Kline Fogleman airfoil
Encyclopedia
The Kline–Fogleman airfoil or KF Airfoil is an airfoil design with single or multiple steps induced along the length of the wing.
) or aerofoil (in British English
) was designed by Richard Kline & Floyd Fogleman.
Also known as the KF airfoil and KFm airfoils (Kline–Fogleman modified). 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). 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 steps all work extremely well on radio-controlled aircraft
. 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. This purportedly prevents separation and maintains airflow over the surface of the airfoil.
They went to see Dr. John Nicolaides, the first head of NASA
, who was teaching at Notre Dame. Dr. Nicolaides was intrigued with the idea. The early wind tunnel testing showed that the step on top had higher lift over drag ratios than when it was placed on the bottom. It was decided to show the step on the bottom in the patent because when an aircraft goes from subsonic to supersonic the L/D characteristics reverse themselves. Thus, supersonically the higher L/D would be available.
Time
published an article, The Paper-Plane Caper, on the paper airplane and its Kline–Fogleman airfoil in the Science section of its issue of April 2, 1973.
Then, CBS
60 Minutes
did a 15 minute segment on the KF airfoil in 1973, and repeated the show again in 1976.
In 1986, Kline wrote a book entitled "The Ultimate Paper Airplane". To publicize the book, he went down to Kill Devil Hills, NC to the site where the Wright Brothers first flew where the first manned flight went 122 feet. A crew from Good Morning America came along to film the event. The longest flight by Kline with his paper airplane traveled 401 feet, four inches.
And according to Bud Bobbitt, chief of NASA’s transonic-aerodynamics division, test showed that the Kline-Fogleman wing was inefficient. The L/D numbers weren’t encouraging, so studying the wing’s resistance to stalling became a low priority.
Max Davis, of the Air Force Flight Dynamics Lab at Wright-Patterson Air Force Base in Dayton, OH, told a similar story. A few tests were performed after all the publicity in 1973, he said, but preliminary studies indicated that the wing was not suitable for a full-size aircraft because it has too much drag and not enough lift.
Recent testing of trapped vortex airfoils indicate that it is impossible to maintain a stable trapped vortex without active control of the vortex cavity by suction and/or blowing Such scientific test results oppose the previously stated (unverified) speculation on the KF airfoil.
The KF airfoil and derivative 'stepped' airfoils have gained an enthusiastic following in the world of foam constructed radio controlled model aircraft. The simple KF airfoil shape lends itself well to construction in foam resulting in an easy to build wing that often has improved performance and handling characteristics compared to the 'flat plate' wing often used in foam radio controlled models. The Airfoils illustrated previously in this article are examples of those used in radio control foam models.
Kline–Fogleman airfoil (KF airfoil)
The KF airfoil (in American EnglishAmerican English
American English is a set of dialects of the English language used mostly in the United States. Approximately two-thirds of the world's native speakers of English live in the United States....
) or aerofoil (in British English
British English
British English, or English , is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere...
) was designed by Richard Kline & Floyd Fogleman.
Also known as the KF airfoil and KFm airfoils (Kline–Fogleman modified). 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
Airfoil
An airfoil or aerofoil is the shape of a wing or blade or sail as seen in cross-section....
(KFm2), or both on top and bottom (KFm4). 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 steps all work extremely well on radio-controlled aircraft
Radio-controlled aircraft
A radio-controlled aircraft is controlled remotely by a hand-held transmitter and a receiver within the craft...
. 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
Vortex
A vortex is a spinning, often turbulent,flow of fluid. Any spiral motion with closed streamlines is vortex flow. The motion of the fluid swirling rapidly around a center is called a vortex...
or vortex attachment. This purportedly prevents separation and maintains airflow over the surface of the airfoil.
Introduction
In the early 1960s, Richard Kline wanted to make a paper airplane that would be able to handle the strong winds outdoors and be able to climb high, then level off by itself and go into a nice long glide. After many experiments he was able to achieve this goal. One day he showed the paper airplane to Floyd Fogleman who watched it fly and resist stalling. The two men decided to file for a patent on a stepped airfoil.They went to see Dr. John Nicolaides, the first head of NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
, who was teaching at Notre Dame. Dr. Nicolaides was intrigued with the idea. The early wind tunnel testing showed that the step on top had higher lift over drag ratios than when it was placed on the bottom. It was decided to show the step on the bottom in the patent because when an aircraft goes from subsonic to supersonic the L/D characteristics reverse themselves. Thus, supersonically the higher L/D would be available.
Time
Time (magazine)
Time is an American news magazine. A European edition is published from London. Time Europe covers the Middle East, Africa and, since 2003, Latin America. An Asian edition is based in Hong Kong...
published an article, The Paper-Plane Caper, on the paper airplane and its Kline–Fogleman airfoil in the Science section of its issue of April 2, 1973.
Then, CBS
CBS
CBS Broadcasting Inc. is a major US commercial broadcasting television network, which started as a radio network. The name is derived from the initials of the network's former name, Columbia Broadcasting System. The network is sometimes referred to as the "Eye Network" in reference to the shape of...
60 Minutes
60 Minutes
60 Minutes is an American television news magazine, which has run on CBS since 1968. The program was created by producer Don Hewitt who set it apart by using a unique style of reporter-centered investigation....
did a 15 minute segment on the KF airfoil in 1973, and repeated the show again in 1976.
In 1986, Kline wrote a book entitled "The Ultimate Paper Airplane". To publicize the book, he went down to Kill Devil Hills, NC to the site where the Wright Brothers first flew where the first manned flight went 122 feet. A crew from Good Morning America came along to film the event. The longest flight by Kline with his paper airplane traveled 401 feet, four inches.
Independent Scientific Testing
In 1979, P.K. Pierpont, then manager of the airfoil-research program at NASA’s Langley Research Center in Virginia, revealed information on three studies, one of them partially funded by NASA. All had come up with the same results: The Kline-Fogleman wing was found to have a poor lift-to-drag (L/D) ratio --- a standard measure of wing efficiency. These results indicated that the airfoil had no practical application, Pierpont said, so no further tests were made.And according to Bud Bobbitt, chief of NASA’s transonic-aerodynamics division, test showed that the Kline-Fogleman wing was inefficient. The L/D numbers weren’t encouraging, so studying the wing’s resistance to stalling became a low priority.
Max Davis, of the Air Force Flight Dynamics Lab at Wright-Patterson Air Force Base in Dayton, OH, told a similar story. A few tests were performed after all the publicity in 1973, he said, but preliminary studies indicated that the wing was not suitable for a full-size aircraft because it has too much drag and not enough lift.
Recent testing of trapped vortex airfoils indicate that it is impossible to maintain a stable trapped vortex without active control of the vortex cavity by suction and/or blowing Such scientific test results oppose the previously stated (unverified) speculation on the KF airfoil.
Applications of the KF airfoil
Poor L/D performance in wind tunnel testing has meant that to date the KF airfoil has not been used on any full size aircraft.The KF airfoil and derivative 'stepped' airfoils have gained an enthusiastic following in the world of foam constructed radio controlled model aircraft. The simple KF airfoil shape lends itself well to construction in foam resulting in an easy to build wing that often has improved performance and handling characteristics compared to the 'flat plate' wing often used in foam radio controlled models. The Airfoils illustrated previously in this article are examples of those used in radio control foam models.
Patents
AIRFOIL FOR AIRCRAFT, filed March 17, 1970, issued December 1972 Airfoil for aircraft having improved lift generating device, filed October 14, 1975, issued September 6, 1977See also
- AirfoilAirfoilAn airfoil or aerofoil is the shape of a wing or blade or sail as seen in cross-section....
- WingWingA wing is an appendage with a surface that produces lift for flight or propulsion through the atmosphere, or through another gaseous or liquid fluid...
- Lift (force)Lift (force)A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the surface force parallel to the flow direction...
- Radio-controlled aircraftRadio-controlled aircraftA radio-controlled aircraft is controlled remotely by a hand-held transmitter and a receiver within the craft...
- Radio-controlled gliderRadio-controlled gliderA radio-controlled glider is a type of radio-controlled aircraft that normally does not have any form of propulsion. They are able to sustain continuous flight by exploiting the lift produced by slopes and thermals, controlled remotely from the ground with a transmitter...
External links
- KF Airfoil Testing
- Kline-Fogleman airfoil comparison study for scratch built foam airplanes
- KF Flight Reports and interview with Richard Kline
- RCFlightCast Podcast, Episode #22: The Kline-Fogleman Airfoil
- Article of the Kline-Fogleman airfoil
- Pictures of aircraft using the KF Airfoil
- Fancy Flights by Scott Morris