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New Section 37 - Fuel Tank

Hi Jerry,

As there are no AD notes for ELSA's we will not have this incentive, but after the first of the year you may find it a good bit harder to sell an unmodified RV-12 with out discounting the sale price by the amount to get this done professionally plus some additional for the down time required. If I were buying it would be $ 2,000 more off the price.

Then there are the insurance companies who may decided to not cover RV-12's unless this SB is accomplished or they may charge more for the additional risk if the RV-12 is not fixed.

So you do not need to do the SB unless you may someday want to sell the aircraft or need to carry insurance on it.

Best regards,
Vern



It's hard for me to believe, that all the owners of all one hundred and fifty-one flying RV-12's and perhaps another hundred, perhaps two hundred or more RV-12's still being built ... all with their non-leaking gas tanks installed and not yet flying will all remove their gas tanks, tear them apart, drill another twelve holes in a fuel tank with hundreds of predrilled holes manufactured in them already, clean the old sealant, add clips, nutplates, drill out and re-rivet and etc, etc. etc. ... ain't gonna happen.

Seems to me, the only way that it would happen would be in the form of an AD (Airworthy Directive). I know I'm not the sharpest tool in the shed and I will if I must but ...
 
I'm getting the modification kit and will take a very detailed look. My tank is not installed yet but it is complete. Now, I have already installed the hole (with cover plate) for the Moeller gauge as Van's indicated was possible (in another thread). So that is a currently non-prosealed access hole for using flex plastic tube attached to a vacuum cleaner to suck out any interior aluminum drill chips. (I REALLY don't want to take out the level sender!) Also, I am thinking that with a sharp bit (put Boelube on it as well - that *really* induces the chips to fly backwards as you drill!), very carefully driven making the holes, and a vacuum hose right there at the bit, you could perhaps drill those clip holes without introducing any chips inside the tank.
I am wondering the purpose of those clips anyway in mitigating the failure mode in the pictures in this thread. I am wondering about glueing/bonding the clips to the side of the tank rather than riveting.

Regarding fatigue failure of aluminum tubing - I don't see this concern as credible. Google "fatigue failure of aluminum" (one link: http://www.sv.vt.edu/classes/MSE2094_NoteBook/97ClassProj/anal/kelly/fatigue.html ) Look at the S/N curve for an aluminum alloy (unfortunately unspecified as to which one). You have to make tens of thousands of cycles at very high stress levels (thousands of psi stress) to even approach a fatigue failure. Each sump check involves less than 20 pounds of force on the tube. Only a small fraction of that force would be off-axis which would thus produce stress from a bending moment. Assume you use the drain for every hour of flight. You have to put 10,000 hours on the plane to get to even the first 10,000 sumping cycles! No way this is a concern. (Where are my old mechanical engineering textbooks? Many years ago I could do a detailed calculation using the detailed measurements of the tube...)
 
Enough said ... I will be sure to have Lockwood aviation at Sebring do the modifications on my gas tank at my annual next year ... As I said before ... In for a dime ... In for a dollar.

Thanks for all the good advice ...
 
I am wondering the purpose of those clips anyway in mitigating the failure mode in the pictures in this thread. I am wondering about glueing/bonding the clips to the side of the tank rather than riveting

There is a specific engineering purpose of the clips.
If you choose to re-engineer the modification, you do so at your own risk.

Regarding fatigue failure of aluminum tubing - I don't see this concern as credible.

I will assume you haven't done much maint. or repairs on aluminum aircraft Bill.

The majority of all component failures in aluminum aircraft are fatigue related. Often precipitated by vibration which is the same as inducing load cycles at a high frequency (many times per second), but sometimes it just caused by enough load cycles. I didn't say that the load induced by taking a fuel sample with fail the fuel lines. I said there is (in my opinion) a strong chance that all of the things combined (loads, vibration, etc.) could cause a failure of a portion of the fuel line.

The primary point is... The RV-12 is in essence, a certificated airplane. It now has many thousands of hours flown that have been testing and proving the overall design.

But, Everyone is free to deviate from that design (after certificate if built as an E-LSA) if they choose, but for anyone to say "I don't see this as a concern" is just guessing until it has been proven to be fact.

I realize that some engineering decisions are just best guesses based on the available information and previous experience .
My previous experience tells me that anyone with this modification on an RV-12 should monitor it carefully. And that guess is based on hundreds of humbling instances when I thought I new something, but ultimately found out I didn't.
 
New tank decision

I guess it would be cheaper for me to order a finished gas tank from Van ($455) with the new clips attached (I figure they would be attached) and pay Lockwood aviation to change out tanks at the annual rather then pay them to bust up the old tank and make the mods.
 
Not quite that cheap

I guess it would be cheaper for me to order a finished gas tank from Van ($455) with the new clips attached (I figure they would be attached) and pay Lockwood aviation to change out tanks at the annual rather then pay them to bust up the old tank and make the mods.

The $455 is just the delta price for having it built, not the price of all the parts..I haven't tallied up all the parts price for that, but I would suspect it could be hundreds more. :mad:
 
Scott - correct - I do not have much experience at this. And I'm always willing to learn which is why this forum is so valuable! Can you share the specific engineering purpose for the clips that you mention? To my untrained eye (only a pretty ancient BSME, and not aeronautical at that), - perhaps they are supplying extra resistance to ensure the bolt separation rather than a tank face rivet separation?
 
I just happened across the tank price, it is $755 for tank, and that does not include the $25 for the upgrade kit, plus installation of it would be in addition to this even.

The $455 is just the delta price for having it built, not the price of all the parts..I haven't tallied up all the parts price for that, but I would suspect it could be hundreds more. :mad:
 
perhaps they are supplying extra resistance to ensure the bolt separation rather than a tank face rivet separation?

In simple terms, Yes.

The selected rivets, and the number of them, should assure that the head on the specifically designed bolt pops before any of the bracketry on the fuel tank yields.
Making any changes to the installation method of the added brackets would probably have a negative effect on their function.
 
removing cured sealant

Let me confess first that I was one of the cheaters, getting the tant pre-built from the factory.

Having established my ignorance about the process, I'd like to know how am I supposed to "...Clean the cured sealant from the mating surfaces of the sender plate and the T-1202 Fwd Tank Bulkhead..."

Are we supposed to use any type of chemical for it, or scratching/sanding would be enough. Any help is appreciated...

By the way, did anyone ask Vans if they plan something around extra support for their pre-built tanks?
 
What I will do ( again ) - -

I get all the gas out I can, then run an air hose inside for a while ( 10 minutes ) to dry it out as good as possible. Then I use a thin flexible blade putty knife and a hammer to drive it under the edge of the sender plate. If you move around the perimeter, maybe more than once, you can then pry it off if only a few small areas are still stuck. It should not take a great amount of prying, or you need to go around it more with the blade and hammer. I use a wire wheel on an angle grinder to clean the sealant off. Next sand it with say 100 paper. Clean up everything, and do the job. I plan to add a little sealant inside over the rivets also as long as you can get to them easily once the plate is off. Follow the instructions with the mod kit after that.

John Bender
 
As we have heard often, Van's claims that the designer owns the design. On the other hand, you own the airplane and legally it is experimental meaning you are free to alter the design or ignore design changes. The event that caused this SB (by Van's own admission) was an impact event that amazingly did not kill the pilot but certainly totaled the aircraft. Unless you are planning to sell your aircraft as Vern suggests, you may be better off simply not crashing your airplane than you would be dismantling your fully functioning gas tank. This is not an event that happened in several instances...it happened one time. You get to decide. That's the joy of experimental aviation.
 
Food for thought

I would think that any emergency off airport landing would enhance the possibility of a gear/fuel tank rupture.

Gary
 
Hey Gary - -

That has been my thought all along. I am lucky in Iowa to have many roads. Iowa is like a giant checker-board. Also, many times of the year, the farm fields could be used. Flipping over is a possibility also, so I like the ( not so tight ) strap over the tank also. Hope I never have to prove either work well, but feel better with them. Things do happen.

John Bender
348 hours as of today.
 
fuel tank refit

I can't see where this will help. I'm not a phd in anything, but I can't see why we can't just use the new bolts and learn how to land the airplane.
Van's is worried about Van's and had to come up w/something.
It might have been a good time to come up w/a new design for this tank!
 
There are many failure modes to consider, but I think Vans nailed this particular failure mode. I will feel quite confident that if I do the same super hard landing I won't get sprayed with gasoline (and I think Vans does too).
 
oops ...

Heck, I get sprayed with gasoline about every 4th. or 5th. time I self-serv the 100LL or Mogas at the different airports. I must have a heavy trigger finger. :rolleyes: I swear I pull the trigger lightly and splash ... the gas overflows ... even if I have only 8-10 gallons aboard to start with.

I still have a lot to learn ... ;)
 
I received my tank fixit kit from Vans today, looks to be a simple but effective cure. I should lhave it installed in no time.
 
Some of you may be wondering about the new breakaway bolt Van's supplies in the tank modification kit. It is a standard AN3-7A bolt. The modification is to take a #27 drill and drill into the center of the bolt head to a depth of 3/16 inch. Measured from the TIP of the drill bit. (A #30 is too small. The #27 fits the hole well. I did not have other nearby sizes to check.)

In installing the kit, I found I could minimize chips getting into the tank from drilling. Use boelube on the drill bit and a vacuum held next to it by an assistant. I was able to see the the chips inside the tank and vacuum them out through the hole for the Moller gauge without taking off the fuel sender plate. To do that I used a piece of 1/2 inch ID flex plastic tubing duct-taped to a larger vacuum cleaner hose. A duct-taped a long 1/4 inch wooden dowel to the end of that tubing so I could maneuver the end. A small flashlight is needed, but the drilled holes let in light illuminating the area where the chips are. Position the tank when you drill so that the chips fall a minimum distance, and do one clip at a time including the vacuuming. Note that these clips use a different rivet (an MSP-42) than the closed-end tank rivets (e.g. AD-41H) used for the rest of the tank - don't know why. The kit has them. The $25 kit also has 2, 25gram cups of tank sealer, each with a separate pre-measured foil pouch of activator. 9-month life on those. One cup was more than enough for both clips, without doing the fuel sender plate.
 
Another hint for getting the goo all off, I used a simple wood chisel to peel the bulk off the aluminum, then used my 1 inch scotchbrite wheel in the die grinder to get rid of the remaining goo and prepare the surface at the same time. It was quick and easy.
I intend to put some duct tape over the inside of the drill area to collect the chips in the sticky. Check my kitlog for photos.
 
Getting the goo off is not a problem as you don't have to. When removing the sender plate (or whatever) let the remaining old goo there. When re installing the plate (or whatever) simply smear the new over the old, and stick it back together. It will seal. Doubtful? Think about it. The old was sealing fine. When you re install with new goo over the old you are just sealing the old to itself. Works for me.
Dick Seiders
 
You are correct, I was referring to the new clips, they are such a precise ft, I needed to get the goo off for them to align properly when drilling the holes.
 
Recieved my tank mod kit today.
What kind of rivets are these MSP-42.
Why did they not use the original AD-41H.
The MSP's are not closed end. Is that why people are coating the outside of the
rivet/flange?
 
My reasoning was - -

Would not hurt anything, and would give another sealing area in case the rivets leak. If you do the inside, some under the clips, and cover the entire outside, you increase the chances of a good seal.

John Bender
 
It was my guess that the "non closed end" ones have an increased shear strength over the closed ones.
 
My opinion - -

They are MUCH stronger than any of the rivets used in the plane. * Monel * I was told. Corrosion resistant.

John Bender
 
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