opened the meeting welcoming everyone on a simply gorgeous day in
Southern California. We started with a round-robin of introductions
since there were a number of people in the audience that hadn't been here
before. Of note were Larry Witherspoon and Bill Hinote, long time
members who were able to finally attend their first meeting. We were
glad to see them and hope they will find opportunities to come back in
the future (long distance travel not withstanding).
Bill Hinote mentioned that he had a handout for anyone who wanted one on his flying wing project called the Alphagrif. It embodies the latest in materials and aerodynamic technologies to create an ultra-efficient airframe. His goal is to create an safe and easy to build aircraft for the kit-aircraft industry.
Paul Ross, who works for Alturair which owns the Kasper 1-80 ultralight flying wing sitting outside the hanger, introduced himself and told us a little bit about the aircraft which was purchased about 15 years ago to test the Sachs single-stage rotary engine being used for power. The engine puts out about 23 hp at 6000 rpm and 21.7 hp at 4800 rpm and was originally built for snowmobiles. Engine life is about 3000 hours and uses a 25:1 mixture on the fuel/oil. As soon as they get the matched set of belts necessary to drive the propeller, they plan on getting the aircraft back in the air.
We watched a short video of the Centurion during its second test flight at Edwards AFB (this was footage taken from a recent CBS news broadcast). This is the next generation of the Pathfinder and is designed to fly at altitudes of 100,000 feet for several months at a time doing research and other types of atmospheric observations, like hurricane watch, etc. This is another product of Paul MacCready's AeroVironment company and is an example of flying wing technology taken to the extreme of technological development.
With no other contributions from the group, Andy introduced John Mitchell who would tell us all he knew about Witold Kasper and his revolutionary aircraft.
John began by explaining how his father had met Kasper about sixteen years ago. His father had been in commercial aviation and switched to commercial electronics with Bell Helicopter in Texas. He began looking for something fun do to on weekends and decided that flying and selling ultralight aircraft was just the thing.
After looking through brochures he decided to take John's brother to Issaquah, Washington, to meet Witold Kasper and discuss Kasper's ultralight designs. They were also met by Steve Grossruck who was assembling an 1-80 ultralight. Steve ultimately gave them a demonstration of the aircraft's performance including the famous "mush mode" of descending. John's father described it as a guy who comes in over the field at 200', throttles back and gets partially out of the harness to shift the CG as far back as possible. This puts the nose into a very high angle of attack and the aircraft begins a very high rate descent. About 25' above the runway the pilot shits his weight back forward, adds a little burst of power and settles softly onto the ground with about a 25' rollout. Although this was impressive, John's father didn't buy a Kasper wing since he really wanted something with full 3-axis control.
After hearing about all of this from his father, John read through Kasper's book (published by Meheen Corp.) and became fascinated with it. Kasper was born about 1907, got a degree in mechanical engineering in Switzerland in 1929, and in 1939 completed a degree in aeronautical engineering. Between 1936 - 1939, Witold was a member of the Polish soaring team, winning the Polish championship four years in a row. Also during this time he had designed several gliders as part of his love for mechanical and aeronautical engineering. An interesting story involved his desire to go home one weekend so he used one of the clubs gliders to fly back to his home town. Upon arriving the local airport manager asked were he had come from and after Kasper told him the manager said he had just flown abut 30 kilometers further than the current world record distance held by the Germans. Apparently Kasper really wasn't impressed by any of this since it was just a fun flight for him and records didn't interest him.
Witold was in the Polish Air Force at the start of WWII and managed to escape to Finland shortly after the war began. He indicated he acted as a Polish secret agent for the Finnish government for the next 5 years. After the war he immigrated to Canada and eventually moved to Seattle and went to work for Boeing in their low-speed aerodynamics section.
In the late 1940's he got the notion to design a tailless glider which eventually became known as the Bekas BKB-1. One of the things that concerned Kasper was the tendency of flying wings to tumble with often drastic results for the pilot and/or aircraft. He studied this problem very carefully and applied what he had learned through his study of birds and insects over the years. What he had discovered was that birds never stall although they can tumble. This was done through their ability to shift the CG and CP. He knew he had to design a wing that was stable but independent of forward airspeed.
Kasper looked at one of the most stable bodies around, a cone. If you drop a cone it always goes the same way, pointy end down, so this drogue stability was what he decided to apply to his glider design. Therefore, the BKB-1 was designed to have drogue stability in all three axes and, either through shear luck or very good engineering their center coincidentally converged in the middle of Kasper's head as he sat in the cockpit. This meant that any abrupt maneuvers, like tumbling, would have a minimal affect on the pilot's inner ear and be much less disorienting than in most other types of sailplanes.
John showed us a picture of the BKB-1 from Kasper's book, where it has a dark leading edge and lighter colored upper surface. Later on, Kasper painted the upper surface all silver and the bottom all black since he was exploring how to do controllable tumbling in a tailless glider. He did his backwards, which was different from what others had tried in the past where they pushed the CG as far forward as possible and then initiated a forward tumble. Kasper also theorized that if you didn't have enough control surface authority to overcome the inertia of the rotation, then you could not recover the aircraft from a tumbling maneuver.
His procedure for tumbling the BKB-1 started with a dive into a loop. At the top half of the loop he would push the stick forward to start the nose moving up then bring the stick to the full back position. This would then cause the glider to tumble backwards. The configuration of a 13 degree swept wing with control surfaces at the outer portions of the trailing edge gave him the moment arm necessary to create this "flight" condition and recover. The first time he did it it was disorienting and he slowly moved the stick forward which caused the glider to stop the tumble after loosing about 300' of altitude. In later flights he went from doing half tumbles to full revolutions and started timing them to determine the rate of rotation. He found that the glider was tumbling at 60 rpm, which was about 2 g's on his body, but not having a great affect on his spatial orientation.
In another test flight he decided to try making it tumble forward by putting a 10 lb. weight in the nose to move the CG. Unfortunately, in the BKB-1 this also shifted the center point of the other axes and he ended up having a rotation point at about his hips. This caused him to have the extra g-forces on both his upper and lower body and, he commented after the experience that he felt a little taller.
The other unusual thing about the BKB-1 was the way in which on the controls worked. Kasper knew how to fly it and without having a 2-place version could only tell other pilots about the use of the control surfaces. The only times the glider crashed was when others were flying it. Contrary to a conventional glider, the BKB-1's controls couldn't be neutralized after making the initial input, but rather they had to be left in the desired position to prevent the glider's natural stability (the drogue/cone effect noted earlier) from returning it to straight and level flight. This was disconcerting to many pilots and they would end up in a PIO situation and claim the aircraft couldn't be flown properly. Another part of the positive stability was provided by the 4 degrees of toe-in on the end plates.
It has good pitch stability since the wing is built flat and the airfoil doesn't have washout in the traditional sense. In order to achieve the affect of washout, he put a non-moving stabilizer at the trailing edge of the wing tip at an angle to create reflex on a wing with 4 degrees of incidence. The airfoil is a Wortmann from a helicopter blade and he was able to make them work with this new reflex stabilizer at the tips.
Kasper later took this one step further with the BKB-N where he installed his vertical spoilers on the end plates. (Click here to details of the spoiler/rudder configuration.) These were not meant to control the L/D, but rather to make the aircraft turn. With movement of the balance tap towards the inboard area, it causes a loss of lift over the stabilizer tap and the elevons, which are also mounted closer to the wing tip than in other flying wings. The outboard movement of the rudder portion of the spoiler causes drag and helps turn the glider in that direction. Kasper found he could get a fully coordinated turn by just using the appropriate rudder pedal. These spoilers could also be used for glide path control by pushing on both pedals at the same time, which caused a pitch up mush mode. Just before reaching the touch down point on a landing, the pedals could be released and the glider would automatically flare for a normal landing and roll out. (Click here for another prespective of this setup.)
The other thing Kasper discovered was that this combination of controls actually created triple redundancy, since any one of them would allow him to fly the aircraft. He also noted that you really didn't need an elevon with his system since the vertical spoilers, when combined with just an elevator placed out towards the tips, was enough to adequately control the glider.
John apologized for not having the video tape of a Kasper wing actually tumbling in flight. However , he noted that the BKB-N was the first aircraft to be certified for a tumbling maneuver (this was in 1970). Kasper did many airshow demonstrations with the BKB-N and would finish with a tumble just before the landing.
To accomplish this feat, he would come down the runway on his "downwind leg" at about 300' inverted. He would then initiate the tumble by pushing the stick forward then pulling back, allowing the tumble to last until about 50' where he would pull out it and land into the wind for a normal touch down. The FAA commented that he had to do a 180 degree turn at the end of the runway to prepare for landing, which he wasn't doing during these early airshows. Kasper solved the problem by just coming in lower and, on reaching the end of the runway would do just a half tumble (180 degree turn) into a landing.
John related the story of how Kasper achieved his tumbling certification from the FAA. He did a touch-n-go at 80 mph right in front of the examiner then pulled up into a half loop of about 300' where he commenced the tumbles. First there was a half revolution backwards, then a half revolution forward followed by another half backward tumble. This left him in a position to accomplish a landing and roll out to put himself on the spot he originally hit on the touch and go. After such a display the FAA examiner had no choice but to issue a certificate.
John showed a plan view of the BKB-1 that had some of the original dimensions. The span was 39', with about 155 sq. ft. of area, an aspect ratio of 10:1 and, an empty weight of 375 lbs. (although the plan view had this crossed out and a weight of 458 entered which may have been due to modifications or a heavy paint job).
The next slide covered some of the material presented in one of Kasper's books on the Bekas aircraft. Kasper commented that the glider had a different behavior than other types he had flown and it required learning a new flying technique. It couldn't be stalled even at a high angle of attack like 40 degrees to the relative wind, since in this attitude it would go into the "mush mode". John said that the video his dad had showed a tuft test session where the airflow was actually coming back over the wing. Kasper noted that lateral, longitudinal and directional control were affective and solid at airspeeds as low as 15 mph even though the calculated stalling speed was 42 mph. It didn't have any dynamic stability, but showed an uncanny stability returning to the original position within half an oscillation when disturbed by a gust or pilot input. This was the results of Kasper designing in the drogue stability mentioned earlier.
One of the more interesting comparisons made by Kasper was in relation to conventional aircraft. He said the a shift of the center of gravity causes a change in the static margin moment and it has to be compensated for by the balancing moment of the force on the horizontal stabilizer. This limits the allowable CG movement to about 12% of the MAC. For flying wings (John noted that Kasper treated flying wings as a separate class than his Kasper wings), because of the lack of horizontal stabilizers they are extremely sensitive to CG shift. For canards, he said the design allowed the greatest permissible movement of the CG in relation to the CP. And, for birds he noted that by moving their wings forward and back in the direction of the CG shift the CP was always above the CG.
On the Kasper wing he commented, it was equipped with horizontal stabilizers at the wingtips. In the case of a shift of the CG, the stabilizer is moved up or down as in a conventional plane; however, it not only creates a stabilizing moment but also shifts the center of lift in the same direction as the CG movement, keeping the "static margin" constant. This permitted a CG shift of 24% MAC on the BKB-1A glider, which is about twice as much as in a conventional plane. It was obvious to John that Kasper had managed to solve many of the problems with flying wings through his design innovations.
The next couple of slides showed some of the control surfaces on the BKB-1 and one of these is shown here. Adverse yaw is eliminated in the following manner: A special trim tab or flap is hinged to the trailing edge of each aileron. The connecting arm between the wing and the flap is positioned to always move the flap up when the aileron is deflected. The tap remains neutral when the aileron is neutral. The ailerons have 1:5 differential in the up and down movement. The peculiar flap has an additional beneficial effect. When the elevons are used as elevators, the sensitivity of the up movement is increased and the sensitivity of the down movement is decreased which equalizes the sensitivity in pitch at high and low speeds.
John then put up a slide showing the changes in lift distribution as explained by Kasper. This diagramed the distribution based on various control inputs on what look like birds, since he had based his design somewhat on how birds operated (click here to see this illustration). He preferred rectangular planforms, again based on the wing of a hawk and the way in which a hawk uses its wingtip feathers to control the airflow around them.
About five years ago John called to talk with Kasper and found out from the housekeeper that he could no longer talk due to a series of strokes he had recently suffered. However, she told John to call Arnold Anderson who could probably tell him everything he needed to know about the Kasper wings. However, no one seems to know what happened to either of the BKB models over the years. There was even a motorized version at one point which was financed by Kasper's brothers. It was subsequently crashed by one of the tests pilots, and John thinks that one of Kasper's nephews may still have all the pieces stored somewhere in Washington. Apparently there are still a number of people in the Evansfield area of Washington that have information related to Kasper and there are still some Cascade Kasperwings in use in the area. As a footnote here, John mentioned that Kasper passed away about four years ago, having returned to Poland shortly after suffering the strokes.
The next slide was one of the Wortmann FX05-H-126 that is reflexed. Someone had taken the information and developed the stations values for both a 48" and 100" chord. There was also a note on the paper that said the elevator and rudders were okay and that elevons are not needed.
John summed up with another antidote about Kasper's experiments with tumbling. When he moved the CG forward the revolutions went from about 60 to 120 rpm and increased the g-load on him to about 4gs. On one of these trials he heard a loud crack so stopped the tumbling to take a look at everything and determine how much trouble he might be in. After giving it a good once over the only thing he noticed was his seatbelt was a little loose. As he tightened it up he heard another crack and quickly determined that the seat wasn't stressed for 4gs and had broken under the load. With that experience behind him he removed the forward weight and never flew the glider at that CG location again.
Gavin asked if John knew anything about a Swedish study. Kasper had two patents issued, one on the BKB-1 and the other on vortex lift generation, since he had figured out what was happening on the upper surface of his wing. He had designed several airfoils that used high pressure air from the bottom of the wing that spun up through a little camber and injected it into the airstream on top creating vortices. The way Kasper explained it, at high angles of attack high pressure air is formed on the bottom and this pressure being bled off helps promote the size of the counter-rotating vortex on the top. As the angle of attack goes up the bubble gets bigger and maintains a very nice flow over the upper surface allowing for even greater angles of attack to be achieved.
Apparently this drew some interest in Sweden in the early 1970's, when they took a large jet aircraft and modified the wing to incorporate this theory with Kasper acting as a liaison to the project. The aircraft's original approach speed was 130 kts and the new test wing brought this down to about 30 kts. However, nothing ever became of the experiment since it was decided it would probably be too hard and expensive to tool up for production.
John also noted that a wind tunnel test of a model version of this type of wing didn't show the same results as predicted by Kasper. However, there was no way to telling if the wing was really configured as planned by Kasper.
Andy asked John if this was the same airfoils that used a cusped leading edge and generated several vortices along the upper surfaces. He commented it was, but that it was never used on a full scale aircraft, even though it had been tested in a wind tunnel with mixed results. John had tried something like it in a model, but couldn't get it to work either.
The question was asked if the CG needed to be moved in order to generate the vortex lift. John explained that it was more a function of the wing design than the CG location and that as angle of attack was increased to a certain point the vortices would begin to form. This is demonstrated on the BKB-1 which normally has a sink rate of 200 fpm at 60 mph, but in the mush mode with active vortices is reduced to 100 fpm at zero airspeed. However, due to the drogue stability you still have complete control of the glider.
In the tumbling mode, you might wonder how he manages to recover it consistently when compared to other types of flying wings. If you recall the CG in all the axes is right at the pilots head, but the wings are swept 13 degrees. Kasper calculated the speed the tips were traveling at the normal rotation rate of the glider and found they were doing about 40 mph, which meant he had full control, since that's where all the control surfaces are located.
Bruce Carmichael commented that in one instance a trapped vortices did what had been calculated by mathematicians. A wind tunnel diffuser was needed in a short coupled wind tunnel to slow the air flow down and no conventional method was working. However, when they installed a diffuser that created a vortex affect, it had the desired results and allowed the wind tunnel to be effectively used. John also related a story of watching a wild fire in his area one day that created a vortex along a ridge line that was quite evident. Another person in the audience also noted that he had an experience in a Twin Otter where he was able to achieve a very high angle of attack while in a very aft CG mode with 24 jumpers gathered at the rear door. He indicated he had gotten to a least a 40 degree nose up attitude with full controllability.
The question was asked about whether or not Kasper had gotten a fair hearing from Boeing on his radical ideas. Although John didn't know anything about this part of Kasper's career, another person indicated that he had heard Boeing basically gave the information to Kasper even through some of it had been developed on Boeing time.
The final question was in relation to John's business as a composite builder which was of interest to at least one member of the audience who will eventually need parts for his planned project.
At this point Bill Hinote indicated he had just donated a set of Bekas BKB-1 plans to the TWITT library. In these plans is an extended wing version of the glider, so Kasper did have a conceptual plan for an improved version. There is enough information on the plans to actually build the aircraft.
Andy closed the meeting reminding people we had some handouts on the Kasper wings and patents and the Kasper library material was also available for review (just don't take any of this stuff since it is our only copies). On that note, we broke up for coffee, donuts and some good old hanger flying.
(NOTE: The Kasper Wing, by Witold Kasper is apparently still available from: Meheen Engineering, 1562 S. Parker Rd. #228, Denver, CO 80231-2720, phone (303) 337-4040. Cost is about $10.)