Re: Fuel Storage on Airliners

Date:         30 Mar 99 01:53:44 
From:         "Jerry" <jerry.williamson@amd.com>
Organization: AMD
References:   1
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Balaji.Ramanathan@ual.com wrote in message ...
> I found out recently that conventional submarines (as opposed
>to nuclear ones) have a double layered hull and the space between
>the two layers is used to store fuel.  I am wondering if this
>approach is viable for airliners.
>
> Extremely rough back-of-the-envelope calculations seem
>to indicate that if a 747 fuselage had a double jacket with a one-inch
>gap for fuel, the fuel capacity can be increased by roughly 10000
>gallons (about 70000 lbs).  I would guess this is quite a significant
>amount of extra fuel and can potentially increase the range without
>impacting cargo storage or passenger space.

If I recall, the design range for the 747-400 is roughly 7500 nautical
miles. The Airbus A340-8000 has a design range of 8000 nautical miles.

The range of these aircraft is getting to the point where one must ask
the question "How far is long enough".

So my first question is, without an increase in engine power -- why
would you want to? Most passengers I've spoken with who have flown the
super long LAX to Singapore or LAX to Melbourne routes were ready to
climb out after 8 hours.

That's barely halfway into the flight!

I see the major thrust (literally) in design requirments to be in
increasing engine power so as to increase capacity. Carrying extra fuel
is important for a 20 hour flight, but my guess is that the extra cost
of carrying a relief flight crew makes it cheaper for them to schedule
a stop after a 12-hour leg.

> What are the issues here?  I am guessing that the landing
>gear has to be significantly strengthened and some runways would
>need to be lengthened/strengthened.  The most important question is
>whether there is a major safety issue here.  Belly landings would
>obviously not be advisable!

Landing gear would absolutely need to be strengthened. I do not think
lengthening runways any longer than they already are is practical.
Runways cost about $2500 to $4000 per foot to build or lengthen (150
feet wide).

The caveat is that Boeing would not want to have to sell an aircraft to
an airline and have only 30% of its destinations be reachable because of
runway length restrictions. [The IL-86 comes to mind...]

Any increase in added fuel capacity must also include an increase in
engine power. Otherwise, on those unplanned for emergencies where there
isn't time to complete a fuel dump,  our big and graceful 747 jumbo
might go off the end of the runway on return to an emergency landing--
and that would be a mess.....

> On the plus side, I would guess that the modifications needed
>to make the fuselage double-jacketed would increase the structural
>integrity of the aircraft significantly.

Yes, but it would also appreciably increase the weight. A 10% increase
in body stiffness would result in a 35,000 to 45,000 lb. increase in the
empty weight of the aircraft. Add to that, the 70,000 lb. increase in
intended extra fuel carried and we are now looking at close to a
1,000,000 lb. 747. The airlines (not to mention the FAA) would never go
for that at the current rated engine power.

> Any comments are welcome.

Very good questions, though.

I hope to see that 1,000,000 lb. 747-600 some day using the GE90 engines
in use on the 777-300 right now. Boeing says there isn't enough of a
market to justify the $10 billion investment in developing the Super
Jumbo. They oughta know.....

I just hope Airbus doesn't take a bath with the A3XX Very Large
Airplane.

/JW