Originally Posted by
tdracer
A big problem with applying FADEC technology to your Cessna is cost. Compared to carburetors, electronics have rather unforgiving failure modes - carbs tend to wear gradually, slowly shifting - while electronics simply quit, often with little or no warning. When that happens in your car, you pull over to the side - when that happens in your GA aircraft, best case is you make forced landing.
That's why commercial airliner FADEC installations are all dual channel, fault tolerant, built with highly screened electronic components. They are also quite expensive - LRU cost for a FADEC is typically between a quarter million and a half million dollars. Yes, the actual cost to screw one together is a fraction of that but still approaches six figures. Further, while GA isn't as bad a commercial aircraft, the FADEC is subject to far greater and much more frequent environmental extremes than automotive installations (and large, frequent, and rapid temperature fluctuations are hell on electronics).
Yes, an actual FADEC - operating a gas turbine engine is a complicated beast, and is not cheap.
But there are millions and millions of Engine Control Modules driving around in cars and trucks today. They start engines in the depths of Alaskan and Canadian Winters, and in the middle of Summer in the desert. Car ECMs look at atmospheric pressure, OAT, mass airflow etc etc, and it would be simple to extend the engine map for an aviation engine envelope. Car ECMs also allow and adjust for load, and optimise the ignition timing and fuel mixture hundreds of times a second. They control emissions equipment and modulate charging systems by varying the mark-space ratio of the drive signal. They can be quite sophisticated.
If a car ECM quits, yes, you just park up and call the tow truck, but in my long electronics experience, most problems come from bad connections - rarely the electronics themselves. In many years of driving, I have only once had a car quit on me through ECM electronics, and it restarted straight away and got me home, (albeit running at reduced performance). I took apart and sprayed all the plugs and sockets around the engine bay, and it was all back to normal, and hasn't missed a beat for 2 years since that happened.
Cars use a lot of plug and socket electrical connections because it makes the build process much quicker, but that also causes the majority of electrical problems down the line. (Gas turbine FADECS use gold plated connectors, which don't corrode and thus are more reliable). So, on your C150, you would not have plugs and sockets, but have screw/crimped/soldered terminals for every connection in the engine bay. You site the ECM in the cockpit, not outside with the engine, thereby protecting the electronics from extremes of temperature and vibration. And, yes, you make it dual channel, screened and fault tolerant. Cars already have a limp-home mode which keeps the engine running at reduced performance if important sensors malfunction. Or they use look-up values in the absence of sensor data. Not difficult, and doesn't have to be expensive.
.