manner. This uncontrollable instability came to be known as the Sabre dance in reference to the number of North American F-100 Super Sabres that crashed on landing as a result. Reducing pitch-up to an acceptable level has been done in different ways such as the addition of a fin known as a wing fence on the upper surface of the wing to redirect the flow to a streamwise direction. The MiG-15 was one example of an aircraft fitted with wing fences. Another closely related design was the addition of a dogtooth notch to the leading edge, used on the Avro Arrow interceptor. Other designs took a more radical approach, including the Republic XF-91 Thunderceptor's wing that grew wider towards the tip to provide more lift at the tip. The Handley Page Victor was equipped with a crescent wing, with three values of sweep, about 48 degrees near the wing root where the wing was thickest, a 38 degree transition length and 27 degrees for the remainder to the tip. Modern solutions to the problem no longer require "custom" designs such as these. The addition of leading-edge slats and large compound flaps to the wings has largely resolved the issue. On fighter designs, the addition of leading-edge extensions, which are typically included to achieve a high level of maneuverability, also serve to add lift during landing and reduce the problem. In addition to pitch-up there are other complications inherent in a swept-wing configuration. For any given length of wing, the actual span from tip-to-tip is shorter than the same wing that is not swept. There is a strong correlation between low-speed drag and aspect ratio, the span compared to chord, so a swept wing always has more drag at lower speeds. In addition, there is extra torque applied by the wing to the fuselage which has to be allowed for when establishing the transfer of wing-box loads to the fuselage. This results from the significant part of the wing lift which lies behind the attachment length where the wing meets the fuselage. Sweep theory Sweep theory is an aeronautical engineering description of the behavior of airflow over a wing when the wing's leading edge encounters the airflow at an oblique angle. The development of sweep theory resulted in the swept wing design used by most modern jet aircraft, as this design performs more effectively at transonic and supersonic speeds. In its