Kind and Risks
We have seen, that many technologies required for a new SCT arc just developed or are under development for subsonic aircraft. Other technology improvements cannot be transferred to an SCT. And Concorde’s technology level is still "comparable” But what are the new technologies which will enable realization of a competitive SCT with sufficient range and operating costs?
1.4.1 Aerodynamic technologies
There are several chapters in this book dealing with aerodynamics. Therefore, here only the important points are mentioned.
Aerodynamic multi point design:
For subsonic aircraft, in the first design step usually a two point design is made for
• high speed cruise and
• low speed take-off and landing.
Often this is achieved via a nearly pure one point design for high speed cruise, whereas low speed performance is achieved using rather complicated flap systems.
A supersonic aircraft must be able to cruise economically at supersonic speed over uninhabited areas and at high subsonic speed over inhabited land. And supersonic cruise only becomes possible if transonic acceleration can be realized. So. we have to design for four points:
• supersonic cruise.
• high subsonic cruise.
• low speed take-off and landing.
• transonic acceleration
Moreover, low speed performance cannot be achieved using additional large flap surfaces like fowlers. Since an SCT has a large wing surface, effect of (fowler) flaps is very limited. And lift slope (Сщ) decreases for small aspect ratio. But lift via high angle of attack, as used for Concorde, is accompanied by large drag, which requires noise producing thrust
Therefore a best combination of aerodynamic s (and other discipline’s) design principles is required to meet the diverging requirements The most important part is selection of a suited configuration, for which aerodynamics conlnbutc strongly in meeting the four aerodynamic design points.
Nonlinear aerodynamics enable minimization of interference losses, e. g. engine and wing-fuselage integration. It is being developed for subsonic transports; but it becomes more challenging for supersonic transports by the combination of nonlinear effects with very weak oblique shocks, strongly three dimensional geometries and boundary layers, and strong shocks around the engines and in the inlets, even with reflected shocks.
Design of the control surfaces depends strongly on the configuration selected. Smart solutions may decide on the viability of a configuration or strongly ease design and operation.
New approaches like acroelastic tailoring or acroclaslic control arc being developed for large subsonic transports. For the slender SCT-configuration. inclusion of acroclasucs in the early design is a prerequisite, at least for static aeroelastics (i. c. inclusion of the shape variation due to aerodynamic loads, but still without vibrations). For many SCT-configu – rations. flutter itself is as important, but hitherto a can be checked only at a more matured design stage, when a more detailed data base was built up.
Aerodynamics, especially nonstationary aerodynamics and dynamic structure calculations are much more challenging for an SCT than for subsonic transports, at least for the flutter sensitive symmetric (Concorde-like) configurations Because По» and structure dimensionally has to be treated completely three dimensional by 2D – or quasi-2D approximations like airfoil flow, sweep theory or beam approximations are not possible.
Aerodynamic damping decreases with speed Therefore supersonic cruise becomes flutter sensitive. But the nonlinear transonic aerodynamics (here high subsonic) also decrease flutter damping, the so called transonic dip. So there is a second high subsonic flutter case which often is even more flutter critical than supersonic cruise |48). This is one of the most challenging calculations in SCT design
Supersonic laminar flow (SSLF):
Supersonic laminar flow (SSLF) may provide strong improvements during cruise flight. But it is still far away from realisation and many questions are unresolved; even some physical principles arc still not yet understood.
Today, we postulate a reference SCT to be viable without SSLF. Because, when a new subsonic aircraft benefits from laminar flow, the SCT must also be improved by SSLF in order to maintain its competitiveness.