Loose Main Gear Legs

rvbuilder2002 said:

Gary, I have already answered this question (to you personally during a phone conversation). Yes it is being looked at. It would be more productive if more people would provide the data download from their D-180's.

I don't think I said anything in my post to imply otherwise. I was simply commenting on the "it sure is surprising" comment.

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Yes, thank you for the reply! Just making sure that nothing has changed since we had our telephone discussion. That's excellent news.

I too, hope that besides the notification forms to Vans, that folks will be willing to submit crucial D-180 info. I can see how this helps TREMENDOUSLY from an engineering standpoint. In the future, perhaps this data will help us all as a result of your findings.

Thanks again for keeping an eye on the forums, and for giving us continual data from the mothership. It is appreciated when us builders (and already flying -12's) know that folks are listening & working on this in Aurora!

N712BK Safety Alert Update

On my old Laptop I found a Dynon datalog_min_max data log dated 10/8/10. The data log starts on 4/19/10 which is N712BK first flight. The max ?gz? value is 1.25. On 5/5/10 the data log shows a max ?vz? of 2.375. This is the same value that I get from the 9/16/12 min_max data log. Assuming that the scaling is correct I interrupt this to show my hard landing was 2.375 vertical g?s. This is preliminary since there are other parameters in the min_max data log file that don?t appear to have credible values, i.e. airspeed shows a value of 497.625. I sent Van?s the 9/16/12 min_max data log with my original RV-12 Safety Alert and will send Van?s the newly found 4/19/10 min-max data log this evening. I looked at the 10/8/10 data log and it does not have data back to my 5/5/10 flight. For those of you that have had a problem similar to mine I would encourage you to look at your Dynon-180 data log files to see what your max ?vz? value was. In my e-mail to Van?s I will ask them to confirm the scaling for ?vz?. What would really give Van?s even more information would be the Dynon-180 data log file that would have values for ?vz? at 1 second intervals. Thanks to Pete and Marty for their inputs to my Safety Alert write-up. Marty also tutored me through the process of posting photos on the RV-12 forum. I indicated to Van?s that I will not re-install the wings in the event that they want additional photos. My RV-12 is hangared at Grand Prairie Airport (KGPM) and I would encourage anyone interested to give me a call (817) 223-1396 (cell) and we can set up a time for you to look at N712BK with the wings off. The wings cover up most of the skin damage and with the fairings on you cannot see any of the wrinkles or the dented brake line.

To anyone with a flying RV-12 please download you?re your Dynon-180 or Skyview data logs and check out ?vz? on your min-max data log. Post your ?vz? value and we may be able to bracket the ?vz? range where the wrinkled side skin starts. I would also suggest that all flying RV-12 owners check their outer landing gear bolts. If the bolt turns with the nut when you apply a ? inch wrench, then I would think you have a problem and report it. Let?s give Van?s some help!

Scott,

Thanks for your follow-up answer on landing gear testing procedures. It was very helpful.

-Dave

Bob Kibby said:

On my old Laptop I found a Dynon datalog_min_max data log dated 10/8/10. The data log starts on 4/19/10 which is N712BK first flight. The max ?gz? value is 1.25. On 5/5/10 the data log shows a max ?vz? of 2.375.

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Thanks Bob

This sort of detail is helpful.

One comment regarding the data collection just so there is no confusion, and people don't accidently jump to any conclusions.....

1 second intervals is actually quite a long time when it comes to recording a peak instantaneous G load in a situation like we are looking at. We can not assume that the max. value anyone has recorded in there D-180 is the actual max. that the airplane has experienced in a hard landing (the peak could have a duration of only 1/10th of a second or so, which could be missed by the data recorder). Having said that, every piece of info we can obtain, is still worth looking at.

Channel update...

Back in post #226, I noted that the milled flange holes for the outboard bolts in my channel were not quite flush with the top surface of the channel, leaving a small step which cut across the bolt holes. The step measured about .02" high and cut into the hole about .03"-.04", leaving a small but visible scallop in the edge of the hole.

I contacted Vans, and they checked more than 20 channels in two separate batches in their current stock and couldn't find one that wasn't perfectly flat. In my case they suggested just filing it flat, which will be easier said than done as there's very little room to move in there with the channel already in the fuselage.

Anyway, maybe mine was a one off, or maybe there are some other earlier kits out there with the same feature. I'm not saying that this would necessarily have caused any problems in the long run, but clearly the washer and nut should bear uniformly on a flat surface to avoid any undesirable stress concentrations around the bolt hole. Maybe this could have been a factor in some of the reported cases of cracking, maybe not. I don't know, but something to keep in mind.

Robert
I Received my Fuselage kit on 06/28/12 and the bolt seats on my F-2014 center section are also above the inside plane of the channel Looks like more than .02 to me. I will measure it tomorrow with a straight edge and feeler gauge.
Filing this flat seems like a bad idea to me, getting this perfectly flat with no scratches in that location looks impossible to me.
I'm thinking about a larger washer with a high strength non-shrinking grout under the washer, something like JB Weld.
I would like to see what vans comes up with first.

rgmwa said:

Back in post #226, I noted that the milled flange holes for the outboard bolts in my channel were not quite flush with the top surface of the channel, leaving a small step which cut across the bolt holes. The step measured about .02" high and cut into the hole about .03"-.04", leaving a small but visible scallop in the edge of the hole.

I contacted Vans, and they checked more than 20 channels in two separate batches in their current stock and couldn't find one that wasn't perfectly flat. In my case they suggested just filing it flat, which will be easier said than done as there's very little room to move in there with the channel already in the fuselage.

Anyway, maybe mine was a one off, or maybe there are some other earlier kits out there with the same feature. I'm not saying that this would necessarily have caused any problems in the long run, but clearly the washer and nut should bear uniformly on a flat surface to avoid any undesirable stress concentrations around the bolt hole. Maybe this could have been a factor in some of the reported cases of cracking, maybe not. I don't know, but something to keep in mind.

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For what it is worth, my holes on the right side are cut leaving an offset that way, but the left side appears to be flush with the bottom of the channel.

G Loads??

We've been ascribing the wrinkled skin cases (very few) to hard landings, even though it seems very hard to see how the gear could move aft far enough (at least 1/2 inch in my case) to crimp the brake line. I was playing around this evening doing steep turns, stalls, chandelles, etc. (all within the definition on non-aerobatic) and noted two things:

1) speed builds up to the top of the yellow arc very quickly going downhill, well above manuvering speed and

2) as we all know, the -12 rolls very quickly and easily; the higher the speed the greater the roll rate.

If I've read correctly, most of the damage seems to be on the right side, where you'd expect the most stress to be in a rolling pullout to the left, the way most of us would do it with the left hand on the stick. The stab is carrying a large down load to pitch the nose up while the vertical is carrying a large load to the right to push the nose left. Rolling pullouts impose the maximum loads on the empennage and fuselage. I was working in the USAF Structures Test Lab during a test to see why a B-58 had shed its vertical tail in flight. When we applied the loads for a left rolling pull-up, sure enough the tail/upper aft fuselage separated (broke off the the right) before the calculated limit load was applied.

It would be very helpful to know if the pilots of the damaged airplanes had been doing any maneuvering, stalls, or even flying in very bumpy conditions before noting damage to the fuselage. You wouldn't have the exceed the airplane's positive/negative G limits if in fact positive G's were accompanied by rapid roll at the same time.

Not saying, just thinking. To me fuselage deformation due to combined application of vertical and lateral G loads seems more reasonable than just due to vertical loads of a hard landing-- especially a "soft" hard landing.

Is it possible to find out what the pilots were doing before the hard landings? Again, I'm not even implying that anyone would have been exceeding the roll/pitch limits for non-aerobatic flight.

Wayne 12024/143WM (35 years as a conceptual design engineer at WPAFB and a year as co-op student in the Structures Lab)

A few more thoughts

A few more thoughts
The fuel tank on the right side of the aircraft adds weight and stiffness right behind the spar.

If the channel is rotating back ( back flange up 70% front flange down 30%) most of the stress would be at the front of the fuel tank.

The left side would have a larger area to flex and absorb the loads

A skin doubler from the back of the spar about 12" back and the size of the wing rib on the outside would add a strength to this section and would not be visible behind the wing.

And in my view the channel is rotating.

I will not rivet this area on my side skins until vans reports their findings,

And for the people that have damage removing the rivets in this area, taking out the wrinkles with a body dolly and a hammer and installing the skin doubler should be easy.

One more case of loose bolts

A friend with an RV-12 that he purchased from another builder stopped by Friday. We looked his airplane over pretty carefully, and found the outboard bolts loose. The airplane only has 40 or so hours on it.

When I put my gear on I torqued all the bolts. Several months later before certification I was doing my condition inspection prior to the DAR inspection and found the outboard bolts needed about a turn. I chalked it up to my carelessness then, but after about 30 hours flying and seeing this thread I checked them again and got a little less than a turn. Not sure what it adds to the discussion, but thought I would pass it on.

Hope you found help

Good to see your post Rick! I remember during my visit to Phoenix you were trying to figure out, and not looking forward to it, how to re-torque those bolts.
Do you use the torque value assigned to the size of the bolt as listed by Vans and also the torque table in the Aircraft construction book?

Another "step" in the gear channel

I decided to measure the depth of the step in my as-yet-uninstalled main gear carry thru channel. This is the discontinuity at the edge of the outer bolt holes that has been discussed elsewhere on this thread. Using a digital micrometer, mine came out to .0125. That's twelve thousandths, not "about two" as I've read recently. Since this occurs literally within the radius of the bolt hole itself, it's not acceptable. In fact, any discontinuity within the radius of the washer is a problem in a highly stressed assembly like this. I haven't done a finite element analysis on the loads, but if the load path actually reverses (bolt loaded to one side by the step geometry, then reverse loaded under landing impact), my old engineering professor would probably forecast stretched bolts and cracked channels. Hmmmm
...and yes, I'll report it to VANs
See picture:

Pat,

I wish I could say the torquing was precise, but it was just whatever I could get in that tight space.

I hope you get flying soon.
Rich.

Bolt Torque

Torqued the bolts tonight after 14 hours of flying and the inner 3 bolts didn't move.
The outer 2 moved between 1/2 and 3/4 rotation each.

gear bolts loose- bolts a bit long?

I have not been following the forum quite as regularly recently but I saw this topic and wanted to share what I found on my RV-12 during last year's condition inspection. I have not reviewed every post but I did not see this referenced.

I also found several of my bolts were loose during the inspection, despite having torqued them appropriately during construction. Upon closer examination and after trying to re-torque them, it became obvious that the nut/washer was bottoming out on at the end of the threads- so while it appeared as though the nut had been torqued appropriately when a wrench was held in place on the bolt, the bolt would still turn. I cannot rule out that this was the case during initial construction, as I had a firm hold on the bolt while tightening the nut. I solved this issue by simply adding a second washer to each bolt and with that addition, was able to appropriately torque the bolt to specs and eliminate any looseness of the bolt.

I did see a mention of potential stretching of the bolts- not sure how likely this is or if the bolt is just on the edge of being a bit too long.

In any event, I wanted to raise this because I wonder if this is the reason a number of builders are finding bolts loose at their condition inspections.

Jeff

jte65 said:

I have not been following the forum quite as regularly recently but I saw this topic and wanted to share what I found on my RV-12 during last year's condition inspection. I have not reviewed every post but I did not see this referenced.

I also found several of my bolts were loose during the inspection, despite having torqued them appropriately during construction. Upon closer examination and after trying to re-torque them, it became obvious that the nut/washer was bottoming out on at the end of the threads- so while it appeared as though the nut had been torqued appropriately when a wrench was held in place on the bolt, the bolt would still turn. I cannot rule out that this was the case during initial construction, as I had a firm hold on the bolt while tightening the nut. I solved this issue by simply adding a second washer to each bolt and with that addition, was able to appropriately torque the bolt to specs and eliminate any looseness of the bolt.

I did see a mention of potential stretching of the bolts- not sure how likely this is or if the bolt is just on the edge of being a bit too long.

In any event, I wanted to raise this because I wonder if this is the reason a number of builders are finding bolts loose at their condition inspections.

Jeff

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Hey Jeff, I was just checking out your build site. Good stuff! Hey, where did you purchase the blue coiled air hose, coming down from the ceiling of your shop? It looks much more pliable than the one I have (the standard yellow ones you see everywhere). Thanks.

Van's Engineering Status Report

If you have not seen this already please read this update on the progress on testing of a fix for the landing gear issue.

http://www.vansaircraft.com/images/open/RV-12 landing gear update.pdf

Another Gear Leg Inspection Completed

Finished my inspection yesterday. I currently have 62 hours over 2 years- many landings, including a couple different grass strips.

Firstly, I confirmed that my outboard bolts were tight prior to removal- I could not turn them at all and they were fully seated.

No wrinkling of the side skins. Removed the brackets and chamfered the corners as per the SB. No cracks visible around the holes. Reinstalled and retorqued exactly as the SB instructs.

Jeff