Oh Clevis, What Are You Doing?

[Brian Massey]

The other day my Chipmonk became very unmanagable. It didn't want to groove, and was very hard to control in manuvers. During my consecutive outside loops it was all I could do to miss the ground. Once on the ground a friend held the elevator while I worked the controls; man, they were sticky, jerky and sloppy (I don't know where Sneezy was). I figured that a clevis has come off of a horn, but managed to stay "looped" over it, as I did have some control; what I had to guess was at which end, the elevator, or flaps. I decided to cut into the elevator controls, when I did, it was scary. I discovered that the clevis  was slipping over the threaded push rod  . I could work the controls, and the push rod would slip through the clevis by as many as 4 or 5 threads. I centered the controls and soldered the bugger; there, that's fixed  . I proudly worked the controls again, and to my dismay the controls were not fixed! I cut into the fuse and found the push rod coming off the bellcrank to the flap horn doing the same thing. 

On my last plane I switched to ball joints, and plan on using them exclusively from now on, but never really considered that a clevis would self distruct in this manner. All I can say, is if you use a clevis, solder the thing up when you get your adjustments all set.

The pictures are of the clevis at the flap horn; the pictures show the amount of slippage; and the elevator clevis was worse.

Brian

[john e. holliday]

I remember when those came on the market.  I was told by one of the older fellows in the RC club that once the controls are set on the plane, either use epoxy or ca to set it to the threads.  Best was to solder it.  Other wise you wrap the part with the threads to keep it from opening using fine wire.  Never had a failure on RC or CL with that type.   But,  Now the ball links are so smooth and easy to set up that is all I use.   I forgot I have a UHP clevis that is in the King Sweep and was used on my Cotton Candy.   Cotton Candy was destroyed by the pilot and not a control failure unless you consider the link between the brain and my hand.

[Tim Wescott]

That's not so much a problem with a clevis as a mechanical device, but a problem with the way that clevises are manufactured.  That sort of thread wear happens any time one or both of the threaded parts aren't made well.  If you could stamp ball joint fittings out of steel with that cheap wrapped sheet thread, you'd see the same problem.

[Don Curry AMA 267060]

You must jam nut the clevise. The vibration of the engine and air loads on any thread will quickly cause the to fail.
Don

[Grady Widener]

While I would not recommend using this style of clevis on anything more advanced than a crude basher profile fun fly kind of machine, for those that insist, the usage of a 4-40 nylock to push the lash out of the thread will go a long way towards preventing the kind of premature reamed ham fiasco illustrated earlier.
The nut must be initiated normal direction on 4-40 thread before it can be installed bassakwards on push-rod stud.

Regards,
Grady

PS
Additionally it should be said that these devices were never intended (as far as I can tell for any semi-realistic life expectancy at all) to be used with metal horns. Also, for the nylock jammer to have any chance at all, it should be employed with the *dogged interlock* (silvery one on the left with jagged seam) style receiver and this one is a Sullivan.

[Chris McMillin]

The other day my Chipmonk became very unmanagable. It didn't want to groove, and was very hard to control in manuvers. During my consecutive outside loops it was all I could do to miss the ground. Once on the ground a friend held the elevator while I worked the controls; man, they were sticky, jerky and sloppy (I don't know where Sneezy was). I figured that a clevis has come off of a horn, but managed to stay "looped" over it, as I did have some control; what I had to guess was at which end, the elevator, or flaps. I decided to cut into the elevator controls, when I did, it was scary. I discovered that the clevis  was slipping over the threaded push rod  . I could work the controls, and the push rod would slip through the clevis by as many as 4 or 5 threads. I centered the controls and soldered the bugger; there, that's fixed  . I proudly worked the controls again, and to my dismay the controls were not fixed! I cut into the fuse and found the push rod coming off the bellcrank to the flap horn doing the same thing. 

On my last plane I switched to ball joints, and plan on using them exclusively from now on, but never really considered that a clevis would self distruct in this manner. All I can say, is if you use a clevis, solder the thing up when you get your adjustments all set.

The pictures are of the clevis at the flap horn; the pictures show the amount of slippage; and the elevator clevis was worse.

Brian

Oh Brian,
I cannot believe that someone didn't stop you from using that type of clevis on the Chipmunk (animal, not a priest).
The use of a jam nut is at the minimum a requirement. I use them on R/C models with a jam nut and then once the model is trimmed I Loctite them. Also I never use them on an internal control system, only where I can watch and inspect them, for they do need replaced periodically.
In the high stress environment of a C/L Stunt model, they are not recommended at all. I still use 3/32nd or 1/8th wire on Stunters, but many use the CLC or Tom Morris ball ends with good success because they are made of hardened material with quality threads and the ball ends are expensive but for good reason (cheaper ones bind eventually and restrict smoothness and eventually movement, an epidemic in Arizona I hear).

I can only see the repair for this is a total replacement of the pushrod, if you have the same thing on the elevator then I would recommend replacing it too. How many flights did you get out of this set-up?
Chris...

[Brett Buck]

You must jam nut the clevise. The vibration of the engine and air loads on any thread will quickly cause the to fail.
Don

  Actually, unless you are building temporary models, you must not use clevises of any kind regardless. They *will* fail, it doesn't matter what you do or how you install them.

    Brett

[Steve Hines]

I allways use the black spring steel ones, allways thought the silver ones were solder on only, and there is a spring keeper that keeps them from opening. They come in a package with the jam nuts also.

[Brian Massey]

Oh Brian,
I cannot believe that someone didn't stop you from using that type of clevis on the Chipmunk (animal, not a priest) . . . I can only see the repair for this is a total replacement of the pushrod, if you have the same thing on the elevator then I would recommend replacing it too. How many flights did you get out of this set-up?
Chris...

Nope, no one warned me. I've been back in the hobby for just over 2 years, and am learning that I still have a lot to learn. The plane is just over a year old and has has probably 250-300 flights. I've soldered the clevises, so I think the problem has been resolved. I have a new plane just coming off the bench and it is all ball joints, as will be the new Chipmonk under construction. I was really happy with the way the Chipmonk flew, but wanted to try the mods made by Dave Fitzgerald; it will be interesting to see.

Trust me, I won't be using the clevises anymore.

Brian

[Claudio Chacon]

Brian,
I totally agree with Brett. If you don't want to lose a plane, stay away from ANY kind of clevises.
Specially the "Great Planes" brand (according to the pic, it seems that's the brand you are using).
Not only the thread WILL fail, but also THE PIN WILL COME LOOSE eventually! (don't ask me how I know this... )
Stick only to the heavy duty type ball links, such as this one:
http://www3.towerhobbies.com/cgi-bin/wti0001p?&P=SM&I=LXFPW8  or the ones that Chris mentioned.

Regards,
Claudio.

[john e. holliday]

Control Line Central(CLC)  and I beleive RSM Dist as well as Brodak Mfg has the ball links also.   

[SteveMoon]

This clevis won't fail: http://www.ultrahobbyproducts.com/Accessories.html
The UHP Ultra Clevis has been tested to 400 lbs. by Noel Drindak. It didn't
fail, he gave up at that weight.

Steve

[W.D. Roland]

You must jam nut the clevise. The vibration of the engine and air loads on any thread will quickly cause the to fail.
Don

Brian
Those look to be same as in my Chipmunk. Gold with lock tab for pin?

They need Jam Nuts to stay tight.

Then since they are rolled to make the threaded tube area the load makes them open up! Bummer also.

This can be cured.
Force a piece of K&S Aluminum tube over the threaded barrel part of clevis.
Now you can jam it and it will stay.
Use the LOCK! Hemostats help.

I no longer build airplane with out simple access to controls. Not only for service but inspection as most crashes are control linkage failures....well except Combat.

[PJ Rowland]

Ive run those clevis for along time, and only had 1 failure, It failed when the bolt snapped. I now use titanium threaded rods.

I've had one one ship over 2500 + flights, the clevis did wear the pin in the time. I now replace the pin every 500 flights.

Im not saying they WONT fail but I havent experience any issues with diligence to your hardware.