US 3117545 A
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HYDROFOIL STABILIZATION OF A GROUND EFFECT MACHINE Filed Feb. 4, 1960 INVENTOR United States Patent ce 1 3,117,545 HYDROFGIL STABHLIZATION 0F A GROUND EFFECT MACHINE Douglas K. Warner, 1937 Panama Drive, Sarasota, Fla. Filed Feb. 4, 1960, Ser. No. 6,791 6 Claims. (Cl. 114-665) This invention relates to a system of hydrofoils mounted on a ground effect machine to stabilize same when it 0perates over water.
One of the problems encountered in designing a GEM is its tendency to violently pitch up as air speed increases. This happens because as the GEM rises, due to the greater aerodynamic lift with speed increase, the center of pres sure, which is rearward of mid chord while close to a surface, moves suddenly forward to its normal position at from 25 to 30% chord in flight away from ground effect. This increases the angle of attack causing either a stall and return to water or if at a sulficient speed, a violent loop, and upside down landing.
It is an object of this invention to prevent pitch up of a GEM operating over water.
It is a further object to prevent said pitch up by the use of hydrofoil means adjacent the front of a GEM.
It is a further object to provide a hydrofoil design suitable for preventing pitch up of a waterborne craft when its speed increases to the extent that a puff of breeze might lift it away from close ground effect.
FIG. 1 is a perspective view of a ground effect machine embodying the invention.
FIG. 2 is a side view of one of the hydrofoil assemblies used in the hydrofoil system of the invention.
FIG. 3 is a detailed view of a front hydrofoil assembly.
FIG. 4 is a cross section taken on the line 4-4 of FIG. 3.
Referring to FIGS. 1 and 2 a ground effect machine is shown which incorporates a central body member 1 having a curved upper surface 2 which provides lift in the manner of an airplane wing when the machine is moving. The machine is directionally stabilized and steered by fins 5. Rear stabilizing wings 47 are also provided. These lift the rear of the GEM only when attack angle is higher than cruising trim, as mentioned in my earlier patents, 2,418,380 and 2,390,859.
On either side of the central body 2 are depending runners 25 which, together with the underside 35 of body 2, form an open ended chamber 7 to retain a cushion of air upon which the GEM is supported with the aid of the suction on the top surface. The lower edges of the runners 25 prevent escape of air beneath them laterally because of the presence of water under them. Rockets 18 are mounted on struts 34 and supply compressed gas to the chamber 7 and starting thrust.
A rear flap 16 is provided, which is pivotable about axis 36 between positions 37 and 38 for purposes subsequently described.
The struts 34 carrying rockets 13 are retractable into chamber 97 within central body 1. A jet slot 3 ejects gas from jet engines or the like in body member 2, to provide propulsion and to move boundary layer air rearwardly over surface 2. Additionally, gas turbines 9 (see FIG. 2) drive propellers iii, located above the rear trailing edge, for the same purposes.
Front and rear hydrofoils 24 and 39 serve to lift the craft at very low speeds. Front stabilizing wings 41) are provided with pivotable roll stabilizers 41 which are used to maintain the craft substantially level during turns.
Depending from each of the wings 4i is a hydrofoil assembly such as shown in FIGS. 3 and 4. Each hydrofoil assembly is comprised of a main strut 45, a large hydrofoil 42, and a further depending smaller strut 46 and hydrofoil 43. As shown in FIG. 2, the top plane of the large hydrofoil i2 is immediately above an extension 3,117,545 Patented Jan. 14-, 1964 of the lower edge of runner 25, for reasons subsequently described. Strut 46 is retractable into recess 49 within strut 45. Each of hydrofoils 42 and 43 has a large central step, and a downwardly directed gas ejection passage 63 immediately behind a small forward step 47. Gas may be introduced thereto by any suitable means. For example, ram air from an air scoop, or the like, might be used.
The craft operates as follows: Struts 46 may be retracted to prevent damage to hydrofoils and allow operation close to shore or thereon. Flap 16 is placed in down position 37, rockets 18 are extended and fired, and jet slot 3 and or props 10 are activated. The craft gains speed and rises until auxiliary foils 24 and 39 are clear of the water. As speed continues to increase, flap 16 is pro gressively raised toward position 38 and strut 46 is extended. As the craft approaches cruising speed, rockets 18 are shut down and retracted. Cruise jet slot 3 and or propellers 10 (see FIG. 2) continue to supply thrust to sustain the craft at cruising speed. The machine is now riding an air cushion, or bubble maintained by ram pressure at the front and the upwardly rearwardly sloping body under surface 35, the water beneath, the inside surfaces of runners 25 and appropriate positioning of flaps 16. The lower edges of runners 25 are immediately adjacent the water. Accordingly, because of the relative positions of each of the hydrofoils 42 and the lower edge of its associated runner 25, as previously described, hydrofoils 43 normally ride not far below the surface of the water. Any tendency of the craft to pitch up causes hydrofoils 43 to rise out of the water and lose their lift, thus counteracting the pitch up tendency. Hydrofoil 42, normally out of water, will instantly prevent dive if this large foil contacts water or submerges therein. Since each pair of hydrofoils is far laterally displaced on each side of the GEMs longitudinal axis roll stabilization is also attained.
I claim as my invention:
1. A ground effect machine for cruise operation above water comprising: a body member, means on said member to provide and sustain an air cushion between said member and the water, propulsion means on said body member, and a pair of stabilizer means, each stabilizer means comprising a large upper hydrofoil and a small lower hydrofoil, one of said pair of stabilizer means depending from said body member far to one side of the longitudinal axis and far ahead of the center of gravity of said machine, and the other of said pair of stabilizer means depending from said body member far to the other side of the longitudinal axis and far ahead of the center of gravity of said machine, each of said stabilizer means depending from said body member to such an extent that said large upper hydrofoil is just above the water surface and said small lower hydrofoil is just below the water surface when said machine is cruising in level attitude.
2. The ground effect machine of claim 1 in which said large upper hydrofoil is mounted on a large depending wedge-shaped strut, and said small lower hydrofoil is mounted on a small, further depending wedge shaped strut, said small strut being telescopically retractable into said large strut.
3. A hydrofoil means comprising a first downwardly and forwardly extending strut, a first hydrofoil having a substantially horizontal planar upper surface, said first hydrofoil being mounted on the lower end of said strut, a second strut telescopically retractable into said first strut, a second hydrofoil having a substantially horizontal planar upper surface, the area of which is smaller than said first hydrofoil surface, being fixed on the lower end of said second strut, a relatively large step near the center of the lower surface of each of said first and second hydrofoils, a relatively small step near the front of the lower surface of each of said hydrofoils, and means to introduce down- Wardly and rearwardly directed pressurized gas immediately behind each of said relatively small steps.
4. The hydrofoil means of claim 3 in which said struts are Wedge shaped, said large strut extending a considerable distance above said large hydrofoil.
5. The hydrofoil means of claim 3 in which said hydrofoils are wedge-shaped in plan view.
6. A ground eifect machine for operation over water comprising: a body member, means on said body member to provide and sustain an air cushion between said body member and the Water, propulsion means on said member, and a pair of hydrofoil means, each having an upper surface, one of said pair of hydrofoil means being fixed on each side of the longitudinal axis and adjacent the forward end of said body member, each said hydrofoil means being further fixed at an elevation such that said upper .4 surface is about 1 chord below the surface of the Water when the machine is in level attitude and at cruising height above the Water, whereby when said hydrofoil means leaves the water the front of said machine is no longer supported by said means and so it maintains its level attitude.
References (Iited in the file of this patent UNITED STATES PATENTS 2,322,790 Cristadoro June 29, 1943 2,444,318 Warner June 29, 1948 2,645,436 Brown July 14, 1953 FOREIGN PATENTS 715,880 Great Britain Sept. 22, 1954