Environmental Engineering Reference
In-Depth Information
the effect of potential loss of laminar flow due to degradation of the surfaces during
flight. This would reduce the benefits in fuel consumption gained by reduced drag.
Hybrid laminar flow has also been considered. These systems aim to keep the flow
attached to the aerodynamic surfaces by sucking ambient air through porous skins.
This type of system continues to be evaluated as it raises a number of safety issues.
Cleaning of the skin surface would also increase maintenance costs. Application of
this technology is believed to have the potential to raise the performance of long-range
aircraft, but may be only marginally beneficial or even detrimental for short-range
craft.
Other aerodynamic concepts
Other aerodynamic possibilities exist. Riblets (tiny grooves in the direction of air
flow) reduce viscous drag and could contribute to a substantial fuel saving if applied
over the aircraft surface. However, degradation of the adhesive plastic film bearing
the grooves could present a problem. This may reduce not only the manufacturers'
enthusiasm to apply the technology, but also that of the airlines. Advanced wing-tip
devices reduce induced drag and could contribute significantly to reducing the total
airframe drag. Advanced manufacturing methods, improving the surface smooth-
ness of the fuselage and wings, would also reduce drag.
Weight
The weight of the airframe is expected to continue to reduce through the application
of lighter alloys for primary structures. Introduction of new alloys requires much
testing before eventual certification, a costly and time-consuming process. For non-
structural parts, composites are being applied. Weight savings can range from 10 to
30 per cent, with an associated fuel burn saving of between 10 and 15 per cent (Aer-
onatique Astronautique, 1998, pp34, 44-48, 71-75).
Other weight reduction options exist, such as reducing seat pitch, in-flight enter-
tainment systems, galleys or the elimination of windows. Given the current health
concerns regarding seat pitch and the requirements and desires of customers, it is
unlikely that these options would be implemented. However, there is the potential
to save approximately 2 tonnes of operating empty weight (OEW), which corre-
sponds to an increase of 1 per cent in fuel efficiency (IPCC, 1999, p227).
Noise
Noise is also generated from the airframe in take-off and landing situations, originat-
ing from the undercarriage, tail-plane, flaps and wings. Noise reduction programmes,
such as RAIN, now nearing completion, have concentrated on reducing airframe
noise and are intended to contribute to the EU Framework 5 Technology Platform
programme. SILENCER, a new research programme, is due to start in April 2001.
R
EVOLUTIONARY
OPTIONS
It is believed that the reductions in environmental impact from evolutionary improve-
ments in engine and airframe design are likely to be outstripped by growth in air
