# Self Sealing Fuel Tanks



## Matt308 (May 17, 2005)

As many of you know the self sealing fuel tank was quite a leap in technology in the early last century. I have a couple of questions.

1) Who (person/country/company/etc) invented self sealing fuel tanks?

2) When?

3) In what airplane were they first installed?

4) Can you describe the technology used?

Here is what spawned my question. I do know that the Germans made use of self sealing fuel tanks in Do17s during the BoB. The fuel tanks were surrounded by a 1cm liner that consisted of alternating layers of vulcanized and non-vulcanized rubber. The final outer layer was actually leather. Apparently, a rifle round would penetrate this outer 1cm thick liner and the resultant fuel leak would set up a chemical reaction that would literally melt the rubber back together. I am assuming the leather was an expedient means of containing the inner layers and prohibiting a "runaway" chemical reaction.

The above questions are hopefully going to stimulate some discussion of the origin of self sealing techniques and where they originated from.


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## FLYBOYJ (May 17, 2005)

I do know in later years some C-130s has self sealing tanks with some foamy crap that eventually broke down and had to be removed because it kept clogging fuel pumps.


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## Matt308 (May 17, 2005)

Well this why I ask, as I don't know how technology has progressed. Many might recall that after the TWA 800 accident and the resultant blame on an explosive center fuel tank, the FAA mandated a change that required insertion of inert gas to minimize the chance of volatile fuel vapors igniting.

I do know that as time has progressed, this was originally a military idea that has now been adopted by civil aviation. This technology is only one of many facets that have been spawned from the WWII era idea of self sealing fuel tanks.

I'm curious if the vulcanized/non-vulcanized rubber solution was universal or if there were other solutions implemented. Seems like a good topic for the forum.


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## DerAdlerIstGelandet (May 19, 2005)

I know we have self sealing tanks in the Blackhawk and it is basically a bag! Exactly how it works I do not know.


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## Glider (May 19, 2005)

Matt. My understanding is basically the same as yours as to how it works, ie the rubber melting back to fill the hole. There is an example in Duxford of a Typhoons self sealing tank which works on the same principle. As to who had them first I don't know but Germany and the UK seems to have developed the basic idea at the same time. In the Battle for France the British suffered heavy losses because of the lack of self sealing tank and armour for the pilot. By the BOB both the Germans and ourselves had the same solution so I would call it a draw. Proof I suggest that necessity is the mother of invention.
The gas was different. I could be wrong here but my belief is that it wasn't there to stop the tank from leaking, more to stop the explosive gas from blowing up.


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## Matt308 (May 19, 2005)

Agreed that the leaking was only a catalyst for the rubber chemical reaction and that the objective was to prevent explosion/fire. Petrol is an interesting solution in that it is only volatile if there is petrol vapor. You can douse a match in liquid petrol, but if petrol vapors are present you have a problem.


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## FLYBOYJ (May 19, 2005)

Matt308 said:


> Well this why I ask, as I don't know how technology has progressed. Many might recall that after the TWA 800 accident and the resultant blame on an explosive center fuel tank, the FAA mandated a change that required insertion of inert gas to minimize the chance of volatile fuel vapors igniting.



I think the Feds are looking to have a way to put argon or nitrogen into the tanks, but I think this would be applicable to aircraft manufactured after 2006. Also the actual wire insullation was always subject too, many thinking that the flight 800 bird still had Kapton insulation wire in the fuel tanks.


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## DerAdlerIstGelandet (May 22, 2005)

Hmm that I did not know. What else do you know about that.


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## FLYBOYJ (May 22, 2005)

I know Kapton wire was a big problem on the early F18s, the wire insulation would break down, heat up and then burn. As far as the Feds looking at inert gas in fuel tanks, I'll look on the FAA website and the the "Notice of Proposed Rulemaking," this will explain the full plan.


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## Nonskimmer (May 22, 2005)

FLYBOYJ said:


> I know Kapton wire was a big problem on the early F18s, the wire insulation would break down, heat up and then burn.


That _might_ explain a few of the accidents with the Canadian Air Force CF-18's, early on. I don't have info on the details of those early mishaps, but I seem to recall some concern about wiring with a couple of them.

Maybe, maybe not.


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## FLYBOYJ (May 22, 2005)

Nonskimmer said:


> FLYBOYJ said:
> 
> 
> > I know Kapton wire was a big problem on the early F18s, the wire insulation would break down, heat up and then burn.
> ...



When the US Navy as first introducing the Harpoon, much of the wiring to the weapon would fry right after the thing was launched, I heard one engineer say "they should just replace the Kapton wire with a giant fuse and light it with a match."


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## Nonskimmer (May 22, 2005)

Not a good thing, to be sure.


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## Andrew (May 23, 2005)

> FPT Industries Limited, formerly Fireproof Tanks Limited, was formed in 1939 to manufacture self-sealing coverings for metal fuel tanks of Military aircraft. This led to the development of flexible fuel tanks and associated products.



This is some info that I managed to find about self sealing fuel tanks.


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## FLYBOYJ (May 24, 2005)

Here the FAA link on a report for using nitrogen in fuel tanks:

http://www.fire.tc.faa.gov/pdf/99-73.pdf

See below as well!

WASHINGTON- The U.S. Department of Transportation's Federal Aviation Administration (FAA) today issued a rule that requires airplane manufacturers and operators to change how airplane fuel tanks are designed, maintained and operated. 

The FAA rule, the most comprehensive fuel tank safety initiative ever put forward, includes a Special Federal Aviation Regulation (SFAR) to minimize the potential for failures that could cause ignition sources in fuel tanks on new and existing airplanes. It also includes a regulation that, for the first time, mandates airplane design changes to minimize the flammability of fuel tanks on new airplanes.

"Although aviation remains an incredibly safe way to travel, our extensive research and evaluation of past design philosophies and certification practices show that it's time for a new approach to fuel tank safety," said FAA Administrator Jane F. Garvey. "The FAA's rule is an aggressive plan that will certainly raise the bar in aviation safety."

Since the tragic Trans World Airlines (TWA) 800 accident in July 1996, the FAA has focused on the three fundamental areas that keep airplane fuel tanks safe: the prevention of ignition sources, fuel flammability, and fuel tank inerting. Based on recent FAA and industry research and tests, the Aviation Rulemaking Advisory Committee (ARAC) continues to evaluate fuel tank inerting and is expected to make recommendations to the agency in July.

The SFAR portion of the rule affects 6,971 transport airplanes with 30 or more seats manufactured by Airbus, Aerospatiale (ATR), Boeing, British Aerospace, Bombardier, De Havilland, Dornier, Embraer, Fokker, Lockheed, Saab and Shorts. The SFAR amends current FAA rules for both existing and new model airplanes. 

For existing airplanes: ·Manufacturers must conduct a one-time design review of the fuel tank system for each transport airplane model in the current fleet to ensure that failures could not create ignition sources within the fuel tank.

·Manufacturers must then design specific programs for the maintenance and inspection of the tanks to ensure the continued safety of fuel tank systems.

Operational changes for existing airplanes: ·Based on the information provided by the manufacturer under the SFAR, operators must then develop and implement a FAA-approved fuel tank maintenance and inspection program for their airplanes. 

For new airplane types: ·Manufacturers must further minimize the existence of ignition sources in fuel tanks. Future transport category airplanes will be designed to better address potential failures in the fuel tank system that could result in an ignition source.

·Manufacturers must develop maintenance and inspection programs to ensure fuel tank safety.

·Some airplane types are designed with heat sources adjacent to the fuel tank, which can heat the fuel and increase the formation of flammable vapors in the tank. The rule requires manufacturers to reduce the time fuel tanks operate with flammable vapors in the tank by designing fuel tank systems with a means to minimize the development of flammable vapors in the fuel tank or a means to prevent catastrophic damage in the unlikely event ignition occurs.

Manufacturers have 18 months from June 6, the effective date of the rule, to conduct the safety reviews and develop maintenance and inspection programs required by the SFAR. Operators have 36 months from June 6 to incorporate an FAA-approved maintenance and inspection program into their operating procedures. Together, these initiatives are estimated to cost the industry $165 million over 10 years. Specifically, the fuel tank review will cost $38 million; changes to maintenance and inspection programs will cost $92 million; lost net revenue will cost $24 million; and additional recordkeeping requirements will cost $10 million. 

The FAA has issued or proposed nearly 40 airworthiness directives (ADs) on fuel tank safety. These actions were taken from lessons learned in the TWA 800 accident investigation or through targeted FAA inspections and service history reviews. The agency may issue additional ADs based on the new data gathered from the design review of existing aircraft mandated by the SFAR. 

The SFAR is available on the FAA's web site at www.faa.gov/avr/arm/nprm.htm. Three fact sheets, dated July 2000, that address fuel tank inerting, flammability, research, and ADs are also available on the FAA's web site at www.faa.gov/newsroom.htm. 

###

An electronic version of this news release is available via the World Wide Web at: http://www.faa.gov/apa/pr/index.cfm


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## DerAdlerIstGelandet (May 24, 2005)

Aha thanks.


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## FLYBOYJ (May 24, 2005)




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## DerAdlerIstGelandet (May 24, 2005)

So how long have you been in the aviation field? I have been it a mear 6 years now.


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## FLYBOYJ (May 24, 2005)

DerAdlerIstGelandet said:


> So how long have you been in the aviation field? I have been it a mear 6 years now.



I'm giving my age away but this year is going to be 28 years. Right after high school I started in A&P school. At the same time I landed a job at an aircraft savage company. I worked with them on and off part time until I completed the A&P course in 1980.


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## DerAdlerIstGelandet (May 24, 2005)

Aha, lots of experience then. I am a newbie compared to you!


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## FLYBOYJ (May 24, 2005)

DerAdlerIstGelandet said:


> Aha, lots of experience then. I am a newbie compared to you!



Maybe less time in the business, but never a newbie. You've maintained and operated aircraft in a combat environment. The skill and determination needed for that over the course of one year is worth 10 in the civilian world in my book!


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## DerAdlerIstGelandet (May 24, 2005)

Thanks. I hope to be doing this for a very long time. I love the work.


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## FLYBOYJ (May 24, 2005)

If its in your blood, you're always be in this business. At times its been rough, but I can't imagine doing anything else, well maybe Bordello Management

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## evangilder (May 24, 2005)




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## DerAdlerIstGelandet (May 26, 2005)

Yeah I thought about renting myself out!


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## FLYBOYJ (May 26, 2005)




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## DerAdlerIstGelandet (May 26, 2005)

Its just a living, someones got to do it.


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## Vahe Demirjian (Jan 5, 2020)

What Italian and Soviet aircraft from WW2 had self-sealing fuel tanks?


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## Greyman (Jan 5, 2020)

As a general rule it seems Italian aircraft did.

I don't have any production narratives but as early as November 1940, the crashed CR.42s and BR.20s examined in England all had self-sealing tanks (though no armour plate).


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## GregP (Jan 6, 2020)

You might try looking at this document: http://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-T/download.php?spec=MIL-T-5578C.013565.PDF 

It is a pdf of the spec for self-sealing tanks. Basically, it specified a tank that withstands the vibration from flight, takeoff and landing (Protection A) and from the hydraulic effect of gunfire and engine damage (Protection B). Interesting read.


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## Koopernic (Jan 6, 2020)

Glider said:


> Matt. My understanding is basically the same as yours as to how it works, ie the rubber melting back to fill the hole. There is an example in Duxford of a Typhoons self sealing tank which works on the same principle. As to who had them first I don't know but Germany and the UK seems to have developed the basic idea at the same time. In the Battle for France the British suffered heavy losses because of the lack of self sealing tank and armour for the pilot. By the BOB both the Germans and ourselves had the same solution so I would call it a draw. Proof I suggest that necessity is the mother of invention.
> The gas was different. I could be wrong here but my belief is that it wasn't there to stop the tank from leaking, more to stop the explosive gas from blowing up.



Some Russian aircraft had a system that ducted engine exhaust gas into the fuel tank voids, the MiG 3 for sure. There are two requirements for getting an explosion in terms of fuel/air vapour concentration. 1 by being above the LEL (Lower Explosion Limit) and 2 by being below the UEL Upper Explosion Limit. By putting in an inert gas you greatly reduced the chance of having an explosion. Modern fighter aircraft generate their own oxygen from an oxygen concentrator system. I imagine the by-product nitrogen is channelled into the fuel tank voids.

Early uses using nitrogen were on the Handley Page Halifax III and VIII, Short Stirling, and Avro Lincoln B.II, which incorporated inerting systems from around 1944 according to Wikipedia.

I think many aircraft also had bladder tanks. If these were penetrated they might rapid form an explosive atmosphere when they leaked into the void of the tank space.

From recollection the self sealing walls of the Do 217 were an inch thick but again used rubber. It's worth mentioning that the Germans had a terrible time getting natural rubber, although they were able to manufacture buna-s and buna-n synthetic rubber it worked much better when a proportion of natural rubber was added (10%-20%).

A CIOS report I read said that the Germans had developed explosion and fire resistant gasoline fuels and this mentioned that the allies had as well. They were never implemented due to cost. This of course conforms to what we know about explosion resistant jet fuels which have never been commercially deployed despite being developed. The SR71 used a jet fuel which has such properties since the fuel tended to leak and was used as a heat sink for hypersonic flight. Kerosene and diesel is of course generally safer than gasoline due to its lower vapour pressure but I have been told that pure iso-octane can be used to douse out fires it so reluctant to ignite. (don't try at home, its hearsay)


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## MikeMeech (Jan 7, 2020)

Matt308 said:


> As many of you know the self sealing fuel tank was quite a leap in technology in the early last century. I have a couple of questions.
> 
> 1) Who (person/country/company/etc) invented self sealing fuel tanks?
> 
> ...



Hi

Although this is an old thread that has re-appeared I thought I would just add some information on the origins of 'self-sealing' fuel tanks from a report by the USAS at the end of WW1. There is a list of various tanks plus some detail of the 'Imber' tank.

Mike

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## Dimlee (Jan 24, 2020)

Vahe Demirjian said:


> What Italian and Soviet aircraft from WW2 had self-sealing fuel tanks?



Soviet.
Some of those types:
R-10
I-153
DB-3/Il-4
MiG-3
Yak-7
Yak-9 (Yak-9DD from the start)
Pe-2
LaGG-3
Yer-2
La-7
probably:
latest SB-2 after modifications done by the team of Arkhangelsky and Ar-2.
Su-2 of later production, after summer 1941.

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## elbmc1969 (Oct 29, 2020)

And more thread necromancy ...

See _Exploding Fuel Tanks_ by Richard L Dunn. Seems to be a self-published volume.


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