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  #111  
Old 12-07-2022, 07:18 PM
KeithO KeithO is offline
 
Join Date: Jul 2010
Location: Jackson,MI
Posts: 149
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This is what the new flexible coupling system is looking like that is being proposed.

First the existing flex plate, flywheel side drive coupling, giubo and gearbox input flange all get removed.

Then a new CrMo flywheel is mounted to the crankshaft. The flywheel will help damp the vibration pulsations from the engine thus making a reduction at the source. Onto the flywheel gets bolted the Centaflex coupling element with 3x M12 bolts. On the gearbox side the splines get cleaned up and coated with high pressure copper slip grease (after pressing off the drive flange and putting the gearbox back together with potentially new bearings and seals)

A new centering bushing is installed in the crank. The far end of the gearbox input shaft, if it has a square edge like some do, it will get a chamfer ground into it to remove the sharp edge and make installation easier. The ID of the bushing likewise gets some high pressure grease because there will always be some relative motion as the flexible coupling does its job.

The new tubular cross section drive coupling is slid onto the splines of the gearbox input shaft. It has 3x M12 tapped holes that align with the radial fastening locations on the new coupling. The gearbox is placed with the input shaft engaged with the alignment bushing and the gearbox mount bolts are tightened. Now the drive coupling can be slid in the axial direction and the prop shaft rotated till the holes align allowing 1 fastener at a time to be installed hand tight before they are all tightened. Blue loctite will be used on all the fasteners.

Special thanks to DanH for his experienced advice on this application and Mark Kettering for playing devils advocate...
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Last edited by KeithO : 12-07-2022 at 10:04 PM.
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  #112  
Old 12-08-2022, 07:33 AM
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DanH DanH is offline
 
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Location: 08A
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Quote:
Originally Posted by KeithO View Post
This is what the new flexible coupling system is looking like that is being proposed.

...Onto the flywheel gets bolted the Centaflex coupling element with 3x M12 bolts. On the gearbox side the splines get cleaned up and coated with high pressure copper slip grease ...The new tubular cross section drive coupling is slid onto the splines of the gearbox input shaft. It has 3x M12 tapped holes that align with the radial fastening locations on the new coupling. The gearbox is placed with the input shaft engaged with the alignment bushing and the gearbox mount bolts are tightened. Now the drive coupling can be slid in the axial direction and the prop shaft rotated till the holes align allowing 1 fastener at a time to be installed hand tight before they are all tightened. Blue loctite will be used on all the fasteners..
Keith, sorry, but that assembly process will need some modification.

The radial bolts, installed last in your description above, are intended to compress the entire Centaflex radially when tightened. The goal is to place all the connecting rubber elements in compression, a key feature of the element. Prior to compression, the diameter of the axial bolt circle is larger than stated in the spec sheet. Without radial compression, it will be difficult to bolt the element to the flywheel...the holes won't line up.

I previously suggested using the "S" (think "slide") mounting pin configuration, with the pins on a nice thick section of the flywheel center. The pins are actually sleeves with the same 12mm bolts. This configuration would mount the splined hub and coupler on the gearbox input shaft, and then the gearbox assembly would then be slid onto the flywheel pins. Note it allows the use of a clamped spline, and the pins accommodate any minor axial inaccuracy due to fabrication or temperature change.

If you really want to bolt to the flywheel as described, there is a work around. You'll need to install and tighten the radial bolts into the splined hub on the bench, then bolt to the flywheel, then either (a) install the gearbox by inserting the input shaft into the splined hub, or (b) remove the hub, install it on the input shaft, install the gearbox, then re-install the radial bolts.

I should note a potential drawback to using this coupler; there is no convenient way to safety wire the 12mm metric allen cap screws. Be sure to use a torque wrench and a good threadlocker compound. I never had any sign of a problem.
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Last edited by DanH : 12-08-2022 at 07:41 AM.
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  #113  
Old 12-08-2022, 11:12 AM
KeithO KeithO is offline
 
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Dan, thanks for the feedback from practical experience of using the coupler. I didnt want to make the splined adapter a press fit and so far I doubt that a standard spline profile is being used. The original bolted input flange was a sliding fit on the splines and going that way with the design means that the gearbox doesnt have to be disassembled to press on the new coupling after removing the old one.

So I would rather constrain the position of the flexible element and allow the opposite end to float. If one needs an assembly aid then one could certainly use the tubular coupler to get the part set up on the flywheel.

I'm attaching a picture of the Aeromomentum flywheel which is close to the sort of design I think would work best, please ignore the 3 giubo attachment holes which fall in a horrible position.... The aeromomentum piece is sold for $200 I believe with the ring gear being separate. I do like the fact that a lot of the racing 4140 flywheels have the starter gear teeth cut directly into the billet before heat treatment. It would obviously have to cost a little more.
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  #114  
Old 12-08-2022, 12:25 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by KeithO View Post
I didnt want to make the splined adapter a press fit and so far I doubt that a standard spline profile is being used. The original bolted input flange was a sliding fit on the spline...
So why the change?

Quote:
I'm attaching a picture of the Aeromomentum flywheel which is close to the sort of design I think would work best...
Good concentration of mass at the outer rim for maximum inertia with least weight. The big holes would make me nervous on a non-balance-shaft 3-cyl due to the vibratory block wobble, but may be fine on a 4-cyl. If you like 'em, plug it into your new FEA tool, and apply pitch or yaw at about 1 radian per second.

Quote:
I do like the fact that a lot of the racing 4140 flywheels have the starter gear teeth cut directly into the billet before heat treatment. It would obviously have to cost a little more.
Is that done for high RPM use? I'd use the money elsewhere. It's easy to shrink a ring gear on a custom flywheel. All you need is an oven, a freezer, and a wife who isn't home

From the way back machine (1999), custom flywheel cut with a flat face to accommodate a viscous disk damper. Stock Suzuki ring gear.

The disk operated in parallel with the Centaflex, oscillating between the flywheel face and the inside of the blue anodized shell, clearance being about 0.010" on each side. Here it's being pumped full of liquid silicone. Compare vibratory torque plot with the undamped runs posted previously.
.
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  #115  
Old 12-08-2022, 12:39 PM
KeithO KeithO is offline
 
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I didnt make the decision to change the fit of the input flange on the shaft, Jan made that back when the service bulletin was issued for the gearbox or even prior to that, because a lot of gearboxes that came back to get the drive flange changed for one with the welded pins already had a pressed on input flange.

Then he released a 2 part video of how to change the drive flange, yet if you actually touched the gearbox your warranty was voided and you were flagged as being non compliant. Apparently the Eric Miller engine passed through 2 sets of hands prior to even getting to him and apparently one of the 2 previous owners changed the gearbox flange or had his A&P do it. That fact alone allowed Viking to say that his engine was not in compliance with the SB, thus nothing that happened with it was the fault of Viking.

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Originally Posted by DanH View Post
So why the change?

.
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  #116  
Old 12-08-2022, 12:50 PM
KeithO KeithO is offline
 
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See the 2 viking flywheels. I know that the aluminum one with all the pockets in it cracked and the next one is a modified flex plate. Not sure why the center was plasma cut on the shown sample, maybe to prevent it being used again ?? The aeromomentum one looks pretty bomb proof compared to either of these.
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Last edited by KeithO : 12-08-2022 at 12:53 PM.
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  #117  
Old 12-08-2022, 05:27 PM
KeithO KeithO is offline
 
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If there is someone reading this forum who owns a Viking 110 powered airplane who would be willing to fly a prototype new coupling system next spring/summer, please contact me. The intention would be to supply the parts for free and provide on site help with the install. In addition, I would like to inspect the customers existing drive flange after which all original material will be returned to the owner.

We would need access to an arbor press in the proximity of the owners hangar to remove the pressed on drive flange and inspect and re-assemble the gearbox. Obviously it would be most beneficial to the community if the person volunteering was someone who flew regularly and put some hours on his airplane.

If this interests you, please send me a PM in this regard. If there are several volunteers we could consider making a small batch of parts from what would potentially be the production vendor, this would be even more interesting than running a prototype assembly.
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  #118  
Old 12-08-2022, 10:11 PM
KeithO KeithO is offline
 
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Last week I had a conversation with Jan in which I tried to convince him that the giubo is a very strong composite component packed full of synthetic fiber and it probably wouldnt fail at much less than 10 000lb. Therefore was more than strong enough to fatigue steel parts like the drive flange. He kept referring to them as "rubber bands".

So he did a little experiment with a single segment and a pair of steel cables and his 2500 series diesel truck and a stout tree and even after breaking the steel cables, bending the 12mm bolts he was still commenting on what a nice flexible rubber part it was... Comical.
https://youtu.be/dgBHff4pVNo
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  #119  
Old 12-09-2022, 08:15 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by KeithO View Post
I didn't make the decision to change the fit of the input flange on the shaft, Jan made that back when the service bulletin was issued for the gearbox or even prior to that...
That's what I was asking...why did Jan make the change? I think you're saying he did not share his reasons. Given switching from a slip-on to a pressed-on spider added significant effort to the fabrication and assembly process, it seems like a flag.

Quote:
The aeromomentum one looks pretty bomb proof compared to either of these.
Might be, but you have an analytical tool. No doubt Jan thought the aluminum flywheel and welded spider looked pretty bomb proof.
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  #120  
Old 12-09-2022, 09:24 AM
KeithO KeithO is offline
 
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Quote:
Originally Posted by DanH View Post
That's what I was asking...why did Jan make the change? I think you're saying he did not share his reasons. Given switching from a slip-on to a pressed-on spider added significant effort to the fabrication and assembly process, it seems like a flag.

Might be, but you have an analytical tool. No doubt Jan thought the aluminum flywheel and welded spider looked pretty bomb proof.
Ah, but Jan couldn't pick out an SN curve in a suspect lineup, nor would he have any idea what such a curve would look like for aluminum vs CrMo steel....
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