Gerard,
Have you turned in the part for an engineering assessment, perhaps to Van’s? Are you relaying Van’s engineers’ direction to suspend the SB? That failure is pretty notable, and I’m glad you two are OK, but I would caution folks against simply ignoring a standing bulletin without getting a solid engineering assessment into why that happened.
An important reminder from the original poster to all RV6 and RV6A owners, many who are new to their aircraft, to verify the status of SB 99-6-1.
Although the SB provides the option to inspect the overhead rudder pedals every 10 hours, and explains how to inspect them, it is a much better course to repair or replace them per info in the SB.
I built my RV6 and have been flying it for 25 years. I replaced my overhead rudder pedals soon after the SB was published and inspection required replacing them. Ordered from Vans and several hours later the new pedals were installed.
I was at Van's for the static testing of rudder pedal assemblies that we did after we first became aware of a weldment failure, and when this SB was issued.
An SB issued by a kit manufacturer has no regulatory basis. An owner can choose to totally ignore it if they like. The compliance time / method is often chosen by us to imply a level of urgency, but to also give some latitude for aircraft repositioning to have the work done by someone else, scheduling of that work, etc., but as already mentioned, it is some what a moot point because there is nothing regulatory about compliance with an SB on an experimental.
The failure noted in the attached photo is nothing like the actual original failure that the gussets prescribed by the SB were designed to prevent.
The gussets might have prevented this failure if they had been installed, because they do change the load distribution, but this failure mode is not the same.
The actual failure mode being prevented by the addition of the gussets was a buckle failure on the side of the tube loaded in compression under load from high foot pressure. That is why the gussets are added to only one side of each tube, and why some are on the fwd. side, and some are on the aft side (depending on which side of the tube is highly loaded in compression when rudder / brake pressure is applied).
The following is my opinion based on experience and a bit of logical reason thrown in for good measure....
I do not think this failure occurred within the span of 10 flight hrs (Reasons described below). An inspection may have been done, but I think evidence of already existing damage was missed.
One piece of info (if known) that would support my opinion is knowing what the total time in service is.
Since the airplane has ungusseted weldments, it is likely an older build (finish kit predating the issuance of the SB in 1999) which has probably accumulated quite a few flight hrs without a failure.
If the failure has occurred through just the past 10 hrs, there would have to be something that changed in the operation of the airplane very recently that made the assembly fail now but not long ago.
I know that the current owner recently purchased the airplane. An RV changing ownership usually results in an investigation of applicable SB's and whether they were complied with.
It is entirely possible that the original builder (and possibly prior owners, if there was more than one) didn't know about the SB and had never inspected the rudder pedal assemblies for this type of failure.
If that were the case, the crack that ultimately cause the failure could have been propagating for quite some time.
Couple of side comments to the main subject-
Painting any welded assembly a dark color (black would be the absolute worst choice) is a very bad idea. It makes cracks just about impossible to visually detect. That is why we have always used very light grey or white for the color on all of our powder coated parts.
Inspection of welded assemblies like the rudder pedals is something that should be done with a high level of scrutiny during a condition inspection. An SB like this is issued to highlight an area that has become know to potentially develop a problem, but in reality it should already have been being inspected.
Primary point there is that just because an SB has been physically complied with, doesn't mean that you don't need to inspect that area any longer.
Scott,
What a well-stated comment. To me the biggest take-away is that the part appeared to have failed in a manner completely outside the failure mode addressed by the SB. Another reason for RV-6 drivers to NOT disregard the SB (as the OP so urgently urges).
Since this part failed at the weld, I’m curious to know whether there is a history of such failures? I can’t tell if the cross tube was internally primed, which is supposed to decrease the chance of corrosion developing at the weld.
Too bad there isn't a way to have a "Tell Tale" incorporated into the system to give a heads up that an overload may have been experienced...
Scott, if possible can you say how much load was applied during the testing to achieve a failure?
Scott,
What a well-stated comment. To me the biggest take-away is that the part appeared to have failed in a manner completely outside the failure mode addressed by the SB. Another reason for RV-6 drivers to NOT disregard the SB (as the OP so urgently urges).
Since this part failed at the weld, I’m curious to know whether there is a history of such failures? I can’t tell if the cross tube was internally primed, which is supposed to decrease the chance of corrosion developing at the weld.
Scott,
What a well-stated comment. To me the biggest take-away is that the part appeared to have failed in a manner completely outside the failure mode addressed by the SB. Another reason for RV-6 drivers to NOT disregard the SB (as the OP so urgently urges).
Since this part failed at the weld, I’m curious to know whether there is a history of such failures? I can’t tell if the cross tube was internally primed, which is supposed to decrease the chance of corrosion developing at the weld.
good. issue the revision and move on.
Got the email from Sterling at Van’s today (been busy picking up an airplane) that the update is in!
I’m Satisfied!!
Also, even though compliance is not mandatory (as with a certified AD), I implore you!! Make the Repair or Swap.
https://www.vansaircraft.com/service-information-and-revisions/sb-99-06-1/
Im the OP who started this thread and swore I’d see this through!!
Smak
The wisdom from local engineers who have looked at the part is that the weld was not "normalized" with heat and this weakened the Torque tube (crystalizing some of the internal metal) which was the point of failure, NOT the weld itself which is entirely intact.
Smak
I made a 90 right on Taxi out, felt something, let's say "weird" and thought it was just the tailwheel taking a bit to recenter. I made a Full Control Check just before takeoff and that's when the right pedal stayed full forward. I now believe the one side/arm snapped off with that first 90 right and the second broke loose with the control check. About 500 hours on a '96 kit completed in 2001.
...
Put the new pedals on!
Smak
The actual failure mode being prevented by the addition of the gussets was a buckle failure on the side of the tube loaded in compression under load from high foot pressure. That is why the gussets are added to only one side of each tube, and why some are on the fwd. side, and some are on the aft side (depending on which side of the tube is highly loaded in compression when rudder / brake pressure is applied).
The instructions I got with my gussets don't talk about installing some on the aft side of the pedals. Seems that all the pedals would be loaded in compression on the forward (firewall) side. Can you clarify how some of the pedals could be in compression on the aft side and which ones need the gussets installed on that side, please?
The outer pedals are loaded in compression at the aft side when the inner pedal on the opposite side is pushed. For example, when the pilot pushes the right pedal (and its forward side is in compression) the torque is transferred via the long tube to the right pedal on the co-pilot side, where the rudder cable is attached. The "pull" from the rudder cable puts a compression force on the pedal aft side.
The instructions that came with the gussets that I got specified installation on the forward side only, so that's what has been done. I expect (and hope) the gussets will strengthen the joint whichever side they are welded. I vaguely recall (so may be wrong!) that there might also be some conflict with installing the finger patches on the same side as the tabs for the brake cylinders.
p.S. My weld joints were 100% rock solid. I think they were purchased over 10 years ago but I just got the kit flying a year ago so they only had about 140 hours on them.
Charlie