Transportation's Role in Reducing U.S. Greenhouse Gas Emissions ...

Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
time when declining air traffic has reduced demand for new aircraft, leading to excess
capacity. Policies that encourage replacing older, less fuel efficient engines with new
engines could accelerate the environmental and economic benefits associated with these
technologies; however, the specific design or potential impact of such policies has not
been investigated.
Advanced Airframe/Wing Design
Overview
The airframe is responsible for approximately
50 percent of an aircraft’s gross weight. Use of
advanced lighter and stronger materials in the
structural components of the airframe, such as
aluminum or titanium alloy and composite
materials, can reduce airframe weight leading
to reduced fuel use (Barzega, 2008; ADL, 2000;
IPCC, 1999). Such materials are being used
increasingly for aviation. For example,
composites will make up approximately
50 percent of the airframe structure of the
Boeing 787 Dreamliner, a sharp increase from
the 9 percent figure for the Boeing 777 (Boeing,
2009). The International Civil Aviation
Organization (ICAO) estimates that adoption
of these materials can reduce an aircraft’s
structural weight by 15 percent.
A large portion of the energy used by an
aircraft is to overcome aerodynamic drag,
including skin friction and induced drag. As
such, drag reduction can significantly improve
the fuel efficiency of airplanes and reduce
emissions. Efforts to reduce “skin friction”
drag include the use of an adhesive-backed
film with micro-grooves placed on the exterior
Figure 3.15 Winglet
surfaces of the wings and the fuselage. However, the lifetime of the micro-groove film is
only two to three years, after which it needs to be reapplied. The fact that the film needs
to be maintained frequently may limit the viability of this technology as the effectiveness
and fuel savings are relatively small and the ongoing maintenance costs are unknown.
Skin friction drag also can be reduced by maximizing laminar flow. Designing the wing
with favorable pressure gradients and mechanisms to protect the wing surface from
accumulating matter such as insect carcasses can enhance laminar flow. Alternatively,
systems have been studied utilizing multilayer panels on the wing surface that allow air to
be sucked through pores on the outer layer and vented away from the wing (Barzega,
3-112
Figure 3.14 Multilayer Panels on Tail
Fins