Fuel Injection or Carburation - Performance v. Reliability?

Without wishing to sink to the level of the primer debate or unnecessarily bring to mind Sam Buchanan's avatar, I am struggling with the carb/fuel injection debate for a new clone 360.
I have read various posts, Stein's article in the Firewall Forward section, and Eustace Bowhay's lengthy post on the subject on the Matronics RV list. I am inclined to conclude that one cannot go far wrong either way, given the (much more knowledgeable and experienced than I) people who reach opposite conclusions, but that still leaves a decision to be made.
For me, the top priority is safe/reliable/troublefree operation. I like the idea of fuel injection. To see all cylinders at or near the same fuel flow and temperature appeals both as a matter of mechanical elegance and good engine management. Higher engine output and better fuel economy is nice. Getting rid of carb heat would also be nice, but not a big deal either way (unless I am missing something).
But these advantages of fuel injection, for me, would be entirely outweighed if a carburettor was safer/more reliable/more troublefree. High fuel pressure lines seem less desirable than low (but is that a real concern?) Injection systems are less tolerant of debris/contamination in the system. Is that a significant factor? What is the sense of people as to safety and reliability of carbs v. fuel injection installations? Are carbs more or less reliable? Is either one less likely to leave you with a dead stick or leaking fuel? Is there any difference in reliability between a Bendix system and an Airflow system?
Bill
RV-6A (about to order an engine if I can ever make up my mind)

My vote is for FI

Troublefree and reliable are also my main objectives,

I have most of my time flying behind a carb, but at least 1000 hours behind Benix FI, (mainly in twins, so does that count for 2x). I never had any FI related problem other than some hard hot starts. Even that is easy to deal with once you have the hang of it. If it is put together right, FI is very relaible.

It is true, a carb is simpler, and makes the system simpler. I have had a few carb related issues, but still think the carb itself is very relaible. It is perhaps less tolerant of water in the fuel. This may not fit the population mean, but it is my experience.

I beleve that an engine with more even power distribution is subject to lower vibration. Less vibration means fewer problems over time. An engine that has more even fuel distribution is less likely to have one high EGT and burn a valve. I think there will be more engine life with an FI engine given they are equal otherwise.

In short, I have more time in carbs, but more faith in Bendix FI.

I simply don't know enough about other FI systems to comment.

I am planning to buy a new O360 clone with a Bendix copy FI for my project.


Regards,
Dale Lambert
RV-6 finishing kit
C177 (with carberetor)

views/experience as to safety/reliability

One vote for fuel injection for safety/reliability.
I asked the question because nearly all of the discussion in various threads to date addressing the fuel injection/carb decision compares performance of the two systems (power, mixture balance, ability to lean and fuel consumption, etc.) On these performance criteria, except for hot starting, fuel injection wins. (there is a suggestion in one thread that fuel injection systems seem to be in the shop more often).
Nearly all of us fly behind carbs or fuel injection. Is the lack of response because I truly am beating a dead horse here? Or that people perceive no safety/reliability difference? Or that there is no difference? Any engine builders or guys that repair these things have a view? Anybody have an unplanned landing because of a carb/fuel injection problem?
Bill
RV-6A (still ready to buy an engine but for this decision)

vote for FI

After 30 years of flying carb equipped planes, I voted for FI when I purchased an IO360 in 2006 for my RV7a. Now after 246 hours of flying the new machine, I have not regretted that decision. The economy and reliability of the FI has been as others suggested in previous discussions on the forums. My key concern was hot starts. They have been a non issue. I am pleased with my decision.

As you hinted in your first post, I think there is no absolute answer. That's why some of these topics get debated ad nauseum. I'm convinced FI is the way to go,as evidenced by the automotive industry. FI long ago becamethe standard, with a host of advantages widely recognized. My NIne will have an IO-320 from Aerosport power with the AP setup. Both the Vans folks and Aerosport power have good things to say aboutthe AP kit. That said, if I fell into a super bargain deal on a good, lowtime, carbureted 320, would I pass it up? Likely not.

To expand a little on the original question, what is the consensus on FADEC equipped engines? More complex than carbs, probably similar to electronic ignition + fuel injection... Obviously the cost is higher, but what's the downside? Is anyone out there flying a FADEC equipped IOF-320 in a -9, or an IOF-360/390 in a -7?

Thanks,
Rich

RichB said:

To expand a little on the original question, what is the consensus on FADEC equipped engines? More complex than carbs, probably similar to electronic ignition + fuel injection... Obviously the cost is higher, but what's the downside? Is anyone out there flying a FADEC equipped IOF-320 in a -9, or an IOF-360/390 in a -7?

Thanks,
Rich

Click to expand...

Stay away from the FADEC. One of the aerospace businesses on the field here tried it on two of their experimental aircraft and the guy behind my hanger who has it on his experimental has nothing but problems with trying to get the FADEC to work properly. The business that is run by A&P's and IA's pulled them off (I/O360 & I/O540) and the other guy is struggling to the point that after one year he is too concerned about the way his brand new engine runs (I/O360) that he still has not flown off his 40hrs. He'll probably bite the bullet and pull his off as well especially after seeing how well my engine runs.

The only thing the FADEC does for you is remove the leaning control and empty your pocket. However, I love their magazine add that goes through the process of changing throttle settings, leaning, then having a discussion of proper leaning technique with the co-pilot.

After years of flying carb planes, mine is the first that I've flown that has FI. I love it. Very smooth running, easy starting even when hot once I figured out the best procedure to do it, fuel efficient, and no worries about carb ice. Coupled with the Lightspeed II it has so far been a joy.

Capflyer said:

Stay away from the FADEC. One of the aerospace businesses on the field here tried it on two of their experimental aircraft and the guy behind my hanger who has it on his experimental has nothing but problems with trying to get the FADEC to work properly. The business that is run by A&P's and IA's pulled them off (I/O360 & I/O540) and the other guy is struggling to the point that after one year he is too concerned about the way his brand new engine runs (I/O360) that he still has not flown off his 40hrs. He'll probably bite the bullet and pull his off as well especially after seeing how well my engine runs.

The only thing the FADEC does for you is remove the leaning control and empty your pocket. However, I love their magazine add that goes through the process of changing throttle settings, leaning, then having a discussion of proper leaning technique with the co-pilot.

After years of flying carb planes, mine is the first that I've flown that has FI. I love it. Very smooth running, easy starting even when hot once I figured out the best procedure to do it, fuel efficient, and no worries about carb ice. Coupled with the Lightspeed II it has so far been a joy.

Click to expand...

Hmm. Do you recall whose FADEC product they were using (there's at least 3 out there I can think of), because the Aerosance website suggests they don't do one for the IO-540?

After a little more digging, everything I can Google or search says it's a Good Thing, if you can live with the price. Aside from the gee-whiz factor, and efficiency improvement, I'm mostly interested because it means one less knob to consider when I find myself in a bad situation...

RichB said:

Hmm. Do you recall whose FADEC product they were using (there's at least 3 out there I can think of), because the Aerosance website suggests they don't do one for the IO-540?

After a little more digging, everything I can Google or search says it's a Good Thing, if you can live with the price. Aside from the gee-whiz factor, and efficiency improvement, I'm mostly interested because it means one less knob to consider when I find myself in a bad situation...

Click to expand...

Two points for you here...

1) - Consider the source of those "good thing" comments - they probably have a dog in the fight and may very well be acting as cheerleaders for FADEC, even if for no other reason than to make themselves feel better about writing that big check.

2) - One less knob to consider in a bad situation is a good thing - unless the absence of that knob is actually the cause of the bad situation. FADEC's can be a valuable tool when they work right - and if/when they don't, you don't have a Plan B to go to. Personally I'm a control freak with anything mechanical - give me the levers, and I'll do the thinking. I might use an auto-tool for 98% of the actual time spent pulling those levers in order to reduce constant workload, but when the auto-tool quits auto-tooling, I want the levers available for me to push/pull myself.

can you run auto fuel in the FI? i must me able to run some form of autofuel due to living on a private strip. thanks

FI will handle autofuel just fine - you just need to make sure ALL parts of your powertrain from fuel tanks to pistons can handle autofuel. That means compression no higher than 8.5:1 (some will say 8:1, but Superior says their 8.5:1 is good for 93UL), no rubber parts in the fuel system (hoses need to be Viton or Teflon core, seals should be Viton), no rubber compounds in the tanks or fuel level sender, fuel pump should be automotive quality or capable of handling autofuel per the manufacturer. It's my understanding that capacitive senders will need to be recalibrated for 93UL vs 100LL, but I don't know that for a fact. Stay away from ethanol blends, you get into vapor pressure problems. Having dual electric fuel pumps in the wing root will help, but all the engine manufacturers that say their engines are good for 93UL specifically forbid running ethanol blends. I've been advised by several people whose opinions I trust that I should alodine all aluminum fuel-exposed surfaces (tanks, ribs, baffles, pickups, and any aluminum fuel tubing) to prevent possible corrosion from water trapped in ethanol blends in the event I should ever have some in the tanks.

Fuel Return Line

Do FI setups require a fuel return line to the tank/tanks?? I am in the process of constructing tanks and am considering fuel injection.

Return line

Some do.

Some dont.

Check with the manufacturer of your chosen system, if you have already chosen one that is.

Pretty easy to put in a fitting, and just cap it if not needed.

And something to consider along those lines - a return line allows you to run a "purge" valve, which will assist considerably with hot starts (and to be fair, also gives another point of failure to keep an eye on). The return line from the FI should be (in my opinion) routed all the way to the tanks instead of Tee'd into the feed line to the pump, so the fuel coming back from the firewall (which has picked up some heat from the engine environment) does not continue to recirculate and get hotter and hotter until vapor lock occurs - this situation would be most aggravated during long periods of low power (low fuel usage, but still circulating and building heat), such as descent into an airport - and then when you need power for a go-around or pattern work, you may be vapor locked at the worst possible time - low and slow. Returning the warm fuel to the tank (preferably one or more bays away from the pickup) keeps cool fuel flowing through all your FWF lines to minimize this source of vapor lock.

24Golf said:

Do FI setups require a fuel return line to the tank/tanks?? I am in the process of constructing tanks and am considering fuel injection.

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Only FI systems based on the Continental design require a return line - of the systems available for RVs, that is the ECi system.
Bendix/Precision systems have no facility for a return line.
The AFP system uses a purge system to circulate fuel to avoid hot start problems only, it is not used airborne.

I disagree with the previous post, the re-circ can T in after the fuel selector & before the electric pump - it does not have to go back to a tank as the heat that is of most concern is from the engine block heat soaking the mechanical pump - firesleeveing all FWF fuel lines and minimizing fuel volume FWF will help a lot. Also you would never use the re-circ airborne - it is only used pre-start or to shut down the engine. I have never experienced the vapor lock scenario described.

Re-circ fuel valves are very expensive and probably not required for AFP.

Hot starting has been discussed here many times before, with some very good explanations of what to do. It is all in your technique. It is possible to get in trouble, but after owing an injected airplane for a short while you will learn what to do.

I think you may have misunderstood what I was trying to say with regard to the recirc of the fuel - I was not implying that any sort of valve be used at all (aside from the purge valve supplied by AFP if that's your vendor of choice). My intent was the return fuel line not be routed back into the intake of the pump, but rather all the way back into the tank. Routing it to the intake of the pump will work, and there are certainly hundreds flying like that, but in certain conditions you will experience high fuel temps in the FWF section. Normally this is not too much of a problem for either 100LL or 93UL, but if you should (accidentally or intentionally) have a tank of 93UL ethanol blend, the higher vapor pressure of the ethanol blend combined with the higher temperatures significantly decreases your vapor lock safety margin. Putting the warm fuel back into the tank instead of the pump intake eliminates this possibility. It's entirely possible that by firesleeving the FWF lines and returning the warm fuel to the intake of a wing-root electric pump you dissipate enough heat just in the return line that it's not an issue, I don't know.

For a 100LL-only aircraft, it's not an issue. For a 93UL non-ethanol-blend only aircraft, it's not an issue. It MAY be an issue for an aircraft running ethanol-blend MOGAS. I intend to run non-ethanol MOGAS, but I cannot absolutely 100% guarantee that I won't ever accidentally get a batch of ethanol-blend fuel, so being that I haven't built my fuel system yet, I am planning it out and will build it to solve that (currently nonexistent) problem before it becomes a problem.

Penguin is absolutely correct in that the heat soaking from the engine block to the mechanical pump is the prime culprit - if it can heat the fuel passing through it enough to boil it, you're in trouble. If you have warm fuel in the pump to begin with, you're in trouble faster. The cooler the fuel is that runs through that engine-driven pump, the better off you are. It's not likely to ever be a problem - but the consequences are severe enough that I intend to eliminate even that small possibility. I would not advocate tearing apart and rebuilding the fuel system of a running aircraft - but since mine is still in cardboard boxes, it will be built as described.