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

Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
2008; Reneaux, 2004; ADL, 2000; IPCC, 1999). These designs were demonstrated by
Airbus on the tail fin of the A-320 aircraft in 1998 (Barzega, 2008; AeroStrategy, 2005;
Schmitt, 2000), shown in Figure 3.14. However, there is considerable concern over the
viability of this technology because of the additional weight, complexity and cost of the
internal systems and challenges of avoiding fouling of the surfaces (Waitz, 2009).
Vortices are formed at the tips of the wings as high air pressure migrates toward lower air
pressure areas. These vortices reduce fuel efficiency by producing induced drag. Induced
drag can be reduced by modifying the wing tips. For example, a winglet is a
commercially available device mounted at the tip of the wing (see Figure 3.15) to provide
a smooth, perpendicular surface that can favorably alter vortex formation (Morris, 2009;
USAF, 2007; ADL, 2000). An alternative design, shown in Figure 3.16, employs a spiroid
tip which is a loop formed at the end the wing to reduce drag. Spiroid tips have been
applied to Gulfstream II aircraft (Ostrower, 2008). Wing tip devices may not be
appropriate for all aircraft as it may require an increase in structural weight to support the
wing tip offsetting the fuel savings
associated with the reduction in drag. This
was the case for the Airbus A-320, which at
one point included winglets that were later
removed because they did not provide the
expected reduction in fuel consumption
(Kingsley-Jones, 2006). Winglet devices
that are better integrated into the wing
Figure 3.16
design may be more beneficial. Spiroid
winglets may offer more benefit but
additional study is required to validate
this technology.
Spiroid Wing Tip
Some of these technologies such as drag
reducing films and multi layer panels are
only now being demonstrated and need
further development before they are
commercially viable. There are no issues
regarding the airworthiness of wing tip
technologies, compared with other drag
reduction technologies which require
additional research.
Figure 3.17 Blended Wing
In addition to these existing technologies, Boeing, Airbus and NASA, along with several
university research programs, are developing a blended wing body (BWB) design (see
Figure 3.17). This approach will significantly improve fuel efficiency as the whole aircraft
contributes to the generation of lift, not just the wings as in the current designs. This
design has been successfully demonstrated on smaller aircraft designs. Additional
research is needed to scale up the design to larger aircraft. This BWB approach may
reduce fuel consumption and greenhouse gas emissions by 20 to 40 percent while also
reducing noise below current stage 4 standards (Morris, 2009; Warwick, 2007; ADL, 2000;
NASA, 1997). BWB aircraft are most attractive for larger applications, e.g., 250-1,000
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