Inside Rotax

It's really a factory within a factory. The company leverages high-volume recreational engine output to help sustain its aircraft motors.


If it’s indeed true that mighty oaks from little acorns grow, the mechanical analog for that lives in a small glass case in the lobby of the Rotax factory in Gunskirchen, Austria. It’s so small, in fact, that you’d surely miss it if a diligent tour guide didn’t point it out.

The artifact is a small hub, about the size of that in a typical bicycle, but it was meant to be a ratcheting or rotating axle for an early motorized bicycle. From rotating axle comes… Rotax; the tiny acorn grew into the $3 billion-plus engine manufacturing giant that Rotax is today.

Pilots and builders know Rotax as an aircraft engine builder, but from the inside, the company views itself as a manufacturer of engines for recreational products, and airplanes are just another form of recreation that includes all-terrain vehicles, snow machines, and personal watercraft. If nothing else, Rotax knows its niche well, but it’s also a company willing to take the risks of large investments and long payouts that are so characteristic of aviation.

Last June, Rotax celebrated both the 25th anniversary of its first four-cycle aircraft engine and the 50,000th engine off the assembly line, a new 912 iS Sport. The company invited a small group of journalists to cover this event and, as part of that, I talked them into giving me a full day to myself of reporting and shooting inside the factory.

Rotax wouldn’t let us shoot the mass assembly side, but this company-provided photo shows machining and assembly operations. Rotax leverages this capability to improve quality and economy of scale on the aircraft side.

Bikes, Boats, Planes

The modern Rotax factory is situated in the industrial triangle of Austria, in the town of Gunskirchen in north-central Austria, not far from the Czech Republic border. It’s not there by accident; this region was traditionally a steel-making and manufacturing center, and both the KTM motorcycle and Steyr diesel engine factories are nearby.

Rotax was originally a German company but moved to Gunskirchen from Germany in 1943. It has been at its present site, much expanded, since 1947, and Rotax aircraft engines are built in the company’s original building.

But that’s not to say Rotax started with aircraft engines. During the late 1940s, Rotax built scooter and agricultural engines, but expanded its two-cycle engine line when Canadian Joseph-Armand Bombardier invented the Ski-Doo line of snowmobiles in the early 1960s. In 1970, with sales booming, Bombardier bought Rotax, renaming it Bombardier-Rotax GmbH.

Thanks to their reputation for durability and reliability, Rotax’s two-cycle engines proved durable and popular for snow machines and led quite accidentally to the company’s entry into aviation. During the 1970s, Rotax noticed a spike in sales for engines, but they weren’t going into snow machines. An investigation revealed the engines were being used in the then-burgeoning ultralight aircraft market. This led to the development of the Rotax 447, the 503, and the 582, all two-stroke, geared aircraft engines, many of which are still flying.

Looking down the length of the assembly line, engines move along a track on a traveler jig. The shop produces about a dozen engines a day, but has higher capacity.

By the late 1980s, Rotax saw potential for small, four-stroke aircraft engines that would be lighter than offerings from Lycoming and Continental and thus suitable for European ultralight aircraft—and Experimentals—that were then on the horizon. Thus was born the 80- and 100-hp 912 series and, eventually, the 115-hp turbocharged 914 engines. Continuing the evolution, Rotax two years ago introduced the 912 iS and in the spring of 2014, it followed with the 912 iS Sport. With electronic fuel injection and FADEC, these engines represent the state of the art in aircraft powerplants, albeit on the low side of the horsepower scale.

By 2014, Rotax had built 170,000 aircraft engines—50,000 of them four strokes. That’s a pile of engines, but it’s a fraction of the current factory’s total output, which is about 215,000 engines a year. Most of those go into the ATV, watercraft, and motorcycle markets, with aircraft accounting for 3000 to 4000 engines a year. Rotax has also dabbled in small industrial and power generation engines, but it sticks to what it knows—small displacement recreational engines.

Unlike conventional aircraft engines, Rotax incorporates the alternator into the flywheel, motorcycle style. This photo shows the alternator windings inside the housing.

Small is Big

Like other European manufacturers, Rotax’s ethos is efficiency, light weight, and environmental friendliness. And that means Rotax isn’t a signatory to the there’s-no-replacement-for-displacement mantra. Its four-cycle engines range from 1211 to 1352cc or 73 to 82 cubic inches, less than half the displacement of equivalent Lycoming and Continental powerplants and about 45 percent less weight. For instance, in the typical small Experimental or LSA, the Lycoming O-235 gives up about 100 pounds to the Rotax 912ULS. The Lycoming has 15 additional horsepower, but the Rotax still enjoys a massive edge in power-to-weight ratio.

How do they do this? One reason is that the engine and components are simply smaller, especially the crankshaft which, unlike traditional aircraft engines, is a multi-part, assembled crankshaft. It consists of 10 separate components—four one-piece rods and six crankshaft components, all pressed together.

“This means,” says Rotax’s Christian Mundigler, “that the crankshaft is 40 millimeters shorter and 40 millimeters narrower and also lighter than a Lycoming or Continental by 12 kg (26 pounds).”

The crankshaft comes into the assembly shop as a pre-pressed piece with single-piece rods already attached. Before installation, it’s checked for lateral runout.

Although the engine is similar to a Lycoming in other respects, to deliver the same power, it’s much higher revving—like about 5500 rpm at peak power, depending on the model. And that brings some disadvantages, one of which is higher piston speeds and resultant frictional losses and also the need for a gearbox, which adds weight. But Rotax turns this around and touts the gearbox as a plus.

“With the gearbox, we can use a larger-diameter propeller which is more efficient and is better for noise,” adds Mundigler. Rotax claims a 15 percent edge in prop efficiency over a direct-drive engine, although Lycoming and Continental drivers might argue that their larger-displacement engines have comparable performance. The words gearbox and “much loved” don’t often appear in the same sentence, but the Rotax box has proven to be quite bulletproof and routinely reaches the 2000-hour engine TBO. The gearbox offers one other advantage that’s unique to Rotax: a dual-mode clutch. (See sidebar.)

As far as fuel economy goes, thanks to smaller displacement, the 100-hp 912ULS typically burns .8 to 1.3 gph less than an O-235 or O-200 or as much as 20 percent less than traditional four-bangers. While that’s significant, it’s often not enough to sway some builders away from traditional engines, despite the weight advantage. I’ve heard so many chainsaw and snowmobile jokes that I’m convinced that what wins the argument for many builders is the sound of the exhaust note. And price. Used O-235s are less than half the price of a new 912 iS.

Rotax hopes the iS’s technology will sweeten its appeal. At 100 hp and 12 extra pounds (5.4 kg), the iS has delivered fuel economy routinely up to 30 percent better than the 912ULS, which already bests the Lycoming and Continental equivalents. It’s also a 16 percent price premium over the 912ULS, but for an owner who flies a lot, that could pay back before TBO.

As with conventional aircraft engines, the build goes from the inside out, beginning with installation of the crankshaft and rods.

Building Them

Rotax’s Gunskirchen plant is really a factory within a factory. The vast majority of Rotax engines are made on a pair of assembly lines more reminiscent of an automotive engine plant than anything we’ve ever seen in aviation.

Compared to Lycoming, Rotax is much more vertical; it makes nearly all of its own parts, although primary founding and forging is done by other companies, many of them in Austria. “This really is an Austrian engine,” Mundigler told me during my day on the factory floor.

The two mass assembly lines for ATV, motorcycle, and marine engines, move at a brisk pace, turning out about 350 engines per shift, but capable of higher output. Start to finish, a Ski-Doo engine goes from parts bins to test-cell ready in about two hours. The line is highly sophisticated, with RFID (radio-frequency identification) technology to track the engines and parts by serial number and electronic torque wrenches recording every bolt and nut turn in detailed databases for future accountability. If a worker misses a step, the line stops and the alarm bells ring. Not a good career move.

There’s not much to the Rotax gearbox. Just two gears, plus a starter gear. The gearboxes have proven reliable and robust.

The insatiable maw of the production line is fed by a massive machine-cell apparatus that’s almost entirely automated. It turns out parts in the thousands for everything Rotax makes, including aircraft engines. It’s not unusual to walk rows of machinery and not see a soul. In one cell, we watched a pair of robots install valve seats. First, it confirmed the right part with a quick snapshot, squirted the seat with liquid nitrogen to shrink it, then plopped it into the seat boss; one after another, every 15 seconds, all day. The machine and assembly area hum with constant clatter and the slow of foot can easily get run down by a parts cart.

The aircraft engine assembly area is rather different. Located a short walk from the main factory in the original Rotax building, it’s like entering a library. It has a production line of sorts, but not an automated moving line. The engines are assembled as they might be in an overhaul shop; they’re one-off and move down an oblong bench on a track traveler. At work stations around the assembly bench, sub-assemblies are built up—the cylinders get their heads, valves, and pushrod tubes, the gearbox is assembled, pumps are built up, the alternator components are prepared and so forth. Assemblers are cross-trained in the various stations and tasks. Most are drawn from inside the factory, having come up through Rotax’s formal apprentice system.

Most critical torque settings are done with electric tools with the production system automatically setting the amount and recording each torque in datasets that live in the engine’s virtual build.

Tracking and Tracing

In any manufacturing, traceability is a tall challenge and more so in aviation. Low volume complicates this. Lycoming and Continental struggle with low-volume/high-mix manufacturing, and although Rotax has less mix—only five base models with little variation—there’s a yawning gap between what the main factory does and what the aviation side does. Mundigler told me Rotax has used this contrast to its advantage, integrating techniques from the mass production side into the low-volume aviation side and vice versa. But the aviation side is still considered the elite.

“Only the best can work here. Everyone wants to work on the aircraft side,” Mundigler told me. The assembly work is far from rote; it requires the skill to measure, analyze, and use discrete tools and processes. Rotax recognizes this and gives the aircraft assembly staff one 10-minute break per hour, while in the main factory, it’s three breaks per day.

For quality control and traceability in assembly, Rotax uses two methods: computer monitoring and so-called four eyes. A program called Filemaker stores a virtual engine as a master.

Rotax cylinder heads are water cooled, while the barrels are air cooled. The heads are attached during assembly, not screwed on to an interference fit, as with Lycoming and Continental.

“We build the engine in reality and in the Filemaker system,” Mundigler explained. “When he is ready and he hands the engine to the next guy, he has to check off to see everything is done.” The file stores all of the principle torques and tightening sequences and traces every part installed. That data lives with the serial number for the life of the engine. For those processes that the computer can’t track through tool monitoring, a second assembler claps eyes on and checks the work—the “four-eyes” method. In addition, incoming parts are subject to inspection, some at 100 percent, such as pistons, and some through statistical process control.

Engine assembly begins, as it always does, with the crankshaft and cam inserted into the case, followed by the cylinders, induction system, and accessories, including the gearbox. In the final stages, the electrics are added and final dressing is done. I didn’t time it, but I’d guess the trip around the assembly bench takes an hour or so. Watching the assembly in detail impressed me with how simple the engine really is and makes me wonder why it gets so complicated when I apply a wrench to it.

Each engine is built both physically and virtually in Filemaker. All the parts right down to fasteners are traceable, as are the torque settings and who did the assembly work.

After final dressing, the aircraft engines are shipped off to the test cells for trials. They’re run for 50 to 90 minutes, depending on the model and whether the engine is certified or not. The major bottleneck in production is obviously the test cells, even in the low-volume aviation side. If a dozen engines trickle off the line a day, the cells have to run multiple shifts to keep up. On the mass assembly side, the engines run for just a few minutes. Nonetheless, the factory burns more than a 1000 gallons of gas (4000 liters) a day just testing engines—seven days a week. It recovers that otherwise lost energy to produce nearly half of the plant’s electricity. As do Lycoming and Continental, Rotax tears down a couple of engines a month as audit engines, inspecting them for wear after initial run-in.

“With this procedure, we learned more about the engines over the years, and we can steadily increase the overhaul times,” Mundigler said.

Pistons are matched to cylinders in two tolerance sizes; each is stamped with its measured diameter. Pistons are checked for weight and must be within 2 grams of each other in the same engine.

Where To?

Given the anemic market, Rotax’s introduction of the 912 iS two years ago was a surprise and the Sport debut—really just improved induction—more so. If this means that Rotax is bullish about getting into the mid-power market with a 150- to 180-hp engine, they were coy about deflecting questions about their plans.

“When you look at the future, people want more power. The industry is going toward four seaters. So that’s something we’re looking into now, what should be our next level. We’re looking at various options,” said Francois Tremblay, head of the BRP Powertrain group. It’s easy to see the market space if not to pencil out a business case. A 160-hp four cylinder that weighs 75 pounds less than a Lycoming IO-320 or -360 might just find a niche, albeit at a higher price point for builders inclined to buy used engines.

From the main assembly line, engines are dressed and prepped for the test cell. These 914s are identifiable by their red valve covers.

Prior to heading for the test cell, engines get final assembly details and inspection.

Price remains a challenge. The 912 iS burned a bunch of money to develop, but Rotax justifies the investment by projecting a 20-year life cycle. Thus far, in two years, it has sold about 500 912 iS engines; not bad, but for the other side of the factory, that’s but a day’s work. And some, if not most, of those sales have displaced 912ULS engines, which Rotax would have sold anyway.

Rotax’s last foray into higher horsepower was the six-cylinder V-6 announced in 2004 and cancelled in 2006. Production tooling had been built and the engine was about to launch when Rotax scrapped it, realizing that the business case for it, weak to begin with, had simply evaporated. Also, the company had undergone a transition, separating into its own entity from the Bombardier Recreational Products mothership. In retrospect, it seems likely they made the right decision.

But Rotax is clearly a company with a vision that extends beyond the next business quarter. It’s not afraid to venture into markets where the payback is years in the making. Around Gunskirchen, BRP CEO Jose Boisjoli is often quoted as having said he didn’t know a thing about aviation, but he appreciated the passion and that was more than reason enough to invest in it. That’s a sentiment not often heard from multi-billion dollar companies and thanks to it, the market has at least a few more choices.

Every new engine is wrung out on the test bench for between 50 and 90 minutes. All operating parameters are stored and retained.


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