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  #11  
Old 01-08-2013, 10:55 AM
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rv6ejguy rv6ejguy is offline
 
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Originally Posted by SvingenB View Post
The Honda engine is designed to run continuously at WOT for prolonged time as a an outboard engine for boats. For aero conversion the Honda is perfect. The Subaru is designed for auto use only.

It is therefore much easier to get it right with the Honda than with the Subaru. I'm not saying that Eggenfellner has everything right with his Honda conversion or that using a Subaru is wrong, but I think there is less likelihood of getting it wrong with the Honda because it is initially designed and tested by Honda engineers for a similar purpose. The Honda is also less HP and that simplifies.

Regarding PSRU, the recipe for endless problem free run is found on the Rotax 912. It's called a clutch. Eggenfelner's PSRU looks a bit strange, nothing to save those cogwheels from beating during start and stop and low load running but I guess if enough steel is used, it will hold together for a light prop.
Incorrect. All auto engines in the last 15+ years are validated for hundreds of hours at WOT and full power by the OEMs before production release. The track record of flying Subarus also proves this. I think 3800 hours in the gyro training environment in a hot climate proves that the engines are very strong.

The Rotax clutch is designed for prop strike protection, it is not active in the TV realm. Sprague clutches have proven to be unreliable as applied to aircraft redrives and other types of clutches like on the ill fated Thielert also have proven unreliable. I personally would not fly with any clutch arrangement which is active during flight operation unless it was well proven with a few thousand flight hours first. There are far better engineering solutions than clutches to cure TV issues.
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  #12  
Old 01-08-2013, 01:14 PM
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Ross, I have not been following conversion news in recent times. How are the Autoflight boxes doing in service?
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  #13  
Old 01-08-2013, 01:21 PM
SvingenB SvingenB is offline
 
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Originally Posted by rv6ejguy View Post
Incorrect. All auto engines in the last 15+ years are validated for hundreds of hours at WOT and full power by the OEMs before production release. The track record of flying Subarus also proves this. I think 3800 hours in the gyro training environment in a hot climate proves that the engines are very strong.

The Rotax clutch is designed for prop strike protection, it is not active in the TV realm. Sprague clutches have proven to be unreliable as applied to aircraft redrives and other types of clutches like on the ill fated Thielert also have proven unreliable. I personally would not fly with any clutch arrangement which is active during flight operation unless it was well proven with a few thousand flight hours first. There are far better engineering solutions than clutches to cure TV issues.
I'm no auto engine engineer (i'm an engineer though, turbines). What we are discussing is reliability, mttf/mtbf. 200-300 hours at WOT for a few test engines is not the same as a TBO of 2000-3000 h or more for a production off the shelf outboard marine engine. It could very well be that the Subaru will hold up just as good in real life (with the proper modifications?), but the Honda is still designed and tested by the factory for this particular purpose, the Subaru is not.

TV is no issue on the Rotax. The clutch is there to protect the gears during start/stop and at no load (zero torque on the propeller) when there is virtually no relative damping. Instead of the gears hitting each other too hard that will possibly cause damage after some time, the clutch sets an upper limit for the instantaneous torque. Indirectly this will also stop TV from developing. The only issue with this setup is the clutch could at least in theory, wear out if you happen to fly often at no torque (rapid descend with low RPM for instance). With this setup the propeller and the engine is decoupled for all practical purposes when the instantaneous load is too high, but still well above the engine torque. Which is exactly what you want.

The alternative is to beef up the gears to increase stiffness and the load the system can withstand without being damaged over time. This will also work, but only if you know exactly what you are doing regarding TV frequencies and stiffness of the total system (engine-gears-propeller). Or you could get lucky, as I think Eggenfelner did by using the 200 HP Subaru reduction drive on the 100 HP Honda.
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Last edited by SvingenB : 01-08-2013 at 02:15 PM. Reason: correcting logic
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  #14  
Old 01-08-2013, 05:46 PM
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Quote:
Originally Posted by DanH View Post
Ross, I have not been following conversion news in recent times. How are the Autoflight boxes doing in service?
The Autoflight boxes have been good so far in most applications. We saw one failure on a Titan T51 with a very heavy, unapproved prop last year I think it was. The guys using the light props seem to be having good success. These use a Centaflex coupler.

The Marcotte boxes don't break but the rubber bushing couplers don't last forever. Depending on the engine and prop, the lifespan seems to be between 150 and 350 hours. Mine were pretty beat at the 357 hour mark. They cost about $60 to change and a few hours, also easy to inspect. Two users have reported much less severe F1/ F2 with heavier flywheels installed so I'm going that route this time as well. Will be an interesting experiment.

I have no reason to dismantle my gearbox as backlash and bearing smoothness are unchanged from new and it does not make any metal and temps are the same as ever. I will make a small external mod to solve a tiny oil seep from the prop shaft. Can't be sure if the oil is getting by the splines and big nut securing the prop hub or through the C/S set screw plug. I can't remove the plug so it it must be very tight. Since it is NPT, I doubt the leakage is there.

I'll post the a link to the page when I create it showing various worn parts.
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Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 441.0 hrs. on the Hobbs,
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Last edited by rv6ejguy : 05-11-2013 at 08:04 PM.
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  #15  
Old 01-08-2013, 06:10 PM
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Quote:
Originally Posted by SvingenB View Post
I'm no auto engine engineer (i'm an engineer though, turbines). What we are discussing is reliability, mttf/mtbf. 200-300 hours at WOT for a few test engines is not the same as a TBO of 2000-3000 h or more for a production off the shelf outboard marine engine. It could very well be that the Subaru will hold up just as good in real life (with the proper modifications?), but the Honda is still designed and tested by the factory for this particular purpose, the Subaru is not.

TV is no issue on the Rotax. The clutch is there to protect the gears during start/stop and at no load (zero torque on the propeller) when there is virtually no relative damping. Instead of the gears hitting each other too hard that will possibly cause damage after some time, the clutch sets an upper limit for the instantaneous torque. Indirectly this will also stop TV from developing. The only issue with this setup is the clutch could at least in theory, wear out if you happen to fly often at no torque (rapid descend with low RPM for instance). With this setup the propeller and the engine is decoupled for all practical purposes when the instantaneous load is too high, but still well above the engine torque. Which is exactly what you want.

The alternative is to beef up the gears to increase stiffness and the load the system can withstand without being damaged over time. This will also work, but only if you know exactly what you are doing regarding TV frequencies and stiffness of the total system (engine-gears-propeller). Or you could get lucky, as I think Eggenfelner did by using the 200 HP Subaru reduction drive on the 100 HP Honda.
Like I said, ALL the OEMs validate their designs with rigorous and prolonged WOT and full power tests these days and have been doing so for years and they do it with hundreds of engines so they have accumulated thousands of hours of WOT before release for production. A few recent examples:

Ford Eco Boost 1000 hours WOT peak torque to peak power.
Hyundai standard test 300 hours for all engines at WOT PP.
Dodge SRT standard 500 hours WOT TP to PP.
10 years ago the GM LS engines were run at WOT PP for 520 hrs. Teardown showed no appreciable wear.

You can say whatever you want about the Honda Fit (which I think is an excellent engine) but it does not have even a fraction of the proven flight time that Subaru engines do. I think the Honda Fit will prove equally reliable however given the same sort of testing it undergoes as all the others. Typically, we don't do any mods to Subaru engines internally except forged pistons for turbocharged ones in some cases. Screwing with the factory engineering is a bad idea in most cases.

Eggenfellner does not use the Subaru gearbox on the Fit, it is a new design and incorporates a rubber TV damper/ coupler. Too soon to tell if it will be reliable at this point.

The Rotax 912 "clutch" is only there for prop strike protection, it is never active during normal running. You can check various sources for this information. The "torsional damper" uses ramped, spring loaded dogs to minimize torsional peaks sent forward. These are two different devices. As far as I know, Rotax still does not recommend low idle speeds on these engines where TV can be pronounced even with the new kit.

Getting back to the original question, I am not aware of too many RV guys currently contemplating a Sube up front, there are a couple ex Egg FF packages floating around that people have bought up. There are a couple STi setups in process still with mods (certainly required). Of course the Sube is still a popular choice on many other non-RV airframes. There are some turbocharged Sube sixes close to flying now in a Cozy and Lancair so it will be interesting to see how those work and perform. I talked a couple guys out of Subaru conversions recently. They were not the type of guys to get involved in this. They'll be looking for mid time Lycomings now. RDM in the NW has been working on a new PSRU design and Subaru engines quietly for several years now, testing a lot. They don't say much which may be either good or bad. They posted this in 2011: http://www.youtube.com/watch?v=_ttLYNfIR-M
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Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 441.0 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi2.htm



Last edited by rv6ejguy : 01-08-2013 at 10:20 PM.
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  #16  
Old 01-08-2013, 09:47 PM
SvingenB SvingenB is offline
 
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Forgot about the dogs (haven't been flying much Rotax lately). But the clutch is there to prevent overload of the gears. All certified engines have this clutch, and it is mandatory for non certified engines with CS propeller. Otherwise it is an option. When this clutch is installed, there is also a free play at the dogs, and it is this free play that can be heard and felt during start (it is not TV though) and is completely harmless due to the clutch acting. Flying at close to no load on the prop can also cause the same phenomenon.

Without the clutch the engine will not run properly at idle if the propeller is too heavy, and TV may start. The no-clutch option does not have this free play as far as I know.

The Verner 133 also have this clutch/spring setup, but without the free play. As with Rotax that engine also have billions of hours with few problems.


Anyway, 500 hrs of testing, what is that compared with year after year with countless hours of real life experience for thousands of engines in outboard marine application? Lots of them may not even be maintained properly, but they still run.
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  #17  
Old 01-08-2013, 10:28 PM
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rv6ejguy rv6ejguy is offline
 
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Originally Posted by SvingenB View Post

Anyway, 500 hrs of testing, what is that compared with year after year with countless hours of real life experience for thousands of engines in outboard marine application? Lots of them may not even be maintained properly, but they still run.
This is 500-1000 hours on a SINGLE example. GM, Fuji, Ford or Toyota may run 100+ pre-production engines through the same tests before release. That is 50,000 to 100,000 hours.

Again, there are only dozens of Honda Fit engines flying and only recently. There have been thousands of Subarus flying for the last 30 years starting with the EA81 which was designed as an aircraft engine from the start by Fuji. Well flight proven. The Fit is not at this point. The RAF gyro fleet using EJ22 and EJ25 engines had accumulated about 125,000 hours as of 2006 according to an owner survey, no doubt a lot higher 7 years later.

Are you arguing that the Subaru does not stand up to aviation use? If so produce some evidence.
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Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 441.0 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi2.htm



Last edited by rv6ejguy : 01-08-2013 at 10:42 PM.
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  #18  
Old 01-08-2013, 11:40 PM
simpkinsona simpkinsona is offline
 
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Anyone considering a Subaru engine should request to join the Subenews forum and do some research. From this you can glean what works and what doesn't.

Ross,

I'd consider using a dual mass flywheel for your next set-up. Mine has held up for 500ish hours now and my opinion (no proof) is that it does a great job of reducing the impulse loads on the gearbox when starting and shutting down. I think the combo of Gen 3 and dual mass gearbox yields a reliable package.

-Andy
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  #19  
Old 01-09-2013, 02:19 AM
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Quote:
My own plane is all apart now after 9 years and almost 360 hours.
Ross, 360 hours is barely run in, and not a test of endurance. Double that in 3 years is more like serious use. The one RV down here that goes very well, as mentioned before has had the gearbox removed with an eye opening failure only a few hours away, and it would be about 360 hours

The engine itself is not so bad, apart from head needing valve work, leaking seals, coolant leaks, etc. Injectors clogging(yeah a Lyc injector would not have known) so while I know you and a few people can succeed with them, they have a hard road to hoe though.

Ongoing work and maintenance heavy is my observation, and that is of the most successful one down under. Gyro's that do local sorties and 30 hours a year ar not a good sample, even over 10 years. Unless they all regularly do 1000-2000 hours with little spanner work, they can hardly be compared.

Just my opinion, I understand some have a passion for the Sub's
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  #20  
Old 01-09-2013, 02:59 AM
SvingenB SvingenB is offline
 
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Quote:
Originally Posted by rv6ejguy View Post
Are you arguing that the Subaru does not stand up to aviation use? .
Not at all. What I am saying is Eggenfellners choice of using the Honda engine is a very good one because it is designed and tested and proven for a similar application with almost identical operation: outboard marine engine. The competition is fierce: Jabiru, ULPower etc and arguably the best aero engine ever produced, the Rotax 912. So far he is doing extremely well, and I believe one of the main reasons is he is using an engine that is more or less designed for it and one that has an unbeatable track record. He tried the Subaru, and that didn't really work out.
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