Aeronautics and astronautics – Landing gear – Water landing
Reexamination Certificate
1999-08-26
2001-09-18
Jordan, Charles T. (Department: 3644)
Aeronautics and astronautics
Landing gear
Water landing
Reexamination Certificate
active
06290174
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to amphibious aircraft with sponsons (hull projections or pontoons).
REVIEW OF THE RELATED TECHNOLOGY
U.S. Pat. No. 4,691,881 discloses an amphibious airplane with sponsons which, together with the underbelly of the fuselage form an inverted channel of constant cross section. Toward the aft end of the plane the sponsons flatten and, at the rear, terminate in a trailing edge (labeled
42
; best seen in FIG.
11
). While the plane floats the sponsons provide buoyancy. During taxiing, landing, or takeoff the sponsons act as a hull, with the trailing edge
42
acting as the rear edge of a planing hull, that is, acting as a hydrodynamic step.
As is well-known, the use of a planing hull reduces the hydrodynamic hull drag at higher speeds because there is no trailing hull portion to generate negative pressure. All the pressure is upward, so the hull rides higher and has less resistance. This effect depends on the rear or after portion of the hull being essentially flat near the trailing edge. If the surface curves up, a low-pressure region is created; this is the slower “displacement” hull shape. If it curves down, extra work goes into diverting the water stream and there is excess churning of the water, which creates drag.
In a boat hull the hydrodynamic step is often formed by two surfaces meeting at approximately right angles: these surfaces are the transom, which is almost vertical, and the planing-surface bottom of the hull, which is generally horizontal. In an airplane a vertical rear surface must be avoided because aerodynamic resistance (which is negligible in a boat) is just as important as hydrodynamic resistance.
A sponson not only acts as a planing hydrofoil, but also provides buoyancy and lateral stability when the plane is at rest. Therefore, a sponson must be fairly thick. This means that the rear end of the sponson has at least one curve converging to the trailing edge.
The trailing edge
42
of the sponson disclosed in U.S. '881 is formed by upper and lower sponson surfaces meeting at an acute angle (FIG.
11
), which lowers the air resistance as compared to a flat rear sponson surface. The lower surface, acts as a hydrofoil must be relatively flat. The upper surface of the sponson therefore must curve downward to meet the trailing edge
42
.
As a result, the air path over the upper surface is longer than over the lower surface, and the overall shape of the sponson is like that of an airfoil, i.e. like a wing. The additional lift is minimal—the sponson is much shorter laterally than is a wing—but it still creates appreciable drag.
It would be aerodynamically more efficient if the trailing edge of a sponson were formed by upper and lower surfaces which both curved, resulting in a zero-lift shape, which is aerodynamically the most efficient. (A “zero-lift shape” only has essentially zero lift when disposed at a “zero angle of attack”, i.e. it is aligned to the airstream instead of tilted. Even a flat board will generate lift when tilted in an air stream.) However, a zero-lift shape is impossible to combine with the flat rear lower surface of a planing hydrofoil because the upper surface must be longer, which will generate lift according to Bernoulli's principle.
SUMMARY OF THE INVENTION
Accordingly, the present invention has an object, among others, to provide a sponson which combines an aerodynamic configuration with a planing hydrodynamic configuration.
The amphibious aircraft of the invention has two sponsons, one of each of the port and starboard sides, which extend vertically below the underbelly of the main part of the fuselage and extend laterally or outwardly to the sides. The two sponsons thus define an inverted channel which runs under the fuselage with a relatively constant cross-sectional shape.
Each sponson includes two portions, a forward portion and an aft portion, on either side of a separation line. The separation line is preferably at the vertically thickest part of the sponson.
The forward portion is fixed to the main body of the fuselage and includes a lower surface which preferably slopes downward toward the rear and then levels off, relative to the longitudinal axis of the airplane, and becomes generally flat as it approaches the separation line. This generally flat surface is the planing surface when the airplane is moving in contact with the water.
The aft portion of the sponson is movable. In a lowered or flight position it forms with the forward portion a smooth, aerodynamic shape which preferably has essentially zero lift when the angle of attack is zero, i.e. it is not tilted relative to the air stream. From the thickest central part of the sponson the upper and lower surfaces of the aft portion converge to a trailing edge which is located approximately at the level of the middle of the sponson. This location provides a substantially zero-lift shape (at zero angle of attack) and therefore low air resistance.
The aft portion of each sponson is movable to a raised or planing position for water landing and takeoff. In this position the lower surface of the aft portion is raised above the surface of the water during planing motion on landing and takeoff, so that planing action is efficient. The aft portion may be lowered to the flight position after the aircraft slows below planing speed, to provide additional buoyancy and lateral stability.
Preferably, the separation line between the forward and aft portions, which runs along the outside of the integrated sponson in the flight position, is the outside of two separation surfaces which enclose the ends of both sponson portions. Preferably the separation surfaces are, at the lower end, generally vertically aligned like the transom of a boat, and, as they rise, curve toward the front. The space between the two separation surfaces form an open-sided inlet air scoop which diverts air down into the space between the water and the bottom of the aft sponson, which otherwise would be a low-pressure area during planing.
The aft portion of each sponson may be made movable by any conventional mechanism, and may be controllable by any conventional manually-operated, automatic, or computer-controlled device.
The air-scoop configuration of the present invention solves a recognized problem of conventional sponsons, which often have a stepped bottom on their sponsons. Formation of a partial vacuum under a sponson, known as “blowing the hull”, sucks the airplane down into the water and increases hydrodynamic drag and wave impact.
Another prior-art problem solved by the present invention is that of aligning the center of buoyancy and the center of gravity. The aft portions of the sponsons can be lifted to any desired height relative to the water line to adjust the buoyancy. Also, the fact that the rear undersurface of the aft sponson portions can curve up increase the range of possible sponson designs, and permits the center of buoyancy to be moved forward or aft for the configuration in which the aft portion is aligned with the forward portion of the sponson.
REFERENCES:
patent: 1273549 (1918-07-01), Sloper
patent: 3190587 (1965-06-01), Fries
patent: 4660670 (1987-04-01), Mattox
patent: 4691881 (1987-09-01), Gioia
patent: 517775 (1940-02-01), None
patent: 668127 (1952-03-01), None
Browdy and Neimark
Jordan Charles T.
Steele George L.
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