Aeronautics and astronautics – Aircraft sustentation – Sustaining airfoils
Reexamination Certificate
2000-04-12
2002-11-05
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Aircraft sustentation
Sustaining airfoils
C244S04500R, C244S130000
Reexamination Certificate
active
06474604
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to certain new and useful improvements in fluid-dynamic efficiency of wings and fluid-dynamic foils which are employed in dual or multiple foil structures or in joined segments of foils that are split into segments and rejoined.
2. Description of the Prior Art
Airfoil shapes and foils moving through a fluid produce pressure differential as roughly defined by the term “lift”. By producing pressure differential, a pattern of circulation is produced around the advancing foil. This circulation is continuous around the length of the foil and is known as a “vortex”, or “vortical flow”. This vortex remains “bound” around a conventional airfoil the length of the surface from root to the tip. The same phenomenon occurs with all fluid foils creating pressure differentials similar to lift. Beyond the tip of conventional fluid foils this rotating fluid circulation “sheds” off into tornado-like “free” vortices or, in the case of aircraft a trailing “wingtip vortex.” Each shed vortex tends to grow into a tighter and more compact rotating fluid mass as it leaves each tip surface into the “free stream” because the differential in pressures (lower pressure from the upper side of the foil and higher pressure from the opposite side of the foil) are attempting to equalize. The vortex, with its high-pressure outer layers rotating rapidly, draws the high-pressure component into its lower pressure core. This suction-creating effect produces undesirable lift-induced drag. The pair of shed tip vortices typically trailing behind conventional aircraft exemplifies this. When in flight, small vortices also shed from the trailing edge of conventional aircraft wings, but the primary drag-inducing vortices are those shed at the outer wingtips. These vortices contain tremendous quantities of rotating mass fluid-dynamic energy.
Long tornado-like rotating vortices behind large aircraft may continue for hundreds of feet or even miles, depending upon the weight of the aircraft, wing area, aspect ratio, and other variable factors. In some cases these vortices endanger other aircraft that may be entering the wake of these energy-laden vortices trailing the aircraft. It becomes obvious that trailing vortices in addition to creating tremendous amounts of fluid-dynamic drag also can be hazardous to pilots and passengers flying small aircraft where larger aircraft are departing and arriving.
Reducing induced drag results directly in decreasing the amount of energy required to sustain fluid-dynamic foil induced lift The purpose of all attempts to reduce drag is energy conservation of one form or another. Some inventors have sought to reduce induced vortice-created drag in aircraft by use of such devices as end plates, winglets at wing tips, propellers with winglet-like projections at the blade tips. Some inventors have sought to improve aerodynamic efficiency by using joined wing systems on conventional fuselages. Joined wings have inherent rigidity and some fluid-dynamic advantage over conventional wings, but there are inherent inefficiencies in prior art joined wing systems in that they do not employ devices that would eliminate or greatly reduce the drag penalty from vortex-induced drag. Up to ½ or more of all induced drag of conventional wings is due to “vortex shedding”—the resulting creation of free vortices from fluid-dynamic foils in the process of producing lift.
Most the multi-wing creations of previous inventors have not reached the maximum potential of aerodynamic efficiency and drag reduction. In spite of the positive (theoretically and experientially demonstrated) potential of joined wing aircraft to reduce induced drag, most joined wing aircraft have wing intersections that unfavorably translate wing tip pressures from the leading wing to the following wing. Forward placed airfoils are commonly joined to aft ones such that vortice translation creates oppositional interference when translated pressure mass from the first airfoil interfaces with counter-rotating circulation mass of the subsequent foil. One advantage of structurally joining wingtips is a shorter, yet stronger span for the same amount of wing area. Decreased wing length results in decreased bending moments. When a wingtip union is properly designed to translate the circulating fluid mass without letting it shed as a vortex, it can also be designed to utilize this potential energy for forward thrust and lift augmentation to the rear lifting surfaces (in a joined wing, biplane system or multilayered wing arrangement). The ideal wing system would reduce overall induced drag rather than creating unwanted induced vortex drag. Utilizing such an invention would enable a designer to significantly reduce wing area because the wing system is producing more lift per square area unit. Reducing wing area also means less profile drag and the amount of energy necessary to sustain forward flight is greatly decreased. The ultimate improvement of aerodynamic or fluid dynamic foils would be to eliminate practically all foil-tip vortex-induced drag by translating this fluid-dynamic flow from a leading foil pair to corresponding surfaces of subsequent foils behind said leading foil pair, or to convert this vortical energy into forward thrust, or both. The ultimate increase in efficiency would result from utilizing inventions which eliminate the greater percentage of all wingtip vortex-induced drag, thus the effect of “infinite” wing is more nearly realized without the more extensive structure and subsequent weight penalty resulting from strengthening and lengthening wings to a high aspect ratio.
THE PRIOR ART
Vortex shedding at the wingtips is a performance liability for conventional aircraft: Shedding wingtip vortices produce ½ or more of the total induced drag of lifting airfoils (wings and propeller blades). Shedding vortices are what causes increased noise from rotating blades and propellers. Inventions such as the “Q-Tip” propeller modify shedding vortices to minimize noise produced at the tips. Other inventions have been created for use on conventional aircraft wingtips and propellers to reduce drag and utilize the dynamic energy contained in these vortices. Such inventions reduce the drag-producing component by “diffusing” or “dissipating” or “suppressing” these vortices. “Whitecomb Winglets” or Hachett's Vortex Diffuser (U.S. Pat. No. 4,190,219) were each designed to disperse the vortex somewhat and also convert vortical energy into forward thrust. Small winglets such as these can improve wing efficiency somewhere near 15%. Most devices that are designed for conventional wings to disperse, reduce, or utilize tip vortice dynamic pressures function with varying, but limited degrees of efficiency in drag reduction. Previous attempts to significantly reduce drag due to vortex shedding have produced limited degrees of success.
Methods of modifying the wingtip vortex formed at the outer tips of airfoils have included the use of end plates to reduce vortex shedding and multiple vanes to “split”, “diffuse” or weaken the vortex, thus lessening vortex-induced drag. Attached panels and upward or downward turned tips have been used with varying degrees of success to present. Some inventions break larger vortices down into multiple smaller vortices to lessen vortex-induced drag, thus not allowing a single trailing vortex to form off each wingtip. Such devices are attempts to reduce kinetic energy in the wake of the wing, and consequently lessen induced drag. Richard Vogt (1951, U.S. Pat. No. 2,576,981), Alexander Lippish (1956 U.S. Pat. No. 2,743,888), Clarence C. Cone, Jr. (1966 U.S. Pat. No. 3,270,988), and Scott Rethorst (1973 U.S. Pat. No. 3,712,564) each invented wingtip devices to diminish vortex-induced drag in aircraft. Nonetheless, such attempts have produced only limited improvement in induced drag reduction.
Dr. Richard T. Whitcomb of NASA (inventor/developer of the “VWhitcomb Winglet”) in his presentation of CONCEPTS FOR DRAG REDUCTION OF AGARD/VKI o
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