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Loose Main Gear Legs

Shadowy Figures

DonFromTX said:
Good questions John.
How I got in the center of this starts with Ron Russ noting his damage after hearing noises when landing he could not identify. He had grown quite hostile about the mud slinging when something like this is mentioned on VAF, does not do photos, and asked me to post his misfortune for others to ponder. At that time it seemed like a single incident he caused by a hard landing. I did that for him, and for what I considered a favor for other owners who might encounter the same fate. I never wished to become a "clearing house" for this or any other problem. For some reason I don't understand, I then became a "wailing wall" for those who had the same damage and did not wish to post it on VAF (probably for the same reasons that show up in this thread, you will get accused of all sorts of things just for bringing it up, and as you might have noticed, many people have no idea how to post photos on the forum). I never resort to name calling, but those you call "shadowy figures" will have to speak for themselves.
After at least two people tried to bring it to the attention of Vans, and were rebuffed with the old story that the plane is just fine since it met some alphabet standards, it is poor pilots that are causing the problem, and in each case were told "this is the first we heard of this" which was not entirely true, it caused someone to say to me what I quoted as their response. I never said it was MY opinion, I still think the RV12 is the finest LSA out there, bar none - and even if it turns out that the landing gear needs a little stiffener or something. Good grief fellows, did you not know it is an EXPERIMENTAL aircraft?
I never intended this thread to be some statistical refined definition of the problem with readily available solutions, but simply a FORUM where others with similar problems or suggested solutions can communicate. I just don't agree with many that feel that ANY criticism of the RV12 should be swept under the carpet and never ever mentioned publicly. The reporting system that Scott mentioned is perfectly proper for reporting these things to Vans, but it appears it is not widely used, or is not effective in informing other owners. Vans DOES study problems for a solution, we have the fuel tank mod and the nose wheel pant fix as examples. We should be thankful that these solutions are carefully studied and proven before we are informed of a fix. I respectfully disagree that such problems should be kept secret from the rest of the owners as you suggest you will do John, but I can however respect your decision to do it that way.
So, I don't feel I deserve a spanking for sharing information that I felt other owners should be aware of. From some of the responses, one would think I was selling a fix for the problem and promoting the problem. I am selling NOTHING, and if you don't like to hear about a problem, I suggest you not read the posts...
Click to expand...

Hey Don don't bring us shadowy figures in to this.:cool:
 
Need More Data

In reading this entire thread, it is obvious that there is not enough information presented to begin to make any logical conclusions as to cause.
Don't blast VAN's for not responding until they have the data they need.
Also, VAN's may choose not to even address problems encountered by RV12s built as EAB with different engine, avionics, fuel and loading configurations.
Following are some of my observations, based on information from this thread, plus my own personal observations from my RV12, both before and after the rebuild.
Some of the affected RV12s are EABs with Viking engines installed. (I think I read that the Viking engine weighs 60 lbs more and provides 110 HP, vs the 100 HP provided by VAN's Rotax.)
How are each of the damamged planes configured? (Weight and operation have a definite effect on how a plane holds up.)
Are they ELSA or EAB?
What power plant is installed?
Any other modifications to the airframe?
What was the weight of the plane at the time of the incident? (It is easy to over gross the RV12 with a couple of hefty guys, not to mention a larger engine, extra avionics, etc., that could contribute to an over gross condition.)
Pilot technique. (Pilot competence is a subjective thing, but I have seen pilots slam down their A model RVs so hard I thought something surely had to break and later bragged about their wonderful landing techniques. Just saying!)
Building technique. (As a tech counselor, I have seen a lot of builds. Everything from beautiful to down right unsafe. Some builders don't even debur anything and expect to win awards. So, the quality of the build is an issue that should be considered, especially in critical areas.)
There are probably a few other items that need to be looked at and studied but these are a few.
I really am interested to see the ratio of RV12 ELSA vs RV12 EAB planes that have been damaged and how modifications have played a part, if at all.
I personally believe that the RV12 is designed to be what it is and shouldn't be modified, if you expect it to hold up reasonably well, but that's me. They are EXPERIMENTALs after all, but if you purposely, or accidentally, exceed the manufacturer's design limits, you will likely have problems. However, you can easily exceed design limits by rough handling, as in very hard landings or consistent rough use, as well as by changing equipment. It happens all the time to all kinds of planes.
At any rate, I am interested to see more data, if the owners are willing to provide it, and maybe a little less bickering. Eventually, we will find out what is causing these issues so they can be overcome. Petitioning the owners to fill out their forms for VAN's is probably the best way to get to the bottom of it.
 
Thanks for that contribution, yours is the ninth that I am aware of now. I am sure you will find that in order to go so far back to kink the brake line, when you remove the wings you will see how it got that far back, at least that seems to have been others experience. For others enlightenment posting photos of what you find would be valuable.
 
Very well stated and logical Steve. Only one, the very first example, has the Viking engine installed, all others appear to be Rotax powered to the best of my knowledge (Your indication was plural, but there is only one Viking powered 12 flying in the USA. Well, WAS flying, now grounded for repairs). The elusive thing to this list of information, is that virtually none can trace back to exactly when it happened! At best some recall an unusually difficult landing way back in time, but not a specific incident. The apparent fatigue cracks in the channel were PROBABLY not caused by one incident anyway based on my looking at the cracks. The damaged planes vary from those who only landed on grass, to those that NEVER landed on grass. Getting someone to admit they regularly overloaded their plane is difficult at best.
sf3543 said:
In reading this entire thread, it is obvious that there is not enough information presented to begin to make any logical conclusions as to cause.
Don't blast VAN's for not responding until they have the data they need.
Also, VAN's may choose not to even address problems encountered by RV12s built as EAB with different engine, avionics, fuel and loading configurations.
Following are some of my observations, based on information from this thread, plus my own personal observations from my RV12, both before and after the rebuild.
Some of the affected RV12s are EABs with Viking engines installed. (I think I read that the Viking engine weighs 60 lbs more and provides 110 HP, vs the 100 HP provided by VAN's Rotax.)
How are each of the damamged planes configured? (Weight and operation have a definite effect on how a plane holds up.)
Are they ELSA or EAB?
What power plant is installed?
Any other modifications to the airframe?
What was the weight of the plane at the time of the incident? (It is easy to over gross the RV12 with a couple of hefty guys, not to mention a larger engine, extra avionics, etc., that could contribute to an over gross condition.)
Pilot technique. (Pilot competence is a subjective thing, but I have seen pilots slam down their A model RVs so hard I thought something surely had to break and later bragged about their wonderful landing techniques. Just saying!)
Building technique. (As a tech counselor, I have seen a lot of builds. Everything from beautiful to down right unsafe. Some builders don't even debur anything and expect to win awards. So, the quality of the build is an issue that should be considered, especially in critical areas.)
There are probably a few other items that need to be looked at and studied but these are a few.
I really am interested to see the ratio of RV12 ELSA vs RV12 EAB planes that have been damaged and how modifications have played a part, if at all.
I personally believe that the RV12 is designed to be what it is and shouldn't be modified, if you expect it to hold up reasonably well, but that's me. They are EXPERIMENTALs after all, but if you purposely, or accidentally, exceed the manufacturer's design limits, you will likely have problems. However, you can easily exceed design limits by rough handling, as in very hard landings or consistent rough use, as well as by changing equipment. It happens all the time to all kinds of planes.
At any rate, I am interested to see more data, if the owners are willing to provide it, and maybe a little less bickering. Eventually, we will find out what is causing these issues so they can be overcome. Petitioning the owners to fill out their forms for VAN's is probably the best way to get to the bottom of it.
Click to expand...
 
I have already said what I had to say , but would just like to add that we're all on the same team here gang, and are making progress in spite of us. Maybe we need to lighten up on one another and remember that while we may have small differences in how we contribute we all contribute to moving along to the best conclusion.
Dick Seiders
 
Just inspected my plane. Let's call her "Geico". :rolleyes:

265 hours TT, E-LSA
Removed the wings, no deformation on side skins.
Inspected the gear bolt nuts, no cracks visible.
Inspected brake lines, no deformation.

No "hard" landings, several cross wind landings exceeding 15 MPH. I dip one wing until that wheel touches to stop drift. Doesn't seem to mind side loading.

I would say moderate braking once in a while to make a taxi way. Never wheel hop or skidding, just solid braking in a straight line using both brakes evenly.

Rarely fly off grass.
 
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One More

I had posted photos of two of the three cracked center channels, here is the third one:
2jdga43.jpg
[/IMG]
 
Coincidence?

Looking back over the admittedly few reports and photos in this thread it seems that the buckled skin/crushed brake line compression damage has all occurred on the right side of the aircraft.

Have there been any reports of this particular combination occuring on the left side? If not, then it might be reasonable to add the load from a tank of fuel sitting on the right baggage floor to the possible list of contributing factors that others have already mentioned.

One other possible factor in all this is additional back-stick aerodynamic down load on the stabilator early in the landing run. Add in some bounce from a rough surface and some heavy braking and I'm guessing there could be some significant stresses generated on the airframe in that area.

Just some thoughts.
 
speculation

Or maybe because most people are right handed and would press harder on the right break ? ( Causing the Skip )

speculation

rgmwa said:
Looking back over the admittedly few reports and photos in this thread it seems that the buckled skin/crushed brake line compression damage has all occurred on the right side of the aircraft.

Have there been any reports of this particular combination occuring on the left side? If not, then it might be reasonable to add the load from a tank of fuel sitting on the right baggage floor to the possible list of contributing factors that others have already mentioned.

One other possible factor in all this is additional back-stick aerodynamic down load on the stabilator early in the landing run. Add in some bounce from a rough surface and some heavy braking and I'm guessing there could be some significant stresses generated on the airframe in that area.

Just some thoughts.
Click to expand...
 
I had noticed that as well, but cannot put a cause to that effect. This may be of value in deciding just why it is happening. Some sort of instinct that makes us brake harder to the right than to the left? Puzzling to me..

rgmwa said:
Looking back over the admittedly few reports and photos in this thread it seems that the buckled skin/crushed brake line compression damage has all occurred on the right side of the aircraft.

Have there been any reports of this particular combination occuring on the left side? If not, then it might be reasonable to add the load from a tank of fuel sitting on the right baggage floor to the possible list of contributing factors that others have already mentioned.

One other possible factor in all this is additional back-stick aerodynamic down load on the stabilator early in the landing run. Add in some bounce from a rough surface and some heavy braking and I'm guessing there could be some significant stresses generated on the airframe in that area.

Just some thoughts.
Click to expand...
 
Whoops, scratch that last post, in going back over the furnished photos I found this. This one happened on the LEFT side:
23mk1f6.jpg
[/IMG]
 
Maybe, but I'm doubtful. There could be a tendancy for right handed people to brake a bit harder on the right, but you'd quickly ease up when you started to drift off the centreline and found yourself heading for the trees. Hands up any left-handed pilots who have right side damage.
 
Another point to ponder, is the effects on braking. Almost all suffered a total closure of the brake line, meaning the brake is locked full on - or you have NO brakes on that side. You just got it on the ground after a wild landing that bent the leg back - and now you have no braking control and maybe do more damage because of that. I think I will bend my brake lines down under the leg to preclude that from happening.
wkkdqq.jpg
[/IMG]
 
Another report - -

Looked at mine this morning. Saw nothing. Did not scrape paint off, but I think something would have shown. I have landed on turf maybe 6 - 8 times total. Normally don't brake much due to long runway we have now, and turn-off is about mid-way.

John Bender
430.6 hours
 
Further investigation 519

Took the wings off this morning and there was quite bit of damage on the right side only. Internally not too much damage but found the outside bolts holding the gear legs had all come loose. I could give each at least 3 full turns and i am sure they were tight and torqued before. No cracks in the channel.
Did some repair work and carried out some landing tests with a buddy with binoculars.
On the paved runway no problem even at firm braking.
On the grass strip he could see the wheels shaking back and forth when the brakes are used. The constuction as it is does however NOT allow any movement in that sense.
I am convinced this is what happened. I landed on a short downsloped grass strip and had to brake very firm to prevent dropping off the runway end.
I did not check the skin at that time.

Looking at the construction the gear legs can bend up and absorb shocks in vertical sense, but there is no way these legs can take any longditudinal forces. These can only rotate the channel beam and transmit the force into the side skin which will easily mess up.
These forces do occur on a not too flat grass strip and will be much worse when braking.

It will in my opinion the construction will cope well with a hard landing creating only vertical forces.
If you do not flare which will also create longditudinal forces the nose leg will be wiped away first.
I do not believe hard landings are the cause of this.

I looked at various landing gears and saw that often a tube is used like the nose leg which can absorb londutudinal forces by bending.
Another one with our type of legs used a vertical hinged wheel with a damper giving the same effect.

The forward aft rigidness of our legs will some time break things i think unless you always land on a paved runway and do not use the brakes on grass strips. Unfortunately you will have to brake some time or another.

I hope VAN's will look into this important issue but sofar i did not get any respons to my mails. Also requested to mail the ASME reporting form which I never received.

This issue worries me a lot and looking at the number of planes having this it requires urgent attention
 
I am understanding why grass strips will be more bumpy and have more vertical loading potential. I am not understanding why braking on grass vs paved is different and would create more fore-and-aft flexing in the gear. Can someone explain? I am putting in a (short) grass strip for use next year.
 
I have come to pretty much the same conclusions with the little information we have so far.
Of note however, one plane with the cracks in the center channel, has never once landed on a grass strip!
 
OK - a request

I am not any kind of engineer not have I slept in any hotel or motel for a few year or so - but it is clear to me that there needs to be an improvement made to the fuselage structure of the RV-12.

I would like Van's to take a proactive approach to this obvious problem. Surely someone at the Van's engineering department could figure out a fix for this 'problem'. Maybe an internal doubler?

As one who has not yet built the fuselage, I would like to see Van's offer me some sort of beef-up for the main landing gear area that I can install as I build my fuselage or do ?????

And leaving those who have experienced this type of bent skins are currently left to their own devices to try to 'fix' the damage. No matter how the fuselages were 'bent', it would be good if Van's could suggest ways to 'fix' the damage.

I think that it is a safe bet that there are other RV-12s out there that are flying that have suffered the same result of some sort of landing or breaking 'incident'. Not all RV-12 owners have ever heard of the VAF and many have not ever pulled their wings off for whatever reason.

I am not a better pilot than those who have suffered this type of damage so I need a 'fix' that I can include into my build.

This is a plea for Van's to make the RV-12 better and safer. This, I hope, will happen before the 'regulators' ground the RV-12 fleet.
 
E. D. Eliot said:
This is a plea for Van's to make the RV-12 better and safer. This, I hope, will happen before the 'regulators' ground the RV-12 fleet.
Click to expand...

Let's don't assume that Van's "officially" monitors this forum just because one of their employees does. Best to ask that kind of question directly to them. A registered letter might be more effective than email in getting their attention.

I've heard more than one of Van's people referring to VAF as "chatter". In a perfect world I would think it would be helpful to Van's and us if they would monitor VAF as a source of their customers' thoughts and/or concerns, we all might learn something.

.
 
E. D. Eliot said:
I am not any kind of engineer not have I slept in any hotel or motel for a few year or so - but it is clear to me that there needs to be an improvement made to the fuselage structure of the RV-12.

I would like Van's to take a proactive approach to this obvious problem. Surely someone at the Van's engineering department could figure out a fix for this 'problem'. Maybe an internal doubler?

As one who has not yet built the fuselage, I would like to see Van's offer me some sort of beef-up for the main landing gear area that I can install as I build my fuselage or do ?????

And leaving those who have experienced this type of bent skins are currently left to their own devices to try to 'fix' the damage. No matter how the fuselages were 'bent', it would be good if Van's could suggest ways to 'fix' the damage.

I think that it is a safe bet that there are other RV-12s out there that are flying that have suffered the same result of some sort of landing or breaking 'incident'. Not all RV-12 owners have ever heard of the VAF and many have not ever pulled their wings off for whatever reason.

I am not a better pilot than those who have suffered this type of damage so I need a 'fix' that I can include into my build.

This is a plea for Van's to make the RV-12 better and safer. This, I hope, will happen before the 'regulators' ground the RV-12 fleet.
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Amen! There are too many instances of this problem that we now have documented, to simply say 'there isn't really a problem'. There obviously is something going on. Whether the damages have shown up on the factory demonstrator or not, that proves nothing. We are seeing photgraphic proof that there is indeed an issue that should be addressed. To everyone who has had these issues, PLEASE send in the forms to Van's as suggested earlier. I am about to start on my fuselage and would like to be able to build in the fix (if Van's suggests one). I could see us (or Vans, for that matter) shrug off one or two incidents as bad landings, etc. But to have this many documented cases already showing up? Not good. And ya'll are right...there are certainly a LOT of -12 drivers out there that probably don't even know this forum exists. As an example, I met a customer of mine last week, who lives in Dallas. He's a pilot for SWA and has an RV-4 and an RV-8. He had no idea what I was talking about when I mentioned the VAF forums.

PLEASE send in your documentation forms to Vans!!!! This issue isn't going to fix itself, and my goodness, replacing those bad areas of the fuselage? That looks like a major major project.

Thanks-
 
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Dont hold your breath

I have followed a number of issues that vans has taken action on and there is a pattern , to me anyway.
In the ruptured fuel tank saga, nothing official was heard from vans for months. People reported encouraging comments made in conversations with vans staff. Eventually they came out with a fix, that is optional by my reading of the information
In the Creeping throttle problem, Vans to my knowledge issued no official fix. But I talked to staff at McFarlanes and they reported that Vans worked with them to design weaker springs that are now available from Mc Farlanes if you ask for them.
With the loose engine mounting bolts fault, Vans responded in record time with a mandatory official fix.
The pattern I see is Vans admitting nothing officially; leaking a few encouraging comments; at the same time beavering away as fast as possible to diagnose, design and test a fix; then announcing it in a way to have the least adverse affect on the product reputation
The only objection I have to that is we dont know if they are listening. Surely every report of an issue deserves acknowledgement of its receipt. Do they acknowledge?
In todays letigious world, I see Vans response as reasonable in most respects. The are not going to acknowledge a problem without a clear path to the next steps required.
So the best we can do is make sure damage to aircraft is formally reported. That report will help you too when it comes to who is to pay up for repairs from a faulty design
My hope is that Vans engineers are rapidly acquiring a -12 fuse to do load tests on, and sort out if it is the brakes, the bending moment over the MLG channel or whatever
Rod
 
I have been away from aviation for a few days to address some unrelated issues. Yesterday I got to my hangar long enough to inspect my airplane. Thankfully, no cracks, no buckled skins, no crimped brake lines. 130 hours, no hard landings, no hard braking, some grass fields.

Having reported that, let me say that I am encouraged by the change in tone of this thread. Most contributors now seem to be saying what I tried to say in my (perhaps poorly worded) post of a few days ago, and that is that the most effective way for the community to encourage Van’s to address these incidents is to notify them directly via official channels, and not depend on one of their employees reading this thread on VAF.

I fervently hope all nine, or whatever the number is, of folks who have experienced skin wrinkles or gear mount bolt hole cracks have submitted the official reports with as much factual detail as possible. How else can Van’s engineering staff analyze the situation and engineer a fix?

My thanks to all who are trying to contribute in a constructive way. Without diminishing their efforts, I must point out that there is a risk of the forum being perceived as an official reporting source, which would bypass the direct contact with Van’s. Everyone who has seen this problem, or something similar, should be encouraged to make direct contact with Van’s engineering department via the channel that has been provided us.
 
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Of course every RV12 driver/builder does not read VAF but I do. One of the reasons I do is this very issue...I get to hear about potential problems before the factory sends me a letter. I would almost bet we all ran out and checked our own channel after seeing several pics. I do not have the cracks or wrinkles and I seriously doubt if it comes from grass (why would it?). I am not talented enough to avoid making a mistake now and then but one thing I do consistently is to land the plane as slow as it will allow...which is pretty darn slow. It not only minimizes the energy transfer at impact, it allows for some outstanding crosswind landings...by the time you touch town (whatever the wind) you are all but walking. We all know a 600ft/min impact will pull the channel back like a sardine can and that a 40 knot touchdown is barely noticeable. Until there is a definitive answer, which there will be, I would practice my full flap, coordinated stalls at altitude (a real stall, not just a horn) and find a comfortable touchdown speed that is well below 60 or 70 knots.
 
Peterk said:
Of course every RV12 driver/builder does not read VAF but I do. One of the reasons I do is this very issue...I get to hear about potential problems before the factory sends me a letter. I would almost bet we all ran out and checked our own channel after seeing several pics. I do not have the cracks or wrinkles and I seriously doubt if it comes from grass (why would it?). I am not talented enough to avoid making a mistake now and then but one thing I do consistently is to land the plane as slow as it will allow...which is pretty darn slow. It not only minimizes the energy transfer at impact, it allows for some outstanding crosswind landings...by the time you touch town (whatever the wind) you are all but walking. We all know a 600ft/min impact will pull the channel back like a sardine can and that a 40 knot touchdown is barely noticeable. Until there is a definitive answer, which there will be, I would practice my full flap, coordinated stalls at altitude (a real stall, not just a horn) and find a comfortable touchdown speed that is well below 60 or 70 knots.
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And lay off the hard braking. ;)
 
For what it is worth, rest assured that the highest level at Vans has been made aware of the perceived problem and the figures. Since most don't really have a good idea of when or why it happened, that does make it pretty difficult for Vans to "cure" it. Lets hope the reporting system helps, but it appears most have not made the report.
 
My own personal, non engineer, unprofessional feeling from reading the reports given by those with damage, is that braking does seem to be the origin of the damage forces. We all do it differently, but I have always been a full flaps, coast to a stop type guy, (mainly to make the tires, brakes, and wheel bearings last longer) this may be a good practice for the 12.

.
Geico266 said:
And lay off the hard braking. ;)
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Share the load

I think the pin in the spar is adding to the problem, if this was a bolt some of the loads would transfer to the skin and ribs in front of the wing.

Also the wing ( Newton's laws of motion )

Just a thought
 
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joedallas said:
I think the pin in the spar is adding to the problem, if this was a bolt some of the loads would transfer to the skin and ribs in front of the wing.
Just a thought
Click to expand...

Joe, I'd love to see your theory be correct! For guys like me who will NEVER remove the wings, this seems like it could be a very simple solution. And if I did have to remove the wings someday? Hey, new bolts are VERY cheap compared to re-skinning and re-building the side of the fuselage. I'm sure looking forward to a resolution from somewhere. Don said very few official forms (reports) have been sent to Van's, and that is such discouraging news. What, folks will spend hours and hours repairing their damage just to see it possibly happen again? Yikes!

Like Scott mentioned (from Vans), the forms are THE way to get an issue directly on front of the Vans engineering staff. While he monitors the forums, he basically stated that this venue isn't a 'Vans raise the caution flag' outlet. The reporting form is the way to proceed.
 
DonFromTX said:
For what it is worth, rest assured that the highest level at Vans has been made aware of the perceived problem and the figures. Since most don't really have a good idea of when or why it happened, that does make it pretty difficult for Vans to "cure" it. Lets hope the reporting system helps, but it appears most have not made the report.
Click to expand...

Don, from your summary above, I'm guessing you submitted some type of a concise report to Vans, with the data and evidence you have gathered?
 
joedallas said:
I think the pin in the spar is adding to the problem, if this was a bolt some of the loads would transfer to the skin and ribs in front of the wing.
Just a thought
Click to expand...

More speculation, but my view is that the front flange of the channel is held in position fairly rigidly compared to the web and rear flange of the channel. The reason is that any tendancy to rotate the front flange of the channel will be resisted by the spar pin assembly transferring moment to the fuselage sides and the wing main spars, with the wing stub spars acting to resist the resulting imposed loads.

However, the channel web is relatively thin and much easier to bend upwards if the undercarriage leg acts as a lever under heavy braking. This will also push the aft flange up relative to the front flange, resulting in compression buckling of the skin above the channel and also in the fuselage side panel aft of the channel. The upward twist would be probably be accompanied by some rearward deflection of the end of the channel, which combined with flexing of the fuselage could result in crushing of the brake line and the vertical crease in the skin adjacent to the rivet line in front of the baggage area. This seems to be reasonably consistent with the type of damage visible in the photos. At the same time the combination of tension and rearward twist on the front bolt and channel web may account for the localised cracks around the bolt hole.

As I said, just speculation and each case of reported damage has been a little different, so take it for what it's worth.
 
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how a chain works

[
Remember how a chain works
Try pushing a chain
Look close at rivets new location in the photos
The NA of the center channel is about the top of flange of the channel + or -
all material above the NA behind the wing is in tension the material below the NA is in compression
BY adding a bolt thru the spar the material below the NA in front of the wing is in tension
you would also require a way to transfer more of the front bolt tension to the vertical flange of the channel to stop the tear through

This is my view of this problem and I will bet on it.

Added Note:
Also the momentum of the wing when stopping would add to the tension on the bolt counteracting the rotation of the channel
I Think the channel is moving away from the spar when it crushed the break line.
Take a look at the area around the wing roller bolt it should be bent







QUOTE=rgmwa;696422]More speculation, but my view is that the front flange of the channel is held in position fairly rigidly compared to the web and rear flange of the channel. The reason is that any tendancy to rotate the front flange of the channel will be resisted by the spar pin assembly transferring moment to the fuselage sides and the wing main spars, with the wing stub spars acting to resist the resulting imposed loads.

However, the channel web is relatively thin and much easier to bend upwards if the undercarriage leg acts as a lever under heavy braking. This will also push the aft flange up relative to the front flange, resulting in compression buckling of the skin above the channel and also in the fuselage side panel aft of the channel. The upward twist would be probably be accompanied by some rearward deflection of the end of the channel, leading to crushing of the brake line and the vertical crease in the skin adjacent to the rivet line in front of the baggage area. This seems to be reasonably consistent with the type of damage visible in the photos. At the same time the combination of tension and rearward twist on the front bolt and channel web may account for the localised cracks around the bolt hole.

As I said, just speculation and each case of reported damage has been a little different, so take it for what it's worth.[/QUOTE]
 
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Bent Parts

Don
I think the NTSB could tell you what happend

The true story is in the bent parts


DonFromTX said:
For what it is worth, rest assured that the highest level at Vans has been made aware of the perceived problem and the figures. Since most don't really have a good idea of when or why it happened, that does make it pretty difficult for Vans to "cure" it. Lets hope the reporting system helps, but it appears most have not made the report.
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Report

I have formally submitted a safety alert with pictures to Van's and a Philip Rivall has confirmed receipt and promised action.

I fully agree with rgmwa the reason being braking forces.
The flat legs cannot handle any shockloads of braking in longitudinal direction and there is no choice than to rotate the channel with the known results.
It seems like a bad idea in my opinion to transfer the loads to the spars as suggested.

I would tend to look for flexibility of the legs in fwd/aft direction.
These legs are perfect springs for vertical loads only and a solution could be tube legs which can bend all direction as are seen on many light aircraft.
Another one could be make the wheel hinged with a form of a damper.

Anyway I am glad Van's is taking this serious now.
 
Not being familiar with the -12 spar structure, I have a question -

How can the spar box rotate that much in the fus. structure to wrinkle the skins and not show any damage at the rear spar fus/wing attach?

I would have thought the root rib would essentially stiffen up this fus. area.
 
That is a good question. The channel we are referring to is not a spar box, it is more of a MLG box. The spar is located in FRONT of the channel, one end of the spar pin goes into the channel. Just looking it over, it would seem that the spar pin would keep it from twisting that much, but somehow it does not do that. That is why someone suggested that if the spar pin were replaced with a large bolt, it would transfer the channel twisting to the spars. Probably would stop the twist, but at the expense of twisting the spars, which could ruin your whole day.
 
This thread is getting interesting now with the thoughts and ideas concerning the cause. I am happy the acerbic comments are gone. I am very happy to hear Van's is now involved as they will surely come up with the best solution. The only problem with that process is we won't hear anything until the fix (if any) is revealed. I think it is very informative to keep the discussion going and that may help to keep the impetus at Van's at a high level to find the cause.
For my part the braking issue as described may likely have a role in the damage, or it may not. I will however keep the landings slow and where I hadn't worried too much about braking befoe I will make a concious effort to avoid any hard braking until we know more. I have made 192 landings in 141 hrs, with only four on grass, and as stated earlier inspection has revealed no signs of any of the issues at this point.
Dick Seiders 120093
 
This is happing through the skins.

Jack
If the forward motion of the wings would not transfer to the landing gear then the wings would keep going.

This is happing through the skins now.

the statement ( It seems like a bad idea in my opinion to transfer the loads to the spars as suggested ) this is a misunderstanding of what I said.

There is no question the F-1204 assembly ( at the bottom of the channel ) moved back from the spar or the break line would not have damage.


Hotscam said:
I have formally submitted a safety alert with pictures to Van's and a Philip Rivall has confirmed receipt and promised action.

I fully agree with rgmwa the reason being braking forces.
The flat legs cannot handle any shockloads of braking in longitudinal direction and there is no choice than to rotate the channel with the known results.
It seems like a bad idea in my opinion to transfer the loads to the spars as suggested.

I would tend to look for flexibility of the legs in fwd/aft direction.
These legs are perfect springs for vertical loads only and a solution could be tube legs which can bend all direction as are seen on many light aircraft.
Another one could be make the wheel hinged with a form of a damper.

Anyway I am glad Van's is taking this serious now.
Click to expand...
 
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Reports

I had lots of further questions from 3 different Van's engineers about my safety alert report which I will try to answer.

To my surprise however They tell me I am the ONLY ONE who did send this.

I read about 9 cases sofar so if you want this to be dealt with in a serious way send the ASME form and photo's !!!!!
 
DonFromTX said:
That is a good question. The channel we are referring to is not a spar box, it is more of a MLG box. The spar is located in FRONT of the channel, one end of the spar pin goes into the channel. Just looking it over, it would seem that the spar pin would keep it from twisting that much, but somehow it does not do that. That is why someone suggested that if the spar pin were replaced with a large bolt, it would transfer the channel twisting to the spars. Probably would stop the twist, but at the expense of twisting the spars, which could ruin your whole day.
Click to expand...

I think the spar pin DOES effectively stop the front flange of the channel from twisting. The twist is mostly occurring in the horizontal web and rear flange, and it's the resulting upward movement of the rear flange that is causing most of the damage. I also agree with Joe that there is some horizontal movement or flexing occurring in the system to cause crushing of the brake line and the vertical creases near the rivet lines.

The wing spar can slide fore and aft on the pins if forced. I believe this is the reason why there is no damage to the fuselage in the rear stub spar area that Gil queried. The fore/aft movement is occuring in the fuselage between the main spar and the rear stub spar. The photo in post #114 seems to show some bending of the skin at the front of the main spar opening that could be caused by the main spar contacting the skin as the channel is forced backwards by the braking load.

However, I believe that most of the buckling damage that we see is due to vertical movement of the rear flange of the channel as it twists. Joe's proposal of replacing the pin with a bolt would stop the fore-aft sliding of the spar, but not the rotation of the channel. The resulting buckling and loss of stiffness of the fuselage would still occur, but would now result in some load being transferred to the fuselage in the rear stub spar area, causing problems there.

Again, these amateur attempts at forensic engineering are just that. We should leave the real work of analysis and the design of a solution to the engineers at Vans.
 
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Schematic?

Would there be an RV-12 schematic available for us non-12 guys to see as to better understand the structure involved?
 
Jerry Cochran said:
Would there be an RV-12 schematic available for us non-12 guys to see as to better understand the structure involved?
Click to expand...

Here's another one
http://vansaircraft.com/pdf/revisions/RV-12/23-03.pdf

The spar pins go through those two bushings you can see. One in the front flange of the channel, and the other in the vertical post assembly. The gear legs are bolted to the underside of the channel. The rear stub spar housing is that semi-circular riveted piece on the larger aft bulkhead.
 
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