Fuel Tank in Cabin: Data pertaining to relative risk

[conodeuce]

I've heard from various sources over the years that having a fuel tank mounted in the cabin is not as safe as having a tank located in the wing. In a crash scenario, I think this is intuitively obvious.
But, aside from casual anecdotes, I wonder if information exists that would clarify whether the increased risk is sufficient enough to make relocating the tank to another location a smart idea worthy of the impact on the design (CG changes etc).

I ask because the designer of my aircraft, an Acey Deucy, specifies the location just aft of the firewall, mounted behind the forward cockpit's instrument panel.

Thanks in advance for any information.
7083

[Sam Buchanan]

Builder's discretion. I guess the fatalistic way of looking at it is to recognize that a crash bad enough to rupture the cowl tank is going to be a very bad day all the way around.........

There is the possibility of a fuel leak getting your legs wet, but......

I have either owned or built four aircraft with cowl tanks (one of which was the ubiquitous J-3 Cub) and I've never spent any time worrying about them (for the above reason...).

[Bob Dingley]

I learned to fly in a J-3 and owned a Champ. Didn't think much about safety until Uncle Sam sent me to Arizona State U to take the Crash Survival Investigators course. I had a flashback to a J-3 accident when the pilot died in a max T.O. stall and a flaming crash. His passenger died 3 days latter. It was the same J-3 that I got my PVT in.
The course at ASU taught me that wing mounted tanks are far safer than 12 gallons of avgas in your lap. The course further suggested that Break-a-way fittings in the wing-fusalage area are the best solution. ( Summit Racing catalogue) Next best is to have slack or a loop in the fuel line at the fuselage juncture to deal with flexing at impact.
The worst arrangement is whats in a Luscombe 8A. A tank BEHIND you. It also has fuel feed problems. I loved my 8A. It had been converted to two 11.5 gal wing tanks.
Bob

[CarlOrton]

Sonex aircraft have 17-18 gals of fuel right over your legs, behind the panel (I built one). With the newer materials, they filled one of their rotationally-molded tanks with water, plugged the openings, and tossed it off the hangar roof. It didn't rupture. As Sam noted, that bad a crash and you've got more to worry about.

[conodeuce]

Exactly. The roto-mold tanks are the way to go. I'll be pricing the cost for a custom tank. Hopefully it's in my budget.

[DaleB]

Exactly. The roto-mold tanks are the way to go. I'll be pricing the cost for a custom tank. Hopefully it's in my budget.
Let us know what you find out, would you? I didn't know you could even get a custom roto-molded tank made. I'd be interested to know where (if) you can, and how expensive it is.

[conodeuce]

Let us know what you find out, would you? I didn't know you could even get a custom roto-molded tank made. I'd be interested to know where (if) you can, and how expensive it is.

I will model the fuel tank using SolidWorks. A company I found during a casual web search earlier this week accepts designs in this format. Once I have a quote, I will post here.

The first company I will approach is MODRoto in Ohio.

See: http://www.modroto.com/custom-molding/get-quote/

[martymayes]

The first company I will approach is MODRoto in Ohio.

See: http://www.modroto.com/custom-molding/get-quote/

That's pretty cool. Are you going to tell them this is for your bobsled?

[planecrazzzy]

.
This one is about 30 gals.... Feel better ?

Most Tailwinds carry at least 20 gal like this.

Gotta Fly...

[rwanttaja]

https://www.slso.org/image/production/image/1617_Spirit_of_St_Louis_500.jpg

Ron Wanttaja

[conodeuce]

Re: (Spirit of St. Louis pic)

The immense size of Spirit's tank was really made clear in this EAA Webinar video (after about one hour in):

http://www.eaavideo.org/detail/videos/webinars/video/5559385924001/webinar--modeling-the-spirit-of-st.-louis-in-solidworks

[PB339]

We all know that aviation has inherent risks. I don't believe any of the fuel systems in light aircraft are designed to purposely impact solid objects. As one who has experienced such a situation, with 25+ gals just behind the panel, I believe it is the luck of the draw. (or maybe the grace of God) My fuel tank split open, the lines were torn loose, and miraculously, there was no fire. I think is equally important, to reduce or eliminate any spark producing appuratus, prior to impact, either by design or physically. (Master)7093

[conodeuce]

That's quite a gash, there, PB339. If you wouldn't mind describing your airplane, I'd appreciate it.

[PB339]

7099The aircraft was a Starduster Too, with a 220 Cont radial. The fuel tank was right behind the firewall, and carried 28 gals.7098

[Frank Giger]

Yikes!

I would be very, very hesitant to move the fuel tank from a position other than what is specified in the plans.

[WLIU]

Aviation is about risk management. There are a very large number of airplanes flying with fuel tanks in front of or behind the pilot. The number of crashes is small. The number of crashes that result in a fire is smaller. The best plan is to avoid crashing. Would we like there to be no accidents of incidents? Of course. But those folks who suffer from the illusion that the aviation accident rate could be zero are best advised to keep their flying hours to zero.

Moving the fuel tank in a proven design requires re-engineering the entire design. And plastic fuel tanks are heavier and have somewhat less capacity if they are sized to fit in the same space as the original AL tank. The good folks at Sonex started from scratch to incorporate plastic tanks in their design. Changing an existing design is generally more work. Best to follow the plans for what you have or build a Sonex. And keep your brain ahead of the airplane to avoid a crash.

Best of luck,

Wes

[conodeuce]

PB339, that is one beautiful airplane. I got to briefly take the controls of one over twenty years ago. For a guy that was flying a Cessna 140 at the time, it was an exhilarating twenty minutes.

[conodeuce]

Let us know what you find out, would you? I didn't know you could even get a custom roto-molded tank made. I'd be interested to know where (if) you can, and how expensive it is.

What I've learned so far is that, once a mold has been created, generating copies of the fuel tank (14 gal) is very inexpensive (perhaps as low as 50 dollars). The particular plastic recommended is Cross-linked Polyethylene (XLPE).

The major cost is in fabricating the mold -- a few thousand dollars (rough quote of 5000 USD). So, this is only economical if a few builders of the same aircraft were to share the expense.

Taking into account the responses in this discussion thread, I feel comfortable proceeding with the fuel tank's designed location aft of the firewall. I'll make a final decision on tank material a little farther down the road.

It has been helpful to have the input of experienced builders. Many thanks.

[Mike Switzer]

Food for thought: For many years the fuel tanks in pick up trucks were behind the seat. Occasionally, due to poor maintenance & not replacing old hoses someone smoking might have a fire but you rarely heard about it. Then, for "safety", Chevrolet (and GMC) started putting the fuel tanks under the front of the bed on the driver's side. If a Chevy truck made during those years was t-boned on the driver's side they frequently caught fire. In later years the fuel tanks on all trucks were moved to be inside the frame rails.

I would think that a fuel tank located inside a steel tube fuselage would be inherently better protected from rupture in the case of a crash. In the design I am working on (on hold due to family reasons) I will probably put the fuel tanks in the wing roots but inside a steel tube structure connecting the spars to the fuselage.

[planecrazzzy]

One other thing to add...

The Aluminum used to make tanks is not 6061....

It's 5051... a softer aluminum...It "Gives" better..
.
Gotta Fly...

[planecrazzzy]

This Tailwind gave it's all... No Fire
.
Gotta Fly...
.