Armor Protection and Self-Sealing Tanks

[Glider]

The first RAF aircraft designed from the start with armour was the Whirlwind. Any other aircraft had it fitted during the early months of the war. Luftwaffe and RAF aircraft in France were the first to be retrofitted and these were plates taken from French fighters which ones I don't know.

 

[stona]

The original 'self sealing' tanks were simply surrounded by a layer of material which expanded seal a hole. This only worked if the hole wasn't too big and the structure of the tank remained intact. Even a rifle calibre bullet passing through the contents of the tank could transfer enough energy to the contents to rupture the tank. It's why I originally said that even calling them self sealing was a bit optimistic. I don't have weights for these materials (like Linatex) to hand but it can't have been hundreds of pounds on or around the typical tanks of that time.
Later self sealing fuel cells were significantly heavier than an equivalent aluminium tank, but 100s of pounds?

The real weight must surely be in armour plate. A standard Fw 190 A-8 carried 145.7 Kg (320lbs) of armour and a heavily protected 'Sturmjager' version 337.3 Kg (744lbs) which shows just how much could be bolted on or into an airframe.

Cheers

Steve

 

[fastmongrel]

I thought the first armour for Hurricanes in France came from crashed Battles or is that an urban myth.

 

[Shortround6]

The Hellcats fuel system weighed about 460lbs ( it is going to vary a few pounds from plane to plane). This includes the weight of fuel lines and valves. Since no F6F was built without self sealing tanks it is a little hard to figure out the difference between non self sealing tanks and the self sealing ones. The weight of the armor was often included in the "armament provisions" category which also makes it hard to break out on it's own.

Self sealing tanks can vary quite a bit in weight since the weight rather depends on the square footage of the tank walls so even for the same type of protection a short fat tank will weigh less than a long skinny tank of the same capacity.

 

[fastmongrel]

It's why I originally said that even calling them self sealing was a bit optimistic.

Cheers

Steve

Possibly a less misleading title would be leak resistant.

 

[Shortround6]

They may have worked fairly well against rifle caliber machine guns bullets depending on the size of the tank, how full it was and if the bullet hit above or below the liquid line.

A single (or even a couple) of rifle bullets are unlikely to burst the seams or even bulge large fuel tanks. 12.7-13mm bullet not only makes a bigger hole, (how many mm from the edge of the hole can the sealant creep in?) but with 3-4 times more energy has a better chance of bursting the tank. 20mm cannon can have 1 1/2 to 2 times the energy of the 12.7-13mm projectiles even without exploding.

For hydraulic rupture to occur the tank needs to be full or nearly full or the shock wave will be dissipated into the empty space. Planes with one large tank are safer in this regard than planes with several small tanks.

 

[stona]

I thought the first armour for Hurricanes in France came from crashed Battles or is that an urban myth.

This comes from an account from Paul Richey of No. 1 Squadron. He claimed that the Air Ministry refused to fit armour to the Hurricanes in France and that his commander 'Bull' Halahan had the armour from a Battle fitted to his Hurricane and flown to Farnborough to show that it could be done. The story is rather fanciful I'm afraid. In fact by mid 1939 the Air Ministry had approved armour behind the pilot on single engine fighters and Hawker mocked up a removable 4mm armour plate to meet the requirement. An Air Ministry report of 29th August stated that "there should be no difficulty fitting this armour in service and the design of the plates is very simple."
On October 20th the Air Ministry ordered back armour to be fitted to all Hurricanes. This came too late for those in France but the facts still rather undermine Richey's story. It's a good story but not strictly true. It should probably be filed under 'aviation myths'. Like most myths it may contain a grain of truth. Maybe Halahan did adapt some armour for his Hurricane, but he certainly didn't fly it to the UK to show the Air Ministry how to do it
Cheers
Steve

 

[stona]

For hydraulic rupture to occur the tank needs to be full or nearly full or the shock wave will be dissipated into the empty space. Planes with one large tank are safer in this regard than planes with several small tanks.

The boffins at Orfordness agreed. Later self sealing fuel cells were often suspended by straps or webbing and not mounted with solid fixings in a further effort to disperse the energy of an impacting projectile.

Cheers

Steve

 

[Garyt]

The other issue with a self fueling fuel tank is that it would hold a significant less amount of fuel than a standard tank of the same volume. Not that this could not be countered by making more of the interior of the plane dedicated to fuel storage, but an issue none the less.

I'd think there might be potential stability issues if you would try to place the same amount of fuel aboard an aircraft that was no initially designed to have self sealing fuel tanks. Similar perhaps to the issues the P-51 had while it's fuel tank behind the pilot was full.

I would think that in order to place self sealing fuel tanks on a zero and to keep similar performance you would have to reduce the planes range somewhat significantly.

 

[Mike Williams]

Regarding early Hurricane armour:

Regarding early Spitfire armour:

 

[Glider]

I thought the first armour for Hurricanes in France came from crashed Battles or is that an urban myth.

I think it must be an urban myth as the Battle didn't have any armour either, no RAF aircraft had armour at the time

 

[stona]

Nice stuff posted in those ORBs. As the Air Ministry and Hawker intended it is clear that the plate could be fitted at the squadron by its personnel and did not require a manufacturer's work party.

I understand that some Battles, starting with 40 Squadron, did receive 'some armour' when they deployed to France before the 'phoney war'. This lends some credence to the origin of Richey's story though it has obviously been somewhat embellished in the telling.

Cheers

Steve

 

[Greyman]

I think it must be an urban myth as the Battle didn't have any armour either, no RAF aircraft had armour at the time

This is very incorrect - I'd go so far as to say that probably most (at least the important types) RAF types had armour by the time the Battle of France kicked off. I don't have time to dig into it immediately but hopefully sometime I can get a rough breakdown on when the main types were getting their armour.

EDIT:

Quick little bit I found off the bat ...

'Deliveries of the armour plate are now coming through to Faireys and Austins at the rate of about 20 sets to each firm per week and are being fitted to current construction aircraft at a rate of a little less than 20 sets per week. ' - Armouring Modifications, Battle, 29 July 1939

 

[stona]

Thanks for that which confirms a note I had about armour being fitted to Battles by early 1940.
Cheers
Steve

 

[Glider]

I stand corrected thanks to all. The book that I was taking the information from was Fledging Eagles by C Shores which proves that everyone is human

 

[stona]

I stand corrected thanks to all. The book that I was taking the information from was Fledging Eagles by C Shores which proves that everyone is human

It is a demonstration of the power of Wikipedia to misinform. It's entry has been quoted or paraphrased on numerous sites on the internet and they are all wrong
It may be that the Wiki entry originates from the same, usually reliable, source that you quoted.
Steve

 

[Glider]

I went from the book which is a pretty good read

 

[stona]

I went from the book which is a pretty good read

I have several of Smith's books, admittedly from a few years ago, but they are generally pretty good.

Steve

 

[pbehn]

from memory Hawkers didnt initially put self sealing in all the tanks on a Hurricane wiki says it was the gravity feed main tank I thought it was the wing tanks ...dont have any books here to read up on it. In the BoB Hirris were much more likely to catch fire than spits because of this. Hurricanes in the BoF didnt all have armour fitted as some pilots were scrabbling about to lash up their own.

 

[stona]

Many Hurricanes in France had only the deflection armour over the cowling. Armour was retro fitted to many aircraft at squadrons, but only if the relevant kit could be provided to them. It was intended to fit the armour to Hurricanes abroad as originally the armour was to be detachable as "it will not be needed for home defence purposes." The order to fit it to ALL Hurricanes did not come until 25th September 1939, too late for some in France.

The officer who pushed hardest for this 'rear' armour was Sholto Douglas. I may have criticised him for many things, but in this case his attitude surely saved many lives. It was Dowding who felt that rear armour was less important than protection from the front, from return fire from the fighters intended target, the Luftwaffe bombers. Dowding pushed hardest for 'armoured' windscreens. Between them they just about got the job done.

Linatex was initially fitted to the wing tanks and not the gravity feed tank of the Hurricane (according to McKinstry). The reason for this omission is variously given that it was difficult to remove the tank and that it was considered well protected, sandwiched between two bulkheads. Sadly it was all too vulnerable and 'Hurricane burns', caused when a pilot opening the canopy caused the flames to be blown into his face, became a terrible legacy of the oversight. This time it was Dowding who demanded that the fuselage tank be retro fitted with a Linatex covering. 75 Hurricanes a month were modified by Hawker. This must have been sometime in late 1940 but I can't find a date.

It is worth saying here that many pilots did not think that the tank in front of the pilot was the main culprit, but rather the two 35 gallon wing tanks. They were much easier to hit and there were no blanking plates between the wings and the fuselage. Burning fuel was drawn into the cockpit by the natural draught patterns. Tom Neil of 249 Squadron wrote that all fighters were "susceptible to the fire hazard; the Hurricane was perhaps worse than some." Short of redesigning a major part of the aeroplane there was little to be done so, according to Neil, the plane was left with " two wells of highly combustible liquid sloshing about asking to be ignited by a passing cannon shell."

Cheers

Steve