Several RV-12 pilot/builders had previously been discussing wrinkled fuselage side skins on the Vans Airforce web portal (www.vansairforce.com). The wrinkled skins along with some crimped brake lines seemed to imply that the center section of the aircraft might be moving excessively upon hard landings of certain RV-12 aircraft. Further investigation did not necessarily imply that simply hard landings or landings on unimproved airstrips were the exclusive symptoms of the airframes experiencing the problems. Moreover, as more pilot/builders began to share their condition inspection reports, the problem of cracks in the center section channel near the attach bolt holes began to enter the discussion.
As more pilot builders checked into the torque of the attach bolts, most reported that they could turn an additional quarter to full turn on their bolts to achieve the required torque. Someone finally surmised that the attach bolts were actually too long and that they were "bottoming out" in the nuts, resulting in perhaps proper torque but less than adequate compression on the gear leg, wear plates and related hardware between the head of the bolt and the nut. This under-tightened bolt situation could allow the gear legs to develop too much play or slop under highly loaded conditions such as hard landings and/or landings and takeoffs on unimproved airstrips. Hard braking and its effect was also conjectured as being a possible cause of exacerbating the gear leg problems.
After Van's Aircraft received enough pilot/builder reports of these incidents, they began their own internal investigation resulting in renewed testing of the landing gear system. On October 3, Van's issued an addendum to the original Service Bulletin. Its purpose was to "...supplements and clarifies the contents.." of the bulletin. Specifically the addendum provided 2 options for the builder/pilot to properly comply with the bulletin's requirement of checking that the landing gear bolts were fully seated prior to torquing. The first option was to drill four, 3/8 inch diameter holes into the F-1276 bottom skin to allow for the insertion of a brass drift in order to access the heads of the bolts. The second option was to remove the F-1275G cover plates by drilling out their rivets, allowing greater access to the bolts.
Below are two pictures showing the cover plate. My plan is to mount 12 nutplates on the 3 sides of each cover plate so they can be removable.
Following is a picture of the mid-fuselage inverted with the bottom skin partially cleco'd in place. At this juncture, the factory has recommended that I await their parts manufacturing in support of the Service Bulletin. Their estimate is that parts will be ready to ship by the end of November 2012. They are stating that while the new parts will be capable of being installed in flying RV-12's, it will be much easier if a builder waits until the parts are ready before installing the bottom skin....so here I will wait.
Fast forward now to November 26, 2012 and Vans has begun shipping the parts for the service bulletin. Officially, that is, Service Bulletin 12-11-09.
From a brief overview of one builder's post on Vansairforce.net, the parts will consist mainly of doublers to the lower fuselage, some additional wear plates and other goodies associated with the main landing gear attachment assemblies. There are even 4 new quarter inch holes to be drilled into the center section channel to enhance the securing of the outboard gear attachment assembly. The location of those holes appears to be accessible from the "interior" of the mid-fuselage, so I believe I could attach the fuselage bottom skin....but I think I will continue to wait.
It's not a total loss as I have begun work on the longerons and the seat backs as I wait on the parts for implementation of the service bulletin.
I had previously mentioned my intentions of installing nut plates and riv-nuts to the landing gear's F-1275G cover plates to facilitate easier inspection of the attachment assemblies. I have cooled to that idea as I don't believe the implementation would be up to my personal standards with regard to asthetics and function.
Fast forward once again to early December and I have completely reversed my stance on the removeable cover plates as well as attaching the fuselage bottom skin. The details on those assemblies can be found in the latest installments of the Mid-Fuselage Parts Assembly, Part 3 blog.
No comments:
Post a Comment