Radial Renaissance

By Rob Neil.

“Real airplanes have round engines,” says a popular pilots’ bumper sticker. Anyone with aviation in the blood knows that it is radials the sticker is referring to and not jet engines (and any aero-Philistine who tries to suggest that jets are also round is likely to be stoned or pilloried). Radial engines epitomise the “golden age” of romantic aviation—an age in which the flying boats that crossed the oceans, and the DC3s, 4s, 6s and 7s, the Lockheed Constellations and Boeing Stratoliners that covered continents were all powered by radial-engines. Most “real” military aircraft all had radials as well: for the “good guys”, there were aircraft like the Wildcats, Hellcats, Corsairs, Avengers, Sea Furies, Tempests, Boeing B-17s and B-29s. Even “real” trainers like the ubiquitous Stearman and Harvard had radials. The bad guys also recognised the radial’s many qualities, and all the “real” German and Japanese military aircraft wore radials: Dorniers, Focke Wulfs, Junkers, Aichis, Kawanishis, Mitsubishis and Nakajimas—radials ruled!

There are many good reasons why radials became the ultimate in piston-engined power before the advent of the jet. Quite simply, for the amount of power they produce, radials are much lighter, simpler and stronger than other configurations. As much as everyone admired and marvelled at the beautiful V12s built by Rolls Royce, Allison and Daimler Benz, which were, undeniably, magnificent technological masterpieces, they were expensive and time consuming to produce, less reliable in service and more easily damaged in combat, and far more complicated to service and maintain.

As a result of their manifold qualities (not to be confused with the quality of their manifolds), radial engines developed a special mystique in the hearts and minds of aviators around the world. Even today, the distinctive sound of a radial engine draws a following wherever it is heard and there still remain applications for which nothing but a radial engine will do. For example, it is no accident that many of the world’s super high-performance aerobatic aircraft are radial-powered; Jurgis Kairys would recoil in horror at the prospect of flying his mind-boggling aerobatic routines behind an engine with a long, flexible crankshaft—only his strong, powerful, reliable radial engine will do!

Until recently, if one wanted a new radial engine, the choices were extremely limited; only Russia’s VOKBM, and Poland’s PZL engines were available. As excellent as these manufacturers’ well-proven engines are, they are too big, powerful and heavy for most light general aviation aircraft, and most homebuilders had little choice but to use horizontally opposed Lycoming or Continental engines, or, more recently, Rotax or Jabiru powerplants.

At least one American company remanufactures and repairs existing old radial engines—those built by Jacobs, Lycoming, Continental, Wright, Warner and others—but while such engines remain available to buy and are rebuilt to factory-new life limits, the smallest such engines, like the 220–250 hp Continental W670, weigh around 211 kg (without accessories). Obviously, such large engines are completely unsuitable for small homebuilts and microlights like the Kitfox, which has a maximum take-off weight of only 703 kg in its biggest and heaviest variant, let alone the weight-limited microlight/ultralight versions, which weigh 150-odd kg less.

And then along came Paul and Matthew Chernikeeff.

Cherni…who? The Chernikeeff brothers are the visionary pair behind the Melbourne-based company Rotec that designs and builds its own radial engines—a seven-cylinder 2.8 litre unit (the Rotec R2800) and the nine-cylinder R3600 of 3.6 litres, neither of which could be described as anything other than exquisite masterpieces of engineering.

The writer visited Rotec’s unassuming Melbourne factory recently and saw both engines being produced. Were there such a religion as “radialism”, then a single afternoon at Rotec in the presence of Paul Chernikeeff’s enthusiasm, surrounded by the beauty of perfectly machined precision components being lovingly crafted into aluminium sculptures would transform any disbeliever into a devout disciple!

It is hard to describe the wonder of seeing plain metal stock—round bars and solid billets of aluminium and steel—being transformed before one’s eyes into the multitude of precision components necessary to turn aviators’ dollars into horsepower.

Most people have the impression—justifiably or not—that internal combustion engines are so “complicated” and “exacting” in their design and construction that their extensive inner workings could only be designed by bearded scientists and engineers, and produced by giant factories with multi-million dollar research facilities, precision machine tools and hordes of skilled technicians.

Rotec Engineering doesn’t have a single bearded scientist. Nor does it have a multi-million dollar research facility or a huge factory. What it does have is a large percentage of all the determination, enthusiasm and sheer gumption in all of Australia, in the form of the two Chernikeeff brothers, their father, Jim, and the handful of highly motivated and skilful artisans at Rotec.

Rotec had its roots in Matthew and Paul’s childhood interest in aviation. Through their fascination with aircraft, both boys became involved in building and flying model aircraft—initially control-line versions and gradually progressing to ever-larger radio controlled (RC) models.

As Paul got older, he became increasingly interested in the largest scale models—some as big as half scale. To someone with Paul’s engineering “bent”, the need to build one’s own engines and props, make glass-fibre cowls and weld airframes held particular appeal.

It was in the area of engine building that Matthew’s specialist skills as a machinist came to the fore and Paul increasingly called on Matthew’s expertise to produce his engine components. Eventually, Paul also built a workshop at home, which he equipped with a mill, lathe and other machine tools.

When Paul built a model of a Gee Bee racer, he wanted to put a radial engine in it. He had liked radials since he was a child, and had studied them and learned as much as he could about them.

The fact that there were no scale radial engines available for model aircraft would have been a disappointment to most people—and that would have been the end of it. Paul Chernikeeff was not “most people”. He simply saw it as a great opportunity and elected to build his own radial engine from scratch. After nearly two years of painstaking effort, in 1997, he produced a gorgeous little seven-cylinder radial engine with a capacity of just 350 cc.

However, after all the time and effort he’d put into building it, it had become so precious to him that he never actually installed it in a model aircraft and never flew it. He realised that if he fitted it to a model and crashed the model (a not unlikely scenario, as most RC flyers would probably agree) he might lose the engine and his two years’ effort would have been in vain. Instead, he put the engine on a test stand and began taking it to shows—model shows and airshows—while he continued to power his models with conventional two-stroke engines.

Paul’s 350 cc original formed the basis for the Rotec engines that he and Paul would go on to build. Paul still owns the original (model) engine, which, he says, still runs like a top—and has still never flown.

At the time, Paul had his own business as an auto electrician, which allowed him to do all the tinkering necessary to build his model engine. From 1990 to 2000, while working in the auto trade, he wasted as little money as possible on fripperies like food and rent, and spent the important money on tinkering with models and building things—including his precious model radial.

Not surprisingly, the beautiful model engine was a big hit at various shows and it when it made the cover of a magazine for the first time, it began to attract lot of national and international exposure. Paul began getting enquiries from “radialists” around the world—homebuilders as well as modellers—wanting him to build similar (and larger) engines for them.

One man in particular—Geoff Hargraves—sowed the seed for what subsequently evolved into Rotec, and really “pestered” Paul to begin building engines. As both Paul and Matthew had “real” jobs at the time (Paul as a self-employed auto electrician and Matthew as a precision machinist), Paul didn’t initially take the requests too seriously, but the more he thought about it, the more he thought it might be worthwhile.

He realised that—unlike he had with his model—he wouldn’t have to make his own pistons, piston rings, carburettors, valves or valve springs, spark plugs or ignition leads for a full-sized engine. He would be able to outsource many such components, making it much less of an undertaking than the model had been.

The fact that his model engine had worked so well featured heavily in his eventual decision to proceed and he believed it would scale up easily. He explained that engineering projects like this always scale up more efficiently than down. “Had the model run like junk,” he says, “I probably wouldn’t have bothered.”

Geoff Hargraves pleaded with Paul to take his model engine to the Caboolture air show, and even paid Paul’s fare and his expenses to ship it. Hargraves was convinced that the engine would be a hit, and so it proved to be. So it was that after the 1999 Caboolture air show, Paul and Matthew approached their father to help finance them into a couple of machines so they could start producing engines.

Initially, both brothers decided they would retain their full time jobs. It would mean working all day, and then downing one set of tools to pick up another and working much of the night and at weekends, but if that was what it would take, they were prepared to do it.

The Chernikeeffs drew up plans for a new engine that was almost exactly a scaled up version of Paul’s model. Apart from the addition of a few accessories and features—things like dual ignition (the model had only a single ignition system) and extra pumps—the engine’s geometry was virtually the same. Even the bore and stroke retained an identical ratio. The resulting engine was a 110 hp 2,800 cc seven-cylinder machine weighing 102 kg (including starter motor, alternator and carburettor).

With their father’s welcome financial assistance, Paul and Matthew rented their first premises—significantly smaller than the factory they occupy today—bought some machines at auction and began building engine parts. They continued the rather unusual and definitely wearying situation of working two “full-time” jobs for some time (the engine building was without financial compensation in the early days, of course).

The brothers sold their first engine to Nestor Slepcev, who wanted a radial engine to power his Feisler Storch replica (the Morane Saulnier MS504/505 Criquet—a French-built version of the Storch—utilised a radial engine). This first sale allowed the Chernikeeffs to build the next five engines. The sales of the next five allowed them to build the next twenty, and so on, until eventually, the brothers were able to give up their “day” jobs and commit themselves full-time to building what—by then—had become Rotec engines.

The brothers still didn’t have money to burn, of course. Being good business builders, they kept just enough to live on while pouring money back into gradually expanding Rotec—buying more machinery as they could afford it. For three years, Rotec remained a Chernikeeff-only band (Dad Jim—Paul and Matthew) until they could finally afford to employ staff.

Then, in 2003, came the first additions to the Rotec team—a couple of machinists and an engine builder, all of whom joined Rotec just before the company moved to its new (current) factory in 2004. Since 2004, the company has continued to grow and now has ten engineering staff as well as some office and marketing people behind the scenes (including Jim).

Happily, Nestor Slepcev was happy to conduct some flight testing for Rotec with the first “production” engine fitted to his Storch. This proved extremely useful for the company, and the Chernikeeffs are grateful for the opportunity to work with Slepcev to develop the engine in these early stages.

At the beginning, the engine was a direct drive unit, but it was soon realised that a geared drive would make much better use of the engine’s power characteristics. A talented engineer by the name of Bill Whitney assisted in the design of a gearbox that would allow the engine to work at peak efficiency.

Slepcev was mightily pleased with the revised engine, incorporating its new gearbox when it went back onto his Storch. His assistance yet again allowed Rotec to identify and then fix some minor teething problems with the new gearbox, which initially utilised needle roller bearings. Since it was subsequently revised to incorporate pressure-fed plain metal bearings in place of the needle rollers, there have been no further problems with the gearbox.

The basic design of the production engine has changed very little since Slepcev’s (geared) engine left the factory. However, because it is not interested in certifying its engines (unnecessary as the Rotec units are all destined for ultralight, microlight and homebuilt “experimental” aircraft), Rotec is able to maintain a process of continuous improvement, and incorporate minor modifications and detail improvements as soon as a need for them is identified.

One such important need identified in the early days was the lack of cylinder drains for the two lower cylinders. Before the now standard drains were fitted, one or two early engines suffered bent connecting rods as a result of hydraulic lock. This occurs when small amounts of oil drain into the lowest parts of a stationary radial engine (the inverted cylinders) and if the oil is not removed before starting, because it cannot be compressed, it will bend the connecting rods. While an appropriate operating technique makes it possible to avoid such damage, Paul and Matthew realised that many first-time radial owners would be unfamiliar with the correct operating technique and the problem would undoubtedly recur. They repaired the damaged engines at no cost to their owners and modified all subsequent engines with the new drains. Today, in addition to having fitted cylinder drains, Rotec supplies an additional supplement to the already comprehensive operating manual specifically dealing with the issue of hydraulic lock and how to avoid it.

Another design modification that the company introduced early on was to substitute cast alloy cylinder heads for the original machined versions. The substitution was primarily to increase production efficiency and reduce cost, as the machined heads were time consuming and expensive to produce. However, in addition to improving production efficiency, the new heads allowed the two spark plugs to be placed 180 degrees apart instead of alongside one another, which has improved combustion efficiency considerably. As a wonderful “bonus” for Rotec and its customers, the new cast heads immediately conferred a much more “authentic” look upon the engines.

Since the beginning, a good deal of deliberate thought has gone into developing processes that allow Rotec to build consistency and “repeatability” into its engines, according to Paul. He said that except for the cylinder drain-related issues, any problems with early engines—although very few—were solely related to inconsistencies in manufacture and nothing at all to do with design. “Now,” he says, “we’ve engineered those inconsistencies out and eliminated the problems.”

The big success of the seven-cylinder R2800 prompted growing numbers of requests for a more powerful engine, and three years ago, the Chernikeeffs eventually relented and the nine-cylinder 150 hp R3600 was born soon after the move to the new factory. Rather sensibly, the 3600 was pretty much a 2800 with two extra cylinders. Obviously, the crankcase needed revising and there were a few unavoidable changes to accommodate the two additional cylinders, but as much as possible of the 2800’s design and componentry was retained and the diameter of the new engine was only 40 mm greater than the R2800. With around 90 percent commonality between the engines, the company didn’t need to re-design or re-equip its factory. “The nine-cylinder worked pretty much straight out of the box because we’d learned so much with the seven,” said Paul.

The 3600 has expanded Rotec’s market considerably, as the higher-powered engine suits many more (larger) homebuilt aircraft than the smaller 2800. Importantly, the great torque of the radials allows them to spin big diameter and relatively heavy propellers. Their great flexibility allows many more “replica” type aircraft to be built to look far more authentic with “proper” radials instead of the previously “mandatory” horizontally opposed fours and sixes.

Several kitbuilding companies, including Canada’s Murphy and American company Storch Aircraft, now offer Rotec radials as options for their aircraft. In addition to the performance benefits they provide, the radials also offer exactly the kind of “authenticity” many owners seek.

The overhaul life of Rotec’s engines has yet to be properly determined, but is currently estimated at 1,000 hours. However, Paul says this is a very conservative figure. He says the highest-timed engine in the field had only reached around 750 hours as at the beginning of June 2008. The reality is that few recreational aircraft owners will ever get anywhere near a thousand hours; Paul’s own Bowers Fly Baby company demonstrator aircraft, which he flies regularly, has only amassed 250 hours in around three years.

It is well known that the quoted “life” of even certified engines is woefully misleading. The “big two” producers of certified aviation piston engines quote TBOs of between 1,500 and 2,000 hours for their various horizontally opposed offerings. As Paul points out, these are just “numbers” for certification purposes and the reality is that—rather like granddad’s axe with its six new handles and three new heads during its “life”—these certified engines will invariably have had cylinders, heads, valves and other assorted accessories and components replaced (often frequently) well before their quoted TBOs.

Another benefit of Rotec’s “non-certified” status is that the company is able to offer good quality lightweight reliable starter motors, alternators and ignition systems in place of the expensive heavy low-tech and increasingly hard-to-get accessories that “certified” engine builders are forced to use in order to comply with certification bureaucracy. “We believe we can control quality much better than by spending millions obtaining an expensive and highly restricting bit of paper,” Paul says.

Rotec has already built more than 400 engines. Most have been seven-cylinder engines—simply because it has been building them longer, but since it has been producing the nine-cylinder as well, the two types have been selling in roughly equal numbers. Most engines have gone to the USA for installation in homebuilt (experimental class) aircraft, but they have sold around the world; a good number have also sold in Europe, and several in Australia.

A big part of the appeal of Rotec’s engines lies in their aesthetics. They are, quite simply, stunning to look at. It would not surprise this writer to hear that a “radialist” or two around the world had purchased a Rotec purely for display. Indeed, for art lovers prepared to pay millions for individual paintings to hang on their walls, a new Rotec sculpture would seem an absolute steal. Paul and Matthew have always stressed the importance of their engines’ visual appeal and no engine is allowed to leave the factory with any blemishes. “I tell all our guys—machinists and assemblers—that the engine’s performance and reliability will speak for itself in service, but from a marketing and sales point of view, it’s all about the aesthetics,” says Paul.

In comparing Rotec engines to alternatives, Paul does not believe they should be compared to lightweight engines like the Rotax 912 or Jabiru, which are considerably smaller. “Neither of them has anything like our torque. They have to spin at high rpm and use significant reduction,” he says. He believes that their only “direct” competition are engines like the Continental O-200 (100 hp range) and Lycoming O-320 (150 hp range). The respective Rotec engines (110 hp R2800 and 150 hp R3600) are lighter than both competitors (Rotec’s weight figures include all accessories, which are excluded from their competitors’ quoted figures).

Paul says that Rotec isn’t interested in building its engines any lighter. “We could build an engine half the size, rev it twice as high and gear it twice as much, but it wouldn’t sound right and it wouldn’t look right—it wouldn’t be a ‘real’ radial,” he asserts.

While complimentary of the quality of the lighter Rotaxes and Jabirus, Paul says he is somewhat sceptical of their published performance figures. “Horsepower ratings are just numbers,” he says. “At the end of the day, performance on the wing is what counts. You can claim whatever output you like for your engine but if it performs like s***, then your customer won’t be happy. On the other hand, if your engine produces the performance a customer expects—and ours does—then the customer is happy and that’s all that matters.

“Many of our customers are so impressed with the performance from our engines that they come back and tell us we are being too conservative with our numbers. However, I suspect it’s more likely the case that other manufacturers are perhaps a little too ‘ambitious’ in theirs!” In support of his opinion, he points out the rather direct comparison between fuel burn and output, and explains that while modern technology has improved thermal efficiency slightly, the ratio of fuel burn to horsepower still varies only minimally between piston engines of all types.

While purists and pedants might argue over outputs and weights, no one can deny the price advantage of a Rotec engine over its “competition”. A brand new R2800 retails for around the same price as an overhauled Continental O-200 (just the core engine without any accessories) and, despite Paul’s reluctance to “compare” with the Rotaxes and Jabirus, is also cheaper than the Rotax and comparable to the Jabiru.

A new Rotec comes with virtually everything except a fuselage and wings, and includes direct factory support, comprehensive manuals and a one-year 250-hour all-inclusive warranty that commences—not from purchase, as with most engines— but from “first start”. This can be a bonus for homebuilders who might purchase an engine months or years ahead of a project’s completion. New owners simply contact Rotec once they start their new engine for the first time to initiate the warranty.

Rotec currently produces between 70–100 engines a year. Paul wants (and expects) the total to consistently exceed 100 engines a year before long.

The return of the radial, thanks to two determined Aussie geniuses, has put smiles on the faces of “real” aviation enthusiasts around the world. The thought of owning a new Rotec engine is even enough to make one consider buying an appropriate aircraft just to be able to hang a Rotec on its nose!

When the writer suggested to Paul Chernikeeff that Rotec’s next project should be to design and build an aircraft specifically to make the most of their inspiring radial renaissance, he was greeted with a rather conspiratorial smile: “Like a Steraman replica…or something, you mean?”