Eggenfellner Engines - Technical Only

[kearney]

Originally Posted by DanH

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?

Hi

I thought I would respond to the first post in this thread. In early January I visited Jan's to say hello and visit my new engine. It was in a crate awaiting Jan's / Gary's / Sal's gentle touch.

In the space of a few minutes, the engine was uncrated and most, if not all, the acessories were removed and scrapped. It was painful to see a new alternator go in the scrap bin but, according to Jan, there wasn't a market for the *new* removed parts

Photos of the before / after can be found at:

http://www.flickr.com/photos/23527073@N03/

Cheers

Les Keaney
RV10 - "some assebly required"

[Geico266]

Originally Posted by David-aviator

Larry,

Take a look at the pdf file Dan linked the thread to. There is a diagram of a dmf on page 13.

Dan, David, Thanks for the link. NOW I get it! I had no idea what a DMF was. Learn somthing new everyday....if you look.

[mcencula]

Jan,

If you have time to reply, I'm hoping you might be able to answer a few questions:

1. What was the thought process that led to a dual helical gear design for the gearbox rather than a planetary arrangement? The reason I ask is that a planetary gearbox has the nice property of containing all pressure angle forces within the planetary cluster rather than being reacted through the housing.

2. Likewise, what was the thought process that led to using single cut helical gears rather than dual opposed helical (i.e. herringbone) gears which could eliminate the thrust loading of the shaft support bearings?

3. What type of analysis or testing has been done to determine the resonance frequency (frequencies?) of the engine / fly wheel / gear reduction / propeller system?

4. Does the DMF have internal damping? If not, what's the advantage of using a DMF rather than using a single mass flywheel with a tuned torsional spring (rubber coupling?) and essentially using the propeller as the secondary mass? Perhaps the propeller inertia reflected through the gearbox wouldn't be sufficient?

5. Can the engine output enough torque to cause the DMF to "go solid" resulting in direct transfer of engine torque to propeller?

6. Were the springs in the DMF selected specifically for your application or is this a stock DMF that's used for automotive applications? The reason I ask is that since spring life is a function of both mean and alternating stresses, even if the max deflection is identical, there can be a huge difference in spring life depending on the case. What I mean to say is that a spring with a 1% mean load and a 20% alternating load will fail far sooner than one with a 20% mean load and a 1% alternating load. Thus, I'm wondering if the mean vs. alternating load expectations of this particular application were taken into account when designing the DMF?

7. What sort of FMEA was performed for the various components in the drivetrain and which component(s) have the greatest likelihood of failure?

8. How much, if any, FEA was performed of the various components in the drivetrain and where are the peak stresses expected? What are the expected peak stress values and types of stress (primary / principal / VonMises)? OT: As a curiosity, what software do you use (if applicable)?

I know your very busy, Jan, so I appreciate any time you're willing to spend answering my questions.

Best regards,

Mike

[DanH]

Randy,
<<looking at all the pictures of the Dual Mass Flywheels, but they really do make me curious about the design of the DMF on my STI engine.>>

One of the reasons I posted that particular .pdf link was that it illustrated three different variations of a DMF. There is a fourth common variation too, a DMF with a slip clutch to limit maximum transmitted torque. None of us know what type Jan has selected, but hopefully he will tell us.

<<I would think the spring rate would be important..... At Jan's suggestion, I am keeping my idle speed high, at around 800 prop RPMs to take it easy on the gear box and the DMF, but I am unsure if this is needed. >>

The torsional stiffness of the DMF is probably the lowest connecting stiffness value is the system. As such it would be a key factor in setting the system's lowest natural frequency, and by extension the RPM at which the system will resonate. I'm pretty sure it is below your 800 prop RPM idle speed, but I can't say exactly how much without a detailed analysis. A detailed torsional model for the MT/G3/6-cyl would include at least 11 stiffness values and 12 inertia values; nobody seems to have all of them. I can make a quick approximation of F1 by consolidation of the above into just a few stiffness and inertia values (some known, some guessed, some gathered), which is why I asked Jan for the DMF's spring rate. Without the above detailed stiffness and inertia values, concern for the proprietary nature of the DMF's spring rate is, well, rather moot.....and as mentioned, any Egg owner can measure it for himself.

Mike,
Excellent questions!

Jan,
Looks like you have a great opportunity here. Almost 2000 views on a thread less than 3 days old. Sure hope you can find time to cover the questions in detail; a lot of people are really interested in the engineering you put into your drive systems.

[Rotary10-RV]

Jan, Thanks for your participation. Dan thanks for your links, while I'm a mechanical engineer most of my friends aren't and the postings allow me to easily show them what we are talking about. The picture worth a thousand words senario. Mike, I believe that if you watch the video link Dan provided it will show you that, yes there are outputs at which the dual-mass flywheel can be limited in travel. The design engineer has the responsibility of selecting a flywheel system with adaquate springs to handle torques equal to or greater than the output of the engine.
Thanks again Dan
Thank you Jan for participating in a reasoned discussion providing us with facts about the product!
Bill Jepson

[Jconard]

Bill I think the question was not whether any DM flywheel could be designed in the way you describe. The question is whether the Egg DMF is single or dual stage and if it is designed to float or go soild during normal use. Collateral equations include within which range of prop weight are these calculations expected to hold true.

[mcencula]

Originally Posted by Jconard

Bill I think the question was not whether any DM flywheel could be designed in the way you describe. The question is whether the Egg DMF is single or dual stage and if it is designed to float or go soild during normal use. Collateral equations include within which range of prop weight are these calculations expected to hold true.

Correct. I am curious about the construction of this particular DMF including spring sizing, over compression protection, natural frequency, mean and alternating stresses, etc.

I didn't take the time to read the full LuK document, but the concept is simple enough...insert a device into the powertrain with a low torsional spring coefficient to lower the natural frequency. However, as anyone who's done design knows...the devil is in the details. :-)

This thread has actually helped me recollect a tour I had of LuK's facility in Wooster, OH some 10 years ago. One of their engineers was kind enough to give me the full $.25 tour including their work on clutches and flywheels. OT: The thing that made the biggest impression at the time was a stop-motion video of valve spring surge in an indy-car engine. That and the fact that the valve springs are designed to incrementally rotate the valves within their seats to even out the wear. Very cool.

[DanH]

<<The design engineer has the responsibility of selecting a flywheel system with adequate springs to handle torques equal to or greater than the output of the engine.>>

.....which would be peak instantaneous engine torque (not mean), or the peak resonant vibratory torque, whichever is greater.

<<However, as anyone who's done design knows...the devil is in the details.>>

Hear, hear! Bring on the details!

Guys, while we're waiting on Jan let me kick something around with you.

(1) Seems to me the fundamental idea behind the DMF is the placement of a soft spring at a larger radius from the rotational center, ie, it allows a softer spring rate while maintaining the same torque capacity. This a likely a good thing in the context of a PSRU.

(2) I'm thinking the "dual mass" part is a secondary benefit, and mostly a vehicle NVH thing. The driven flywheel adds inertia to the gearbox input gear, across the short, probably stiff splined shaft. That should lower that particular element's frequency, ie reduce the angular velocity of gear clatter at some vibratory orders. I don't see much benefit to the second flywheel mass in the context of reducing resonance at F1 and F2.

Thoughts?

[janeggenfellner]

How many test hours has the driver and flywheel system been exposed to and other what conditions?

The new drive system had to survive 200 hr full power on our test stand. We do not test for propeller loads, other than thrust, because this part of the drive has adequate bearing support. We are mainly interested in the interaction of the propeller / reduction drive / engine. We also ran two destructive tests to instant stoppage with no damage (other than the propellers) from 2700 RPM.

Jan

[janeggenfellner]

How many test hours has the driver and flywheel system been exposed to and other what conditions?

The new drive system had to survive 200 hr full power on our test stand. We do not test for propeller loads, other than thrust, because this part of the drive has adequate bearing support. We are mainly interested in the interaction of the propeller / reduction drive / engine. We also ran two destructive tests to instant stoppage with no damage (other than the propellers) from 2700 RPM.

I think many have now looked at the DMF information. as you can see, the benefit of the dual mass is less at high rpm and the additional mass is not desirable in an airplane. So we use only the aft portion of this setup. Someone asked about testing. We had MT do a vibration analysis with strange gauges to see how the #'s turned out. Results were very low compared to a direct drive engine.