KF Airfoil
Here are some things I have found online as I have been researching planes and how they fly.
Kline Fogleman Airfoil Study
Kline Fogleman Airfoil (Excerpt from The Ultimate Paper Airplane) Gives a preview into his exploration of airfoil design. I own this book and highly recommend it to anyone interested in the subject. Book is available from many retailers including Amazon.
Book Synopsis (Richard Kline and Floyd Fogelman have perfected “The Ultimate Paper Airplane,” the last word on the fascinating field of paper flight. Their plane has soared to unprecedented heights and traveled unprecedented distances. More than just a fanciful toy, it has earned its inventors two separate patents. Featured on “60 Minutes” and in “Omni” magazine, it has also been tested by NASA and the manufacturers of commercial aircraft. Here is the story of this remarkable plane, from its inception to its subsequent rise to fame. Here, too, revealed for the first time, are the secrets behind its extraordinary performance, along with detailed instructions that will enable you to fold and fly seven different models of this unique craft.)
Origins of The Ultimate Paper Airplane (Read) (source)
I received the following an email from Dick Kline with more info oh the story and accomplishments of the KF Airfoil.
In 1985, Simon & Schuster asked me for a big idea to kick off my book The Ultimate Paper Airplane. The idea I came up with was to challenge the distance record of the first manned flight set by the Wright Brothers of 122 feet. I went down to Kill Devil Hills, NC where they actually flew and attempted to break there distance record. My longest flight was 401 feet, four inches. Now, here is the interesting part. The history books state that they flew from Kitty Hawk. But the history books are wrong. They sent the telegram from Kitty Hawk, so Kitty Hawk got all the publicity. Things are not always the way they’ve been recorded.
In 2004, Frank White wrote a book called Fluid Mechanics. On page 500 he shows several NACA type airfoils and their stall points. He also shows a KF airfoil (with sharp leading edge). However, the KF airfoil continues to generate lift out beyond 50º AOA. But, no one seemed interested in this phenomenon. It was ignored.
Recently a man named Paul Wheeler put the KF step on the tip of his prop. He flies powered parachutes. He found that his thrust was increased almost 9%. And, the sound from the tips was also reduced.
Here is a list of the positive characteristics that the KF airfoil has shown to date:
#1 – The KF airfoil handles a wide range of speed from very slow to very fast.
#2 – Normal airfoils are designed to either generate a lot of lift in order to carry more weight, which means they must be thicker to produce more lift, or they need to be thinner in order to fly faster thus sacrificing lifting heavier loads. The KF airfoil can do both of these jobs extremely well.
#3 – The KF airfoil has a much greater range for its center of gravity (CG). A conventional airfoil would normally have a CG about 33% back. The KF airfoil can be moved back as much as 40%, thus allowing it to carry a heavier load. The further back the center of gravity is the more desirable it is because of the center of balance. And, it can also handle a shifting CG and still give you control authority.
#4 – The KF airfoil has great control authority. It’s control surfaces remain effective through a large range of angle of attack (AOA). Even beyond a 60º AOA. This is also evident by its ability to have a very fast roll rate with full aileron and rudder control at very high angles of attack.
#5 – Normally, all flying wings require some reflex in flight. Reflex, which will produce some drag, means that the ailerons are angled upwards slightly in order to keep the nose of the aircraft pointed up. It is also well known that flying wings are extremely unstable and stall easily in flight. The KF airfoil requires zero degrees reflex on a flying wing which means no drag from the reflex action. It is a very stable platform. It is capable of flying without stabilizers or rudder, which means that two components which cause drag are eliminated.
#6 – The KF airfoil appears to have better air penetration. High winds seem to have little effect on how it performs. People have reported not being able to fly their aircraft during strong wind periods while the KF airfoil continues to fly smoothly. It appears as if it rides on rails.
#7 – In addition, the KF airfoil doesn’t appear to be affected by weight increases. It has been reported that the handling of the aircraft doesn’t seem to be affected by adding additional weight. In one case, 4.5 oz. of lead was added and it was able to handle the added weight with ease. In another case, a KF glider which was facing 22 mph wind, flew very well when nearly 100% lead weight was added to it.
#8 – At high angles of attack, the KF airfoil remains unstallable. The center of gravity and center of pressure appear to move backward thus preventing a loss of lift.
#9 – The possibility exists that the KF airfoil may be more fuel efficient because one quarter of the airfoil produces little friction due to the trapped vortex pitting air against air. A normal airfoil produces friction over the entire surface.
#10 – Unmanned aerial vehicles are extremely expensive aircraft. The loss rate in the military is rather high – over 20%. The KF airfoil is a minimal structure which is very strong and simple to build. It would greatly improve on the survivability of these planes because of all the reasons outlined above. In addition, because it penetrates the air so well and is extremely stable, it will produce better photography. Because of a better center of gravity, it will be able to carry more weight, either extra cameras or extra batteries for longer flights. And, because of its ability to penetrate air better, it is not affected as much by higher wind gusts. It has been shown to fly in strong winds when all other RC aircraft were grounded.
And, now for the most amazing aspect of all… the KF airfoil has no apparent bad habits, vices or negatives that have shown up. All airfoils have their positives and their negatives, because each one is designed to do a specific job. Thus, a given airfoil can do certain things well, but do poorly in other areas. To date, nothing negative has appeared on the KF airfoil.
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On the KFm4 airfoil, 50% of this airfoil produces no direct friction or drag because it is air against air, which might explain why it is faster than the other configurations.
-Dick Kline
Link Results
Time Magazine, The Paper-Plane Caper (Monday, Apr. 02, 1973) (source)
1974 NASA Investigation of the Kline-Fogleman airfoil section for rotor blade applications (source)
Forum Excerpt RE: A Strategic Advance in Another Direction (Youtube Clip) (source)
Vortex Lift - Step Research and Images (source)
Continued Research (KF Patent Expired 1990, this paper was published 1998)
Meet Dick Kline, Interview with the Kline of Kline Fogleman Airfoil.
Tony RCGroups Kline Fogleman Airfoiled Wing Discussion (KF Comparison PDF Link) (source)
The Slim Beagle, High Wing Pusher Prop KF Airfoil (Lots of images and info on several different KF Designs)
Paper Airplanes a paper by John P. Crotty (mention of KF step)
Dick Wood, Info about Dick Wood who built and flew in an ultralight with the KF airfoil
Audio Results:
RC Flight Cast #22 The Kline Fogleman Airfoil (Download 38.7 MB) (source)
Video Results
(Several Videos of KF application.)
RavenOden
KFM3 www.youtube.com/watch?v=zyHSQdfAcvU
Regal49
KF Bi-Plane www.youtube.com/watch?v=iTIEMScZPBw
KF Regal www.youtube.com/watch?v=bqcNcUZlQXQ
KF Regal Slow Flight www.youtube.com/watch?v=glumpfS8qDI
KF Blue-Baby www.youtube.com/watch?v=tm3OWZ2JWsw
Fissmoll7
KF-Flying Wing (indoor) www.youtube.com/watch?v=dcYVRhXC4k0
DeanMackey
KF Paper Airplane www.youtube.com/watch?v=C52E7pHwzPw
Davereap
KF Delta wing www.youtube.com/watch?v=2fHO0cXZKBc
KF Wing Glide Tests www.youtube.com/watch?v=nkEIKWRJhN8
KF Double Wing www.youtube.com/watch?v=9TiLX1aSEVM
KF Glider “Ferret” www.youtube.com/watch?v=u0dtYrzs13Q
KFM3 Modified Ferret www.youtube.com/watch?v=g5oxDK46iLc
KF Wildcat www.youtube.com/watch?v=shQLKiEZ3Lk
KF Nutball www.youtube.com/watch?v=aPkZdaOZ0Qo
ShadegrownRC
KF Mig-29 www.youtube.com/watch?v=b2Ctzw0Kj_w
RCPower
KF SU-35 High alpha www.youtube.com/watch?v=1_Eh3pMC-1o
KF X-36 Tailess Plane www.youtube.com/watch?v=E-5ctTWQODk
Macsimc
KF Slim Beagle www.youtube.com/watch?v=eRBW4HJ2nBc
KF Windy Flight www.youtube.com/watch?v=0kkhXPNXCig
KFM3 Aerobatics www.youtube.com/watch?v=KK6NHgusx40
Burkefj
KFM1 B-2 Bomber www.youtube.com/watch?v=0ldpofto0xQ
KFM1 F-117 www.youtube.com/watch?v=6AHIMqEoTLs
BR5499a
KF Revert www.youtube.com/watch?v=-581uOg4fmk
KF Blue Funder www.youtube.com/watch?v=V6bmGRQ9MeI
Ghostfit
KF Crossbow (Glider) www.youtube.com/watch?v=TfJC9yxwHyc
Nightshade8088
KF Slowstick www.youtube.com/watch?v=ePhYX8UgC8s
SnakeCharmer1
KF Wacoish Bi-Plane www.youtube.com/watch?v=mzs7A3V1vLg
RocketManRC
KFM2 YADA (Yet Another Delta) www.vimeo.com/1896430
KFM2 YADA Glide Test www.vimeo.com/1917903
KF Revert Glider www.vimeo.com/1720621
DarthElevator
KF Flying Wing www.vimeo.com/806507
KF Revert Glider Drop Tests www.vimeo.com/812064
KF Combat Wing - Cross Country www.vimeo.com/815531
Prof100
KFM2 F-22 Maiden HighAlpha Stunts Part1 Part2
Patrick Schutte
KFM1 Hand catch www.vimeo.com/1352334
Piper Pawnee www.vimeo.com/2441619
KFM1 42″ Flying Wing www.vimeo.com/1475565
KFM1 62″ FPV www.vimeo.com/1328282
KFM3 60″ Flying Wing FPV Flying
More to come…
Glossery
Aerodynamic Center
The aerodynamic center is a point along the airfoil or wing about which the moment coefficient does not vary with an angle of attack change.
Airfoil
An airfoil is the cross section of a wing. The airfoil shape and variations in angle of attack are primarily responsible for the lift and profile drag of the wing.
Angle of Attack
The angle of attack is defined as the angle between the plane of the wing (airfoil chord) and the direction of motion (free stream velocity). The angle of attack can be varied to increase or decrease the lift acting on the wing. An increase in lift often results in an increase in drag.
Center of Pressure
A point along the airfoil about which the moment due to the lift is zero, i.e., it is the point of action of the lift. The center of pressure will change its position when the angle of attack changes.
Chord
The chord is the dimension of the airfoil from its leading edge to trailing edge.
Circulation
Circulation is a measure of the vorticity in the flow field. For an inviscid flow field, the lift is equal to the product of the circulation about the airfoil, the density and the velocity.
Coandă Effect
Is the tendency of a fluid jet to stay attached to an adjacent curved surface that is very well shaped.
KF / KFM
Kline Fogleman, named for Richard (Dick) Kline and Floyd Fogleman / Kline Fogleman Modified design (see image below) Image by Tony
Computational Fluid Dynamics (CFD)
Computational fluid dynamics is the term given to a variety of numerical mathematical techniques applied to solving the equations that govern fluid flows and aerodynamics.
Modern CFD results can rival the accuracy of wind tunnels in testing airfoils, wings and entire airplanes for certain test configurations.
Density
The mass of a substance contained in a given volume divided by the volume. For a incompressible fluid, the density is considered to be constant throughout the flow field. However, for a compressible fluid, the density can vary from one location to the next in the flow field. The speed of sound in a fluid depends on the ratio of pressure changes to density changes in the fluid.
Drag
Drag is an aerodynamic force opposing the direction of motion. Drag can be due to surface viscosity (friction drag), pressure differences due to the shape of an object (form drag), lift acting on an finite wing (induced drag) and other energy loss mechanisms in the flow such as wave drag due to shock waves and inefficiencies in engines.
Drag Coefficient
The drag coefficient is defined as the drag/(dynamic pressure * reference area). The reference area is usually the plan-form or flat projection (the wing’s shadow at noon) area of the wing.
Dynamic Pressure
The dynamic pressure is defied as the product of the density and the square of the velocity divided by two. The dynamic pressure has units of pressure, i.e. Force/Area. The dynamic pressure is used to non-dimensionalize forces and pressures in aerodynamics.
Flap Deflection Angle
The flap deflection angle is the angle between the deflected flap and the chord line. The angle is positive for a downwards deflection of the flap. Deflect the flap downwards to increase the airfoil’s lift.
Lift
The lift is a force acting perpendicular to the direction of flight. The lift is equal to the fluid density multiplied by the circulation about the airfoil and the free stream velocity. In level flight, the lift developed by an airplane’s must be equal to the weight of the entire airplane.
Lift Coefficient
The lift coefficient is defined as the lift/(dynamic pressure * reference area). The reference area is usually the plan-form area of a wing or horizontal projection of the wing.
Mean aerodynamic chord
This chord is located along the wing and has the aerodynamic property of the two-dimensional wing.
Panel Method
This numerical method places singularities along the airfoil. In the case of VisualFoil or 3DFoil , the singularities are vortices. The vorticity is distributed linearly along the panel.
Plain Flap
A plain flap is a hinge attachment near the trailing edge of an airfoil. The length of the flap is measured as a percentage of the chord and the deflection is measured in degrees.
Pressure Coefficient
The pressure coefficient is a non-dimensional form of the pressure. It is defined as the difference of the free stream and local static pressures all divided by the dynamic pressure.
Reynolds Number
The Reynolds number is a non-dimensional parameter that compares the inertia to viscous forces. If the Reynolds number is low, then viscosity plays an importatant part in the simulations.
More information about Reynolds Number can be found (here).
Stall
At low angles of attack, the lift developed by an airfoil or wing will increase with an increase in angle of attack. However, there is a maximum angle of attack after which the lift will decrease instead of increase with increasing angle of attack. This is know as stall. Knowing the stall angle of attack is extremely important for predicting the minimum landing and takeoff speeds of an airplane.
Streamlines
Contours in the flow field that are tangent to the velocity vector.
Wing Loading
The total weight of the airplane divided by the planform area of the wing.
Wing Span
The span is the total length of the wing.
Misc Sources
Hanley Innovations
Accurate and affordable Airfoil Analysis Software. Ues for aerodynamics analysis of airfoils used for airplane wings, propellers, rudders, keels, hydrofoils, turbines and other aerodynamic surfaces.
