which control bar end rod bearing ?

jm-urbani

Junior Member
Joined
Dec 21, 2010
Messages
292
Location
French Riviera
Aircraft
home built mono seat
Total Flight Time
200ish
Hi All,
I am currently makin my control bars ( I hope this is the proper name)
I am wondering what kind of end rod bearing has to be mounted ?
last time I did it I had bought my end rods from DTA (unibal) but this time I'd like to find the bearings myself, not to pay less but only to be independant
I can't find unibal bearing anymore on the net !
everytime I type unibal bearing I it leads me to sites displaying askubal bearings ... is it the new name of unibal ?
I can't finf the unibal references on the beearing I have on my flying gyro
my problem is that I don't know what to choose among hundreds of bearings
which resistance ?
which metal ?
etcetc
ok it would be easy to get the same end rod thent magni or autogiro or whatever but is does not make it possible to understand the criterias
as for the bushings to be installed at the end of control tubes, wich metal do you use ? (last time I used 2017 aluminum) how to you fix them ? ( glue ? rivets ? screws ? glue+rivets , glue+screews )
thx
 
Last edited:

Kolibri

FW and Gyros
Joined
Oct 17, 2014
Messages
1,636
Location
Wyoming
Aircraft
Cessna 152, 172, 172RG, 177, 206 -- Piper 180 -- RV-7A -- Calidus -- RAF2000 -- Sport Copter II and
Total Flight Time
1000+
While they're probably nothing really wrong with Unibal, you can't go wrong with Aurora in general, such as their CAM-6 (3/8ths shank, high-angle misalignment).
The cost difference between a merely adequate rod end and an excellent one is only a few dollars (e.g., $8 vs. $4).

Many mfg. bolt in the threaded aluminum sleeves within the aluminum control push tubes.
Sport Copter uses steel tubes and sleeves, and welds in the sleeves.

If there were areas where I'd "overbuild" it would be the rotor and control systems.

Good luck in your project!
Kolibri
 

Doug Riley

Platinum Member
Joined
Jan 11, 2004
Messages
6,312
The main difference between cheaper rod end bearings and more expensive ones is the presence/absence of a non-ferrous lining in which the ball turns. Aircraft-grade rod ends have the linings; commercial-grade ones don't. Sometimes they are distinguished by referring to 2-piece vs. 3-piece bearings.

I like the aircraft-grade units, despite the cost. I have used unlined commercial rod ends, but bought them in bulk and had them individually inspected by magnetic-particle testing. The welds employed in manufacturing these units have proven defective on occasion, resulting in breakage.

Loss of control rods has proven fatal more than once. It's important to use good bearings and to make sure that they do not exceed their maximum mislignment angle throughout the control range (if they exceed this limit, the stems will break off).

Design of the pushrod tubes themselves is a separate topic, in which there can be some non-obvious factors. Steel may or may not be "better" than aluminum in this application.
 

jm-urbani

Junior Member
Joined
Dec 21, 2010
Messages
292
Location
French Riviera
Aircraft
home built mono seat
Total Flight Time
200ish
Hi all,

first of all thanx for your replies, it always helps me a lot
in fact my concern is to find out why taking a rod end that resist a 6000 DaN loading rather then on that resist a 1000 DaN loading ?
not that I don't want to over pay or that I don't want to over construct but just that I would like ti understant that's all in fact

I was there ate the averso rotor factory in montélimar when the DÜV came to make tests to on the jyro DTA and I remember having been told that their requirements as for the control resistance was a spec of 40 kg loading .

40 kg is nothing for a rod end , even for a cheap one

Doug you said that loss of control rods had proven fatal, but do we kown what kind of force has brokent the end rods ?
does the rupture arrised after a rotor flapping in fligth ( where the forces are huge but in a situation where the aircraft is already lost when the rods brake)
do we know if it is the rod itself that has broken or if the rod shaft has been extracted from the the metal where it was screwed ?
 
Last edited:

Jean Claude

Junior Member
Joined
Jan 2, 2009
Messages
1,859
Location
Centre FRANCE
Aircraft
I piloted gliders C800, Bijave, C 310, airplanes Piper J3 , PA 28, Jodel D117, DR 220, Cessna 150, C
Total Flight Time
About 500 h (FW + ultra light)
Among all aircraft manufacturers, gyroplanes builders are the ones who care least about useless weight. Because of the low L / D ratio, this should be the opposite.
 
Last edited:

Doug Riley

Platinum Member
Joined
Jan 11, 2004
Messages
6,312
JM -- I know of accidents of three types that involved rod-end failure.

First was one in which the rod-end bearing was not locked in place by a jam nut, tightened against the threaded insert in the push rod tube. The bearing was able to move up and down slightly in the threaded insert, eventually causing the threads in the insert to strip. The rod end bearing then was no longer attached to the pushrod tube.

Second, the threaded stem broke off the bearing housing (ring). This can be caused by bending loads on the stem. This, in turn, can result from the use of a control fork (upper or lower) that restricts the bearing's tilting action as the controls are moved to their limits.

Third, I have heard of (but never encountered myself) bad welds in the round housing in the 2-piece bearings. The round housing, or ring, breaks in half (for instance, it may break at the 3 o'clock and 9 o'clock positions) releasing the ball.

I have not heard pf a pushrod tube itself breaking. These rods are critical in compression (column loading). Resistance to column loading is more a function of the DIAMETER of the tube than the material it is made of. Example, the Gyrobee plans call for pushrod tubes of 9/16" diameter x .065 wall 4130 steel. Despite the use of steel, these rods are weaker in compression than, say, an Air Command pushrod of 7/8" diameter and .058 wall 6061-T6. Neither rod will withstand more than about 200 lb. of compression without buckling -- the 9/16" steel a little less than 200.
 

Jean Claude

Junior Member
Joined
Jan 2, 2009
Messages
1,859
Location
Centre FRANCE
Aircraft
I piloted gliders C800, Bijave, C 310, airplanes Piper J3 , PA 28, Jodel D117, DR 220, Cessna 150, C
Total Flight Time
About 500 h (FW + ultra light)
Yes, Doug. But as you report, the failures mentioned are never due to insufficient strength of the rod ends. Each time, it is an associated part that fails: breakage of the axis without clevis, unscrewing of the thread, buckling of the tube, exceeding the angular limits.
 

jm-urbani

Junior Member
Joined
Dec 21, 2010
Messages
292
Location
French Riviera
Aircraft
home built mono seat
Total Flight Time
200ish
@ Doug ,
yep, as usual you don't "talk" for nothing, I like guy's like this
thx
 

Doug Riley

Platinum Member
Joined
Jan 11, 2004
Messages
6,312
JC and JM -- The only failure of a bearing that I know of that is NOT attributable to misuse is the one in which the bearing housing (the "banjo" or "ring") broke in half through a bad weld. That is a manufacturing defect, not really a case of the load exceeding the bearing's RATED strength.

An installation that imposes a bending load on the stem is probably the most common problem in this area. Again, not really an overload but instead poor installation.

Despite all this, i believe in providing a VERY generous safety factor in control assemblies. The control system experiences a constant 2-rev vibration in flight, plus unpredictable shock loads when taxiing on the ground (especially on unpaved surfaces such as those where I live). For this reason, i use only 3/8" rod ends on my own gyros, despite certain gyro plans that call for 1/4" or 5/16" bearings. Others disagree.
 

j bird

Gold Supporter
Joined
Nov 11, 2005
Messages
1,685
Location
Cave Junction,OR.
Aircraft
Dominator/Airworthiness Certificate 9/06/12
Total Flight Time
26.5 duel,RAF,Sparrow-Hawk,Cavalon,Calidus.
Can't find male shank 3/8"-24 thread x 1/4" bore, rod end, looked every where! any one know where to find?
 

jm-urbani

Junior Member
Joined
Dec 21, 2010
Messages
292
Location
French Riviera
Aircraft
home built mono seat
Total Flight Time
200ish
as for taxiing it also seems important to me that the he mechanical stops ( that prevents the rotor head from tiliting too mutch) are built in the rotor head itself and not in the controls system
certain stock gyroplanes have stop built in the controls
 

Doug Riley

Platinum Member
Joined
Jan 11, 2004
Messages
6,312
J-Bird: Commercial rod-end bearings typically have the same diameter hole and shank. Aircraft grade bearings OTOH are available with 3/8" shank and 1/4" hole. Commercial bearing distributors don't necessarily sell them. They're available through aircraft suppliers such as Wicks, Aircraft Spruce, etc. Hold onto your wallet.

If you're stuck with a 3/8" hole bearing of good quality, you can insert a commercially available 3/8" x 1/4" oilite bushing. Be careful not to distort the bushing; slide it onto a bolt, support the bearing ball with a block of metal with a hole in the middle, and carefully tap the bolt head, as gently as possible. Better to buy the real thing, however.

JM: The "classic" advice regarding control stops has been this: Have stops at both the rotor head and the stick, but adjust them so that the stick stops engage first, just before the head stops. This prevents high stick loads from being transmitted into the pushrods and bearings. The pushrods have plenty of tensile strength, but relatively little compressive (column) strength.
 

j bird

Gold Supporter
Joined
Nov 11, 2005
Messages
1,685
Location
Cave Junction,OR.
Aircraft
Dominator/Airworthiness Certificate 9/06/12
Total Flight Time
26.5 duel,RAF,Sparrow-Hawk,Cavalon,Calidus.
Thanks Doug, I just want to add, your amazing knowledge of the gyro-world is well appreciated!!!!!!!!!!!!!
 

Doug Riley

Platinum Member
Joined
Jan 11, 2004
Messages
6,312
J-Bird: No problem. I happened to have looked a bit into rod-end bearing issues when I started selling them through my little ol' gyro-supply biz, back in the day.
 

Kolibri

FW and Gyros
Joined
Oct 17, 2014
Messages
1,636
Location
Wyoming
Aircraft
Cessna 152, 172, 172RG, 177, 206 -- Piper 180 -- RV-7A -- Calidus -- RAF2000 -- Sport Copter II and
Total Flight Time
1000+
Maybe others unknown to me use 1/4" eye 3/8" shank rod bearings, but I've seen them OEM only in Sport Copter.
And, yes, they pay a premium for them.
 

j bird

Gold Supporter
Joined
Nov 11, 2005
Messages
1,685
Location
Cave Junction,OR.
Aircraft
Dominator/Airworthiness Certificate 9/06/12
Total Flight Time
26.5 duel,RAF,Sparrow-Hawk,Cavalon,Calidus.
How about my stock rod ends (heim) 1/4"x3/8"on my Dominator's push tubes.
 

jm-urbani

Junior Member
Joined
Dec 21, 2010
Messages
292
Location
French Riviera
Aircraft
home built mono seat
Total Flight Time
200ish
JM: The "classic" advice regarding control stops has been this: Have stops at both the rotor head and the stick, but adjust them so that the stick stops engage first, just before the head stops. This prevents high stick loads from being transmitted into the pushrods and bearings. The pushrods have plenty of tensile strength, but relatively little compressive (column) strength.

Doug I am personnaly reluctant to add stops on the stick ... I had one time my controls limited in their travel, I had detected a hard point when I did the control square test before taking off... I assumed the stick travel was limited by the fact that the rotor was at 3H/9H and tilted ... and took off... when I tried to push the stick ahead after lifting the wheels, the gyro when letf .... the prerotator hard shaft was pushing the rotor head left ... I had to take the stick with two hands to get enough force to bring back the gyro on an horizontal attitude and managed to hit the kill switch ... I landed the bird wondering how the hell I had not broken it.. (I am still wondering)
to make a long story short someone had involuntarily moved up a little bit my engine mount (which can be moved up or down in my design) but had neglected the fact that the hard prerotator shaft would have it's travel shorten doing this ...
of course this story has nothing to see with stick stops but.... it will take quite a long time to be before I install any stops of any kind on my stick ( it is a psychological reason)
 
Last edited:
Top