Motor Head #7: Are We Making It Harder Than It Needs To Be?

For many years, FADEC electronic engine systems have been like glass cockpits in the low end of GA: just over the horizon. Well, glass is here, but FADEC is still not available in mainstream, certified aircraft. AVweb's Marc Cook has some thoughts about why that is, and why he still hasn't tried it, in this month's Motor Head column.


A recent story in one of the big aviation glossies on the supposed advantages of piston-engine

How To Program Those Black Boxes

I have carefully studied the Aerosance-produced FADEC for the Continental engines — but, in the interests of full disclosure, have not flown it yet (more on why later) — and I believe I have a good understanding of how the system works. It does a couple of things that I would not do to my own engine. For one, it strives to set the mixture for best power on takeoff and climb. That’s fine for performance, and I would expect the airplanes powered by the new FADEC to have slightly better takeoff and initial climb performance; not by a lot, but it would be noticeable.The trouble with best-power mixture at high power settings is that it puts the engine right near the point of highest cylinder pressure and, therefore, will create very high CHTs. The whole point of running extra fuel during takeoff — and why so many savvy owners of big-bore Continental engines insist that the redline-gauge fuel flow is a minimum not a maximum value — is to slow down the combustion process and reduce cylinder pressures. The result is moderated CHTs. Well, shouldn’t the computer take care of that? Sure, it does; but my reading of the specs (confirmed by the published reports) is that the FADEC doesn’t start to respond until one of the cylinders has reached 435 F, when it then starts adding fuel and/or retarding ignition timing. Unless that installation is dramatically well cooled for takeoff and initial climb — thus making it way over-cooled for cruise and descent — I’m fairly sure one or more of the cylinders will reach that threshold in the initial climb and the computer will have to respond.Unfortunately, that’s a CHT value way above what I would let my own airplane experience. Even the slightly troublesome Cessna T210 that I fly from time to time can keep its #5 cylinder below 380 F during the climb. (Due to baffling issues with that installation, #5 runs significantly hotter than the others.) And once the CHTs are up, it’s hard to get them to start back down without a big increase in airspeed or fuel flow. There goes your fuel savings — or at least part of them.Then, in cruise, you have a choice of a high power setting that appears to me to be rich of peak EGT, probably around that magic number of 50 F rich that just happens to coincide with peak cylinder pressures and the highest possible CHTs. (Actually, according to the Advanced Pilot Seminars doctrine and data, that point is 40 F rich.) The economy setting is probably lean of peak but at low power settings. I confess to seeing the merits of LOP operations, but I think you have to put the power back or the speed loss will make you think it’s just not worth the effort. Running LOP is absolutely most useful at high power settings.

No Pilot Control

The other issue with FADEC that doesn’t exactly fill me with joy is the possibility that the pilot can’t choose the combination of settings that result in the smoothest engine. If FADEC decides you’re going to run 24 inches of manifold pressure at 2500 rpm for high power, that’s what it will do. But my experience has been that every installation has a sweet spot, vibration-wise, and if it isn’t in the FADEC’s way of doing things, you’ll just have to suffer with it. For example, my old P-35 Bonanza used to like just shy of 2500 rpm in cruise. Teledyne Continental Motors listed 2450 as the max cruise setting; but there, working with the original two-blade prop, it was considerably shakier. I very much appreciated the chance to set the engine to the smoothest setting.I know I’m sounding like a Luddite, a True Believer in the Sect of the Three Knobs. But that’s not it. I just want to have choices in how my engine is run and the tools to keep it out of danger, temperature-wise. Just because the manufacturers say, for example, that 460 F is an acceptable CHT doesn’t mean I have to agree. My powerplant management has evolved to consider CHT as the primary instrument. I don’t much care what the MP and RPM combinations are — or even, strictly, fuel flow (and certainly not absolute EGT except as a cross-check on takeoff fuel flow because CHTs lag so much) — as long as my target CHTs are hit.Using CHT as the marker has dramatically simplified engine management for me. Just think of the point at 40 F rich as the hottest temp you could have — and the point you’ll be closest to detonation — and manage mixture accordingly. Rich of peak? Simply add fuel to reduce temps. Running LOP? Further reduce fuel flow to get the temps down where you want them. Conversely, you can add fuel LOP to get whatever target you want.

Crime of Navet

So why haven’t I flown with FADEC yet? Good question. It boils down, like so many crimes, to motive and opportunity. Up to now, my efforts to fly a private FADEC-equipped airplane have not been realized. And while I don’t doubt I could cadge a ride in a Liberty with the FADEC-shod IO-240, that’s not the kind of engine and installation that is stressed enough to show the real merits of the system. Perhaps it’s time to call Cirrus after all.But then there’s the motive: Until one of these FADEC airplanes is equipped with an engine monitor visible to the pilot in flight, there’s not a whole lot to it. Welcome to the av-journalist’s big problem: Once around the patch in an unfamiliar airplane with minimal data-gathering equipment makes for a necessarily short (and shallow) evaluation. Without seeing the actual data — what are my fuel flows, EGTs and CHTs — it would be hard to learn much about the system aside from the fact that the engine runs, starts easily (yes … a real advantage to FADEC!) and appears to have all its parts on landing.The big question to which I have not yet had an answer is this: What’s in the data stream coming out of the FADEC controller and who can view it? As I understand it, there are several levels, probably to be described as Customer, Shop and Factory. The issue for me is this: If I could see the data, would I like it?As with glass cockpits, I believe that we’re going to have some form of FADEC on our airplanes in the future, though perhaps not the near future. And I think it will evolve quickly past the current levels, as it did in autos. Remember the Bosch K-Jetronic? It was the high point of fuel injection design for many years, but the system on any Japanese sportbike would now put it flat to shame.Maybe one day I’ll be able to pull up the configuration page of the integrated flight-display/FADEC controller and set my own limits, tell FADEC how I want it to fly. Maybe then you can take away the other two knobs on the panel.

DIY Engines … Sort of …

As another example of how aircraft homebuilders are just so delightfully whacked — as in, slightly nuts — comes this news: Superior Air Parts, which builds engine components — and, indeed, entire engines — has seen a huge response to its build-your-own engine program for experimentals. In mid-June the program was already booked through the following March. The demand well outstrips the company’s ability to host the show, which it does once a month for three days.Superior’s program has two primary options: Come to Cordell, Texas, (practically inside the DFW parking complex, it’s that close), and watch one of Superior’s techs build your engine, or come on down and do it yourself.Before you recoil in horror from any experimental with a self-made Superior on the nose, understand that the class is highly structured. You don’t just show up, open the box and start work.The program opens with a discussion of what’s to be accomplished over the three-day program, including shop safety, engine concepts, quality assurance and break-in tips. Then, on the afternoon of the first day, you start assembling your engine. I have no doubt that the knowledge and confidence gained in seeing the gory internals of your engine will make you a smarter mechanic after the airplane is flying. (Don’t forget that builders of experimental/amateur-built aircraft get a Repairman’s certificate for that specific airframe and can legally do anything including an engine overall. Even if they really don’t know how to do it.)It’s also worth mentioning that the Superior program comes with a great build manual with every step outlined and clearly stated, and that the build facilities are nicer than my business office: clean, modern and air conditioned. It’s vastly nicer than just about every engine shop I’ve seen.Superior charges you $500 if you want to watch your engine being built, and $1000 extra if you want to do much of the work yourself. I’d call it cheap education.

Got motors on your mind? Check out the rest of Marc’s columns.