February 28, 1998 Katana Gets a Continental

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by	Paul Bertorelli
	This article originally appeared in THE AVIATION CONSUMER and is reprinted here by permission.

About the Author ... Paul Bertorelli is a professional aviation journalist and editor. He's Editor-in-Chief of The Aviation Consumer and editorial director of AVweb and Belvoir Publications' Aviation Division. He's a 4,500-hour ATP and CFIA/CFII/CFIME. He owns a Mooney 231.

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When Diamond Aircraft's snazzy little Katana emerged into the flight training scene three years ago, it seemed an easy setup for a bloody nose or two.

"Way too small," some said.

"A plastic airplane? Are you kiddin'? That thing won't last a month on the training line."

"No way I'm instructing in any airplane with a chainsaw engine."

While that carping may have some merit, the Katana has nonetheless established itself as the leading-edge trainer for the 1990s, with some 300 airframes toiling away at flight schools across the country. That Diamond has the new trainer market virtually to itself doesn't hurt. But the fact remains, the Katana seems to be delivering on its promise of being a new-age trainer that's both fun and cheap to fly.

Still, those wisecracks about the engine have scored some hits. It's easy to get past the Rotax 912's braaapy exhaust note but not so easy to ignore its 81 HP, which delivers respectable cruise speed but anemic climbs at high density altitudes and high weights.

Diamond's response to this shortcoming rolled off the company's London, Ontario assembly line last fall in the form of the Katana C1, an improved airframe sporting a 125 HP Continental IO-240. Frankly, warts and all, we liked the Rotax-powered version well enough to recommend it without noteworthy reservations. The C1 represents significant enough improvements over the original to nearly qualify as a different airplane.

Diamond plans to sell both Continental- and Rotax-powered Katanas but both engines will be installed in an improved, lighter airframe. The TCM version is the Katana C1, the Rotax version will be called the Katana A2. (The original Rotax model is now the Katana A1.)

Editor's Note: Since this article was published in early 1998, Diamond has dropped the Rotax engine for new Katanas and is offering only the Continental-powered version. However, it continues to support the Rotax-powered models and many are available on the used market.

Hard to say how the market will respond but we predict that if Diamond sticks with the realistic marketing plans it has thus far pursued, the C1 will eventually displace the Rotax version and likely earn a reputation in the training arena similar to the venerable Cessna 150/152 series. Assuming, of course, that the IO-240 develops no nasty maintenance traits and that its higher fuel burn isn't a significant issue.

Rotax vs. Continental

When Diamond morphed the Katana from the Austrian-designed Super Dimona motorglider design, it took a sizeable gamble on the Rotax powerplant. Rotax is well-known in Europe and in the U.S. for two-cycle ultralight engines, which have also found their way into homebuilts.

But the four-cylinder 912F3 represented its first foray into FAR 33-certified aircraft engines and Diamond openly admits to an uphill battle convincing buyers that this was no snowmobile engine. Indeed, with electronic ignition, autoleaning carburetors and water-cooled cylinder heads, the Rotax has more in common with a Honda Accord than a Cessna 152. Moreover, it has a controllable pitch prop, which some flight schools were bound to shy away from due to worries about training and maintenance complexities.

Although relatively cheap to replace — $6000 initially for both an exchange engine and prop — the Rotax's out-of-the-box TBO was only 1000 hours. TBO has since been raised to 1200 hours but the exchange cost has ballooned to $10,100, meaning the hourly engine cost is about $8, versus about $6 for the Cessna 152's O-235 Lycoming. However, since the Katana burns half the fuel, its direct hourly operating costs — on paper, at least — edge out the 152 by a couple of bucks or more.

In nearly 200,000 hours of total fleet time worldwide, says Diamond, the Rotax has turned in a respectable if not stellar service history. Some operators have easily exceeded the recommended 1200-hour TBO and, of course, a few have come up short. The Rotax has had its share of cylinder problems and inevitable operator-induced glitches, plus a handful of premature failures, none of which involved the engine's bottom end. Maintenance-wise, mechanics haven't exactly taken to the Rotax like ducks to water.

"We find that sophisticated operators — the UNDs [University of North Dakota] and the larger schools — love it. Some of the smaller operators don't," says Diamond CEO Michael Slingluff. "If it's in Pete's Aircraft Maintenance, Pete is trying to find the mags so he can tap on them to get it going, just like he does with a Lycoming. That's not going to work on this engine."

More to the point, the Rotax is an adequate performer in moderate weather and light weights but a bit of a dog when the weather turns hot and humid or at high density altitudes. Operators have complained about 300 FPM climb rates in the pattern than can make a few touch and goes an all-day affair. Even a ratted-out 152 can do as well or better.

Further, Diamond is learning what other airframe makers have: Putting all your eggs into one vendor's basket is risky. Although Slingluff and Diamond's sales manager, Jeff Owen, say they're still sold on the Rotax, they also note that the company has not raised its profile in the U.S. with the kind of national advertising and behind-the-scenes technical support that Lycoming and Continental have routinely provided.

Although Rotax has technical developments in the works — including a 100 HP 912 variant — Diamond has had to shift for itself on many technical problems that engine vendors traditionally tended to in the past. Further, Diamond needed to address the Katana's anemic climb performance forthwith, preferably with an off-the-shelf engine.

Clean Sheet

Continental's IO-240 is a clean-sheet powerplant introduced four years ago, primarily for the homebuilt market. The initial version, the IO-240 A1, had fuel injection but with TCM's traditional log-and-runner induction system. But Diamond wanted a more state-of-the-art powerplant.

The IO-240B is just such. It has a balanced topside induction system similar to that used on the larger displacement IO-550G found in the Mooney Ovation. Otherwise, its systems and components are identical to those found on any other trainer and will thus be familiar to any maintenance shop.

In comparing the two installations, we noted a striking contrast: The Rotax, with its watercooling and electronic ignition, is festooned with hoses, wires and sensors, while the Continental has but a few umbilicals. The IO-240's accessory case-including the oil filter and mags-are readily accessible for maintenance, although it's a tight squeeze for the mags. The alternator — a belt-driven 40-amp Nippondenso — is mounted frontside, automotive style. Production C1s will have a TCM lightweight starter. Outwardly, the C1's snout is less pug nosed and the overall length is 1.6 inches greater. Natch, since the Continental is air cooled, the Rotax version's sealed cowl has given way to a couple of small cooling inlets. There are more changes beneath the skin; the emergence of the C1 model is coincident with a number of minor but significant airframe improvements which will be incorporated into both the TCM C1 and Rotax A2 airframe.

To account for the Continental's higher weight — 246 pounds versus 160 pounds for the Rotax — Diamond squeezed 60 pounds of excess weight from the airplane, chiefly by retooling to produce composite parts more precisely and with better repeatability and by switching from steel to aluminum gear struts.

To account for the more forward CG, the wing sweep was increased 1.5 degrees, the nosegear tire size was decreased and the battery was moved from the firewall to a bulkhead behind the baggage compartment shelf. Further, the C1's gross weight was increased to 1653 pounds, from 1609 on the Rotax-powered version.

Other changes include:

• A redesigned horizontal stab and elevator that's larger and reduces parts count by eliminating an anti-servo tab
• Replacement of simple hinged flaps with modified slotted flaps
• Improved two-stage canopy latch
• Improved brake master cylinders
• Instrument panel moved higher and more forward, creating more knee room
• Higher recline angle on seatbacks
• Improved heating and defrosting system
• Additional instrumentation, including EGT, fuel flow and large tachometer

Price, Payload

IO-240: As the Numbers Crunch In its initial sales pitches, Diamond predicted an hourly direct operating cost of about $23 for the Katana, compared to $31 for an elderly Cessna 152. This was based in part on the Katana's miserly fuel burn and relatively inexpensive engine replacement costs. Although the Rotax had only a 1000-hour TBO, it initially cost only $6000 for an exchange engine and prop, a figure which Rotax has since increased to $10,100. Using the Rotax's recently approved 1200-hour TBO, that works out to $8.40 per hour for engine replacement, plus $7 for fuel ($15.40 total) compared to about $18 for the Cessna 152, $5 for the engine and $13 for fuel. The IO-240 is so new that reliable overhaul figures aren't yet available. TCM pegs the factory reman price at $16,470 but a more realistic field overhaul cost is probably about $15,000. Over a 2000-hour TBO, that's comparable to the Rotax, at $7.50 per hour. If the Rotax is taken beyond TBO-and some operators have-its hourly cost drops. Specific fuel consumption is virtually identical between the Rotax and the Continental, but the IO-240 delivers more power which comes at the price of higher fuel burn. In economy cruise, the Continental's burn is comparable to the Rotax but trainers aren't often operated in economy cruise. They fly full-power climbs and trudge around the pattern. Composite fuel burn drives the cost equation. If that turns out to be two gallons more than the Rotax, hourly direct engine costs will inch upward, possibly exceeding the Cessna 152 benchmark. Overall operating costs, however, should still remain competitive, since the Katana's overall maintenance costs-engine and airframe-may be marginally less than the 152's.

The C1 sells for $114,260 versus $112,125 for the new A2. The numbers cover a basic airplane, certified for night and day VFR but not IFR. Diamond has no plans to certify either model for IFR, which has been a source of some irritation to buyers. The DA 40 four-place version, under development in Austria, will be IFR-certified. It will also be Continental-powered, using a 170 HP version of the same IO-360-ES Cirrus picked for the SR 20.

A line-by-line performance comparison between the C1 and the existing Katana reveals that the higher horsepower doesn't yield improvements across all categories. The C1 cruises and climbs faster, but its payload with full fuel is 364 pounds versus 394 pounds for the Rotax-powered variant. However, the C1 carries 4 more gallons of fuel than the A1, so with equivalent fuel, they're about equal in payload.

In the real world of flight training, this means that in the C1, a student and instructor each weighing 200 pounds can launch on a cross-country with 18 gallons of gas. They'll have to watch fuel consumption carefully; learning leaning will be a must.

According to Diamond's preliminary specs, at 65 percent power and 123 knots, that 18 gallons will last a bare two hours or, with careful leaning, about 2:35. Reducing to the max range cruise of 50 percent power drops the fuel flow to 4.8 gallons leaned at a speed of 109 knots, stretching the endurance to 3:45.

In the Rotax version, student and CFI taking off with the same 18 gallons could cruise at 110 knots, burning 4.5 gallons for an endurance of 4 hours.

The A1 Katana has a service ceiling of 14,000 feet, versus 13,000 feet for the C1. Landing and takeoff distances are comparable, although the C1 enjoys a slight edge in landing performance.

Flight Impressions

Right from start-up, the C1 clearly has a noticeably different personality than the Rotax-powered Katana. Rather than the car-like start procedure used to fire up the Rotax, the IO-240 starts like a real airplane motor: mixture rich, pump on and crank. You can feel the loppy idle through the airframe, rather than sensing it as a distant vibration somewhere beyond the instrument panel, as with the Rotax.

The downside of fuel injection is usually cantankerous hot starting. After our flights, we did try a couple of hot starts. With throttle open and mixture at idle cutoff, the engine seemed to catch and fire within a half dozen blades.

However, with that light prop up front, the engine screams to max RPM right now. On hot starts, a student will have to be both dexterous and quick with throttle and mixture or risk having everyone on the ramp dash for cover. One shortcoming of the Katana is a certain nervousness during taxiing. Since it lacks a steerable nosewheel, differential braking keeps it on the yellow line. However, the brake pedals are close together and in the original model, all but the daintiest feet collide with a structural shelf on the back of the firewall.

In the C1 and A2 airframes, the shelf is gone and improved brake cylinders give the airplane more manageable ground handling. The ground turn radius is also smaller, thanks to a limit adjustment in the nosewheel.

When we flew a prototype C1 in late fall, Diamond hadn't yet settled on a prop for the new design but will probably offer a choice of three: two Senseniches — one a cruise pitch, the other a mid-range — and one Hoffman pitched for cruise speed. We flew first with the Hoffman prop, then Diamond flight test pilot Bob Salton did a quick prop change so we could try the Sensenich.

Before flying the C1, we took a few turns around the patch in a Rotax-powered Katana to re-familiarize ourselves with its performance. By comparison, on the takeoff roll, the C1 with the Hoffman cruise prop accelerated more briskly, although not dramatically so.

Rotation is at 50 knots, same as the Rotax version. Climb rate is dramatic. Diamond claims an initial rate of 920 FPM for the Hoffman-equipped C1 and we noted a bit more, nearly 1100 FPM at 80 knots, this despite the fact that the rather coarse prop limited static RPM to 2350.

We noted that the airplane could easily maintain 800 FPM in a cruise climb to the practice area without heroic deck angles. Noise and vibration of the Continental/Hoffman combination are perceptibly different than the Rotax but not necessarily greater, in our view.

Diamond claims a cruise airspeed for the C1 of 132 knots TAS at 75 percent power at 6000 feet, which, according to the draft POH, will burn 7.3 to 8.3 GPH leaned. We noted about 126 knots TAS, at about 70 percent power at 2500 feet. By comparison, the Rotax Katana typically cruises at 110 to 115 knots on 4 to 4.5 GPH. With the flatter Sensinich prop, the IO-240 cranked to 2500 RPM on the takeoff roll and literally careened down the runway with noticeably quicker acceleration and an initial climb rate of 1300 FPM at 80 knots.

However, Diamond notes that this prop will need repitching for use in a trainer; it's simply too flat. Even in a 90-knot climb, it's possible to reach the engine's 2800 RPM redline and full throttle in cruise will easily exceed 3000 RPM. Our guess is that the ideal prop is the Sensinich pitched closer to the Hoffman's cruise setting.

How about a constant speed prop, as in the Rotax-powered version? While we feel that prejudices against a CS prop in a trainer are unjustified, it may not be an option for the C1 because of excess weight and the fact the IO-240 lacks a hollow crankshaft to flow oil into a prop hub. Diamond is considering an electric three-blade CS prop, but it won't be an option in the first C1s, if at all.

No Surprises

With the additional weight out front and larger tail section, we wondered if the Katana's handling characteristics had changed. It appears to retain the same handling of the original, with light to medium maneuvering stability and no tendency to drop a wing or bite in a stall, no matter how aggravated. (The C1 airframe has stall strips, the earlier airframe doesn't. They were installed to correct a slight wing drop tendency.)

In our view, the addition of Fowler flaps which deploy to 45 degrees versus 40 degrees for the A1 made little noticeable difference in approach and landing characteristics, although preliminary data for the C1 says it will land over a 50-foot obstacle in 1280 feet versus 1490 feet for the Rotax Katana. With the climb-pitch prop, reducing power induces a high sink rate, so it was hard to judge the effectiveness of the flaps.

In both airplanes, using the recommended 60-knot approach speed into a 10-knot quartering headwind, we were easily able to make the first turnoff on London's runway 27, a distance of about 1100 feet. In our opinion, the Katana remains an exceptionally easy airplane to land well, a desirable characteristic in a trainer. With practice, we're sure 600-foot landings would be a snap.

Although it's not obvious at first glance, Diamond has improved the Katana's cockpit layout by more logically grouping switches and adding additional conventional instrumentation for the IO-240 version. The extra knee room under the panel is a welcome addition as are minor touches, such as redesigned controls for the heater and defroster and the ability to mix heat and defrost, plus convenience improvements such as a pocket in the baggage compartment for a couple of quarts of oil.

Students and instructors have complained about the Katana's torturous and non-adjustable seatback angle so the improved version reclines more gracefully. At first, this seems to place the pilot too far from the stick and panel but it's not troublesome in flight, once the adjustable rudder pedals are set. We didn't fly the C1 long enough to judge the seat comfort; we'll wait until the model is in the field and contact operators for their views.

Conclusion

There's no doubt in our view that the C1 engine/airframe addresses the Katana's few faults, especially the anemic climb performance. Over the long haul, its slight additional purchase cost is not significant.

The Katana has found virtually no market as a weekend fun flier; it's a working airplane and a few grand leveraged over the life of the airframe is trivial, in our view. Whether the IO-240's higher fuel burn will raise operating costs enough to be a bottom-line factor remains to be seen.

There's also little doubt that the IO-240 performs as advertised and seems to us like a terrific choice for the Katana. The great unknown is how this relatively untested engine will fare in the day-to-day grind of flight training. Diamond reports the 240 has survived the rigors of certification flying without a hint of complaint but students have a way of driving wedges into the tiniest flaws in trainer engines.

The IO-240 won't be proven until a few C1s bounce through a couple of thousand hours of training. Nonetheless, worries about the motor wouldn't stop us from buying a TCM-equipped C1.

Ironically, the C1's introduction represents nothing less than a real-market flyoff between the high-tech Rotax and the old lump-of-iron approach of TCM. (Okay, so it's a tuned-induction lump of iron.) When we visited Diamond last spring, one company official jokingly referred to the C1 as a "Fred Flintstone engine in a George Jetson airplane."

There's sad truth in that observation. Buyers have whined for years about the industry's lack of innovation so Diamond is offering two clear options: Pay about the same amount of money and take your choice between bleeding edge and improved but old technology.

Continental has recently purchased Aerotronics Controls, Inc., an electronic engine control company, with the stated purpose of developing electronic controls — presumably single power lever-for TCM engines. The time line is reportedly aggressive and we wouldn't be surprised to see such controls applied to the IO-240, nudging it toward the technological equivalent of the Rotax, less the water cooling.

For any buyers considering a Katana, we recommend flying both versions before deciding. The C1's additional climb performance could be a must-have and worth the few extra dollars for a flight school suffering through the doldrums of high density-altitude summers.