![]() |
Carb vs FI vs EFI Reflections on reliabilty
The shortcomings and blessings of carbs are well known:
Low pressure, easy start but poor distribution and floats sink. ? controlled leakage? Bendix style FI can be well balanced, use a mechanical pump but can be a hot start problem with more plumbing and hardware than a carb. EFI offers ?car start? elegance with the requirement of two electric pumps due to high pressures and reasonable but required aux electrical plan. Here is my point; I passed on EFI for my current project because Priority #1 was reliability for a 2 seat ship. Simplicity was also a priority because I want to fly, not develop and debug MAP,temp and O2 sensors ! BUT, after committing to ?a controlled leakage ? system, I have learned that the EFI software can be and is written to default to ?get me home safe? parameters in the event of sensor misbehavior. This has caused me to be more open to EFI as conservative flyer. I offer this for anyone wresting with the decision..Larry |
It's interesting how people evaluate the reliability of electroincs vs. mechanical devices. This is often done on the basis of past experiences.
Well designed mechanical devices, when properly installed and maintained are generally pretty reliable. Modern electronics, ditto. It's the occasional anomaly that can throw a wrench into reliability. For carbs, sinking floats, broken float arms, jet problems etc. For Bendix style injection, maybe split diaphragms, cracked line or a piece of debris in a nozzle. For EFI, maybe a broken wire, bad chip, sensor failure. Mechanical devices do indeed fail and we've all had an experience with that in our lives or know someone else who has. Interestingly, people often feel just fine with one carb supplying fuel to an engine but are not ok with one ECU or a couple of EIs supplying fuel or spark delivery. People 15 years ago didn't think too much about glass panels replacing their mechanical gyro instruments and steam gauges in GA aircraft, now almost nobody installs steam gauges. Electronics with a backup (also usually electronic these days) are fully accepted now. So, in the EFI industry, we give the people what they want. If they worry about electronics failing, we have dual ECUs, dual sensor suites and dual fuel pumps along with backup power sources. That being said, we have sold over 1500 aviation ECUs and EFI kits which were employed in single setups and about 400 as dual setups, most of those, more recently. Over half a million flight hours shows that our stuff is extremely reliable. As Larry pointed out, on our systems, most sensor failures (air temp, CHT, TPS, MAP) are not critical to maintaining engine power. In the case of the crank sensor, we've never seen an electronic failure of our Hall Effect sensors in 20 years and millions of hours collectively. You should always fly what you are comfortable with. If that's a carb and mags, that's just fine but always be aware that in a single engined plane, there are plenty of critical single points of failure. Cars haven't used points and carbs for 30 years now and coming from that industry before, I can say that EFI and EI resulted in the single most important leap in auto reliability ever. It reduced maintenance and repairs massively. Finally, I always like to point out that one of our ECUs ran on the bench 24/7 for years, accumulating 145,000 hours without failure or any maintenance. I doubt if any carb, Bendix or mag can make that same claim. Just another point of reference. |
I fly commercially, and have had this discussion with several dozen out of the several thousand pilots I have flown next to. I have 6 civilian type ratings, and 4 military jets as well. I have had to memorize, and fly, other peoples system designs.
Airplanes have redundant systems because aviation grade electrical components are from the dark ages of the middle of the last century. Production light aircraft fell of a cliff 35 years ago, so they never improved. They are still in the dark ages. 50+ years ago, aviation grade was the gold standard. It still is in some regards (raw materials, fasteners, etc). But the auto world passed up aviation 30 years ago, and never looked back. Instead of redundancy, modern cars (and consumer electronics) went for "perfect". And they have nearly achieved it. EFI and EI, properly done, bring a Lycoming into the 1990's, at least. Everything as "automotive" as possible. Every modern car has 1 alternator, battery, single engine sensors, single ECU, single fuel pump. They just don't fail (except for Fiats). Towing companies make their money towing illegally parked cars. The EFI's for airplanes actually have more redundancy than I would require. I would be happy with less. I don't know if they chose the redundancy, or it was demanded of them by users. But I won't complain about the redundancy, and will use one as designed. Each of us is comfortable with some level of technology. For some it is carbs and magnetos. Frankly, they scare me. But, to each, his own. |
Debating the reliability of "electronics" or mechanical devices" is pointless. The real questions are...
1. The reliability of each individual component, as installed. 2. The reliability of any required supporting system(s). Quote:
Consider the ordinary fuel injector, a remarkable electro-mechanical device. The installed environment is very different in a car (intake manifold, attached to a water cooled head held at 210F, and generally distant from exhaust components), in an SDS installation (top of an air cooled head), and the upcoming EFII installation (bottom of an air-cooled head, adjacent to a red hot exhaust header). Although all may have a low failure rate, should we believe the failure rate will be the same for all? Even if you wish to believe the reliability of the individual component will be the same regardless of how installed, we must still consider supporting systems. That injector requires a machined screw-in mount for the aircraft head, an o-ring seal, a plastic electrical connector, wire crimps, pins and sockets, a signal wire, and a fuel supply hose or pipe. I am not opposed to electronic fuel injection. Professionally, I love fuel injection. It's the best thing that ever happened to cars and trucks. But gang, let's quit the huge generalizations. The airworthiness of a particular airplane is a function of the application, fabrication, and condition of both individual components and support systems, here as installed by individual builders. The huge jump in road vehicle reliability is not just a matter of better components. It is a equally due to close attention to installation details, at the design level. |
Dan brings up good points as usual.
The single most important part of Experimental EFI installations is probably wiring since there are multiple areas where a poor connection or strain relief could cause an open circuit. Dan rightly points out that auto OEMs can test and refine wiring installation and practices and then make every one the same on that model. We can't do that on varying, individual installations. The best we can do is insure that every crimp/ solder joint is excellent, proper strain relief is provided, wires are not routed near high temperature components without proper thermal protection and wires are protected from chafing. Second area of concern (or perhaps first) is electrical system design- batteries, primary wiring, alternators, switching. I see a lot of incredibly complex schematics in this area being posted on VAF and I can't say I like many of these. Keep it simple, keep connections to a minimum and concentrate more on the most likely failure modes and scenarios rather than parts that might fail .001% of the time. Third would be fuel systems. I'd urge people not to deviate from what we recommend for pumps, pump mounting, line size, fittings, line routing and filtration. Best reliability generally comes from following time-proven reliable practices. We should not generalize overall system reliability, especially between brands with limited or no demonstrated track record. With regards to injectors on air cooled engines, I haven't observed a noticeably higher failure rate on D-Jetronic or Motronic EFI equipped VW and Porsche engines despite the higher operating temperatures they're exposed to. Highest temps in aircraft we see from instrumentation are after hot shutdown, not during operation where air is passing over the components and cooling fuel flow is high. Different mounting positions may see higher temperatures. My first post assumed that people do a proper installation job on their EFI system as this is assumed (or hoped) on a carb, mag or Bendix installation as well. If you do a poor installation on any of these, it can bite you. |
Proper installation ?
So Ross, we have all read Bob Knuckles and some good references in VAF threads. Is there one source for reference regarding ?though shalt ? use these connectors, strain relief shrink tube length, solder /don?t solder etc. We all think we are OK, but probabably not ?optimized?. Maybe Dan would be kind enough to author a short course 😊
|
Quote:
For FF connections, most everything is crimped and strain relieved within the connector. These practices have stood the test of time- literally millions of hours collectively in environments much more severe than what our airplanes see. We have some limited info here: http://www.sdsefi.com/wiring.htm and hope to add some more photos/videos of other connections as time permits. One thing I'm not too keen on is people using vinyl clad crimp connectors in aircraft. They don't offer great strain relief. I prefer non-insulated ones, solder or crimp and then slide a long piece of double wall, glue infused heat shrink over the joint. Time consuming and a PITA to do in many locations and cases but WAY better strain relief, corrosion protection and retention qualities. See the photos below: ![]() Your EFI system totally depends on reliable ground and power connections. |
Quote:
|
Well, there are crimp terminals, and then there are crimp terminals....
The crimp terminals we use as an OEM are sized appropriately for the wire, and the strain relief portion is metal. Used with the appropriate crimping tool, these are bulletproof. This is a long way from the DIY kit you get at Pep Boys. |
Quote:
Boeing/Douglas approved, millions of flt hours have proved their reliability. https://www.alliedelec.com/te-connec...SABEgLKBPD_BwE https://www.alliedelec.com/te-connec...9275/70089871/ |
| All times are GMT -6. The time now is 08:36 AM. |