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  #1  
Old 12-28-2013, 05:36 AM
clarkefarm clarkefarm is offline
 
Join Date: Mar 2005
Posts: 67
Default Subaru to destruction

I have been persevering with Subaru engines in a 9A since starting with an NSI package about nine years ago. The latest iteration was an MPS 2.6 "stroker" modified EJ253 with a compression ratio of 10.4:1. It had about 5% more capacity than a stock EJ25 and was the subject of some discussion in the forums a couple of years ago when its performance in the now defunct MPS's Glastar was queried.
I finally got around to flying behind this engine which for me was Subaru #6 and was concentrating on fuel mapping to give ROP at 5,000 RPM or higher and LOP at lesser revolutions. I am still using the NSI 2.12:1 gearbox and prop (which has 22⁰ of reverse pitch available).
There has been significant concern about this engine since the first one to fly failed in the Glastar due to piston damage causing the oil to be blown out through the rocker cover breathers.
At about 7 hours total run time I experienced a similar failure in flight and the event was captured on a panel/cockpit camera. Footage is on Vimeo along with some other footage which gives a better look at the farm strip I fly off. Links are https://vimeo.com/82777093 and https://vimeo.com/82713897.
I am ashamed to say that I did not pick up the loss of oil pressure for a couple of minutes (the gauge is the small middle one to the left of the tacho) so expect things to look pretty bad on disassembly.
Other aspects which I should probably mention is that power is controlled by adjusting prop pitch with the L-R function of the coolie hat switch on the stick. You can see the very significant power drop when the engine goes >120⁰ LOP (peak is about 1450⁰) at 5,000 RPM and vice versa.
The landing was not well judged with 90 KIAS over the fence to a downhill strip but winding the prop back into beta always works well because the sprague clutch in the gearbox allows the prop to windmill without impedance and then this energy is used as an air brake as the pitch goes negative.
Earlier in the video you can see the aircraft's maximum performance which is about 163 KIAS at 2,000' although the density altitude on the day was closer to 3,500' which would suggest a KTAS of about 172.
I have thought about starting again with a proven engine/prop configuration but will probably go again with Subaru as I am still enjoying the challenge.
Regards from Australia.
Rupert Clarke
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  #2  
Old 12-28-2013, 06:42 AM
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FORANE FORANE is offline
 
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Location: East TN
Posts: 609
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Rupert
How about one of these Subaru motors?

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  #3  
Old 12-28-2013, 06:59 AM
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Kevin Horton Kevin Horton is offline
 
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Location: Ottawa, Canada
Posts: 2,365
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Tough news about your engine, but congratulations on a successful landing. Well done!

We all tell ourselves that we?ll pay close attention to the engine parameters, but there are many other things we need to do too when we are flying. This event is a good example of why it is important to have an engine monitor that provides some very alerting indication if an engine parameter goes out of limits. They are more expensive than simple gauges, but they add safety, and can pay for themselves if they allow a problem to be caught early when it may be cheaper to repair.

Good luck with the teardown and rebuilding.
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  #4  
Old 12-28-2013, 10:28 AM
n801bh n801bh is offline
 
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Please post pics of the autopsy ....
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  #5  
Old 12-28-2013, 10:29 AM
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rv6ejguy rv6ejguy is offline
 
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Location: Calgary, Canada
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Rupert, can you tell us how you were leaning to achieve LOP with the MoTec ECU? How many seconds would it take to go from say 12 to 1 AFR to 17? My concern would be a slow pull through stoich and with this high CR and possibly relatively low octane fuel, you could easily get detonation for a few seconds each time you go through a leaning event.

Were you running 100LL or auto fuel and what octane?

Ignition timing at WOT and above 4000 rpm?

Do you retard spark at high MAP?

Knock sensor fitted?

Spark plug heat range?

My preference on hard use engines is to use 2618 alloy forged pistons which will handle quite a bit of mild detonation without issues usually. The stock cast pistons are known to be quite weak with regards to even light detonation and the 4032 alloy, high silicon forgings also suffer from being relatively brittle compared to 2618 and don't do well in this environment.
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 450.6 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
https://www.youtube.com/channel/UCiy...g2GvQfelECCGoQ



Last edited by rv6ejguy : 12-28-2013 at 10:32 AM.
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  #6  
Old 12-28-2013, 11:10 AM
David-aviator David-aviator is offline
 
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Rupert congrats on surviving another Subaru event.
There are EGG H6's for sale over here but shipping to down under may not be worth it.
Good luck persuing the challenge - you can always hang a reliable boring Lycoming if it wears off.
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  #7  
Old 12-28-2013, 05:11 PM
clarkefarm clarkefarm is offline
 
Join Date: Mar 2005
Posts: 67
Default Engine control

Thanks all for the replies.
Kevin, I have a flashing red LED bank which was actually the first thing that drew my attention because it is fairly large. The BMA Efis also throws up out-of-whack engine parameters but the flashing warning is pretty small and the very bright sunlight does not help. Still no excuses because there had been a momentary shudder earlier and I should have been more perceptive.
Ross, lots of interesting questions so many thanks. I have looked at the data log file and taking half second intervals the numbers on lean to rich go Lambda 1.19, .9 and .8. On rich to lean the numbers were .82, .995. 1.14 and 1.17.
I am running premium unleaded which has an Australian RON of 98 but this less than the US values (I think 98 Aus might be roughly equivalent to 94 US). I have set a fixed advance of 30⁰ for anything above 4,000 RPM and do not have any knock sensing (used to but wasn't happy with the complexity). I am using pretty ordinary plugs but will need to go to the hangar to check.
David, the idea of a 6 cylinder might present a bit of a challenge. The NSI package has a horizontal radiator behind the engine and internal cowl ducts to direct air into a plenum above it. (It works exceedingly well as without the thermostat the engine will barely reach 150⁰ at maximum power). Due to this you could already describe the plane as an RV-9A "Long Nose" and I have not been able to reduce the weight on the nose wheel below 310 lbs.
I am also pretty happy with the performance and still have much to do as I have induction losses of 45 millibars (1,500') and an inlet temperature of 10⁰C above OAT because I am drawing air from inside the cowl. I also have a huge 130 square inch cowl outlet which is not required for cooling so I think that I might end up giving the 9's 180 kts VNE a nudge before I am through. Before I get chastised for this the main aim is to be able to cruise at 155 kts burning about 7 gal/hr.
Rupert
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  #8  
Old 12-28-2013, 05:20 PM
clarkefarm clarkefarm is offline
 
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Posts: 67
Default Image of plane

Will try again to post image of the plane.

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  #9  
Old 12-28-2013, 06:13 PM
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rv6ejguy rv6ejguy is offline
 
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Quote:
Originally Posted by clarkefarm View Post
Thanks all for the replies.

Ross, lots of interesting questions so many thanks. I have looked at the data log file and taking half second intervals the numbers on lean to rich go Lambda 1.19, .9 and .8. On rich to lean the numbers were .82, .995. 1.14 and 1.17.
I am running premium unleaded which has an Australian RON of 98 but this less than the US values (I think 98 Aus might be roughly equivalent to 94 US). I have set a fixed advance of 30⁰ for anything above 4,000 RPM and do not have any knock sensing (used to but wasn't happy with the complexity). I am using pretty ordinary plugs but will need to go to the hangar to check.
Your fuel would seem to be close to our standard premium 91-92 AKI we commonly have available in North America.

I believe with your CR, you could easily encounter detonation during the leaning event to LOP with 30 degrees of total timing although this would be of very short duration judging by the Lambda figures and your data log sampling rates. Heat range 7 NGK plugs would be advisable in aviation use.

When you disassemble, it will be interesting to see the failure mode of the piston. Ring land breakage is almost 100% due to detonation whereas edge distortion/failure of the crown usually indicates pre-ignition or sometimes just general overheating of the crown. Does this engine have under-piston oil squirters installed?

I have seen countless photos of damaged Subaru EJ/EZ pistons now and believe most are due to too much timing and/or too lean mixtures. The factory is very conservative at WOT on both these parameters. I've seen timing on the atmo versions down to 22 degrees and AFRs as rich as 11.2. The jury is out on LOP operation of these engines, you are the first to try this that I have heard of so it was interesting to see your figures.

It seems like your coolant temps and EGTs are under good control.

Aural warnings are the best by far for out of limit parameters. Blinking lights or displays often don't get your attention quickly, especially with sunlight on the panel. Been there before myself and the airliner designers know this well too, hence the aural warning systems prevalent today.
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 450.6 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
https://www.youtube.com/channel/UCiy...g2GvQfelECCGoQ



Last edited by rv6ejguy : 12-28-2013 at 06:31 PM.
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  #10  
Old 12-28-2013, 10:40 PM
clarkefarm clarkefarm is offline
 
Join Date: Mar 2005
Posts: 67
Default WOT settings

Thanks Ross, interesting info.
I was actually tossing up whether to throw a second hand engine from a wrecker's yard into the plane until i was happy with the tuning. i probably destroyed a few engines already by relying on the notion that best power is around Lambda .89 (AFR 13) and setting up WOT 80-100% MAP to run at this. (Naturally I had backed off a bit with this last engine so some disappointment.)
I had thought that if I installed a stock engine (apart from the low price) I could put a car/wagon with a similar motor on a dyno to see what settings Subaru use. You might have saved me the trouble but I guess that I would be passing up some horsepower with an AFR of 11.2 and timing of 22⁰.
I will check to see if the MPS 2.6 engine had under piston oiling.
Regards
Rupert
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