Thursday, January 2, 2014

No Tanks, I've Already Got One

Having never owned an airplane of such recent vintage as the RV-12, I had no idea how much refinement of the design continues as life in the wild environs of actual fleet usage points out weaknesses both major and minor in the original design. These refinements are passed out to those of us with completed airplanes via the innocuous sounding name of Service Bulletins.  The other, and more insidious, method is via revisions to the plans and kit contents. The latter is intended to fix issues for planes either in the process of being built, or for future kits.

While the improvements that are made via plans revision are optional for completed planes, Service Bulletins are arguably not.  Whether mandatory or not in the eyes of the FAA, I consider them certainly worthy of consideration. Having just gone through the painful process of selling an airplane, I know that the seller had better have answers for the well-informed buyer. For that reason alone, it is a good practice to acquiesce to the demands of the manufacturer when they create a Service Bulletin. Besides which, Van's does not go to the time and expense of creating these things and sending the parts (free of charge) for inconsequential trifles.

The RV-12 fuel tank has been the subject of a number of revisions and Service Bulletins.

It is now subject to another.

No one like messing about with the fuel tank. At best, it's a tedious and smelly job if it involves breaking open the ProSeal sealant that leak-proofs the tank. ProSeal is one of those horrible smelling chemical compounds that provides a valuable function, but does so at the cost of being a royal pain to work with. It carries with it an attitude of staunch recalcitrance, primarily exhibited by its preternatural penchant for sticking to everything but the place you want it to stick to, up to and very much including human skin. And did I mention that it stinks? I did? Well, it smells so bad that it bears repeating. Adding injury to insult, it is relatively expensive and has an unconscionably short shelf life. Conventional wisdom has it that storing ProSeal in the freezer will prolong the shelf life, which is why it is not an uncommon occurrence for me to periodically happen across a jar or two of it that had been tossed in the icebox and forgotten.

So, the newest Service Bulletin, which goes by the name of of SB 13-12-19, is more than a little frustrating because it is intended to enhance a previous Service Bulletin that came more than a year ago.  To understand the original problem, you have to be aware of where the fuel tank is in an RV-12, and how it is mounted. And to understand my trepidation in breaking it open for repair, you need to know that I opted not to build the tank myself for fear of crafting an expensive sieve.

Unlike pretty much every light plane in the world, the RV-12's fuel tank rides inside the airplane, rather than being built into the wings. The reason for this is that the wings on the RV-12 are removable and having a few hundred pounds of fuel in them would make the removal of the wings fraught with difficulty. In the picture below, you can see that the lower front of the tank is bolted to the aft face of the U-shaped channel that is the very backbone of the fuselage.

This channel, officially known as the "center section," also provides a strong airframe member to which the landing gear is mounted.  This is the crux of the problem intended to be solved by both the first tank related bulletin and the new, enhanced version. What has happened twice now is that a severely bollixed landing has applied enough rearward pressure on the landing gear legs to cause the center section to rotate forward. This forward pull of the aft face of the center section has ripped open the bottom of the fuel tank with predictable results. No one enjoys being bathed in gasoline, for any number of reasons.  This needed to be fixed, even if it is one of those very rare, "probably won't happen to me" cases.

The Service Bulletin resulting from the first accident had us install a doubler behind the flanges that the bolts go through to secure the tank.

The theory was that this more robust flange would provide enough retaining force to allow a new "frangible" bolt to just pop off its head, thereby allowing the tank to remain behind as the center section pulled away from it.

A second accident of the same variety disproved that theory.

Here is the NTSB finding, inclusive of a mis-identification of the manufacturer ("Rans" makes kit planes, but "Van's" makes the RV-12):

NTSB Identification: CEN13CA569
14 CFR Part 91: General Aviation
Accident occurred Sunday, September 29, 2013 in Hatley, WI
Probable Cause Approval Date: 12/02/2013
Aircraft: RANS RV 12, registration: N817RV
Injuries: 1 Uninjured.

NTSB investigators used data provided by various entities, including, but not limited to, the Federal Aviation Administration and/or the operator and did not travel in support of this investigation to prepare this aircraft accident report.

During the landing flare to a private field, the airplane encountered a crosswind from the southwest. The wind pushed the airplane to the north and the airplane landed prematurely on a high berm located to the north of the runway. The landing gear collapsed and the airplane was damaged by the postimpact fire. The pilot did not report any mechanical anomalies with the airplane.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:
The pilot did not maintain control of the airplane while landing with a crosswind.

Note that this accident happened on the first flight of the airplane. I feel for the builder - what a horrible thing to happen, although he was blessed with no injury - that could have been SO much worse.

So, here we are with another Service Bulletin to try again.  This one sounds fairly simple: add a couple more doublers. Problem is, this time they're inside the tank.  That means breaking the ProSeal seal and opening up the tank.

The two new doublers are depicted using dashed outline lines:

To get inside the tank, I will have to remove the large circular panel. You can see the outline of ProSeal around its circumference.  That will be a chore to remove, but it is by no means the most difficult part. Rivets will have to be drilled out to allow for new rivets to be used to attach the doublers, Those too are slathered with ProSeal that will need to be removed. The replacement rivets will also have to be installed "wet," which means that they need to be dipped in ProSeal before pulling them.

As long as I'm going to be doing all of that, I decided to also install a new mechanical fuel gauge that Van's deemed a nice enough addition to add it to new kits with a revision, but not safety-related enough to reach the plateau of a Service Bulletin, a decision I heartily agree with.

The mechanical gauge was developed out in the field by a guy that was not satisfied with the method Van's used to allow for a visual inspection of the fuel level. With wing-mounted tanks, this is typically addressed with a simple calibrated dip stick. The location of the filler neck on the RV-12 precludes that: the dip stick would have to be both flexible and lengthy. Instead, Van's provided a series of small holes in the side of the tank, running vertically from top to bottom. There is a plastic "window" mounted inside the tank to keep the fuel from simply pouring out through the holes. The idea is that you can look through the holes to see the fuel level.

Clever, but not nearly clever enough. The window material used in early tanks wasn't particularly fuel proof, and the installation was a major pain. Even when done successfully, the fuel level could not be seen from two out of the three positions that one would really want to be able to see it: while fueling, and while flying.  The far more serviceable if not quite as clever fix was to install a mechanical float gauge on the top of the tank. After a couple of years if foo-fooing the new gauge, Van's quietly adopted it into the design and ditched the idea of the windows. To their credit, they provide a retrofit kit for the gauge.  

I will install it. Why?  Well, for two good reasons: I will be opening the tank anyway, and I recently had occasion to want to visually see how much gas is left in the tank rather than trust the word of the skittish Ms. Sky View.

I am currently in the preparation phase, mostly because the parts from Van's have yet to arrive. There's nothing stopping me from getting the tank opened up, though. It's already out of the plane (I'm halfway through the annual inspection) and down in the basement shop waiting to have rivets drilled out. That necessitated the purchase of a new drill, the one I used to build the airplane having given up the ghost in the way that most tools die these days: the batteries are fried, and replacements cost nearly as much as the entire drill kit cost.

I made a trip to Home Depot to pick up a new one. There is an incredibly diverse number of options in the selection of cordless drills, especially when considering the utter simplicity of their function. I tend to buy on the low side of the price curve when it comes to simple things like drills.  And sure enough, here was a Black & Decker at a "New Lower Price," which I understood to mean "will come up at the checkout at the old Higher Price."  This not being my first experience with this kind of thing, I pulled my trusty cell phone (which these days come with more functions that the bastard child of a Swiss Army knife and a Leatherman) and snapped a picture.

A few minutes later, I was at the self checkout. To my utter lack or surprise, the computer popped up the price as I scanned the bar code: $69.97.  Plus tax.

I called over the self checkout attendant to point out the error. She grabbed a phone and called for assistance, presumably from someone able to go verify the suspicious story I was telling her. Her face crumbled. 

"Well, for how long?" she asked plaintively.  "Really? I have a customer waiting."

"Well, if this helps," I interjected, "I've shopped here before and I pretty much expected this to happen. Here, take a look at this."

She studied the picture above, compared it to the box I had already put in a bag, and broke into a wide grin.

"Never mind, he took a picture of the price card. I can take it from here."

I thought she might be a little insulted that I had taken a picture as evidence, clearly having no faith in their ability to manage their point-of-sale system. Quite the opposite happened: she was vociferously thankful. She didn't want to stand around waiting with an irritated customer anymore than the soon-to-be irritated customer did.


No comments:

Post a Comment