Failures

[W.D. Roland]

After worrying about clevis failures for weeks I thought that starting a thread where everyone could post surprise failures that lead to the destruction or damage of our nice stunt planes might be a good thing.

Structural, control linkage parts or other problems.

If you have had a failure please post it so that us retreads and beginners don't repeat others crashes.
Solutions would be good also.
Service life of parts for maintenance?

At this moment I think the 4/40 sized clevises with keepers are OK and the brass threaded solder on couplings that come with them are not.

I plan to retro fit existing airplanes with steel threaded rod and steel tubing couplers on the push rods.

I think annual clevis replacement would be a good idea and/or after X number of removal for adjustment.

Future airplanes will get heavy duty Ball links like Paul posted here
http://stunthanger.com/smf/index.php?topic=16086.0

On the ball link rod end when not mounted in double shear will use a washer on the off side so that the arm can not pop off the ball( requirement on formula car suspension rod ends).

David


??

[Ward Van Duzer]

I see one more screw to loosen up...

BTW, I see this as a great subject.


W.

[Marvin Denny]

The most common failure that has (and still does) happened is a disconnedt in the control mechanism.  The disconnect occurs between the brain and hand---- the brain sez PULL OUT---- the hand sez  awwww wait a while.
  Back to the building board.
  Added by edit--  Would that be called a lack of communication???

  Bigiron

[Juan Valentin]

   I had read about it previously so when it came time to use one in my arf Nobler  I made sure to use a steel threaded rod then I wound some copper wire over the threaded end of the clevis and soldered with sta brite silver solder. Also I silver soldered the pin to the clevis because I heard of the pin departing it and since I didn`t have enough space I used heat shrink tubing to keep it close. Since the airplane is a take apart I will be inspecting it often  in hopes to avoid a disaster.
                                                                                                                       Juan

[Randy Powell]

I lost my Ringmaster Deluxe due to a bellcrank failure, but that was sort of self induced.

[john e. holliday]

I remember the thread on that one.  Really great looking plane.  Did you give the manufactuer H*** for the component? 

[Ward Van Duzer]

What caused the BC failure? Would you care to clue us in so we won't do the same action...

I know there have been several reported music wire failures. Would anyone care to chime in on those? These were several years ago. Has our wire gotten any better lately?

W.

[FLOYD CARTER]

These days, I always test a new piece of piano wire.  Put it in the vise and whack the exposed end with a hammer to make a sharp bend.  If it doesn't crack, I'll use it.

Floyd

[Martin Quartim]

If you haven't changed the original Brodak ARF lead outs, ohhhh you better do traction test every time, it will take a few years but it will fail. The ones in my Pathfinder ARF that I got in March 2006 failed today.

Martin

[Bill Little]

Hmmmmm............ both of the failures I have witnessed in the recent past (15 years) have been Lead Out breakage.

I was with Bob Hunt at teh '96 NATS the evening his Saturn was lost due to the up line breaking.

My son, Aaron, had the down line break on his Fancy Pants after that.  It was watching Bob do a dance towards and away from the plane to minimize the impact that saved his plane.  Aaron's LO failure was due to the aluminum BC sawing through the lead out wire.  He built it by the book (it was a product review for Stunt News) and did not bush the BC with brass nor the LO wire, so it just sawed through the cable.  The plane still flies today needing only minor repairs (but with a nylon BC!).

Big Bear

[W.D. Roland]

Bell crank and lead out sawing each other has become a worry since stunt planes last longer than combat planes!!!
For my lead outs to bell crank connection I put a small eyelet like on the line end and the a 2/56 bolt and nylocknut with a hat shaped eyelet over the bolt so that it is more like a bearing.
The Bell crank gets threaded and the bolt locktighted in to it.


Although I think that using the balls will be the way on new builds the clevisis currently in use on my air farce should be ok.

The one I am using now have a keeper for the off side of the pin and the way it is done prevents the pin from coming out if the pin becomes loose on the other side.
The threaded/rolled section I shrink a piece of aluminum tubing over so this cannot spread.

The threaded brass coupler is a worry....


David





David

[Larry Fulwider]

. . .  my air farce . . .

Sometimes your subtlety goes unnoticed 

*/*/*/*/*/*/*/*/*/*/*/*/*

On a steel clevis (left picture), the pin is only 1/16" diameter and is simply spot welded to one of the side arms. That is where the clevises break. (Note missing pin on left clevis in pic). Tying the clevises solidly to the pushrod only diminishes some percentage of the failures. Also, the 1/16” pin is sometimes assembled to a 3/32” hole horn. Sloppy, sloppy, controls. 
   The bulkier DuBro (center) doesn't have the broken pin issue nor the coming loose from a threaded rod issue -- the pushrod attachment is the same as ball links. There is a safety clip on the other side of the clevis to retain the pin. I have never heard of one of these breaking, coming off the pushrod, or losing a pin. However, the pin is still only 1/16” diameter, so check for fit with the horn. These are probably OK up to ?? (you pick) size planes.
   The UltraHobby clevis (right) is bulletproof, and was purposely made for demanding CL apps. It has a screw-in 3/32 pin. Steve Moon, who makes these, says on .35 or smaller planes, even he has used the DuBro.

If you use a clevis, don't use the spot welded ones.

No one has any real data on clevis pin breakage. Who knows, failure rates might be as low 1% per 50 hours of use – which means you can find many casual flyers with 100% success rates with steel clevises. Say, optimistically, about the same odds as playing Russian roulette with a 200 chamber pistol? Not too risky, but why play if you don’t have to? What, $3 per airplane?

Whatever the odds of failure, we know it is a non-zero number for steel clevises of any breed.

       Larry Fulwider

[Michael Massey]

This is odd enough as to be a very strong theory but I am unable to conclusively prove the event.  But here goes...

I had a 2-56 pushrod and Great Planes clevis connected to the flap control horn, on the second hole from the top control horn hole.  The control horn was the type that had a metal "horn" soldered to the wire that connected the two flaps.  I had the silicon "sleeve" pushed on to the clevis to keep it from separating. 

The elevator pushrod had a 4-40 Great Planes clevis and pushrod connected from the top hole in the flap control horn and that also secured with the silicon sleeve. 

About 2 months before last weekends "crash" I had experienced a very strange event.  While doing the second or third consecutive outside loop, I was low so gave a strong "down" control to avoid the ground.  When I did that, it seemed like the plane did not want to respond to the control input and even more strange, seemed like it wanted to level out upside down.  Couldn't find any reason for it so thought it was a "senior moment" since I have only been back into the sport for about a year and a half.  (My prior experience is TOOOOO dated and insignificant to really count.)

This weekend, the same scenerio.  Third outside loop, too low, gave a hard "down" control, no real response and seemed like it wanted to level out upside down.  But this time it pancaked inverted.  Minimal damage but ...

At home on the bench, I could not duplicate any failure but a close examination revealed the 4-40 clevis was "sprung" on the thread and loose.  Not enough to cause the symptoms I described but I soldered it none the less.  Then I noticed the silicon sleeve on the 2-56 clevis was cut at the point that faced the rear of the plane and about half way towards the forward part of the plane.  Then I discovered that I could push the flap control horn hard, simulating a hard "down" control and the tip of the control horn would contact the silicon sleeve of the 2-56 clevis.  Contact it enough that it pressed where the cut was located.

So my theory is that the tip of the control horn was "pushed back" momentarily by the silicon sleeve and during the maneuver, any slight reduction in line tension allowed the sleeve to exert more pressure towards neutral control.

So I guess the answer is, fly higher.  By the way, I did change the relative position of the two pushrods so the flap pushrod now goes to the second hole and the elevator pushrod goes to the top hole.

Any thoughts?

[frank williams]

I've got one that isn't control system related.

I had a Saito 56 4c in an electric ARF conversion.  I had an RC engine mount bolted directly to the plywood firewall.

Every now and then the engine would start backwards and run since I was running muffler pressure .... and it didn't occur right off to me that the the engine was using the exhaust as the intake and the venturi as the exhaust.  It seemed to run quite well and, like I said, I didn't get it shut down right away.

Well the exhaust out the venturi is really really hot gas and its dumping right into the engine compartment.  Hot enough to soften the (chinese) gule holding the plywood firewall to the airframe.  One day the engine just kinda' pivoted down and I went into the concrete at about 90 degrees.  It disasembled that Saito as if you were working on it in the shop.  I found the wristpin and conrod, which were neatly seperated, but I never found the piston.  Still looking.

Note to self, if a 4c starts backwards, just put your finger over the exhaust exit and it will stop instantly.

[Paul Wood]

After several steel clevis failures in our R/C club, we have stopped using 2/56 steel clevises.  The pins will fail, but we've actually had most of our problems with the engine vibration causing the threads to strip.  We only use the nylon clevises in the 2/56 size.  We do use steel 4/40 clevises in our larger models, and they work very well because the threads are much stronger.  I prefer the Dubro clevis that Larry posted above because the body is not steel and the threads seal tightly to the rod.  I would recommend only nylon in the 2/56 size and the Dubro in the 4/40 size.

Paul

[Bob Reeves]

My 2c

The failed clevis in the above photo is a china POS typical of what is supplied with some ARF's, looks like the ones that were in my Score. Never use them for anything. A Sullivan Gold 4-40 would not have failed. ALWAYS USE A LOCK NUT ON ANY METAL CLEVIS, even the UHP....

Michael Massey, Replace the 2-56 clevis with a 4-40 and solder it if necessary to avoid replacing the rod although the rod should also be replaced. 2-56 hardware is not strong enough for anything in CL except maybe a trim tab or rudder adjustment.

Frank, Main reason I always use an electric starter, only takes one backwards start to ruin your day  

[W.D. Roland]

Larry
I cant really see what color the clevis's to the left are. I think they are silverish? Kavan made some like this years ago and they seemed to hold up although I think I have one laying around that the pin is missing from it.
The modern China cheepies are silverish.

I agree with Bob on the Sullivan Gold 4-40. Even with out the pin's safety retainer clip it seems ridged enough to not open up under load. I use the safety clip!
The barrel/ threaded section of clevis is rolled with an interlocking seam so just to be safe I Shrink/press a piece of aluminum or brass tube over that area.
After finding the thread worn severely from not using a lock nut I make sure that they are locked down tight now.
Sometimes have found the lock nut backed off so nylock nuts will be retro fitted in  the near future.

The weak link in the Sullivan seems to be the Brass coupler. They can be bent when in difficult areas and then will fail soon after straightening them and this only from a very slight bend!
Hope to make up some steel couplers soon. need to find the right size tubing.

For the slop fit of the pin to the horn I cut a short piece of aluminum tube to fit over the pin and then drill horn to tube od for zero slop fit.
With slop it shows up in the overheads when reversing directions. After flying a zero slop linkage airplanes the airplanes with slop miss the turn point consistently! Zero slop is nice............

Have Been checking out the push rods that Down Under uses with the DuBro ball link and with the addition of a pin I think this is what my next build will have.

Mike, I had similar problems using tubing to retain clevis, the safety clip on the Sullivan is nice solution.

Nylon clevis to nylon horn ok, nylon clevis to steel horn---not ok     ??
 
Frank, never seen that happen! Hope you find the piston!

For R/C having the servo mix switch on when you don't use mixing will produce wild aerobatics from take off to landing(crash). Solution: adjust switch with cutting pliers . No switch--no problem! other than building new aerobatic plane.

David

[Andrew Borgogna]

I was test flying Larry Renger's 1/2a Tech Terror this past week and I was just starting a simple lazy eight when the clevis attaching the push rod to the elevator broke in half.  The plane did a perfect lawn dart maneuver, buried the engine to the firewall and did zero damage other than a broken prop.  Plastic clevises are dangerous, I will not use them.
Andy

[Lester Nicholson]

Failures - My Brodak Cardinal ARF was lost when it left the circle - both lines came undone at the bellcrank and it climbed out and gradualy turned right and finally hit the top of a tall oak 250 yds from the circle. In our club in Clanton Alabama one other Cardinal and a Vector (both Arfs) have suffered the same fate. The lines did not break, they slipped out of the connections at the bellcrank. Now I have an ARF, a Brodak Vector, that I stripped, and re-did in silkspan and dope (done before the crashes). I'm afraid to fly it - I know I need to cut it open and re-do the control system but it looks so good I just can't bring myself to get out the scapel. I wrote this to reccomend to anyone doing an ARF to take a close look at every aspect of the control system.    Nick

[Andrew Borgogna]

"Failures - My Brodak Cardinal ARF was lost when it left the circle - both lines came undone at the bellcrank and it climbed out and gradualy turned right and finally hit the top of a tall oak 250 yds from the circle."

Is this information being fed back to Brodak?  The same "product liability law suits" that Toyota is worried about could do serious harm to Brodak if God Forbid somebody were harmed or killed by a rogue plane.

I have had two Cardinals and an Oriental with no problems, but after reading about these failures I would not fly one without doing the controls myself.
Andy

[Larry Fulwider]

Larry
I cant really see what color the clevis's to the left are. I think they are silverish? . . .
 . . . I agree with Bob on the Sullivan Gold 4-40. Even with out the pin's safety retainer clip it seems ridged enough to not open up under load. I use the safety clip!
 . . . The barrel/ threaded section of clevis is rolled with an interlocking seam so just to be safe I Shrink/press a piece of aluminum or brass tube over that area.
The weak link in the Sullivan seems to be the Brass coupler. They can be bent when in difficult areas and then will fail soon after straightening them and this only from a very slight bend!

Yes, “silverish” from an older Nobler ARF. They have the extra “washer” where the spot weld is, like the Sullivan  Gold 4-40.

I don’t understand the reluctance to use the Du-Bro 817 Quick Link. Retail is $2.20 a pair for the Du-Bro, vs (Tower) $2.00 a pair for the Sullivan Golds. That’s a nickel per clevis, hardly a major financial decision. There are no bulk or weight disadvantages for the Du-Bro compared to the Sullivan Gold.

The Du-Bro is superior to the Sullivan Gold in three significant ways:

     1. The nylon base is self-threaded onto the pushrod. That is as secure a fastening as any ball-link, without any patching, soldering, tubing reinforcement, lock-nut, or any sort of modification of any kind. Just screw it on to the pushrod and use it.

     2. The steel pin is a push fit with a solid head (like the head of a bolt) that cannot pull through the clevis.

     3. Easy to clip closed and easy to unclip. The retaining clip rides in a molded slot, so it does not get lost if you loosen it. The locking clip slides back and forth in the slot, and is either clipped closed, or in the correct position ready to clip closed. The retaining clip pushes on easily, and requires no tools to hold it in position when closing it. See pics of open and closed below. (Compare to the Sullivan Gold where the clips can disappear / break in a heartbeat, and seldom clip on the first push as it is difficult to find the correct alignment.)

By contrast, I see no advantages to the Sullivan Gold over the Du-Bro, so no reason to consider the Sullivans.

. . . For the slop fit of the pin to the horn I cut a short piece of aluminum tube to fit over the pin . . .

Same idea as yours. Brass is “solderable, so no loose tiny pieces to mess with. Even with the messy soldering job, it cleans up easily with a Dremel / file as show in the finished pic. The piece of corrugated is a brace to hold the tubing in place while soldering.

       Larry Fulwider

[Clancy Arnold]

I lost a SIG SkyRay 35 and a great running OS 25 FSR engine because the Nylon Control Horn on the elevator broke about 1/4 of the way through a loop. At that point it was pointed straight up and continued that direction until the pavement behind me jumped up and smacked it.

After the crash I looked at the control horn and there was dark oil stain on one half of the broken piece.  Obviously it was cracked long before total failure.  ALL nylon control horns went in the trash when I got home.  Those on planes were replaced with metal control horns before their next flight.  The OS 25 FSR was destroyed beyond repair.  Cracked case, Bent crank and a broken carb.  Yes it had a throttle and my U/Tronics, but I forgot to close the throttle before it hit. Don't know if that would have helped.

Clancy

[Bob Reeves]

I don’t understand the reluctance to use the Du-Bro 817 Quick Link. Retail is $2.20 a pair for the Du-Bro, vs (Tower) $2.00 a pair for the Sullivan Golds. That’s a nickel per clevis, hardly a major financial decision. There are no bulk or weight disadvantages for the Du-Bro compared to the Sullivan Gold.       Larry Fulwider

No reluctance here, I have a couple ships with Du-Bro's on the elevator. Only item I don't care about is if you loose the little pin (which is easy to do) you have to buy another clevis. I solved the problem by buying a bulk pack of 12 (or whatever is in the bulk pack). Gives me plenty of spares.

[W.D. Roland]

Tried out the Du-Bro clevis on recent R/C build and mostly like them.
The pin and clip can be lost easy and the threaded fit to the push-rod is so tight that it would be next to impossible to adjust in an internal installation. They are ok on external use where things can be grabbed with pliers and wrenches.

In another thread that I can not find now someone mentioned using the Sullivan with out the jamb nut.
This is not good as the nut stops vibration from wearing out the threads on the rod and clevis.

I like the ball joint idea except for the twisting loads put on the horn. After awhile fatigue would take its toll on the horn assembly not to mention the bending loads on the bolt through the ball.
2 horns side by side with the ball in between may be the best solution for the long term.

Changing the Sullivan clevis one or twice a year is my current plan.
That and doing away with the threaded brass adapter and replacing with steel tube and bolt.


Gravity sucks

David

[Randy Powell]

On the bellcrank failure: this was, as I said, self inflicted. It was a bellcrank remnant from a 3/8" thick job (made by me) that I cut down. I cut it too thin. Probably would have been fine, but there was a small bubble right where the pivot post went through. Had I been using my brain cell (and not lent it out to Pat Johnston that week) I would have reinforced the pivot and the plane would still be flying. But it was one of those 11:30pm on Saturday night decisions: Oh, that will be fine. Duh!

The new one that is just about ready for finish has a Brett Buck type sandwich bellcrank with 2026 aluminum for plates. The thing would probably lift my car.

[W.D. Roland]

Randy
Can you post a link or pics and info on sandwich bell crank?
The extra thickness it sounds like it would have could be helpful in a pivot bearing idea that's been bouncing around in my head. This is the last area of removing slack in the control system on stunt planes and having it serviceable as well.

Thanks
David