Having backup ECU's for Auto engine or not

[10_Dreamer]

Yesterday, I spoke with Bud Warren (really a nice guy btw) about his RV10 package and was asking questions about the computer system they use. They are using a programmable GM performance computer with a standard ls1. They remove the drive by wire system and use a regular butterfly. The package seems very simple (which I like), but I am not very familiar with PSRU's.

My question is, how concerned do we really need to be about ECU failures and having an engine actually stop from that failure. In all my time driving, and even modifying of vehicles, I have yet to have an ECU crash and completly stop the engine while driving. Even when ECUs do fail (after a car crash or damaged sensors, thay have always ran in a "limp mode" to get you home or whatever. Adding additional components as backup seems to make even more possible failure points. Something as simple as Ross's system should do the trick.
http://www.sdsefi.com/

My other question/comment is, what make these kits so darned expensive! I'm trying to add up the components and I just can't get to 30k! I realize they are making a profit, but what components are expensive other than the PSRU at ~9k? After calling Van's, I only get ~$450 back for not using thier motor mount, and I would also save about 5k from the Firewall forward package that I wouln't need (still need a prop gov though).
Anyway, just me thinking out loud. I'm eyeing a couple cheap 540's but would love to go the LS1 route.
Wyatt

 

[Randy]

This is one of those highly debatable subjects. Some feel that just adding a second ECU and all the wiring and switching can add enough failure possibilities to shelve the idea.

Others incorporate a second ECU inside the same enclosure..

My feeling is that the wiring that supplies current to the ECU and the critical sensors is much more prone to failure than the ECU itself.

All engines have single point failure items, especially if they are to be light enough to work in an airplane.

The OEM ECUs are produced and developed in such large numbers they simply have to be extremely reliable. We just do not hear about very many cars failing do to the ECU failing. The problem with those ECUs is they are programmed for car applications, and this can be very different than aircraft application.

Limp Home is not an option in an airplane..

If you are really trying to save money, you might be better off to go with the tried and proven engines. There is considerable risk of incurring additional developement costs and TIME when installing a package that has not already been tested in many other aircraft before you came along... Ask me how I know...

Randy C
RV7A Turbo Subaru using SDS

 

[Rotary10-RV]

Ground testing

There was a thread on one of the Rotary newsletters about ground testing. What does it give you etc... If you look at older issues of Contact! magazine you can find articles about failures caused by auto ECUs. The problem was that some of the ECUs treated a 2-3+ minute wide-open-throttle operation as a FAILURE! I would suggest that if your cooling system is up to it a 5 minute WOT test could tell you if this was built into your ECU. I would suggest at least checking for that or going with an established aftermarket system like SDS. Most asftermarket systems are designed for racing or other high-output operation and are designed to operate there for extended periods. I'm using a rotary (wankel) and the rotary responds very well to LOP operation to improve BSFC, so I want a system I can actively lean which rules out a standard auto unit. Personally I think anything that took out the first ECU unit would probably knock out a second. (Exception lightning!) But we shouldn't be flying in that kind of weather anyway right?
Bill Jepson

 

[az_gila]

Would a double...

..ECU system work, but with a split - each one feeds half the cylinders - rather than in parallel?

I know some of the bigger auto like engines used in planes have this system.

Working on the principle that half of your cylinders working is better than no cylinders...

It would somewhat depend on how the FI is set up...

 

[rv6ejguy]

We've supplied some dual ECU setups in the past with manual switching/ isolation recommendations. If done right, it can work fine. If not, you actually increase the likelihood that the switch gear will cause failures of both systems. Most users now have gone back to a single ECU.

As far as the electronics go, you can say for most purposes of argument that you are never likely to have the ECU fail in your flying lifetime. They are way, way more reliable than your engine, cooling system, gearbox and even propeller as far as MTBF goes. One of our bench test ECUs here has run for nearly 100,000 hours now.

What you have to worry about is getting moisture into the ECU, poor wiring connections and fuse or breaker failures. These can't be blamed on the ECU of course but still put you into a field.

What is of more worry is inappropriate software responses in the aviation environment. The auto designers of these units never gave any thought to these being used in aircraft. Their design objectives are heavily influenced by part throttle fuel economy, emissions and the protection of the engine to reduce warranty claims. None of these would be a consideration on a clean sheet aviation ECU. Additionally the integration of many chassis control features which may be interrelated with engine control functions reduces the clarity of what is essentially a simple task running an aviation engine.

It worries me that chassis controls and design objectives make using an OEM ECU potentially unreliable and indeed these issues have caused a number of accidents. I don't believe anyone other than the engineers who designed and programmed these ECUs really understands all the combinations and permutations which could cause engine running issues. These are very complicated devices running over a million lines of code. Simple things like not having the gas cap tight in a car, or not have a cannister purge solenoid in your airplane can cause problems. These are entirely unrelated to engine control in aviation.

I hope LOTS of testing preceeds use before release of the product. Robinson has been flying OEM GM ECUs for years now (with some closed loop tweaks) and the older LS1 units may be a better choice than a new LS2 or LS3 ECU which are vastly different and vastly more complicated from both a hardware and software standpoint. The newer the ECU, the scarier and harder it is to use in aviation.

Aftermarket ECUs do not have billions of in service hours on them but they run a fraction of the code and programming responses are usually predictable with far fewer external variables to worry about.

Bottom line, customers should not be test subjects unless they understand that they are.

A number of people have asked about using our new 8F ECU on aviation engines and I know I've disappointed or annoyed some people by saying that they won't be released into the aviation market until we get a lot more out into the automotive market for feedback and proving their reliability.
With the economy as it is, these are not hot sellers so it may be years before we are comfortable selling them for aircraft. Sorry, that's just the way we do business. I don't want to see anyone hurt because we didn't test enough in the real world.