FOR REDUCING INDUCED AND INTERFERENCE DRAG,

AND ENERGIZING STAGNANT FLOW

TECHNICAL FIELD

The present invention relates to improvements to foils and related fluid dynamic structures for

influencing or controlling aerodynamic or hydrodynamic flows to reduce drag, such as drag and turbulence induced by wingtip vortices of an aircraft, cooling and

ventilating drags, or such as is found in the wake of a watercraft . The invention also relates to slot-like structures for fluid dynamic foil bodies.

BACKGROUND ART

Slots have been used for years in many aircraft wing designs in order to prevent the airflow from

, separating prematurely from the wing at high angles of attack, and thereby reduce the stall speed and improve handling at low speeds. Air from below the wing

accelerates through the slot and exits rearward and substantially parallel to the upper wing surface,

energizing the boundary layer and delaying separation. A similar approach provides a pressurized discharge from wing surface openings, either from compressed air tanks, pumps, or from the jet engines, to accomplish a similar goal. Because many of the slot designs also tend to contribute to drag at cruising speeds, retractable slats may be used instead to provide a leading edge opening that can be closed when not needed. Slots may also be used to reduce wave drag under transonic conditions to distribute pressure and increase the critical Mach number, thereby improving performance at such speeds.

Variations of this basic theme of using slots, slats or other openings to ensure more attached flow across the wing surfaces and delayed boundary separation are

described in U.S. Patent Nos . 2,041,786 (Stalker);

2,507,611 (Pappas et al.); 2,571,304 (Stalker); 2,587,359 (Milans); 3,208,693 (Riedler et al . ) ; 3,363,859 (Watts); 3,897,029 (Calderon) ; 4,641,799 (Quast et al.); 4,664,345 (Lurz); 5,255,881 (Rao); 5,788,190 (Siers) ; 6,293,497 (Kelley-Wickemeyer et al.); 6,328,265 (Dizdarevic) ;

6,905,092 (Somers); 7,048,235 (McLean et al.); and U.S. Patent Application Publication No. 2007/0034746

(Shmilovich et al) .

Another problem in aircraft design is the production of trailing vortices and wake turbulence during flight. Throughout the history of aeronautics, aircraft designers have had to deal with the energy consuming effects of wingtip vortices, which form at the tip of a wing where higher pressure air from beneath the wing flows in a generally span-wise direction around the wingtip to the lower pressure region above the wing.

Wingtip vortices have been considered by many experts to be an essentially unavoidable consequence of a wing producing lift. Due to the nature of these vortices, they are associated with lift-induced drag and are a major component of wake turbulence. Smaller vortices are induced at other points on an aircraft wherever there is an abrupt change in planform or contour, such as at the outboard tips of wing flaps, ailerons, horizontal

stabilizers, elevators and other flight control surfaces. The drag and wake turbulence from the vortices have a negative impact on fuel efficiency and flight performance of the aircraft, and also pose a safety hazard to any aircraft that follow too closely or otherwise cross the wake. Various solutions have been developed in an effort to reduce the production of trailing vortices, especially wingtip vortices. Since wingtip vortices only affect that portion of a wing closest to its tip, one partial solution is to use a higher aspect ratio wing (longer wingspan and/or reduced chord) , but this also tends to reduce aircraft maneuverability and adds

structural weight. Another approach is to modify the lift distribution along the span to generate more lift at the wing root and less toward the wing tip, either by using an elliptical or tapered wing planform, increasing the mean camber or asymmetry of the airfoil section near the wingtip, or using a washout (span-wise twist of the wing) to reduce the incidence near the wingtips.

However, these solutions do not make full use of the wingspan to efficiently produce lift.

A number of wingtip devices have been designed to allow nearly the entire wingspan to produce lift, while simultaneously altering the airflow near the wingtips in order to partially interfere with the

production of vortices or to change the pattern of vorticity so as to reduce the associated drag. The ■ intended result is an improved lift-to-drag ratio, with a corresponding improvement in fuel efficiency. Drooped (Hoerner) wingtips focus the vortex away from the upper wing surface. Winglets, a near-vertical upward or downward extension of the wingtips, cause the vortex to strike the outboard surface of the winglet so as to generate an inward and slightly forward force, and thereby converts some of the vortex energy into an apparent thrust. Wingtip fences are winglet variations that may have surfaces extending both above and below the wingtip to reduce the span-wise component of airflow that leads to wingtip vortices, but create vortices of their own at the fence tips and interference drag, albeit - A - displaced from the main wing. Blended winglets smoothly curve up, increasing their cant gradually to reduce interference drag that would otherwise occur at the wing/winglet junction. Raked wingtips have a higher degree of sweep than the rest of the wing. Various wingtip devices are described, for example, in U.S.

Patent Nos. 5,039,032 (Rudolf); 5,634,613 (McCarthy); 6,722,615 (Heller et al.); and 6,892,988 (Hugues) .

In U.S. Patent No. 5,823,480, La Roche provides a wing grid having at least two parallel staggered

"winglets" extending outward from the free end (tip) of the wing. The winglets, which in this case are

essentially parallel to the main wing rather than upward extending, subdivide the air circulation at the tip so that the span-wise lift distribution is more regular, decreasing induced resistance. In one embodiment, this wing grid can be retracted into the end of the wing.

In U.S. Patent No. 4,478,380, Frakes discloses a wingtip vortex suppressor that utilizes a scoop having an inlet at a lower leading surface and an outlet at an upper trailing surface to reduce the pressure

differential at the wing's trailing edge. The scoop is inboard of a turbulence fence at the wingtip. In another arrangement, U.S. Patent No. 5,806,807 to Haney, has both a deflector extending from the top surface of the wing inboard of the tip and an air passage extending from an inlet on a high pressure side of an airfoil through the airfoil to an outlet on a low pressure side of the airfoil, with the outlet positioned between the deflector and the wing tip. The deflector and air passage work in combination to attenuate the wingtip vortex. In both patents it appears that the fence or deflector is an essential component for vortex reduction. In U.S. Patent No. 5,791,875, Ngo describes a system providing a source of positive fluid pressure interior to the wing and a fluid router (curved slots in lower surface of the wingtip) that directs the fluid inboard against the outward airflow in order to reduce the wingtip vortex. Similarly, in U.S. Patent No.

7,134,631, Loth provides a tip circulation control that blows air out from the very end of the wing in order to cancel opposing vorticity. In U.S. Patent No. 7,100,875, Shmilovich et al discharge a jet air stream from a set of nozzles at the wingtips and moves them cyclically back and forth in order to dissipate and scatter wingtip vortices. Although from a safety standpoint any

reduction in trailing vortices is an improvement, from an energy efficiency standpoint the amount of energy

required to sustain such counteracting airflows tends to defeat any fuel savings that might be achieved by a decrease in drag.

Trailing vortices and wake turbulence can also cause drag in other fluid dynamic structures, such as in rotor blades in helicopters and wind-power turbines, sails (which are also airfoils), as well as underwater surfaces such as hydrofoils, hulls, centerboards, keels, rudders and screws of various watercraft including submersibles. U.S. Patent No. 5,374,013 to Bassett et al. describes one approach to reducing drag in a truck by providing a pressure shell around the rear of the truck body with better boundary flow around the truck. In any of these fluid dynamic structures, it is desired to realize fuel savings and safety improvements by reducing trailing vortices and wake turbulence, whether from wings and other flight control surfaces on aircraft, or from any of the other foil-like or bluff bodies. SUMMARY DISCLOSURE

A fluid dynamic section in accord with the present invention comprises a foil body for use in a fluid dynamic environment and having one or more fixed size escapelets in the form of static passages integrated into the foil body and leading from a first higher pressure surface of the body to a second lower pressure surface of the body. Each escapelet is configured in size, shape, location, orientation and number so as to redirect any span-wise component of energy in a kind of shortcut from the high-pressure side to the low-pressure side of the structure, beneficially releasing energy and preempting the normal formation of vortices. Whatever span-wise component of fluid flow that might leak around an end of the foil body gets caught up in the high velocity current exiting longitudinally from the

escapelet outlets. Unlike conventional slots, each escapelet is sized and positioned to minimize its impact on the longitudinal component flow, thereby improving the lift-to-drag ratio and resulting in dramatic fuel

savings. Despite creating passages from the higher- pressure side to the lower-pressure side of fluid dynamic structures, the elimination of unproductive components of fluid flow from the use of these escapelets results in an overall increase in the effective aspect ratio by as much as 50% or more. Thus, the escapelets act to harness, redirect and release fluid dynamic energy in a manner that prevents chaotic energy dissipation and minimizes energy loss. As an additional benefit, escapelets located near wingtips effectively increase control authority to ailerons, thereby improving such authority even at high angles of attack up to and including spin conditions, while escapelets located inboard on the wings near the fuselage and/or on the horizontal tail sections may further improve spin recovery whenever needed. Escapelets have fixed sizes that are typically such that their widths range from 1% to 15% of the foil body's local chord. Escapelets are generally installed between the structural ribs of the foil body, so lengths of the individual escapelets do not extend a full span.

The cumulative span of a set of escapelets along a common planform of the foil body is usually less than a half- span of the foil body. In one embodiment, the locations of the escapelets may be confined to an outer 15% of the foil body half-span. Escapelet outlets from the lower- pressure side of the foil body usually have a height normal to the surface that may range anywhere from 10% to 110% of the length of the corresponding escapelet inlet on the higher-pressure side of the foil body, with the higher values generally applying to craft of higher design speeds. Escapelet outlets are located downstream or aft of the escapelet inlets, with a center-of-inlet to center-of-outlet mean line of an escapelet oriented chord-wise ranging anywhere from 10° to 80° relative to the chord line, with the lower value generally applying to craft of higher design speeds. The span-wise

orientation of the escapelets generally follows the planform of the foil body. For example, where the escapelet openings include one or more leading escapelets and/or one or more trailing escapelets, the leading escapelet openings may be substantially parallel to a leading edge of the foil body, while the trailing

escapelet openings may be substantially parallel to a trailing edge of the foil body. The escapelets

preferably have a smooth shape conducive to streamlined efficient fluid flow, and may include a preformed liner insert to eliminate any discontinuities or sharp

intersections and ensure such streamlined smoothness. The fluid dynamic structures encompassed by this improvement may include not only aircraft wings, but also aircraft control surfaces, such as ailerons, flaps, aircraft empennages, canards, including stabilizers, elevators, fins, rudders, together with rotor blades, propeller blades, turbofans, ducted fans, and wind tunnel drive fans, as found on both helicopters and wind-power turbines, as well as foil bodies on various watercraft, including sails, wing sails and various underwater structures like keels, and also cables, guy-wires, poles and towers, as previously mentioned. The presence of the escapelet openings in the various foil bodies

significantly reduce trailing vortices and wake

turbulence, with a consequent reduction in drag and corresponding improvements in energy efficiency of more than 12%, a fourfold or better improvement compared to most prior approaches.

BRIEF DESCRIPTION OF THE DRAWINGS

Figs. 1A-1C and 2A-2C are various plan and isometric views of an outboard end portion of respective upper and lower wing surfaces for an unswept wing

implementing an embodiment of the present invention.

Figs. 3A-3C and 4A-4C are various plan and isometric views of an outboard end portion of respective upper and lower wing surfaces for a swept wing

implementing another embodiment of the present invention.

Fig. 5 is a chord-wise sectional view through an escapelet for the wing of Figs. 3A-3C and 4A-4C.

Figs. 6A-6F are various span-wise vertical sectional views showing some different embodiments of escapelet endwalls on the aircraft's starboard wing.

Figs. 7-11 are plan views of alternative wing embodiments in accord with the present invention. Fig. 12 is a top plan view of a wing attached to a fuselage, and illustrating several different

potential positions for escapelets in accord with the present invention.

Figs. 13A-13B are perspective views of respective upper and lower surfaces of a horizontal tail section implementing an embodiment of the present

invention.

Figs. 14A-14B are chord-wise sectional views of generic fluid dynamic structures provided for specifying dimensions of escapelets. Fig. 14B also illustrates possible incorporation of an escapelet in a flight control surface, such as an aileron.

Figs. 15A-15B are respective side and isometric views of an airfoil used as a parachute, hang glider or kite and implementing escapelets in the airfoil in accord with the present invention.

Fig. 16 is an isometric view of a rotary blade embodiment of the present invention.

Figs. 17A-17C are various sections of an end of a rotary blade, as in Fig. 16, with one or more

escapelets, for a propeller blade, a wind turbine blade and helicopter main and/or tail rotor blades,

respectively.

Fig. 18 is an isometric view of a guy wire embodiment having a foil frame with escapelets in accord with the present invention.

Figs. 19A-19C are a cross-sectional view and two isometric views of segments of the foil frame in Fig. 18.

Figs. 20A-20B are respective side and top plan views of a ship having foil sails with escapelets therein in accord with the present invention.

Fig. 21 is an isometric view of a foil sail in Figs. 20A-20B. Fig. 22 is a side view of an underwater portion of a ship having a keel embodiment of the present

invention.

Figs. 23A-23B are sectional views taken through the lines 23A-23A and 23B-23B in Fig. 22.

Fig. 24 is an isometric view of a wing keel embodiment of the present invention.

Figs. 25A-25B are sectional views illustrating the presence of escapelets provided in a high performance cowl that houses an air-cooled aircraft engine.

DETAILED DESCRIPTION

In order to better understand the improvements, we note first that slots, slats and slotted flaps have the purpose of increasing the maximum lift coefficient, thereby reducing the stall speed, while the escapelets provided within the various fluid dynamic sections in accord with the present invention have instead the purpose of preemptively redirecting fluid flow energy before it can cause fluid dynamic havoc manifesting as vortices, turbulence, wake and drag with consequent wasteful energy dissipation. The escapelets harness, redirect and release the energy beneficially so as to minimize such energy losses. In addition to the benefits already discussed, escapelets may also be employed to reduce turbulence due to flow separation, thus making the associated flows more efficient.

• "slot" (noun) - a long and narrow opening as between a wing and a Fowler flap; specif, a long and narrow spanwise passage in a wing usually near the leading edge for improving flow conditions at high angles of attack.

• "slat" (noun) - any of certain long narrow vanes or auxiliary airfoils, e.g. as used in an automatic slot. • "automatic slot" (noun) - a slot in the leading edge of a wing created by the movement of a slat that is retained in the leading edge contour of a wing at most angles of attack, but automatically lifting away to create a slot as the stalling angle is a approached.

• "fixed slot" (noun) - a slot that remains open at all times; distinguished from an adjustable or an

automatic slot.

A slotted flap is an adjustable mechanism on the trailing edge of a fluid dynamic foil that moves into position when deployed. In contrast, an escapelet is a static passage built into a fluid dynamic foil.

The structural design differences lead to different modes of operation. In all cases, while in function, slots, slats, and slotted flaps will change the geometry, mean camber line(s), and dimensions of the original foil section, amounting to an adjustable

geometry by extending the chord, reshaping the mean camber line(s), from the leading and trailing edges respectively. Since a slat is permanently or adjustably positioned ahead of the leading edge of a fluid dynamic foil, its implementation will always result in a change to the fluid dynamics of the foil, increasing drag while extending the chord and altering the original section profile and camber of the foil. In contrast, the

integral passages that form the escapelets through the foil body act to improve fluid dynamic characteristics without physical changes in chord or camber of the foil, acting to reduce induced and interference drag by

preempting or significantly reducing the formation of vortices. Additionally, the changes to fluid flow arising from the use of escapelets in some locations improve control authority of ailerons and/or other control surfaces and high-lift devices and enhance spin recovery. The end result is a device that accomplishes aerodynamic results never before achieved in the history of aviation.

With reference to Figs. 1A-1C, three views of the top of an end portion of a wing 11 with a leading edge 13 and a trailing edge 15 of the wing 11 are seen. The wing has escapelets 17 and 19 inboard of a wingtip 21 in accord with the present invention. An aileron 23 on the trailing edge 15 of the wing 11 is also seen. Figs. 2A-2C show three views of the bottom side of the same wing 11. As seen in the various views, the escapelets 17 and 19 are passages leading from the lower wing surface 25 through the wing 11 to the upper wing surface 27. In this embodiment, two escapelets 17 and 19 are provided in series. A series of anywhere from one to seven

escapelets could be provided along the local chord of the wing.

With reference to Figs. 3A-3C, three views of the top of an end portion of another wing 31 with a leading edge 33 and trailing edge 35 of the wing 31, escapelets 37 and 39, and an aileron 43, are shown.

Figs. 4A-4C show the corresponding bottom side of the wing 31. Again, escapelets 37 and 39 are provided through the wing 31. In this instance, the wing is a swept wing, whereas in Figs. 1A-1C and 2A-2C, an unswept wing was used. Escapelets can be provided with either an unswept wing 11 or swept wing 31 designs.

In both cases, the escapelets generally follow the planform of the wing. In the case of the unswept wing 11 in Figs. 1A-1C and 2A-2C, this leads to the escapelets being oriented substantially parallel to the corresponding leading and trailing edges 13 and 15 of the wing 11. In the case of the swept wing 31 in Figs. 3A-3C and 4A-4C, the leading and trailing edges 33 and 35 and the escapelets 37 and 39 essentially follow the planform of the wing 31.

The positions of the escapelets 17, 19, 37, and 39 on their wings 11 and 31 do not necessarily line up with the ailerons 23 and 43 or any other flight control structure of the wing. In the first case, the outer ends of escapelets 17 and 19 do happen to align with the outer edge of the aileron 23, but this is not required. The aileron 23 is seen to extend inboard beyond the views and beyond the inner ends of escapelets 17 and 19, but again, this is not necessarily required. In the swept wing example, the ends of the escapelets 37 and 39 do not align with either edge of the aileron 43, but rather the escapelets 37 and 39 are positioned to overlap the outer edge of the aileron 43. These escapelets 37 and 39 could just as easily align with say the outer edge of the aileron, as in the unswept wing example. Generally, it may be preferred for optimum performance that one or more escapelets be associated in some manner, either by being aligned or overlapping with, the outer edge of the aileron 23 or 43, but it is not an absolute requirement. The mere presence of the escapelets and their action upon the airflow across the foil or foil body helps to

transfer better control to the ailerons and other similar foil structures.

With reference to Fig. 5, a cross-section of the swept wing embodiment of Figs. 3A-3C and 4A-4C is seen. The section for an unswept wing design would be similar. The escapelets 17 and 19 extend through the wing 11 from inlets 51 located in the lower wing surface 25 to the outlets 53 located in the upper wing surface 27. The general direction of the escapelets 17 and 19 is aft, i.e., the inlets 51 are closer to the leading edge 13, while the outlets 53 are closer to the trailing edge 15 of the wing 11. The escapelets 17 and 19 also tend to be streamlined in their shape for best performance.

Fairings or fillets 55 may be inserted into the escapelet passages to eliminate any sharp edges, corners, or discontinuities in order to eliminate turbulence and interference drag. Preferred dimensions will be

discussed later with respect to Fig. 14A.

As seen in Figs. 6A-6F, the span-wise sections show examples of some possible choices for the ends of the escapelets. These ends may be straight as in Figs. 6A-6C or have some curvature as in Figs. 6D-6F. The inlets may be longer than the outlets as in Figs. 6B, 6D and 6E, may be approximately the same length between inlet and outlet as in Figs. 6A and 6F, or may even be longer on the outlet side as in Fig. 6C. Typically, a shorter outlet would often be preferred, leading to airflow acceleration within the escapelet passages, but the other choices may also be viable or even preferred in some escapelet applications, whether on wings or other surfaces.

Figs. 7-11 show a variety of possible positions for escapelets on a wing. In Fig. 7, a pair of escaplets 61 and 63 is located outboard of a leading edge slat 65, and also overlapping with the outboard of an aileron 67. In Fig. 8, a first escapelet 71 closer to a leading edge 73 is shorter in length than a second escapelet 75 closer to a trailing edge 77. Thus, the escapelets in a series need not have identical lengths. Likewise, in Fig. 9, escapelet 81 is shorter than escapelet 83. In Fig. 8, the span-wise centers of the two escapelets 71 and 75 are substantially aligned, while in Fig. 9, the outer ends of the escapelets 81 and 83 are aligned. Either embodiment or any other relative positioning of a series of

escapelets could be employed. In Fig. 10, the leading escapelet 91 is longer than the trailing escapelet 93 in the series. Additionally, the respective ends of the escapelets 91 and 93 follow- common contours 95. In Fig. 11, the common end contours 97 are straight, whereas in Fig. 10, the common end contours 95 are curved. Either design could be used.

While Figs. 1-11 have focused on the outer ends of wings, near the wingtips, mainly to preempt formation of trailing vortices, other escapelet positions can be used. As shown in Fig. 12, in addition to the escapelets 101 found near the wingtips and/or associated with the ailerons, additional sets of escapelets 103 may be provided on one or both sides of the engine pylon mounts or may be associated with other structures attached to or part of the foil or foil body. Still further, escapelets 105 may be provided on the wing adjacent to the fuselage 107. This later positioning of escapelets helps to substantially reduce interference drag at the higher angles of attack when the aircraft is ascending,

descending, or maneuvering. Additionally, they preempt or reduce the formation of vortices and/or other

undesirable fluid-dynamic phenomena that could interfere with the airflow over the tail section or other parts on a craft.

With reference to Figs. 13A and 13B, respective upper and lower views of a horizontal tail surface 111 show that provision of escapelets, as shown at 113, 115, 117, and 119, need not be confined solely to the main wing of an aircraft, and preferably will indeed be provided on such tail surfaces. One should be reminded that horizontal tail surfaces are inverted from those of the main wing in order to provide a pitch-corrective downward force, using elevators 125 on the trailing edge as pitch control surfaces. Escapelet inlets are on the higher-pressure upper surface 121 of the horizontal tail section 111, while escapelet outlets are on the lower- pressure lower surface 123 of the horizontal tail surface 111. As in the main wing, escapelets 113 and 115

provided near the tip of the tail section preempt or reduce the formation of trailing vortices, thereby substantially reducing induced drag. While vortices from tail surfaces are not nearly as prominent as those from a main wing, they are still not insubstantial, and fuel savings can be realized by providing escapelets on these tail surfaces as well as on the main wing. Escapelets 117 and 119 located inboard near the intersection of a vertical stabilizer/rudder can help substantially to control yaw and recovery from spin situations that might occur. Additionally, escapelets can help to counter adverse yaw due to asymmetric engine thrust, as when one engine of a twin- or multi-engine aircraft fails and the remaining engines provide all of the thrust from one side of the plane. Figs. 13A and 13B show a horizontal tail section' s inboard escapelets 117 and 119 which allow energized air to reach the vertical stabilizer/rudder (not shown) , providing more control to be transferred to the aircraft's rudder.

With reference to Fig. 14A, dimensions for the escapelets are generally defined relative to a local chord line (0) of the foil body extending from the leading edge to the trailing edge, the length of which is assumed to be 100%. As already noted, there may be one, two, or more escapelets (1) in series spaced along the chord (0). Four escapelets (1) are seen in Fig. 14A. Fig. 14B shows that the aft-most escapelet 131 could be formed in a flight control surface 133, such as an aileron, elevator, or flap, e.g., pivoting relative to the main wing or tail section 135 about some pivot point 137. However, in most cases, the escapelets will be completely contained within the main foil surface.

Escapelet outlets (2) are measured normal to the aft surface (6) of the escapelet (1) from a point (5) at the trailing edge of the fore surface (7) of the escapelet (1). The outlet measure (2) may range anywhere from 0.75% to 15.4% of the chord (0). Likewise, escapelet inlets (3) are measured normal to the aft surface (6) of the escapelet (1) from a point of tangency of the

original foil body and the escapelet fore body (7) intersection shown as point (8), to the shortest

dimension to the aft escapelet body (6) . The size of the inlet (3) may range anywhere from 0.85% to 40.65% of the chord (0). The escapelet (1) may either converge or diverge, as required, but generally, the outlet size (2) ranges anywhere from 10% to 110% of the inlet size (3), with the higher values in the range generally applying to craft with higher design speeds. Escapelet outlets are located downstream or aft of the escapelet inlets, with a center-of-inlet (9) to center-of-outlet (10) mean line of an escapelet oriented chord-wise at an angle (θ) ranging anywhere from 10° to 80° relative to the chord line, with the lower value generally applying to craft of higher design speeds.

With reference to Figs. 15A and 15B, the use of escapelets is not confined to fixed-wing airplanes, as in Figs. 1-14, but could be applied to other airfoils 141, such as parachutes, hang gliders, ultra-light aircraft, work kites, recreational and emergency devices, and even toys and toy kites. As seen in Fig. 15B, an airfoil 141 of this type may have one, two, or more escapelets 143- 145 located near both outer portions of the foil 141. By preempting or reducing the formation of vortices and ensuring proper airflow, these escapelets increase the effective aspect ratio significantly when compared to similar foils without such escapelets. A higher stall angle of attack and reduction of the stall speed is also a consequence of the improved airflow brought about by the escapelets.

With reference to Fig. 16, a rotary blade 151 is seen, with a point of attachment 153 to a rotational shaft (not shown) , respective leading and trailing edges 157 and 155, and provided with escapelets 159 near a blade tip 161. The rotary blade 151 provided with such escapelets 159 can be positioned within a wind turbine, a propeller, or helicopter blade at one or more locations along said blades as shown by the respective sections seen in Figs. 17A-17C. Although each type of rotary blade 151 may have slightly different foil cross- sections, based on such factors as optimum angle of attack and rotational speed for the particular

application, the design is further optimized by the presence of escapelets. Although only escapelets 159 located near the blade's outer tip 161 are shown, other escapelet locations might also have some benefits, particularly in countering the naturally outward radial flow over a rotating foil.

With reference to Fig. 18, a foil frame 171 for placement around guy wires, cables, power lines, towers and stacks is shown. Figs. 19A-19C show various

isometric views of individual segments 173 of such a foil frame 171. Such foil frames are added to guy wires to control flutter and the wind-driven whipping action and vibration that causes fatigue and potential structure damage. The frame 171 acts to direct the wind smoothly around the guy wires. To minimize turbulence and

decrease turbulence (by preventing the von Karman vortex street vortex flow) , the foil frame 171 in accord with the present invention includes an escapelet 175 passing from one side of each segment 173 to the opposite side. Alternate segments 173 may have escapelets 175 and 175' directing air in opposite directions from one side to the other, as in seen in Fig. 18.

With reference to Figs. 20A-20B and Fig. 21, the use of escapelets can be applied to watercraft as well. Here, a boat or ship 181 having one or more wing sails 183 is seen. Each wing sail 183 may have one or more sets of escapelets 185, 187, 189, 191, etc.

Preferably, both upper and lower ends of the wing sail 183 will have such modifications, with one or more sets of escapelets 185 and 187 near the top of the wing sail and one or more sets of escapelets 189 and 191 near the bottom of the wing sail. Furthermore, the escapelets are preferably organized in pairs with one set of escapelets 185 or 189 of a pair passing air through the wing sail 183 from port to starboard and another set of escapelets 187 or 191 of a pair passing air through the wing sail 183 in the opposite direction from starboard to port. This allows the full effect of the escapelets to occur no matter from which direction the wind is coming. Each wing sail 183 can be turned about its pivot axis 193 established by the respective masts 195.

Fluid dynamic structures having foil bodies with escapelets need not be confined solely to

aerodynamic structures, but can also apply to

hydrodynamic structures. As seen in Fig. 22 and Figs. 23A-23B, a ship or boat keel 201 acts as a hydrodynamic body with corresponding problems of trailing wakes and associated drag. Due to wake turbulence, the maximum hull speed is limited based on the length of the

waterline. Additionally, the bow wave has erosion effects on nearby shorelines, causing speed limits to be imposed on watercraft to avoid causing a wake. The keel 201 may therefore be provided with one or more sets of escapelets 203 and 205. Again, the sets of escapelets are preferably organized in pairs, with a set of one or more escapelets 203 passing water through the keel from starboard to port and another set of one or more

escapelets 205 passing water in the opposite direction through the keel, i.e., from port to starboard. As in the aerodynamic case, the shape of the escapelets is streamlined for optimum performance.

A variety of keel types can employ such escapelets. As seen in Fig. 24, a wing keel 211 has a pair of underwater wings 213 projecting outward from a vertical keel 215 and forming foil bodies that provide lift to the vessel. As in aircraft wings, the underwater wings 213 are provided with one or more escapelets 217 and 219 passing water from a higher-pressure underside of the wings 213 to a lower-pressure upper side of the wings 213. The escapelets may be positioned near the wing tips, more inboard near the vertical keel, or across nearly the entire wingspan. The vertical keel 215 might also be provided with escapelets as in Fig. 22, but such escapelets are usually not needed due to the effective action of the wind and escapelets. Other underwater structures including hydrofoils, movable keels, dagger boards, rudders and the like may also advantageously be fitted with escapelets to ensure optimum water flow across the structures.

Figs. 25A and 25B show a typical high performance cowl for housing an air-cooled aircraft engine. The cowl includes an escapelet installation with inlets 220 and outlets 222 along its walls. There may be one or more escaplets anywhere on the cowl. (Two per ' side are shown in the illustrated embodiment.) In

addition to streamlining airflow around the cowl and reducing drag, the escapelets have the added benefit of improving the engine cooling efficiency of the cowl.

Escapelets inlets 220 are located in areas of the cowling walls where relatively higher pressure air is expected during normal flight, while escapelet outlets 222 are located in areas of the cowling walls where relatively lower pressure air is expected during normal flight, so that air flow through the cowl is enhanced by the

pressure differential between inlets 220 and outlets 222. The pressure of the escapelet inlets provides cooling air to the engine within the cowl, while the presence of the escapelet outlets improve extraction of the warmed air.

Tests were devised to demonstrate the effectiveness of the escapelets. Model test aircraft were built, and test flights of the models were performed over a realistic flight sequence from takeoff to level flight at specified cruising speeds to landing, both with and without the equipping of the aircraft with

escapelets. Introduction of the escapelets did not require any trim changes.

In order to assure the veracity of data collected in the test flights, a flight profile was developed that would be followed for each test.

Comparative flights with and without the escapelets were conducted immediately after each other, minimizing the possibility for atmospheric change. All times were recorded with a stopwatch, and all fuel measurements were taken with a digital scale. The test flight profile was as follows:

1) Start, radio check, taxi, hold (2 minutes)

2) Takeoff

3) Fly one lap around field at full power

4) Reduce to cruise power

5) Time lap speed and fly several laps in a

racetrack pattern

6) Land, taxi, stop

7) Accurately measure weight of fuel required to refill tank Fuel burn was measured to the nearest gram. Some of the modified flights with equipped escapelets ran a few seconds longer than standard flights with the unmodified aircraft. Therefore, fuel burn data on the equipped aircraft was adjusted to match the equivalent flight time of the unmodified vehicle, when necessary. Then, fuel consumption comparisons were made.

Test Vehicle One

The recorded flight speed for Test Vehicle One was an average of 50 mph, and the coefficient of lift (CL) was calculated to be 0.25.

Conditions:

Wind: 0-5 mph gusting

Temperature: 68° F

Barometric Pressure: 29.92 inHg

(Conditions were recorded but may have changed during testing, and are therefore considered approximations.)

Standard Flight (without escapelets) :

Duration: 900 seconds

Fuel Burn: 107 grams Modified Flight (equipped with escapelets) :

Duration: 900 seconds

Fuel Burn: 93 grams

Fuel Savings, %:

12.54% overall

16.99% cruise Test Vehicle Two

The recorded flight speed for Test Vehicle Two was an average of 60 mph, and the coefficient of lift (CL) was calculated to be 0.5.

Conditions:

Wind: 0-2 mph

Temperature: 27° F

Barametric Pressure: 29.92 inHg

(Conditions were recorded but may have changed during testing, and are therefore considered approximations.)

Standard Flight (without escapelets) :

Duration: 606 seconds

Fuel Burn: 178 grams

Modified Flight (equipped with escapelets) :

Duration: 606 seconds - adjusted from 616 seconds Fuel Burn: 138.71 grams - adjusted from 141 grams

Fuel Savings, %:

22.08% overall

29.98% cruise Test Vehicle Three

The recorded flight speed for Test Vehicle Three was an average of 78 mph, and the coefficient of lift (CL) was calculated to be 0.3. Conditions:

Wind: 0-2 mph

Temperature: 82.6° F

Barometric Pressure: 29.82 inHg

(Conditions were recorded but may have changed during testing, and are therefore considered approximations.) Standard Flight (without escapelets) :

Duration: 509 seconds

Fuel Burn: 228 grams

Modified Flight (equipped with escapelets) :

Duration: 509 seconds - adjusted from 515 seconds

Fuel Burn: 192.7 grams - adjusted from 195 grams Fuel Savings, %:

15.48% overall

20.98% cruise