Environmental Engineering Reference
In-Depth Information
travel. To meet the challenges of the future, innovative configurations, fuels and tech-
nologies are being considered as potential directions for the long-term future of the
aviation industry. While many evolutionary concepts can be easily separated as apply-
ing to either the engine or the airframe, many of the revolutionary ideas require con-
sideration as a fully integrated system.
Some of the options can be applied not only to more radical designs, but also to
existing airframe/engine configurations. Such developments include the application
of extended 'fly-by-wire' or 'fly-by-light' control systems, full hybrid laminar flow
control, geared fan engines, or alternative liquid fuels. Other options can only be
applied to radically different airframe/engine configurations.
Innovative developments for existing configurations
Aircraft systems
Extension of existing fly-by-wire and the development of fly-by-light (using fibre
optics) technology to include wing load alleviation and pitch stability augmentation
has a potential to improve fuel efficiency by 1-3 per cent. Active centre-of-gravity
control, reducing tail-plane area by up to 10 per cent, could offer an increased fuel
efficiency of 1-2 per cent. On the negative side, flight safety improvements could
lead to an increase in OEW, thus counteracting some of the savings created (IPCC,
1999, p228).
Replacing the auxiliary power units (APUs) with advanced fuel cells could reduce
noise, fuel burn and emissions at ground level, but could add weight, thus reducing
fuel efficiency when in the air. Aerodynamic integration of the interface between the
engine and airframe, with the aim of passing the airframe boundary layer through
the propulsor, thus eliminating the airframe wake, could provide an increase in pro-
pulsive efficiency of up to 5 per cent (IPCC, 1999, p233).
Innovative engine configurations
One potential way to improve the efficiency of the engine is to move from a simple
Joule thermodynamic cycle to an inter-cooled recuperative cycle (ICR). This has the
potential to substantially improve the thermal efficiency of the engine, while at the
same time reducing NO
x
emissions. A study has been carried out on the feasibility
of such an engine (Plohr, 1999). While the addition of heat exchangers adds to the
weight of the engine, it was estimated that this technology could contribute up to a
10 per cent reduction in specific fuel consumption and reduce NO
x
emissions by up
to 35 per cent. The ongoing CLEAN programme for the European Commission's
(EC's) fifth framework programme is aiming to demonstrate this technology.
The More Electric Engine (MEE) and More Electric Aircraft (MEA)
The More Electric Engine
(MEE), as seen in Figure 10.8, features electrical genera-
tors attached to the engine shafts from which electricity is generated. This can be used
in the engine to improve operability or to improve relight capability. Additional features
include replacing mechanically operated accessories by those driven by electricity,
