Accident involving rotor bearing

[Doug Riley]

Greg: We used MRC's in the Black Beauty head. The writing on the SIDE of the bearing housing was upside down when the bearing was correctly installed. It is best to get the instruction sheet that comes with the bearing, however, and follow it closely.

[Harry_S.]

Jim: Go to a good Bearing shop/store and they can cross reference practically all bearing numbers and mfg's. DON'T tell them it's for an aircraft. If they ask, tell them it's for whatever you can think of...self designed lawn mower; exhaust for a paint booth...whatever.

[Harry_S.]

Some years back, a short story was printed in the PRA Magazine about two buddies flying together. This was back in the days when most everybody was flying single seat Bensens. Some of you old timers may recall this story and make any corrections to it; please.

As I recall, one of these fellows performed some maintenance on his gyro, including some work on the rotor head. One thing he did was to replace the main bearing (5206) in the rotor head. After all the work was done, they went flying together one day. After they formed up at about 200 ft. and were flying along, this fellow looked over at his buddy, who was slightly below his level and as he was looking, his buddies complete rotor seperated from the gyro and the gyro dropped to the ground. Examination later revealed the 5206 bearing came apart and the main bolt pulled thru the bearing. It was determined the 5206 bearing was installed upside down.

The loading groove (half moon) should be installed FACE DOWN .

If you old timers find any of the above to be in error...please correct.

[Greg Mitchell]

Doug,
Thanks for getting back to me. I haqve some detail on this Bearing MRC 5206 CZZ.
The C Suffix on the 5206CZZ stands for:

“Double-row angular contact, non-filling notch ball bearing, with outwardly convergent contact angles, rigid design.”

The ZZ Suffix stands for two shields.

It doesn’t matter which way you turn this bearing.

The dynamic load rating of this bearing is 6,660 lbs.

Regards,

Mitch.

[John_Read]

Thanks again, folks. I have installed the 3206 bearing which can be either way up....

Better safe than sorry!!!

John

[Jim]

I have a few catalogues from manufacturers such as BCA and SKF. These are usually free from industrial supply stores who carry bearings. They have very good information.

Recently I also went on line to http://www.ina.de. They have an excellent site. Type in the number of the bearing in question and a description and sketch of the bearing comes up. Answered all my dumb questions in an earlier posting. I found that http://www.skf.com is also good.

Jim

[gyroplanes]

Originally Posted by Greg Mitchell

Doug,
Thanks for getting back to me. I haqve some detail on this Bearing MRC 5206 CZZ.
The C Suffix on the 5206CZZ stands for:

“Double-row angular contact, non-filling notch ball bearing, with outwardly convergent contact angles, rigid design.”

The ZZ Suffix stands for two shields.

It doesn’t matter which way you turn this bearing.

The dynamic load rating of this bearing is 6,660 lbs.

Regards,

Mitch.

I have installed many MRC5206MZZ bearings as they were standard equipment on Air Commands for many years. We also used them on our SnoBird "Black Beauty" rotorheads.

At some point, several years ago MRC started to enclose a little piece of paper in every MRC5206MZZ bearing box which told you to install it a with the thrust loads on (or away from?) the bearing side with the part number etched in.

I'm certain that of the hundreds of Air Commands sold that half of the MRC5206MZZ bearings were installed without regard to orientation as most were sold before this warning was enclosed. I haven't heard of any failures.
Just wondering.

[Doug Riley]

Tom, I've heard a story or two from people who changed the bearings in their rotor heads and claimed that "it was trash after an hour of flying." No way to prove it, but one explanation might be that they put a loading-slot bearing in upside down.

When AEROTEC had its turn building and selling the "Black Beauty" heads, I used to take that MRC instructional slip you mentioned and staple it around the teeter bolt to (I hoped) catch people's attention.

[gyropilot]

From the MRC catalog:

MRC double-row ball bearings are manufactured in
two main types: C-type (conrad construction) and
M-type (maximum capacity with filling notches). Each
row has a 30° contact angle.

C-type

Conrad construction, or C-type, double-row ball
bearings have contact angles that converge outside
the bearing, thereby increasing resistance to
misalignment. This type does not have filling notches.
These bearings are recommended for applications
where single-row bearings are inadequate, but radial
loads are not so great as to suggest a filling-notch
bearing. They will take heavy radial loads, and axial
loads equally in either direction. The C-type design
fully meets the requirements of American Petroleum
Institute Specification 610.

Both the inner and the outer rings have closure
grooves. These bearings are available with seals,
shields, and snap-rings.

M-type

This type has filling notches on one side to permit
assembling the maximum number of balls into the
bearing. Contact angles converge outside the
bearing. All inner and outer rings have closure
grooves. These bearings may be equipped with seals,
shields, or snap-rings; or a combination of these. The
M-type bearing has very heavy radial capacity. It also
has thrust capacity in one direction, with the ability to
accommodate light thrust load in the reversing
direction.

Part numbers on M-type double-row bearings are
normally located on either the side face or the O.D.
The side face marking is always on the side opposite
the filling notch and the O.D. marking is offset from
the center away from the filling notch. Therefore,
double sealed or shielded bearings with the filling
notch covered from view can be oriented correctly.

Ball Cages and Types

The cage supplied with C-type and M-type bearings is
one-piece, heat-treated steel for maximum retention. It
is snapped into place after the full quota of balls has
been introduced between the inner and outer ring.

Load Ratings (lbf):

Dynmaic Radial = 6,430

Dynmaic Axial (thrust load)= 5,208

Static Radial = 4,590

Static Axial (thrust load) = 3,029

Speed rating when grease filled and double seals = 7,000 rpm

[RHerron]

Harry,

I guess I am an old-timer. As I remember it, the fellow left the large-area washer off the main (vertical) spindle bolt and only the press-fit center spool held the head together long enough to get him airborne.

Originally Posted by Harry_S.

Some years back, a short story was printed in the PRA Magazine about two buddies flying together. This was back in the days when most everybody was flying single seat Bensens. Some of you old timers may recall this story and make any corrections to it; please.

As I recall, one of these fellows performed some maintenance on his gyro, including some work on the rotor head. One thing he did was to replace the main bearing (5206) in the rotor head. After all the work was done, they went flying together one day. After they formed up at about 200 ft. and were flying along, this fellow looked over at his buddy, who was slightly below his level and as he was looking, his buddies complete rotor seperated from the gyro and the gyro dropped to the ground. Examination later revealed the 5206 bearing came apart and the main bolt pulled thru the bearing. It was determined the 5206 bearing was installed upside down.

The loading groove (half moon) should be installed FACE DOWN .

If you old timers find any of the above to be in error...please correct.

[Aussie_Paul]

I would have thought that the extra balls that the loading slot allows would spread the load over a larger suface area and that tiny loading slot would not cause any problems at all. Maybe in an industrial application, where the bearing is being used to its maximum capacity, a problem may develop.

I flew many hours, before I knew about loading slots, with the loading slot the wrong way and after 1000 hours I bought a new bearing but I never installed it as the was more manufacturaing tolerance movement in the new bearing than the was in the old one installed the wrong way!!!!

Aussie Paul.

[C. Beaty]

I have no recollection of someone falling from 200 feet as the result of an upside-down bearing. In fact, the older MRC catalogues I have don't even list a loading slot bearing. That's not to say it didn't happen.

I did hear a report that Bob Arnt (Commander Bob) reassembled his rotorhead with the bearing block upside down which places the thrust retaining lip on top and the rotor went its own way during a high speed taxi as the blades approached flying speed. I think I recall hearing he did the same thing all over again.

I believe the entertainment took place at Cross City, Florida.

Too bad no one got it on film. It might have been a winner on that Stupid Tricks TV show.

[Douglas Riley]

Aussie Paul, a footnote for others reading your post: new bearings often feel sloppy when they come out of the box. That's because there is a calculated amount of play in the assembly, to make room for the grease. Some manufacturers ship them dry or nearly so. Once they're packed with grease, they tighten up and even become harder to turn. But, of course, they are supposed to be packed.

[Victor Duarte]

Doug, can i ask you a question, have you heard about the use of GRAPHALLOY bearings ?
thank you

[Harry_S.]

That would have been a classic Chuck; if caught on film. I take it...he wasn't hurt...physically?