Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
These concepts include slotted airfoils or actively heated/cooled surfaces, but the benefits still need to be proven. If wing-mounted prop-fan (un-ducted powerplantssee
Section 7.4.3.) propulsion technology were to be adopted in the future, laminar flow airfoils that could tolerate the effects of propeller efflux over the wing surface
would need to be developed. Alternative mounting arrangements, such as aft fuselage-mounted prop fans, may also be considered.
Laminar flow suction systems for wing, fuselage, stabilizers, and nacelles have been and continue to be reviewed and evaluated. Development of these systems,
which aim to keep the flow attached (laminar) to aerodynamic surfaces by sucking ambient air through
porous skins, is a high-risk technical challenge that is likely to require a longer time frame for full development and airline introduction (after 2015). A key consideration
is the weight of the laminar flow systems (and their power requirements) compared with savings from drag reduction over the complete mission. Contamination of the
porous skin surface by insects/debris can significantly reduce the performance of laminar flow systems and increase maintenance cost. Work in this field to date has
not reached the point where these penalties, together with the effects of system failure or other risks, have been fully evaluated and balanced against fuel savings.
7.3.7.2. Other Aerodynamic Improvements
Other potential aerodynamic improvements requiring further development and investigation
include attachment of riblets (tiny groves in the direction of airflow) to the fuselage, wing,
and horizontal tail to reduce turbulent flow areas; advanced passive flow control devices (e.
g., vortex generators) to enhance lift; advanced winglets on outboard wings; supercritical
wing technology to enhance and optimize cruise lift/drag ratio; advanced CFD design
methodologies; and advanced manufacturing methods to improve fuselage and wing
surface smoothness to reduce drag.
7.3.7.3. Weight Reduction
It is expected that the weight of the airframe structure will continue to decrease through
gradual incorporation of improved aluminum alloys and aluminum-lithium composites for Figure 7-5: 2016 subsonic airplane.
sections of primary structures (i.e., fuselage, wing, and empennage), and composites for
secondary structures. For primary structures, the process of introduction is slow because of the certification process for structural design, material property
characterization, and safety issues, which involve lengthy and costly durability and strength test programs.
Thrust reversers enhance landing performance, especially during wet runway conditions. Significant weight reductions could be obtained by removing them from some
aircraft configurations. Estimates indicate that maximum take-off gross weight could be reduced by about 0.3-1%, depending on aircraft configuration and size.
Removal of thrust reversers could also improve internal nozzle flow characteristics (e.g., reduced internal thrust losses). This matter needs further study. Further
weight reduction could be achieved via reduced passenger amenities, such as the elimination of windows, in-flight entertainment, and galleys or reduction in seat pitch.
These measures may be more applicable to short-range routes. The weight of in-flight entertainment systems is likely to be reduced in the future by technology.
However, it is questionable whether such changes would ever be accepted by fare-paying passengers. Increasing demand for passenger comfort items such as flight
entertainment systems may also limit changes. Interior cabin furnishings and passive interior noise treatment (e.g., wall bags/environmental control ducts) for cabin
noise control may be reduced in the future if active noise control technology is successfully developed for attenuation of broadband and tonal noise sources.
Estimates of weight reductions accruing from successful implementation of these strategies, applied to a medium-range, wide-body aircraft, suggest that 2,000 kg of
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