The following are some of the common questions and answers submitted by customers following the publication of the Van’s Aircraft Engineering videos that cover testing of laser-cut parts, and related results. We will be adding to this list of Q&A throughout January.
Q: Why stop laser-cutting?
There are a few reasons:
- Outsourced laser-cutting is more expensive than CNC-punching
- In-house CNC-punching capacity has increased to support production with more machinery and three shifts
- Part appearance, the ability to protect components in shipping is superior with vinyl-coated parts; that coating is not compatible with laser-cutting
- Laser-cutting is a more variable process than CNC-punching and results in a lower yield rate of acceptable parts
Q: Was vibration considered in fatigue testing and analysis? Past service bulletins show this may be a factor.
Yes. Predicting the exact conditions that components and assemblies are subject to is difficult to achieve precisely. The “unknowns” are countered by conservative aircraft design, conservative design-of-experiments, and factors applied to calculations. Historically, acoustic fatigue in RV’s has occurred in skins where forces load the material “out-of-plane.” This creates localized bending stresses that will fatigue the rim of the dimple much faster than any edge. This is true of both punched and laser-cut parts, resulting in an assembly that has the same susceptibility to fatigue.
Q: Alternate solutions have been proposed in place of part replacement, when will those be available and what locations? In what order are they being completed?
Alternate solutions are being developed for difficult-to-replace components, and are prioritized by the largest number of kits affected. This has focused our initial effort on the RV-10 and RV-14.
Wings, ailerons, and flaps will require the replacement of Red-labelled/classified components, no alternative solutions will be developed. Service information will be released that provides instructions for replacement and the initial timeline for replacement. This documentation is not required to replace these components, builders can proceed with replacement at their discretion.
There is no alternative being developed for Yellow-labelled components that support boarding step loads, these are the parts located in the baggage area on numerous aircraft. Builders should continue to inspect these areas over time.
All alternative solutions are developed to:
- Reduce stresses
- Reduce rivet loads
- Provide redundant load paths
These will increase the fatigue life of the components to be as good or better than the punched equivalent.
RV-10 Fuselage Center Section Bulkhead, F-1005A is developed and in review. This will involve the replacement of certain fasteners. No additional parts will be required.
- F-1044A Forward Fuselage Rib is under review, and it is unlikely that any change will be required after further analysis.
- RV-14 Fuselage F-01405A, F-01405D-L, and F-01405D-R are currently in development. This will require additional components and fasteners. we do not anticipate having parts available to customers for at least two months (as of 1/12/24).
- RV-8 Landing Gear Bulkheads will be the next focus. This will require further detailed load analysis to determine a course of action.
Q: How is fatigue performance impacted by “non-dimpled” holes?
Non-dimpled holes were tested and analyzed. Extensive variables were evaluated and compared to a “baseline” of punched coupons. The trends were similar to the dimpled hole data presented.
Q: When will I receive my replacement parts?
Replacement parts are in production and shipping to customers. The vast majority of production has been dedicated to replacement components for the last two months. Due to the large number of customers affected this will take some time to complete, as the replacement program progresses, accurate estimations of the completion date will be made.
Q: Are Quickbuild kits currently shipping with laser-cut parts?
No, only kits containing punched components are shipping.
Q: Is cracking not an issue with blind riveted structures (LP4 rivet, RV-12 type structure)
Cracking in the fastener hole is not an issue identified in testing. Our long-form video presentation goes into some detail on the LP4 riveted structure at 1:22:10. Accelerated life testing has shown a very long service life can be expected. This testing of highly loaded rivets demonstrates that the rivet will fatigue before the hole, regardless of whether the fastener hole was punched or laser-cut. Lightly loaded fastener holes will fatigue before the rivet, but with a dramatically longer fatigue life that is many multiples of the life of an aircraft.
Q: Are you replacing Elevator components with bonded ribs and trailing edges?
Yes, components that are overly burdensome or impossible to reuse will be included at no charge with the replacement parts order.
Q: These laser-cut parts don’t match AC43.13, how can that be acceptable?
AC43.13 is broad guidance on best practices, it is written without consideration of the unique characteristics and design of individual components. Our analysis is specific to RV structures for components that may be laser-cut. Specifically analyzed components and designs can deviate from general, broad guidance.
When evaluating these components for use, a great deal of consideration was made to understand if these components had an elevated risk of metal fatigue. Parts accumulate fatigue damage everywhere while in use, but the locations of higher stresses accumulate fatigue damage at a much faster rate. These locations of high stresses, where we expect fatigue cracking to occur first, should be thought of as the “fatigue critical feature.”
This does not mean that we expect the part to crack, but it does point to the location where the part will “wear out” or crack first. If laser-cut holes have an expected service life far above these other locations, the “weakest link of the chain” remains the same point it has always been, and will occur at the same point in time as the punched equivalent.
This is touched on in a few segments of the long-form video:
Q: Does the data from residual strength testing of the RV-10 wing correlate to the other RV models?
Yes, The RV structures are closely related in design philosophy and operating stresses. The RV-10 was selected for the test because it experiences the highest bending and torsional stresses in certain flying conditions.
We will expand this list of questions and answers throughout January. You may review the engineering videos and access the form to submit questions at this link.