Plastic engine - JetA1 and FADEC

FADEC. The word is out. There has been a large buzz arround this word in the light aviation world for the last months, if not years. Thielert uses the acronym ECU, meaning Engine Control Unit instead, but have a look to the meaning of FADEC.

Full Authority Digital Engine Control. And to reword that in a "For Dummies" style: electronics controls your engine.

The kind of engine proposed by Thielert and SMA is a variation of the Turbo Diesel Injected automotive engines. I'm not expert enough in engines to go in the full diesel theory, but one important point is that diesel is injected under very high pressure (several hundred bars), to warm it.

The power delivered by the engine depends directly from the frequency and duration of the injections. We are here speaking of tousands of injections per seconds, so this is something that can not be controlled by a mechanical or human process, and this is where the electronics comes in the game.

The larger consequence of that is that in case of total loss of electrical supply, the engine will fail. Read that again, and think of it.

You should normally be partly scared now. But as you might guess, the engine manufacturers studied that in detail, and they propose various solutions, including dedicated backup batteries.

If you're a non plastic kind of pilot (yet), think of that. On good old Lycoming engines, there are two mags. But quite often there is a single mechanical axis driving both of them.

I know that I won't convice hard-core plastic opponents, and this is not my goal. Once again, I'm just exposing my experience.

Amongst the advantages of FADEC controlled engines, are:

1) Easiness of use - a single lever controls the powere delivered by the engine. No more prop / mixture lever
2) Easiness of use - A single button to press for engine and FADEC test
3) No carb heat, and under some implementations, no pumps
4) As a consequence of the no-mixture mode, no risk dirty of spark plugs
5) Tubro diesel means that maximum power is available up to at least 10'000ft
6) As engine are water-cooled, it is possible to go from full power to idle at any time without any thermal shock risks
7) Did I mention that a DA40 at 75% power, flying at 120kts, sips only 5.5 USG of JetA1 per hour ?

Obviously, there are some disadvantages, including:

1) JetA1 is not as easy to handle as AVGAS
2) JetA1 is more temperature sensitive than AVGAS, so fuel temperature must be closely monitored
3) JetA1 is denser that AVGAS, so water contamination is not so obvious to detect
4) When refueling on airports offering truck service, be sure that they send you the JetA1 truck, not the AVGAS one
5) As the prop is controlled by the smart FADEC, it changes RPM in way a human pilot won't use (like low RPM under certain low power conditions)

This post is kind of a summary of what will follow, as each of the points here above deserves a full post. I just want to close this post by two anecdots.

A long long time ago, I can still remember... I taxied a PA32 to holding point 23 for an IFR flight. During engine check, the mags test was so shaky that I was really close to cancel the flight. It took me more than 10 minutes at various power / mixture conditions to clean the spark plugs. Apparently the previous pilot did not knew how to use the mixture lever. After ten minutes, hopefully, my take-off slot was still 1 minute long ! No way this could happend on a diesel engine.

To remain balanced, an anti-FADEC story now. After taking of from an airport at 3'500 ft AMSL, climbing towards 7'500 ft (VFR flight), under 90% load to avoid overheating, the FADEC just "decided" that 65% was a better power setting. The black box shown that I did not moved the power lever. This reduced power condition did last for about 15 seconds, then 90% were available again. The rest of the flight was totally uneventful. By luck this did not happen after take-off from a short field.

A suivre...