Big News! Dick Kline Inventor of the KF AirFoil Contacts rcFoamFighters.
The following posts are excerpts from e-mails sent to us from Dick Kline along with information provided by him on the various types of KF Airfoils. If you are thinking about experimenting with any of these airfoils or just want to know more about them this information should be very helpful.
(Copy of Email from Dick Kline to rcFoamFighters on 3/28/09)
Hi Frank and Paul…
You both are more than welcome to do a video of the KF airfoil.
I’m delighted that you are interested in this concept that has been trashed by the experts for over forty years. They claim that it is too high in drag. However, when the step is applied to a flat plate it appears to go faster. The KFm4 goes even faster than the other KFm variations.
When a KF step was applied to the end of a prop it increased the thrust by almost 9%. If the step produces too much drag, how can it become more efficient.
Personally, and I’m no expert, but I believe that 50% of the KFm4 produces no direct friction or drag because it is air against air. That’s kind of mind-blowing to think that half of the airfoil doesn’t come in direct contact with the air around it.
Have you guys ever heard of the Kamm effect? In the 1930s, Wunibald Kamm who was a German aerodynamicist, chopped off the rear end of his racing car. At that time it was thought that the tear-drop shape was the most aerodynamic. The blunted rear end proved to be more aerodynamically efficient, which is why most cars today come with blunted rear ends. That includes the hybrids, which are looking for fuel economy.
In fact, the Boxfish has inspired blunted rear end designs.
Here is one study done in 1998 that shows some positive characteristics of the step concept.
Finally… 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.
The concept behind the Kline-Fogleman airfoil may be hard to understand because it is so different from present aerodynamics. The KF concept uses a vortex, which attaches itself to the KF airfoil behind the step and becomes part of the airfoil. This means that one-quarter of the KF airfoil is air against air. This also means less friction and greater efficiency penetrating the air. It is important that the step be between 7% and 9% at 50% of the chord on top. When the step is on the bottom, the step should be at 40% of the chord. When the step is on top, it will produce higher lift than on the bottom, but the airfoil works well right side up or upside down. With the KFm4 airfoil, which has the step on the top and bottom, 50% of this airfoil is air against air, which means no direct friction or drag.
– Dick Kline
P.S. I’d be very interested in your own personal experiences with the KF airfoil concept. I think that there may be a difference between what is seen or studied in lab conditions is not the same as what happens in the real world. So many people who first see the KF airfoil react to it by saying, “That thing can’t fly.” Somehow it does inspite of everything that we have learned about the way a wing is supposed to generate lift.
Thanks again, guys, for your interest.
Pictures of KFm Airfoil Variations:
Pictures of Kline-Fogleman Effect:
rcFoamFighters would like to thank Dick Kline for
sharing his thoughts, words, time and the above documents
We will soon be using KFm Airfoils on up
coming projects and seeing how they perform.
Please click on the below link for more in depth information
on the performance of the KF airfoil provided to us from Dick Kline along with the information in this post.