Brantel said:
How many of these have failed in the failure mode being discussed here? The RV12 has been around since 2006 and RV’s have used the same bearing on flaps for a lot longer than that. How many have failed to the point of falling off of the ball?
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Perhaps none have (yet) failed to the point of falling off of the ball, in RV's. However, Van's still specify the fender safety washers to be used on rod end bearings that are not captured on both sides by the structure. Some RV builders have also been concerned enough about the flap bearing to replace it with a different bearing plus a safety washer (per some VAF postings).

Presumably there have been instances of rod end failures in other applications; for interest see this Pegasus racing bulletin:

Why use Safety Retaining Washers? - Pegasus Auto Racing Supplies

Safety Retaining Washers from Pegasus Auto Racing Supplies can prevent a separated rod end or spherical bearing from turning into a catastrophe. Read this article to see an example!
www.pegasusautoracing.com www.pegasusautoracing.com
 
A lot of solutions looking for a problem here. Looks to me like the root cause was incorrect assembly. Read the plans. They are quite clear. Double check the drawings, triple check when controls are involved. Have someone else check your work. Whatever it takes to make sure it’s done right
. I’m not an engineer, but looking at that ball joint operating in that orientation would have me scratching my head. I’m amazed that it was not picked up by anyone during the build. The ball joint was never intended to transfer loads in the direction shown in the photo. I remember that part of my RV12 build. Access is pretty tight in that area, but it can be done without rejigging the whole setup.
A sad outcome that reinforces the mantra…”RTFM”
DaveH
120485
 
PaulvS said:
Perhaps none have (yet) failed to the point of falling off of the ball, in RV's. However, Van's still specify the fender safety washers to be used on rod end bearings that are not captured on both sides by the structure. Some RV builders have also been concerned enough about the flap bearing to replace it with a different bearing plus a safety washer (per some VAF postings).

Presumably there have been instances of rod end failures in other applications; for interest see this Pegasus racing bulletin:

Why use Safety Retaining Washers? - Pegasus Auto Racing Supplies

Safety Retaining Washers from Pegasus Auto Racing Supplies can prevent a separated rod end or spherical bearing from turning into a catastrophe. Read this article to see an example!
www.pegasusautoracing.com www.pegasusautoracing.com
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Maybe they are a solution for a problem that does not exist in the applications Vans uses them in?

After all, this accident had nothing to do with the bearing coming apart.
 
I hope that this particular ball joint manufacturer bats 1000.
I hope nobody else installs the ball joint backwards.

The control system on the 12 is the only RV in the fleet that depends on the above.
 
Jcurry said:
Has anyone replaced a ball joint due to extreme play between the ball and housing?

Thank you
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30 plus years (and counting) working on many different RV aircraft, I think I have replaced 2.
One was an outboard elevator hinge that I think went many years without being lubricated, and one on an engine control cable that I think failed as a result of vibration (very poor prop balance.
Neither of these had actually failed, they just had excessive play.
I have never seen a stud style (like the subject of this discussion) fail or be worn to a point I felt it needed to be replaced.
Just one persons experience though. It would be interesting to hear what experience history someone like Vic has.
 
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I’ve seen several posts saying that ‘they were going to train themselves to reach over and grab the other stick…’. I think this is the wrong approach. After all, maybe the problem is further aft, and both sticks are affected. Pilots should train to, as much as possible, keep the plane in trim at all times; and, if a pitch issue develops, to reflexively use pitch trim to return to level flight. IIRC the 182 POH outlined the procedure for landing with complete loss of yoke functions (pitch and roll).
As to the builder error here: I think we sometimes forget that the ‘A’ in ‘EAB’ stands for ‘amateur’. Mistakes can and do happen, hence the passenger warning placard. Anyone who thinks their hobby is risk-free is only fooling themselves. I don’t mean to imply we shouldn’t try, as best we can, to build safely. But in the real world these sort of things do happen (both Piper, and a start up biz-jet company, had fatal accidents after aileron controls were inadvertently reversed.)
 
DeltaRomeo's post #16 shows one of the two pictures from the FAA accident report. The other picture in the report was taken from a different angle. (I'd post it but I'm technologically challenged) That picture shows an obvious dent in the fuel line under the rod end that did not disengage. Can't see under the pilot side of the flaperon mixer bell crank, but my recollection is that the fuel return line runs there. If there was interference between the rod end and the fuel line could that have caused/allowed the incorrectly installed male studded rod end, CM4MS, to unscrew? Any thoughts?
 
BobTurner said:
After all, maybe the problem is further aft, and both sticks are affected.
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There could definitely be a different problem somewhere else altogether but in this instance the ball joints are located where the ball joints are located and in this scenario using the other stick could be life saving.
 
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azonslow said:
If there was interference between the rod end and the fuel line could that have caused/allowed the incorrectly installed male studded rod end, CM4MS, to unscrew?
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You can see the fuel line in post #38. No interference possible if installed correctly but with that rod dangling down and the pilot desperately moving the stick trying to get a reaction the rod would easily dent the fuel line. I suppose the rod could eventually puncture the fuel line if flying in this scenario and slinging the stick around furiously which could bring about a whole different can of worms!
 
Amadeus said:
You can see the fuel line in post #38. No interference possible if installed correctly but with that rod dangling down and the pilot desperately moving the stick trying to get a reaction the rod would easily dent the fuel line. I suppose the rod could eventually puncture the fuel line if flying in this scenario and slinging the stick around furiously which could bring about a whole different can of worms!
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The dented fuel line is not on the pilots side where it could be due to to loose control rod impacting it; it is on the copilots side. It might be crash damage, but could also be due do interference from incorrectly installed eyebolt.
 
Jcurry said:
Ii would say it's a major benefit. I am very concerned about rod-end bearing failures where the rod-end housing pops off leaving the bolted on bearing behind. I've seen that exact scenario many times on engine controls. That's why we started using large surface area washers to protect in case of complete bearing failure. To me, the upside down CM-4MS is definitely the weak link in the system since you cannot install a large area washer on it. I believe the rest of the aileron system is protected by large area washers and or the rod-ends are captured in fittings.
I think I will change my rod-ends to CM-4M, install large washer and use a castellated nut with a cotter pin .
Any reason why I shouldn't do this?
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You might not have enough room underneath to do this without interference.
Personally, I think the worry about these rod ends failing is a bit overwrought. The CM-4MS has a design radial load of 2200 lbs. The design load that will size the control system is the pilot effort load (Jam condition), which is 100 lbs at the top of the stick, which becomes about 300 lbs in the rod and rod ends below. A factor of safety on limit load of over 7.
 
RV12M4 said:
You might not have enough room underneath to do this without interference.
Personally, I think the worry about these rod ends failing is a bit overwrought. The CM-4MS has a design radial load of 2200 lbs. The design load that will size the control system is the pilot effort load (Jam condition), which is 100 lbs at the top of the stick, which becomes about 300 lbs in the rod and rod ends below. A factor of safety on limit load of over 7.
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Thank you for the stats.
 
I’m sure it’s more than robust enough. I just don’t trust ball joints.
Some of this could be a holdover from days gone by. My Bucker was designed in the 1930’s, very rare to have ball joints in control systems back then. Like all the other RV’s, each joint is captured. I’m sure the ball joint world has progressed since then and failures due to defects are probably super, super rare.
However, if that joint comes apart, you’re going to have a bad day. In any other RV, it’s probably a non event.
I don’t know of any ball joint failures in any RV’s. I just don’t like the design, but that’s just me, and I’m nobody, no dog in that fight.
All airplanes have single point failures in many systems. I just don’t understand why Vans deviated from other designs and introduced one more. I guess we trust that they knew what they are doing.
Nuff said.
 
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