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-   -   Would you consider FADEC? (https://vansairforce.net/community/showthread.php?t=38366)

Andy_RR 01-13-2009 02:38 PM

LOP?
 
Most mag-ignited aero engines run with a fixed ignition angle, starting with impulse mags notwithstanding.

LOP is merely a means of finding a quasi-optimum mixture point for the the fixed speed and ignition parameters you have.

If you can change the ignition and the mixture, then the FADEC will probably always run the engine lean where EGT, CHT and other temperature limits allow. (Automotive engines don't do this generally because of emissions control constraints which don't apply to aero engines)

For any given engine speed and power requirement, there is a manifold pressure, ignition angle and mixture setting point that produces the optimum fuel consumption. You pick the MAP with your throttle and the FADEC will control the fuel and ignition to reach this point. EGT then becomes an irrelevance for the pilot (note I did not suggest the pilot ignores CHT!) and he can then spend more time looking out of the window

The same thing will happen for cold starting, hot restarting etc. Electronic fuelling and ignition control allow very fine tuning for virtually perfect first-time starting

John Clark 01-13-2009 04:45 PM

Cost/Benefit Ratio
 
Most mag-ignited aero engines run with a fixed ignition angle, starting with impulse mags notwithstanding.
True

LOP is merely a means of finding a quasi-optimum mixture point for the the fixed speed and ignition parameters you have.
There is a lot more to it than that. I suggest you Google John Deakin and read the many benefits of LOP.

If you can change the ignition and the mixture, then the FADEC will probably always run the engine lean where EGT, CHT and other temperature limits allow. (Automotive engines don't do this generally because of emissions control constraints which don't apply to aero engines)
"Probably run lean?" No, it will due whatever it was programmed to do.

For any given engine speed and power requirement, there is a manifold pressure, ignition angle and mixture setting point that produces the optimum fuel consumption. You pick the MAP with your throttle and the FADEC will control the fuel and ignition to reach this point. EGT then becomes an irrelevance for the pilot (note I did not suggest the pilot ignores CHT!) and he can then spend more time looking out of the window
Not really. In a true FADEC (Full Authority Digital Engine Control) you are not going to have a "throttle" you will have one lever to select the power output, not MAP. A true FADEC controls all the engine parameters including RPM (prop). None of this is new, it was done on the Porsche Flugmotor used in Mooneys and a few Cessna 182s.

The same thing will happen for cold starting, hot restarting etc. Electronic fuelling and ignition control allow very fine tuning for virtually perfect first-time starting
Very true, it would be the answer to hot starts.

My issue with a complex FADEC in a small piston aircraft is the cost/benefit ratio. Unlike an automobile engine we are running aircraft engines in a narrow RPM range (400-500) other than idle and not asking the engine to produce torque at very low RPM, as you might in a manual gearbox car. So, since the original question was "Would you consider FADEC," my response would have to be no. With the cost of the technology, the required backups to support it, and the complex diagnostic and repair issues I doubt will ever be covered by the small fuel savings.

John Clark
RV8 N18U "Sunshine"
KSBA

Andy_RR 01-13-2009 05:50 PM

Quote:

Originally Posted by John Clark (Post 289440)
LOP is merely a means of finding a quasi-optimum mixture point for the the fixed speed and ignition parameters you have.
There is a lot more to it than that. I suggest you Google John Deakin and read the many benefits of LOP.

No John, it is really just that. Anything more to it is making it unnecessarily complicated. I know there are "many benefits" but really all you are doing is minimising BSFC for the speed and power you want. The LOP method is the way of reaching that operating point. My original point was that "Lean of Peak (EGT)" makes no sense when you are optimising both fuel mixture and ignition angle.

Quote:

Originally Posted by John Clark (Post 289440)
If you can change the ignition and the mixture, then the FADEC will probably always run the engine lean where EGT, CHT and other temperature limits allow. (Automotive engines don't do this generally because of emissions control constraints which don't apply to aero engines)
"Probably run lean?" No, it will due whatever it was programmed to do.

Yes, I know it will do what it's programmed to do, but under all conditions where it is not EGT/CHT limited, it will (probably) be programmed to run lean, where the best BSFC point lies.

Quote:

Originally Posted by John Clark (Post 289440)
For any given engine speed and power requirement, there is a manifold pressure, ignition angle and mixture setting point that produces the optimum fuel consumption. You pick the MAP with your throttle and the FADEC will control the fuel and ignition to reach this point. EGT then becomes an irrelevance for the pilot (note I did not suggest the pilot ignores CHT!) and he can then spend more time looking out of the window
Not really. In a true FADEC (Full Authority Digital Engine Control) you are not going to have a "throttle" you will have one lever to select the power output, not MAP. A true FADEC controls all the engine parameters including RPM (prop). None of this is new, it was done on the Porsche Flugmotor used in Mooneys and a few Cessna 182s.

Yes, I am not precluding prop control in FADEC operation. By your definition of FADEC you will need electronic throttle control, which is both heavy and expensive to engineer. I doubt (but I'm not 100% sure) that the PFM3200 had that either, since such devices were still being looked upon with great suspicion even in automotive circles.

You could label the knob as % power if you wish, but ultimately it is cheaper and arguably better for this application to have it pulling on the throttle valve.

Quote:

Originally Posted by John Clark (Post 289440)
My issue with a complex FADEC in a small piston aircraft is the cost/benefit ratio. Unlike an automobile engine we are running aircraft engines in a narrow RPM range (400-500) other than idle and not asking the engine to produce torque at very low RPM, as you might in a manual gearbox car. So, since the original question was "Would you consider FADEC," my response would have to be no. With the cost of the technology, the required backups to support it, and the complex diagnostic and repair issues I doubt will ever be covered by the small fuel savings.

I'm not going to argue with your conclusions, except to add that the cost of the technology may not actually be that high - it's just the return on investment is uncertain. Add up the new cost of a mech FI or a carb and mags and see how much you've spent!

Diagnostic and repair information is improved with electronically controlled devices in the automotive sector. The people who tell you otherwise I will call luddites who usually refuse to understand how it all works.

Fuel savings may (or may not) be small, but they will become critical when leaded AVGAS is substituted by lower octane unleaded fuels. Converting to ULG in the auto industry is part of what spurred development of electronic control and, if you "normalise" the data, has delivered dramatic fuel economy and performance improvements compared with what the world was driving 20-30 years ago. The same thing could happen for piston aero engines, but this actually happening is not at all a certainty.

Shockwave 01-13-2009 06:05 PM

Quote:

Originally Posted by Mel (Post 289297)
I find it very interesting that almost 50% of the voters are interested in price, and less than 18% are concerned with reliability.

I don't personally require a 20 year track record before I'd be convinced. I'd hope the reliability is a bit north of the E/P mags, but that's why I voted for price. I view electronics as far more reliable than any mechanical device so I have no trouble with them being paired down in redundancy. Some sort of watchdog to monitor it and perhaps provide a limp home mode would be fine.

But then I'm a young whippersnapper who grew up on Atari and barely remembers cars without EFI. The only carbed / mechanical car I drove was a Chevette, and if you drove one you'd want to forget everything about it too! :D

John Clark 01-13-2009 07:15 PM

No luddite...
 
I spent 15 years working for Mercedes Benz and am familiar automotive fuel and ignition systems. As I stated, my questions are about cost/benefit not the technology. In fact, my RV8 is a little tiny bit ahead with a Lasar ignition system. And yes, it runs a little smoother and burns a little less fuel due to the variable ignition.

The single thing that would push light piston airplanes into less than stone-age technology would be emission rules. In the US of A the powers that be have already passed regulations regarding gasoline lawn mowers, so we can't be far behind. I laughed at Shockwave's reference to a Chevette (Holden Gemini to those in Oz). Yikes! That was the height of the auto industry trying to make old technology pass modern emission standards.

I once flew a Porsche powered Mooney and it did have a single lever engine control, but I have no idea how they accomplished it. I doubt, as you do, that there were servos involved.

John Clark
RV8 N18U "Sunshine"
KSBA

rv6ejguy 01-13-2009 10:38 PM

There is a world of difference in what is being developed for the certified market by Lycoming in the form of IE2 and what presently exists for experimental engines. This revolves mainly around cost vs. redundancy requirements set by the FAA. Clearly, we don't need all this for reliable electronic engine controls for experimentals and the costs that goes along with it.

IE2 is an awesome system and near state of the art even compared to the latest automotive systems but the wiring harness alone costs more than a complete system available for experimentals (minus the propeller control). I was able to talk to some of the techs developing IE2 and their initial target is for high end airplanes, not RVs. There was interesting discussion about IE2 making reliable, powerful turbocharged piston engines a reality and a valid competitor to small gas turbines. Eliminating the ham fisted pilot pulling the levers and causing premature problems with IE2 was seen as a way give high output turbo engines a better reputation. You can't over temp, over torque or over boost it so it actually lives.

In a steady state condition like aircraft engines generally operate under, FADECs probably offer little advantage in fuel flows during cruise compared to a savvy human with proper instrumentation to set LOP. FADECs show more gains outside the cruise range and especially so on turbos which may have to run on lower octane unleaded avgas in the future. The FADEC monitors everything important simultaneously and adjusts for max efficiency constantly while keeping the machinery within safe limits.

Until we get something like BMW's Valvetronic system, gasoline aircraft engines will continue to have a throttle plate controlled directly or indirectly by human hand to set power.

Well designed and tested electronics are certainly more reliable than the mechanical systems they replace or are attached to as one poster stated. Diagnostics are way easier with electronics compared to legacy hardware. Costs need to be reasonable before you'll see a lot of the old guard switch however.

It takes a lot of convincing sometimes to trade our VORs, maps and steam gauges in for GPS and glass and letting go of that red knob to have a microchip do the work. FADECs will never be for everyone but for those open minded enough to take the plunge, most see the light and are quickly converted. Some day, FADECs will be nearly as common on higher end piston engines as they are now on most gas turbine engines.

osxuser 01-13-2009 10:42 PM

I still feel that an educated pilot and a well monitored engine will be more reliable than a FADEC system (and so far I've been right from the limited exposure I've had to the TCM FADEC system). Someday it may be viable, but for now tune those injectors, get a single EI, and run LOP.

L.Adamson 01-14-2009 06:52 AM

Quote:

Originally Posted by rv6ejguy (Post 289531)
It takes a lot of convincing sometimes to trade our VORs, maps and steam gauges in for GPS and glass and letting go of that red knob to have a microchip do the work. FADECs will never be for everyone but for those open minded enough to take the plunge, most see the light and are quickly converted. Some day, FADECs will be nearly as common on higher end piston engines as they are now on most gas turbine engines.

I still prefer the benefit of my Lyc being totally independent of the aircraft's electrical system. I traded in the VORs many years ago, use a 696 because I'm a GPS "junkie"; yet I have no desire to get rid of the "red" knob.

L.Adamson --- RV6A

William Slaughter 01-14-2009 10:31 AM

Quote:

Originally Posted by RichB (Post 289125)
That might explains why the http://www.fadec.com website is gone from DNS. What's up with that decision? it seems like a bad time to be reducing market coverage, although their (ex) competition must be thrilled. Any reasons you know of?

Talked to Teresa (Theresa?) at TCM yesterday about this. Aerosance developed their FADEC system as an independent company, and had been allied with TCM for several years now. Aerosance gave it up, and the program has now been brought in-house at TCM, where the whole system is under review. They have quite a few of the factory IO-240 FADEC controlled engines out in the field, particularly in Australia, in addtion to the RV installations, and are not getting out of the FADEC business at this time. Future availablity of aftermarket systems for Lycomings is unknown at this time, but has not been ruled out. We'll see.

JonJay 01-14-2009 11:44 AM

I like the challenge of flying...
 
... take my knobs away, and part of the interest and fun just went away. I found myself playing with my power and mixture settings a lot at first, and still some today, just to verify what is supposed to be happening in my own mind against what the manual says.
Also, I just like to play with knobs!


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