Tuesday, December 14, 2010

N4468N FADEC Jet-A Diesel: Still the queen of the fleet

The acquisition of 89Q—our G1000 C172—has dominated the conversation at PFC lately, but before 89Q came along, we had 68N, the first in our long term effort to modernize and diversify our fleet. 68N is a 1980 Cessna 182Q converted to run on Jet-A fuel with the SMA FADEC Turbo Diesel. There is a lively debate going on in the aviation press about the future of 100LL. We would like to think that we were quite prescient when we decided to go ahead with the conversion two years ago. Our plane has been featured in Aviation Consumer and AvWeb, but with a couple of years of experience under our belt, it might be a good time for a quick report of our own.
When I first flew the plane, I didn't know quite what to expect.  I turned the key gingerly in the ignition. The engine instantly came to life. No finicky priming, no aux-fuel-pump, no need to tweak the throttle, no cranking or sputtering—just set the power to idle and turn the key. Almost "automotive" in its simplicity. At first, the engine seemed a tad rough, and I had the overwhelming urge to advance the throttle a little to even things out. That's when Stanley (one of our CFIs) sitting in the right seat said, "Just leave it alone, it will even out." And in a matter of a few seconds, the FADEC did its thing, and the engine was idling smoothly. The engine sound is reminiscent of a big diesel Mercedes, and a little quieter than other C182s. Once he was satisfied that I had done the startup checklist, Stanley quipped, "Better give me back my keys before you forget." (Oh right, no mags.)
We taxied out to the runway, and I advanced the throttle to full. The three bladed props and the torquey engine pull the plane with authority, quickly accelerating to rotation speed. Once airborne, the throttle is reduced to 65 inches of manifold pressure. That's it!?! As we settled in for the cruise out to the practice area, I had a really nagging feeling that I was forgetting something. I glanced around the gauges and around the cockpit. Sensing my discomfort, Stanley quipped, "Relax, you haven't forgotten anything. You don't have to lean, or adjust the prop or the power. You can fly this thing at full throttle if you want to and you won't hurt anything. You might not get great fuel burn, but you won't hurt it. Just set the throttle to the power you want, and the FADEC will do it's thing." And so it did.

In all other respects, 68N flies just like any other C182—completely predictable and docile in all phases of flight. In fact, most of our pilots who move up to 68N from the C172s find this an easier airplane to fly once they've mastered the different feel of the C182 (like the heavy nose in the landing flare). Even with basic maneuvers or day VFR flight, the simplicity of the FADEC system is appreciable, but it's in IFR flying, especially shooting instrument approaches where that little bit of work load reduction turns into a big advantage.

Pilots, of course, will worry about what happens when the lights go out.  The beauty of mating a FADEC to a compression ignition engine is that ignition is not dependent on "spark." The SMA has a backup "mechanical" mode that will keep the engine going even in the face of an electrical or FADEC failure.

The only quirk specific to the SMA C182 is that the POH requires a pretty high manifold pressure (45 inches) through short final. The purpose is to keep engine temps high on approach to avoid any possibility of a flame out (where compression is no longer sufficient to ignite the fuel). This makes for a slightly faster approach than normal, but once the throttle is pulled back to idle, and the flaps are dumped in, 68N settles on the runway just like any other C182.

How we got here
In 2008, the engine on our C182 required replacement. One of our members suggested that we evaluate the SMA engine along side the OEM Continental. SMA had just received FAA certification for its Jet-A engine retrofit for the C182Q in July of 2006. They had a good track record in Europe, but they were just getting started in North America.  We were probably among the first dozen conversions, and certainly the first in a club environment.

PFC pulled together a 9 member team to evaluate all aspects of the SMA conversion. Along side a careful and detailed analysis of the financial implications of such a choice, the team evaluated every aspect of this relatively new technology conducting extensive discussions with SMA, the FSDO, insurers, installers, maintenance facilities, and other owners. Two of our members flew to Sun-'n-Fun to meet with representatives from SMA, and take a demonstration flight in their aircraft.

The SMA represented a significantly larger initial outlay than a simple replacement with an overhauled Continental ($80k vs $40k), the board voted to recommend that the club proceed with the SMA option, and the general membership concurred. We thought that with the cost of 100LL soaring past the $5 per gallon mark at the time, and its future uncertain, the fuel sipping SMA running on Jet-A represented the wave of the future. More importantly, between the lower fuel consumption, the lower price of Jet-A, the lower cost of routine maintenance, we projected that the SMA would reduce hourly operating costs by some 30% in the long run.  In fact, we expect that the hourly tach-rate to our members will be comparable to our steam gauge C172s once the club has amortized the initial cost of the conversion.

Operating costs and other benefits
So how is it performing? In a nutshell, our expectations on the operating costs have been fully realized. Fuel consumption seems be in the 8-9 gph range with a cruise speed of ~130 knots. For example, on a trip out to Osh Kosh, our chief pilot reported that he did the entire 660 nm trip in 5 hours, burning a total of 47 gallons of Jet-A at nearly max continuous power. This equates to an average speed of 132 knots and 9.4 gph of fuel burn—or something like 16.2 mpg (about what you might expect from an SUV cruising at highway speeds). At an average price (in the NE according to www.100LL.com) of $4.65 per gallon, that translates into $218.55 worth of fuel, or about $44 per hour. (And he still had 41 gallons in reserve at the end of the trip.)

Had he done the same flight in our C172, the cruise flight time would have been at least 6 hours (at 110 knots), with at least one, but possibly two, fuel stops along the way. At 10 gph, the trip would have required 60 gallons of 100LL, not counting the take-offs and landings for the fuel stops, which at $4.97 per gallon (again, according to www.100LL.com) would have cost $298.20. The SMA C182, then represented a cost savings of about 30% on this particular trip, while taking a couple of hours (including the time required to land and refuel) off of the trip.

In addition to the significantly reduced cost of operation and reduced pilot work-load, one of the big benefits of the SMA engine is the phenomenal range of the plane, and the loading flexibility it gives us. The C182 with the OEM Continental had long legs to begin with. But with the fuel-sipping SMA the range is simply astounding. The tanks have the standard 88 gallon capacity, which at 9 gph and 130 knots translates into nearly 10 hours and 1200 nm with IFR reserves.

The empty weight of 68N is 1,947 lbs. Max gross weight is 2,950 lbs. That leaves 1,003 lbs of useful load. Jet-A does impose a weight penalty, coming in at 7 lbs/gal, so full fuel payload is 387 lbs—about 2 standard adults plus a suitcase or two. But no one in their right mind really flies 10 hours straight. You could take four standard adults and 100 lbs of baggage, and still have enough fuel to go 3.4 hours at full power (360 nm with IFR reserves), or 4.5 hours at cruise power (about 450 nm with IFR reserves). All the while, the FADEC manages the fuel flow, so all you have to do is set the throttle to the target manifold pressure and go.

Cold weather operations and other issues
When the SMA was initially released, it had a number of cold weather related operating restrictions—the diesel seems to be more sensitive to low engine temps than avgas engines. These restrictions have been largely addressed by the FAA approved winterization kit—basically a kit that covers up the gills and part of the oil radiator to dramatically reduce engine cooling and keep temps in the proper operating range. So from an operational perspective, it has been a non-issue even in the northeast.

On the other hand, the diesel seems to be more sensitive about starting in the cold. The FADEC doesn't like prolonged cranking as in an avgas engine, so we've had to train our members to properly preheat (and in some case start the engine in backup mechanical-mode) to make sure the engine is at the right temperature for start.

There have certainly been other minor transition issues. For one, there was pilot training that we had to do in order to qualify all our pilots on the FADEC. But in fairness, the FADEC is an easy transition for those stepping up from a fixed-pitch C172. There are still the occasional FADEC issues and updates—all minor, but an indication that SMA is continuously working to improve the system. We do get the occasional quizzical look from FBO linemen—the club has a rule in place that the PIC has to be present when the plane is being refueled—and most, but not all fields have Jet-A.
Maintenance has been in line with our expectations—certainly no more expensive than maintaining a stock C182. There have been instances where the aircraft developed problems while away from home base, where we've had to put 68N in the care of mechanics who have had zero experience with the SMA. On such instances SMA has worked with us to get the necessary information to the mechanics (including full schematics), to get us on our way as quickly as possible. On the positive side, SMA is expanding its network of installers and service providers—our very own shop, C&W at Caldwell, now one of them.

In our experience fuel burn has been at or slightly better than POH numbers—we are routinely getting 8-9 gph which is phenomenal for a high performance aircraft. One area where the FADEC is particularly useful is in taking the pilot out of the leaning equation, especially in a club environment like ours. While we stress pilot training on proper leaning technique on our avgas aircraft, and equip our aircraft with engine monitoring instruments like JPI, we have still found that leaning technique varies from pilot to pilot. And even in the best circumstances, proper leaning in traditional aircraft can only reasonably be expected in the cruise phase of flight.  The FADEC ensures that the engine is properly running lean of peak throughout all phases of flight—allowing us to be green and economical at the same time.

So what is there left to say? Our members love this aircraft. It was, by a significant margin, the most popular aircraft in our fleet this past year. (That, in spite of the fact that it is still more expensive to fly than our C172s.) Our pilots love the phenomenal range, unprecedented economy and the mission flexibility it gives us, all in the familiar and easy-to-handle C182 platform.

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