Eggenfellner Engines - Technical Only

DanH · #1 02-03-2008, 06:52 PM

Ok guys, Milt said it best....let's have some restraint. Technical issues only, please. Same rules for everyone, including Jan. No discussion of business practice, resale value, the market acceptance of auto conversions, or any of the 1000 other things not strictly technical and mechanical.

Kahuna has agreed to moderate, which is pretty darn generous given the difficulty sometimes found in polarized subject matter. Let's make it easy for him.

Jan, an easy question to get the ball rolling. How do you prepare the base engine when it arrives at your shop, before adding accessory items and the gearbox?

Randy · #2 02-03-2008, 11:20 PM

This is one of the reasons I purchased an engine from Jan in the first place. He does not open up the engines to make any internal modifications, at least that has been my understanding. If the basic engine model from Subaru is rated to make the horsepower needed or wanted, all that is needed is the right packaging, care and feeding to make it a good candidate for an aircraft, plus a very reliable reduction gearbox of course.

Once a vendor opens up these engines the customer must place a tremendous amount of faith that the vendor's theories and machine practices will not result in an internal failure of some sort from internal modifications. In my opinion, if the engine is up to the task, it should not need internal changes.

It is a difficult enough task to get a package together that will work in an aircraft, without adding the additional complications of making internal modifications.

What is needed is a properly designed cooling system, a good supply of clean fuel with reduncy, a good flow of electrons to the ECU with reduncy, but most of all a good gear reduction unit so the engine can run in the RPM range where it makes it's best power.

I probably would not have purchased a Subaru engine from Jan or anyone else if it had internal modifications.

A person with a decent mechanical aptitude can make external changes to enhance the engines required operating environment with out too much difficulty. I would not want to be dealing with all the external stuff while wondering about what has been done to the inside of an auto conversion engine.

My technical .02 for this eve

I like the idea of this thread staying technical and leaving the personal and business practice junk behind. This is the fun stuff!

Randy C

PS. I guess to be complete here I need to throw in the fact that I did need to defeat the variable valve timing function on my STI as part of an upgrade program. This involved replacing the intake cam shaft sprockets and plugging some oil passages with tapered pins. I did not know about this requirement when I made my purchase and it would have effected my purchase decision. I guess this is not very deeply internal but close enough to be of concern.

janeggenfellner · #3 02-04-2008, 04:03 AM

Question: How do you prepare the base engine when it arrives at your shop, before adding accessory items and the gearbox?

Answer: My answer is identical to that of Randy. We do nothing to the original engines other than the removal of anything that looks like it has any weight

When we use engines that have run before, we run compresion and oil sample checks.

Jan

Geico266 · #4 02-04-2008, 06:00 AM

Jan, Can you address the technical reasons for the Gen 3 gear box? What makes it better than the Gen 1 & Gen 2? I helped a buddy replace his Gen 1 and I must say the Gen 3 in an impressive "chunk of hardware" (technical term

) The biggest change we noticed was going from an external input shaft to female set up with the shaft "adapter" bolted to the flywheel.

1. A new bearing was added to the center of the flywheel to accommodate a stub shaft from the "adapter shaft" for what appears to be side loading? Was / is that an issue with the old box? What bearings did you use inside the new box, ball or roller bearings, both?

2. While the "engine mounting plate" appears stout enough, have you measured for "flexing" under the sever gyro force load of the spinning prop? Is that where side loading may be developing?

3. What temperatures rises (over ambient air temp) should a new Gen 3 gear box see during break-in and normal operation?

4. Do you suggest having an oil analysis done at regular intervals? Do you have any base lines for "normal wear".

Thank you in advance for your comments.

janeggenfellner · #5 02-04-2008, 08:29 AM

1. A new bearing was added to the center of the flywheel to accommodate a stub shaft from the "adapter shaft" for what appears to be side loading? Was / is that an issue with the old box? What bearings did you use inside the new box, ball or roller bearings, both?

The bearing you refer to is identical to a clutch pilot bearing used with a manual transmission car. This small sealed bearing does not turn but does move slightly when the torsion damping flywheel is exercising it's damping function. Its function is just to center the splined drive shaft perfectly on the crank centerline. From your description, it sounds as though you were working on an engine with a solid flywheel, and in that case, the bearing is only used for centering purposes during assembly. The new drive exclusively use ball bearings. To support the input gear, G1/G2 drives had a single input bearing and an internal roller bearing to the gear. G3 drives have two different sized ball bearings, spaced apart, on the outside of the input gear and a single ball bearing internal to it. Side loading is not the issue in this area. Creating a system with plenty of support, easy oiling and large enough bearings to handle the impulses from the engine, yet small enough for the RPM is the key. These are the fastest tuning bearings in the drive unit.

2. While the "engine mounting plate" appears stout enough, have you measured for "flexing" under the sever gyro force load of the spinning prop? Is that where side loading may be developing?

You are confusing the entire plate with what happens inboard of the bell housing perimeter. The plate is bolted in 10 places around the bell housing, effectively making it one with the housing. Then, only 1" inboard, the structure from the aft drive section, further reinforce the integrity and assure consistent alignment of the drive input shaft to the crank centerline. We have tested this by flexing the tip of the plate forward 4" with less than 0.001 deflection inboard of the bell housing perimeter. Many mistakes this plate for being very heavy. In fact it is not. The weight is only 7.5lb and provide the engine with an engine mount, gearbox mount, starter mount, oil cooler mount and cooling system mount. the plate is reinforced by traditional aircraft triangulation, using 4130 N steel tubing.

3. What temperatures rises (over ambient air temp) should a new Gen 3 gear box see during break-in and normal operation?

There is no brake-in period. The temperature should remain 15 F below the engine coolant temperature. Max engine coolant temp. is 220 F. Enough air cooling of the drive should be provided to maintain this ratio. The spinner to cowling gap is directly related to the temperature of the drive unit and a 1/2" gap is preferred over a smaller gap. This also allow for easy cowling installation / removal.

4. Do you suggest having an oil analysis done at regular intervals? Do you have any base lines for "normal wear".

Yes, send in a sample every 50 or 100 hr. The company you send it to will provide a guide for normal wear. What you are really looking for are trends, comparing your first analysis to the next, to the next.

Jan

David-aviator · #6 02-04-2008, 08:42 AM

With regard to GEN3 operating temperature, my unit has about 40 hours since last summer and it has not been above 180F on the hottest days. Last time I flew in January, it barely got up to 145. This unit runs cooler than GEN1-2.

DanH · #7 02-04-2008, 08:55 AM

<<G3 drives have two different sized ball bearings, spaced apart, on the outside of the input gear and a single ball bearing internal to it.>>

Here is a photo borrowed from Jan's website....picture worth 1000 words:

Jan, do you have a photo with the components spread out like an exploded drawing? Safe bet that not everyone understands the power transmission path or the bearing support scheme by looking at the asssembled components.

<<2. While the "engine mounting plate" appears stout enough, have you measured for "flexing" under the sever gyro force load of the spinning prop?>>

The MT prop has a low MMI; 0.36889 slugs-ft^2. If you assume airframe pitch or yaw at 360 degrees per sec and 2500 prop RPM, the gyro moment is only 101 ft lbs. In the big picture, it is one of the little loads. Jan's bend test is very sensible.

STUPID ALERT! (2-7-08)

The above calculation is wrong. I skipped one multiplication and used prop RPM in revolutions per second. The correct value is prop RPM in radians per second. The equation is (yaw in rad/sec)x(RPM in rad/sec)x(prop MMI), and if the MMI is in slugs-ft^2 the answer is in ft-lbs.

Yaw = 360 deg/sec = 6.28 rad/sec
RPM = (2500/60) x 6.28 = 261.7 rad/sec
MMI = 0.36889 slugs-ft^2

So, 6.28 x 261.7 x 0.36889 = 606 ft-lbs

Duh!

Geico266 · #8 02-04-2008, 10:36 AM

Quote:

Originally Posted by janeggenfellner

2. While the "engine mounting plate" appears stout enough, have you measured for "flexing" under the sever gyro force load of the spinning prop? Is that where side loading may be developing?

You are confusing the entire plate with what happens inboard of the bell housing perimeter. The plate is bolted in 10 places around the bell housing, effectively making it one with the housing. Then, only 1" inboard, the structure from the aft drive section, further reinforce the integrity and assure consistent alignment of the drive input shaft to the crank centerline. We have tested this by flexing the tip of the plate forward 4" with less than 0.001 deflection inboard of the bell housing perimeter. Many mistakes this plate for being very heavy. In fact it is not. The weight is only 7.5lb and provide the engine with an engine mount, gearbox mount, starter mount, oil cooler mount and cooling system mount. the plate is reinforced by traditional aircraft triangulation, using 4130 N steel tubing.

Jan

I did notice the inboard bolts and the area where the "bell housing" would be in the automotive application. That is one stout plate!

Jan, one more question. Is there a need (like the Rotax 912 / 912S) to adjust / check the preloading tension of the Gen3 gear box? I'm not sure if that is the correct term, but Rotax needs to have their gearbox serviced to check the "breakout force" to get the gear box to turn on it's own every 100 hours or so. Is there a need for that or any other servicing with the Gen3 as parts wear?

I greatly appreciate your responses here and to everyones questions. You are to be commended for your contributions to experimental aviation. Thank you for your dedication and hard work.

janeggenfellner · #9 02-04-2008, 04:43 PM

1) Pictures of the reduction drive unit laid out: I will take some pictures of the input section next time we assemble the units.

2) "Breakout Force": I believe they use a cam / Belleville disk spring system between the engine and drive unit. With this system I imagine you could turn the propeller, and hold the engine, until the shaft is passing over the internal cam lobe, then back down on the other side. Our system does not use this type of damper. To read about, "dual mass" flywheels, just Google it. That is what we use. As a preflight test, gently pull on a propeller blade and you will be able to pull it for an inch, prior to the engine turning.

Jan

DanH · #10 02-04-2008, 10:18 PM

<< I will take some pictures of the input section next time we assemble the units. >>

I'm sure everyone will find that helpful.

<<"dual mass" flywheels>>

Ahh, that kind of dual mass flywheel. "Dual mass"" had me thinking perhaps it was a suspended ring type. Not a damper of course. Can you share the inertia figures for the two wheels and the connecting spring rate?