VansAirForceForums  
Home > VansAirForceForums

-POSTING RULES
-Advertise in here!
- Today's Posts | Insert Pics

Keep VAF Going
Donate methods

Point your
camera app here
to donate fast.






VAF on Twitter:
@VansAirForceNet

  #41  
Old 11-15-2022, 08:39 AM
KeithO KeithO is online now
 
Join Date: Jul 2010
Location: Jackson,MI
Posts: 123
Default

John, the plate might start out 1" thick but they did machine away a considerable amount of that material, so its not suitable for a hand calculation, the only way to determine deflection is a) to measure it like I have proposed or b) do an FEA calculation. Obviously I can pretty readily do the first, while I would have a lot of work to do the second. If Jan would make a step file available, that would make it easy, but I think the likelihood of that is very low.

I did discover today while doing a google search that the alternate style flex disc that I was proposing is already made by several suppliers. Picture attached. This style of flex plate has a carrier plate that transmits the engine power instead of relying on cordage embedded in the flex coupler. It also has very specific amount of elastomeric material (much more than in the current part) which can be compressed in either direction. The PU bushings can be changed so one can try different shore hardness for the specific application.
Attached Thumbnails
Click image for larger version

Name:	V110 Mounting plate.JPG
Views:	19
Size:	54.8 KB
ID:	33890  Click image for larger version

Name:	Flex disk alternate.JPG
Views:	56
Size:	82.9 KB
ID:	33891  
Reply With Quote
  #42  
Old 11-15-2022, 09:16 AM
rv6ejguy's Avatar
rv6ejguy rv6ejguy is offline
 
Join Date: Mar 2005
Location: Calgary, Canada
Posts: 6,410
Default

PU doesn't have the same characteristics as rubber at these frequencies. Be sure you explore that.
__________________

Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 460.7 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
https://www.youtube.com/channel/UCiy...g2GvQfelECCGoQ


Reply With Quote
  #43  
Old 11-15-2022, 09:17 AM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 11,082
Default

Quote:
Originally Posted by KeithO View Post
I did discover today while doing a google search that the alternate style flex disc that I was proposing is already made by several suppliers. Picture attached.
Keith, suggest you consider natural rubber torsional couplers made specifically for this sort of application. Lovejoy Centaflex is a personal favorite, but there are other couplers in various styles. PU bushings are poor for alternating angular displacement...too much hysteresis.

BTW, don't be pushed toward a BMW driveshaft coupler because Viking made that choice. Looking for something to fit the existing driving/driven flanges is a constraint. Climb out of the box.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Reply With Quote
  #44  
Old 11-15-2022, 10:06 AM
KeithO KeithO is online now
 
Join Date: Jul 2010
Location: Jackson,MI
Posts: 123
Default

Ross, and Dan, your feedback is appreciated. I was looking for a coupling that would be softer than the stock BMW unit which is mostly cordage and extremely stiff when in tension (from torque application). Since Viking cuts the stock one into 3 pieces, I'm not sure what it is doing in an over-run situation.

All I know is that if you misalign the shafts, one is very quickly stretching the segments of the current coupler, which is very strong in that mode and one can quickly apply the sorts of loads which will result in fatigue failure. If we find only 1 ear damaged on the failed gearboxes, it will suggest that there was asymmetry in the pin positions of either flange to the point that a single pin was carrying the entire load, together with any load created by misalignment and one could see that failing quite rapidly. It is interesting to note on the originally pictured fatigue crack how it runs almost exactly square to the centerline of that "leg" of the spider. If one thinks about it, the engine load is applied at almost a 90 degree angle to the centerline of the drive ear. So one would not expect a fatigue crack from engine load to be where the crack has appeared. On the other hand, a load from misalignment could be expected to be in the radial direction and that lines up perfectly with the orientation of the crack.

Given that the gearbox input flange broke in both cases we could model that up since its not very complex and make a determination how high the forces would need to be to get stress levels high enough that one could fail in the kinds of service durations that we had seen.
Reply With Quote
  #45  
Old 11-19-2022, 07:16 PM
KeithO KeithO is online now
 
Join Date: Jul 2010
Location: Jackson,MI
Posts: 123
Default

This video illustrates some of the kick back issues on starting that was one of the complaints against the stock ecu.
https://youtu.be/lXb_N60vAHs

The 800 hour engine has shipped in MA, now just a question of how long it takes to thread through the snow disaster that is the I80 corridor.
Reply With Quote
  #46  
Old 11-27-2022, 03:17 PM
KeithO KeithO is online now
 
Join Date: Jul 2010
Location: Jackson,MI
Posts: 123
Default Pictures of the failed 134 hour SB compliant drive flange

See attached the first sample failed gearbox input flange. This is the 134 hour unit that had all the SB compliant version parts in it and lead to the total loss of the customers airplane in a forced landing.
I think anyone can understand why it is important to get both flywheel side and gearbox side drive flanges inspected for cracks as soon as possible if you own one of these.
Attached Thumbnails
Click image for larger version

Name:	IMG_0373.jpg
Views:	111
Size:	490.9 KB
ID:	34311  Click image for larger version

Name:	IMG_0374.jpg
Views:	86
Size:	412.5 KB
ID:	34312  

Last edited by KeithO : 11-27-2022 at 03:19 PM.
Reply With Quote
  #47  
Old 11-27-2022, 07:33 PM
PilotjohnS PilotjohnS is offline
 
Join Date: Jan 2016
Location: Southwest, USA
Posts: 2,532
Default

Quote:
Originally Posted by KeithO View Post
See attached the first sample failed gearbox input flange. This is the 134 hour unit that had all the SB compliant version parts in it and lead to the total loss of the customers airplane in a forced landing.
I think anyone can understand why it is important to get both flywheel side and gearbox side drive flanges inspected for cracks as soon as possible if you own one of these.
Scary stuff if one is not over the flat lands of Kansas.
__________________
John S

WARNING! Information presented in this post is my opinion. All users of info have sole responsibility for determining accuracy or suitability for their use.

Dues paid 2022, worth every penny

RV9A- Status:
98% done, 2% left to go
To Go: wing mounting, engine baffles, wing tips, move to airport
www.pilotjohnsrv9.blogspot.com
Reply With Quote
  #48  
Old 11-27-2022, 09:13 PM
KeithO KeithO is online now
 
Join Date: Jul 2010
Location: Jackson,MI
Posts: 123
Default

Adding a few more pictures. The first showing the gap between the input gear and the bearing on the inside of the gearbox, where I plan to try to fit a bearing splitter to support the bearing inner race while pressing the input shaft, with gear out the drive flange.

Also a wider angle shot showing how the engine slung the broken off ear around and "machined" out the back plate flange until the guibo finally let go. It seems fairly obvious that the crack initiated at the outer diameter of the boss in the center of the drive flange where the bending load was concentrated. Likely the outer crack originated where the boss is located on the ear to hold the drive pin, there is another sharp change in section there.

Fundamentally the material looks brittle. Based on the coloration this may have been caused by the welding process that Jan used to "further improve" the drive flange.
Attached Thumbnails
Click image for larger version

Name:	IMG_0375.jpg
Views:	79
Size:	161.5 KB
ID:	34340  Click image for larger version

Name:	IMG_0376.jpg
Views:	113
Size:	278.3 KB
ID:	34341  
Reply With Quote
  #49  
Old 11-29-2022, 12:29 AM
skylor's Avatar
skylor skylor is offline
 
Join Date: Aug 2009
Location: Southern California
Posts: 1,079
Default Gyroscopic Loads

Quote:
Originally Posted by Marc Bourget View Post
If I was given the responsibility for ground testing the new PSRU plate, I'd mount the engine/propeller assembly on a Tilt-Yaw table to check (both the old) and the new plate's response to the gyroscopic loads.

There should be digital measuring "cells"? to check relative motion created by the gyroscopic load testing
Gyroscopic forces are easily calculated. The PSRU plate can simply be statically load tested with the calculated gyroscopic forces applied the the propellor drive flange. No need to design and build a complex and expensive gimbaled test stand for this.

Skylor

Last edited by skylor : 11-29-2022 at 12:31 AM.
Reply With Quote
  #50  
Old 11-29-2022, 07:20 AM
Marc Bourget Marc Bourget is offline
 
Join Date: Apr 2009
Location: Stockton, California
Posts: 385
Default

Granted, I didn't consider that. On further "associative memory" reflection, recalling the Lockheed Electra in-flight failures there could be a "whirl mode" issue?

This is a "just thinking-what if" observation. Not saying it's necessary.

Hoping you have an additional cogent insight.

Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 08:33 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.