Cessna 182 JT-A
Cessna 182 JT-A
Cessna 182 JT-A
Over the years I’ve flown around a dozen varieties of the Cessna 182, from the latest glass-panel turbo models to impeccably restored early birds, but I’d never experienced anything like this. As I advanced the single black lever in Cessna’s new 182 JT-A to roll around the corner onto 19L at Wichita’s iconic Mid-Continent Airport, I felt a smooth surge of power.
If I hadn’t known that there were four big pistons up front, beating their way up and down inside a beefy metal case, I’d have thought this thing was jet powered. I advanced the short-throw power lever smoothly and reveled in the smooth rush of power, and we were off. At 55 knots we were flying; I stowed the flaps, pointed the nose upward and just listened.
As we climbed out through the impossibly clear and hot Kansas day, I couldn’t help but think of all those Cessna 182s, those tens of thousands of sheet metal birds that had rolled off the line these past 50-odd years, and I knew I was hearing something different, a sound that would very likely be the future of light GA. It’s the sound of a piston compression engine. That’s right: a diesel.
In Oshkosh, Wisconsin, in late July, Cessna announced that it would replace its T182T turbo Skylane in favor of a model that burned jet-A. The new model, at first dubbed the 182 NXT but now referred to as the 182 JT-A, is on track for certification early next year with deliveries by the middle of the year.
The decision by Cessna to not only introduce a diesel model but also to discontinue the turbocharged gas piston version speaks volumes about the confidence that the Wichita manufacturer has in the new engine and its new partner, SMA. It was a bold business decision, but that confidence seems to have already begun to pay off in orders from North American and overseas customers.
Why Diesels, Why Now?
For the past couple of decades, there have been high hopes for the future of aviation diesel-engine technology. Today, the technology’s future seems especially bright, in part because everyone agrees that the future of 100LL, our current avgas, looks so dim. The Environmental Protection Agency, which regulates contaminants (but not airplanes, luckily), hasn’t announced just when it will pull the plug on 100LL, but it could happen at any time, and there’s no telling how long the agency would give us to make the transition.
Diesel engines, which historically have been regarded as dirty, loud, sooty and inefficient, are getting better in just about every way imaginable. Today’s automotive diesel engines are clean, powerful and remarkably fuel-efficient. A couple of engine manufacturers, Thielert (now Centurion Engines) and Austro (a sister company of Diamond Aircraft), have leveraged automotive diesel engine technology into aviation diesels that are certified and flying on hundreds of airplanes, though all has not gone smoothly. The Thielert engines famously suffered from early and severe reliability woes, largely due to issues with their accessories, mainly their gear box.
While the search is on for an unleaded avgas alternative, it doesn’t look like a short process. There are no early favorites and no clear timeframe for the adoption of a new standard avgas. Cost issues, moreover, are complicating the matter. While in North America 100LL is easy to find and no more expensive than jet-A, in some parts of the world, low-lead avgas is difficult or impossible to find; we’ve heard reports of 100LL costing as much as $20 per gallon. Jet-A, on the other hand, is available worldwide.
While it’s not realistic to expect that owners are going to replace their gas piston engines en masse with diesels, new-production airplanes outfitted with diesel-technology engines are a natural next step and will doubtless achieve great popularity in many parts of the world where it’s hard to get or afford 100LL but where jet-A is at nearly every airport.
Diesel engines bring a number of additional benefits beside that of simply not using 100LL. In terms of emissions, diesels emit fewer harmful emissions (for the most part) while being able to drive the prop at low rpm (for substantially lower noise levels). They have the huge additional advantage of being extremely fuel-efficient at the altitudes where small airplanes mostly operate. In theory, a well-designed, powerful diesel engine (or a pair of them?) would be a tough matchup for any other comparably powerful engine technology — piston, turbofan or turboprop — up through the low 20s.
SMA is not a brand-new company, and some of our readers might recall an SMA diesel aero engine from the recent past. Indeed, French company SMA, which began as a joint venture between Socata and Renault, launched a diesel engine, the SR305-230, in 1997. First flight was in 1998 in a Socata TB-20 Trinidad. That engine, which was not a big seller, was a purpose-built 230 hp engine with direct drive (no prop-reduction gear box), modest turbocharger capabilities and low rpm. It earned European certification in 2001 and FAA approval a year later. The engine was initially marketed toward the retrofit market, and an STC was awarded for the installation in some existing models of Cessna 182s.
Last year the company, which is today part of the Safran group, earned certification from the European Aviation Safety Agency and the FAA for a greatly enhanced model, the SR305-230E. A close variant of this engine, the SR305-230E-C1, is the model that Cessna will install in the Skylane.
The new engine is based on the original 305 design but features a few game-changing improvements. First, its turbocharger is bigger and more powerful, resulting in greatly enhanced performance and operating envelope. As installed via STC in existing Cessna 182s, the original engine had a ceiling of just 12,500 feet and a critical altitude of sea level. The critical altitude is the altitude at which the turbo will no longer bring the power up to a sea level value. Thus, even though the former engine was technically turbocharged, it behaved for all intents and purposes like a normally aspirated model.
The new version boasts a critical altitude of 10,000 feet and gives the Cessna 182 JT-A a ceiling of 20,000 feet. There is, not surprisingly, a new, larger intercooler too, to keep up with the hotter-running turbo. There’s also a feature that automatically adjusts the timing to allow for optimum performance at idle, at low power and for starting. Indeed, the new engine starts more easily when it’s cold, and it restarts more readily at altitude (in the case of a flameout). It also boasts improved temperature margins for better reliability, as well as a backup fuel pump for smoother operations at altitudes above 15,000 feet. Cessna is going to try to certify the JT-A for operation without anti-icing additives as well. TBO stands at 2,400 hours, and there are indications that it could climb even higher. All things considered, the E-model engine represents a quantum leap for SMA.
While the name SMA is not well known to most North American pilots, the company has solid roots. Its sister company Snecma is a global manufacturer of commercial aircraft engines, engines for military applications and rocket motors, among other products. It employs nearly 60,000 people, has 35 locations around the world and had sales of around $14.5 billion last year. Snecma manufactures the Silvercrest engine that Cessna announced would be on the new large-body Longitude jet it unveiled at EBACE (European Business Aviation Convention and Exhibition) earlier this year.
The missing ingredient in the relationship was service. While SMA has headquarters in France and its parent Safran has facilities in Grand Prairie, Texas, Cessna decided to make sure that there were adequate service options for future 182 JT-A operators, so it reached an agreement with sister Textron company and engine manufacturer Lycoming to provide service for the SMA engine at any one of the dozens of Lycoming service centers around the country. Lycoming, which has no production diesel product line of its own, will work with SMA to get up to speed by the time the engine enters service, a process that Cessna JT-A project manager Brian Cozine said was already under way by the time the new model launched at Oshkosh.
Jet Powered Skylane
For whatever reasons it might have, Cessna prefers to refer to the new Skylane as a jet-A powered airplane and will go out of its way to avoid using the “D” word. For some folks diesel technology conjures up images of Soviet-era truck motors. Today, though, diesel technology has gone upscale. Turbodiesels from Mercedes, Volkswagen and Renault (the original co-developer of the 305 engine) are clean, powerful, quiet and sophisticated.
When it comes to the new Skylane, that’s the image Cessna is hoping to project, and based on my experience flying the new model, it is on track.
There was remarkably little that had to be done to the Cessna 182 to accept diesel power. There’s a new engine mount, of course, as well as a new squared-off cowling, which gives the JT-A an aggressively modern air. Very importantly, there’s no gear box to reduce the rpm of the prop, as there are on two existing diesel engines from Austro and Centurion (the former Thielert), both of which are derived from automotive products. The Cessna installation also did not require a fuel radiator. Such a device is sometimes necessary to cool off bypass fuel (fuel that gets pressurized for injection but is not needed and, so, is returned to the fuel tanks). Because the Skylane’s wings are sheet metal — the fuel tanks are of the wet wing variety — there’s not the same Thermos effect as on some composite airplanes. The wing of the Cessna is, in essence, an effective enough fuel cooler.
There’s also a new carbon fiber Hartzell three-blade prop that is light and responsive, turning at just 2,200 rpm. There’s no prop control. The computer keeps it at an optimum setting for the conditions and the power commanded by the pilot. The new prop helps keep the entire weight penalty for the diesel at just 15 pounds.
Flying the JT-A
After departing from KICT with Cessna test pilot Charles Wilcox, we flew the 182 JT-A throughout its performance envelope.
Climbing out from Mid-Continent, I put the airspeed on best rate of climb, which is 82 knots, and watched as the airplane climbed surely and steadily. Because the SMA model in the new Skylane is a true turbocharged engine, we saw 100 percent power up through 10,000 feet while burning just 12.1 gph, this compared with between 28 and 20 gph in the climb for the gas piston model. As great as the low fuel burn is, the engine management is at least as important an improvement. For climb you set power at 100 percent simply by pushing the lever all the way forward. The computer takes care of setting the rest of the variables to give you that percentage of power.
Fuel flow is a big deal, because it’s such a little deal. At 90 percent power — set the power using the Garmin G1000 MFD, coming soon to the JT-A — you’ll see a fuel flow of right around 11 gph, which gives you around eight hours of endurance. At 150 knots true airspeed, that will give you around 1,200 nautical miles of no-wind range. Pull the power back even more and you can go at reasonable speeds for extremely long distances. Trips of 1,500 nm are quite possible, though you won’t get there quickly at that fuel burn. The optimum scenario will be at 10,000 to 12,000 feet msl, where an 1,100 nm range at high power with reserves is likely.
Payload figures will improve too. Because of the huge range of the airplane, you can leave off fuel and take along what people and bags you want to load aboard. Cozine commented that the Cessna 182 JT-A “uses so much less fuel that you can always take more payload than [on a] gas piston 182.” This will allow pilots to fill the seats while leaving off fuel, while still having plenty for long legs with good reserves.
As I said, power management is simpler than it is on a turboprop — set it and forget it. The power is controlled electronically — there is no mechanical linkage. The engine control unit (ECU) has a backup mechanical system (should some extremely unlikely system failure take out the ECU). The SMA engine, thanks in part to Cessna’s modifications to the system to help it run cooler and with better margins, ran so far within the limits despite the hot day (ISA+12) that it looked as though the needles were painted on the temperature gauges no matter what abuse we dished out.
That abuse included several scenarios not discussed in the POH, including extended slow flight, full power cruise at 12,000 feet and an engine shutdown in flight.
That last point is key, since one of the FAA’s big concerns about diesels is their stubbornness about getting back to business once they’ve been shut down for a time. In our case, we were loitering over a conveniently quiet and out-of-the-way Kansas airport, Kingman, when Charles gave me the OK to shut down the engine. Now, unlike with gas piston engines, which become immediately quiet after a shutdown, with a diesel engine the shutdown can seem like a gray area. To ensure the engine had indeed stopped doing its thing, I raised the nose and watched the rpm degrade, a good sign (or a bad sign, depending on whether you wanted to shut down or not). After a two-minute glide (it didn’t seem as long as that sounds), I tried the restart. I wish I could say it was a harrowing experience that will live with me forever, but the truth is far more pedestrian. The four-cylinder diesel immediately sprang to life and we were under power again. Ho-hum.
With 230 horses again at our disposal, we circled down to Kingman to do a couple of touch-and-goes. The first one, with full flaps, was uneventful. The speeds and feel were nothing different from what you’d experience in any Cessna 182. Such was not the case with minimum or no-flap approaches. The engine and Hartzell prop combination doesn’t yet have the same aerodynamic braking characteristics as in existing Skylane power plants. The result for now is that you need the flaps to get down to landing speeds. Cessna is working to reconfigure the details of the system (prop, software and power lever) to allow finer pitch for greater prop braking while on approach. Once that’s been done, it’s safe to say that the landing performance of the JT-A will be hard to discern from that of the gas piston Skylane, which is to say, excellent.
That might be the big lesson of the new model for Cessna. With a well-designed power plant, thoughtful integration of that engine into the new model, and patient development, even a legendary light airplane like the gas piston Cessna 182 can start using jet-A and can do so while enjoying the benefits of high fuel efficiency, single-lever power, readily available fuel and higher payloads, all features that are difficult or impossible to get with conventional light airplane power-plant technology.