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Black box in light aircraft ? Affirm !

This is not by design, it is a byproduct of electronic engine management. As the FADEC controls the engine, it knows each and every engine parameter (temperatures, pressures, voltages, …) and monitors all of them.

As a consequence, each time a parameter is out of the normal rage, the FADEC gives an alert to the pilot. This could lead to an apparent higher rate of alerts, but this is only due to the fact that the FADEC has nothing else to do than manage engine and generate alerts.

Can you, as a pilot, pretend that your oil temperature is never slightly above the limit during climb ? Be honest, you cannot monitor constantly all parameters, and the precision of the gauges usually found in light aircraft are not so accurate. Please don’t missunderstand me, I’m not saying that FADEC are generating alerts all the time, or that we never saw parameters on limit values before. The only message is that FADEC helps in detecting transient conditions that could not be noticed with classical (and non-memorizing) gauges.

Thielert even put more safety in its FADEC, as some alerts can not be cleared by the pilot, but only by a mechanic. The flight can be continued, but if such an alarm occurs, the next flight will not be possible. The FADEC will not prevent to start the engine, but obviously no pilot will take-off with a warning on its engine control unit. Would you ?

After any problem, or during periodical maintenance, the mechanics will be able to access all these stored values and parameters. More on that later when I will post on some problems.

As a consequence, in collective flying (club, or shared ownership), some would feel that the FADEC is spying them, and that they could be blamed because of that. This is a purely psychological thing, especially as the pilot can not do anything wrong, except may be switching the FADECs off, or going to IDLE power at an improper time. But in terms of managing the engine, the only thing left is setting power, so how could you do something wrong ?

For maintenance people, this also provides improved way to monitor engine health, as they can follow all parameters over time. So yes, FADEC is a black box, and this is good for anyone.

Bis nächste… tschüss

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Category: Modern Aviation
Tags: Black-box FADEC

Let’ s have now a closer look to plastic engine operations. The first change compared to classical engine appears during pre-flight check. The good old oil level check is still present, but an additional check is needed: the level of coolant. This is because these engines are water cooled, so a visual check of the coolant level pops-up on the pre-flight checklist.

Engine startup is slightly different as well. The classical sequence looks like:

1) Electrical power on

2) Engine master on

3) Glow - No Glow

4) Startup

5) Check oil pressure within 3 seconds (yes, three, not thirty)

6) Warm-up

The engine master is the switch / key that turns the FADECs on. The point 3 is probably the most unusual for classical engine pilots. To burn correctly, the JetA1 fuel must be warm enough. For startup, there are “glow plugs”, that bring cylinders and fuel to a good temperature.

The glow plugs activity is indicated by a particular light on the panel. After turning the FADECs on, the glow plug is activated, and then pilot must wait until the glow plugs are off before starting.

Starter can then be activated, either via a key or a push button, and normally, the engine fires-up quickly and easily. Here comes a BIG difference compared to AVGAS engines: the oil pressure must be in green range within 3 seconds !! If not, the engine must be stopped by switching the FADECs off. This very short time for oil pressure comes form the very high injection pressure.

Once started, engine can not be taken to more than 1400 RPMs before all temperatures (oil, cooling, gear-box) are in the green. This normally takes less than 2 minutes.

After taxi, comes the time of engine check. This is where FADECs help you, pilot, to save time. Just press and hold the ECU test button. Then FADEC “B” will be activated, and change prop pitch, after what FADEC “A” is re-activated, and also changes prop pitch. If all alert lights are off, the engine check is finished. The whole sequence lasts for about 10 seconds.

An additional check on the Diamond aircrafts, is to force activation of FADEC B (more on that in a later post), to ensure that both work fine.

Not more to say. For take-off, just push the power lever forward, check that more than 95% power is available, and fly. Full power can be maintained, as long as the temperatures remain in the green. In summer, it is better to reduce to 90-95% for the climb.

Most manufacturers recommend to fly in cruise with power setting arround 70-75%, but as I mentionned before, there is no restriction, and it would be perfectly legal to fly 100% all time.

One more advantage of water cooling is that power can be reduced to 0% at any time without any thermal shock risk. Quite helpful for high approaches. One must just note that most diesel engines are producing thrust even on IDLE power.

After landing, a cooling time is mandatory on Diamond aircrafts, but strangely not on Cessnas. The engine is stopped by simply switching the engine master (FADEC) to off. Be warned, these engine do stop quite abruptly.

More on engine parameters error reporting in the next post.

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Category: Modern Aviation
Tags: FADEC Jet-A1 procedure

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.

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Category: Modern Aviation
Tags: ECU FADEC Jet-A1 Thielert turbo