Environmental Engineering Reference
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overall fuselage. The engine is a super efficient General Electric GEnx with
all composite fan case and blades as well as nozzles. It operates at lower
temperatures with few hydrocarbon emissions.
In the time frames considered for the introduction of hydrogen-pow-
ered aircraft, renewable energy could be a viable option. Even if renew-
able energy was available for centralized production, the hydrogen would
require a method of transport to the aircraft. Hydrogen can be piped, but
gaseous hydrogen molecules are able to pass through solids, even stain-
less steel. In addition hydrogen makes steel brittle and more susceptible
to fracture. An option is to store the hydrogen in a medium that releases
it when heated. Research on this has focused on hybrids and pure carbon,
or carbon nanotubes doped with metals, but there is a weight penalty.
Liquid hydrogen is the way to store the volume needed for an aircraft ac-
cording to the United Nations' International Energy Agency's hydrogen
NASA is focusing on liquid-hydrogen power as part of its Vehicle
Systems program. This includes a zero-emissions hydrogen-powered
fuel-cell aircraft with cryogenic electric motors in the wing.
The European Union has similar goals and in 2002 it completed a 3-
year Fifth Framework program called Liquid Hydrogen-Fueled Aircraft
Systems Analysis, also known as Cryoplane. It involved 35 organizations
across the EU and assessed practical solutions for the introduction of
hydrogen aircraft. Computer models were used for fuel system simula-
tion and aircraft propulsion systems. Defining the airport infrastructure
for fuel production and distribution was also a major component. Since
2002, the EU has continued its study in hydrogen fuel and aviation with its
Helicopter Occupant Safety Technology Application (HELISAFE) project.
A Sustainable Fuel project is researching the use of a sustainable bio-
mass fuel source for aviation that can be integrated into the existing infra-
structure. It aims to create a safe and economical way of supplying hydro-
gen fuel.
NASA and the California-based company AeroVironment built the
Helios solar-powered remotely operated aircraft. Helios had a 235-kg non-
regenerative fuel cell, but crashed into the Pacific in 2003 before it could use
power from the fuel cell after breaking up in turbulence. AeroVironment
achieved a major milestone more recently when it successfully flew the
world's first fuel cell-powered unmanned air vehicle (UAV). The aircraft
was a scale model of the planned Global Observed high-altitude long-
endurance UAV and it was the first powered flight of its kind. The flight
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