Jet & ESA Fly From Sonex Hornet’s Nest
By Scott Spangler on August 31st, 2009
At EAA AirVenture Oshkosh, Sonex Aircraft pulled back the curtain on its research and development department, called the Hornet’s Nest, and unveiled three projects it’s been working on for the past handful of years. One of them the E-Flight Power System, was covered in a previous post (Old Fashioned Focus Sustains Sonex), but there were two surprises. One was the SubSonex jet and the other was the Onex (pronounced One-X), a single seater. Given the breadth of information Sonex shared on my recent visit, this post will look at the turbine and electric airplanes. I’ll serve up the Onex next week.
Sonex is not taking orders for these R&D projects, and it does not have any concrete information on price or availability. That information will come in time as the projects mature and there’s a proven demand for them. Sonex will post updates on its Hornet’s Nest website. “Each project airplane does not compete with current products, but all of them adhere to Sonex themes of affordability, simplicity, versatility, performance, quality, engineering, and ease of maintenance,” says CEO Jeremy Monnett.
With an impish grin, Sonex Founder and Chairman John Monnett, standing next to the jet’s single-seat cockpit, pleads guilty to a bit of carbon trading with the SubSonex, drawing a lifetime of making efficient airplanes leading up to the E-Flight Sonex. “It’s been my pet project since I first saw the BD-5J in the 1970s.” Only now, with the development of a new generation of small turbine engines has it entered the realm of affordable.
Everyone mistakenly called the SubSonex’s turbojet a model airplane engine, says John, but a British company, Heward Microjet, designed it for all sorts of aircraft and drones. After building two examples of the engine, Heward “decided to move onto another career, which is designing miniature turbines,” says John. “That left us with an engine and no way to run it,” because it lacks an ECU—electronic control unit—which manages every aspect of the engine’s operation.”
Drawing on the electrical engineering talent behind the E-Flight Power System, Sonex designed and built an ECU for the Heward. “It’s ready to go, but it needs programming, which means a test program.” The question is whether to invest the needed time and effort. A US company bought the rights to the Heward engine, but its production future is uncertain.
“We knew that once we introduced the airplane that other interested engine makers would come forward,” John says. Sonex is now in negotiations with two companies that make suitable turbines. “Our minimum thrust is 150 pounds, and an engine that produces 170 to 200 pounds would be just dandy!”
Sonex rolled out the jet at its open house just before AirVenture, and fun—including aerobatics—is its only mission, John says. “With 32 gallons of fuel, it has about an hour’s duration, depending on how the pilot exercises the thrust lever.” At AirVenture, the prototype SubSonex was up on pylons, and many people thought it was a two-seat Waiex with a jet engine, John says, wondering if they were “spatially handicapped.” Besides being smaller, the SubSonex only has one seat. It’s an all-new airframe with a 300-mph VNE, and it will fly as soon as the Sonex settles on an engine.
The Sonex E-Flight Power System is also close to flying, John says. It was supposed to make its maiden flight at the end of September, but a last minute problem with its lithium-polymer (LiPo) battery pack put it on hold until the company that makes the LiPo cells troubleshoots the problem, John says. Hopes are that it will fly before the New Year. Until then, N270DC, for the battery pack’s direct voltage, which will turn the 80-hp electric motor for roughly an hour, waits patiently in the Hornet’s Nest.
Everything else, from the instrumentation and motor control unit to balancing unit that keeps the 76 LiPo cells in check, is ready to go. The motor itself is giving off a bit too much heat, but John says that should be an easy fix. “Our R&D is not on batteries, we’re powerplant guys, and electricity is our fuel,” John says, holding a single LiPo cell while standing behind the hand cart that holds an 800-pound stack of lead-acid automotive batteries that stand in for the 200-pound 76-cell LiPo battery pack on the ground.
In its finished form, the E-Flight Power System will come in three pieces, John says: the motor (with its switching circuitry), the motor control unit, and a standard battery pack with a built-in balancing unit and charging circuitry. The engines will be available to Sonex customers and builders of other aircraft in the 70-to-80-hp arena.
“With electric power comes the new Sonex Electric Sport Aircraft, or ESA, that’s optimized for the power system,” says Sonex CEO Jeremy Monnett. The goal is to split the difference between the Waiex and longer-winged Xenos to create an aerobatic, sport-pilot-eligible ESA “that maintains a sporty feel and still has a reasonable flight duration given current energy storage technology.”
Walking back to the SubSonex, John notes that its 32-gallon fuel tank, behind the seat, sits right over the center of gravity. “It weighs the same as the ESA’s battery pack,” he says, the wheels clearly turning, “and if you had an electric ducted fan…”—Scott Spangler
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