Creating a Mini Personal Jet

What happens when an aircraft builder becomes a jet pilot?

John Monnett
Sonex Aircraft founder and president John Monnett fulfilled his desire to be a jet pilot by building the SubSonex.Photo by Jim Koepnick

John Monnett always thought of himself as a jet pilot, but as his 50s began drawing to a close he realized the only way that was going to happen was if he built one himself. Luckily for Monnett, his day job is founder and president of Oshkosh-based Sonex Aircraft, a kit builder already known for airplanes like the Sonex-B, the Xenos-B and the OneX.

Flying caught up with Monnett at Sun ‘n Fun earlier this month and coaxed the story of the company’s single-engine jet kit, the SubSonex, out of him. Getting him to talk about building airplanes didn’t demand much coaxing though.

Monnett traced his interest in a jet back to the early days of Jim Bede’s airplanes, including the BD-5 Jet he remembered in the 1983 James Bond movie Octopussy.

“But that airplane was unobtainable by most people,” Monnett said. “The engine alone cost $150,000, and that was 35 years ago.” But still Monnett remembered the BD-5 Jet as a cool machine. He thought for certain that other pilots would want a jet, if it was affordable.

Fast forward a few decades and Sonex had just finished creating the Xenos motor glider. Where should the company focus next, he wondered? After a stint studying electric propulsion, Monnett and his co-designer Pete Buck began to notice what was happening in the model aircraft industry.

“There was this jet engine we heard about that could produce 150 pounds of thrust, so we began putting some numbers and designs together trying to figure out what a jet might look like,” Monnett recalled. “Late in the process, we found out there was no way to control the actual engine and at this point we almost had the airframe built. We knew this wasn’t going to work.”

Then the Sonex team heard about another small jet engine with 250 pounds of thrust built in the Czech Republic, and by 2009 the SubSonex was certified. But there were still a couple of tweaks the airplane demanded before it became the jet thousands of people had watched at AirVenture and Sun ‘n Fun.

There are five SubSonex presently flying with another nine in various stages of construction.Rob Mark

For instance, “We got the airplane certified with a single wheel gear,” Monnett said. “That turned out to be one of the dumbest ideas we ever had. It was a tail dragger and when we leveled out the aircraft, the fuel would start sloshing around in the tank so we had to add fuel-tank baffles. Then we learned that with the high thrust line, adding takeoff power made the tail come up eary, before it was really ready to fly. That put the pilot at the mercy of wherever the airplane’s nose was pointed.”

Monnett offered a big grin as he explained, “I initially made a few excursions all around the airport dodging lights, crossing taxiways, but luckily never damaging the airplane, much,” except on one excursion on the ground when he punched a hole in the fuselage. The Sonex team realized the airplane needed a nose wheel and traditional main gear, a modification that just happened to fit where John had already punctured the fuselage. The tweaks to the original design eventually morphed into the JSX-2 SubSonex the company sells today.

Although he had always wanted to fly a jet, when it came time to earn the FAA Letter of Authorization Monnett would need to fly solo, he had to admit he had no experience in jets. He did eventually convince the FAA he’d be a safe bet to fly the airplane he helped create.

Was it worth the wait, I asked?

“It’s really easy to fly,” he said. “I flew it first on a day when it was bumpy, but realized that once it got off the ground the airplane was awesome to fly, right up to its 250-knot redline. It cruises about 230-240 knots at 92 percent power. With a 40-gallon fuel tank you can fly for 2.5 hours, burning about 17 gallons an hour on the Fadec-controlled engine.”

Monnett said there are five SubSonex presently flying with another nine in various stages of construction. The quick-build aircraft kit costs $47,000. Add another $55,000 for the engine and some cash for avionics and you can own your own jet for about $130,000.

Monnett likes to call the SubSonex “his personal hot rod.” There is just one problem confronting him these days as a pilot. “Flying a jet is really cool. I’m so spoiled now that all I want to fly is a jet.”