Laser cut holes in parts causing cracks- reject

[A2022]

I saw this video from Van's about laser cut parts causing cracks when dimpled. I would hate to be the engineer that had to justify by analysis why this is OK. he must have been forced into a corner with a sledgehammer. my opinion, when you see parts like this, simply REJECT them, like they do in any other aircraft assembly factory. REJECT, REJECT, REJECT. only assemble good parts. it's a no brainer. Van's aircraft are delicate machines, don't build in cracks. I am an old aviation engineer.

https://www.youtube.com/live/gO1pKlyPqvk?feature=share

[A2022]

Laser cut holes causing cracks - reject. don't mess with it. dimpling already shortens the fatigue life of an alum skin. adding a built-in crack will decrease that even more. you would think with all this information available at our fingertips; Van's would know better. successful companies make quality products, or someone else will. I get ease of build considerations for the average guy in his garage, but I also believe he wants the most durable product he can reasonably achieve. even if it adds some build time, it will save time in the long run from unnecessary repairs, and in the end he will be happy.

I really do understand this is a major blow to Van's, but this one was in their control. so, no sympathy for them. pain is the best teacher, but it is better to learn from others pain and avoid it as much as possible. I trust they will correct and do the right thing, although they may need to increase prices to financially recover. I think the market could bare a price increase.

******

an interesting study and comments from professionals.

https://apps.dtic.mil/sti/pdfs/ADA357973.pdf

As a part of a collaboration program between the Federal Aviation Administration (FAA, USA) and the Department of Civil
Aviation (RLD, the Netherlands), the Dutch National Aerospace Laboratory (NLR) has carried out fatigue tests on riveted lap joint specimens. The specimens are representative of the longitudinal lap joints of a commercial aircraft in which multiple-site damage (MSD) was found in service. Two different rivet configurations, dimpled and countersunk riveted joints, were investigated. The countersunk riveted specimens were bonded as well. Four different bonding qualities ranging from fully bonded to fully unbonded were tested.

The results of the test program showed that the fatigue life until failure of the dimpled lap joint specimens was about one-quarter of that of the unbonded countersunk specimens. The bonding quality is a major parameter for the fatigue life. Fully or partly bonded specimens did not show fatigue cracking within 500 or even 1000 kilocycles. Specimens with a fully degraded bonding layer have slightly better fatigue properties compared to fully unbonded specimens.

*******

the proper method to prepare a dimpled hole....

Dimpled holes MUST start with a small match-drilled hole(at 1 if not 2 sizes smaller) in all sheets. Deburr all hole-lips to prevent cracking when dimpled [labor intensive]. Dimple the holes [separately or gang-dimple] for small diameter tension head. Reassemble structure with next larger diameter clecos. Drill-enlarge the thru hole to final diameter [preferably nominal rivet Dia + 0.004--+0.008]; then install a shear-head [NAS1097 style] rivet.

NOTES:

The hole lip in the dimple gets stretched and has a tendency to crack: deburring is critical!

The dimple dies must be polished and have a specified radius for the sheet alloy/thickness to be dimpled. Precision fit/alignment of the male and female dies is critical. Also “best dimple dies” will have a significantly undersized pilot tip [with a tiny pilot hole required]… to allow the [noted] clean-out drilling to size when structure is reassembled.

Drill-enlarging the rivet hole to final diameter. This will “mostly”: (a) eliminate stressed metal; (b) realign hole center [best done with a countersunk drill guide]; and (c) eliminate jagged steps from each dimpled sheet-metal layer that limit driven rivet gripping/clamp-up. A “perfect”, ready-to rivet dimpled hole will “look” like a countersunk hole [straight thru]!!!!

Generally, all thickness of 2024-T6/-T8 and 7075-T6/-T73 (etc)... and 2024-T3, 0.063+ thick sheets... will require "hot" dimpling to be successful… and absolutely require enlarging the hole to clean-out streched metal. Even Cold dimpling 2024-T3 0.050-in(+) thick sheet metal will take a lot of mechanical effort… and still need “care” to avoid splitting the hole-lip or cracking the dimple radius.

Generally dimpled holes should have ONLY driven-rivets or tight-fitting blind rivets. AVOID installing Hi-Loks, flush-head screws/nuts, etc… unless the bottom sheet is thick and countersunk to match top-sheet(s) dimple(s).

*******
and I could also do fracture mechanics crack propagation analysis for this condition, but it's not worth it. simply, don't assemble a new delicate kit aircraft with built-in cracks.

[A2022]

I have had a couple people ask me what I thought about LCP cracks at dimpled rivet locations. my response is always the same, why would you want to build-in cracks in the airframe? Van's aircraft are lightweight, fun to fly, delicate machines, that have a history of published crack repairs. to get the most life from the airframe, do not build-in cracks. adhere to standard build practices.

[A2022]

Van's latest video on LCP cracks....

well, I suppose desperate times call for desperate actions and an effort to convince folks that skin cracks at some rivet locations are OK. Van's pockets are not deep enough to correct the condition completely, so they are trying to limp by and zone the lower stressed rivets for LCP. at higher stressed rivets they required LCP to be replaced by punched parts. it's a tough sell with Van's history of numerous Service Bullitens for cracks. when I am around, I see a lot of cracks and stop drilled holes on aircraft that have not had any LCP issues. the baseline kit with dimpled holes has potential to create cracks for the below average builder, thereby adding built in LCP cracks at holes is only going to make it worse. in my opinion, the kit should be robust enough for the below average builder as not to develop cracks. I want Van's to survive, and they don't have much cash. so, I would support them in this effort to limp by. It will put additional stress on builders to do the best job they can and then develop an ongoing crack inspection program.

my overall opinion has not changed, just say NO to LCP cracks and reject for maximum resale value. how the quality department ever let those parts out is beyond me. I am sure someone raised their hand in concern but was shot down.

my 2013 RV9A has been great with no cracks on the airframe and one crack on the engine baffle. I am a happy camper.

**********

I believe Van is trying to stabilize the business and then will sell it. Age is the limiting factor.

https://youtu.be/p21B4ZZ3meE?si=wNdAiJ_R1EYUNWR-

[LCDR Fitz]

Totally agree with Steve. Finished my RV (8-A) in 2011. Do mild aerobatics rarely over 4 G's and have 875 hours on her with no cracks. Vans got kind of like the shuttle program and got a little too over confident. Instead of losing 40% of the vehicles and 14 lives Vans lost a big chunk of their reputation which will never come back to where it was. I just hope they will be forthcoming if more cracks do start appearing down the road and not wait till the peasants are at the gates.

Tim