Mixed bearings? (radial + angular contact)

[RaceMechaniX]

Just thinking out loud and looking for feedback is anyone has attempted to replace the small end deep grove ball bearing with an angular contact bearing and pre-load spring. Although I prefer to run square drive where possible to eliminate the thrust load it is difficult to do with all setups especially wire drives. Starring a sectioned VAC91 it looks like it would be possible with some minor machining to replace the output side with an angular contact bearing that could handle the thrust loads in addition to the radial loads better and wear less.

Anyone tried this?

 

[John Beardslee]

Jerry Betke and I tried angular contact bearings in our OS Max 46 vrm’s many years ago. Found no better bearing life or performance gains. It’s been a number of years so it might be worth revisiting. As you know a good quality bearing installed using proper procedures is key.

 

[dwilfong]

I had bearing problems with my VAC 1.05 I built. Had a set of full complement ceramic bearings built up and it all went away. They will handle twice as much load in all directions including thrust. There is a place that will make them up for no more $ than a standard bearing. You can also have them set the clearance up a little loose to avoid over heating. I will post a link if you like.

 

[LohringMiller]

I think the engine bearings are quite capable of carrying propeller thrust loads. Do you actually know of any failures, especially front bearing failures? Below are the thoughts on mechanical design from two of the last great nitro model engine builders.

Lohring Miller

 

[Mike Betke]

I would think that an angular contact bearing would probably separate under load from the shaft. You're best bet would be to use square drive.

Also, I'm pretty sure that you would pull the bearing together and lose all of your clearance in this application. Thinking back to my days of building precision spindles, we would grind the step on the shaft or have a spacer on the ID to set the clearance on the bearing backlash for angular contact bearings. That was 25 years ago, so I could be wrong.

 

[RaceMechaniX]

The difference is clear to me. If you ask someone who runs a collet drive how often they have to change bearings versus someone who runs square drive it's significant. It's difficult to make angular contact bearings work with an aluminum housing and steel shaft due to the CTE unless you have a compensation system like a preload spring. Balancing preload to reduce ball skidding versus drag is tricky.

 

[LohringMiller]

My experience with collet drives is in industrial type gas engines. Their bearings have no problem with thrust loads and last a long time. However, I always ran square drives on my nitro boats. Maybe another Idea to take the thrust would be to add an external needle thrust bearing between the collet drive and the crankcase. They would need regular greasing and are easy to replace. It's a lot less expensive solution.
https://www.mcmaster.com/thrust-bearings/roller-bearing-type~needle/
Lohring Miller

 

[Terry Keeley]

I've thought of this also but came to the conclusion that the thrust we put on the front bearing isn't enough to warrant an angular contact bearing.

I thing I do know from experience tho is that hybrid ceramic bearings fit to a high C3 clearance will outperform standard bearings significantly...