While the basic principles of flight that the Wright brothers applied still pertain, there have been enormous changes over the years to the means by which those principles are understood and applied. The most pervasive and influential of these changes is the broad variety of applications of computer technology in all aspects of aviation. A second factor has been the widespread development of the use of composite materials in aircraft structures. While these two elements are the results of advances in engineering, they are also indirectly the product of changing social and legal considerations.
The social issues are manifold and include the increasing global interdependence of business, the unprecedented political revolutions in every part of the world, and the universal human desire for travel. All these come at a time when diminishing fossil-fuel resources have caused large increases in fuel prices. As a result, both computers and composite materials are necessary to create lighter, stronger, safer, more fuel-efficient aircraft.
The legal issues are equally complex, but for the purposes of this section revolve around two elements. The first of these is that the design, test, and certification of an aircraft has become such an extraordinarily costly project that only the most well-funded companies can undertake the development of even relatively small aircraft. For larger aircraft it is now common practice for several manufacturers, often from different countries, to ally themselves to underwrite a new design. This international cooperation was done most successfully first with the Anglo-French Concorde supersonic transport and has since been evident in a number of aircraft. A component of this process is the allocation of the production of certain elements of the aircraft in certain countries, as a quid pro quo for those countries not developing indigenous aircraft of a similar type.
Since the mid-1960s, computer technology has been continually developed to the point at which aircraft and engine designs can be simulated and tested in myriad variations under a full spectrum of environmental conditions prior to construction. As a result, practical consideration may be given to a series of aircraft configurations, which, while occasionally and usually unsuccessfully attempted in the past, can now be used in production aircraft. These include forward swept wings, canard surfaces, blended body and wings, and the refinement of specialized airfoils (wing, propeller, and turbine blade). With this goes a far more comprehensive understanding of structural requirements, so that adequate strength can be maintained even as reductions are made in weight.
Complementing and enhancing the results of the use of computers in design is the pervasive use of computers on board the aircraft itself. Computers are used to test and calibrate the aircraft's equipment, so that, both before and during flight, potential problems can be anticipated and corrected. Whereas the first autopilots were devices that simply maintained an aircraft in straight and level flight, modern computers permit an autopilot system to guide an aircraft from takeoff to landing, incorporating continuous adjustment for wind and weather conditions and ensuring that fuel consumption is minimized. In the most advanced instances, the role of the pilot has been changed from that of an individual who continuously controlled the aircraft in every phase of flight to a systems manager who oversees and directs the human and mechanical resources in the cockpit.
The use of computers for design and in-flight control is synergistic, for more radical designs can be created when there are on-board computers to continuously adapt the controls to flight conditions. The degree of inherent stability formerly desired in an aircraft design called for the wing, fuselage, and empennage (tail assembly) of what came to be conventional size and configurations, with their inherent weight and drag penalties. By using computers that can sense changes in flight conditions and make corrections hundreds and even thousands of times a second—far faster and more accurately than any pilot's capability—aircraft can be deliberately designed to be unstable. Wings can, if desired, be given a forward sweep, and tail surfaces can be reduced in size to an absolute minimum. Airfoils can be customized not only for a particular aircraft's wing or propeller but also for particular points on those components.
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