavy structure to support a piston engine and no linkages for throttles and props, the SubSonex is an exceptionally simple build. The engine is FADEC controlled and throttle by wire, so the only connections are the fuel line and a few wires. Carleton told me when he tours with his Salto glider for airshows—same engine—he unpins the engine and takes it into his hotel room at night. Try that with an IO-320.

Of course, the piper always demands his pay and that's the other side of this jet's coin. It has a short TBO— 300 hours. What this means exactly in operating costs is a little murky. Cost of the engine is nominally about $46,000 at current exchange rates or $153 per engine operating hour. Ouch! But Carleton told me the engines are overhauled on condition so he expects they'll be shipped off to the Czech Republic and brought back to fresh condition for some percentage of the full cost, perhaps 15 percent as an educated guess. At the moment, there just aren't enough engines out there turning hours to have reliably repeatable data. As the engine gains more fleet experience, the overhaul times will probably increase, so at least the cost trend is in a favorable direction.

So is this really a second coming of the microjet or just the sui generis of lucky timing? Hard to say, but my guess is that it has better legs than the BD-5 did which was, after all, somewhat of an accidental jet. It got the TR-18 turbojet when the planned piston engine development ran off the rails. The BD-5, don't forget, was a huge seller with some 5000 kits ordered. The demand was even stronger for a factory certified version that I'm not sure could have been certified then (1972) or now, even if Bede hadn't run out of money and folded. The kit price was about $3000 or about $17,000 in 2015 dollars. So the SubSonex costs nearly 10 times more, but it's also intended to be a jet. There's a lot of wealth out there looking for distinctive rides like this one.

No, it'll never be everyman's jet. But it's at least accessible for those who are just hot to burn up a bunch of Jet A. If you gotta have it, you can get it. Personally, I think that makes it a uniquely cool airplane. I hope they sell hundreds.