Limp mode a concern?

[captain_john]

Well, I know Chad is seriously considering the Egg engine and so did I at one time. What I couldn't overcome is the possibility of the computer entering limp mode during a short field departure or at some other inopportune time.

The liklihood of this happening is probably greater than any other event with any other engine considered.

If a sensor squawks an issue that triggers the engine to go into limp mode, the engine puts out approximately 45 horsepower until the issue is cleared. To the best of my knowledge, it cannot be cleared from the cockpit.

This is a primary concern of mine. Does it bother you?

CJ

[cjensen]

Nope. It's not any more likely than dropping a mag at the same inopportune time.

To my knowledge, this has never happened at a time like that. That's not to say it won't. Fact is, it is just as rare as losing a cylinder or a mag.

I see 'limp home' as a positive mode if a problem develops in cruise, just as two mags are a positive if one fails.

I'm not sure about it being able to be cleared from the cockpit. The new ECU is different than the stock one they were using, and there are more 'aviation' type modes programmed in now.

[cjensen]

Well, I know Chad is seriously considering the Egg engine...

More than considering...

The liklihood of this happening is probably greater than any other event with any other engine considered.

Why??

If a sensor squawks an issue that triggers the engine to go into limp mode, the engine puts out approximately 45 horsepower until the issue is cleared.

Where does this info come from?

[captain_john]

Chad,

I can still drop one mag and have 90% plus power. Mags drop alot, but that's why there are 2 of them.

The liklihood of this engine squawking a code (REAL LIKELY! Like any car.) is because it uses auto OBDII and any sensor (and there are ALOT!) will trip the check engine light and depending on what the problem is... bingo, limp mode.

The info comes from Subaru.

Lemme know what the Egg man says.

CJ

[cjensen]

The liklihood of this engine squawking a code (REAL LIKELY! Like any car.) is because it uses auto OBDII and any sensor (and there are ALOT!) will trip the check engine light and depending on what the problem is... bingo, limp mode.

The info comes from Subaru.

Lemme know what the Egg man says.

CJ

Okay. I can't see or agree to the REAL LIKELY possibility of this happening. I can't remember the last time I had a check engine light come on on any of my vehicles. And that last time it did happen, the engine didn't quit or even lose power.

If this were happening even infrequently to the Subie flyers, we'd hear about it on the group site, or email.

Even so, I still don't see limp mode as a threat, any more than losing a cylinder...percentage or risk-wise.

I guess the 90% power when losing a mag depends on the engine. We had a Malibu shuck a mag on take off, and it barely made it around the pattern, and wouldn't go any higher than about 300ft agl. Scary.

[cjensen]

Don't know if you'll get this before you head south CJ, but here's the answers straight from Gary and Jan...

From Gary-

"Limp home" ('flutter home?') was something Subaru did a few years
ago. It does very little for anyone flying an airplane. This no
longer exists in engines we sell today.

From Jan-

The Subaru ECU's insert learned data to keep the engine running as if the sensor was there.

Jan

[Spike]

So does that mean he is replicating data for the ECU if a sensor goes bad?

[cjensen]

Not sure how to answer that one. I don't know that they are replicating data, but I'm also not really sure what you mean by that...

[Spike]

It sounded by your quote of Jan that if sensor information goes away or becomes bad, that the electronics just reuse information that they previously learned.

[svanarts]

One answer from Egg's FAQ:

QUESTION: Is the engine computer the same as the automotive??

ANSWER: Yes it is, up to 2004 model engines. After this we use our own system.

I thought I read a description of how the computer worked with the sensors on his website somewhere but I can't find it now.

Chad's making me consider "the dark side" of engines.

[cjensen]

I posted a question to the Subie group about learned data, but the guys are all at Sun N Fun as of yesterday. I think they'll check messages each night, but it may be a while before I can properly find your answer.

Scott,
I looked at the FAQ section on the Eggenfellner site, and it abruptly ends at the bottom and some of the categories are not addressed. This is new to me, so I wonder if they know about the missing info.

I'll check with Jan on that too...

[deuce01]

I'm not sure about Subarus but I worked for Honda for 15 years and the way the ECU worked was like this. Now things may have changed...but here is the rough idea.

Before the ecu gets power it has no data from the sensors (obviously)
When the ecu first gets power it is in learn mode. What that means is that each sensor is feeding it data. For each sensor the ecu records a min, max and average based on output. this average is computed as the min and max fluctuates. When a sensor fails the ecu uses the last value that is in memory for the average. When replacing a sensor always reset the ecu so it relearns the new data.

It is more complex that this....but thats the basic idea.

Not every system is the same so if this is not accurate... please disregard.



Deuce01

[Spike]

Thanx for the info.

[jim_geo]

I have always thought the Suburu was a good choice. What put me off about it were problems with the cooling not being worked out. People seemed to be fighting with drag problems caused from cooling their radiators. Also the fact that you’re pretty much stuck with an expensive composite prop was a problem for me. Other than those two fairly minor problems (for me) I think there is a lot to be said positively for the conversion.

[cjensen]

The cooling issue was solved with the third radiator. Cooling drag has been solved with a larger exit area with the new SJ cowl that was designed specifically for Eggenfellner's current line, and is retrofitable to older ones with the third radiator mod.

The prop cost can be solved by using an IVO Magnum. Not the most ideal prop for this engine package, but I know a guy in Missouri that has one with his H6, and absolutely LOVES it.

It's all a series of compromises, regardless of what engine is put up front.

[1:1_Scale]

Automotive engine ECU's typically run in two modes from what I understand (my friend started http://www.efi101.com so I've picked his brain more than once)- open and closed loop. Closed loop mode is when the ECU is relying on data from all of the sensors to calibrate the air/fuel ratio and timing advance. For example, the O2 sensor tells the ECU what the air/fuel mixture currently is, so if the engine is running rich, it tells the ECU and the ECU shortens the duty cycle of the injectors until the feedback from the O2 sensor says that the mixture is correct.

Open loop is when the ECU is running on a pre-programed map. Typically, cars are running open loop whenever they are at full throttle. My car runs in open loop all the time for mixture since I don't have an O2 sensor. We mapped all load and RPM points on a dyno with an O2 sensor, so something would have to change drastically in the engine or fuel system to really foul things up.

Some engine management systems have two sensors for essentially the same job. For example, current VW/Porsche/Audi cars have a mass airflow sensor (MAF) and a manifold absolute pressure sensor (MAP). If one fails, the other can still do the job. With my ECU, I only have the MAP sensor. I think if that fails, the ECU will use input from the throttle position sensor and crank position sensor (RPM) to estimate the MAP, I'm not 100% sure on that though, but I'll find out later

Hope my rambling helps a bit

[captain_john]

Thermos, Antony and I were talking about this tonight.

We all had the same question. Ok, if it uses the last value and flies like the sensor were there and working properly and it really ISN'T... then what?

Does a light come on? How do you know there is a code stored?

Also, I suppose the severity of the issue depends on the sensor that failed. What would be the worst case scenario? A TPS switch? Erratic RPM control? No RPM control?

Dunno???

CJ

[cjensen]

I posted your questions to the Yahoo group, and this is the short answer I got from Jan...

The system will compensate for sensor error and shine a warning light. The pickup sensor for timing and RPM information is critical but also very robust without any moving parts.

Jan

Is that an answer???

[Spike]

There is a sensor that monitors crank position. Many times they use the "hall effect" to do it. The general rule is that if it goes bad, the engine stops. Thats probably why Jan was talking about how robust it is.

[captain_john]

Guys, I dunno... I suppose the only REAL way to find out is to fail thee items individually and collectively.

As the builder of my own airplane, I would want to know these answers before I fly it. This takes time and lots of record keeping.

I couldn't rest easily taking one man's (the engine builder's) opinion.

In case you don't know me, there is really only one opinion I care about and I will let you guess whose that is!

Sooooo, I guess what I am saying is... if I were installing the engine in my airplane, there would be LOTS of ground testing.

Egg doesn't like to answer these questions. I am not sure why. Maybe there are several reasons. One of them is probably because most of us wouldn't know what he means without sufficient time and effort getting up to speed on the design. This is probably justified. I am sure he also feels that he has already figured all this stuff out and we, the end user need not b troubled by the answer. The rub is, my answer/solution might be different than his and I would want to know it!

Case in point, what happens when any and all sensors go belly up?

He would be well served to have a demo engine at the airshow and fail stuff in front of curious people. It could build confidence in his product in the minds of disbelievers. I am sure he wouldn't do that because it could be a double edged sword.

CJ