Thoughts on gas tanks and a point.

Builders,

One of the most enduringly popular stories I have written is this one from 2012: Steel tube fuselages, “Safe” planes and 250mph accidents. The surface subject is a discussion of fuselage materials, but the bigger point behind it is getting builders to think about developing their own personal risk management assessments.

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Another one, focused more on todays topic was this one from 2016: Dated Sources of Information: Example – Fiberglass fuel tanks. Again, it has a deeper point, that what is popularly deemed “acceptable risk” changes over time, and todays builders should not blindly accept yesterday’s standards, particularly because some critical elements of building environment have changed.

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Today’s story is a bit more specific look at some example gas tanks, but it also has a bigger point drawn from it.

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Would you fly in a plane which had a plastic fuel tank in the fuselage with walls just the thickness of a spark plug gap? How about if that plane had no firewall between the motor and the gas tank? What if it had open vents also? What if I also told you these vents would pour gas on the engine if the plane was put on its back? Think I’m making this combination up? Guess again, this is the actual fuel tank from a Kolb mark III pusher aircraft, and it sat right behind the occupants, directly below the engine. This particular one was signed off by an FAA inspector, and flown for early 20 years. The fact it never burned the plane down is one of those things that leads me to repeat my personal mantra; “god has a sense of humor which I am yet to understand.”

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OK, some plastic tanks are very good. In the center of the picture above is the plastic tank from my 15′ Boston Whaler. It is indestructible. It was made by Jazz, a fuel cell manufacturer, and it came from Summit Racing. It was less than $200. In the field of experimental aircraft, the best known tank of this style is the custom made one that goes in a Sonex aircraft. These are excellent, and they have nothing to do with the glorified milk jug from the Kolb.

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On the other end of the picture, is the milk jugs replacement, an aluminum gas tank folded up, which I’m TiG welding up for my friend Alex to put back in the Kolb. There are two of them in the plane, they will be slightly over 5 gallons each. I am making them in such a way where they can be heavily distorted in an accident without bursting a seam. This is done with several subtle details, like having generous radiuses, having no butt welds, and having the ends be inserts with outward facing flanges. Of course the vents will be properly located, the plane will now actually have a sump to drain the tanks and check for water on pre-flights. Alex is a good guy. Friends with TiG welders don’t let other friends fly with milk jugs for fuel tanks.

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The Bigger Point: Every year, many people quit their project, because they hit a serious stumbling block they don’t like on the design. In about 90% of the cases, particularly with first time builders, they have picked the wrong system or detail to get bent out of shape about. They just need to talk to some other experienced builders and learn why a particular part is done the way it is. However, there are cases of things which builders may have a legitimate discomfort with. In that case, instead of fretting over it for months and letting it sap motivation, the solution is to enlist some help from AVIATION PEOPLE, NOT “RACE CAR” PEOPLE, and come up with a good workable solution, like I did with the tanks above, and get on with making it, and get back to finishing the plane. Don’t be one of the countless builders who allow a small issue to sap their motivation, let their project languish, and eventually never come back to it. Point: if you have an issue, go to the experienced builders with your specific plane, and only if you need to, align the detail design to better suit your own acceptable risk management standards.

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