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RV-12: Fuel Tank Information / Modification

Look at the failure mode in the pic. The head of the bolt pulled open the tank. Now, with no head on the bolt, since the center section member ROTATES in this failure, a strong bolt with no head might still "grab" inside the section and not just come out of the hole. The result could then be the same as a bolt with a head. (So the less a strong bolt or pin projects inside the member (as seen looking forward), the better.) But a bolt that would either easily shear or easily bend would not pull forward with the rotating section and tear open the tank. In normal flight, the current bolt or replacement is just carrying a vertical load - it is not keeping the tank from moving appreciably forward or aft.
 
Hey Bill - -

That is why - I - recessed the 'pins', and greased the holes also. They are only engaged in the channel by maybe 1/4". I am VERY confident they will pull out of the channel ( if needed ). The strap will keep it in general position.

John Bender
322.7 hours
 
That is why - I - recessed the 'pins', and greased the holes also. They are only engaged in the channel by maybe 1/4". I am VERY confident they will pull out of the channel ( if needed ). The strap will keep it in general position.

John,

While encountering flight turbulence and vertical forces during takeoffs and landings, especially on eneven, sod surfaces, wouldn't the aft connection of the tank be subjected to bending and metal fatigue?
 
My personal feelings on the tank are that I'm happy with the design but will take note IF Van's feel a modification is necessary.

Regarding the canopy latching, perhaps because we are in cooler climes but I never taxied the RV-6 with the canopy anywhere but latched and have the same plan with the 12. Shut the canopy and lock it, go fly, stop and open canopy!

What I did do (because it's fun making widgets for the SkyView like for wing pins in/out) was to position a simple PTT type press button switch on the canopy latch plate.

To link it to a canopy 'open'/'locked' widget on the SkyView, I used one wire from the interior flood light to go to the canopy switch abd SkyView, then simply put the flood light staight to earth on the roll bar with the other wire providing power as normal to the flood light.

Works a treat - red widget 'open', green widget 'locked'.
 
Good point - -

If it happens, I'll let you know. I do fly off turf once in a while. If it comes out of place, I think it will be very obvious. The filler holds it quite a bit also. I think it is fairly stable. I did land on a 'new to me' turf field near Des Moines late last week. Seemed to stay in place ok. It was not a super smooth strip either. Got bumped around a lot. Thanks for the point.

John Bender
 
The risk is very high

I think there is a real need for a fix to this issue, in days not months. Joe in post #41 expects it to take a long time for Vans to come up with an engineered, tested solution. Larry in his post #29 sees waiting as an option. I cant agree. The likelihood of a fractured tank in a forced landing on rough terrain seems to me to be 100%. It makes me nervous to fly just thinking about it.
Let?s hope Vans sees it this way. It is only going to take one fire to ground the fleet.
In my opinion, all we can do in the meantime is assess the options ourselves and make a change.
Rod
 
Try race car fuel cell...

I am not a fan of the RV-12 fuel tank and I made changes after my airworthiness inspection; but I think that any changes Vans makes to the RV-12 tank design will most likely be more easily done by just installing a 20 gallon tubular fuel cell. They sell in racing catalogs for under $300. and can be mounted in cradle/clamp mounts quite easily. I really think this is an application and a time when we really shouldn't have to re-invent the wheel.

Just thinking out loud...

Jay Sluiter
Albany, OR
 
Fuel Tank

Years ago I built a Rotoway Exc which had two custom molded , left & right tanks. They had a CD, which I still have, showing them dropping at height of maybe fifty feet full of fuel and showing no signs of leaking. They are probably still using the same tank. The tanks were held in place by metal straps.

I took with my RV9 tilt up and failed to lock the side latch. I was at 4m when I noticed a gap between the canopy and the frame. I didn't want to tell my passenger I erred I just told him we were going to do a stall. As I pulled up I continued to put pressure on the latch until the internal pressure neutralized and the latch engaged the pin. Passenger didn't know my error. I didn't panic. With the 12 don't overreact. Years ago I went for a demo ride in Vans RV9A slider with one of there best pilots. We took off and got about fifty feet in the air when he realized he didn't close the slider. He dove down and landed immediately to correct the problem. Was this the right thing to do?
Ron Russ
Viking RV 12 and other planes
 
Agree

with Jay and Rod - caution is necessary here. I trust Van's to come up with a real 'fix' not a quickie 'good enough fix'. I like the spun tank idea - no metal seams to open up - again, I say, I'll be happy to pay a lot of $ for a really good fix. I don't want anyone to take a gasoline shower as the result of flipping it over on rough ground or landing out.
 
with Jay and Rod - caution is necessary here. I trust Van's to come up with a real 'fix' not a quickie 'good enough fix'. I like the spun tank idea - no metal seams to open up - again, I say, I'll be happy to pay a lot of $ for a really good fix. I don't want anyone to take a gasoline shower as the result of flipping it over on rough ground or landing out.

Perhaps you would like to talk to ATL they make great fuel tanks for just about everything, I had one for my car many years ago and it worked fine. Take a look at their web site it is very interesting.

http://atlinc.com/index.html

Best regards,
Vern
 
Looks good

to me - I believe that something along the lines of these fuel tanks is likely the answer. Again, I am no engineer and will leave it up to Van's engineers to decide what us best. I like the feature of no riveted joints in a tank - also, these spun tanks are strong. Irregardless of what Van's does, I'll likely put a spun glass/plastic tank in my 12 after initial inspection. Time will tell.
 
How about a wing tank option for those who plan on putting the wings on and leaving them on. Get the fuel out of the cocpit altogether.
 
Belt and Suspenders

For what it's worth: the RANS S-19 has plastic tanks between the spars in the non-removable wings. But I believe it's a significantly slower build. And it's heavier.
 
what are the dimensions of the fuel tank? LxWxH ?
and the empty weight?

I am looking at racing fuel cells and if they would fit, seem to me to be a great idea.
There are plenty of 22gal versions (or 24/32 or more if you want).
the lightest ones are around 22lbs with foam and baffling.

they make them in various different configurations, so one of them should fit in the baggage area I would imagine.
 
The shape is not exactly rectangle, and the return line needs to be above the fuel level to prevent siphoning (that detail can be worked out latter). I doubt you could find an off the shelf tank with the fuel lines on the bottom, but I'll bet the manufacturer would be interested in building some for us if the quantities were there. Certainly, one could be built but at what cost? What would people be willing to pay? $200 .... $400?

Here are the general dimensions.... 23" x 17" x 12"
 
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The shape is not exactly rectagle, and the return line needs to be above the fuel level to prevent syphoning (that detail can be worked out latter). I doubt you could find an off the shelf tank with the fuel lines on the bottom, but I'll bet the manufaturer wouyld be interested in building some for us if the quantities were there. Certainly, one could be built but at what cost? What would people be willing to pay? $200 .... $400?

Here are the general dimensions.... 23" x 17" x 12"

A quick cursory look at the ATL catalog shows this fuel cell:
gal part# Lbs L" W" H"
22 SUBA122B 21 25.13 16.75 13.75
 
I would be willing to pay alot if it meant the difference between being a crispy critter or not. But, my first preference would be for a Vans analysis and, if required, solution.
 
The RV-12 fuel tank has baffles to keep part of the fuel from moving to the aft of the tank during a climb, especially at takeoff. Suppose an RV-12 on a long cross-country trip arrives at the destination with 3 or 4 gallons of fuel left. It becomes necessary to go around for some reason. Without baffles, all of the remaining fuel falls to the back of the tank, possibly uncovering the outlet port. The outlet port of an alternate fuel tank should not be uncovered in any normal flight attitude when the fuel level is low. What good is a fuel reserve if it can not be used? There could be other requirements for the fuel tank that we might not be aware of.
Joe
 
Agree

with Larry and John - there either 'is' or 'can be' a spun glass/plastic fuel tank that some manufacturer has or can make to Van's specifications.

Hopefully, Van's is investigating these options. In my opinion, a safe fuel tank is paramount to the safety of the RV-12. After what we have learned about the current tank, I don't think that the fabricated aluminum tank is safe. I'm not an engineer of any kind - I just want a safe tank in back of my seat in my RV-12. I have pretty much decided to find and install a spun glass/plastic tank in my 12 after inspection. I really hope that Van's will offer a spun glass/plastic tank - maybe as an option as I am pretty sure that Van's can do a better job than I of picking my tank.
 
Impact-resistant, rotationally molded, cross-linked polyethylene

This is what I would like to see in the RV-12 custom molded with all the fittings in the right place.


With the number of 12s that Van's is selling this would ad just a few dollars to to the kit.


Impact-resistant, rotationally molded, cross-linked polyethylene fuel tanks.


Most if not all new cars and trucks use this type of tank.


http://www.westmarine.com/webapp/wc...toreNum=10106&subdeptNum=10443&classNum=10444
 
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An alternate approach to reducing the risk of the current system would be to make appropriate modifications that add strength to the center section to prevent it from rotating aft.

Dave
 
In my opinion, a safe fuel tank is paramount to the safety of the RV-12. After what we have learned about the current tank, I don't think that the fabricated aluminum tank is safe.

There is no evidence to suggest that the current tank is inherently unsafe. The problem was caused by the way the tank was rigidly fixed to the channel, and I'm sure Vans will come up with better tank fittings. Chances are an alternative tank fixed in the same way would also be damaged.

I'm still a bit puzzled by the lack of any full depth ribs or stiffeners in the tunnel under the channel to help prevent the kind of severe rotation caused by a heavy rearward impact on the main gear as shown in the photos. The whole channel assembly appears to rely almost entirely on the cockpit sides for support. There is no attempt to use the floor ribs to share the load or to generally stiffen the struture in that area.

Granted that Van's may have very good reasons for deciding to leave the tunnel open (such as ensuring that excessive loads are NOT transferred to the cockpit floor under the occupants in the event of a crash), but otherwise this seems to be an area where the strength of the structure could be improved.
 
It will take a lot of time I suspect, this is a change to an SLSA plane, so it is not as easy as the old days of kits, it will have to go through lots of testing and approvals. I am not so sure the tank itself is faulty, no problems have been encountered (once the leaks are fixed) in lots of hours. It was in this case not the tank, but the location of the attachment that caused the problem, and that can be changed or improved easily. I think the smart money is on the people currently flying that have come up with an easy effective fix while the gears turn at Vans.
 
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Crash load design

Unless you have aircraft structural engineering design knowledge, I think you should not be redesigning the attachment structure for this tank. I am a retired (Air Force civilian) structures engineer and know a little about design for crash conditions.

The controlling design loads for crash is 16 G forward, 9 G lateral, and 3 G vertical. According to Mil-Std-1290A design shall be computed with a 75% full tank. The cg of the tank with fuel would be elevated over the aft floor. In a forward crash the tank would tend to rotate (****-toe action) about its forward edge. From the pictures first shown in this thread, it appears that the current attachment did its job in retaining the tank to the airframe and only the forward attachment was compromised due to roll of the carry-through structure. I would not be altering the forward attachment bolts. If they are there to carry the shear loads in case of a vertical acceleration (tip over onto tail) I would want all of the bearing area of those bolts in those holes, even if the carry-through rolls.

As to John Bender's design change, it does not look adequate. It looks like he is planning on taking the any vertical tank loads through two tie-wraps holding down the over-the-tank strap hook. The tie-warps would easily rupture and if the forward attachment (now pin) slips out of the hole you are now depending upon the floor attachments to withstand the 3 G vertical load. In addition, what structure is he tying his bracket to under the floor? Assuming the strap worked, could the floor attachment fitting separate from the floor?

What do I think Vans Aircraft might do? I think it is a given that he will eliminate the tie to the carry-through and then perhaps beef-up the floor structure attach points and change the fastener size and/or fastener pitch.

That's my educated two cents worth
 
As someone who sounds like he can answer this question....at what point is a compromised fuel tank considered part of a crash? This tank was tested to ASTM standards. Won't they all be destroyed at some point? I don't want fuel in the cockpit...but then I don't want to hit the pavement at 600fpm either. Thank you for the G force ratings...I'm just not able to relate them though I understand 16G's is a bunch.
 
I understand your concern about fuel in the cockpit during a crash condition. I am just trying to convey to the community that caution is in order when making mods to this important structural tie to the airframe. I think it would best be left up to the designers to make the mod since they understand the load paths and can best make a redesign that is both safe and efficient. I put my background into the posting so that you know I have some knowledge of what I am talking about.

George Dowell
Dayton, OH
 
Hey George - -

Appreciate your comments. Not that this makes a big difference, but there are 4 heavy tie-wraps on each side. The slots were smoothed out fairly well. As has been stated, this is designed to be temporary. I feel my risk factors are less than the original design factors. Larry posted this to make people aware of the potential SERIOUS problem. I chose this for a temp fix. Each person should decide their own risk and go accordingly. The accidents we have seen so far have been similar in nature. Not possible to design for every situation.

John Bender
 
I understand your concern about fuel in the cockpit during a crash condition. I am just trying to convey to the community that caution is in order when making mods to this important structural tie to the airframe. I think it would best be left up to the designers to make the mod since they understand the load paths and can best make a redesign that is both safe and efficient. I put my background into the posting so that you know I have some knowledge of what I am talking about.

George Dowell
Dayton, OH

First and foremost Welcome to VAF. :D

Thanks for the good info. Keep it coming.

I tried to convey your message in my first post. I agonized for several weeks about posting this info after contacting Vans. I tried to do it in an informative and cautious way. In the end, we fly experimental aircraft. We must all decide for ourselves what is our level of comfort, but my first responsibility (IMHO) was to let the RV-12 community know of this one and only incident so they can decide what to do for themselves. Like I said, a good option is to do nothing.
 
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Thanks John . . .

Thanks for the follow-up comments. I am sorry to come down hard on you in my discussion, but I wanted to make it clear as to what you are "messin' with" here. I am glad to learn that you smoothed out the edges of the pass-through slots in your attach fitting. I was concerned not only about the strength of the tie-wraps themselves but the potential knife edge of the slots.

George Dowell
 
Hi George - -

If I had wanted my 'fix' to be permanent, I could have made brackets with the nylon straps going thru them, and sewn together to make a nicer looking arrangement. I did not test it, but I would guess the 'S' hook would bend before breaking 4 heavy tie-wraps. In most all of the RV tip-overs, there seems to be a fairly uniform story, they flip over rather slowly. I feel the strap will keep the tank in general position. Forward initial forces will still be absorbed at the front attach points, but with greased pins, the channel can twist and not pull the tank apart. I hope a good factory fix is coming that we can feel good about. I feel better about my temp fix for now. If someone comes up with something I like better, I can change mine. I have not changed any of the components involved.

John Bender
 
George, thank you for your valuable input. It's convinces me that my earlier thought on waiting for Van's fix is the way to go. Lots of good suggestions were put forward, but most of us RV12 drivers do not possess the technical expertise to determine what will do the job.
Dick Seiders
 
But on the other hand Dick, it might be a long time (or never) before Vans makes a public fix, and thinking about happenings in that time period is what has people concerned.
 
Hey Don, anything is possible. I have expressed my dislike for the tank design several times in as many threads, and I still feel that way. I do however have confidence that Vans will see to the fix as soon as possible.
Dick Seiders
 
Yeah, I am one of those that thinks the fuel should not be inside the cockpit either, although I had never considered the likes of what happened to this one..
 
Don, I don't think the location of the tank is a problem. Rather it is the way it is attached, and prone to failure in the type of incident we are all talking about. No design is foolproof. I lost two good friends a year ago last week in a firery flat impact off field landing in an RV6A which carries it's fuel in the wings.
Dick Seiders
 
I know that we should wait for Van's to come up with the official fix. But I still lie awake at night thinking of a way to fasten the tank. :D Here is my latest idea. Since the tank is now fastened to the floor behind the forward side of the tank, the tank rivets will no longer be in tension. The new aluminum strap is simple and lightweight and will bend to absorb energy without pulling the tank apart.
Tank%252520Fasteners%2525202.jpg

Joe Gores
 
Hey Joe - -

I am trying to figure out how you would get at the outside bracket ? The inside one makes sense. ? ? ?

John Bender
 
I am trying to figure out how you would get at the outside bracket ? The inside one makes sense. ? ? ? John Bender
Gee, I don't know. It looks like I will have more sleepless nights ahead. :D
Joe Gores
 
OK John, I have figured out how to get at the right side. Instead of using a washer and nut on the aft side of the attachment strap, rivet a nutplate on instead. Bolt the right attachment strap to the floor before installing the tank. On the right side of the F-1204 heavy center channel, drill out the existing hole large enough so that the flat head of the 10-32 screw will slide through. A screwdriver can tighten the screw through the spar pin holes. Or an offset screwdriver will work like you used. The tank is NOT attached to the F-1204 channel. The enlarged hole in the F-1204 only provides access to the tank fastener on the right side.
Joe Gores
 
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John and Joe

I've decided when you two get too old to type you need to share a room at the nursing home. Are you sure you aren't twins that were separated at birth? lol
 
Good idea Joe

Joe, I like your idea. I would do more with the underfloor reinforcement. Consider making it a vertical plate about 6"x4" with a 1"flange on the top edge to take the nutplate. For the inboard mount, rivet it against a rib with an array of rivets (5x2) to fix it to the web of the underfloor ribfor the inboard mount, and a line of rivets through the baggage cpt floor into the flange. For the outboard mount make the flange wider, rivet the vertical face of the new underfloor bracket to the fuse side skin, and more rivets to the baggage compartment floor.
Also consider making the retaining bracket from .063" thick 4130 cromolly.
Sorry I cant quote RV12 part numbers but my plans are at the hangar
 
That's the ultimate fix.

Absorbs shock like nothing else, contracts with atmospheric pressure and depending upon the manufacturer, is self sealing against punctures.

Problem is ............. $$$$

How much is your life worth? If a tank ruptures and spills fuel into the cockpit, it could have devastating consequences. After spending 50 to 60 thousand dollars building an aircraft, the cost of a racing bladder type fuel cell isn't all that much, as compared to the benefits. Fuel Safe, ATL, etc. makes them in various sizes. I would imagine one could be found that would fit quite nicely.
 
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slow down

I know everyone with ideas has the best intentions in mind BUT we must step back and wait. This problem was caused by an aircraft CRASHING we havent seen pics of the rest of the damage and by modifiying the tank mounts then reinforcing the floor then what the fuselage etc we are playing design engineers when we are not. We dont know what the real scale of the impact was I realise that we dont want the tank to rupture but some of the suggestions may result in being hit by a full tank bouncing around a cockpit
 
Nylon???

Instead of making any changes to the design, you could probably use nylon bolts in those two spots. They would be plenty strong for normal use, but the heads would likely break off, or strip the threads, under the stress of a crash.
Someone could probably test it out pretty easily.
 
slow down or speed up

Crashly, most of us I'm sure know you are right about the need for an engineers approved solution. But that wont stop people musing about a fix. What would stop the chatter is a few official words from Vansaircraft. I have not read anywhere a written response from them. I feel I am being ignored as a customer about a safety critical issue. We have been left to make up our own judgement about the safety of the aircraft, which is as much an engineer's judgement, as is the best way to design an adequate fix. Come on Vans. Fair go. Talk to us!
Rod
 
Has anyone actually emailed Van's Aircraft and asked them for a direct comment?

As I've said before, personally I am content with the design but would take heed of any modification that Van's thinks is necessary IF they think a modification is required.

As a UK equivalent of an A&P, I'm certainly not qualified in anyway to come up with a better design than the team at Van's Aircraft.

Crashing an aircraft is bound to cause damage and potentially, injury. To design an aircraft that is 100% safe come what may is never going to happen. From what I gather the incident that started this thread wasn't in the book of normal flying.
 
Vans has a full set of pictures of the airplane that suffered the damaged fuel tank.

Van's engineering has also acknowledged that they are working on a solution. Implement one of the temporary solutions as suggested in this thread or wait for the revision from Van's. I am going to wait. Industry has taught me to wait for the engineered modification. A lot to consider and test. BUT, keep the suggestions coming, the folks at Van's watch VAF.
 
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It's constructive to talk about these issues, and it gives us a few ideas to mull over while we are waiting to hear what Vans solution is going to be. I like Joe's now that he has explained the right side attachment, and all are of them are interesting, but I am waiting, waiting, waiting, and flying as well.
Dick Seiders
 
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