They concluded that the trapped vortex formed by a cavity or step could not be held in place without such active control. The model aerofoils used in their wind tunnel tests were equipped with numerous small holes through which air could be blown or sucked in an active way. Further testing has shown that this airfoil is effective in low Reynolds number flow.Ī 2008 study by Fabrizio De Gregorio and Giuseppe Fraioli at CIRA and the University of Rome in Italy tried this out. Indeed, "vastly different configurations may be needed during a single maneuver." The idea works, Finaish and Witherspoon concluded, but only with active automated re-configuration of the shape of the steps during flight. However, they concluded that a single configuration could not be best solution at every angle of attack and flight speed. While many made wing performance worse, they got promising results with backward-facing steps on the lower surface of the wing – in some cases giving considerable enhancement in lift without much of a drag penalty. A 1998 study by Fathi Finaish and Stephen Witherspoon at the University of Missouri tested numerous step configurations in a wind tunnel. In the 1990s, with 20 years of technical progress opening up new possibilities and with the original patents expired, researchers returned to the topic of stepped wings. In 1974, a NASA-funded study prompted by Kline and Fogelman's claims and the resulting national coverage found the airfoil to have worse lift-to-drag ratio than a flat plate airfoil in wind tunnel tests. KFm2 airfoil showing purported laminar flow vortex The longest flight by Kline with his paper airplane traveled 401 feet 4 inches (122.33 m). A crew from Good Morning America came along to film the event. To publicize the book, he went down to Kill Devil Hills, NC in 1985, to the site where the Wright Brothers first flew where their first manned powered flight went 122 feet (37 m). In 1985, Kline wrote a book entitled "The Ultimate Paper Airplane". Time published an Aparticle, The Paper-Plane Caper, about the paper airplane and its Kline–Fogleman airfoil.Īlso in 1973, CBS 60 Minutes did a 15-minute segment on the KF airfoil. This purportedly prevents separation and maintains airflow over the surface of the airfoil. The purpose of the step, it is claimed, is to allow some of the displaced air to fall into a pocket behind the step and become part of the airfoil shape as a trapped vortex or vortex attachment. It can also be used with two steps on the top (KFm3), or two steps on the top and one on the bottom (KFm7). The two patents, US Patent # 3,706,430 and US Patent # 4,046,338, refer to the introduction of a step either on the bottom (KFm1) or on the top of an airfoil (KFm2), or both on top and bottom (KFm4). The two men then filed for a patent on the stepped airfoil.įurther development resulted in two patents and a family of airfoils known as the KF airfoil and KFm airfoils (for Kline–Fogleman modified). He presented the paper airplane to Floyd Fogleman who saw it fly and resist stalling. After many experiments he was able to achieve this goal. In the early 1960s, Richard Kline wanted to make a paper airplane that could handle strong winds, climb high, level off by itself and then enter a long downwards glide.