RV-12: Fuel Tank Information / Modification

[rgmwa]

If the main gear rotated backwards at an impact angle of only 5-6 degrees, then maybe the centre channel needs some additional support as well, although I don't think it would be an easy fix. While it would be unrealistic to think that you could engineer out all the impact damage in the event described, I would like to think that Vans are looking at that aspect of the RV-12's design as well.

[JBPILOT]

With this hard an impact, something has to give. The landing gear is very strong, and the channel is obviously strong, so this is probably good as anything to absorb the energy, although it really twist things up. The only issue ( at this point anyway ), is the fact the fuel tank is mounted to that channel. Stopping the channel from opening the tank seems to me to be the main issue. An off-field landing could cause the mains to pull back and do what we have seen here. I have always thought the plastic in the side was the most serious issue with this tank. This is potentially worse it seems.

John Bender
322.7 hours

[Mich48041]

There is an old saying, "It is not the fall that hurts, it is the sudden stop". Stopping an aircraft over a distance of several feet will hurt much less than stopping in several inches. I agree with John that bending metal absorbs energy. If the aircraft were made stronger, it would not bend as much. Instead it would stop quicker in a crash, which would hurt more. In this crash, the pilot walked away. The RV-12 is a pretty good airplane. With a few improvements, it will be perfect.
Joe Gores

[D&M Dan]

I have often wondered why a bladder, similar to a race car fuel cell cannot be used. No more proseal, very little risk of a rupture.

[dick seiders]

How about placing stiff foam under the existing tank to hold it's present elevation above the floor, remove the AN3 bolts on the front, and install 2 or 3 elastic holdown straps that are anchored to the floor (pilot side) , and the longeron on the right side? (We would need to drop the elastic connection on the right side with a pair of brkts to anchor the restraint below the tank top). Another item is to connect the tank to the pump and vent using long enough stainless steel braided fuel lines. If the channel rotated in an impact it would be a non issue (hopefully) . If the floor pushed upward the tank and fuel lines would move with it. If any upward force was applied to tank independent of the floor it would move upward against the elastic retaining straps. The question is how will the rear 1/4 bolt securing the tank handle the upward movement? I suspect it may be OK as the tank brkt would likely rotate on the bolt. I am certain someone out there could determine the correct travel (aka resistance) allowed by the straps while still restraining the tank sufficiently in normal flight activity. These moves may be sufficient alteration for the flying RV12's out there. Van's will undoubtedly come up with a new tank before too long.
If they are interested I would like to suggest two 12 gallon tanks with each one mounted on either side of the baggage area allowing the baggage bulkhead removal and slightly aft of the gear channel. Just my two cents.
Dick Seiders 120093

PS Make the 12 gallon tanks out of vynil ester fibreglas.

[David Paule]

Originally Posted by D&M Dan

I have often wondered why a bladder, similar to a race car fuel cell cannot be used. No more proseal, very little risk of a rupture.

My Cessna 180 has bladder tanks. Each one holds 30 gallons. They lasted about 50 years and then started leaking. No complaints, and I hope the new ones do as well.

They are heavy and need to be snapped into the wing so that they hold their shape. They go aft of the main spar and forward of the rear spar, with the control runs going aft of that spar. Electrical connections go forward of the main spar. They have integral provisions for outlets, fillers, drains and gauges and with all that, aren't cheap.

There are failure modes associated with them. These are the two worst: they can have wrinkles which trap water, and they can come unsnapped if the vent clogs and suck up as fuel is burned. Since the tank bottom is lifting, the fuel gauge float doesn't show that it's running dry. There have been ADs for both of these.

All in all, they work pretty well. They've been reliable for me and when they leaked, it was a small leak. They've held 80/87, 100LL, 100/130 and unleaded non-ethanol car gas. They've had gasoline laced with Marvel Mystery Oil a few times.

I'm satisfied.

Dave

[Driftdown]

Originally Posted by D&M Dan

I have often wondered why a bladder, similar to a race car fuel cell cannot be used. No more proseal, very little risk of a rupture.

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 ............. $$$$

[Peterk]

The first take-away from this event should be the reminder that in-flight distractions kill. Any accident that compromises the fuel system will most likely take the occupants with it. No one enjoys the thought of a fuel fire but prevention begins in the left seat and this pilot was the first one to stress that.

Of course you can't avoid that distraction if you are not comfortable with the system you have installed. You are experimental so set it up to your comfort level and then please, "fly the plane with all of your attention."

Please don't take this as preaching....not intended...just don't think the topic is complete without bringing it up.

[Geico266]

Originally Posted by Peterk

The first take-away from this event should be the reminder that in-flight distractions kill. Any accident that compromises the fuel system will most likely take the occupants with it. No one enjoys the thought of a fuel fire but prevention begins in the left seat and this pilot was the first one to stress that.

Of course you can't avoid that distraction if you are not comfortable with the system you have installed. You are experimental so set it up to your comfort level and then please, "fly the plane with all of your attention."

Please don't take this as preaching....not intended...just don't think the topic is complete without bringing it up.

Good point Pete.

A couple of other key points is that Vans (IMHO) is more than a little concerned with everyone running in all directions to fix this, and it may not be necessary, and infact may be adding to the danger we are trying to avoid. Please remember this is the one and only incident out of several crashes inwhich the fuel tank was compromised. The RV-12 is a safe and proven airplane when flown properly and with respect. This particular tank was breached after a very hard landing in a nose down attitude. Fly the airplane and it would not have happened.

Granted, I modified the bolts, and will be adding the "Bender Binder" strap, but I would have felt very comfortable waiting for a couple of months for Vans official fix. Doing nothing is a viable option and your existing fuel tank set up would be safe for decades to come if you fly the plane.

Weight the options and decide for yourself. Waiting is a viable option also.

I really appreciate everyones interest and ideas. Keep them coming, but lets think this through very carefully.

[DonFromTX]

Another option I see little discussion on, is a plastic tank. Sonex has used that for years, no problems I know of. When I visited their hq I think they called them "rotationally molded tanks" whatever that means. Solves the leaking problems we have had, will distort in a small crash without spilling gasoline, and I would guess a heck of a lot cheaper as well.