WO2004094227A1

WO2004094227A1 - Apparatus and method for the reduction of drag

Info

Publication number: WO2004094227A1
Application number: PCT/CA2004/000581
Authority: WO
Inventors: Frederick C. Weir
Original assignee: Weir Frederick C
Priority date: 2003-04-22
Filing date: 2004-04-19
Publication date: 2004-11-04
Also published as: CA2426219A1

Abstract

The present invention relates to an apparatus for reducing drag of an aircraft utilized in combination with an aircraft surface (12), where the local airflow has an upward momentum due to the free air stream being deflected upward by the aircraft surface. The apparatus comprises an ancillary airfoil (1) having a cambered top surface (10), a leading edge (14) and a trailing edge (17) and a generally concave louver surface (9); mounting members for mounting the ancillary airfoil above the aircraft surface (12) in a spaced apart manner and at a positive angle of attack with respect to the local airflow (3); and an expansion chamber (11) formed between the lower surface (9) of the ancillary airfoil and the aircraft surface (12). The expansion chamber (11) is located where a distance (13) between the louver surface of the ancillary airfoil and the aircraft surface gradually increases.

Description

APPARATUS ANDMETHODFORTHEREDUCTIONOFDRAG

Field of the Invention

The present invention is concerned with a method and an apparatus to reduce aerodynamic drag. More specifically, the present invention discloses the use of ancillary airfoils mounted so as to exploit areas on the exterior surfaces of an aircraft where airflow has been deflected upwards by the shape of the structure to generate forces which are in opposition to the forces of drag affecting an aircraft.

Background of the Invention

It is desirable to reduce the forces of drag acting on an aircraft in flight. Various wing and aircraft designs have been suggested for this purpose.

U.S. Patent 3,389,879 to Grebe discloses an aircraft capable of supersonic speed with low induced drag energy loss. This patent provides a single or multi-section moveable flap assembly having an upper member positioned above the upper surface of the airfoil or wing shaped fuselage. The flap is adapted to convert into thrust compressed air near the airfoil surface at the leading edge and prevent it from becoming "wasted sonic boom energy" as the air passes through and exits from the opening between the flap and the fuselage.

U.S. Patent 6,138,958 to Gaunt discloses an aircraft funnel slat system including a pair of slats or flat members angled above the leading edge of the aircraft wings. This patent is concerned with providing increased airspeed above the wing and increased lift from below the wing.

U.S. Patent 1,787,321 to Orr discloses an airplane wing having, proximate the leading edge, a pair of airfoils. The main function of the airfoils is to accentuate the air pressure on the lower side and diminish the air pressure on the upper side. This patent is concerned with obtaining increased lift.

U.S. Patent 2,282,647 to Dillon disclosed an improved wing or airfoil having an air passage therethrough whereby the wing enables the lift available to be increased and avoids the introduction of undesirable drag.

U.S. Patent 2,041,793 to Stalker discloses a slotted wing arrangement which is adapted to reduce the drag of slotted wings. In this arrangement, the wing structures have an opening where air flow is directed from the lower surface of the wing to the upper surface thereof in an attempt to reduce the drag.

Summary of the Invention

In accordance with an embodiment of the present invention there is provided an apparatus for reducing drag of an aircraft in combination with an aircraft surface where a local airflow has an upward momentum due to the free air stream being deflected upward by the aircraft surface. The apparatus comprises: an ancillary airfoil having a cambered top surface, a leading edge and a trailing edge and a generally concave lower surface; mounting means for mounting the ancillary airfoil above the aircraft surface in a spaced apart manner and at a positive angle of attack with respect to the local airflow; and an expansion chamber formed between the lower surface of the ancillary airfoil and the aircraft surface, the expansion chamber being located where a distance between the lower surface of the ancillary airfoil and the aircraft surface gradually increases.

In accordance with another embodiment of the present invention there is provided an improved aircraft structure. The improvement wherein the structure has a main body of a generally airfoil shape, the main body having an upper cambered surface, a leading edge, a trailing edge and a generally planar bottom surface. The main body is adapted to provide an area which provides an upward momentum to local airflow. An ancillary airfoil is mounted spaced apart from the upper surface of the main body at a positive angle of attack with respect to the local airflow. The ancillary airfoil has an upper cambered top surface and a lower concave surface. An expansion chamber is formed by the lower concave surface of the ancillary airfoil and the top surface of the main body where a distance between the lower surface of the ancillary airfoil and the top surface of the main body gradually increases. End plates are mounted at each side of the main body, the end plates being of a sufficient height to contain air pressure disturbances created by the ancillary airfoil and the main body while in flight.

Brief Description of the Drawings

Figure 1 is an end elevational view of an ancillary airfoil according to the present invention mounted relative to a wing structure of an aircraft;

Figure 2 illustrates the reactive force exerted on the lower surface of an ancillary airfoil of the present invention;

Figure 3, illustrates an end elevational view of an ancillary airfoil according to the present invention mounted on an alternative aircraft arrangement/design; and

Figure 4 is an end perspective view of the fuselage, airfoil, wing combination of the present invention.

Detailed Description of the Invention

The major benefits to air transportation which are achieved by means of the present invention occur while in level flight at cruising altitude because of the extremely high percentage of flight time which is spent operating in this mode. Unless otherwise noted, all explanations and illustrations represent this mode of operation, thus aircraft path and relative wind as well as the forces of thrust and drag will be acting horizontally at right angles to the forces of lift and weight which act vertically to or from the earth's center. However, it will be appreciated that all principles apply with only minor differences to other modes of operation such as landing, take off, climb and descent. Referring to Figure 1, the ancillary airfoil, designated generally with reference numeral 1, of the present invention is mounted above the front portion of a wing structure 2. Although the ancillary airfoil 1 is shown mounted with respect to the wing structure 2, it will be appreciated that the ancillary airfoil 1 could also be mounted on any other suitable surface of the aircraft, such as the fuselage, etc. The airfoil 1 is mounted at a positive angle of attack with respect to local airflow 3 over the portion of the wing structure 2 where the free stream airflow 4 has been deflected upwards by the cambered upper surface of the wing structure 2. The ancillary airfoil 1 is mounted above the wing structure 2 and thin walled pylons or support members (not shown) may be utilized at intervals for mounting the ancillary airfoil 1 to permit short spans and thin ancillary airfoil

I cross sections.

As shown in Fig. 1, the ancillary airfoil 1 has a cambered top surface 10 and a concave lower surface 9. The ancillary airfoil 1 is configured and mounted in such a manner that there is provided an expansion chamber 11 between the lower surface 9 of the ancillary airfoil 1 and the top surface 12 of the wing structure 2. The expansion chamber

I I is defined by the area between the top surface 12 of the wing structure 2 and the lower surface 9 of the airfoil 1 where the distance between the top surface 12 and the lower surface 9 of the ancillary airfoil 1 gradually increases from front to rear and is shown as being between the dashed lines in Fig. 1.

As illustrated in Fig. 2, the reactive force 5 being exerted on the lower surface 9 of the ancillary airfoil 1 can be resolved into a forward acting horizontal component 6 and an upward acting vertical component 7. Generating this forward acting component 6 is of importance as it acts forward in the direction of flight 8 and counteracts a portion of the total forces of drag affecting the aircraft. The vertical component of reaction 7 adds to the forces of lift supporting the aircraft, and there is no penalty of induced drag associated with generating this lift. Again referring to Fig. 1, the leading edge 14 of the ancillary airfoil 1 is mounted at a distance 13 above the upper surface 12 of the wing 2 where air pressure has recovered significantly above that existing at the wing surface and local airflow 3 at the inlet passage 16 between the ancillary airfoil 1 and the wing 2 is still substantially parallel to the top surface 12 of the wing 2. This distance 13 will vary depending on the wing thickness and camber.

The ancillary airfoil 1 is oriented to this local airflow 3 at a positive angle of attack that will generate maximum forward acting component. It will be appreciated that the angle of attack and the spacing between the wing 2 and the ancillary airfoil 1 to achieve optimum results depend on design variables and can be accurately determined for any given application by routine wind tunnel testing.

The expansion chamber 11 forces the streamlines to diverge and thus increases the pressure on the lower surface 9 of the ancillary airfoil 1 in accordance with Bernoulli's theorem. This increase in pressure, along with the effects of the cambered top surface 10 of the ancillary airfoil 1, significantly increases the magnitude of the reactive force 5 and thus, the magnitude of its forward acting component 6. As noted hereinabove, the ancillary airfoil 1 is oriented to the airflow 3 at a positive angle of attack that will generate maximum forward acting component 6 of the reactive force 5.

The ancillary airfoil 1 may have a movable section 15 at its trailing edge 17. The movable section 15 permits the adjustment of the size of the gap or opening formed between the trailing edge 17 of the ancillary airfoil 1 and the top surface 12 of the wing structure 2 for the purpose of equalizing the pressure between the top surface 19 and bottom surface 20 of the movable section 15. In accordance with Bernoulli's theorem, airflows over the top and bottom surfaces 19, 20 will then be at the same velocity and will blend aft of the trailing edge 17 of the ancillary airfoil 1 without turbulence or extra drag. The reduction of drag will result in a proportional reduction in fuel consumption and thus result in reductions in operating expense, environmental impact and the economic sensitivity of airlines to fluctuations in fuel costs. Additionally, reduced fuel consumption results in a reduction in the amount of fuel required for any specific flight and thus translates directly into increased maximum payload.

It will be appreciated that the benefits of the ancillary airfoil 1 of the present invention could be greatly enhanced by an alternate aircraft arrangement to increase the area over which airflow has been deflected upward thus permitting the employment of larger ancillary airfoils. In this regard, reference will be had to Figs. 3 and 4 which illustrate a further embodiment of the present invention where the ancillary airfoil 1 is utilized in conjunction with a combined structure where the wing and fuselage are combined into a single structure hereinafter referred to as the main body 30. This structure has an airfoil shape and cross section will be constant from tip to tip giving a rectangular planform shape. Aspect ratio values will fall in the range of from about 0.5 to 1.0 in order to keep form drag at an acceptable level.

The top surface 31 of the main body 30 is cambered. The ancillary airfoil 1 of the present invention is mounted above the main body 30 extending from tip to tip and from the leading edge 34 aft to near the point of maximum camber 33.

The movable section 15 of the ancillary airfoil 1 serves the same purpose of smoothing airflow aft of the ancillary airfoil 1 as described hereinabove with respect to Fig. 1.

End plates 36 are mounted at each end of the main body 30, the end plates 36 being of a sufficient height to contain the air pressure disturbance created by the main body 30 and the ancillary airfoil 1 in level cruising flight at the airspeed providing maximum range. The rear portion of the end plates 36 extend upwardly and rearwardly to form a vertical fin and rudder 37 to provide directional control and stability to the aircraft.

An additional ancillary airfoil 1' of the present invention in conjunction with horizontal stabilizer 35 could be mounted full span at the top of vertical fins 37 for the purpose of further increasing the area where airflow has been deflected upward thus generating additional forward acting component of reaction. This arrangement also provides for longitudinal stability and additional lift to compensate for the forward position of the center of pressure due to the lift generated by the forward ancillary airfoil 1. The horizontal stabilizer 35 has a cambered upper surface 41, a leading edge 43 and a trailing edge 45, and should, in conjunction with the placement of heavy aircraft components, be sized to position the center of pressure near mid point of the main body 30 during level cruising flight. Elevons 38 (combination elevators and ailerons) are mounted on the trailing edge 45 of horizontal stabilizer 35 to provide lateral and longitudinal control.

In similar manner to ancillary airfoil 1, the fin top ancillary airfoil 1' provides a further expansion chamber and can be provided with a moveable section 15'. This fin top ancillary airfoil 1' is similar to ancillary airfoil 1 discussed hereinabove and thus works in same manner.

The fin top ancillary airfoil 1' and horizontal stabilizer 35 could be supported at intervals across the span to permit light construction and thin cross sections in the airfoils. Vertical fins or alternately duplicate fin structures (not shown) at suitable intervals could provide this support with size adjusted so that the combined area of all the fins would provide the required keel surface behind the center of gravity to achieve directional stability of the aircraft.

In such an arrangement as shown in Figs. 3 and 4, the power plant configuration could consist of one or two engines (not shown) which would operate at near maximum fuel efficiency during low drag cruising flight and two or more auxiliary engines (not shown) for use during high drag take off, landing, and climbing operations. The auxiliary engines could retract completely inside the aircraft structure when not in use so that no drag penalties from this source would be incurred during cruising flight. The engines could be mounted centrally near the trailing edge 40 of the main body 30 and intake air drawn in over the top surface of both the main body 30 and ancillary airfoil 1 through an area that is fenced or partitioned (not shown) from the leading edge 34 to the trailing edge 40 to sufficient height to isolate this airflow from adjacent lower velocity airflows during level cruising flight. Routing engine intake air over the upper surface of the main body 30 and ancillary airfoil 1 in this manner will result in extra lift and forward acting component of reaction being generated due to increases in both mass airflow and velocity.

The advantages of drag reduction by means of such an alternative arrangement as shown in Figs. 3 and 4 and as further described herein are that, while operating in level cruising flight:

(1) End plates 36 and the equivalent effect of the vertical fins 37 will eliminate spanwise movement of airflow due to the difference in pressure between upper and lower surfaces of both primary and ancillary airfoils thus eliminating wingtip vortices and the resultant induced drag.

(2) Fences or partitions (not shown) separating the airflow over the areas containing the mixture of over wing airflow and engine intake air from the lower velocity air flow over the rest of the aircraft at cruising speed will maintain unidirectional flow and further reduce induced drag.

(3) The large area of lifting surface will reduce wing loading allowing near zero angles of attack on the main body 30 during level cruising flight. This brings the reaction vector to the near vertical position thus resulting in reduced induced drag from this source.

(4) The complete structure will have negligible interference drag due to the unidirectional airflow over all surfaces.

(5) The highly cambered shape of the ancillary airfoil 1 and the main body 30, with curvature extending right to the trailing edge will delay or eliminate the change from laminar to turbulent flow in the boundary layer of these devices thus reducing skin friction.

Such an alternative aircraft arrangement also has the benefit of greatly reduced airframe strength requirements. The complete weight of the structure, fuel load and payload acting through the center of gravity is equal and opposite to the lift forces acting through the center of pressure regardless of the G forces being imposed by accelerations such as air turbulence and control inputs. The major weight carrying structure in this design is a rigid platform 42 (shown in Fig. 3) comprising the lower surface of the main body 30 structure which needs to provide only strength sufficient to accommodate weight distribution loads. If all loads were equally distributed over the platform area, G forces would be felt only as compression loads at ninety degrees to the platform structure 42, equally exerted on both the top and bottom surfaces, and bending loads imposed by G forces would thus be zero. For practical purposes, weight and lift forces in flight will always remain balanced and cannot build up large moments as long as proper load management procedures are observed, and thus the tremendous stresses which can build in the wing and other components of a conventionally constructed aircraft due to G forces are impossible in this type of construction. Additionally, the virtual absence of major stress concentrations in the remainder of the structure would reduce fatigue problems and extend the expected life of the aircraft.

A movable section 46 can be affixed at the trailing edge of the main body 30 as shown in Fig. 3. This movable section 46 serves the same function as the movable section 15 (shown in Figure 1 and 3 and discussed herein above) in eliminating turbulent airflow aft of the structure.

The alternative design will also permit an extremely large cargo compartment 44 to be contained laterally across the full span of the main body 30 which, along with the surplus lifting capacity inherent in the design, would greatly expand the options open to the air carrier to carry large and heavy items and to install passenger carrying facilities.

Still further, in the alternative aircraft design, large over capacity in capability to withstand aerodynamic loads is inherent. The combined structure of cargo compartment 44 and platform 42 having the strength to withstand normal floor and pressurization loads will withstand many times over any possible aerodynamic loads. Gross weight will be limited only by the availability of thrust necessary to meet the requirements of high drag operations at the increased weight and the strength of the undercarriage system to withstand landing loads.

Low wing loading permits low minimum speed and low runway length requirements. Additionally, the large spread between normal lift requirements and the maximum lift available provides a huge reserve of lifting capacity. An aircraft of this design will operate at altitudes above 40,000 feet at low angles of attack, and this capability offers the dual advantages of decreased fuel consumption due to the low density of the air and operation at pressure levels where true air speed is in the order of twice indicated air speed or more.

Still further, the alternative aircraft design described above will result in significant reduction in aircraft construction costs. The low tech structure, simplicity of design, reduced structural strength requirements and the complete absence of compound curves in the aircraft structure will permit greater use of low cost materials and greatly simplify construction methods and procedures. Aircraft designers operating virtually without weight and space restrictions are free to incorporate features providing a large over capacity in safety, reliability, and durability, all of which leads to increased life and decreased operating and maintenance costs.

A still further benefit of such an alternative aircraft design is improved take off performance which would be achieved from ground effect. An airfoil of this size operating at a height equivalent to 10% or less of the span would obtain a large increase in lift without any corresponding increase in drag.

As noted herein above, the ancillary airfoil of the present invention provides benefits to air transportation when used on aircraft of conventional construction and provides further benefits when utilized in combination with the alternate aircraft design described herein.

Although the present invention is described with reference to aircraft, it will be appreciated that the same principle could be employed on other vehicles, such as trucks, ships, etc. On ships the present invention could be employed to reduce the resistance of the ship's passage through the water by mounting hydrofoils on each side of the bow where water is being deflected outwards. In such use, a forward acting component of the reactive force can be generated in the same manner as described with respect to the ancillary airfoils of the present invention.

It will be understood that various variations and modifications can be made to the method and apparatus of the present invention without departing from the concept and spirit of the invention.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An apparatus for reducing drag of an aircraft in combination with an aircraft surface, where a local airflow has an upward momentum due to the free air stream being deflected upward by the aircraft surface, the apparatus comprising: an ancillary airfoil having a cambered top surface, a leading edge and a trailing edge and a generally concave lower surface; mounting means for mounting said ancillary airfoil above said surface in a spaced apart manner and at a positive angle of attack with respect to said local airflow; and an expansion chamber formed between said lower surface of the ancillary airfoil and the aircraft surface, said expansion chamber being located where a distance between said lower surface of said ancillary airfoil and said aircraft surface gradually increases.

2. The apparatus as defined in claim 1, wherein said ancillary airfoil has an adjustable portion at said trailing end, said adjustable portion adjustable to vary the distance between said trailing end and said top surface of said wing.

3. The apparatus as defined in claim 1 or 2, wherein said aircraft surface is an upper surface of a wing.

4. The apparatus as defined in any one of claims 1 to 3, wherein said mounting means are spaced apart pylons.

5. In an aircraft, the improvement comprising: a main body of a generally airfoil shape, said main body having an upper cambered surface, a leading edge, a trailing edge and a generally planar bottom surface, said main body adapted to provide an area which provides an upward momentum to local airflow; a first ancillary airfoil mounted spaced apart from said upper surface of said main body at a positive angle of attack with respect to said local airflow, said first ancillary airfoil having an upper cambered top surface and a lower concave surface; a first expansion chamber formed by said lower concave surface of said first ancillary airfoil and said top surface of said main body where a distance between said lower surface and said main body gradually increases; and end plates mounted at each side of said main body, said end plates being of a sufficient height to contain air pressure disturbances created by said first ancillary airfoil and said main body while in level cruising flight at an airspeed providing maximum range.

6. The aircraft as claimed in claim 5, further comprising: a horizontal stabilizer having a generally airfoil shape, said horizontal stabilizer having an upper cambered surface, a leading edge, a trailing edge and a generally planar bottom surface, said horizontal stabilizer adapted to provide an area which provides an upward momentum to local airflow; a second ancillary airfoil mounted spaced apart from said upper surface of said horizontal stabilizer at a positive angle of attack with respect to said local airflow, said second ancillary airfoil having an upper cambered top surface and a lower concave surface; and a second expansion chamber formed by said lower concave surface of said second ancillary airfoil and said top surface of said horizontal stabilizer where a distance between said lower surface of said second ancillary airfoil and said horizontal stabilizer gradually increases.

7. The aircraft as defined in claim 5, wherein said first ancillary airfoil has a moveable portion at said trailing edge, said movable portion adjustable to vary the distance between said trailing edge and said upper surface of said main body.

8. The aircraft as defined in claim 6, wherein said first and second ancillary airfoils have a movable portion at said trailing edges, said movable portions adjustable to vary the distance between said trailing edges and said upper surfaces of said main body and said horizontal stabilizer.

9. The aircraft as defined in any one of claims 5 to 8, wherein said first ancillary airfoil is mounted to said main body through the use of pylons.

10. The aircraft as defined in claim 6, wherein said second ancillary airfoil and said horizontal stabilizer are supported by vertical fins or duplicate fin structures mounted on said aircraft.

11. The aircraft as defined in any one of claims 5 to 10, wherein said main body has a movable portion at said trailing edge to smooth airflow aft of said main body.