On a conventional rectangular wing, the CoP meets the aircraft at the point on the chord running directly out from the root. While the same analysis will reveal a center of pressure point for a swept wing, its location may be considerably behind the leading edge measured at the root of the wing. For highly swept planforms, the CoP may lie behind the trailing edge of the wing root, requiring the wing to meet the aircraft at a seemingly far-forward location. In this case of a swept wing, changes to the CoP with angle of attack may be magnified. The introduction of swept wings took place during a move to more highly tapered designs as well. Although it had long been known that an elliptical planform is "perfect" from an induced drag standpoint, it was also noticed that a linear taper of the wing had much the same effect, while being lighter. Research during the war led to widespread use of taper, especially in the post-war era. However, it had been noticed early on that such designs had unfavourable stall characteristics; as the tips were more highly loaded in high angles of attack, they operated closer to their stall point. Although this effect was unfavourable in a conventional straight wing aircraft, on a swept-wing design it had unexpected and dangerous results. When the tips stall on a swept wing, the center of pressure, the average lift point for the wing as a whole, moves forward. This is because the section still generating considerable lift is further forward. This causes further nose-up force, increasing the angle of attack and causing more of the tip area to stall. This may lead to a chain reaction that causes violent nose-up pitching of the aircraft. This effect first noticed in the Douglas D-558-2 Skyrocket in August 1949, when a 0.6 G turn suddenly increased out of control to 6 G. This was not entirely surprising; the effect had been seen earlier in wind tunnel simulations. These effects can be seen at any speed; in the Skyrocket they occurred primarily in the transonic (the Weil-Gray criteria) but with more highly swept and tapered planforms, like on the North American F-100 Super Sabre, the effect was common at low speeds as well (the Furlong-McHugh boundary), when the aircraft flew at higher angles of attack in order to maintain lift at low speeds. In addition, swept wings