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Subaru FF Alternatives

rv6ejguy

Well Known Member
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You have a lot of hours on your subaru conversion - how about details on your plane? I don't think I've seen that anywhere.

Kevin Belue
RV-6A
RV-10
 
I believe in many other discussions here and elsewhere we've seen a fairly strong consensus in describing unproven PSRU's as the weak point in many Subaru conversions. How is the (former) Geared Drives PSRU in terms of field experience and overall technical merit?

(Disclaimer: I fly a Lycoming and a Continental, but I drive a Subaru. After a 12 year build cycle for our current aircraft I'm the first to admit it will be quite a while before I'm ready to install any new powerplant on any airplane again. I remain very interested in seeing how a modern-technology engine from the automotive world can be made to work well in an aircraft.)
 
I believe in many other discussions here and elsewhere we've seen a fairly strong consensus in describing unproven PSRU's as the weak point in many Subaru conversions. How is the (former) Geared Drives PSRU in terms of field experience and overall technical merit?

I posted the autopsru links for those possibly contemplating a vendor solution.

I know of only 2 Subes which have flown with their 200Z gearboxes. One was an EZ30 (6 cylinder) and it suffered a tooth failure at around 30 hours I believe. There was a post on that by the builder, Jetmech I believe. Not sure what the cause was. The second one is an EJ25 and had over 350 hours on it trouble free, last I heard.

I'm not sure how many of the Autopsru conversions have flown and how many flight hours on the fleet. I suspect not many given the price and amount of time on the market.

Perhaps the company owner, Stuart Davis, will speak to that if he sees this thread.
 
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I'm a Subaru fan and really wanted to install a Subaru EE20 in my airplane but I couldn't make it happen. I didn't want to extend the build time that much.

I'd really like to see someone develop a PRSU for the Subaru that encludes a governor pad for a hydraulic prop. If that existed I'd probably have a Subaru engine on the nose if my plane right now.
 
I'm a Subaru fan and really wanted to install a Subaru EE20 in my airplane but I couldn't make it happen. I didn't want to extend the build time that much.

I'd really like to see someone develop a PRSU for the Subaru that encludes a governor pad for a hydraulic prop. If that existed I'd probably have a Subaru engine on the nose if my plane right now.

Autopsru builds such a drive.
 
I want there to be some good alt engine packages out there, too. But pragmatism and rational analysis is essential for success, for both vendors and users.

According to the info from one of their reps in the alt engine tent at SNF this year, just the clutch alone in that system weighs around 30 lbs. That's over half the weight of entire high quality drives from other mfgrs. Perhaps others who can speak with more authority than me, will address whether a clutch (even if it didn't weigh 30 lbs) is the best way to handle the engine/drive interface.

They had a mockup of their proposed rotary engine setup at SNF. When I questioned the rep about it, he had so many things wrong about the rotary's characteristics, it was almost frightening.

Anyone notice that the weights on all their stuff are 'TBD'? I would have thought that if they've got flying engines, they would need to know that, to get the a/c weight & balance right.

Charlie
 
I want there to be some good alt engine packages out there, too. But pragmatism and rational analysis is essential for success, for both vendors and users.

According to the info from one of their reps in the alt engine tent at SNF this year, just the clutch alone in that system weighs around 30 lbs. That's over half the weight of entire high quality drives from other mfgrs. Perhaps others who can speak with more authority than me, will address whether a clutch (even if it didn't weigh 30 lbs) is the best way to handle the engine/drive interface.

They had a mockup of their proposed rotary engine setup at SNF. When I questioned the rep about it, he had so many things wrong about the rotary's characteristics, it was almost frightening.

Anyone notice that the weights on all their stuff are 'TBD'? I would have thought that if they've got flying engines, they would need to know that, to get the a/c weight & balance right.

Charlie

AutoPSRU is a newish company. Assuming I recall the history correctly, Stuart bought the rights from Bud's estate. Stuart has since embarked on a redesign to make the system more economical and lighter. Further, Bud was constantly evolving the system, so there were many variations of the design over the years.
Hence, a lot is TBD.

Tim
 
I'm not a fan of these clutches which don't do anything to alleviate TV above idle rpm. The 2 most successful drives out there, Autoflight and Marcotte don't use clutches.

I'd be interested to know how many packages are flying. I don't think any vendor should be selling FF packages unless several examples have accumulated at least 500 hours each with no issues.
 
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Adapting the clutch to an engine with less cylinders has a catch.

Assume a prop/PSRU/engine system with a fundamental natural frequency of 50hz, i.e. a drive system without a torsional soft element to lower natural frequency.

If we excite that system with a force oscillating at 50 hz, it will resonate, vibrating torsionally and causing very high shaft loads. Running at a resonant RPM is what breaks PSRUs, immediately or long term, via fatigue.

The most powerful exciting force is firing events. For a four stroke, exciting frequency in hertz = (RPM x #cyls) / 120. Run the numbers:

four cylinder at 600 RPM idle: (600 x 4) / 120 = 20hz

eight cylinder at 600 RPM idle: (600 x 8) / 120 = 40 hz

Without a clutch, both engines would excite the 50 hz system when the throttle was pushed forward, as RPM passed through the resonant range. The resonant RPM = (50 x 120) / # cyls.

That would be 1500 RPM for the 4 cyl, or 750 RPM for the 8 cylinder.

A clutch set to engage at 1000 RPM would work pretty well on the 8 cylinder engine, as it does not connect the driveline (create the torsional system) until the exciting frequency is above the system's fundamental natural frequency. Although as Ross said, it does nothing to alleviate other resonant periods higher in the RPM range, those resonant periods are less powerful. The fundamental, when excited by firing events, is the whopper.

So, the catch...mount the same PSRU and clutch on the 4-cyl, and if the 1000 RPM clutch engagement speed is maintained, the system will still resonate badly at 1500, the RPM at which natural frequency and exciting frequency are matched. In order for the clutch to be useful on the 4-cyl, its engagement speed would need to be raised to some RPM above 1500. Resonant periods are actually a range with a peak, so that clutch speed would need to be around 1800 RPM. Yes, that would mean no thrust below 1800.

Moving the resonant range down the RPM scale so the 1000 RPM clutch speed could be maintained would require a torsionally softer drive, here about 25 hz. All design is compromise; I suspect the softer drive may lower resonant loads enough to make the clutch superfluous. That would be the path chosen by Autoflight.
 
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Dan,

Would it be inaccurate to add that a centrifugal clutch is one of the heaviest, complicated, and most failure-prone methods of dealing with torsional resonance?
 
Torsionally soft drive line

Virtually all of the successful Egenfellner Subaru engines use the so called "dual mass flywheel ". As Dan has pointed out in the past, this flywheel is modified to to remove most of the second mass but retains the spring connection between engine flywheel and PSRU input shaft. This drive system seems to be the key to making a gear drive system last and provide smooth operation. While there are still occasional problems with the gearboxes, they have been few and none have resulted in a power loss inflight as far as I know (and I make an effort to know).

-Andy
 
Dan,

Would it be inaccurate to add that a centrifugal clutch is one of the heaviest, complicated, and most failure-prone methods of dealing with torsional resonance?

No, I don't think so.

"Heavy" is relative, so we would have to examine the alternatives to make a judgement. As examples, some alternatives really should incorporate a fair bit of flywheel inertia, which is also heavy, even when the flywheel concentrates its mass at the rim. The Marcotte box is arguably heavy; call it the "make it massive" approach to reliability.

The flyweight-style pressure plate system used by AutoPSRUs is not real complicated. I have no way of judging its reliability, which may change a lot (for better or for worse) with simple mods.

Above clutch lock RPM it's a hard system; the clutch has no effect on resonant behavior, other than the aforementioned increase in flywheel inertia, a good thing.

I think the key to reliability is to simulate torsional loads in the design phase, and measure them at the prototype stage. Can't realistically reduce weight without knowing component loading.

Well, ok, there is the 1000 Monkeys approach ;)
 
The Marcotte M300 weighs 47 pounds bare. Russell and me run about 12-15 lb. flywheels

The complete 200Z is around 68 including flywheel/ clutch.

The Autoflight EA (rated to 160hp) is about 37 pounds bare.

I couldn't find a weight on the Autoflight Heavy box but having seen some photos compared to the EA, it has to be at least 10-15 pounds heavier than the smaller EA box.
 
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Popular Subaru engine overview

On the Sube engine front, the EA81, EJ20, EJ22, EG33, EZ30 and some versions of the EJ25 have had mainly good success in aircraft when properly cooled and with proper ignition timing and fueling.

The EA81 is an old pushrod design, suited for about 85-90 hp. Simple, easy to work on, robust, cheap to overhaul.

The EJ22 is a 4 valve, SOHC design, suited to make around 125 hp. More complex, reliable, plentiful still today. A turbo version is one of the strongest Subarus made with a closed deck block, tougher pistons and piston oil squirters.

The EJ25 comes in both SOHC and DOHC versions, again 4 valves/ cylinder. Many versions have a deserved reputation for eventual head gasket failures and some less widespread problems with valve guides moving down in the heads. A newer HG design seems to fix the first problem and the press fit on the guides can be checked during overhaul. The EJ255 and 257 engines are turbocharged models with some more robust parts and seem relatively trouble free outside of some isolated issues with the oil pump pickups coming loose with consequent engine destruction coming soon after. Atmo models are good for around 160hp, turbos good for 225 with low boost.

The EJ20 over in North America is mainly confined to turbocharged models. Has a reputation for being tough. Small displacement means you'd probably want to leave it turbocharged for aircraft use.

The EZ30 is a 6 cylinder engine, 4 valve, light, complex and compact, used extensively by Eggenfellner. Seems to work well, no widespread issues if fresh and treated well. Good for around 200hp if properly inducted and exhausted which the Egg conversions weren't.

EG33 is the older DOHC 4 valve six. Complicated but reliable. Good for 230hp and does not need to rev as high as the EZ engines to make power. A number of people are flying this engine successfully even though it was built in relatively low numbers compared to other Sube engines.

EZ36, which is based on the EZ30 has a bigger bore and much longer stroke. These generally have not fared well in aircraft use. Of the four I know flying, 2 suffered serious piston failures (one of them twice) and 1 had minor piston damage which was heading for major failure when taken apart to have forged pistons fitted per my recommendations. The stock pistons simply won't handle the continuous thermal loads imposed in this application. All these failures happened in under 60 hours of operation.

As with most auto engines, the stock pistons are usually the weakest link due to the much higher specific power output compared to traditional aircraft engines. Ignition timing needs to be kept short of causing detonation at all times and AFRs need to be kept rich (11 to 11.5) at high power to ensure reliability.

High time Subaru I've heard of flying in aircraft was an EJ22 with a reported 3800 flight hours (never opened in that time) in a gyro used for flight training in Australia. There are a few other EJs with right around 1000 hours and hundreds which have 400 to 700 hours on them.

You can pick up good used engines for $400-$1500 and rebuild them for $1000 to $3000 depending on parts used so the engines themselves can be a fraction of the cost of a Lycoming however you'll need some other bits like a PSRU, rad etc. to make it all work. Realistically a well overhauled four with a PSRU and all the bits needed can be done for $9K-$12K. Sixes $10K to $15K ready to turn a prop.

New EJ257 shortblocks are available for around $2K and a popular mod for aircraft use is to fit SOHC heads on them to save weight since high rpms are not required for aircraft use. This would be my choice for most RVs. I believe you could build a reliable 225hp from this basis for about $15K ready to run with a PSRU. Weight, depending on gearbox, would be around 10-20 pounds more than an angle valve IO-360.

We know the turbo EJ257s make good power as the one built by Ralph Inkster showed awesome speed and good fuel burn. Randy Crothers also built a 7A with this engine. Both would easily exceed Vne in level flight with modest manifold pressures at 8000+ MSL.
 
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Gearbox Update

There is a closed Yahoo group called Subenews which was started by the late Peter Krok, to support the Eggenfellner conversions after Jan pulled the plug.

This group shares info and experiences with others flying Egg conversions.

In a fairly recent development, one of the members, Mike Talmadge, has been designing and improving on the basic Egg Gen 3 gearbox used in most of the EZ30 powered planes today. All the identified weaknesses have been addressed and new-build gearboxes will hopefully be available sometime in 2018 to members.
 
Ross,

Last time I checked (just now), non-members couldn't even read the posts to that group. I can understand the desire to keep down the 'noise level' by excluding those who aren't flying the engine. But it's a shame that those with an interest in doing a conversion can't learn from 'lurking' and reading through the experiences of those already flying.

I know you don't 'own' the group, but has there ever been any discussion of opening it up 'read only' to the rest of us?

Charlie
 
Ross,

Last time I checked (just now), non-members couldn't even read the posts to that group. I can understand the desire to keep down the 'noise level' by excluding those who aren't flying the engine. But it's a shame that those with an interest in doing a conversion can't learn from 'lurking' and reading through the experiences of those already flying.

I know you don't 'own' the group, but has there ever been any discussion of opening it up 'read only' to the rest of us?

Charlie

The intended purpose of the group is only to support Egg conversion owners. At the time it was organized by Pete, the situation with Jan's support was in limbo and there was an effort to try to recover monies owed to customers. Pete wanted only actual Egg owners to be invited in and it served the purpose well. With Pete's death, I'm not sure who, if anyone is in control of the group now. I haven't seen any discussion on opening it up to "outsiders". The posts are almost all from Egg owners so you don't need to wade through a lot of useless posts and chaff which is kinda nice compared to places like HBA where there is 75% useless content from people who will mostly never build or fly anything.

There are many other closed groups on Yahoo and elsewhere.

The Flysoob Yahoo group exists for all others interested in sharing and learning about aero Subarus.
 
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With Pete's death, I'm not sure who, if anyone is in control of the Subenews group now. I haven't seen any discussion on opening it up to "outsiders". .

Pete and I were co-owners of the Subenews group for several years before he passed, now I'm watching over it.

As Ross mentioned, the Subenews group is restricted to owners of Eggenfellner engine packages to keep the discussions on point. Most of what is discussed isn't terribly applicable to Subarus in general, and the items that do come up of that nature are often shared on the FlySoob Yahoo group.

Technical information on the Eggenfellner conversions can be found on the Subenews Wiki at https://subenews.deej.net

Other than the newsletters, the Wiki is open read-only to the world.

-Dj
 
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Unfortunately, the flysoob group is restricted, too. I have nothing to offer through posting to that group, but I learn from many seemingly unrelated sources, & it would be nice if we could simply read the info. Plus, it could help potential users make the decision on whether to try a conversion.

Perhaps Yahoo's system won't allow that (wouldn't surprise me) but most forums I've encountered will allow non-members to read the forum; they just can't post without joining.
 
Unfortunately, the flysoob group is restricted, too.

It is not open to the world, that is true. However, it is open to anyone that wants to join. When you sign up you can select not to get emails and just read the info on the web site if that is your preference. The Yahoo group settings do prevent opening up a group to Public (ie, read-only to non-members) once it has been made restricted (I just checked).

I'm co-owner of the FlySoob group as well, and I'm happy to approve your membership if you want to sign up.

-Dj
 
One of those interesting little details, just something I noticed today.

Each pair of Lycoming counterweights (technically pendulum absorbers) are designed to damp a particular order of torsional vibration.

New service bulletin today, just a bunch of revisions really:

https://www.lycoming.com/sites/default/files/SI1012J Counterweights and Rollers.pdf

However, check out Fig 3 and the following engine list. The geared engines are the only sixes with three sets of pendulums.
 
Pete and I were co-owners of the Subenews group for several years before he passed, now I'm watching over it.



-Dj

DJ,

Thanks for your efforts with maintaining this site. I have used it often.

Steve

RV8-Subaru H6 - 700 hours.
 
Seems to me the automotive method to deal with TV externally is a whole lot simpler and less expensive. A lot of the TV issues may be a consequence with the Lycoming crank design- few main bearings, no pin overlap, long drive snout.
 
Seems to me the automotive method to deal with TV externally is a whole lot simpler and less expensive. A lot of the TV issues may be a consequence with the Lycoming crank design- few main bearings, no pin overlap, long drive snout.

What is the automotive method?
 
Automotive method.
I've often wondered why automobiles don't seem to have torsional vibration problems like aircraft engines and marine propulsion systems (my day job). Some of the differences are:
1. Many auto engines use a torsional damper as part of the vee belt drive from the front of the crankshaft.
2. Manual transmission vehicles have a set of springs (four or six) between the driving and driven portions of the dry clutch.
3. Automatic transmission vehicles have a torque converter (fluid coupling) between the engine and transmission.
4. Some auto engines use a Guibo (rubber) coupling at the output end of the transmission.
5. The drivelines (FWD or especially RWD) are relatively long.
6. All vehicles transmit the drive through rubber tires.
All of the above provide a little or a lot of torsional damping in the system.

In contrast, direct drive aircraft and marine engines drive a relatively large polar moment propeller which has very little torsional damping in the fluid (air or water) they are driving.

Reading the accounts of piston aircraft engine (R-R, Allison, Pratt and Whitney) testing in the 1930s and 1940s one is struck by how often torsional vibrations led to damaged engines, PSRUs or accessory drives on the test stand. So this is not a new thing. Nor is a mass-elastic diagram and a mathematical torsional vibration analysis a guarantee of trouble free operation. It seems that a combination of analysis and test is required even today. Whenever I have asked the question of alternative aircraft engine vendors of how they have analyzed and tested for torsional vibrations I have invariably found they have not analyzed the system and have not done any torsional vibration testing.
 
What is the automotive method?

Terrye answered that very well.

Today on the engine at least, a TV absorber on the front of the engine and usually a dual mass spring or fluid filled absorber on the drive end. Have never seen pendulum type dampers on a production auto crankshaft in the last 30 years.

The auto OEMs obviously have massive resources to model and test for TV so you don't see crank failures on many stock auto engines (except Subaru EE20 diesels). However once we remove the transmission, stock flywheel system and install a prop, all bets are off.
 
pendulum absorber

VW and BMW both now use pendulum absorbers on their dual mass flywheels.

000196C6.jpg
 
If there is an "automotive method", it would be that the auto industry actually understands torsional vibration, and incorporates vibratory analysis into the design process. It is good application of fundamentals, not magic parts.
 
If there is an "automotive method", it would be that the auto industry actually understands torsional vibration, and incorporates vibratory analysis into the design process. It is good application of fundamentals, not magic parts.

Absolutely and as Terrye said, few in the aircraft auto conversion/ PSRU world either understand or test their packages for TV issues. Powersport and EPI come to mind who do test.

Tracy at RWS did design for this and Neil Hintz at AutoFlight as well although I'm not aware the latter two did any instrumented testing on specific engine, drive/ prop combinations. These two do have tens of thousands of hours collectively on many drives though without many failures which would seem to confirm their TV solutions work.
 
I am curious if Ross would agree,but my personal experience w J25 is std stock flywheel and rubber coupling ,makes for smooth running combo ! Sometimes our obsession w
Weight is a detriment ! Tom
 
I am curious if Ross would agree,but my personal experience w J25 is std stock flywheel and rubber coupling ,makes for smooth running combo ! Sometimes our obsession w
Weight is a detriment ! Tom

I was involved in an effort to get MT to come to US and do vibration analysis of MT prop and H6 engine.

The results were very good which gave confidence to continue the effort.
So far as engine, psru and prop were concerned, it was a comfort.

But that in flight testing probably is different than what is being discussed here. PSRU failure happened down the road and must have been caused by bearing load factors, not vibration.
 
I am curious if Ross would agree,but my personal experience w J25 is std stock flywheel and rubber coupling ,makes for smooth running combo ! Sometimes our obsession w
Weight is a detriment ! Tom

I think you're flying with an SPG-3 or 4 gearbox correct?
 
I was involved in an effort to get MT to come to US and do vibration analysis of MT prop and H6 engine.

The results were very good which gave confidence to continue the effort.
So far as engine, psru and prop were concerned, it was a comfort.

But that in flight testing probably is different than what is being discussed here. PSRU failure happened down the road and must have been caused by bearing load factors, not vibration.

It seems on the Egg Gen 3 boxes there were 3 somewhat common failures- drive splines, broken gear welds and bearings falling apart. There were also some TV issues on startup for some people which were addressed by adding a bunch of ign timing during cranking. Counter-intuitively, this seemed to fix the dreadful sledgehammer blows experienced. Hopefully the revised box design by Mike addresses all these issues.
 
Egg gearbox

The spline shaft failures were all on aircraft with solid flywheels. The adapter bolted to the flywheel would eventually strip out due to fretting from the piston impulses. The dual mass flywheel seems to have eliminated that problem although frequent inspections are still a good idea.

The weld issue is a continuing problem that seems to be related to the bearing failures. It's always the same bearing and it's attached to the welded output shaft. I have one gearbox that has more vibrations and develops leaks at the front seal. It had some roughness in that bearing when I inspected it before replacing that bearing. My other gearbox has 850 hours on it and runs smoothly with no issues. I haven't taken apart the bad gearbox yet but my suspicion is that the welded shaft is warped slightly from the welding operation and that causes the vibration and bearing failures.

I think if you have a good smooth egg gearbox it will last indefinitely. I'm planning to try find a better output shaft or make my own for my spare gearbox.

-Andy
 
Yet I know of some solid flywheel Eggs with 500+ hours and no spline failures (so far) so I don't think we can be sure that is causal. Without a TV study, we really don't know the differences in amplitude at flight range frequencies to point a finger.

I thought there was a spline failure on a DM equipped engine but I could have the owner mixed up with another guy. I'll poll Subenews and see if anyone reports a spline failure on a DM setup.
 
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This just in from Flysoob:

"The Ghost Run Air Race took place yesterday. Our Glasair/Subaru dominated all other piston aircraft. We came in second behind Mike Patey and his turbine powered Extreme Lancair Legacy.

Our Subaru EG33 ran its fastest race ever. The average speed over a 155 nautical mile course was 256.91 MPH.

Man, I love this Subaru!

Russell Sherwood"

This is Russell's 6th class win this year in SARL (has won every race entered this year). People still wanna believe Subarus can't work well in aircraft?
 
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Russell just set a new SARL class record on Nov. 11- 261.60 mph running the entire race at 5250 rpm.

Below are the season results of his 2017 races

Texoma Air Race - 145 mile closed circuit - Average speed 250.94 MPH

BCAF Air Race - 159 mile closed circuit - Average speed 252.95 MPH

Hardin Air Race - 135 mile closed circuit - Average speed 251.92 MPH

Big Muddy Air Race - 137 mile closed circuit - Average speed 254.77 MPH

Indy Air Race - 133 mile closed circuit - Average speed 256.66 MPH

Ghost Run Air Race - 155 mile closed circuit - Average speed 256.91 MPH

Rocket Air Race - 159 mile closed circuit - Average speed 261.60 MPH

The Lycoming guys will have some work ahead to catch him next year.
 
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Ross, yes I had SPG- 4. I don't claim to be an engineer, but was very impressed with the use of a BMW/Mercedes drive shaft type rubber coupling to act as shock/torque absorber. Plus the 3 blade cool prop (which fits rotax hub) very light. Airtrikes indicated it was good up to 160HP. I think they may have raised HP.
 
Mike Talmadge just posted this weekend that he received the first of the new Egg replacement gearbox cases from the anodizer. I hope he'll have one assembled for testing before the year is out.
 
Empty weights

I polled on the Subenews site and got some replies on RV empty weights with EJ25 four cylinder engines fitted:

1107 IFR equipped but no paint
1167 well equipped complete with paint
1166 on my turbo 6A with heavy paint, steam gauges, 2 full sized AGM lead acid batteries, sound proofing, extra wiring for R&D/ test purposes, roll servo, various patches for airframe mods over the years and a heavy repair on the cowling.

No doubt in my mind that you can easily get below 1100 pounds with a 4 cylinder Subaru, especially using the SPG redrive instead of the M300 or Egg Gen 3 gearbox.
 
Mike Talmadge has received the new parts and assembled the first of the new re-engineered gearboxes for Egg Subaru packages. This is good news for the Egg Sube engine community as it gives them a new supplier of these critical parts to keep on flying their conversions. Second nice thing is the new box is 8.5 pounds lighter. Kudos to Mike for all this hard work in getting to this point.

On to testing soon.
 
Mike Talmadge has received the new parts and assembled the first of the new re-engineered gearboxes for Egg Subaru packages. This is good news for the Egg Sube engine community as it gives them a new supplier of these critical parts to keep on flying their conversions. Second nice thing is the new box is 8.5 pounds lighter. Kudos to Mike for all this hard work in getting to this point.

On to testing soon.

Can you define "re-engineered" for us? Did a valid Torsional Vibration study occur, and if so with which propeller?
 
Can you define "re-engineered" for us? Did a valid Torsional Vibration study occur, and if so with which propeller?

The original Egg Gen 3 box was reverse engineered and improved in areas where previous problems have been revealed by users.

At this time, no testing has been done and I'm not sure what tests Mike intends to perform outside on running tests on an engine, likely with the common MT 3 blade electric prop.



There does not appear to be any serious TV issues on engines equipped with the dual mass flywheel. Many thousands of flight hours collectively on the Gen 3 boxes now.

Main areas addressed were bearings and lubrication, elimination of the welded shafts and improved splined shaft.
 
I haven't heard of Mike giving it a designation yet. Should maybe just call it the Mike box since it's really an all new design with the same mounting footprint as before for retrofit purposes.
 
Hello Ross , Dan and others,
I appreciate the discussion about TV but wonder where the secondary harmonics might be for a four cylinder EJ25. I am still flying an NSI package which includes a sprague clutch but use an idle of around 2,000 rpm (943 prop rpm) which would be above the 1,500 primary area and also above the level where the clutch is apparently locked.
I also wonder if it is possible to monitor the effects of vibration with knock sensing. The newer Motec M1 series ECUs will monitor 4 user defined frequencies per cylinder.
I have always noticed quite an improvement in smoothness from 5,500 to 5,000 or 6,000 rpm but I suppose the prop has quite a bit to do with it too.
I was also quite surprised about how much extra fuel and reduced timing Subaru use on a NA 2009 Forester which we ran on the dyno at high power settings. At 6,000 rpm 90 kPa we saw an AFR of 10.5 and an advance of 23 degrees. There was a massive jump between 4,000 and 4,500 rpm 80 kPa in fuel from AFR 14.4 to AFR 11.9. Timing was also taken out by 3 degrees; 24.5 to 21.5.
I guess the take home message is don't skimp on fuel when you are looking for power unless melted pistons make you happy.
I may be wrong but is there potential for a relationship between knock or a faster fuel burn rate and torsional vibration ?
Rupert Clarke
RV-9A, EJ253 SOHC, NSI A40 gearbox, NSI CAP 200 72" prop (composite blades by Whirlwind)
 
Rupert, we've known about what the factory does for timing and fueling from the factory for about 15 years to keep the pistons alive at high power. Those who fail to duplicate those settings usually destroy pistons. I've seen it many times now.

I would not think there is a strong relationship between AFRs and TV. Knock is to be avoided at all costs from a longevity POV.

TV studies for aircraft would normally involve instrumentation of the prop shaft rather than somewhere on the engine itself.
 
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