On The Trail Of A Radial Alternative To Rotax

by ANN Correspondent Kevin R.C. "Hognose" O'Brien

"What in the blue blazes is that?" I asked, at least partly involuntarily. I like to think I know aero engines. I've skinned knuckles on aero engines. I have books on aero engines. (I'm always looking for more). But this small, five-cylinder radial was a new one on me. It didn't resemble any of the radials I knew, like Kinners, Warners or the uncommon experimental HCI.

The engine was sitting on the deck at the Replica Fighters Association (RFA) building at Oshkosh. One of the RFA members answered my question, after a fashion.

"It's Tom Preuss's engine," he said. "You have to ask Tom about it. All I know is that it comes from Australia, it's only $8,000, and Tom is putting it on an 82% scale Boeing P-26."

This led to a discussion of a P-26 project that has been showing up at Oshkosh for years; it turns out that's a different plane, a full-size replica under construction by Tim O'Connor (read more about it here). When I finally figured out that we were talking about two different P-26s, a man appeared who knew all about Tom Preuss's P-26, and all about Tom Preuss's engine.

He was, in fact, Tom Preuss, and quickly confirmed that he was building an 82% P-26 based on a heavily modified Bowers Fly Baby design -- completely different from O'Connor's metal Peashooter. And now I discovered exactly what it meant that this mystery radial was "Tom Preuss's engine": Preuss owned it. He knew some details of the engine, but it was built by someone else. He saw some parts last year and talked to the guy, and committed to be the launch customer for the prototype of the engine.

Fortunately, Preuss, an interesting guy who has already built and is flying a highly modified Loehle P-51 kit, knew who the real designer was, and I finally had a name: Peter Walker. Walker made the engine, casting and machining most parts. Walker was, Preuss said, from New South Wales, Australia. For a moment I forgot how pleased I was to have found out who made the engine, so disappointed I was that he was so far away.

"He's not far away right now," Preuss said. "He's right here at the show. And there he is!" At this point, the man himself appeared: Peter Walker. After a brief introduction, Preuss went inside the air-conditioned RFA building and Walker squinted into the afternoon sun, and told the story of his engine.

Walker's one-man company, Werombi Engineering (Werombi is a place name in Australia), has but one product, of which exactly one prototype example existed: the one sitting before us. The R2740 5-cylinder radial engine is designed to make 75 horsepower and the prototype weighs 149 pounds with manifolds and normal accessories. Walker thinks that there is the certainty of some weight reduction, probably about 15 lbs. worth. (Note the picture of Walker holding the engine).

Walker pointed with pride to certain features of his engine. It was built to be robust. The head is a standard part that is used on overhead valve stationary engines -- engines that are used to run generators or pumps, and which have a similar duty cycle to an aircraft engine.

"The hard part is up here, in the head," Walker said, pointing to the cylinder head of stationary-engine provenance. "And that's already done for us. The rest of it is pretty straightforward."

The cylinder barrels (nikasil lined) and the crankcase are cast from aluminum alloy and machined; the crankshaft is cast from steel and machined. Intake manifold and exhaust collector ring are tubular steel (on the prototype, at least).

The four-stroke engine will make its 75 HP at 2500 RPM. Like the 15 HP one-lung stationary motors from which it's derived, it isn't straining to do it. It displaces 2740cc, or 167 cubic inches. The engine should be able to replace the Rotax 582 in many installations. At least at first, there will be no firewall-forward packages, and the buyer will have to have a motor mount made; Werombi Engineering, Walker's company, will provide the drawings that make it possible. The engines will also ship with an engine mounting stand which works to line the engine up properly, and sets it up at the right height, and in the proper attitude, for mounting or installation.

Many who express interest in the R-2740 are attracted by the retro appeal of the radial. "Look at what's really happening in aviation now," Walker urges. "The classic, retro lines of a radial have a strong appeal." But he's interested in far more than the "retro" market, stressing that his engine is a reasonable replacement for the Rotax 582 that offers a longer TBO (he expects 1000 hours) and less sensitivity to maintenance.

He's far from a 582 basher; he's quick to point out that most people who fail to make TBO or have unexpected stoppages have not followed the recommended maintenance procedures in the manual. "You have to use the right oil and the right operating procedures, and you'll be very happy with a Rotax. This engine [the R-2740] is designed to be more durable; to get it to break down you'd have to do extreme things to it, run it without any oil or something." He was particularly critical of torturing the engine to exact the last percentage point of performance, at the expense of durability. "Yes, many pilots don't make TBO. But that doesn't mean the Rotax is bad. In Europe, they're getting 600 hours out of them." His advice: adhere strictly to the recommended procedures in the manual.

And you should still follow the recommended procedures in the manual with the R-2740; it'll last longer that way.

Until now, Walker hasn't had a website. "Too many guys come here with a fancy website, with a computer rendering, but no real product. I told them when I came here last year and showed some parts that I wasn't going to do a rendering and wasn't going to make a website full of empty promises. I was going to make and show people real parts and real engines. So last year I came with parts and this year with an engine."

"Next year, there should be three planes here with these engines in them. At least." Walker explained that one kit maker interested in the engine was Aerolab of Italy, which already offers the Rotec radial, an unrelated engine that's also from Down Under, in its two-seater aircraft, which resemble a Spacewalker with the retro aspects of the design played up. The R-2740 (named for its metric capacity) would power a lighter, single-seat version. In addition to Tom Preuss's P-26 scaled replica, several other projects are under construction.

Meanwhile, back in Australia, Walker has thought of a clever way to torture test his engine. One will be installed in a Wag-a-bond that will be placed at a local flying club -- the members will be able to fly the plane for the cost of fuel only, which he believes will quickly build up a lot of hours, "in the hands of average pilots, and maybe some ham-handed ones." This will help him see how the engine holds up in "real" service.

Peter Walker explained how he planned to sell and service the engines. As I'd heard, the price is expected to be about $8,000 US. All sales will be direct, and all warranty service will be through Werombi Engineering in Australia -- if your engine needs warranty service, you'll pack it back in its original box and send it back, and Werombi pays the freight. When the engine is repaired, as long as the damage isn't due to abuse, it'll be shipped back to the customer, anywhere in the world. 

It will be some time before the jury is in on Peter Walker's new engine design, but his explanation of its projected advantages is plausible, and enough early adopters have committed to the engine that we should know in a finite amount of time how successful the design is.

Meanwhile, it can be seen on the deck of the Replica Fighters Association building at Airventure in Oshkosh -- for a limited time only, before Tom Preuss takes it home to power his P-26 replica.

FMI: www.r2740.com  [note: site is expected to go live soon, but may not be right now]