Mat,  as always I really don't know, but I am considering making the reduction drive self contained with its own oil supply.  That seems to be the simplest option as once it is full of oil it will heat and I really cannot see it generating much heat on its own with say 2/3 full of oil.  Only one way to find out!!  Will give me something to do. 

Neil.

On 1/14/2019 2:10 PM, Matt Boiteau mattboiteau@gmail.com wrote:

Should we try restricting the oil input even more? To 1/16th ?

- Matt Boiteau

On Sun, Jan 13, 2019 at 5:43 AM Neil Unger 12348ung@gmail.com <flyrotary@lancaironline.net> wrote:

Steve,

                 You appear to have proved what I was coming to suspect, mainly that the gearbox actually fills with oil under load.  Why this happens I cannot say as the drain is possibly 10x the input as per size.  Sure the input is at say 70 psi and restricted to 3 mm or 1/8 inch while the return is gravity at 1/2 inch dia.  I found this while testing when I removed the return line immediately after shut down and got covered in oil which should not have been if it was running on a small amount of oil as it is meant to do.  As usual there is always much to be learned and I thank you for the good information provided.

Neil.

On 1/13/2019 1:40 PM, Steven W. Boese SBoese@uwyo.edu wrote:

Tracy and Neil,

In order to prove to myself that the RPM is divided between the stacked thrust bearings, I installed a Hall effect sensor in the mounting plate and silver brazed triggers to the middle thrust washer.  An inductive pickup was installed to monitor the rotation of the flexplate (input shaft).  This allowed the determination of the input shaft RPM as well as the middle washer RPM under various conditions. The load on the drive was from a 3 blade 72" dia  Warp drive prop with the tip angle set to 20 degrees.   

All new bearing components as used in the -C drive were tested along with a used cupped middle thrust washer from a C6 transmission.  The cupped thrust washer was tested because it was possible that the cup overlapping the 3.5mm shaft side thrust washer would prevent the middle washer from contacting and causing wear of the input shaft.  After seeing the results from the used cupped washer, new cupped washers were obtained and tested also.

In the course of testing the thrust bearing configurations, it was found that the reduction drive always operates completely filled with oil.  The added triggers may have affected the behavior of the bearing stack due to drag between them and the surrounding oil.  To see if this was the case, the drive was modified such that the drive contained about 5 to 6 oz of oil during operation rather than the about 20 oz of oil when completely filled.

The results are shown in the attached plots.

These results indicate that, with all new components including a new flat middle washer, the RPM was reasonably well divided between the two thrust bearings and affected little by the amount of oil in the gearbox.  With the used cupped middle thrust washer, essentially all the RPM was seen by the mounting plate side bearing.  With the new cupped middle thrust washer, the RPM  distribution between the thrust bearings was affected by engine RPM when the gearbox was completely oil filled but little affected by RPM when the gearbox was drained.

All the results were obtained with an input shaft that didn't have a groove worn in it by the middle thrust washer.  

My conclusion is that with all new bearing components and unworn shaft the system behaves as desired.  With used components, the behavior is unknown.  The cupped thrust washer is not a solution to the shaft wear issue because of the uneven RPM distribution when submerged in oil and since shaft wear has resulted from the bearing cages as well as the middle washer. 

The internal gearbox pressure with -6 drain lines was about 4 psi when cold and about 2 psi when warm which may have implications in terms of input seal leakage and the seal coming out of its bore.  The completely oil filled gearbox consumes extra power which is converted to heat but apparently not so much as to cause serious problems.

All the above are simply results of my curiosity.  You are most welcome to draw your own conclusions.

Steve Boese  

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