CLEVIS FAILURE :Quicker than you can count to Three
03-15-2012, 06:26 PM
#26
RE: CLEVIS FAILURE :Quicker than you can count to Three
ORIGINAL: invertmast
Condolences on your loss Danno... Question, does the aileron control horn have a ridge on the clevis pin hole? It appears that the clevis pin has a fairly circular shear fracture on it. If their is any sort of ridge in the control horn from the manufacturing process, it is very possible that the horn slowly ate into the pin causing its failure.
Condolences on your loss Danno... Question, does the aileron control horn have a ridge on the clevis pin hole? It appears that the clevis pin has a fairly circular shear fracture on it. If their is any sort of ridge in the control horn from the manufacturing process, it is very possible that the horn slowly ate into the pin causing its failure.
I'll look at that !! I have seen rubber groove steel before !!! Hard to believe it but it happens !!! .. I'll let you know, I may have missed that in Autopsy!!!
Danno
03-15-2012, 06:32 PM
#27
RE: CLEVIS FAILURE :Quicker than you can count to Three
ORIGINAL: rcjetsaok
I'll look at that !! I have seen rubber groove steel before !!! Hard to believe it but it happens !!! .. I'll let you know, I may have missed that in Autopsy!!!
Danno
ORIGINAL: invertmast
Condolences on your loss Danno... Question, does the aileron control horn have a ridge on the clevis pin hole? It appears that the clevis pin has a fairly circular shear fracture on it. If their is any sort of ridge in the control horn from the manufacturing process, it is very possible that the horn slowly ate into the pin causing its failure.
Condolences on your loss Danno... Question, does the aileron control horn have a ridge on the clevis pin hole? It appears that the clevis pin has a fairly circular shear fracture on it. If their is any sort of ridge in the control horn from the manufacturing process, it is very possible that the horn slowly ate into the pin causing its failure.
I'll look at that !! I have seen rubber groove steel before !!! Hard to believe it but it happens !!! .. I'll let you know, I may have missed that in Autopsy!!!
Danno
I have seen this ridge on a few control horns.. so it was worth a mention. It may be good practice for us all to start running drill bit by hand in these control horns just incase!
03-15-2012, 06:40 PM
#28
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RE: CLEVIS FAILURE :Quicker than you can count to Three
Danno,
I seem to recall that the holes in some of those BVM carbon fiber control horns are slightly undersized for the clevis pin. I have had to drill them out (carefully) to get a Sullivan clevis to go through. Do you think you may have forced the clevis through a slightly undersized hole when you built it, then the extra friction over time ended up weakening the clevis pin?
I seem to recall that the holes in some of those BVM carbon fiber control horns are slightly undersized for the clevis pin. I have had to drill them out (carefully) to get a Sullivan clevis to go through. Do you think you may have forced the clevis through a slightly undersized hole when you built it, then the extra friction over time ended up weakening the clevis pin?
03-15-2012, 06:49 PM
#29
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RE: CLEVIS FAILURE :Quicker than you can count to Three
Sorry for your loss...I can tell you from recent experience that things can happen fast....
My Story:
Out flying the flash, its like flight 285 or so, so suffice to say that I have experience with the airframe....anyway its the end of my flight and I pop gear and half flaps for my gear check fly-by...three down and locked and all is well. Power up a little and make my crosswind to down wind turn...all good, turn base to final and all is good. It is at this point that I pop full flaps, as I have done several hundred times before and thats when all hell breaks loose! Severe NOSE DOWN input requiring me to almost give full up to arrest the decent.....major PIO ensues and its a fight all the way to the deck. I get her on but I break two struts in the process....*** happened? Well, upon investigation I find that I got full flaps and the subsequent down elevator trim, but no crow! Turns out that when we set up the crow we set it up on a mix switch so we could turn it off if it was to much....well it was perfect on the first flight and that was that. Forgot all about that switch and never had an issue until that day....needless to say, the switch is deactivated and the lesson was learned. My Flash was only slightly damaged, not a total loss like yours, but it could have been....
Things happen fast, you have to have your A game when flying these things.....
My Story:
Out flying the flash, its like flight 285 or so, so suffice to say that I have experience with the airframe....anyway its the end of my flight and I pop gear and half flaps for my gear check fly-by...three down and locked and all is well. Power up a little and make my crosswind to down wind turn...all good, turn base to final and all is good. It is at this point that I pop full flaps, as I have done several hundred times before and thats when all hell breaks loose! Severe NOSE DOWN input requiring me to almost give full up to arrest the decent.....major PIO ensues and its a fight all the way to the deck. I get her on but I break two struts in the process....*** happened? Well, upon investigation I find that I got full flaps and the subsequent down elevator trim, but no crow! Turns out that when we set up the crow we set it up on a mix switch so we could turn it off if it was to much....well it was perfect on the first flight and that was that. Forgot all about that switch and never had an issue until that day....needless to say, the switch is deactivated and the lesson was learned. My Flash was only slightly damaged, not a total loss like yours, but it could have been....
Things happen fast, you have to have your A game when flying these things.....
03-15-2012, 08:48 PM
#30
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RE: CLEVIS FAILURE :Quicker than you can count to Three
Kevin, he didn't build it so we may not know or be able to find out.
All, I was standing right beside him - in fact was flying the airplane just about 90 seconds before this happened. The important thing to remember now looking at this with hindsight is that not only did it happen very fast - but appeared to be a radio problem - it wasn't even until we got to the crash site that we identified the broken clevis. Dan said as he passed in front of us (on what was to be the last upwind) at about 250-300ft and attempted left hand turn "I don't have it," this was before gear or flaps were deployed. Apparently, he had varying degrees of "having it" over the next few seconds but I can tell you, confidence that the airplane was in his control and following commands from his transmitter was very low in the square footage around where I was standing. I mention all this not because I am questioning whether the radio link was solid (it definitely was) but because a failure can mimic many things rendering those few seconds even more useless...
All, I was standing right beside him - in fact was flying the airplane just about 90 seconds before this happened. The important thing to remember now looking at this with hindsight is that not only did it happen very fast - but appeared to be a radio problem - it wasn't even until we got to the crash site that we identified the broken clevis. Dan said as he passed in front of us (on what was to be the last upwind) at about 250-300ft and attempted left hand turn "I don't have it," this was before gear or flaps were deployed. Apparently, he had varying degrees of "having it" over the next few seconds but I can tell you, confidence that the airplane was in his control and following commands from his transmitter was very low in the square footage around where I was standing. I mention all this not because I am questioning whether the radio link was solid (it definitely was) but because a failure can mimic many things rendering those few seconds even more useless...
03-15-2012, 09:35 PM
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RE: CLEVIS FAILURE :Quicker than you can count to Three
Sorry you lost one man. Never, ever, try to change a configuration when a control surface is suspect. On the real stuff if a control surface is not behaving like it should, all the checklists require that nothing else be tried. Leave it all alone and land when possible in the last configuration before the failure.
03-16-2012, 06:48 AM
#32
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RE: CLEVIS FAILURE :Quicker than you can count to Three
Would Have, Could Have, Should Have is always after Crash thoughts and are very Normal. But we all can learn something from this very tragic Crash. I for one am going to make a few changed to my radio set up and Every 25 flight inspection program.
1. Have a number drill size that is the same as the clevis pin in MM. as a Go-No-Go so there is no binding when the clevis is working.
2. Have a flight mode that will allow the full flap without crow to be elected if needed.
3. Make up a emergency procedure in my pre landing check list that is to remember not to make any changes in flight modes if a control surface has a problem
just maintain control and land.
1. Have a number drill size that is the same as the clevis pin in MM. as a Go-No-Go so there is no binding when the clevis is working.
2. Have a flight mode that will allow the full flap without crow to be elected if needed.
3. Make up a emergency procedure in my pre landing check list that is to remember not to make any changes in flight modes if a control surface has a problem
just maintain control and land.
03-16-2012, 02:59 PM
#33
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RE: CLEVIS FAILURE :Quicker than you can count to Three
ORIGINAL: gene737
Sorry you lost one man. Never, ever, try to change a configuration when a control surface is suspect. On the real stuff if a control surface is not behaving like it should, all the checklists require that nothing else be tried. Leave it all alone and land when possible in the last configuration before the failure.
Sorry you lost one man. Never, ever, try to change a configuration when a control surface is suspect. On the real stuff if a control surface is not behaving like it should, all the checklists require that nothing else be tried. Leave it all alone and land when possible in the last configuration before the failure.
Been there.
03-16-2012, 03:37 PM
#34
RE: CLEVIS FAILURE :Quicker than you can count to Three
ORIGINAL: rcjetsaok
I did send the Manufacturer a letter of the event and they responded. I had mixed feelings about sharing this with everyone because I do not want anyone to get the idea that I am out to point blame at this or any manufacturer in a truly freak accident, but instead to help them understand that even the smallest pieces of equipment that we use are all very important in our success. We all know that anything mechanical can break... That being said, the following is my e-mail and their response ( in reverse order )
I was impressed first of all that they responded and second of all I think they are concerned if there is a problem with their product.... Here it is, Take what you want away from it.
Dan
Dan,
This is a first for me although I have only been with Sullivan for 9 years, which around here is considered a short tenure. My first thoughts are that I am very sorry to see such a nice looking plane go down. It is always a sad and frustrating thing. My next thoughts are, why would this happen in this case, what could cause this type of failure in a clevis. We ship out a few hundred thousand a year and they just don't fail. This is greatly attributable to the fact that the clevises are stronger than any servo out there but I know servo technology just keeps getting better and they are even ganged together in some cases, although I don't expect that is the case on your aileron. In any case, even with the best manufacturing protocols in place there is always the possibility for defects or problems. It will be hard to determine with full certainly what happened here but we will do our best to investigate anyway to be sure there is no endemic problem that has made it through QC. We will start with some additional pull tests on our current inventory and check with our sources for any material or process changes that would relate to them. In the mean time perhaps you can help me with some things I am curious about that you may have answers to:
Do you have any clevises left from the pack that was used (a long shot but worth asking)
Were they used on other places on the plane?
What servo(s) / voltage was driving it?
What type of retaining device is used (stock clips, silicone tube, other?)
Sincerely,
Kevin Peryea
Sr. Engineer
Sullivan Products
1 N Haven St
Baltimore, MD 21224
P: 410-732-3500
F: 410-327-7443
www.Sullivanproducts.com
On 3/13/2012 10:58 PM, Dan Massey wrote:
> Dear sirs,
>
> I would like to share with you an experience I have had with one of your many product I have used and sold for you in our Hobby Shop for many years. I live in the greater Austin Texas area and our shop is located here as well. I have been an avid RC Modeler or 25+ years and yesterday I had a problem I have never experienced before. I was in Waco Texas flying at the HOTMAC flying site with some fellow Jet modelers from Austin and Ft.Worth. I was flying my BVM KingCat when I experienced a control failure in the roll axis. After a futile attempt to regain control af the aircraft it crashed. Upon inspection of the aircraft and all Radio equipment checked out, it was determined that the right Aileron push rod clevis pin (part#S526) had failed and causing the loss of the airplane.The clevis was properly installed and inspected before the flight and it flew normal into the flight for 3:25 minutes. The failure occured in a normal climbing left turn at aprox. 140mph, at that time the roll control was compromised and an attempt to control and land was unsuccessful. The Turbine was commanded and did shut down prior to impact, however the aircraft was a complete loss. All componets involved are being sent back to origin for complete evaluation and inspection, ie, Engine and Radio equipment for unseen damage, I wanted to make you aware of this situation in hopes that it can be addressed from a manufacturer stand point. In this case it was a very expensive loss, but thank God there was no injuries or property damage.It's very hard to believe and sobering that such a small inexpensive Item can cause this type of loss and the potential of a very dangerous situation.
> Please call me if you would like to visit more about this, I would be more than happy to share all the small details if it will better help you understand the chain of events that lead me to send you this letter.
>
>
> Sincerely,
>
> Dan Massey
> 512.650.3110
> [email protected]
> thehobbyexpress.com.
I did send the Manufacturer a letter of the event and they responded. I had mixed feelings about sharing this with everyone because I do not want anyone to get the idea that I am out to point blame at this or any manufacturer in a truly freak accident, but instead to help them understand that even the smallest pieces of equipment that we use are all very important in our success. We all know that anything mechanical can break... That being said, the following is my e-mail and their response ( in reverse order )
I was impressed first of all that they responded and second of all I think they are concerned if there is a problem with their product.... Here it is, Take what you want away from it.Dan
Dan,
This is a first for me although I have only been with Sullivan for 9 years, which around here is considered a short tenure. My first thoughts are that I am very sorry to see such a nice looking plane go down. It is always a sad and frustrating thing. My next thoughts are, why would this happen in this case, what could cause this type of failure in a clevis. We ship out a few hundred thousand a year and they just don't fail. This is greatly attributable to the fact that the clevises are stronger than any servo out there but I know servo technology just keeps getting better and they are even ganged together in some cases, although I don't expect that is the case on your aileron. In any case, even with the best manufacturing protocols in place there is always the possibility for defects or problems. It will be hard to determine with full certainly what happened here but we will do our best to investigate anyway to be sure there is no endemic problem that has made it through QC. We will start with some additional pull tests on our current inventory and check with our sources for any material or process changes that would relate to them. In the mean time perhaps you can help me with some things I am curious about that you may have answers to:
Do you have any clevises left from the pack that was used (a long shot but worth asking)
Were they used on other places on the plane?
What servo(s) / voltage was driving it?
What type of retaining device is used (stock clips, silicone tube, other?)
Sincerely,
Kevin Peryea
Sr. Engineer
Sullivan Products
1 N Haven St
Baltimore, MD 21224
P: 410-732-3500
F: 410-327-7443
www.Sullivanproducts.com
On 3/13/2012 10:58 PM, Dan Massey wrote:
> Dear sirs,
>
> I would like to share with you an experience I have had with one of your many product I have used and sold for you in our Hobby Shop for many years. I live in the greater Austin Texas area and our shop is located here as well. I have been an avid RC Modeler or 25+ years and yesterday I had a problem I have never experienced before. I was in Waco Texas flying at the HOTMAC flying site with some fellow Jet modelers from Austin and Ft.Worth. I was flying my BVM KingCat when I experienced a control failure in the roll axis. After a futile attempt to regain control af the aircraft it crashed. Upon inspection of the aircraft and all Radio equipment checked out, it was determined that the right Aileron push rod clevis pin (part#S526) had failed and causing the loss of the airplane.The clevis was properly installed and inspected before the flight and it flew normal into the flight for 3:25 minutes. The failure occured in a normal climbing left turn at aprox. 140mph, at that time the roll control was compromised and an attempt to control and land was unsuccessful. The Turbine was commanded and did shut down prior to impact, however the aircraft was a complete loss. All componets involved are being sent back to origin for complete evaluation and inspection, ie, Engine and Radio equipment for unseen damage, I wanted to make you aware of this situation in hopes that it can be addressed from a manufacturer stand point. In this case it was a very expensive loss, but thank God there was no injuries or property damage.It's very hard to believe and sobering that such a small inexpensive Item can cause this type of loss and the potential of a very dangerous situation.
> Please call me if you would like to visit more about this, I would be more than happy to share all the small details if it will better help you understand the chain of events that lead me to send you this letter.
>
>
> Sincerely,
>
> Dan Massey
> 512.650.3110
> [email protected]
> thehobbyexpress.com.
Sorry about your loss!
Barry
03-16-2012, 03:47 PM
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RE: CLEVIS FAILURE :Quicker than you can count to Three
So sorry to hear about this, must have happened shortly after I headed for home. I have crow set-up on my BVM T-33 but I may have to rethink how I have it programmed. Right now it is mixed to raise both ailerons when the landing gear switch is moved to "Down". I have no way to shut if off or bypass it. I think I better figure out how to program an "on/off" switch or some other setup. Atleast you know the reason for the crash, nothing worse than never knowing what happened for sure. Just ask Ron S regarding his Bobcat. I dont think he ever did know with any certainty what took it out. Glad to hear the engine and other equipment isnt too badly damaged. Chin up !
03-16-2012, 04:41 PM
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RE: CLEVIS FAILURE :Quicker than you can count to Three
Can't now remember where I saw it, and I may not get the terms exactly correct........but:
There is some evidence that carbon fibre and metal (clevis pin) can create an electrical potential that will result in a situation similar to electrolysis or "EDM" (electrical discharge machining).
Wondering if this could be a factor in this failure of the clevis pin?
-Mike
03-16-2012, 05:47 PM
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RE: CLEVIS FAILURE :Quicker than you can count to Three
Danny, did you check to see if all the receiver lights were solid? If not then I agree with Smitty's post that the probable cause for the crash was a radio link problem. I don't think the clevises caused the crash. If you are flying ANY JR radio you have to make sure that all the lights on the receivers are on and solid! If they are not, a loss of signal will result during the flight then gravity takes over! I have experienced this personally and now make checking the receiver lights as part of the pre-flight.
Sorry to hear that your beautiful jet got destroyed.
Sorry to hear that your beautiful jet got destroyed.
03-16-2012, 06:46 PM
#38
RE: CLEVIS FAILURE :Quicker than you can count to Three
ORIGINAL: speed is life
Can't now remember where I saw it, and I may not get the terms exactly correct........but:
Can't now remember where I saw it, and I may not get the terms exactly correct........but:
There is some evidence that carbon fibre and metal (clevis pin) can create an electrical potential that will result in a situation similar to electrolysis or ''EDM'' (electrical discharge machining).
Wondering if this could be a factor in this failure of the clevis pin?
-Mike
03-16-2012, 07:37 PM
#39
RE: CLEVIS FAILURE :Quicker than you can count to Three
ORIGINAL: invertmast
Yes, aluminum and carbon fiber will corride, im sure steel will do the same. I was always told if you have to put carbon over a metal, put a layer of fiberglass between the
ORIGINAL: speed is life
Can't now remember where I saw it, and I may not get the terms exactly correct........but:
Can't now remember where I saw it, and I may not get the terms exactly correct........but:
There is some evidence that carbon fibre and metal (clevis pin) can create an electrical potential that will result in a situation similar to electrolysis or ''EDM'' (electrical discharge machining).
Wondering if this could be a factor in this failure of the clevis pin?
-Mike
Danno
03-17-2012, 03:58 AM
#41
RE: CLEVIS FAILURE :Quicker than you can count to Three
ORIGINAL: turnnburn
Did you have a data logger on board or happen to plug one in after the flight ?
Did you have a data logger on board or happen to plug one in after the flight ?
No I didn't... I took it out a couple of flights before to put Gary's GPS unit in there, and didn't put the logger back in.. Didn't even think about checking after the crash... I always flew that airplane with the logger, and had never had any unusual numbers.
Danno
03-17-2012, 04:01 AM
#42
My Feedback: (8)
RE: CLEVIS FAILURE :Quicker than you can count to Three
Hey Danno,
Real sorry for the loss brother. We used to change these out every 100 flights back in the ducted fan days due to vibration. That has long since gone. I never change them at all any more and will take an occassional look from here on out. I have had the same failure in my shop over the years but it was due to me forcing them into thick carbon control horns. Pin stay's in the horn and clevis breaks loose. I now carfully drill out my control horns with a #'ed bit for easier installation. As I said I have forced them when this has happened. I have the drill bit in the tray with the clevis's, cannot remember what size it was.
These are the best clevis's in the industry bar none! Honest excellent response from Sullivan. Very reputable manufacturer and I will continue to use their products exclusively.
Now get back to the shop and get something built. Looking forward to seeing you at Kentucky!!!
Real sorry for the loss brother. We used to change these out every 100 flights back in the ducted fan days due to vibration. That has long since gone. I never change them at all any more and will take an occassional look from here on out. I have had the same failure in my shop over the years but it was due to me forcing them into thick carbon control horns. Pin stay's in the horn and clevis breaks loose. I now carfully drill out my control horns with a #'ed bit for easier installation. As I said I have forced them when this has happened. I have the drill bit in the tray with the clevis's, cannot remember what size it was.
These are the best clevis's in the industry bar none! Honest excellent response from Sullivan. Very reputable manufacturer and I will continue to use their products exclusively.
Now get back to the shop and get something built. Looking forward to seeing you at Kentucky!!!
03-17-2012, 12:02 PM
#44
RE: CLEVIS FAILURE :Quicker than you can count to Three
ORIGINAL: John Redman
Hey Danno,
<SNIP> I now carfully drill out my control horns with a #'ed bit for easier installation. As I said I have forced them when this has happened. I have the drill bit in the tray with the clevis's, cannot remember what size it was.
<SNIP>
These are the best clevis's in the industry bar none!
Hey Danno,
<SNIP> I now carfully drill out my control horns with a #'ed bit for easier installation. As I said I have forced them when this has happened. I have the drill bit in the tray with the clevis's, cannot remember what size it was.
<SNIP>
These are the best clevis's in the industry bar none!
Thanks
Greg
03-17-2012, 01:13 PM
#45
RE: CLEVIS FAILURE :Quicker than you can count to Three
Guys.
This is an E-mail I got and am forwarding to you because of you interest in my KingCat clevis failure. It was sent to me as a copy to his fellow Modelers in his local club, from Albert Watson in Washington state, A fellow Turbine Jet Modeler and retired Boeing Structural Engineer for 30+ years who's job at Boeing involved alot of R&D of structure and pin applications in aircraft design. He did some testing of the Clevis in question and found some interesting results that even surprised him.Read his summation and draw you own conclusion, but it tends to shed some light as to what happened in my case... I think the keeper came off and the clevis opened just enough and the load was too great for the welded side to hold it and the pin sheared. ...
Dan....
Hi All,
I'm sure that some of you have seen the thread on RCU in the Jet Forum titled '' Quicker than you can count to three'' where a Kingcat was destroyed when a Sullivan clevis failed. That particular airplane used to belong to Bob Brusa who sold it to Dan Massey in Texas.
Anyhow this event really got my attention because Sullivan gold clevises have been my clevis of choice for a long time and I use them in most all my airplanes. The picture that Dan posted on RCU showing the pin fracture site was interesting so I decided to run a couple of simple tests myself. Took (2) new 4-40 clevises and using a Dremel cut off wheel removed the side of the clevis with the pin in it. Held these pieces in a vice and using a pair of needle nosed pliers tried to bend the pin. Surprise - the pins did not bend but snapped off under very little load. These were classic brittle failures - failures where little or no yielding of the material took place. If the clevis opens up and the pin is loaded in bending this could be disastrous as this simple test demonstrated. When the clevis is closed as designed the pin is in double shear and will be capable of withstanding much higher loads. So it's very important to make sure that the retaining clips are in place. As an additional security measure I plan to add short pieces of good quality silicone fuel tubing over the clevises like we used to do in the old days. Belt and suspenders so to speak!
I also took a look at some Dubro 4-40 clevises that I had laying around. Dubro uses a spring device to hold the halves closed and that does not fill me with confidence. Also the pin is very short so it would be very easy to become disengaged from the side piece. The Sullivan clevis also uses thicker material which is a good thing. I did the same pin test that I did with the Sullivan clevis with very different results - the pin did not fracture and I was able to bend the pin and the side piece.
So where do we go from here? The Sullivan clevis suits our requirements better than the Dubro does but we must be diligent about making sure that they do not open in flight. The best solution would be for Sullivan to change the material of the pin so that it would tolerate some bending. As a Structural Engineer we were taught early in our careers not to use brittle materials in critically loaded applications.
I have added a few pictures to this email for your information.
See You at the Field if the Rain Ever Quits,
Al
This is an E-mail I got and am forwarding to you because of you interest in my KingCat clevis failure. It was sent to me as a copy to his fellow Modelers in his local club, from Albert Watson in Washington state, A fellow Turbine Jet Modeler and retired Boeing Structural Engineer for 30+ years who's job at Boeing involved alot of R&D of structure and pin applications in aircraft design. He did some testing of the Clevis in question and found some interesting results that even surprised him.Read his summation and draw you own conclusion, but it tends to shed some light as to what happened in my case... I think the keeper came off and the clevis opened just enough and the load was too great for the welded side to hold it and the pin sheared. ...
Dan....
Hi All,
I'm sure that some of you have seen the thread on RCU in the Jet Forum titled '' Quicker than you can count to three'' where a Kingcat was destroyed when a Sullivan clevis failed. That particular airplane used to belong to Bob Brusa who sold it to Dan Massey in Texas.
Anyhow this event really got my attention because Sullivan gold clevises have been my clevis of choice for a long time and I use them in most all my airplanes. The picture that Dan posted on RCU showing the pin fracture site was interesting so I decided to run a couple of simple tests myself. Took (2) new 4-40 clevises and using a Dremel cut off wheel removed the side of the clevis with the pin in it. Held these pieces in a vice and using a pair of needle nosed pliers tried to bend the pin. Surprise - the pins did not bend but snapped off under very little load. These were classic brittle failures - failures where little or no yielding of the material took place. If the clevis opens up and the pin is loaded in bending this could be disastrous as this simple test demonstrated. When the clevis is closed as designed the pin is in double shear and will be capable of withstanding much higher loads. So it's very important to make sure that the retaining clips are in place. As an additional security measure I plan to add short pieces of good quality silicone fuel tubing over the clevises like we used to do in the old days. Belt and suspenders so to speak!
I also took a look at some Dubro 4-40 clevises that I had laying around. Dubro uses a spring device to hold the halves closed and that does not fill me with confidence. Also the pin is very short so it would be very easy to become disengaged from the side piece. The Sullivan clevis also uses thicker material which is a good thing. I did the same pin test that I did with the Sullivan clevis with very different results - the pin did not fracture and I was able to bend the pin and the side piece.
So where do we go from here? The Sullivan clevis suits our requirements better than the Dubro does but we must be diligent about making sure that they do not open in flight. The best solution would be for Sullivan to change the material of the pin so that it would tolerate some bending. As a Structural Engineer we were taught early in our careers not to use brittle materials in critically loaded applications.
I have added a few pictures to this email for your information.
See You at the Field if the Rain Ever Quits,
Al
03-19-2012, 10:07 AM
#46
Join Date: Dec 2004
Location: Abilene TX
Posts: 136
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RE: CLEVIS FAILURE :Quicker than you can count to Three
So sorry to hear about your King Cat! It is so frustrating when an inexpensive part brings down an aircraft. Thanks for posting everything you have about this. I will definitely be upgrading the "belt and suspenders" trick on all my control horns.
When I fly my King Cat again, I will definitely practice some more no-flap landings.
Best of luck in getting a new bird up and flying.
Cheers,
Mark West
When I fly my King Cat again, I will definitely practice some more no-flap landings.
Best of luck in getting a new bird up and flying.
Cheers,
Mark West
03-19-2012, 10:31 AM
#47
My Feedback: (1)
RE: CLEVIS FAILURE :Quicker than you can count to Three
I just finished (or so I thought) refurbishing my 11 year old Bobcat XL. It has over 1300 flights on it now so it was time for new fuel and air lines again, and various other structural and cosmetic repairs. I had thought about changing the clevises but decided not to bother with it since I didn't want to worry about messing up the trim. After reading more of this thread I think I will go ahead and change all those suckers out now.
03-19-2012, 11:39 AM
#48
RE: CLEVIS FAILURE :Quicker than you can count to Three
ORIGINAL: Kevin_W
I just finished (or so I thought) refurbishing my 11 year old Bobcat XL. It has over 1300 flights on it now so it was time for new fuel and air lines again, and various other structural and cosmetic repairs. I had thought about changing the clevises but decided not to bother with it since I didn't want to worry about messing up the trim. After reading more of this thread I think I will go ahead and change all those suckers out now.
I just finished (or so I thought) refurbishing my 11 year old Bobcat XL. It has over 1300 flights on it now so it was time for new fuel and air lines again, and various other structural and cosmetic repairs. I had thought about changing the clevises but decided not to bother with it since I didn't want to worry about messing up the trim. After reading more of this thread I think I will go ahead and change all those suckers out now.
Kevin,
Another thing that has come to light is the clearance in the hole that the keeper side of the pin goes through. Al has found clevis's with .005 to .013 /in of slop between the pin and edge of the hole.( Half that amount on either side ) If the pin is moving back and forth in the hole depending on the load, I.E. .. up or down elevator, left or right aileron/rudder, and if the metal in the pin is so brittle it does not allow flex, It will eventually shear because the pin only has a solid anchor on the welded side.... It is not in " Double Shear " ... Still more to come, I will keep everyone informed as I hear more.
Danno
03-19-2012, 12:16 PM
#50
RE: CLEVIS FAILURE :Quicker than you can count to Three
ORIGINAL: SECRET AGENT
Danno, first off, sorry for your loss bro. That really sucks.
Secondly, are these links any good for our application, or are they weaker than the metal links you were using.
Danno, first off, sorry for your loss bro. That really sucks.
Secondly, are these links any good for our application, or are they weaker than the metal links you were using.
Danno