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HelicopterMain Discussion › Tapered Bearings
12-09-2008 04:53 AM  8 years agoPost 1
husky385

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Eugene

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I sure would like to see one of these bearing manufacturers make tapered roller bearings sized for rc heli main shafts. I bet they would last longer than radial bearings and eliminate any need for thrust bearings.
Kevin

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12-09-2008 05:28 AM  8 years agoPost 2
Heli 770

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Well there would be a design limitation, were are you going to put the tapers on the main shaft.

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12-09-2008 01:19 PM  8 years agoPost 3
MikeSherman

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You don't need tapers on the main shaft. Taper roller bearings are available just like radial and ball bearings with parallel inner and outer bores.

The difficulty would be correctly setting the endplay. The bearings life and capacity is directly related to its endplay. You would need shims or bearing nuts to set this endplay. Just more parts and complexity.

Radial contact bearings are sufficient. They just need to be sized correctly.

-Mike

Team QuickUK Pilot
Team Heliproz

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12-09-2008 03:54 PM  8 years agoPost 4
TaleGunner

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Deer Park WA

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I agree with the above posts and not only would the parts count and complexity go up so would weight

CRASH! GLUE! REPEAT!
Spectra-G, Ion X-2

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12-09-2008 11:19 PM  8 years agoPost 5
husky385

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Why would it be more complex? Basically you have a outer race (bearing cup) inner race and bearing combo. Granted you wouldn't have a shield. Why would it be any harder to set the preload. With my HDX 450 all I do is set the main shaft collar to just take out the end play of the main shaft. Seems to me that would work as well for tapered bearings. Do you know of any manufacture that makes tapered ones that small. I would love to try it. I kind of like to go against the grain. I am testing permanent lubed bearings in my Scorpion motor, main shaft, tail drive shaft and tail shaft. So far I see no adverse effects of doing so. I have read over and over that there would be to much drag.
Kevin

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12-09-2008 11:24 PM  8 years agoPost 6
Heli 770

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SDP/SI, might have some.

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12-10-2008 12:17 AM  8 years agoPost 7
husky385

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I believe the reason tapered bearings are not used is they just don't make em that small. Bet it would work though.
Kevin

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12-10-2008 03:20 AM  8 years agoPost 8
MikeSherman

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I don't believe they make them that small...that's where radial, ball, and thrust bearings come into play.

You can't just use a main shaft collar and expect to set end play unfortunately. You must be accurate to .001-.002". That must be shimmed from a shoulder on the shaft, bearing endcap, or bearing locknut arrangement.

I'm not saying it wont work - it's just overkill for the application. There is nothing wrong with a correctly sized radial contact bearing to take up axial thrust and radial loads.

-Mike

Team QuickUK Pilot
Team Heliproz

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12-10-2008 05:25 AM  8 years agoPost 9
husky385

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Raptor30Heli I remember working with front wheel bearings when I was younger. Tighten the nut up till snug back it off a quarter turn till you found a hole for the cotter key. That was certainly more slack than 1 to 2 thousands. I haven't changed a wheel bearing in years, have they changed that much? I know these bearings being smaller would have tighter tolerances. Using your fingers pinch the main gear auto-rotation sleeve to tension the lower main and the upper main with the collar. Adjust with finger pressure until the main shaft turns freely without slop and you are good to go. I came to that conclusion to no one makes them.
Kevin

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12-10-2008 05:31 AM  8 years agoPost 10
husky385

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The problem with using radial bearings only is you are putting side load on them that they are not designed for. I have tried greasing and oiling they just do not last very long. Always they are notchy on one side or the other.
Kevin

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12-10-2008 05:47 AM  8 years agoPost 11
husky385

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Eugene

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You guys talking about complex. Take a look at the Bergen Gasser that's complex. I can't remember where I saw it but one heli uses thrust bearings on its main shaft. Since they don,t make the right kinds of bearings for the application then the the thrust bearing should be part of the design of these heli's, In my humble opinion.
Kevin

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12-10-2008 01:45 PM  8 years agoPost 12
MikeSherman

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That was certainly more slack than 1 to 2 thousands.
Yup - that was a .625" bore spinning at about 950rpm.

Our heli's run .393" bore spinning at 1500-2400rpm. Higher speed equates to tigher tolerance. This helps reduce vibration as well.
I know these bearings being smaller would have tighter tolerances.
You got it! I think here inlies the difficulty - accurately setting this clearance without adding weight or complexity. Not saying it can't be done, but it needs to be done easily, repeatably and affordably. I'm guessing the bearing would need an endplay of 0 to .0005". That's pretty tight! Most pilots on this forum that own a dial indicator probably have one that has a resolution of .001". Setting this bearing would be guessing between the tick lines on that indicator.

Then you would also need to incorporate a way to hold the grease or oil in. By their design, taper roller bearings don't have shields or seals. Typically the housing or endcap have the seal to hold in the lube.

For our helicopter applications, we are currently stuck with radial contact bearings and/or ball bearings with an additional thrust bearing. These can be combined to create bearing packs for upper and lower bearing blocks.
The problem with using radial bearings only is you are putting side load on them that they are not designed for.
There is nothing wrong with a ball bearing taking a thrust loading. It just needs to be sized accordingly.

-Mike

Team QuickUK Pilot
Team Heliproz

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12-10-2008 02:17 PM  8 years agoPost 13
husky385

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There is nothing wrong with a ball bearing taking a thrust loading. It just needs to be sized accordingly
Apparently mine aren't sized correctly. They get notchy to damn quick to suit me. I am going to work on incorporating thrust bearings in mine. My lathe and milling machine should help. As long as my old eyes cooperate with parts that small.
Kevin

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12-10-2008 02:29 PM  8 years agoPost 14
Heli 770

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They do make bearing blocks with thrust bearings for a limited amount of Helis.

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12-10-2008 02:57 PM  8 years agoPost 15
husky385

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Eugene

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None for my HDX450. I like to tinker so maybe I can come up with something. I just got a Email from Boca Bearings telling me that no one they know of makes tapered roller bearings that small, so I guess we will never know weather it would be usable in our application.
Thanks guys
Kevin

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12-10-2008 04:15 PM  8 years agoPost 16
OT45

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The preload as mentioned is critical and I'm not certain if the expansion/contraction of your frames will exceed the tolerances for a proper fit. If you want to go this route, how about a set of angular contact bearings (machine tool bearings) insted of tapered rollers? I don't know if they are available down to the size you need.
I would stack and lock them on one end of the shaft and the other end mounted with a regular radial bearing. This way your preload will be easier to control.
As Raptor 30 said, you will have to come up with a way to keep oil in as I believe angular contact bearings usually don't have seals. You could build that into your custom bearing blocks.
I do think it's overkill for a small heli! I would just buy a better grade of radial bearings....

scratch building is not just for planks

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12-10-2008 04:44 PM  8 years agoPost 17
husky385

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I do think it's overkill for a small heli!
Yes it is overkill I have so much time on my hands now it will give me something to do besides lurking on these forums so much.
I would just buy a better grade of radial bearings....
I have tried some of Boca's better bearings, no luck. I have not tried ceramic. A little to much for my income level.
Kevin

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06-03-2009 03:05 PM  8 years agoPost 18
Helos4Me

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About the preload. If there is a little play to begin with, centrifugal force will remove that during operation. The blade grip, bearings etc have over 200lbs of force on them at 10,000rpm. Yea it should be pretty close to begin with.

To Fly Is Heavenly, To Hover Divine!

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