Blenheim self-sealing fuel tanks and weights?

[Pinin]

First question, it appears to me that Blenheim never had self sealing fuel tanks, at least looking that the capacity of main fuel tanks remained the same. Can this be confirmed?

Second Question:
I am a bit stuck with explaining Blenheim empty weights that increase a lot.

Blenheim I = 8100lb
Blenheim IV = 9823lb - for this i can account only for a double machine gun instead of a single one in top turret and respective ammo plus the new fuel tanks with associated pipes and controls. I am not aware of increased armor. I would not give more than 500lb for the fuel tanks,etc and maybe 100lb for the extra machine gun+ammo.
This would put the aircraft at 8700lb not 9800lb So if my data is correct where the weight came from?


There is also the case of improved engines but i doubt it would increase that much the aircraft weight.

 

[herman1rg]

Maybe the difference is because of the extended nose?

 

[stona]

The Blenheim IV was based on the Bristol Type 149. It was quite a bit longer (I remember 3ft in the fuselage) and of course had the extended nose. Two 94 gallon fuel tanks and associated plumbing would add a significant weight. Did they include a fire surpression system? These were quite heavy. Add to this the Mercury XV engines and also a heavier propeller unit ( De Havilland as opposed to the Rotol 'bracket' unit of the Mk I) as well as minor increments in the weight of internal fittings (small things like a table for the navigator) and the all up weight soon creeps up.
Cheers
Steve

 

[Pinin]

Of course the extended nose!

My only excuse is that was late in the day.

 

[Greyman]

The Blenheim was getting self-sealing tanks (Semape) in February 1940 at the latest.

I think a Blenheim IV in 1941 generally had a modifications-incorporated list about 150 strong. Self-sealing tanks, armour plate, and increased defensive armament to name some of the weightier items.

 

[Pinin]

Self sealing tanks usually change the tank capacity i have never seen that regarding Blenheim.

 

[Greyman]

Same here. I suppose they had enough room to not lose any notable capacity.

Figures I have for the Blenheim Semape covering are 19/32 inches thick - 1.40 pounds per square foot.

 

[Pinin]

Thanks. But that would be a rarity, i think we lack information.

 

[Greyman]

I don't have the full picture as of yet - but between Feb and Jul 1940 the 'Semape Covering Programme' produced 1484 Blenheim tank coverings ... so I don't think it was that much of a rarity.

 

[Pinin]

Sorry, by rarity i mean a case where a semaped tank has same fuel capacity as a non semaped one.

Edit:
A semaped tank has a much bigger volume, in wing tanks for example it would need not only to compensate for the lost volume in horizontal plan but also in vertical plan because initial Blenheim designers would not have wasted vertical space in first non self sealing tanks.

 

[Greyman]

At 15mm in thickness, I could see how there would possibly be enough spare room to have a negligible effect on tank capacity. Especially since I have a hunch only the main, inner, 100-octane tanks were self-sealing.

Again, I don't have the full picture yet and I'll keep my eyes open.

 

[Pinin]

Thanks

 

[fubar57]

Blenheim Mk.V. fuel capacity...

 

[Pinin]

That's the information i have for IV also.