Future Transportation Systems - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 275

Future runways, taxi ways and aprons must be able to carry over 500 t (492 lnt,
i.e., 1.102 9 10 6 lb), compared to 350 t (344 lnt, i.e., 0.771 9 10 6 lb) today. They
will have to manage wing span widths of 85 m (278.7 ft), instead of 60-70 m
(196.7-229.5 ft) currently, to keep parked airplanes from touching each other.
Will the fight for market share produce still bigger and faster airplanes? Air-
planes will probably not be bigger or faster than the most recent large airplanes in
the foreseeable future. In large airplanes, the design of the space for the passen-
ger's compartment represents the greatest challenge, because more passengers
must be accommodated in the cabin. Besides the fuselage, the wings and all other
parts require new designs. The development is cost intensive and requires time.
17.2.2.2 Laminar Flow
Reducing air resistance permits flights at higher speeds and improvements in the
glide ratio. In the last few decades, the average Mach number of civil aviation has
increased from M 0.78 to M 0.82.
Adding winglets and improving the wing profile provides only a limited
improvement. Apart from this technology, improving laminar flow will be a really
revolutionary step. Currently, the boundary layer leads to friction resistance which
is half of the complete resistance of a commercial aircraft while cruising. The
Reynolds number determines whether the bordering layer will be laminar or tur-
bulent. In flight there is a Reynolds number between 20 9 10 6 and 70 9 10 6 ,so
the boundary layer is always turbulent. With artificial laminar flow, the friction
resistance could be reduced by 90%. No other measure yields such large benefits.
This will be the central topic in future aeronautical research [ 37 ].
Improving the wing construction will produce laminar boundary layers. In
practice, only a part of the wing will have a laminar flow, but with an artificial
vacuum, 75% of the wing area will be attainable. At this way, friction resistance
will be lowered to 30% and the glide ratio will be correspondingly improved. The
profits will be considerable. 10% fuel will be saved on short range flights. Long
range flights will save up to 20%. However, tests are still in progress.
17.2.2.3 Oversized Gliders
Wing load is the loaded weight of the aircraft divided by the area of the wing. The
faster an aircraft is flying, the more lift is producing by each unit area of the wing,
so a smaller wing can carry the same weight in level flight with a higher wing load.
Correspondingly, the takeoff and landing speeds will be higher. High wing load
also decreases maneuverability [ 38 ].
Table 17.4 shows the parameters of airplanes with different wing aspect ratios.
The airplane of tomorrow can be constructed like an oversized glider with
efficient aerodynamics, but the enormous wings will have to be reinforced through