Do It Yourself: Hooven's Paper Flying Wing
THE FLYING WING is the simplest possible flying device. Having no fuselage, stablizer or rudder, its stable speed range is limited, and it is more than ordinarily susceptible to disturbances. On the other hand, its lack of parasite resistance gives it a favorable ratio of lift to drag and consequently a good gliding angle and a low rate of descent.
The technique of folding and cambering paper wings is best learned on what might be called a "general purpose" model made of fairly heavy paper, which is much easier to handle than the very light tissue necessary for long duration flight. Models of this kind are generally more fun to fly. In any case the best paper to use is medium-weight sulphite tablet paper. High-grade Bond paper is too hard to form while heavy paper produces too thick a section. Begin with a sheet about 8½ X 3½ inches cut from an ordinary sheet of tablet paper. Considerable care is necessary in folding to make sure that the paper is unstressed and not warped in the process. The first fold is made down the middle of the long dimension of the sheet by doubling it over as shown in cross section in Figure 1. This divides the wing into two equal halves, one of which will be the wing itself, and the other will be the foldedover leading edge. The leading half of the wing is then doubled over to make fold #2, as shown in Figure 2, and it will be noticed that the edge of the paper is brought down abouts 1 millimeter forward of the first fold. Fold 3 is made as shown in Figure 3 by doubling this over again to the same line producing a section having four thicknesses and a width of ¼ that of the unfolded half. This section is then folded over the original fold as shown in Figure 4 and fastened down with Scotch Tape. Some care is necessary in applying the tape to avoid stretching it and thus introducing warping stresses into the paper. All folds are then creased down as sharp as possible.
At this point the wing should be inspected for flatness. If it is warped or twisted, the best thing to do is throw it away and start again, and this time be more careful in the folding process. If the wing is not warped or twisted, it should fly in this condition, although its progress may be somewhat uncertain with a tendency to flutter. The performance will be considerably improved by cambering, and some skill is required. The leading edge'should be cambered first, and this can be done over the edge of a table with the fingers as shown in Figure 5, moving the wing back and forth with short strokes parallel to the wing chord while exerting as uniform a pressure as possible with the fingers, repeating the process until the whole span is cambered uniformly, roughly as shown in Figure 6. The same process is repeated to apply the slight reverse camber to the trailing edge, as shown in the same figure. The best way to get a feel for the amount of camber re. quired is by trial and error, remembering that the least reverse camber required to prevent nose-diving is the best. The wing will fly without a dihedral angle if it is perfectly proportioned, but ordinarily it is best to finish the job by bending a slight dihedral angle.
The foregoing proportions produce what might be called a basic model of the flying wing. It is probably the best proportion for a duration model, but better glide angle characteristics can be obtained with a farther forward position of the center of gravity. This can be done by altering the proportions of the Original fold so as to produce a leading section having six or even eight thicknesses over the first quarter of the chord. However, the resulting increased thickness tends to offset the gains of the farther forward center of. gravity. The same effect can be accomplished somewhat more efficiently by the addition of one or two layers of Scotch mending tape to the leading section since this tape is thinner and heavier than most paper, or if one wishes to be even less of a purist, he may insert a very thin strip of spring steel.
The wings must be launched with some care by projecting them at a velocity somewhere near their stable flying speed and without twist or initial rotation of any kind. After some practice the flier will learn that a good model can be launched in a suitable angle of bank so that it will return to him very neatly - boomerang fashion - but this seems to be almost the limit of acrobatics.
One gradually learns what to do to make these models fly straight and true. If they have been carefully constructed and cambered, they will invariably do so without further ado. If the model curves, it is generally twisted or the camber is not the same on one side as the other. Too much reflex angle at the trailing edge will cause the airplane to fall off on one wing and flutter aimlessly - whereas too little will result in a prompt nosedive. A certain amount of research on the properties of airfoil sections may be conducted if one bears in mind that whenever the airplane flies in a curve, the half on the outside of the curve has a better lift-drag ratio and sinking rate than the half on the inside.
I doubt if the flying wing that I have described will make any contribution to the future of aviation. Nevertheless, it is a wonderful toy and has limitless possibilities for innovation and variation. Who knows what unsuspected benefits lie in their future exploration?
FIG. 6 FINISHED CAMBERED SECTION
Fred Hooven's flying wing set the flight record - 10.2 seconds -in Scientific American's First International Paper AirplaneCompetition (1967). He now teaches engineering at ThayerSchool, which printed a more technical version of this paper.
