Abstract:
A funnel strip is added to a rotary airfoil, which utilizes the Bernoulli principle to increase the velocity of air over the suction side of the rotating airfoil to increase the lift. The device is applicable to thrust-producing devices, such as propellers, as well as to wind-powered devices.

Description:
BACKGROUND OF INVENTION 
     This invention relates to the field of aerodynamics, and more particularly to improvements in rotatable airfoils such as propellers, helicopter rotors, and wind powered devices for converting wind energy into electrical or mechanical power. All such devices use blades, which are rotatably mounted and have aerodynamic airfoil shapes designed according to well-known a conventional rules using aerodynamic formulas known to those skilled in the art. 
     The same laws of aerodynamics applying to rotary airfoils also apply to aircraft wings. The conventional formulas utilize the terminology appropriate to the aerodynamic forces on an aircraft wing, as follows: 
     
       
         Lift= C   L ρ/2 V   2   S   
       
     
     and 
     
       
         Drag= C   D ρ/2 V   2   S   
       
     
     where C L  is the coefficient of lift, C D  is the coefficient of drag, ρ is air density, V is the air velocity, and S is the wing area. A line from the leading edge to the trailing edge of the airfoil is the “chord” of the airfoil, and an angle α between the chord and the direction of airflow relative to the airfoil is termed the angle of attack. C L  depends mainly on the angle of attack. C L  values range from negative to about 4.5, but are usually from 0.3 to 1.5. Conventional wings stall (lose lift) above an α of about 15°. C D  usually ranges from 0.004 to 20, and is composed of frictional drag due to air passing over the surface of the airfoil plus other drag forces produced by separation of airflow at the top of a wing at high angles of attack and air circulating lengthwise over the wing. 
     It is evident that lift and drag differ only in the coefficients C L  and C D  in the above formulas. The coefficient of drag, C D  at medium speeds (below 0.8 of the speed of sound) is due mainly to frictional drag, which increases as velocity squared. The coefficient of lift, C L  increases linearly; therefore, the lower the angle of attack (α) the larger will be the L/D. The highest efficiency of a rotary airfoil when the airfoil is rotated by an energy source depends on attaining the highest lift to drag ratio possible. 
     The design considerations are different when the rotary airfoil is receiving energy from the wind and operating a wind powered device. The basic aerodynamic formulas of an airfoil are same, except that the angle of attack α is selected to produce the maximum lift. The blade is mounted to account for the velocity of the wind relative to the rotary movement of the airfoil in a direction perpendicular to the wind velocity. Here, the object is to produce the maximum lift, which is translated to torque on the shaft of the wind powered device. Although the drag is also great, it is accommodated by the structure holding the rotating blade. 
     Lift or thrust is known to increase as the square of the air velocity according to the above conventional formulas. If conventional air velocity across the top of an airfoil were increased, the resulting increased imbalance in air pressure would greatly increase the lift. Suggestions have been made in the prior art for increasing the velocity over an aircraft wing for this purpose. U.S. Pat. No. 6,138,954 issued Oct. 31, 2000 to Gaunt proposes retractable slats angled above the leading edge of aircraft wings so as to form a funnel over each wing to provide increase air speed over the wing and increase lift. 
     U.S. Pat. No. 5,772,155 issued Jun. 30, 1998 to Nowak proposes retractable delta flaps deployed above the wing to delay flow separation on the back of the wing at increased angles of attack. 
     U.S. Pat. No. 1,787,321 issued Dec. 30, 1930 to Orr proposes a pair of complementary airfoils located on either side of the leading edge of an aircraft wing to form a Venturi opening in proximity to the leading edge of the wing funneling air over both the top and bottom of the wing for the alleged purpose of increasing the lifting effect during the forward propulsion of the aircraft. 
     Leading edge slots (known as “slats”) are well-known in the prior art of aircraft wings. These comprise auxiliary members forming a contoured slot through the airfoil with an opening on the pressure side below the leading edge and exit on the suction side above and beyond the leading edge. Slats are formed by rigidly attaching a curved sheet of metal or a small auxiliary airfoil to the leading edge of the wing to form a Venturi-shaped slot. The slat prevents the breakdown in the flow over the upper surface of the wing and extends the working range of the angle of attack. The primary purpose of the slat is to prevent detachment of the airflow over the suction side of the wing. 
     Slats have been applied for a similar purpose to rotary airfoils, specifically propellers. U.S. Pat. No. 4,840,540 issued Jun. 20, 1989 to Kallergis, and British Patent Number 460,513 dated Apr. 4, 1936 in the name of Fairey Aviation Company Limited add slats to aircraft propellers in order to suppress flow separations and reduce noise. The propeller slats create a Venturi with opening on the pressure side of the airfoil section and exit at a higher velocity on the suction side of the airfoil section. The propeller slats of the aforementioned patents do not extend the full length of the blade, since they are intended to function only along a portion of the blade length. 
     Accordingly, one object of the present invention is to provide an improved rotary airfoil system providing increased lift. 
     Another object of the invention is to provide an improved rotary airfoil system in which the lift to drag ratio is maximized for propellers and the like. 
     Another object of the invention is to provide an improved rotary airfoil system for producing increased lift in a wind powered device. 
     SUMMARY OF INVENTION 
     Briefly stated, the invention comprises a funneled rotary foil comprising a rotatably mounted hub having an axis of rotation, a plurality of circumferentially spaced blades mounted on the hub so as to extend in a generally radial direction from the hub to a blade tip so as to be rotatable in a plane of rotation about the axis, each blade having a cross-section defining an airfoil with a suction side, a leading edge, a trailing edge, and defining a chord extending therebetween, the airfoil increasing gradually in thickness from the leading edge to a point of maximum thickness and thereafter decreasing in thickness, a fin attached to the blade tip and adapted to block radial flow from the blade tip, and a funnel strip mounted on each of the blades uniformly spaced from the suction side thereof and extending in a generally radial direction along the full length of the blade, the funnel strip having an inlet edge defining a funnel inlet area with the airfoil leading edge and having an outlet edge spaced from the suction side at approximately the point of maximum thickness to define a funnel outlet area, the funnel plate being oriented with respect to the chord so as to scoop in and increase the velocity of air flowing over the suction side of the airfoil, and dimensioned such that the ratio of inlet area to outlet area lies between and including the range of 2:1 to 20:1. Funnel angles are specified according to whether the funneled rotary foil is functioning as a wind-driving device or as a wind-driven device. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The invention will be better understood by reference to the following description, taken in connection with the accompanying drawings, in which: 
     FIG. 1 is a front elevational view of a funneled rotary airfoil designed as a propeller, only one blade of the propeller being illustrated, 
     FIG. 2 is a side elevational view of the propeller FIG. 1, 
     FIG. 3 is an enlarged cross-sectional view of a single blade of the propeller taken along lines III—III of FIG. 1, 
     FIG. 4 is a front elevational view of a funneled rotary foil for a wind powered device using the present invention, 
     FIG. 5 is a side elevational view of the funneled rotary foil of FIG. 4, 
     FIG. 6 is an enlarged cross-sectional view of a single blade of the funneled rotary foil of FIG. 4 taken along lines VI—VI of FIG. 4, 
     FIG. 7 is a side elevational view of a wind powered generator using a single funneled rotary foil, and 
     FIG. 8 is a side elevational view of a wind energy device utilizing a double funneled rotary foil. 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIGS. 1 and 2 of the drawing, a propeller, shown generally at  10  comprises a hub  12  and blade  14 . Blade  14  is one of a plurality of blades, which could number from  2  to  6  or more. Only such blade  14  is shown in FIG. 1, it being understood that the actual number of blades, numbering  2  to  6  would be circumferentially spaced around the hub  12  in a conventional fashion. 
     Blade  14  extends in a generally radial direction from hub  12  and rotates in a direction indicated by arrow  16  about an axis  18  of hub  12  in a plane of rotation. The tip of each blade is provided with a fin attached to the blade tip to block radial flow of air longitudinally along the blade. 
     Referring to FIG. 2, the propeller is conventionally supplied with a fairing cone  22  and is rotatably mounted on a shaft in bearings as depicted schematically at  24 . 
     In accordance with the present invention a funnel strip  26  is mounted above the top (suction side) of the airfoil and adapted to create a funnel-shaped passage designated to increase the velocity of air flowing over the suction side of the airfoil. 
     Referring to FIG. 3 of the drawing, the enlarged cross-sectional view of the funneled rotary foil shows an airfoil cross section designed as a supercritical airfoil. The airfoil includes a leading edge  28 , a trailing edge  30 , a suction side  32 , a pressure side  34 , and a downwardly angled cusp  36  near the trailing edge. The thickness of the cross section increases from leading edge  28  to a maximum thickness at point  38  on the suction side, and then decreases very gradually with a nearly flat surface for 70% of its length, before curving down to form cusp  36 . The method of design of such a supercritical airfoil cross section is well known to those skilled in the art. The chord of the airfoil is shown at  40  as a line extending between the leading and trailing edges of the blade. The airfoil is deployed on the hub to form an angle of attack α between line  40  and the plane of rotation of the blade, which is indicated by line  42 . 
     In accordance with the present invention, the funnel strip  26  is mounted and attached to the blade  14  to run the entire length thereof from the hub  12  to the fin  20 . Additional supporting struts  44  may be spaced longitudinally along the propeller blade to hold the funnel strip  26  in the position shown in FIG.  3 . Funnel strip  26  is a substantially flat plate as shown in FIG. 3 with an inlet edge  46  and an outlet edge  48 . A line  49  from the trailing edge  30  of the airfoil to the inlet edge  46  of the funnel strip forms a larger funnel angle β with the plane of rotation  42 . 
     Funnel strip  26  is oriented so as to be with respect to the chord  40  of the airfoil and, as seen from the drawing, functions as a funnel to scoop air in at an inlet  50  to an outlet  52  as the blade rotates in the plane of rotation. The funnel passage from inlet  50  to outlet  52  is bounded at the blade tip by fin  20  and at the blade root by the hub  12 . 
     The dimensions and location of funnel strip  26  are such that the ratio of total area of the inlet  50  divided by the total area of the outlet  52  lies in a range between 2 to 1 and 20 to 1. In the embodiment shown in FIG. 3, this ratio of inlet area to outlet area is 4 to 1, the angle of attack α is 5°, and the funnel angle β is 10°. These parameters are only exemplary of a range of values, which vary with the design. Angle α may vary from 3° to 7° while angle β varies respectively from 8° to 12° for a given blade and funnel geometry. 
     Airflow through a funnel can increase the velocity of the air as much as twenty fold with little loss of energy. Aerodynamically, area 1 ×velocity 1 =area 2 ×velocity 2  minus drag due to friction. Hence the theoretical air velocity over the top, almost flat, suction side  32  of blade  14  in the arrangement shown in FIG. 3 is four times that of the conventional air velocity. Hence, the theoretical lift is sixteen times as great minus the losses due to the drag. Since the blade is designed or oriented for the highest L/D, a greatly improved thrust to the propelled device is the result of the funnel strip attached to the blade. 
     As an example, a small prototype was constructed for a rotary airfoil without the funnel strip, which performed according to the following table. 
     
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                 Lift 
                   
                 RPM/lb. 
                   
                 Lift/Drag 
                 Lift (lb.)/ 
               
               
                 RPM 
                 (lb.) 
                 Actual HP 
                 of Lift 
                 Drag (lb.) 
                 (L/D) 
                 HP 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 5000 
                 1.6 
                 0.054 
                 3125 
                 0.13 
                 12.3 
                 29.6 
               
               
                 7000 
                 3.2 
                 0.09 
                 2188 
                 0.15 
                 21.3 
                 35.6 
               
               
                   
               
             
          
         
       
     
     Calculations indicate that a funneled rotary airfoil constructed like the prototype, but adding the funnel strip according to the invention, would probably have the characteristics according to the following table. 
     
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                 Lift 
                   
                 RPM/lb. 
                   
                 Lift/Drag 
                 Lift (lb.)/ 
               
               
                 RPM 
                 (lb.) 
                 Actual HP 
                 of Lift 
                 Drag (lb.) 
                 (L/D) 
                 HP 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 5000 
                 9.0 
                 0.09 
                 360 
                 0.15 
                 93 
                 100 
               
               
                 7000 
                 12.6 
                 0.11 
                 390 
                 0.16 
                 106 
                 115 
               
               
                   
               
             
          
         
       
     
     Wind Powered Device 
     Referring now to FIGS. 4 through 6 of the drawings, a funneled rotary foil is illustrated which is designed for a wind powered device. Contrary to a propeller, in which an energy source applies torque to the hub to cause the blades to rotate, a wind powered device is designed to receive energy from the wind and convert the energy to torque applied to the hub and attached shaft. The type of wind powered device driven by the funneled rotary foil is immaterial to the present invention, but could be an electric generator, compressor, pump, etc. The airflow is perpendicular to the plane of rotation as in the case of the propeller. However, the design criteria are different, since the funneled rotary foil is designed and oriented with respect to the plane of rotation so as to produce maximum lift. Hence the angle of attack α and funnel angle β will be different. 
     Referring to FIG. 4, a funneled rotary foil  54  comprises a group of circumferentially spaced, radially extending blades  56  attached to a hub  58 . The funneled rotary foil  54  of FIG. 4 has twelve blades. However, the number of blades believed to be practical for wind powered device ranges from six in number to twelve in number. Blades  56  are identical and are of substantially uniform width from the hub to the blade tip. The blade tips are connected to a circular rim  60 , which both serves to prevent longitudinal flow along the blade, as well as to stabilize and strengthen the device. 
     Referring to FIG. 5 of the drawing, the side view of the funneled rotary foil is illustrated. The direction of the wind, indicated by arrow  62  is perpendicular to the plane of rotation of blades  56 . The blades and hub rotate about an axis of rotation  64 . A fairing cone  66 directs flow into the blades, which are oriented and designed to provide the maximum lift. Lift, as calculated by the previous formulas is translated to torque applied to a rotatable shaft  68 . 
     In accordance with the present invention, each of the blades  56  is provided with a funnel strip  70  designed, oriented and dimensioned to increase the effective flow velocity over the suction side of blades  56  to increase the lift. 
     Referring to FIG. 6 of the drawing, a cross section of the blade  56  is seen, which is a cross section taken along lines VI—VI of FIG.  4 . As seen in the cross section, the airfoil has a leading edge  72 , a trailing edge  74 , a suction side  76  and a pressure side  78 . The blade increases in thickness from the leading edge  72  to a point of maximum thickness  80 , and thereafter decreases in thickness to the trailing edge. The airfoil cross section is a conventional shape designed to extract energy from wind of an average velocity that may be between 5 and 50 feet per second. 
     In accordance with the present invention, a funnel strip  70  is mounted to blade  76  by one or more struts  77  and extends radially in uniformly spaced relationship to the blade. The funnel strip is arcuate with a convex side directed toward the suction side of the blade. The funnel strip has an inlet edge  82 , which defines an inlet  84  with the leading edge  72  of the airfoil leading into a funnel shaped passage. The strip has an outlet edge  86 , which defines an outlet  88  with the suction side  76  of the airfoil at the point of maximum thickness of the airfoil. The funnel shaped passage is bounded at the outer blade tip by rim  60  and at the blade root by hub  58 . The ratio of the area of inlet  84  to the area of outlet  88  lies between the range of 2 to 1 and 20 to 1. 
     A chord of the airfoil is shown at  90  extending from trailing edge  74  to leading edge  72  of the airfoil cross section. A line directed from the trailing edge through the inlet edge  82  of funnel strip  70  is shown at  92 . The angle of attack on the blade  56  when it is stationary is the angle α between chord  90  and the wind vector  62 , which corresponds to the axis of rotation  64  when the blades are properly oriented toward the wind. The rotational velocity of the blade  56  (which depends upon the radius at which the velocity is computed) results in a resultant airflow over the airfoil at a lower effective angle of attack. Since the actual velocity of the wind varies, a compromise is necessary under an assumed wind velocity and assumed rotational velocity of the blades. 
     The preferred arrangement shown in FIG. 6 mounts the blade  56  on hub  58  such that the line  92  forms a second funnel angle β of approximately 30° with the rotational axis  64 . In this case, the angle of attack is about 20° . These parameters are only exemplary of a range of values, which vary with the design. Angle α may vary from 14° to 26°, while angle β varies respectively from 24° to 36° for a given blade and funnel geometry. The profile of a single blade  56  is shown superimposed on rim  20  in FIG. 4, in order to show the orientation of the blade on the hub. 
     In the preferred embodiment shown in FIG. 6, the ratio of areas of inlet  84  to outlet  86  is 8 to 1. Under these assumed conditions, the airfoil is designed according to conventional design formulas to produce the maximum lift, assuming a theoretical velocity increase over the suction side of the airfoil of 8 to 1. 
     FIG. 7 illustrates one embodiment of a wind powered device using a funneled rotary foil  54  as previously described in FIGS. 4-6 of the drawing. The drawing depicts a streamlined fuselage  94  pivotably mounted on a tubular column  96  by means of a bearing  98 , so as to be able to pivot when the wind direction changes. A tail structure  100  with an adjustable rudder  101  facilitates pivoting the fuselage  94  like a weather vane, so that the plane of rotation of funneled rotary foil  54  is always perpendicular to the direction of the wind. Column  96  is mounted on top of a base  102  containing equipment to be powered. The equipment (not shown) could be an electric generator, a heat pump, a compressor, or any one of a myriad of devices designed to derive power from the wind. Means for transmitting torque from the rotatable shaft  68  is depicted schematically as a bevel gear  104  meshing with a bevel gear  106  on a vertical shaft  108 . The type of power transmission to the wind powered device in  102  is immaterial to the present invention and could comprise various types of mechanical drives, or alternatively hydraulic, pneumatic or electrical devices for transmitting power. The adjustable rudder  101  may be used to counteract any reaction tending to pivot the fuselage around vertical shaft  108 . 
     FIG. 8 illustrates another arrangement for a wind powered device in which two funneled rotary foils are mounted on the same fuselage, indicated at  110 . The funneled rotary foil  54  and power transmission train comprising shaft  68 , bevel gear  104 , bevel gear  106 , and vertical shaft  108  may be identical to those in FIG. 7, as well as the supporting column  96  and base structure  102 . 
     An additional funneled rotary foil, designated  112  is rotatably mounted in fuselage  110 , with power output shaft  114  and bevel gear  116  meshing with the same previously described bevel gear  106 . The gear arrangement is such that funneled rotary foil  112  rotates in the opposite direction from that of funneled rotary foil  54 . A profile of the oppositely oriented blade with attached funnel strip is superimposed on the rim as indicated at  118 . In order to pivot the fuselage so that the plane of rotation is always perpendicular to the wind, a tail structure  120  is added to the fuselage. 
     Conclusion 
     All of the above shows that a funneled rotary airfoil is a unique technology that can profoundly improve propulsion, lift and also convert wind energy into electrical or mechanical power. It could achieve 75-95% efficiency. Many variations are possible. One example would be to use wind power to operate a commercial heat pump, which converts mechanical energy into heat energy at an efficiency of 400-500%. The normal energy process for powering a heat pump involves burning a fuel such as coal, oil or natural gas to generate steam. Fuel to steam conversion is about 90% efficient. A steam turbine converts heat energy into electrical energy at about 40% efficiency, and an electric motor turns it into mechanical power at about 90% efficiency. The motor operates a compressor at about 90% efficiency. The heat pump, if operating at 400% of its mechanical input only achieves about 29% of the initial heat energy input at the compressor: 0.29×400=117% of the heat energy of the original fuel input. Nearly all non-nuclear future electricity generating plants will release carbon dioxide and nitrogen oxides. Wind energy harnessed by this upper wind powered generator requires no fuel at a 90% mechanical energy input (compressor) to get 400% mechanical-to-heat energy. This totals at least a 360% efficiency heating method with no adverse gases. The energy of the wind is amplified 3.6 times for home/business/building/factory, etc. heat during the cold months and air conditioning during the warm periods. The funneled rotary foil, wind powered generator would be an excellent energy generating device, converting nearly 100% of the wind energy into mechanical energy or about 90% of the wind&#39;s energy into electricity.