When Jon Sharp and his air racing team flew the NemesisNXT kit airplane to a qualifying speed of 409 mph at the Reno Air Races last September, they not only became the first in the Super Sport category to break 400 mph, they also made hearts beat faster among light-airplane owners and pilots who fly behind the traditional horizontally opposed piston engines that have powered smaller aircraft for decades. That a conventional Lycoming engine—admittedly hand-built and tweaked to extract every last bit of horsepower—could hit speeds previously reserved for the Unlimited and Jet classes was like a hot shot of adrenaline for aviation buffs everywhere.
“We’ve known for a long time the plane would get there,” Sharp says. “We just needed to get the right combination of things going at the same time. We came close in 2007, but with just a few little tweaks and mods here and there, plus the pilot getting better in the plane….” When Sharp gets excited, which is most of the time, he sometimes doesn’t complete a sentence, but you know what he means.
Sharp attributes the airplane’s success partly to a design that focuses on one goal: achieving 400 mph. The first versions were designed around tandem seating until aerodynamics dictated that the fuselage outline follow the width of the engine until a point aft of the wing’s trailing edge. (The happy side effect: Sharp and wife Patricia, who recently donated a kidney to her husband, can hop into the side-by-side cabin with an overnight bag and fly home after a race.) With its elliptical leading edge, the wing looks like the leading half of a Spitfire’s, and the raked wingtips are adapted from a NASA design Sharp calls a “sheared tip.”
For air-cooled engine installations like this one, engine cooling adjustments are mostly trial and error. The trick is to take 400-mph air into the engine room, slow it down so it can do its cooling thing, then move it out the exit as close to 400 mph as you can. “As we learned more about the plane, and what it wanted to go fast,” says Sharp, “we refined the ratios of all the inlets to the exit sides to help reduce the cooling drag a bit.”
Sharp says his partners at Lycoming provide the TIO-540-NXT engine with twin turbochargers and twin intercoolers. “They’re always doing little refinements, and they don’t always tell me what they’ve done,” Sharp says. “Sometimes that’s for the better, because you know pilots can’t keep a speed secret under their hat.” He knows Lycoming worked on the anti-detonation injection (ADI) system, which squirts a 50-50 mix of water and methanol into the river of induction air downstream of the turbochargers. As it flash-evaporates, it absorbs heat from the air and softens the combustion within the cylinder, thereby “reducing” (Sharp won’t use the word “eliminating”) any tendency to pre-ignite and “turn the engine into a grenade,” in Sharp’s words. Lycoming rates the engine at 350 horsepower. To get to 409, it’s got to be producing well over 400 ponies, but Sharp winks and says everything runs to stock specs. So it’s difficult to describe the NemesisNXT as a “kit,” although that’s what it is. And the fact that anyone can go out to a garage and build one makes it all the more wonderful.