Head Bearing Quality ?

[mikeconcannon]

Iv never yet replaced a rotor head bearing and will probably send my head back to Magni factory when the time comes to do so.
BUT heres a question that Iv often thought about..... Are there cheap bearings, and bearings that we accept are the normal quality, and then realy expensive super quality bearings for use in rotor heads ? In other words, can you get bearings made by the same factory that makes em for eg, the space shuttle, and pay the price, and know that they are the best that money can buy. Or do all the rotor head manufacturers realy just use run of the mill, ordinary over the counter SKF average type bearings ???

[brett s]

The difference in the certified aircraft world would normally be just quality control & a full paper trail back to the manufacturer - still made by the same folks if you're buying a name-brand bearing from one of the major makers though.

[DennisFetters]

Iv never yet replaced a rotor head bearing and will probably send my head back to Magni factory when the time comes to do so.
BUT heres a question that Iv often thought about..... Are there cheap bearings, and bearings that we accept are the normal quality, and then realy expensive super quality bearings for use in rotor heads ? In other words, can you get bearings made by the same factory that makes em for eg, the space shuttle, and pay the price, and know that they are the best that money can buy. Or do all the rotor head manufacturers realy just use run of the mill, ordinary over the counter SKF average type bearings ???

Just get the number off the bearing and give it to your local bearing distributor, and save a bunch of money. They can even get you the same brand. If the number is the same, you are home free. If they took off the number, just measure the dimensions and pop off the seals and count the balls, it's probably a high pack, which means they stuff two more balls in it.

In reality, you only need to wash it and repack it with blue bearing grease, if it's still tight and not making noise.

[JEFF TIPTON]

Do not mix bearing manufacturers. The Bearing ID and OD dimensions will be the same but the angle of the race may be different. It will show up as a wobble if you set the race in the cone and move it by hand.

[DennisFetters]

Do not mix bearing manufacturers. The Bearing ID and OD dimensions will be the same but the angle of the race may be different. It will show up as a wobble if you set the race in the cone and move it by hand.

Well, I hope you didn't think I was saying to take out the balls. Please let me clarify that you do this only if the bearing number and letters are gone, and to count the balls, so you can tell your bearing house and they will know what to buy. If you have the number off the bearing, then any brand will be the same so long as the numbers and letters are exactly the same. Different race angles are indicated by different numbers and letters. Only use the bearing with the numbers and letters that exactly match the one you have.

[JEFF TIPTON]

Not the ball count. I first noticed this when trying to mix a Bowers brand race with a Timken cup. Of course I mean this in reference to tapered bearings.

[Brent Drake]

I've never seen a rotor head with a tapered bearing. At least on a gyro

[DennisFetters]

Not the ball count. I first noticed this when trying to mix a Bowers brand race with a Timken cup. Of course I mean this in reference to tapered bearings.

Well THERE'S your problem!! ;-)

[mikeconcannon]

what is the usual set up and why. Eg. why use tapered or why ball? Are there different type rotor heads use different types and what bearing manufacturer aew known as being the BEST
Also is there a prefered type of grease to do the job??

[GYRO J]

5206 Zz Benson Or Brock Single Place

[EI-GYRO]

I think it's 5206zz for Bensen, or 3206zz in Europe, IIRC.

[Mike G]

Mike
The bearings on the M16 is given in the manual as 7206BECBP and there are 2 of them. I imagine it would be the same on your gyro but you should check your manual I doubt if Magni has tried to hide the reference.
This is an SKF reference and any good bearing supplier should be able to get you an SKF bearing.

This particular bearing has a basic dynamic load rating of 23800 Newtons (2380 kg or 5236 lbf) and a max speed of 8500 rpm (grease lubricated), which means that a 500 kg gyro at 350 rpm isn't going to bother it much.
At 350 rpm and continually loaded at 500 kg it has an expected life of 6190 hours.
That is theoretical based on correct clean lubrication which is seldom the case, most bearing failures (I'm talking about industrial use of bearings not specifically gyro rotors) are due to lubrication contamination. So Dennis's comment about cleaning, inspecting regreasing and putting the bearings back makes sense although the judgement of the quality of a used bearing is always difficult especially since these are "angular contact" ball bearings which have a lot of play in them when they are not mounted. Therefore I'd be tempted to say that whilst I'd be happy to follow Dennis's recommendation for my car or bike I'd probably go for a new bearing for the gyro simply to be on the safe side.

These bearings are design to be fitted as pairs and there are 3 ways to assemble the pair (see attachment), I don't know which way they are assembled for the Magni I would imagine back to back because this is a stiffer arrangement but it is very important to put them back correctly.
For grease use a Lithium based grease not a moly or graphite grease because they contain particles (SKF supply greases to go with their bearings, it's a lot safer to use their grease than save a few euros and get the wrong one).

If you have a reasonable amount of mechanical experience you shouldn't need to send the head back to Magni but if you're in any doubt there's no point flying around worrying about if you did it correctly, so send it back and enjoy the peace of mind that it gives you.

Your question about why ball bearings or taper roller bearings (like on most cars) is a good one and I'm not too sure of the answer. I think they tend to use ball bearings because you can mount these angular contact bearings right next to each other so they take up less space. If any one knows why we use ball bearings rather than taper rollers I's like to know as well.
Mike G

[DennisFetters]

That is theoretical based on correct clean lubrication which is seldom the case, most bearing failures (I'm talking about industrial use of bearings not specifically gyro rotors) are due to lubrication contamination. So Dennis's comment about cleaning, inspecting regreasing and putting the bearings back makes sense although the judgement of the quality of a used bearing is always difficult especially since these are "angular contact" ball bearings which have a lot of play in them when they are not mounted. Therefore I'd be tempted to say that whilst I'd be happy to follow Dennis's recommendation for my car or bike I'd probably go for a new bearing for the gyro simply to be on the safe side.

Well, I have to agree with Mike, so again I better further qualify what I said. "I" inspect and re-grease my bearings, because I know what to look for. On the other hand, if you don't know what to look for, better go buy a new one. It's not like they cost a lot.

[mikeconcannon]

Thanks for your informed reply Mike. Seing as the bearing in the rotor head is such an important component, Im surprised that it is the least discussed component of our flying machines. We place our trust in the manufacturer to use the best (and, Im sure, rightly so) but theres no harm in knowing a bit about them. For example, if I leave the rotor brake on again, Im going to re-grease the bearing, then Im going to need to at least know what type of grease to use. I got aircraft wheels once upon a time and the bearings looked as if they came out of a kids "lucky bag" they had to be ditched and better ones used. So I have seen one end of the spectrum of bearing quality, whats at the other end? Is SKF the top manufacturer? do SKF have different grades of quality for the same dimension/fitting bearings.
P.s. are you going to Bois de la Piere? Im not sure if I am till the end of the week

[Mike G]

Mike
The 7206 BE bearing is easily good enough for the service it has in the Magni and SKF is probably the best known supplier.
We use this range of bearings (although larger in size) in all our industrial pumps the only difference being that we would use the 7206 BEGAM model which you buy in matched pairs and has a slight preload (the GA means light pre load, the CB on Magni is a normal axial clearance) and a solid brass cage (the M is a machined brass cage and the P on the Magni is a plastic cage) instead of a plastic one.
As a perfectionist I'd prefer the pre load and brass cage but I wouldn't recommend you change anything, go with the bearing in the manual and insist on exactly the same reference.

If you regrease the bearing don't overdo it, too much grease can cause problems as much as too little. The recommendation is to completely remove old grease and that the free space in the bearing be completely filled and the free space in the housing only half filled. This is to allow the grease to expand and not get pushed out as it heats up.
Looking at the data for this bearing the expected interval between re greasing at 350 rpm and 70°C is 1.5 x 10^4 hours that's 15000 hours and it would be 3750 hours at 100°C which I doubt if your bearing would see even if you left the brake on all the time.

The only other area of concern is that there are a lot of counterfeit bearings out there and we (at work, nothing to do with gyros) recently had a number of bearing failures with brand new bearings from a reputable supplier because he was buying back original unused bearings from the stock of factories that had closed and bearings deteriorate just sitting on the shelf due to things like micro fretting and corrosion. I shouldn't really tell you all this because there's absolutely nothing we can do about it the counterfeits usually look just like the real thing and the ex factory stock items are the real thing. What probably saves us is that in the Magni (and probably most gyros) the bearing is so overrated that it can handle a of of misuse.

Dennis What do you look for? I handle these sorts of bearing a lot and because you can't easily seperate the balls and cage, detailed inspection for mico pitting and corrosion is difficult, if not impossible, to see. We monitor our bearings by analysing the noise/vibration signals and that way you can pick up early changes but that requires some pretty special equipment.

Mike G

[DennisFetters]

Mike
The 7206 BE bearing is easily good enough for the service it has in the Magni and SKF is probably the best known supplier.
We use this range of bearings (although larger in size) in all our industrial pumps the only difference being that we would use the 7206 BEGAM model which you buy in matched pairs and has a slight preload (the GA means light pre load, the CB on Magni is a normal axial clearance) and a solid brass cage (the M is a machined brass cage and the P on the Magni is a plastic cage) instead of a plastic one.
As a perfectionist I'd prefer the pre load and brass cage but I wouldn't recommend you change anything, go with the bearing in the manual and insist on exactly the same reference.

If you regrease the bearing don't overdo it, too much grease can cause problems as much as too little. The recommendation is to completely remove old grease and that the free space in the bearing be completely filled and the free space in the housing only half filled. This is to allow the grease to expand and not get pushed out as it heats up.
Looking at the data for this bearing the expected interval between re greasing at 350 rpm and 70°C is 1.5 x 10^4 hours that's 15000 hours and it would be 3750 hours at 100°C which I doubt if your bearing would see even if you left the brake on all the time.

The only other area of concern is that there are a lot of counterfeit bearings out there and we (at work, nothing to do with gyros) recently had a number of bearing failures with brand new bearings from a reputable supplier because he was buying back original unused bearings from the stock of factories that had closed and bearings deteriorate just sitting on the shelf due to things like micro fretting and corrosion. I shouldn't really tell you all this because there's absolutely nothing we can do about it the counterfeits usually look just like the real thing and the ex factory stock items are the real thing. What probably saves us is that in the Magni (and probably most gyros) the bearing is so overrated that it can handle a of of misuse.

Dennis What do you look for? I handle these sorts of bearing a lot and because you can't easily seperate the balls and cage, detailed inspection for mico pitting and corrosion is difficult, if not impossible, to see. We monitor our bearings by analysing the noise/vibration signals and that way you can pick up early changes but that requires some pretty special equipment.
Mike G

Mike, you said about everything. I wash out the bearing and use a micro tip magnifying bore scope to inspect the inner and outer races for pitting. Just for the record, I never find any problems except for some old bearings that some Bensen drivers use, because they were shielded instead of sealed bearings, and some water caused only a little corrosion, and that was enough to pit the bearing after continued use.

Another test for looseness is to stick the bearing in a round aluminum housing with the side split, and chuck it up in the lathe with a 1 foot shaft press fitted in the ID of the bearing, and measure the play in the end. Only problem is, I forgot what the tolerance was. We did this with the Air Command bearings to make sure they were suitable for use.

As you say, they are so over rated for how we use them, it's never a worry.

[Mike G]

Dennis

Did you use the double row angular bearings (3206 or 5206) on the AC or two single row angular contat bearings (7206) as a matched pair as Magni do?

Mike G

[DennisFetters]

Dennis

Did you use the double row angular bearings (3206 or 5206) on the AC or two single row angular contat bearings (7206) as a matched pair as Magni do?
Mike G

We used the MRC 5206-MZZ. I did use the matched 1206 in my Mini-500 rotor cones, 3 per cone.

I don't know why Magni uses two 7206 bearings, unless he feels with a heavy machine like his it gives him the option of using two in tantem with of on top as the supporting bearing if he ever needed to.

[Mike G]

Dennis
In my book the ZZ (or 2Z) is a shielded bearing not a sealed one. In your post #16 above you implied you prefered sealed bearings. Have I misunderstood something?
Were your bearings with brass cages, the M usually means a machined brass cage?
Since the 5206MZZ is a double row bearing (with shields) I really don't see how you managed to see anything with your boroscope but I now undertsand how you did you clearance check because the bearing is complete. With the 7206 arrangement it's more awkward because you have to assemble the two bearings with a bearing nut to get an idea of the clearance.

The 5206 has a better basic rating (28100 N) than a single 7206BE (23800N), but a pair of 7206BEs (called a 7206BECB) has a rating of 39000N. For all that the 5206 bearing would seem to be a better choice for homebuilt gyros because you can't put it in wrong, if you put a pair of 7206s inthe wrong way around I'm not sure what axial load it could take.

Mike G

[DennisFetters]

Dennis
In my book the ZZ (or 2Z) is a shielded bearing not a sealed one. In your post #16 above you implied you prefered sealed bearings. Have I misunderstood something?
Were your bearings with brass cages, the M usually means a machined brass cage?
Since the 5206MZZ is a double row bearing (with shields) I really don't see how you managed to see anything with your boroscope but I now undertsand how you did you clearance check because the bearing is complete. With the 7206 arrangement it's more awkward because you have to assemble the two bearings with a bearing nut to get an idea of the clearance.

The 5206 has a better basic rating (28100 N) than a single 7206BE (23800N), but a pair of 7206BEs (called a 7206BECB) has a rating of 39000N. For all that the 5206 bearing would seem to be a better choice for homebuilt gyros because you can't put it in wrong, if you put a pair of 7206s inthe wrong way around I'm not sure what axial load it could take.
Mike G

Hi Mike,

Sorry for the delay, I took a much needed vacation and just returned.

On only the MRC bearings, the "M" stands for Max, meaning it has extra balls, and the "ZZ" stands for 2RS, or two seals. If you want a shielded MRC bearing, you need to order "FF" for 2RS. Please don't ask me why MRC does this, I just don't know and it's always been confusing to me. Maybe they have changed these days. That's why these days I always use SKF.

The bore-scope I use has a micro tip, which is small enough to fit into the corner and see the ball and race.

As for the ratings between the two types of 5206 bearings, even the weakest one you could find would be good enough for the loads a 350 pound AC two-place with full fuel and two 230 pound passengers and pulling tight corners. They are just such an overkill, with for their price is good.

I agree, 7206 can, and would be assembled wrong, and that's why in the Mini-500 we assembled the rotor cones. Also using two 7206, facing each other, you are only using one bearing for the load. If you want to use that design, then you need to use one 7207 and one QJ 206, which has a split inner race, and will take half of the load while keeping the 7206 loaded.

[Mike G]

Dennis
Interesting, although I'm not sure what you gain by your combination of 7206 with a QJ206. I'd prefer to go for a pair of pre loaded 7206 bearings for myself but maintain the KISS principle with a single 5206 for anything that was going to be worked on by someone else.

Mike

[DennisFetters]

Dennis
Interesting, although I'm not sure what you gain by your combination of 7206 with a QJ206. I'd prefer to go for a pair of pre loaded 7206 bearings for myself but maintain the KISS principle with a single 5206 for anything that was going to be worked on by someone else.

Mike

Well, I would not use that combination, but it would be better than using two 7206 bearings, because only one of the bearings would be consuming the loads, while the other was merely keeping the play out.

If you use the combo of 7206 and QJ206, then both bearing are sharing the load.

But as I said, I would use nether. I was just answering a previous question as to why you should not use two 7206 bearings in place of a 5206.

I would, did and will again use the 5206 bearing. As you said, Keep it simple Sam.

[Harry_S.]

For what it's worth as my knowledge of bearings is very pedestrian...

The RAF factory installed a single 3206 bearing in the rotorhead. Their statement at the time...for using the 3206 bearing in place of the 5206 bearing...was the 3206 could be install either way whereas the 5206 had to be installed with the loading hole "down." I understand now, the newer 5206 does not have the loading hole?!

Sometime later when time came to change out the 3206 bearing, I decided to upgrade my rotorhead...and upgrade my comfort factor...by going to a dual bearing and new bearing block, plus taller towers. I now have tandem 3206 rotorhead bearings.

This has no effect on load capacity and only affects the safety/comfort nuance in my head, right?! A single bearing is just fine, a dual bearing is just double fine. ;)


Cheers :)

[Mike G]

Harry

Here's my understanding, Dennis jump in and correct anything you think is wrong.

There are 3 types of bearing

3206 A
5206 A
5206 E

The "A" types have the same rating and do not have filling slots so can be put in any way.

The E type has a slightly higher dynamic rating and 30% better static rating (which isn't much use to us). It has filling slots and must be installed the right way around.

These bearings have very small internal axial clearance so putting two in would probably increase your load capacity but not double it, there will always be one bearing that takes the majority of the load.

Putting two bearings in will create a stiffer assembly and increase the capacity to absorb tilting loads.

So your analysis would be correct and you can continue to fly with the same comfort factor in your head.

Mike

[Mike G]

Dennis
I'm still not sure your installation of a 7206 and a QJ206 will do what you want it to do.
The QJ 206 has a large axial clearance (56 to 106 microns). The clearance designed into the 7206 is 18 to 26 microns for a pair mounted back to back, so a single 7206 would be effectively half of that.

My understanding of such an installation is that unless you assembled it with pre load, the QJ206 wouldn’t contribute to the thrust carrying capacity in flight, the QJ206 would only give you a thrust bearing for the rotor when static and during the beginning of pre rotation.

I may be wrong (it wouldn’t be the first time) so would appreciate a little more detail on how you designed this installation.

Attached is a very, very oversimplified series of sketches (I’ve not included the radial clearance for simplicity) to show my understanding of what happens when you assemble a pair of 7206 bearings and what happens when you assemble a 7206 with a QJ206.

I don't work with the QJ bearings so may be missing something.

Mike G

[DennisFetters]

Dennis
I'm still not sure your installation of a 7206 and a QJ206 will do what you want it to do.
The QJ 206 has a large axial clearance (56 to 106 microns). The clearance designed into the 7206 is 18 to 26 microns for a pair mounted back to back, so a single 7206 would be effectively half of that.

My understanding of such an installation is that unless you assembled it with pre load, the QJ206 wouldn’t contribute to the thrust carrying capacity in flight, the QJ206 would only give you a thrust bearing for the rotor when static and during the beginning of pre rotation.

I may be wrong (it wouldn’t be the first time) so would appreciate a little more detail on how you designed this installation.

Attached is a very, very oversimplified series of sketches (I’ve not included the radial clearance for simplicity) to show my understanding of what happens when you assemble a pair of 7206 bearings and what happens when you assemble a 7206 with a QJ206.

I don't work with the QJ bearings so may be missing something.

Mike G

Mike, I believe your diagram reveals my point exactly, using two 7206 bearings back to back would have only one bearing taking the load.

I'm sorry I was not more specific on my previous posts, as I said I would not use this on a gyro rotor head, and I didn't know we were going to discuss this in depth. No problem, I enjoy talking with you about it.

As I said, I would use the 7206 and the QJ206, but it is deeper than that. The combination is a BA2B series, which is a 7206 paired with a GJ206 which are ground to mate at the bearing factory, which reduces the play so it could be used in this case. It's called a "Thrust Pack", and allows two rows of bearings to share the load, rather than one bearing taking the full load, as two 7206 bearing would do.

[dcarr4321]

Many helicopters have temperature sensors on the rotor bearing. If it overheats or begins to run hot this gives an indication of pending problems. Would this be of any use on a gyrocopter:flame: ?

[DennisFetters]

Many helicopters have temperature sensors on the rotor bearing. If it overheats or begins to run hot this gives an indication of pending problems. Would this be of any use on a gyrocopter:flame: ?

Sure it would. But, It's unnecessary in my experience. If a bearing is going bad, it starts to get hot, but first it starts to drag. In a helicopter we are driving the rotor system with power, and it's hard to tell if the bearing is going bad from the drag because we just unknowingly apply more power.

In a Gyroplane, we would feel that drags affects very soon, our first indication of trouble.

The other reason I would not install temperature reading devices (except for maybe tell-tale temp tape), is because in all my years of gyro experience, I have personally never heard of a bearing failure that effected the flight in any way.