(Gairns) suggested that I say something on the subject of tailless airplanes.
I shall try to recollect all my limited experiences. Occasionally
events in oneís past seem to commit an individual for a lifetime, marriage
not necessarily being one of those events.
In my case, it happened in Poland in the mid 1920's when as a small boy I heard and saw for the first time an airplane flying overhead. I know that the magic of that event hooked me on aviation to this day. Since the war, I worked for Canadair where I frequently browsed through the library. There, in one of the European aviation magazines, I spotted a picture of a pre-war German sailplane, the Horten IV. It was a silhouette of a long, swept back wing pictured against the clouds. It had virtually no protrusions to spoil the ideal, so I thought, flying wing. This picture also made an indelible impression. Horten Brothers had begun before the war a systematic development of tailless airplanes. The last, and the most extravagant of them was the Horten VI sailplane, also a swept wing of some 25 meter span with an aspect ratio close to 30. There was only a tiny pod under the wing for the legs of the pilot housed within the airfoil in a sort of praying mantis position. If I recall correctly, that sailplane was chosen by famous R. Kronfeld to set the distance record by soaring along the coast, of South America.
The desire to go aloft, to go faster and further is with us since the Icarus. This drive motivates us to create ever more successful flying machines.
Purists maintain that the flying wing is the answer. In practice, like any ideal, it is hard to achieve. I said hard, but not impossible. In some applications, the flying wing may even be the only solution. Look at the hang-glider or at the just revealed glimpse of the stealth bomber, Northrop B-2.
The applicability of the concept depends on what has to be lifted, how far and fast, how safely and I must add on who is to pay for the development.
The first question deals probably with the most severe limitation of the wing only airplane concept. It offers very small internal volume to carry things. This drawback would manifest itself be it a sailplane or a flying wing replica of the 747. The requirement of speed brings the profusion of design problems. The laws of aerodynamics impose different demands on shapes suitable for low sub-to hypersonic flight.
Finally, the safety of flight is strongly related to the quality of flight. We don't want any high performing Bronco's. Therefore, the inherent stability and easy control must be a feature of the design.
As we know, stability and maneuverability are mutually antagonistic features, yet all flying machines must possess an acceptable compromise to the pilot.
The birds are not bothered by these human deficiencies. They are able to instinctively and instantly reconfigure to cope with the disturbance. Our own creations have to be stable enough to relieve the pilot of the need for instant and continuous reactions.
Currently, the requirement for inherent stability is being relieved for some airplanes thanks to the artificial stability provided by active controls. This is made possible by the developments in electronics and computers bringing us one step closer to birdsí flight.
This development permits the Northrop B-2 stealth bomber to be a real flying wing. Yet not so long ago, Northrop's similar flying wing bomber XB-49 was rejected by the pentagon for not being a steady enough bombing platform. So much for generalities.
You probably are wondering what entitles me to all these judgements? Just after the war, there were at Canadair a few Canadians and some European émigré glider pilots. Soon we started the Canadair soaring club. It was an ambitious name considering that, at the time, there was nothing to fly, let alone to soar in. Private ownership did not exist since there was nothing to own.
There were some antiques in Montreal area, all in need of repairs. Eventually, we got some heavy, surplus, military gliders, and a Schweizer built trainer. We needed something that would perform better than what we had.
Having served the club for some years as a general repairman, I felt that need more than others. With a Silver "C" earned before the war, personal temptations channeled my creative notions towards a high performance sailplane. I embarked on a design of a 15M, fully flapped V-tailed sailplane. Some discussions with the interested individuals resulted in conclusion that its construction would be outside of our means.
That was the time when I saw that picture of the Horten IV. Its ultimate simplicity of form and racy silhouette was irresistible. Closer scrutiny revealed its large size (20m span). There were intricate flight controls. Lots of thin gauge, steel tubing welded assemblies around the cockpit. Apparently, it was also prone to flutter at higher speeds. Head first position of the pilot, could mean head to stump confrontation on any outlanding. Another dream had to be given up.
Yet the infectious idea persisted. In a few weeks, I prepared a 3-view, drawings of the structural details, and performance predictions for a little bird. It had no tail, the wing was rectangular, but it was swept back 13 degrees. The pilot was seated in a short nacelle. The span was 40-ft (12m), aspect ratio only 10, and the total length 10-ft. All controls were located at the wing tips.
I was anxious to show it to my gliding associates at Canadair : Witold Kasprzyk and Fred Bodek. Surprisingly, they approved, Kasper became an instant enthusiast.
In no time, he imported aircraft quality plywood from Finland and cleaned up his basement in preparation for construction. We adopted the BKB-1 designation after our first letters. It was winter of 1956.
We notified the D.O.T. and had an official inspector designated. I spent many long evenings catching up with the drawings and the stress report. Parts were already being made.
In the spring, we had the wings on the jigs, leading edges upwards, partly skinned with plywood. Then came the springtime deluge. The Cartierville (Montreal) basement flooded above the trailing edges of our wings. I shall not elaborate on the concept nor details of this little sailplane. It was described at the OSTIV Symposium in Cologne in 1960, in my name by the late Bev Shenstone. Subsequently, the articles and design data were published in Swiss Aero Revue (Nov. 1960, May 1961), in the World's Sailplanes 1963, and Jane's Airplanes of the World.
Just before completion of the BKB, my partners first Kasprzyk and several years later Bodek, migrated to the United States (Boeing) in search of better jobs. On parting, we decided that the glider would remain in Canada for the initial flying, then it would be shipped to the States.
The flight tests started in Sept. 1959, under the experimental license CF-ZBK-X. Initially, the glider was flown from Pendelton, Ontario where we were fortunate to have paved runways.
We had some troubles. The BKB would not even leave the ground on initial car tows. Lowering the position of the tow hook solved that. Bumping along the runway, we quickly decided that the elevons unlike the conventional ailerons must be mass balanced. At the first aero tow take-off, the evening sun was glaring blindingly at the end of the runway. In the middle of the take-off, the canopy suddenly decided not to go with us. This disturbance resulted in a severe wallop against the runway, damage to the nacelle, my back, and my pride.
After repairs were done, Dave Marsden, glider and an ex-F-86 pilot, volunteered to carry on with testing. He flew very impressively in spite of the glider's sensitivity in pitch and continuing trimming difficulty. Here I quote some impressions from his report to the D.O.T. :
"After a considerable amount of ground testing, using car tows, and some minor modifications, the BKB-1 took to the air on its first aero tow on the 10th of October, 1959. During the following weekends up until the 15th of November, 10 flights were made for a total of 4 hrs. 15 minutes in the air.Later, a number of other pilots flew the BKB, among them Dave Webb, Canadian soaring champion at times. He must have liked flying it since he soon suggested (1960's) a larger version that he would like to build. I still have a model of it, but in the meantime Dave also left Canadair and the project collapsed.
The flying, analyzing results, alterations continued. The last Canadian flying permit expired in November of 1963. Come the time, in accordance with the partners agreement to ship the BKB to the States. It was trailered to California to my Americanized partners.
Having obtained a U.S. Pilots License and the new Registration for the glider, Kasper started flying it. After some modifications to improve the trimming system to his taste he began to explore low speeds at progressively further aft CG. locations.
I began to receive letters from him and articles in which he claimed most unusual behavior for the glider. Having known Kasper since 1930s, and his prowess to claims, I soon lost the sense of reality.
I shall read you some excerpts. This is from his letter. I was very surprised to read about these 'apparently' authorized aerobatics since the BKB was not designed to the requirements for the aerobatics category.
At the time Kasper sent me a short 8mm film of the BKB flying, taken without a telephoto. I transferred it lately to the video tape. It may give you some impression of the bird and a chance to appreciate the music.
THE REVOLUTIONARY KASPER WING
From the distance, and after a lapse of years, (Kasper must be close to 90 now, last seen somewhere in Portugal) there are some unanswered questions :
1. Why the American Authorities permitted unlimited aerobatics to be performed over the crowds of air shows in a machine not designed for it. Perhaps as a result, one Curtis McPhail, 2nd officer for Northwest Airlines and fighter pilot in the reserve was killed in the BKB in November 1971.Yet, he deserves and has my respect for his energy, for gutsy and inquisitive flying. It lead to the discovery of the BKB's '2-phased stall' associated with a strong vortex occurring just above the wing. It also led to the discovery of the unique capability to tumble controllably.
Both features are the unforeseen result of the effort at the design stage to avoid tip stall and tumbling. Without the benefit of any previous experience with the swept wings, these measures were overdone thus precipitating early root stall with the ability to maintain control at all stages of motion.
So much about the BKB and Kasper.
After the tragic end of it, my interests drifted towards boats. My personal fortunes begun to have ups and downs paralleling those of Canadair and rest of the industry at the time. My son earned a degree in engineering and became a willing and an excellent partner.
Three years ago, while at Hawkesbury, we met Dave Webb and Gunther Geyer-Doersch (Canadian D-G representative and expert composite fabricator/sailplane repairman) again while visiting the club. A little reminiscing brought the BKB from the past. Are there any chances of bettering standard 15- meter. class with something like it? We promised to look for an answer, Dave promised to look for a likely sponsor.
Both parties are now in the 3rd year of that search. The standard class includes top-notch sailplanes representing the latest in aerodynamics and technology of materials. They are the result of years of progressive evolution and they are expensive. Any real advance achieved by radical departures from convention would be very risky and also expensive.
We started to contemplate different approaches. Variable geometry, chase of extensive laminarity were discarded, although these complexities do not clash with the flying wing concept.
Since any large improvements are not expected, the calculations must be carried out in detail and to conclusion to define any meaningful gains. The use of computers involves writing specific programs and debugging - also a lengthy business.
Obviously concepts of a tailless sailplane dominated our thinking. We also believed that gains in performance and cost reduction could be realized by elimination and reorganization of components.
Apparently, that approach is shared with the others. Last year, we learned of a similar development, also aiming to improve the 15 meter class, being conducted by the Akademische Fliegergruppe Braunschweig in Germany.
After 6 years of work, their SB-13 Nurflügler, or flying wing, reached the flight test stage. Performance gains were confirmed but some serious deficiencies of flying quality also become evident.
I shall only briefly describe the evolution of thought guiding our own work. The reduction of components started with an attempt to accommodate the prone pilot in an effort to reduce frontal area.
But, what was feasible for the large, slow flying Hortens with its 5-ft. chord, makes no sense for a modern sailplane whose root chord is half that length. Try as you may, you would end up with a sizeable bulge. The provision of visibility would ruin the airfoil shape, as was the case with the Horten. Headfirst landings would be the cause of unnecessary excitement.
The model, that you see now, illustrates the next attempt in which we are trying to accommodate the pilot in a supine position. The height of the nacelle is only 26 in. The spar caps are separated vertically across the cabin offering a through space for pilots legs, and for the leading arm suspension of the retractable main gear.
The wing panels divide in center plane, nacelle splits at the bulkhead. The structure could be light but poor visibility defeats the concept. The manufacture of distortion free glass panels would be a problem in itself.
The next model accommodates the pilot in a conventional-semi reclining position thus adding 4 inches to the vertical dimension. We accepted defeat not being able to reduce frontal area.
The optimum slenderness of the aerodynamic body is about 3 to 4 resulting in a nacelle length of some 10 feet. That also is the length of the BKB and is required anyway to provide stable ground runs. We notice that the aft end of this nacelle - or fuselage, reaches aft of the wingtips'. It provides long enough arm, aft of the CG. to carry an effective empennage. Does it mean the defeat of the flying wing concept? The comparison with the SB-13 will provide some answers. Both projects aim to improve the performance of the standard 15 meter. Thus, the results measure degree of success.
SB-13 people have chosen to be faithful to their Nurflügler. We, in our pragmatic approach end up with a hybrid. For yaw stability and control SB-13 resorted to large, wing tip located stabilizers and rudders.
We have a single vertical fin, as an integral part of the T-Tail. But the directional control is accomplished solely by wing tip located small plates which deflect outwards only. These rudders were found to be very effective on the BKB providing directional control even at the low speed phase of the take-off run.
We feel safer without the large objects at the tips of the flexible wing - very likely invitation to flutter.
We tried to change the configuration of the conventional sailplane to make each component contribute to stability in pitch and in yaw.
The forward location of the swept back wing reduces the length of the fuselage, thus eliminating the destabilizing effect of the conventional cockpit.
The use of the stable airfoil and arranging for the appropriate elevon deflection made the wing stable in pitch. Its sweepback provides a degree of directional stability.
The pilots CG coincides now with that of the structure thus eliminating the need to re-trim. All these steps nearly eliminate the need of the tail but, it's presence makes for safer testing.
A lot of effort was devoted to obtain and maintain elliptical loading throughout the flight by juggling the sweep angles, tapers and elevon deflections.
Overall effort seems to be justified by comparing the carefully calculated performances with those of the representative current sailplanes. The high L/D and high speed glides encourage us to continue the effort.
After 3 years of not necessarily every day, but persistent effort, we might
say : "Habemus Papam". Our last configuration yields promising enough
performance to warrant continuation of work.