Future Supersonic Commercial Transports
Realisation of a new Supersonic Commercial Transport (SCT) must meet challenging environmental and cost requirements (Figure 105). It can be certified only when meeting the future rules on emissions and noise, and if it will bring some profit to manufacturers and airlines. Drag is directly related to fuel burned, emissions and operating costs; but it influences also noise via aircraft size and weight. At the time being, the perspective for a new SCT improves; although emission restrictions may question "if, whereas noise and costs ask "when" it becomes possible.
Figure 105 A New Supersonic Commercial Transport
An SCT makes sense only for long ranges of at least 2000 nm. The longer the distances the more it becomes attractive for the passengers. At flight times of more than 4 to 6 hours most passengers feel uncomfortable and many see flight time as a waste of time, even tourists. But the SCT has to compete against future new subsonic aircraft (Figure 106) providing more space and comfort for better accomodation of a long flight time. These aircraft will have low operating costs which cannot be met by an SCT. So the SCT has to compete with speed comfort and productivity against efficiency and space comfort.
Figure 106 Future Long Range Aircraft
To meet these challenges, the aircraft must be optimized mainly respecting the four different design points:
• very efficient supersonic cruise at Mach 2 to 2.4.
• quiet take off and landing at steep flight path angles.
• high subsonic cruise capability (Mach 0.9) for flight over inhabitated areas, where supersonic flight is not permitted.
• transonic acceleration at about Mach 1.1.
For all four points minimisation of aerodynamic drag is one of the challenges Drag contributions arc:
• wave drag
• vortex drag
• friction drag.
In this chapter emphasis is put on friction drag reduction by lanunarisation
An SCT has a large wing area, about 3 times the size of comparable subsonic aircraft (Figure 107). It cruises at low angle of attack and low lift coefficient Cl due to the high lift dependent drag (consisting of wave drag and induced drag). Fnction drag contributes by about 35% to overall drag during supersonic cruise. It can significantly be reduced by lanunarisation. Present SCT-designs achieve a lift to drag ratio (L/Di of about 8 5 for a turbulent wing With partial laminarisation nearly 10 may be possible. The goal is at 9.5 for turbulent and 11 for laminar flow. The maximum range of a 250 – 300 passenger SCT in the year 2010 is expected with a turbulent wing at less than 5000 nm and w ith laminarisation at about 6000 nm. for a take off weight below 400 tons.
large wng area
ca. 35% fnctxm drag
Design range at realization limit:
laminar < 6 000nm 10 (11)
Figure 107 SCT-Charateristics