Kevin_W

My Feedback: (1)

Well I am heading to the hobby shop to buy some new clevises this evening. I will be sure to inspect them closely while I am changing them out.

carbunkle

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airraptor

My Feedback: (66)

It is in double shear if both sides of the clevis stay on the pin. The picture above is best style of set up for super high speed large planes. All most all full scale planes use that setup for everything.

dbsonic

My Feedback: (3)

The original failure was on a 4-40? Long ago I remember seeing a failure like this on a 2-56 but dont remember maker of clevise.
Sullivan usually provides a clip or you can use the old fashioned fuel tubing method of a safety, so that the clevise remains closed which of course is beneficial for so many reasons, double shear included(loading the pin across 2 different parts of the pin cross-sectional area).

Couch Potato

To the original poster who lost his beautiful KingCat, I'm very sorry for your mishap.

I have found that when trying to attach this type of clevis to a fibreglass or carbon fibre horn, the clevis has to be splayed so that the pin can of course engage through the hole in the horn. If the horn is quite sturdy, say > 1.5mm wide, sometimes the clevis does not naturally want to close so that the pin is secured at both ends. It has been over stretched. In this instance you are dependant on the retaining clip or fuel tubing ring to close the clevis.

These clips can be knocked off easily, eg when putting wing bags on, or the tubing can split. The end result is the same: the clevis now opens and the pin is only supported at one end.

Using a M3 ball-link between two control horns does not have any such problems.

SUMMIT120

Dan,

First of all I am sorry to see you lose the aircraft. I know how much you liked it and how long it took you to find one.

Dave Dennison from Rochester, Minn. had one just like yours for sale on RCU last week. I don't know if he sold it or just let the add expire.


Mike Danchak

Hnorth

Dan, 

airraptor

My Feedback: (66)

these clevis's take well to solder. so once you have them adjusted solder the clevis to the wire then once the clip is on you can add a small bit of solder to the retaining tab to keep it on.

Eddie P

My Feedback: (4)

Thanks so much in posting this whole thing for us to see. I try to make sure I always have retaining pins on my clevises but have flown in the past when one has fallen off before getting back home to replace them with stock on hand. This really is a preflight "each start" thing now, and a no go issue if there is no retaining pins or backup tube retainer for me now (I'll add those to my field kit). The test with pliers was revealing... I certainly have learned something very useful.

aquaskiman

My Feedback: (46)

This is what I have been using

jetnuno

Hi George

Which brand are those?

Regards

Nuno

tms261

I just got my first jet, and was somewhat dismayed that it had single horns. I'm used to doubles on all my gassers. Granted they have big surfaces, but its nice to have that security and a bolt for a pin. There are a few KingCats at our field but I never noticed that they had single horns. I guess jets have gotten away with this for a long time and 99.9% of the time are just fine. I don't know what to do now with my jet.

Does anyone know of a glue in horn that has a bearing, and a clevis that is big enough for a bolt?

rcjetsaok

My Feedback: (7)

I have drilled and tapped out the phenolic/carbon horns to accept 4/40 and used the Dubrp #259 4/40- Swivel Ball Link assmy... Very good combo!! I have more info on the Clevis investigation I will post as soon as I can see good enough to do it...( Had Retina surgury yeasterday and I'm on Instruments right now.... Follow up was this morning, Doc says everything looks good... Be layed up about a week....


Danno

aquaskiman

My Feedback: (46)

Nuno they are great planes here is the link http://www3.towerhobbies.com/cgi-bin...?&I=LXEVC8&P=7

area51jmitch

My Feedback: (82)

Sorry your plane went in. I use crow on my jets, but I put the enable on a differant switch. I can turn it on or off.

rcjetsaok

My Feedback: (7)

Well Guys, This may be the final chapter in the saga at hand... I appreciate everyone's thoughts and input on this ordeal. The following E-mail is from Kevin Peryea at Sullivan Products, He is their Sr. Engineer there and has taken a serious look into the possible problem at hand. He has also been in contact with Al Watson, fellow Jet Modeler and retired Boeing Structures Engineer and together talking that Engineer language that I certainly don't understand, they have done some extensive test on the clevis's and here is what Kevin has concluded. Kevin told me to share this with all of you and if there are any perticular questions you have, he will be glad to visit with you about them. This has been a interesting and expensive experience for me, and I hope it has given everyone some insight on the subject.

Danno




Dan,

After you called but before talking with Albert I did some testing that goes beyond the normal 100# proof testing we do on production samples as a matter of course. In that test we load some samples to make sure they hold 100# of tension when connected properly. I wanted to see where they would fail when the load was extended beyond that as well as where and how they would fail if abused a little.
- The first test was to find ultimate failure when connected properly, well the only thing about this test that failed was the test. My test apparatus was built for the 100# proof testing and only loads to 200# and I did not have any of the 10 pcs I tested fail up to that point. The test apparatus has a thick metal tab (.100") with a hole for the clevis pin which represents the thickest horn they can go over, and a .025 tab on the other end which represents the thinnest horn you would find. Both are important because the thick tab requires opening the clevis the most and the thin one puts the load unevenly on the pin instead of spreading it evenly.
- The next test wast to use the same type of set up but leave off the keeper clips. In this case I would get failure somewhere between 90# and 130#
- The last test I did was to open the clevis really wide when installing it so that it did not want to stay closed then put it on without the keepers. This resulted in failures at forces as low as 10#

Now to put this into perspective a little, your servo, when operating at 6.6V can theoretically produce 352 in-oz. So if you put the servo side connection as close as 3/8" from the center of the arm it could put up to 58# of force on the linkage and horn. Of course normally you would connect further out on the horn so that is a worst case number but that is what we like to work with when doing testing and analysis :-)

Albert and I connected by phone later on in the day after I had done the work above and we discussed some of his findings as well as insights he had from speaking with other club members and builders in the Jet world over the years. The conversation was quite pleasant and as you suspected we speak the same language. I am actually a graduate from ERAU's Aircraft Engineering program so our views on things come from similar backgrounds.

Right off we both agreed that no clevis is going to survive if it opens during operation. So going beyond that Albert and I mostly discussed the bending test that he did which you forwarded to me. We recognized the fact hat they break is one thing, but really what is is important to know how far they bend before hand and if they could break with the clevis shut, so we talked about how much bending force may have been involved or how many degrees they flexed before snapping. Unfortunately, as Albert mentioned, he was not doing these in the old Boeing lab but rather at home on a bench so there was no real quantifiable data to be had. So the question remained as to whether the pin could flex enough under normal use with wear and tear to snap assuming the clevis was closed and the keeper was in place. At the end of the call we still had no good way of determining this but I was going to think about some sort of pin bending test to perform. Shortly after hanging up Albert called back with a great solution to the problem. His thought was to elongate the receiving hole to allow the pin to flex .015 or so before making contact with the other half of the clevis. This would account for the normal oversize of the hole plus any manufacturing tolerances plus a decent amount of wear. I loved the idea and decided to take it one step further and double the number to .030. I carefully machined a number of parts and measured them to all be within .030 to .033 of gap and started testing. The tests were done with the same set up as above, one think horn, one skinny horn and with the keepers in place.
Results - of the 10 I tested none failed even when taking the load to 200#! This means that even though they are more brittle than the Dubro units they still have enough flex to deal with any bending they will see if the clevis is closed.

In reading some of the comments on the RCU post and talking with Albert I realized that a lot of people use silicone Tubing on our clevises as a keeper. Some folks seem to use it in addition to the clips and others in place of it. Having just been dealing with the forces at play I was concerned about the viability of replacing the keeper with silicone and since the test stand was "all warmed up" I thought I would take a moment to see what the real world results were.
Results - Failures occurred between 100 and 160#. This correlates quite well to what I saw with no keeper. The distribution of the failures was more on the high side of the range, where it was more on the lower without the keepers at all but the IMPORTANT thing is that Silicone is no substitute for the real keeper. That being said I think it is a GREAT ADDITION in as much as it may act as a guard for the keeper if something hits them. Even though we all try to preflight well you never know when a wing may drag on landing or get swiped across a tailgate or benchtop.

So getting back to what may have happened on that fateful day...
The most likely scenario that Albert and I could come up with was that the clevis keeper had come off un-noticed at some point and during flight some extreme loads were induced, perhaps because of a manuever or perhaps some flutter occured and this lead to the clevis opening up under the loads the pin snapping. Carbon to steel wear is also a likely , I tend to agree with this assesment only because the plane had MANY MANY flights on it and the problem occurred late in life rather early. If you would like to send in some of the linkage assemblies we would love to look at them in detail. It would be great to be able to see how long term installation in carbon horns effects them.

I really appreciate you bringing this to our attention. It is really great to take some time to get down into the details of one of our products. Please feel free to share this with the community. If you agree with our assessment please be kind enough to review the posts in RCU to make sure they reflect the findings. It is very important that everyone know how much difference such a tiny piece of metal makes in the strength of the control systems.

Best regards,
Kevin Peryea
Sr. Engineer


Sullivan Products
1 N Haven St
Baltimore, MD 21224
P: 410-732-3500
F: 410-327-7443
www.Sullivanproducts.com

carbunkle

go get ur credit card,
not exactly what u wanted but best there is, imo, after much r&d. >

http://store.rc4wd.com/Aluminum-4-40...l-1_p_629.html
http://dreamworksrc.com/catalog/airp...pe-p-1533.html
http://dreamworksrc.com/catalog/mach...nk-p-1064.html
http://dreamworksrc.com/catalog/hard...50.html?page=3
http://www.fastener-express.com/4-40...of-4-pcs-.aspx
http://www.fastener-express.com/4-40...e-Qty.-25.aspx

Everything is 4-40.. The titanium rods have one end left and one right hand threaded, which is good for adjusting.. some rod ends similar to those above are not a ball but a bearing and will not swivel. The rc4wd "swivel ball" rod ends are the best I'v found, but they only have right hand threaded. You will need some small washers to space them to swivel more if needed. The one's from dreamworks are the only left hand 4-40's I have found, lube them before u move them. Use the left hand rod end on the servo arm and put the side that the ball was installed in at the factory facing away from the arm so it can't come off if it comes apart. Use the rc4wd's on the control surface double horns. Assemble with titanium screws and aluminum locknuts.

MaJ. Woody

My Feedback: (28)

Wow!! Now that is concern for their customers and concern for producing a quality product! Many manufacturers can take a lesson here....

rcjetsaok

My Feedback: (7)

I tend to agree with you on that !


Dan

roger.alli

Great response from Sullivan. Gives me confidence to continue using them.. However, it seems the retaining clips are not optional. They need to be installed.

Roger

jetflyr

+1!
Greg

Eddie P

My Feedback: (4)

Agreed. Pretty impressed by the response.

flyinfool1

My Feedback: (2)

So from the response (Thanks to Sullivan for taking the time) we can tell that we DO need to have the keepers installed at all times.
Since the keeper is not just a safety but actually a critical structural part, and that critical part is easily knocked off, we now need to come up with a keeper keeper.

I have done preflights and verified that all keepers were in place, at the next preflight during the same outing I have found keepers missing. I fly from a grass field that is sometimes long enough to be touching the linkages on some aircraft. There is no way to know if the keeper was pulled off during taxi out, takeoff, landing or taxi back. I really doubt that it came off in the air.

After reading all of this I am now considering soldering the keepers on mine once the plane is trimmed, If down the road I need to adjust or service the control surface the cost of a new clevis is nothing compared to the peace of mind.

I am now trying to think of a way to measure actual loads on a linkage during flight.
I am thinking a amp meter that will record the peak amps of a servo during a flight and then use a scale to to pull on that servo to get the same amp reading to get the approximate actual load on the linkage. The right way would be to build a linkage with a strain gauge but that is well above my pay grade.

[email protected]

My Feedback: (2)

Any time there is a in flight failure of one component of any aircraft that I fly it is not just forgotten.

I work on a fix, It has kept me alive for over 40 years of Flying Here in ALASKA.

My plain was to replace all of the CLEVIS on my JETS. Take A LOOK AT THE PHOTOS ONE OF THE CLEVIS WOULD NOT TAKE A SAFETY LOCKING CLIP. The Clevis are all new.

mr_matt

My Feedback: (10)

Thanks for the links carbuncle.

The 4/40 swivel you found, what is the whole size in the ball? I have never found one that had 4/40 on the link thread and #4 hole in the ball as well. maybe Todd has them

And don't even try to find a #6!