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HelicopterMain Discussion › Grip Bearing Arrangement
01-27-2013 03:23 PM  4 years agoPost 41
ShuRugal

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Killeen, TX

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Havoc, I had actually misread your second response, which was posted while i was doing the diagram/writeup (i saw it while using preview to make sure all my color coding was correct). That post (including doing the diagram) took me some 45 minutes to produce, and it was after 1 am when i read your post.

As i have said, it was an honest mistake and i apologize for wrongly implicating you. If you still wish to take issue with it, that is your own problem and you can kindly piss off. If not, how 'bout we drop it before this thread gets any more seriously derailed?

AMA 700159

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01-27-2013 03:34 PM  4 years agoPost 42
Havoc

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Ky.

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If you still wish to take issue with it, that is your own problem and you can kindly piss off. If not, how 'bout we drop it before this thread gets any more seriously derailed?
Btw, your apologies are horrible.

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01-27-2013 05:21 PM  4 years agoPost 43
BobOD

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New York- USA

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Funny stuff.

Here are some calcs to compare the two arrangements in a given amount of space.

Team POP Secret

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01-27-2013 06:04 PM  4 years agoPost 44
Wave

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Illinois

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Without a doubt widely spaced radial bearings are the way to go.

Unfortunately the proper application of a radial bearing requires that its outer and inner races be fixed ( slight press fit or anerobic compound ), so that radial loads are transferred efficiently ( theres that word again ), and accurately. Thus allowing the rolling elements to do their job.

A sliding fit radial bearing is laughable at best, and at worst can cause galling, binding, heating, and performance issues.

so..... Taya-san et all appear to be misguided in their design methodology, although the design does work, it is not " correct ".

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01-27-2013 06:25 PM  4 years agoPost 45
BobOD

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Thanks for bringing this up Wave. I've been wishing someone would. It's wrong on two counts.

1. You suppose that the outer radial bearing has to move to prevent a thrust load from transferring between inner and outer race. WRONG. The bearing is up against the thrust bearing which prevents movement. The only way for this to be a problem is if you glued the bearing in the wrong position (not against the thrust).
Very simple here. Thrust bearing prevents axial movement. No movement means no thrust load on the radial.

2. Although it does not matter, your statement indicates a different level of understanding of what is considered precision and high performance. Every self respecting engineer, machinest or assembler I have ever met would never glue a bearing in its housing and call it a high performance, quality job. The use of glue to center and or hold a bearing in place is an abomination. I assure you a proper fit yields better results.

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01-27-2013 06:57 PM  4 years agoPost 46
OICU812

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Edson, Alberta, Canada

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Although there have been some clarifications here It's not really clear why such a thread exists? Lol.

...Once upon a time there were Nitros, flybars and frequency pins...

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01-27-2013 07:01 PM  4 years agoPost 47
Wave

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Illinois

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1. I was ignoring the thrust load and speaking of the radial load on the radial bearing.
PROPER radial bearing application requires that the races be fixed.

2. Press fit or retaining compound...the PROPER application of radial bearings require the races to be FIXED.

No self respecting engineer would design it otherwise.

Like I was saying.....Taya San's designs ( sliding fit radial bearings ) work fine, but from an engineering design perspective are incorrect.

The use of sliding fit radial bearings are an obomination sir.

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01-27-2013 07:03 PM  4 years agoPost 48
Wave

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Illinois

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Although there have been some clarifications here It's not really clear why such a thread exists? Lol.

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01-27-2013 07:15 PM  4 years agoPost 49
BobOD

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New York- USA

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I prefer them to be fixed properly myself. And I'm not considering any specific manufacturer or their methods or designs. Just basic mechanical engineering princepals.
Which are you challenging?

Please try to stay focused on what you are arguing. My rebuttal was that the outer race of the radial bearing does not have to slide. So what point are you trying to make. We know you do not like the outcome of this discussion...and we don't care about that.

Team POP Secret

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01-27-2013 07:20 PM  4 years agoPost 50
OICU812

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Edson, Alberta, Canada

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It's obvious this threads not for me or anyone in community actually Bob, its for you and your need for attention and to be able to mention you are an engineer?... lol.

At least its more education for some then useless nitro debate ill give ya that. This thread has ran its course you poked Dood like ya wanted to which could have continued through pm as mentioned? Time to make a creative thread without self glorification purposes perhaps and help others in process? Just a thought there Bobby... Have a great weekend.

...Once upon a time there were Nitros, flybars and frequency pins...

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01-27-2013 07:21 PM  4 years agoPost 51
ZS-JAF

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Houston, TX

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You guys have taken bearing arrangment to the next level!

This is why my wife makes fun of RC guys and the stuff we talk about. I just wanted to point out that no one has brought up, done the math on or computer illustrated thrust bearing then two radial bearings.

I have a 3D heli, I don't understand why it doesn't do 3D

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01-27-2013 07:43 PM  4 years agoPost 52
Wave

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Illinois

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We know you do not like the outcome of this discussion...and we don't care about that.
Actually it would be you who does not like the fact that I pointed out the proper application of radial bearings, due to the way that you seem stuck on the radial, thrust, radial design which requires that the outer radial be a sliding fit.

Bottom line...due to the low velocity and loading involved, it would work fine if the outer radial was a sliding fit.

It would work...but it ain't correct.

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01-27-2013 07:54 PM  4 years agoPost 53
Brokenlink

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Oakdale

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Hate to break it to you Dood, but you're flat wrong here.
Now you've done it You will be on his ignore list.

Jamie Griffith

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01-27-2013 08:08 PM  4 years agoPost 54
BobOD

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New York- USA

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Stop making argument for argument sake. The outer radial does not have to be a sliding fit. Third time I said it.

Shawn, stop making accusations. If you want to make a reasonable, intellegent argument, go for it. If you don't like the subject, just leave for crying out loud.

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01-27-2013 08:15 PM  4 years agoPost 55
OICU812

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Edson, Alberta, Canada

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Sorry for pointing out painfully obvious. Please drive thru..

...Once upon a time there were Nitros, flybars and frequency pins...

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01-27-2013 08:35 PM  4 years agoPost 56
BobOD

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Nice try Shawn. You're not bothering me one bit. And it's obvious to all why you keep posting. No need for it.

OK, before I move on to the less obvious, but very important, disadvantage that rad/rad/thrust arrangements have, I'll summarize what we have so far for the rad/thrust/rad stack.

-Both radial bearings can be securely fixed in their grip bores.
-No thrust load is transmitted through the radial bearings.
-No radial load is applied to the thrust bearings.
-The radial bearings are under substantially less load than if the radial and thrust are switched. (380 lb versus 574 lb illustrated above.)
-The thrust load applied is only from the centrifugal force exerted by the spinning mass. Not so with rad/rad/thrust BTW. This is the point that will come next.

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01-28-2013 03:50 AM  4 years agoPost 57
BobOD

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New York- USA

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One more disadvantage of rad/rad/thrust

This is a very little known mechanism and can be as much an issue as the increased forces demonstrated above.

When an upward or downward force is applied to the grip, from collective and cyclic load, there will always be some movement. And, obviously, the amount of movement is greater the farther out you go. It will also be greater the closer the two radials are to each other.

The problem this causes is best explained by first looking at the rad/thrust/rad bearing stack. In this case, the thrust bearing is flanked by the two radial bearings. In this arrangement, the thrust is isolated from up/down movement.

Now, when you move the radial in closer and the thrust outside, it is now in an area where there will be more up/down movement.

This places a radial load on the thrust bearing. And, since this has balls riding in grooves, it causes the balls to ride up out of the grooves, pushing the two races apart. Since these are rather shallow grooves, there is a huge magnification of this radial load into thrust load.

This causes multiple problems. One is that it puts additional thrust load on the bearing...additional to the centrifugal load.
Secondly, it is not a steady load like centrifugal. The cyclic loading causes the thrust bearing to spread cyclically...hammering on the grip bolt. This is likely the leading cause of bolt breakage, and thrust wear.
And finally, if the thrust bearing is spreading, and pushing on the bolt, what is it pressing against on the other side? The inside radial bearing pressing against the damper. That's right, this causes the radial bearing to have hammering thrust loads on it.

This is a triple whammy kind of issue. The radials are closer, so there will be more forces and movement. Plus, the thrust is moved farther out (more movement again) and in a position not protected by the radials. Wham wham wham.

Can it, does it work? Yes. But it does not exactly have finesse.

This problem is avoided by the radial/thrust/radial arrangement.

I don't figure you'd want to illustrate this ShuRugal. I think it would be cool...but a lot of effort. I can describe...not so good with illustration.

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01-28-2013 06:47 AM  4 years agoPost 58
misskimo

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Alaska 17 years, before mississippi for 31y

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Huh! Bob. One min you making some since, but electrical, a whole different ball game.
I like and agree with bearing , thrust and bearing, to me it seams best

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01-28-2013 08:11 AM  4 years agoPost 59
Ravenhyper50

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Canada's Capital

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Dr.Ben said...
Some of the most veteran helicopter desginers in the world use radial/thrust/ radial arrangement
This is so true, I cant believe some did not know this?

All my Machines go r/t/r I remember having an odd kit that said to assemble r/r/t but from habit building others kits, I assembled it the "Veteran helicopter designers" way

I think this is a great thread because people can learn from these type of posts if they really care to. Others ...well ...I wont go there...I hate forum fights

I wish people would stop the hate of others!

Raven

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01-28-2013 10:53 AM  4 years agoPost 60
Volidas

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Thessaloniki-Greece

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I would also like to say my opinion with all the respect to everyone' s else, just forgive me for my poor english.
As the rotorhead is spinning, the inner radial bearing receives the centrifugal force only the one created by its own mass, so if we would like to "help" it with this force we should put the thrust bearing right after it as this is the side that is stressed by the centripetal force.
But keep in mind that the outer radial bearing receives the centrifugal force created by the mass of the inner bearing, the thrust bearing, the blade grip they are housed in, the blade attached and of course its own mass.
The stress between the two radial bearings is incomparable as the load at the outer bearing is absolutely higher. If we put the thrust bearing in the middle we "help" the inner radial to work with less load, but we leave the outer one to to be pushed by the outer plate from the thrust bearing (just push as the bearing "sees" only a plate pushing it, no matter it is thrust or radial or whatever bearing) with no help.
Also, the enormous centripetal force (because of the mass of all the blade parts), is applied from the little washer that is attached at the spindle shaft bolt directly and only at the outer side of the outer radial bearing (and specifically at the inner race).
By this way, not only we have the outer bearing being highly stressed, but also the force is applied on it, dis similarly (high stress by centripetal force at inner race - high stress by centrifugal force at opposite direction at outer race.
So, the "best" solution is to put two thrust bearings, one in the middle and one at the end. Of course this solution is rejected because of the extra mass, the extra thrust bearing, the larger blade grip and maybe other reasons.
As now we have the ability to "help" unload only one of the two radial bearings, I think it is better to put the thrust bearing at the end because of what I have written at the previous paragraphs.
Thank you for reading.
Spiros

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HelicopterMain Discussion › Grip Bearing Arrangement
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