Video: Van's Engineering Laser-Cut Parts Detailed Analysis and Results

[greghughespdx]

LINK: https://www.vansaircraft.com/2024/0...ing-analysis-and-results-for-laser-cut-parts/​

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The Van’s Aircraft Engineering team has recorded two presentations related to the acceptability, use, and testing results of laser-cut parts in RV aircraft. The videos include an 18-minute summary presentation with an introduction by Dick VanGrunsven, as well as a highly-detailed, 2-hour presentation by the Van’s Engineering team. These presentations have been made to groups of civil aviation authorities as well as a group of kit industry experts.​

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In short, the results of extensive testing of laser-cut parts manufactured for Van’s Aircraft shows that the parts are safe for use in aircraft construction. Van’s Aircraft worked with a third-party professional company that specializes in fatigue and materials testing in the design and execution of its test program, which included the same tests being run at both companies to validate methodology and results. Van’s has applied a significant engineering margin to the test results, assuming the combined worst-case scenarios in terms of fatigue and aircraft operational usage. Specifically:​

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• Calculations related to aircraft and part lifetimes were made using worst-case conditions, evaluating dozens of variables.
• Aircraft usage calculations assume that the airplane is flown 30 minutes of each hour at full aerobatic air show loads, and the remaining 30 minutes of each hour at flight-school loads; this represents an effectively impossible use case, but ensures the calculations more than cover any possible realistic use of the aircraft.

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Given these extreme calculations, the aircraft’s lifespan is considerably higher than would be expected for an RV aircraft and is considerably longer than any flying RV. When calculating for actual, typical use the lifespan is many multiples greater than for any RV.​

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If, after viewing the below videos you have questions that have not been answered, please feel free to submit them via the form at the end of the web page on the Van's site. The Van’s Aircraft engineering staff will answer commonly asked questions during January, and we will post some of the more common questions and answers as they are compiled.​

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https://www.vansaircraft.com/vans-engineering-laser-cut-parts-presentations​

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[Paul Thomas]

I've only watched the short video and it is very informative. The big takeaway -- which was published earlier but I forgot -- from the study is that you should get cracks from fatigue before the crack (notch) from the laser cut hole propagates into a crack.

The more I think about that, the more questions I have. I'll have to watch the whole video.

 

[greghughespdx]

I've only watched the short video and it is very informative. The big takeaway -- which was published earlier but I forgot -- from the study is that you should get cracks from fatigue before the crack (notch) from the laser cut hole propagates into a crack.

The more I think about that, the more questions I have. I'll have to watch the whole video.

After you've watched the long-form video, please do send us any questions that remain. That invitation goes for anyone, of course. There's a form on the web page linked in the original post where you can submit questions.

 

[Jckeenum]

Well, I'm convinced! Can you ship me my finishing kit already.

 

[rv6ejguy]

Greg, thank you for publishing the long video. Most comprehensive and informative.

Viewing tip- watch at 1.5X speed and you can slow to normal speed when you reach an area of high interest.

 

[Tewbert]

Quick build kits

Is this why Vans is not replacing quick build kits? It seems there is conflicting information. Red/ yellow parts should be replaced but if you’ve already installed those parts you’re good to go? I have no intention of rebuilding wings/ailerons and flaps that I paid Vans to build.

 

[PhatRV]

I only watched the short form presentation video. I feel a lot more confident that my RV will withstand the test of this novice builder and the test of time.

The screen grab is the chart is what I was looking for to find out the residual strength of the airframe after over 10,000 hours on an airframe that has been subjected to an airshow aerobatic load for 1/2 of its life. The single highest rivet load is still less than the residual load while the rest of the airplane is a lot less than this. I don't fly my RV this hard or fly this many hours if I fly for over 20 years.

 

[gotyoke]

Question to Greg and the Van's team: will Section 5 be further updated to reflect the findings of the engineering assessment? I will submit this question on the web page too.

 

[Bullpup]

Question to Greg and the Van's team: will Section 5 be further updated to reflect the findings of the engineering assessment? I will submit this question on the web page too.

Seconded! I've been accused of doubting the engineering assessment, but my only issue was with the now conflicting guidance. So long as I have build instructions which clearly identify which cracks are acceptable, and where, that will go a long way.

Anyone still going to deburr dimpled holes on non-red parts?

 

[AeroEngineer]

The screen grab is the chart is what I was looking for to find out the residual strength of the airframe after over 10,000 hours on an airframe that has been subjected to an airshow aerobatic load for 1/2 of its life. The single highest rivet load is still less than the residual load while the rest of the airplane is a lot less than this.

I think you’re using this term incorrectly. “Residual strength” refers to the strength of the structure after fatigue cracks form and grow. Until fatigue cracks start growing, the strength of the structure (even after many thousands of hours of aerobatics) does not go down (unless you have corrosion, or impact damage from hail, or other problems).

What that graph shows you is that, if a rivet sees ~150 lbs of load during each limit-load event (e.g. 6g pull-up), then you can expect fatigue cracking around that rivet possibly as soon as 13,000 hours (with all those layers of conservatism they talked about: loads purely in-plane with no prying/peeling, the lowest outlier e.g. most poorly manufactured hole out of dozens tested, and more aerobatics than anyone realistically does, i.e. In real life it would be a lot more than 13,000). And that 150-pound number represents the most highly-loaded hole in an RV; All the other rivet holes see loads that are at least slightly lower, so they can go many more hours before fatiguing.

Edit: In other words, that graph does not show “strength capability decreases over time”. What it shows is “Depending on how much of the strength capability of each hole is realistically needed - and, for most holes, it’s not much - here’s how many flight hours you can fly before there is any deterioration in strength in the material around that hole”. If most holes only see 100 to 120 pounds of load - and that, only during a 6g pull-up - then the material around those holes should be able to last well over 100,000 hours before they show any sign of fatiguing, according to the graph.

 

[scsmith]

Is this why Vans is not replacing quick build kits? It seems there is conflicting information. Red/ yellow parts should be replaced but if you’ve already installed those parts you’re good to go? I have no intention of rebuilding wings/ailerons and flaps that I paid Vans to build.

So don't bother to replace them! The airframe will only survive 5--10--20 normal flying lifetimes!! Just finish it and fly it!

 

[scsmith]

Seconded! I've been accused of doubting the engineering assessment, but my only issue was with the now conflicting guidance. So long as I have build instructions which clearly identify which cracks are acceptable, and where, that will go a long way.

Anyone still going to deburr dimpled holes on non-red parts?

It is not really "conflicting" guidance. It is new information vs. standard best practices. There is not really an incompatibility here. Yes, continue to do your best to smooth edges, deburr holes, avoid cracking where ever you can.

And, testing shows that small cracks at hole edges of dimpled holes are not the problem we may have once thought it was.

These two bits of info can live in harmony.

 

[Bullpup]

It is not really "conflicting" guidance. It is new information vs. standard best practices. There is not really an incompatibility here. Yes, continue to do your best to smooth edges, deburr holes, avoid cracking where ever you can.

And, testing shows that small cracks at hole edges of dimpled holes are not the problem we may have once thought it was.

These two bits of info can live in harmony.

I'll respectfully disagree - the guidance on hole preperation (deburr, etc.) and why (to avoid cracks) was clear, and included some scare language about the potential impacts of cracks ("lots of very thin air..."). The new information is in clear conflict with the build procedure and workmanship guidance prior to July of 2023, and that discrepancy should be acknowledged and addressed.

 

[AeroEngineer]

…the guidance on hole preperation (deburr, etc.) and why (to avoid cracks) was clear, and included some scare language about the potential impacts of cracks...

That’s true. And language about how to remediate cracks in dimples…

LCP … have 1/2 to 1/3rd the fatigue life at any given loading of the non-LCP control group.

Really? That’s not what the video said. Unless I missed something (which is totally possible, I watched it at 1.5x…)

 

[agent4573]

Is this why Vans is not replacing quick build kits? It seems there is conflicting information. Red/ yellow parts should be replaced but if you’ve already installed those parts you’re good to go? I have no intention of rebuilding wings/ailerons and flaps that I paid Vans to build.

Do you have the link to the Vans page that says they aren't going to rework QB kits? Neither the short or long video addressed QB status, it only said they would provide replacement parts

 

[Jonnyb]

Do you have the link to the Vans page that says they aren't going to rework QB kits? Neither the short or long video addressed QB status, it only said they would provide replacement parts

Was in the recent email. Vans will give you the parts, but you’re doing the work yourself.

 

[agent4573]

Was in the recent email. Vans will give you the parts, but you’re doing the work yourself.

I'm not affected, so I didn't get the email. Has someone posted a copy on the forums anywhere by chance? If you still have the email, would you mind PM'ing me a copy of it? Thanks.

 

[Jonnyb]

I'm not affected, so I didn't get the email. Has someone posted a copy on the forums anywhere by chance? If you still have the email, would you mind PM'ing me a copy of it? Thanks.

There’s a thread on the chapter 11 section with it posted

 

[scsmith]

... the guidance on hole preperation (deburr, etc.) and why (to avoid cracks) was clear, and included some scare language about the potential impacts of cracks ("lots of very thin air...").

"was" being the operative word. All that guidance predates the huge amount of data that now shows, in this instance, that the scare language was over-stated and probably unwarranted.

The new information is in clear conflict with the build procedure and workmanship guidance prior to July of 2023, and that discrepancy should be acknowledged and addressed.

.

Yes, the new information contradicts the earlier information.
And Yes, Van's should probably address that directly.

You know, it is the unique thing about science that it actually is able to - willing to - revise and update what the prevailing viewpoint should be, based on new data and insight. That doesn't mean the old viewpoint was 'wrong' necessarily, only that the new viewpoint is "more right".

General Relativity didn't prove Newton's Laws 'wrong'. It only showed what is more correct. Newton's Laws are still very useful and valid for many applications. We now know that there are circumstances where it is not quite as close to correct, not as useful, as the more modern theory.

In the same way, the new data on dimple-edge cracks doesn't suddenly make the old guidance 'wrong'. It is still very useful guidance. We now know that there are circumstances where it is not quite as correct as the newer information.

 

[Clayvt]

After watching the long form video is there actually any significant advantage to replacing any red LCP parts with punched? They both fail, albeit as stated above the LCP is about 10% sooner, but the data set shows more consistency and “predictability” with LCPs.

Or is it because there are more known flying examples of punched parts? Or to just put customers at ease given all the doom and gloom language from before?

After seeing the data I’m kind of willing to just press on with the red LCPs.

 

[Jonnyb]

"was" being the operative word. All that guidance predates the huge amount of data that now shows, in this instance, that the scare language was over-stated and probably unwarranted.




Yes, the new information contradicts the earlier information.
And Yes, Van's should probably address that directly.

You know, it is the unique thing about science that it actually is able to - willing to - revise and update what the prevailing viewpoint should be based on new data and insight. That doesn't mean the old viewpoint was 'wrong' necessarily, only that the new viewpoint is "more right".

General Relativity didn't prove Newton's Laws 'wrong'. It only showed what is more correct. Newton's Laws are still very useful and valid for many applications. We now know that there are circumstances where it is not quite as close to correct, not as useful, as the more modern theory.

In the same way, the new data on dimple-edge cracks doesn't suddenly make the old guidance 'wrong'. It is still very useful guidance. We now know that there are circumstances where it is not quite as correct as the newer information.

Very well put!
The number of people who struggle with this concept is just astounding!

 

[vic syracuse]

I’ve remained quiet on this subject while I got educated. I’ve been to Vans and seen the testing and data firsthand. It’s amazing what they have done, and have been doing for some time. At the same time they had it verified by a third party and the testing results overlapped each other. That was the epiphany for me. If I were building an RV right now, depending upon where I was in the process, I would have no problem putting the LCP replacement parts from Vans on the shelf and just keep building. If I were at a stage where they were
easy to replace then I might be tempted to replace them.

I honestly don’t think LCP parts in the aircraft are going to make any difference in the life of the aircraft, certainly not in our lifetime or perhaps even the next. My experience from building, flying, and working on RV’s over many, many years has shown me that there are other areas that will rise to the top before the LCP issue does. Overall, the fleet is very young. Vans has done a bang up job of issuing SB’s over their history, and I would expect that to continue.

All of us are responsible for ensuring our aircraft are in a condition for safe operation. I’m sure we will be watching for cracks in the future just as we have been in the past. If LCP parts begin to show fatigue cracks, I’m sure it will be reported.

From what I saw I sincerely doubt anyone alive now will see a crack perpetuated from an LCP part.


I don’t think the guidance has changed on best practices around building metal aircraft. What we have learned is that all cracks aren’t equal and do not have the same impact.

I know not everyone is ever going to be happy with the conclusion. That’s your prerogative. But I’d like to think I have earned some credibility in this industry that when I tell you something is not a problem, it’s not a problem.

Many of you have lost valuable building time due to the LCP issue. I understand that. Now, I would encourage you to get 2024 off to a running start and get your dream moving again. There’s a reason we have such a large RV community. The airplanes themselves are fantastic, but it is the memories you are going to build and the new friends you are going to meet once you are flying that makes it so rewarding. The sooner you get there the more fun you are going to have.

I know. I’ve been there and am still there. It’s a blast,

Vic

 

[spatsch]

Yes, continue to do your best to smooth edges, deburr holes, avoid cracking where ever you can.
.

But why? Doesn’t the new data show that at least for dimpled holes ( the data says nothing about none dimpled holes ) small cracks at the rim have no significant impact? Aren’t we supposed to adapt to new data in science?

Oliver

 

[deMan]

Not all cracks are equal

But why? Doesn’t the new data show that at least for dimpled holes ( the data says nothing about none dimpled holes ) small cracks at the rim have no significant impact? Aren’t we supposed to adapt to new data in science?

Oliver

The data shows that MANUFACTURING cracks at that location don’t grow. This seems to be because the residual forces hold them together and first need to be overcome before the crack grows which does not seem to happen.

What the data doesn’t show is what happens if there is a weak point on the edge of the hole that causes a stress concentration which in turn leads to premature fatigue cracking.

As someone else said, “not all cracks are equal”. Data for one type of crack/weakness doesn’t automatically apply to all kinds of cracks/weaknesses.

All this data really does is add a well researched exception to the “all cracks are bad” rule commonly applied. That’s all it does.

-Lars

 

[AirShowFan]

…the guidance on hole preperation (deburr, etc.) and why (to avoid cracks) was clear, and included some scare language about the potential impacts of cracks...

“was" being the operative word. All that guidance predates the huge amount of data that now shows, in this instance, that the scare language was over-stated and probably unwarranted.

Yes, the new information contradicts the earlier information. And Yes, Van's should probably address that directly.

You know, it is the unique thing about science that it actually is able to - willing to - revise and update what the prevailing viewpoint should be based on new data and insight. ...

That’s a very good point!

 

[Bullpup]

"was" being the operative word. All that guidance predates the huge amount of data that now shows, in this instance, that the scare language was over-stated and probably unwarranted.




Yes, the new information contradicts the earlier information.
And Yes, Van's should probably address that directly.

You know, it is the unique thing about science that it actually is able to - willing to - revise and update what the prevailing viewpoint should be based on new data and insight. That doesn't mean the old viewpoint was 'wrong' necessarily, only that the new viewpoint is "more right".

General Relativity didn't prove Newton's Laws 'wrong'. It only showed what is more correct. Newton's Laws are still very useful and valid for many applications. We now know that there are circumstances where it is not quite as close to correct, not as useful, as the more modern theory.

In the same way, the new data on dimple-edge cracks doesn't suddenly make the old guidance 'wrong'. It is still very useful guidance. We now know that there are circumstances where it is not quite as correct as the newer information.

I'm sorry I gave the wrong impression - this is my field as well (although not as directly as you), and I both understand and welcome updates as our understanding of the situation evolves.

That said, I previously had a role in the non conformance process (for military, not experimental!) and we frequently reached a point where it was clear what the update should be, but we still had to go through the process of updating job notes, procedures, and documentation. In this case, and I know and appreciate that EAB doesn't have the same requirements, we still have some remaining uncertainty.

I ask this not because I am one of the "no LCP" team, but because I have general question still remaining. For example, right now section 5 is clear that I should file out cracks in dimples. The LCP guidance seems to be different. Should I still file out cracks? What if I have a cracked dimple in a non-LCP part?

I'm really not trying to just argue, and I also haven't been able to watch the long video, so I may be out of line here.

[Edited following full viewing of the video; I had drawn incomplete conclusions from the single frame copied above. My apologies]

Thanks all for the informed discussion-

 

[spatsch]

The data shows that MANUFACTURING cracks at that location don’t grow. This seems to be because the residual forces hold them together and first need to be overcome before the crack grows which does not seem to happen.

What the data doesn’t show is what happens if there is a weak point on the edge of the hole that causes a stress concentration which in turn leads to premature fatigue cracking.

As someone else said, “not all cracks are equal”. Data for one type of crack/weakness doesn’t automatically apply to all kinds of cracks/weaknesses.

All this data really does is add a well researched exception to the “all cracks are bad” rule commonly applied. That’s all it does.

-Lars

I am trying to learn something here (don't take this as complaining) so let me ask some more questions.

What they call a manufacturing crack is a crack caused during dimpling because of the stress raisers (caused by LCP) during the dimpling process if I understood the video.

So if I cause a crack during dimpling because I didn't deburr what's the fundamental difference in those two. Don't both get created by stress raisers during the dimpling process? Aren't both manufacturing cracks?

As you said what they did show is that the residual strength at that edge despite manufacturing caused cracks at the edge is sufficient to last for the life time of all typically used airframes.

So still trying to understand why manufacturing cracks caused by lack of deburring are different.

At least this would provide a strong suggestion that if you repeated the study with poorly deburred parts which cause manufacturing cracks the results would be very similar.

I think others are asking a similar question. Does that mean I can ignore all manufacturing cracks at the rim of a dimple (not just the once caused by a stress raiser from LCP) ? If not why not ?

Oliver

 

[MIKE JG]

I only watched the shorter video but I have a question about vibration. Has the effect of vibration been addressed in any of the testing? Can you even simulate a 1000 hours of aircraft vibration on cracked parts??

Obviously vibration from one aircraft to another is not going to be consistent so I can see how that would be hard to simulate. But surely they've taken this into consideration??

 

[Jonnyb]

I only watched the shorter video but I have a question about vibration. Has the effect of vibration been addressed in any of the testing? Can you even simulate a 1000 hours of aircraft vibration on cracked parts??

Obviously vibration from one aircraft to another is not going to be consistent so I can see how that would be hard to simulate. But surely they've taken this into consideration??

It’s addressed at the end of the long video.

 

[gotyoke]

I'm eagerly awaiting the announcement of Van's latest addition to its own training and demo fleet: an RV-14 constructed with the leftover LCPs for every applicable part, and all the "alternative solutions" applied, and shown off at Oshkosh as a glorious testiment to the company's confidence in its own engineering assessment. Heck, I'll donate some of my LCPs if they are lacking any.

 

[RVFan671]

Discounts

I'm eagerly awaiting the announcement of Van's latest addition to its own training and demo fleet: an RV-14 constructed with the leftover LCPs for every applicable part, and all the "alternative solutions" applied, and shown off at Oshkosh as a glorious testiment to the company's confidence in its own engineering assessment. Heck, I'll donate some of my LCPs if they are lacking any.

I think they should offer heavily discounted full LCP kits for those who'd build them. Would enable at least a partial recoup of their inventory write off. And as you said, demo or trainer fleet of their own, but doubt they want to invest in the labor to build them.

 

[Low Pass]

I think they should offer heavily discounted full LCP kits for those who'd build them. Would enable at least a partial recoup of their inventory write off. And as you said, demo or trainer fleet of their own, but doubt they want to invest in the labor to build them.

Agree. After watching the short video I'm totally relieved of concern with LCPs. I'd build according to their recommendation with zero reservation. Replace only the few most concealed and critical parts with non LCP.

Many years ago, Van's faced another problem that caused big concern. The prototype -8 lost a wing. In time, they were able to explain the issue and create a good path forward. Not surprisingly, they've done the same here with the LCP issue.

I comment as a mechanical engineer, an early -8 builder/27 year Van's customer, and owner of an LCP inclusive -9 wing kit.

 

[jclark]

"I reserve the right to get smarter"

"was" being the operative word. All that guidance predates the huge amount of data that now shows, in this instance, that the scare language was over-stated and probably unwarranted.




Yes, the new information contradicts the earlier information.
And Yes, Van's should probably address that directly.

You know, it is the unique thing about science that it actually is able to - willing to - revise and update what the prevailing viewpoint should be based on new data and insight. That doesn't mean the old viewpoint was 'wrong' necessarily, only that the new viewpoint is "more right".

General Relativity didn't prove Newton's Laws 'wrong'. It only showed what is more correct. Newton's Laws are still very useful and valid for many applications. We now know that there are circumstances where it is not quite as close to correct, not as useful, as the more modern theory.

In the same way, the new data on dimple-edge cracks doesn't suddenly make the old guidance 'wrong'. It is still very useful guidance. We now know that there are circumstances where it is not quite as correct as the newer information.

When at Van's with Steve and Vic, I had certain views/perceptions that a really serious "UPDATE". Before I left, I got "smarter".

To date, I too had the notion that a crack is a crack. That a crack at the hole would be the first thing to propagate.

Well, the showed that even in holes with "manufactured cracks" the weak point or point where a crack will start from is based on OTHER stresses. Stresses that (as I recall) are related more to the dimple!

And while I my current project does not have LCP, I did arrive with concerns for the impact they may have for my friends who DO have some. Those concerns got put aside by what I saw and heard.

While the long and short presentations go into MUCH technical detail, they (in my case) do NOT have as much POSITIVE impact as actually seeing and touching the MANY samples that were tested, seeing the test wing with intentional missing rivets and "cut through" ribs, and seeing the rig that continuously put a control surface through full stress cycles.

They took a long time to communicate this, but the thorough engineering that was done resulted in no technical question that we had going unanswered (as I recall).

By the way. I think that some of their analysis went as deep as to know the exact rivet that would have maximum load throughout the flight scenarios.

Will the LCP matter delay your project some. Of course. But in my case, life matters delayed my projects mush longer. Will the LCP end up costing some more. Yes but the airframe is a NECESSARY item and I, for one, have spent (am spending) a LOT more other OPTIONAL add-ons. Will the LCP likely have a shorter lifetime for the airframe. MAYBE, and if so, it looks like maybe a thousand hours off anywhere from 5-20 LIEFTIMES of flying!

Just one person's view after seeing it all up close and personal with the option to ask ANY tough question and challenge ANY answer received.

BTW .... In case anyone is wondering, it must be said that at NO time did Van's try to put words in my, Steve's, or Vic's mouths. They don't operate that way and THEY know that neither do we.

 

[Fltonc]

I'm eagerly awaiting the announcement of Van's latest addition to its own training and demo fleet: an RV-14 constructed with the leftover LCPs for every applicable part, and all the "alternative solutions" applied, and shown off at Oshkosh as a glorious testiment to the company's confidence in its own engineering assessment. Heck, I'll donate some of my LCPs if they are lacking any.

I also willing to donate several of my laser cut parts. These parts will have horrifically bad divots from the laser cut process that are much worse than anything shown in the long Van's video. I will also donate parts removed from my vertical stabilizer and rudder, after I accomplish a total tear down of those components. I'm sure several of the parts that I donate from the tear down will display snow men resulting from drilled out rivets.

 

[FinnFlyer]

Points I found interesting:
The manufacturing crack from the laser cut dimpled hole is somewhat self-healing.
Fatigue racks most likely originates at the rim edge of the dimple.

As to why you still want to deburr, I'd think that you'd have more points around the edge where a crack could start, rather than just the one solidification zone of a (badly) cut laser hole (in addition to the self-healing property of the laser cut dimpled crack during dimpling).

From their analysis you could build with red-coded parts and still have an RV with a 10,000+ hours lifetime. What's the highest-hour RV now?

Finn

 

[greghughespdx]

Kitplanes just published a panel discussion with James, Steve and Vic (and moderated by Paul), all of whom have been commenting here.

We are grateful for the time these folks took to visit our factory in Oregon and share their many years of deep industry experience with us. Most industries don't have the high level of expertise that the kit plane industry counts among its customers and other individuals who run related professional businesses. So, we consider ourselves fortunate that we can all benefit from the knowledge these people bring to the table. They asked hard questions and provided constructive, helpful feedback that we very much appreciate.

The Kitplanes article is located here.​

 

[deMan]

From their analysis you could build with red-coded parts and still have an RV with a 10,000+ hours lifetime.

And when the first parts start cracking there is a good chance you got an outlier punched part that cracks before any LCP.

-Lars

 

[spatsch]

Points I found interesting:
The manufacturing crack from the laser cut dimpled hole is somewhat self-healing.
Fatigue racks most likely originates at the rim edge of the dimple.

As to why you still want to deburr, I'd think that you'd have more points around the edge where a crack could start, rather than just the one solidification zone of a (badly) cut laser hole (in addition to the self-healing property of the laser cut dimpled crack during dimpling).

From their analysis you could build with red-coded parts and still have an RV with a 10,000+ hours lifetime. What's the highest-hour RV now?

Finn

I must have missed the self healing part in the video. I thought the catch line was that the residual strength of a crack at the rim of a dimple is sufficient to not be the weak point of the structure under the load paths used in RVs. They suspect stress cracks originate at the base but could not conclusively proof that but they did statistically proof that they do not originate from the rim crack.

If there is really such a big difference between rim cracks caused by laser cut parts vs. none deburred parts how should we inspect this. What I mean is:

You see a rim crack during inspection of an RV you know nothing about.

Case a: caused by LCP => no action required
Case b: caused by lack of deburring => action required

How do I distinguish those two cases if as you and others have implied they are fundamentally different. As far as I can tell they will look the same.

Oliver

 

[vic syracuse]

I must have missed the self healing part in the video. I thought the catch line was that the residual strength of a crack at the rim of a dimple is sufficient to not be the weak point of the structure under the load paths used in RVs. They suspect stress cracks originate at the base but could not conclusively proof that but they did statistically proof that they do not originate from the rim crack.

If there is really such a big difference between rim cracks caused by laser cut parts vs. none deburred parts how should we inspect this. What I mean is:

You see a rim crack during inspection of an RV you know nothing about.

Case a: caused by LCP => no action required
Case b: caused by lack of deburring => action required

How do I distinguish those two cases if as you and others have implied they are fundamentally different. As far as I can tell they will look the same.

Oliver

An LCP crack should not progress past it's original length. If it does, it should be treated as any other (fatigue) crack and stop drilled.Also, certainly communicate with Vans about the finding. After what I saw at the factory, I think if you find one of these you should go by a lottery ticket, as I don't think it should occur in our lifetime.

I'm also not so certain that cracks are caused by lack of deburring. As a DAR I have seen more than a few metal airplanes that weren't deburred at all, and they aren't seeing any problems. I think if a fatigue crack is going to occur, it's going to occure whether or not the hole was deburred. Perhaps it happens faster, I don't know.

Again, continue with best practices, and we will all keep inspecting for cracks, as we have always done. Some are corrected by stop drilling, and others may need doublers. It happens in both the certified world and our amateur-built world.

Vic

 

[deMan]

I must have missed the self healing part in the video. I thought the catch line was that the residual strength of a crack at the rim of a dimple is sufficient to not be the weak point of the structure under the load paths used in RVs.

The “self-healing” is that the two sides of the crack are still pushing against each other. The crack is made/grown during riveting. Every time the hammer strikes the rivet it gets squished and is temporarily a little larger. When the hammer releases, the river springs back to a smaller diameter.
This means that after riveting is done, the outwards forces are less than when the crack formed. So for the crack to keep growing, the forces first need to be raised to what they were during riveting before any extra force causes the crack to grow.
That was mentioned in the part where they talked about the dehaviland Comet.

-Lars

 

[BTG1996]

Again, continue with best practices, and we will all keep inspecting for cracks, as we have always done. Some are corrected by stop drilling, and others may need doublers. It happens in both the certified world and our amateur-built world.

Vic

Great point. I was talking with a guy about getting help with some sheet metal- I met in him in his hangar while he was putting a doubler on the spar of a King Air because of a crack in it.

Prudence/commitment to safety always, but I'm starting to think these airplanes are much tougher than we give them credit for.

 

[Jonnyb]

There’s a time line of events presented by Rian in the long video. Not sure how that compares.

 

[togaflyer]

My -10 build dates before the laser issues so I have no skin in the game. I understand the apprehension of the owners with those affected kits. But Van’s has gone a long way to work this issue out both with the replacement of parts and all the recent testing they did to insure the product is safe. I never saw this much effort done to satisfy customers in the certified world. If there was an issue from a certified manufacturer you found out via a SB or AD and most of the time you ate the entire cost of the correction needed. Just hang in there, work with Vans, finish your build, and you will have a plane that will last longer than most of us.

 

[Crash-Down]

What happens if the FAA does an accident investigation and traces the probable cause back to laser cut parts? Would the entire fleet that has LCP be grounded?

 

[Radomir]

What happens if the FAA does an accident investigation and traces the probable cause back to laser cut parts? Would the entire fleet that has LCP be grounded?

For that manufacturer, yes

 

[KayS]

What happens if the FAA does an accident investigation and traces the probable cause back to laser cut parts? Would the entire fleet that has LCP be grounded?

probably not, this is the non-certified world. i don't have statistics available, but if we would compare the number of GA accidents caused by cracks in the structure with the numbers caused by all other technical issues, we would relax alot.

please forget about LCP, pound these parts together and aim for high build quality in regard to electrical, fuel system, oil supply, ignition etc. and you're good to go.

most likely after first flight you will love your great RV and will not spend one single thought on laser cut holes anymore. these airplanes really deserve to be finished indipendent from some ugly looking holes hidden by rivets for the next 100.000 flight hours.

 

[RV8JD]

What happens if the FAA does an accident investigation and traces the probable cause back to laser cut parts? Would the entire fleet that has LCP be grounded?

Highly doubtful.

As an example, in the early 2000's the Zodiac CH 601 XL and CH 650 airplanes exhibited aileron flutter and design strength issues leading to several fatal accidents. The FAA did an in-depth review of the design and worked with the Zenith to affect design changes. What the FAA did was issue a Special Airworthiness Information Bulletin (SAIB) and halted the issuance of new airworthiness certificates until the safety related issues were addressed.

Below is a link to the FAA's January 2010 Special Review Team report. Note what the FAA says about type-certificated aircraft versus experimental amateur-built aircraft.

https://www.faa.gov/sites/faa.gov/files/aircraft/gen_av/light_sport/Zodiac.pdf

From the Conclusions:

"The FAA has taken steps to notify the public of the safety related issues with this design and called for owners and operators to make modifications to their aircraft as proposed by the manufacturer. On November 7, 2009, the FAA issued SAIB CE-10-08 to inform owners and operators of potential safety issues with the CH 601 XL and CH 650. The FAA also issued an action November 12, 2009 to cease issuance of new airworthiness certificates until the safety related issues are addressed. Concurrently, AMD issued a safety directive for the S-LSA versions of the CH 601 XL and CH 650 to address the situation and to communicate details of modifications required before further flight. Zenith Aircraft also communicated similar information to owners and operators of experimental versions of the CH 601 XL and CH 650.
......

With type-certificated aircraft, airworthiness standards play an important role in establishing an acceptable level of safety. The special review team recognizes that if this were a 14 CFR part 23 type-certificated aircraft, it is likely the FAA would have taken airworthiness directive action to address an unsafe condition. Similarly, the consensus standards play an important role in establishing an acceptable level of safety for S-LSA aircraft. Manufacturer’s safety directives are used to address S-LSA safety issues.

However, with experimental amateur-built aircraft, the aircraft’s design need not meet either airworthiness or consensus standards. Instead, the operating limitations play an important role in establishing the appropriate level of safety for these aircraft. Without design standards for amateur-built aircraft, it is difficult to determine whether in-service airworthiness concerns warrant FAA action."
​

 

[QuixoteAg]

Greg - could Vans publish the locations of the highest load rivets for each of the models - i'd love to put the higher load rivet locations on my annual condition inspection to make sure i target those areas.

yes, i know i should check everything regardless but calling out specific locations on my plane would be helpful.

 

[Adambuilds]

Very Helpful

Kitplanes just published a panel discussion with James, Steve and Vic (and moderated by Paul), all of whom have been commenting here.

We are grateful for the time these folks took to visit our factory in Oregon and share their many years of deep industry experience with us. Most industries don't have the high level of expertise that the kit plane industry counts among its customers and other individuals who run related professional businesses. So, we consider ourselves fortunate that we can all benefit from the knowledge these people bring to the table. They asked hard questions and provided constructive, helpful feedback that we very much appreciate.

The Kitplanes article is located here.​

Thank you to Paul, Vic, Steve and James for your posts, your perspective and publishing this video. Taken with the information that Van’s published yesterday, it is providing much needed clarity and shows a pointed effort by Van’s to improve communication. I am not directly impacted by the LCP issue but I am planning to build an RV-14 soon and this is further boosting my confidence in my decision to keep moving forward with my plan. I hope it also plays a significant role in helping Van’s move past their financial difficulties and continue to deliver some of the best kit planes out there.

Adam

 

[AeroEngineer]

I think that some of their analysis went as deep as to know the exact rivet that would have maximum load throughout the flight scenarios.

could Vans publish the locations of the highest load rivets for each of the models

This was shown in the video. Screenshots attached. And: Reminder that they pointed out that the relief notches on the flanges see higher stresses than the rivet holes.

for any given repeated load, the bulk of LCP parts had a reduced life compared to most of the control group.

This is not true. I would be curious to know where you got that from. The video said and showed repeatedly how the lowest outlier was lower for punched parts than for LCP. Sure, the average for LCP was a little lower, ok. But you should care about the lowest outlier much more than you care about the average or about the "bulk" of parts. Do you care more about how many flight hours until the first hole in your airplane fatigue-cracks, or about how many flight hours until 50% of the holes in your airplane have fatigue-cracked? (That's not a rhetorical question. I think we would all agree "The first hole"). If you keep that in mind, then the graph with the error bars (also attached a screenshot of that below) basically says that LCP are superior from a fatigue point of view.