Thrust bearings for main shaft? Micro Heli frame has them.

[everydayflyer]

Anyone know of any other heli frame which uses thrust bearing on the main shaft? I can not understand the logic as the shaft has mostly radial loads and the thrust bearing take up space where longer or addational radial bearging could be used instead..

[DoubleCH]

Mainshaft bearings CAN get quite some axial loads. With a well balanced rotor radial load on the mainshaft may actually be much lower in comparison. Most 3D helis are spec'ed to pull about 3-4g's. My 300x pulls 2000g no problem. This force is loaded all on a single bearing, top or middle one on the mainshaft depending on full positive or full negative collective.

That said, I am a bit surprised to see no heli runs thrust bearings on the mainshaft.

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[Nelsonisms]

There was a short discussion about it in the 450X forum a few weeks back. I'll link Brian James' response.

https://www.helifreak.com/showthread...36#post5929236

[everydayflyer]

Thanks for the link and I agree that thrust bearings are not really the way to go most especially when they grately reduce the length of the radial bearings.While I do realize that there are thrust loads on the main shaft I feel that the radial loads are much greater. How many glow,disel,or electric motors used in RC ghave thrust bearings?

I started a thread on RC Groups in the Electric Heli TAlk Forum and it seems very few helie use thrust bearings on the main shaft..

http://www.rcgroups.com/forums/showthread.php?t=2209325

[DoubleCH]

Originally Posted by everydayflyer

While I do realize that there are thrust loads on the main shaft I feel that the radial loads are much greater.

If you don't dynamically balance the rotors good but rely on stiff CF frame to mask the slight out of balance then yes the mainshaft bearings will get much higher radial load. Every single retired mainshaft bearing I pulled out of my 300X has more axial play than radial play because I dynamically balance the rotors as much as possible. My current mainshaft bearings have been on for hundreds of flights plus a few crashes.

How many glow,disel,or electric motors used in RC ghave thrust bearings?

That's a totally different scenario. All motors/engines for RC helis assert radial load to drive gears or pulley. You don't lift/pull/accelerate/decelerate the whole heli by pulling up/down on the motor bearings like you do mainshaft bearings. The most axial load on the motor bearings are when you run slant gear. Even that there's very little percentage of the driving (radial) load on the motor bearings that generates axial load.

[everydayflyer]

[That's a totally different scenario. All motors/engines for RC helis assert radial load to drive gears or pulley.

Sorry I posted

How many glow,disel,or electric motors used in RC ghave thrust bearings?

Guess I should have said used on air planes or planks to make it clearer. My point is that there are more motor and engines without thrust bearing which are dealing with both radial and thrust loads than there are heli main shafts. .

[DoubleCH]

I think even 3D planes most of them pull around 2g's, not like heli's typical 3-4g's. Without collective pitch and heli-size blades you don't see planes catapult like 3D helis do.

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[ahahn]

Not an expert on thrust bearings, but one thing that comes to my mind is that most of our hell applications use the thrust bearing loaded in one direction. I think you would need two, one located in the bottom bering stack location and the other at the top to handle both positive and negative loads---if they would be needed at all.

My guess is that we don't see them because they aren't necessary--that the radial bearings we use can easily handle these thrust loads. 3g's probably isn't a lot compared to the "centrifugal" forces put on our blades.

Another observation, yes balancing the blades helps the main bearings out, but the radial loads are more likely dominated by cyclic moves and the fact the main rotor is acting like one huge gyroscope, getting that to actually pitch/roll takes a lot of force.

[DoubleCH]

Originally Posted by ahahn

Another observation, yes balancing the blades helps the main bearings out, but the radial loads are more likely dominated by cyclic moves and the fact the main rotor is acting like one huge gyroscope, getting that to actually pitch/roll takes a lot of force.

Agree about the gyroscope thing, but the fact is my retired mainshaft bearings all have more axial play than radial play.