Thanks, But No Tanks?

Yes it's aerodynamically and structurally far more efficient than a tube and wing, but the usual criticism of Boeing's blended wing-body (BWB) airliner concept is that for most, maybe all, of the passengers there would be no windows.

Forget about the lack of windows, how would you feel sitting in an airliner surrounded by a fuel tank - full of cryogenic liquid hydrogen? That's the prospect raised by a new U.S. patent granted to Boeing (number 7,871,042) for a "hydrogen fueled blended wing body ring tank".

Graphic: USPTO

The engineering logic is impeccable. Hydrogen has higher energy density than jet fuel, so for the same weight of fuel an aircraft can fly further. And it virtually eliminates emissions, producing water when burned. But hydrogen weighs a lot less than jet fuel, requiring huge tanks. Huge and heavy, as the hydrogen has to be cooled and pressurized so it can be stored as a liquid.

Previous designs for hydrogen-fuelled aircaft have either had insufficient fuel to be useful, have sacrificed passenger space for fuel volume or have simply been bulbous and unaerodynamic, Boeing's patent, applied for in 2006, gets around this by embedding a toroidal fuel tank within the generous mold lines of a blended wing-body.

A continuous ring avoids the end domes found on cylindrical pressure tanks, reducing weight for a given fuel volume. The BWB's shape also allows the ring tank to be enclosed within an aerodynamic form, without encroaching on the passenger or cargo areas inside.

What isn't clear is quite how those passengers and cargo would get in and out of the aircraft. And encircling the passengers with a ring of liquid hydrogen would seem only to make worse those two recurring criticisms of the BWB - the lack of a view outside and the ability to evacuate the aircraft quickly in a fire.

(To be fair, the patent does actually propose tilting the ring tank nose-down so it forward part passes under the pressure cabin, presumably to allow for access and egress via for forward fuselage.)

Still, if we are ever to have zero-emissions hydrogen-fuelled aircraft, the BWB might make more sense than flying around with a giant cryogenic fuel tank sitting above the passengers' heads. Although at least you could still see out of the window...


Photo: European Commision

Tags: tww, Boeing, BWB, propulsion