| For aircraft flying at or near supersonic speeds, the | | | | particularly structural, and are more difficult and |
| air flow over the aircraft is very different from that | | | | expensive to build than simple straight wings. |
| in subsonic flight, and the designer has a new set of | | | | Aerodynamic problems associated with swept wings |
| problems to face. An aircraft flying through the air | | | | include an increased likelihood of tip stalling, which can |
| generates pressure waves, which move at the speed | | | | lead to spinning, and a reduced lift-to-drag ratio. |
| of sound. At speeds below the local speed of sound | | | | Once flying above the speed of sound, the airflow is |
| these pressure waves warn the oncoming air that | | | | changed to become steady again, although quite |
| the aircraft is approaching. As aircraft speeds | | | | different to subsonic conditions. Shock waves form |
| approach the speed of sound, these pressure waves | | | | whenever there is a change in airflow direction, and |
| no longer travel significantly faster than the aircraft, | | | | curved shapes no longer produce the lowest drag - |
| and a shock wave will begin to form on parts of the | | | | sharp edges create a single shock wave, and are |
| aircraft. Air pressure, speed and temperature change | | | | generally more efficient than curves. The plan form |
| very suddenly across this shock wave, and the flow | | | | of wings becomes very important, and a low aspect |
| behind it is quite turbulent. The effect on the aircraft | | | | ratio and highly swept wings are most suitable. The |
| is a reduction in lift, an increase in drag, changes in | | | | reduced aspect ratio of these wings makes life easier |
| trim and possibly buffeting of the controls. Designers | | | | for the aircraft structural design, but the loads are |
| have reduced the effects of these problems with | | | | very high, and the structure must be strong and stiff. |
| better designs, particularly swept wings. To | | | | The main disadvantage of swept wings is that, at a |
| understand how this is achieved, consider the airflow | | | | given angle of attack, they produce less lift than an |
| to be made up of two components - one at right | | | | unswept wing of the same general dimensions. This is |
| angles to the wing leading edge and one parallel to | | | | because the geometry of the sweep angle acts to |
| the leading edge. By sweeping the wings back (or | | | | reduce the effective angle of attack. So when the |
| forwards), the component at right angles to the | | | | aircraft is flying slowly, for instance during take-off, a |
| leading edge is reduced as the cosine of the sweep | | | | larger angle of attack is required to provide sufficient |
| angle. The larger the sweepback angle the higher the | | | | lift. Sweepback changing in flight has been tried on |
| speed at which this component will remain subsonic. | | | | some aircraft. Delta wings have high sweepback and |
| Highly swept aircraft wings give other problems, | | | | are strong with a large chord at the wing root. |