Gee that makes me feel bad. I'm not cool like a modern fighter pilot. I'm only in my 40's and fly modern airliners; I want to be cool, but I still like moving the mixture knob once or twice a flight. It just not a big deal to me. I admit if my engine could run perfect mixture automatically, that would be cool. Is that what the Subaru does in a plane?
Quite frankly, for a community of experimental aircraft builders, I find the way these discussions turn out fascinating. Some of us find production aircraft not to fit our needs, wants and budget and have no problem building a "better" airplane like an RV which until recently could hardly be considered "proven". Yet some of those same people are adamant that the same mentality cannot be applied to the engines that go in these airplanes. For the sake of discussion I'm not saying that Subaru is better. But to say that nothing can be better than (insert choice subject) is to say you might as well give up on life and commit hara-kiri. My personal thinking is that there is always a better way. We're flying airplanes right? Of course nobody could possibly find a better way to get around than driving, right?
Jan, I understand you don't use the O2 sensor. I also recall reading you have dropped the mass-air or throttle position sensor? How do you maintain perfect mixture control with your EFI system?
I am not cool; I still think old farm tractor technology, mags and mechanical FI or Carb are still cool in their own way, even if the cool kids don't like it. ha-ha
You can search the net for any engine +"problems" and the result is the same. This doesn't indicate anything particular.I disagree. The 1.7 engines are rarely making it to TBR and one flight school in the UK is now suing due to the dreadful experiences they've had with their Thielerts. I have a friend who owns a Diamond maintenance facility here 2 blocks from my shop and they also see many problems with these engines. They are hour hogs (good for them, bad for the customer and Thielert). http://www.avweb.com/avwebflash/new...sDiamondOverDiesels_196928-1.html?CMP=OTC-RSS
While the 1.7s are not failing catastrophically in most cases, serious problems with pistons and rings and extreme oil consumption is afflicting many with well under 500 hours on them.
To their credit, Thielert is paying most of the bills and applying lessons learned to the new 2.0 engines yet customers are generally unhappy with these engines. Aviation Consumer had an expose on this Dec. 2007 and you can find plenty of references to problems on the net- just type in Thielert 1.7 problems or similar. You can find other posts from Europe on various forums if you do some digging as well.
An engine which burns 35% less fuel than a Lycoming is no good if you have to fix it all the time or pull it to plug a new one it well before TBR. Some do not consider the performance to date very good for a certified engine, despite it being a new design and having had over $200M invested in the development and certification.
You can search the net for any engine +"problems" and the result is the same. This doesn't indicate anything particular.
It is not only burniing 35% less fuel, it is burning 35% less of a fuel that cost 50% less.
When diesel aero engines actually go 2400 hours without a ton of maintenance hours, they will have arrived. Nobody has proven that yet.
Interesting comment, should it not apply to any alternative engine and the required components necessary for their installation on our airplanes??
Bill I agree with your comments; well said. To be fair, even certified engines are not TESTED, except many be initial break-in. "Compliance" is making sure every part is made exactly the same way it was made on the "approved" test engine'(s) certified. Every engine after is a "CLONE". It's how the parts are made, the process, paper trail that gives the pedigree. Even the CLONE engines have certified parts. If you buy a new Lyc cylinder regardless of the vendor, it can go on a "clone" or certified engine.An experimental is not LEGALLY required to meet these standards. (true) A experimental engine, and that includes the Lycoming clones, is not tested to those standards. (a clone lyc is not really experimental) A Manittuck assembled Superior IO-360 clone is an EXPERIMENTAL engine and the combination of parts may never have been tested to certified standards. (not true its made with the same certified parts)
If you ask for a certified engine the price instantly goes up several thousand dollars, even if the same parts were used you are now paying for the paper trail. (true) I'd just as soon avoid that. A Timken bearing for the front wheel of a 1972 DODGE is about $9.00 at the auto parts store, The exact same bearing for Grumman Tiger with a single different character etched on the bearing race goes for $50.00+ if you can even find a place that sells them. Just bear that in mind. (Bill I hear you)
You are welcome to believe the hype if you wish. You find out if ANY 1.7 has reached 2400 hours. I think you will find the answer is no.
Jet and avgas are essentially the same price over here. Downtime waiting for engine changes will eat up any savings in fuel. When diesel aero engines actually go 2400 hours without a ton of maintenance hours, they will have arrived. Nobody has proven that yet.
I know that the Thielert have had some issues, but it is nowhere near this big catastrophe as you describe it to be. The TBO is not 2400 h yet as far as I know. It is 1000 h, and then you get a replacement engine for free. At 2000 h, you get a new engine at reduced cost. The aim is more than 3000h TBO in the future.
I know that the Thielert have had some issues, but it is nowhere near this big catastrophe as you describe it to be. The TBO is not 2400 h yet as far as I know. It is 1000 h, and then you get a replacement engine for free. At 2000 h, you get a new engine at reduced cost. The aim is more than 3000h TBO in the future.
As far as I know (could be wrong) this is more of a business strategy, you get an overhauled or rebuilt engine where only the worn parts are new, then you need 100% control of all the parts. I guess it is more practical, economical and better quality vise to ship the entire engine to one (or a handfull) service facility with all the proper tools and knowledge instead of training thousands of mechanics. It is also the only way to get proper measurements of the wear for proper feedback for eventual re-design of parts. This is a brand new engine, and the factory cannot possibly know how it will hold together under various conditions, there are just too many unknown variables. Their aim is 3000h, and this is not an easy achievement. The certified Rotax'es are still only 1500h.B,
I hope Thilert can fix some of the issues they have had. I'm am almost a dogged champion of alternate engines, I do worry though that Thielert had to certify as TBR, Time Between Replacement, rather than the common TBO. I would like to find out why this restriction went into place. Like Dan H has mentioned is it the number of cycles? (heat, vibration, otherwise) I worry any time that the base engine core isn't suitable for re-use. I would also like to know if this was imposed by Thielert or the FAA. What part is marginal enough to need the engine replaced? Or to turn the other side of the coin are they doing this as a simple precaution to check out the early engines wear points? Any time you see a different requirement you wonder about the reason for the different requirement. Consider it like Dan's request for the vibrations studies from Eggenfellner so he could satisfy himself it was done correctly. I do believe that Diesels will become a common GA engine it just makes sense.
Bill Jepson
As far as I know (could be wrong) this is more of a business strategy, you get an overhauled or rebuilt engine where only the worn parts are new, then you need 100% control of all the parts. I guess it is more practical, economical and better quality vise to ship the entire engine to one (or a handfull) service facility with all the proper tools and knowledge instead of training thousands of mechanics. It is also the only way to get proper measurements of the wear for proper feedback for eventual re-design of parts. This is a brand new engine, and the factory cannot possibly know how it will hold together under various conditions, there are just too many unknown variables. Their aim is 3000h, and this is not an easy achievement. The certified Rotax'es are still only 1500h.
It is a simple matter of MAP and air temperature to calculate the amount of air entering the engine. The ECU can then simply add the right amount of fuel for any condition. The altitude is not important, just the MAP and air temp.
Jan
<snip>
Right. The vital question is amplitude. Material stress in steel parts should be below the knee in the SN curve.
There are two kinds of system control.
- Open loop control - The system generates an output (fuel quantity) based on one or more inputs (MAP and air temp in this case). Essentially it's a best guess methodology.
- Closed loop control - Works just like open loop control, but there's an additional input...an O2 sensor. This provides a feedback correction to compensate for other variables. So the computer says, ok for this MAP and air temp I think I need to supply X amount of fuel. Then it checks the O2 sensor and says hrm, it looks like my guess was a bit too high (or low), so I'll reduce (or increase) the fuel flow a bit. The method of correction is historically a PID loop.
Without an O2 sensor (or some other type of feedback to allow closed loop control), the engine likely won't run as efficiently as it would in a Subaru (equipped with O2 sensor).
Edit:
After thinking about this some more, an open loop computer controlled system could actually be less efficient than a standard lycoming with an engine monitor running LOP. In the LOP scenario, that's essentially a closed loop system...it's just that the pilot is closing the loop.
There are a couple factors that could help Lyc's run more efficiently:
- Engine efficiency is very directly related to compression ratio. Since the Egg runs on auto gas, it will require a lower compression ratio than an engine running 100LL. Thus, any Lyc with a higher compression ratio than the Egg will benefit from this.
- As a general statement, for a given throttle position an engine will produce more power per stroke at a lower RPM than at a higher RPM due to losses in the intake and exhaust system. Certainly there are lots of other variables at play here, but this could also give a lower RPM Lyc an advantage over a higher RPM Subie.
There are a couple other concerns about using a MAP sensor. I've had personal experience with at least three cars (none Subaru) that would not run with a failed MAP sensor. It makes me wonder what would happen if the MAP sensor on the Egg failed low, high, or anywhere in between. This is the kind of thing I was referring to when I asked about FMEA in the previous post.
Automotive engines have a much lower octane requirement today than aircraft engines. Witness many engines today with CR around 10 to 1 which run on 87 octane. Modern combustion chambers and liquid cooling make this part much better optimized than their older air cooled cousins. We have many designs today topping 11 to 1 which run on 91 octane.
The volumetric efficiency of the modern Subaru surpasses the Lycoming by a substantial margin due to AVCS, induction pulse tuning and 4 valves per cylinder. Where it loses out is in frictional losses at high rpm. This negates any advantages it might have due to modern features and technology so we don't see auto engines offering any improvements in SFC at this time.
Mike Starkey, that is a distraction but you are right. Noise - Lyc would be too loud in a car by today's standards, even if you ran full mufflers and tail pipes; you would hear the clacking with out water jackets. My Acura can't be heard running. Lyc could not meet noise regulations. Pollution wise, yep the Lyc could not pass the state emission test, but than a plane doesn't need to meet this test. Acceleration and deceleration over and over would not be desirable with the Lyc-O-car. A car engine with it's smaller inertial mass, pistons, valves, displacement is a higher revving design, better suited for drag racing off a stop light, with fast acceleration, over and over all day. Not something we do in a plane, which is made to run at constant RPM's. A Lyc would be a dog on the drag strip. That just shows you the different mission and design. It's not a put down of the Lyc, but shows its made specifically for this one application. In all designs there are compromises. A Lyc would make a terrible car engine. To the Subaru's credit, it's a great car engine, and works well in a plane. The Subaru is very versatile engine. Now if you modified and adapted a Lyc in a car, you could get it to "work", go down the road. It would be unique. I guess the "air-boat" is the best adaptation of a small aircraft engine. A 18 wheeler truck engine, Formula Race car, Drag racer, Large Farm equipment, boat, plane, motorcycle all have different missions and their engines are compromises or optimizations towards that mission.Just for a little mental distraction, try to figure out how effectively to use a Lyclone in a modern auto. Don't forget smog/safety/CAFE/etc requirements. And, oh yes, you need to obtain equal or better performance, longevity, and fuel economy.
One thing that always seems to get lost in the traditional vs. auto engine discussions, is that most if not all of each designs "pluses" result from the engine fitting into the operational environment it was designed to operate in.
Just for a little mental distraction, try to figure out how effectively to use a Lyclone in a modern auto. Dont forget smog/safety/CAFE/etc requirements. And, oh yes, you need to obtain equal or better performance, longevity, and fuel economy.
Couldn't agree more, actually when I started thinking about adapting an aircraft engine to automotive use, I quickly got to the point of "why bother?"
An excellent metal exercise. But I think the analysis goes both directions...
Automotive engines have a much lower octane requirement today than aircraft engines. Witness many engines today with CR around 10 to 1 which run on 87 octane. Modern combustion chambers and liquid cooling make this part much better optimized than their older air cooled cousins. We have many designs today topping 11 to 1 which run on 91 octane.
Open loop control can be quite precise....
<snip>...lots of acronyms here....<snip>
....IAT is defaulted to 70F and CLT to warm engine.
The EC2 controller (by Tracy Crook) that I am using with my Mazda 13B comes with a mixture control knob so the pilot can leave it at the 12 oclock position and let the computer set it where it should, or manually adjust it to a leaner or richer point. The rotary of course doesn't have valves to burn out if running too lean of peak and Tracy reports that increased fuel economy can be had by cruising the rotary in that regime on cross country flights. I'm glad Tracy's unit gives me the option since it is just another thing that makes this "experimental" thing fun and educational.
Doug Lomheim
RV-9A, 13B
OK City, OK
You could actually put a O2 sensor on a Lyc, but how long do they last with 100LL. I see they are as cheap as $30. You could make a little meter to read the volts and calibrate it to be meaning full? hummm any lyco drivers do that?I am also using the EC2 controller and like the mixture knob. I also went to the automotive store and bought a O2 gauge so I can monitor how the engine is running.
Dang Pierre, when ever I have my flights of fancy, you bring me back to earth. Good thing, , you're right, thanks. O2 silly idea, K.I.S.S. Heck young whipper snappers are shocked that we once flew with out even one CHT / EGT gauge, in the "old days". If you don't have a 20 channel engine monitor today.......to simplify things, George. Recently I was flying my buddy's -4 with a Dynon 180. Cruising along, I did what I've been doing for 41 years, leaned his Lyc 160 'til a slight RPM loss and enriched it a tad...1/4" maybe. He was in the back seat and pointed out that in the upper right corner, the Dynon said ROP!!
Some things never change...
But, assume Thielert didn't want to incorporate a wet clutch into their gearbox. Then why cobble up a coupling? The really crazy thing about this deal is ignoring the endless variety of commercial soft couplers made specifically for diesel applications....most of which are fail safe.
Just because one of 1500 units only lasted 177 h hardly makes it a statistically significant event. Take 1500 brand new Lycomings and see how many of them have some failure (overheating, piston, ignition and so on) before 200 h. With a TBO of only 1800 h, the probability of at least one failure before 1800 h of at least one unit is as good as 100%. Also remember that the 1.7 has accumulated 350,000 h of operation, 230 h on average for each unit, and most of that from 2006. The certification process and constant feedback from the field means it will only get better as time passes.I use this type of thing to illustrate my point that just because something is professionally engineered and certified does not mean it is reliable. The proof is in the long term pudding. Maybe some should not be so hard on Jan's designs. I think the E6/ Gen 3 combos are going to last longer than 177 hours.
I will read these threads with interest and hope someone will come out with a proven watercooled design that will stand the test of time.
Quite a few "homebuilders" have designed better systems than this one, including Jan.