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Boeing's Hybrid Electric Airliner of the Future
fergus07 writes "Borne out of the same NASA research program that gave birth to MIT's D 'double bubble,' Boeing's Subsonic Ultra Green Aircraft Research (SUGAR) Volt concept is a twin-engine aircraft design notable for its trussed, elongated wings and electric battery gas turbine hybrid propulsion system — a system designed to reduce fuel burn by more than 70 percent and total energy use by 55 percent. The goal of the NASA supersonic research program is to find aircraft designs that will significantly reduce noise, nitrogen oxide emissions, fuel burn and air traffic congestion by the year 2035."
Flying wings have many excellent characteristics but mass passenger transport isn't one of them.
In order to accommodate large passenger loads the flying wing shape becomes abused which leaves behind many of the characteristics which make the flying wing attractive in the first place. Once you modify the flying wing shape to accommodate large passenger loads, you more or less have a shape which is portrayed in the designs presented. And once you accommodate construction/materials issues, it almost exactly looks like the designs presented.
In other words, I'm not really seeing a problem. But, as you mention, hopefully some designers won't be silent.
Look at diesel-electric trains for the model, not hybrid cars.
The bypass ratio refers to the mass of air moved around the core to the mass moved through the core, not the ratio of thrust. For any given mass of air being put through the core, it will produce more thrust than the same ratio outside the core because it gets hotter/faster.
The press release is devoid of details, but a google search turns up that they're decoupling the jet engine (which generates the power) from the bypass fan (which generates most of the thrust).
For those not up to speed on jet engine technology, modern turbofans are essentially ducted propellers. The engine itself occupies a small section in the center. It burns fuel and throws the air it consumes out the back at a higher speed. This generates about 20% of the total thrust. The rest of the energy goes into spinning the bypass fan blades. Just like a propeller, they grab large chunks of air which never goes through the combustion chamber, and push it out the back at higher speed to generate about 80% of the thrust.
In current engine designs, the blades of the two are locked together (although some of the compressor blades inside the engine may rotate at a different speed). For the bypass fan blades to be spinning, the engine must also be on and spinning. The idea behind this hybrid is to decouple them so they can operate independently of each other. The bypass fan would be spun using an electric motor. I don't know the numbers involved, but theoretically that would mean you could always run the jet engine at its most efficient RPM to generate electricity, and even turn it off if there's little thrust required and the batteries have enough juice to run the bypass fan (e.g. descent).