Flight Test & Theory

Flight Test & Theory of Operation

The engine is an all-aluminum four cylinder, four-cycle, dual overhead cam turbocharged diesel. It drives an MTV-6-A/187-129 3-blade propeller through a 1.69:1 reduction gearbox. The propeller and engine oil circuits are separate, so engine oil does not get into the governor or hub. Engine/prop/turbocharger control is all via FADEC with a single throttle lever. There is no separate control for the prop or the turbocharger wastegate. A wet vacuum pump is included.

There are two completely separate FADEC systems. Under normal circumstances the aircraft operates off the "A" system, and switches to the "B" system in case of a failure. Electrical power is necessary for the engine to operate. A backup battery is installed, and if the aircraft battery is run completely dead the backup battery will operate the engine and FADEC system for another 40 minutes.

The engine is certified for operation on Jet A and a particular specification of diesel fuel. At this writing the diesel is not available in this country.

Cabin heat is supplied from the oil cooler. The fuel system includes a thermostatically controlled heater using either the radiator or oil cooler-I forget which at this point.

Early versions did not have a "both" position on the fuel selector, but the newer ones and the plane I flew do. There is also a 1 gallon header tank under the floor, so even if you manage to unport the selected tank it shouldn't matter.

Fuel capacity is reduced from 40 to 33 gallons; you fuel only to the bottom of a sleeve that's installed in the filler. The fuel injection is a full flow system that pulls much more fuel to the rail than is used, and then returns the excess to the tanks. The extra room is there to accommodate the returned fuel.

Starting is straightforward although takes some getting used to. Throttle is set to minimum and the aircraft master is turned on. That brings the engine instrumentation up, which runs through a short test sequence. The engine master is turned on, and a glow plug indicator comes on. Once it goes out, you push the starter button until the engine fires-typically between three and five blades. Starting, like the rest of the engine operation, is completely controlled by the FADEC and is equally easy from cold or when the engine is heat-soaked.

For the runup, one leaves the throttle at idle and pushes another button. The FADECs cycle the prop and then each FADEC is tested. After that you run it up to full throttle momentarily (we saw 104%). Fuel, oil and coolant temps all have to be in the green, and then you're ready to go. Everything is thermostatically controlled, and they say that even in the coldest weather it shouldn't take more than three or four minutes for things to warm up sufficiently

Takeoff was uneventful, although much more right rudder than I had expected was required. It was around 90 degrees, and we saw about 550 fpm climb-pretty much in line with the book figures. The aircraft seems slightly more nose-heavy than what we're used to, but this was a newer airplane and that might have had something to do with it as well.

I set things up similar to a traffic run with 95 knots at 1400'. That worked out to 60% power and 4.8 gph on the computer. Steep turns were normal-other than the fact that it is quieter and smoother, it flew like any other 172. Approach and landing, ditto.

As noted above, the engine is noticeably quieter and smoother than the Lycoming it replaces. That should translate into reduced fatigue for the occupants and less wear and tear on instruments, avionics, and so forth.

Some parts are stocked in Florida. Major components have to come from Germany, although for AOG situations they ship overnight. It is expected that by the end of the year everything will be stocked at Superior's distribution center in Dallas.

The entire package is expected to go 2400 hours. The gearbox gets replaced every 600, and the prop gets overhauled at 1500. Anything that fails in the meantime is covered at no charge. That includes the alternator, starter, turbocharger, FADEC, and everything else. The only other routine maintenance is oil changes at 100 hours (that will go to 200 shortly) and filters.

To answer questions that came up from some of you who reviewed the manual:

Normally, the engine runs on the "A" FADEC and only goes to the "B" unit in case of failure. There is a way to force it to the "B" unit, but the factory does not recommend it under normal circumstances. All operating parameters for both FADEC's since installation are retained. As noted above everything is easily monitored with a laptop. At every 100 hour inspection, the entire FADEC file is downloaded and emailed to Thielert. There are two purposes for this-one is to simply gather more operating data, but the other is to watch for any potential problems on the horizon.

For our purposes, this will be a Jet A only operation. The particular type of diesel fuel that is approved for the engine is not available in this country.

This system has been flying for five years, and was certified for the 172 well over a year ago. There are several of these planes in south America and Africa, and to date there have not been any significant problems or failures. There were two customer conversions underway when we visited, one of which is going to Oshkosh for a major announcement. These engines are going to start to show up in greater numbers after that.

I also have to say that the distributor, Epic Aviation of New Smyrna Beach, FL rolled out the red carpet for us. They were very giving of their time, and we had a very good, thoughtful, and frank discussion.

More information is on the websites for Thielert and Epic-links on previous page.

More when I know it.

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