WO2009066322A1

WO2009066322A1 - Airfoil structure for wing vortex reduction

Info

Publication number: WO2009066322A1
Application number: PCT/IN2008/000686
Authority: WO
Inventors: Sundararajan Vidhyasagar Lappasi
Original assignee: Lappasi Sundararajan Vidhyasag
Priority date: 2007-11-22
Filing date: 2008-10-17
Publication date: 2009-05-28

Abstract

The invention is an airfoil structure for significant reduction of wing vortex. The structure consists of an outer portion and an inner portion. The outer portion is symmetrical, thin and of small chord length and its span from the tip is conveniently chosen. Being symmetrical the pressures over the upper and lower surfaces remain same as the airfoil moves in the fluid medium. Being thin and of small chord length the outer portion is of small volume. Both these prevent vortex formation at the outer portion. The inner portion's upper half is characterized by increasing upper bend's distance (13) and height (8) (upper camber's distance from the leading edge (1) and its height from the chord (6)) and by gradual change in the curvature of the upper up sloping surface (2) such that the average angle of collision of relevant air molecules on this surface is lesser than that on the lower down sloping surface (11). Both these aspects of the upper half achieve gradual reduction of fluid pressure on the upper surface as one goes towards the root. The lower half is kept the same or almost same or may be absent (flat bottomed). This prevents the strength and amount of airflow, towards the root from the outer portion and downwards, minimal.

Description

Airfoil structure for wing vortex reduction. Field of invention: Aircrafts, rotors. Brief description of the drawings: Fig. Ia shows the parts of an asymmetric airfoil. Fig. Ib shows an airfoil and a flat plate moving at zero angle of attack. Fig. Ic shows an airfoil and a flat plate moving at positive angle of attack. Fig. Id shows an airfoil and a flat plate moving at negative angle of attack. Fig. Ie shows the forces that arise when a flat or curved surface does work on a fluid molecule.

Fig. If shows the forces that arise when a surface is moved in air at positive angle of attack.

Fig. Ig shows the forces that arise when an airfoil moves in air at zero angle of attack. Fig. Ih shows the pressure waves sent by an airfoil for ground effect. Fig.2: Upper-front view of the inventor's airfoil structure. Background art

[0001] When an asymmetric airfoil moves in air, a swirling mass of air called 'wing vortex' forms at the outer portion of the airfoil. The vortex remains behind, so it is called 'trailing vortex' or 'wing wake¹. The vortex causes problems. E.g.l. The wings of an aircraft are airfoils. When an aircraft passes through the wing vortex of another aircraft the vortex may swirl the aircraft, which may lead to an accident. 2. The blades of a rotor may be airfoils. The wing vortex of a blade causes vibrations of the trailing blades, which results in stress and strain on the blades and noise production. The term airfoil hereafter refers to asymmetric airfoil.

[0002] Significant reduction of wing vortex is one unsolved problem. Many active and passive means have been tried. All these means have been unsuccessful because of insignificant reduction in vortex and detrimental side effects like stress and decrease in efficiency of devices using the airfoil. And the cost for many of these means is very high.

[0003] The cause of the wing vortex formation is known.

Air (or any gas), under normal conditions of pressure and temperature applies equal pressure on all sides. When an airfoil is not moving, the pressures on the upper and lower surfaces are equal and opposite in directions. When the airfoil moves the pressure on the upper surface becomes lower than that on the lower surface. So, as per the gas law, ¹A gas flows from a point of higher pressure to a point of lower pressure until the pressures are equalized', air flows from the sides to over the upper surface; from under the lower surface to the sides around the tip; the air over the upper surface moves downward into the vacuum left behind by the moving airfoil. The net flow is the almost circular vortex.

So, the cause of wing vortex is due to two factors. J. Lowering of air-pressure on the upper surface 2. Vacuum left behind by the airfoil.

[0004] But the cause of the lowering of air- pressure on the upper surface is not known.

Another result of this lowering of pressure is a net upward pressure, so a net upward force on the lower surface. In aircrafts, this force lifts the air craft. This force is called ' aerodynamic lift force". And there are many other observations related to the lift. The cause of the lift and the observations are not known for the past 50 years. There are many theories to explain them. 1. Newtonian theory 2. Equal transit theory 3. Venturi effect theory 4. Kutta-Joukowski lift theorem 5. Coanda effect theory. 6. Circulation theory.

None of theories explains all the observations of lift. So, none of them is accepted by all.

A saying in science is, ¹If there are many theories to explain a phenomenon then no theory is correct and so, the exact cause of the phenomenon is not known'.

[0005]. The inventor finds that not knowing the correct theory is the cause of failure to know the cause of lowering of pressure on the upper surface, which in turn is the cause of failure to find effective means to reduce the wing tip vortex. The inventor presents a theory which explains all the observations and on which his invention is based.

[0006] Defining the structure of present asymmetric airfoil: (Fig. Ia)

It has two functionally important surfaces meeting at two functionally important edges.

Upper surface: Called "upper* because it remains upper when an aircraft gets lifted while moving horizontally. It slopes up from the leading edge then bends down towards the trailing edge.

Lower surface: Also called under surface. It remains lower when the aircraft gets lifted.

Generally it slopes down from the leading edge, and then bends up towards the trailing edge.

Leading edge (1): When the airfoil moves to get lifted this edge leads to meet with the air resistance first. Trailing edge (5): The other edge.

Tip and root (Not shown in the fig.) The two surfaces end at two opposite sides. At one side they meet to form a free edge called tip. At the other side called 'root' they get attached to the supporting structure e.g. to the body (fuselage) of an aircraft, to the hub of a rotor.

Upper bend (3): The edge at which the upper surface bends.

Lower bend (10): The edge at which the lower surface bends.

Chord (6): It is the straight line distance from the leading edge to the trailing edge. It divides the airfoil into two halves. 1. Upper half: The portion above the chord 2. Lower half: The portion below the chord

Upper bend height (8): The displacement between the upper bend to the chord perpendicular to the chord.

Lower bend height (9): The displacement between the lower bend to the chord perpendicular to the chord.

Upper bend distance (13): The distance between the leading edge and the^ point the upper bend height meets the chord.

Lower bend distance (12): The distance between the leading edge and the point the lower bend height meets the chord.

Upper up sloping surface (2): The portion (area) of the upper surface between the leading edge and the upper bend.

Lower down sloping surface (11): The portion of the lower surface between the leading edge and lower bend.

These two surfaces together are called 'leading sloped surfaces'.

Upper back surface (4): The portion of the upper surface between the upper bend to the trailing edge.

Lower back surface (7): The portion of the lower surface between the lower bend and the trailing edge. Gc : Centre of gravity.

[0007] Characteristics of asymmetric airfoil (when held at zero angle of attack): 1. Upper up sloping surface and lower down sloping surface i.e. the leading sloped surfaces are smoothly curved and/or sloped from the leading edge to the upper bend and lower bend respectively.

2. The 'upper bend distance¹ (13) is about 30% to 45% of the length of the chord. The lower bend distance is about 10% to 15% of length of the chord. The 'upper bend height' (8) is generally greater than the 'lower bend height' (9). These two features are such that the area of the 'upper up sloping surface' (2) is much greater than that of the lower down sloping surface¹ (11).

3. The curvatures of the leading sloped surfaces are such that, as the airfoil moves at zero angle of attack, the average angle of collision of air molecules on the 'upper up sloping surface' is greater than that on the 'lower down sloping surface'. The average angle near the upper bend is still greater than that near the lower bend.

4. The upper back surface is flat or curved and down slope to the trailing edge.

5. The lower back surface is generally flat horizontal or slightly curved upwards. Symmetric airfoil: The upper and lower halves are symmetrical.

[0008] Observations in aerodynamic lift

Angle of attack (ΘA): It is the angle between a surface and the earth's horizontal when the surface moves.

Positive angle of attack: If the surface is inclined above the horizontal then the angle is positive angle; the surface is said to be moving at positive angle of attack.

Negative angle of attack: If the surface is inclined below the horizontal then the angle is negative: the surface is said to be moving at negative angle of attack.

Zero angle of attack: If the surface is parallel to the horizontal the angle is zero.

Consider an asymmetric airfoil and symmetrical regular bodies like a symmetrical airfoil or a flat plate being moved horizontal to earth in 'static' air in sufficient velocity. In the figures M_D is direction of motion of the structures and also the horizontal.

A. The structures moved at zero angle of attack (Fig.lb):

Airfoil: 1. It is lifted. 2. Airflow from the leading edge towards the trailing edge forms over the upper surface and under the lower surface, very near the surfaces. It means the flows bend at the upper bend and lower bend respectively. The flow over the upper surface is called 'upper air flow'. The flow under the lower surface is called 'lower air flow'.

3. The velocities of the two flows are greater than the velocity (called 'free stream velocity¹) of the surrounding air molecules.

4. The velocities vary according to area and curvature of the leading sloped surfaces. This results in different amounts of lift for differently shaped airfoils.

5. The velocity of the upper air flow is greater than the velocity of the lower air flow.

6. Pressure on the upper surface is much lesser than the pressure on the lower surface.

7. If there is no lower half (called 'flat bottomed' airfoil) the lift increases. Ground effect:

8. When the airfoil moves within a certain height from the ground the lift increases. This additional lift is called 'ground effect¹.

9. The ground effect is more during the short distance in which the airfoil enters (at a small negative angle of attack) from above this height and moves horizontally.

10. The ground effect increases as the velocity of the airfoil increases.

11. The ground effect increases as the airfoil moves nearer the ground.

12. The ground effect is temporarily lost at an acute turn of the airfoil.

13. During the ground effect, the resistance/drag (called 'induced drag') to the motion of the airfoil decreases.

Symmetrical structures:

14. They are not lifted however fast they are moved.

B. The structures moved at positive angle of attack (+ ΘA) (FigΛc): Airfoil:

15. Lifted. The lift is more than that at zero angle of attack.

16. The lift increases as the angle increases up to a critical angle called 'stall angle' (generally around 15 deg), which is a constant for a given shape of the airfoil.

17. The lift then decreases as the angle increases above the stall angle. Symmetrical structures:

18. They are also lifted. C. The structures moved at negative angle of attack (-ΘA) (Fig.ld): Airfoil:

19. Up to a small negative angle (generally around 3 deg) some airfoils may be lifted. Others are pushed down.

Symmetrical structures:

20. They are not lifted however small the negative angle is. Instead they are always pushed down.

Present theories:

[0009] In these theories it is assumed that whether a body moves in static air or the air flows across the body, now stationary, in the opposite direction in the same velocity, the effects are the same. So, all the theories explain the lift in terms of wind blowing across the airfoil; so, conduct wind tunnel experiments, where air is blown across a stationary airfoil, to study the lift of the airfoil. The inventor finds that the assumption is wrong in some aspects.

[0010] Newtonian theory: This theory is based on Newton's third law (NTL). 'When the wind hits the under surface of the airfoil, the airfoil deflects (action) the wind downward. As a 'reaction' the wind pushes the airfoil upward'.

Defects.

1. This theory explains observations 15 and 18, not any other.

2. For observation 1. If the lower down sloping surface deflects the wind downward for a lift upward the upper up sloping surface will deflect wind upward, which will produce a 'push down'. In fact the push down will be greater because the area of the upper up sloping surface is greater.

3. If there is no upper half of the airfoil: The centre of gravity of the airfoil is behind the line of the push up force of the wind up on the lower down sloping surface. So, this force will only cause a torque and spin the airfoil.

4. Newton's third law is wrongly applied here. When the wind hits the lower surface it applies a collision (action) force, which is directed upward and backward [0020]. This force or its backward component cannot act because the airfoil is prevented from moving backward. The vertical component is free to act and lifts. Note that the lift is explained without bringing in NTL. By the law, the lower surface will apply a reaction force on the wind. This force deflects the wind downward and backward. So, the law explains the deflection, not the lift. Equal transit theory and venturi effect theory:

[0011] These two theories consider observation 5 and apply Bernoulli's theorem. Theorem: 'When a fluid flows faster its pressure (lateral pressure/ pressure perpendicular to the direction of the flow) becomes lower; faster the flow lower is the pressure'. Since the upper air flow is faster the pressure on the upper surface becomes lower; so a net upward pressure and force on the lower surface results. This net upward force lifts. The two theories differ in giving the cause of the faster flow over the upper surface. [0012] Equal transit theory: It assumes that the upper and lower airflow meet at the trailing edge, taking equal time to travel over the two surfaces; hence, the name 'equal transit (time) theory¹. Since the path over the upper surface is longer (because the upper surface is more curved) the flow over the upper surface becomes faster. Defects:

1. It has been proved that the two flows do not meet at the trailing edge in most cases i.e. they do not take equal time to travel to the trailing edge. Actually, in many cases, the velocity of the upper air flow is much greater than that required for it to meet the lower air flow at the trailing edge.

2. How does the upper air flow know, at the leading edge, that it has to travel a longer distance?

Since the theory is based on wrong assumptions it must be wrong which is accepted by all now. The theory cannot explain all other observations also.

[0013] Venturi effect theory: It brings in the phenomenon called 'venturi effect': 'A fluid flows faster through a smoothly narrowed part (called 'venturi') of a tube; narrower the venturi faster is the flow through it'.

Explanation given for the venturi effect: The curved surfaces, called 'venturi surfaces', of the venturi have a squeezing effect on the fluid'. Narrower is the venturi more curved are the surfaces, so more is the squeezing, so faster is the flow.

The theory states, 'The upper and lower surfaces of the airfoil behave as venturi surfaces.

The upper surface is more curved, so the upper air flow is faster. Defects:

1. The explanation for the venturi effect is wrong. Squeezing needs force of some energy. From where do the venturi surfaces get the force and the energy for this force?

2. The upper and lower surfaces of the airfoil cannot behave as venturi surfaces because they do not face each other as in a venturi.

3. The upper and lower surfaces of the airfoil do not behave as venturi surfaces. In airfoils the velocity of (layers of ) the air- flows decreases as one goes away from the surfaces reaching the free stream velocity of the surrounding molecules but in a venturi the velocity increases as one goes away from the venturi surfaces reaching maximum velocity at the middle/centre line of the venturi. Since the theory is also based on wrong assumptions it must be wrong which is accepted by all now. The theory also cannot explain all other observations.

[0014] It is known that the other 3 theories, Kutta-Joukowski lift theorem, Circulation theorem and Coanda effect theory do not actually explain the lift but only give equations to calculate the lift. Equations of a phenomenon give only the mathematical relationship of the physical quantities involved in the phenomenon i.e. they tell how much one quantity will change when the related quantity/quantities change in some amount, not why the quantity changes. In science, explain a phenomenon or why a phenomenon occurs means tell the natural laws according to which the phenomenon occurs. [0015] Present explanations for ground effect

1. It is due to the formation of 'compressed air¹ between the airfoil and the ground. Defects:

(i) How does compressed air form is not explained.

(ii) Compression of air is not possible because the air between the airfoil and the ground is not in a closed volume, which is required for compression.

2. The ground partially blocks the trailing vortex and decreases the amount of 'down wash' (the downward flow of air over the upper back surface). The reduction in downwash increases the effective angle of attack so that it creates the additional lift. Defects:

(i) The trailing vortex, whether blocked or not by the ground, cannot have any effect on the leading airfoil. (ii) What is meant by 'effective angle of attack¹ is not explained. Inventor's theory: Collision theory.

[0016] So far, in this field, air and wind are considered as a continuous fluid medium, not as consisting of discrete molecules (Bullet theory). The inventor disagrees. The arguments against air or wind as consisting of individual molecules are unconvincing. And, when a structure moves in air collision occurs between it and the air molecules. So, laws of collision will come into play, so must be considered but have not been considered so far. The inventor's theory is based mainly on these laws. Relevant laws

[0017] 1. The molecules of a gas are individual, solid, practically spherical (when related to surfaces of collision in our cases) particles. The attractive intermolecular force is so weak that, with the kinetic energy at ordinary atmospheric temperature and pressure, a molecule in a volume can overcome the attractive forces of thousands of surrounding molecules and flow freely away from the volume.

[0018] 2. The molecules of a gas, while in same pressure and temperature, travel in all directions in the three dimensions of space in equal average number across equal areas in equal average velocity; so apply equal force on equal areas, so apply equal pressure all around.

[0019] 3. A gas flows from a region of higher pressure into a region of lower pressure until the pressures are equalized.

[0020] 4. When collision occurs between a spherical surface (like that of air molecule) and another less curved or flat surface, the component of force collision^όr linear motion inside the collided body is perpendicular to the collided surface at the point of collision. In Fig.le a flat surface collides on a spherical body like the air molecule moving in the opposite direction (Dc) with the force of collision Fc. FR_C is the reaction force the spherical body applies. C is the centre of the spherical body. Note that Fc will pass through the centre of sphere (radially directed), whatever be the direction of the collision of the molecule.

Angle of collision (θc): It is the angle between the direction of collision of air molecule and the normal at the point of collision on the collided surface. If the force of collision cannot act then a component of the force may act. [0021] When a gas molecule like the air molecule collides on a surface and gets reflected then, whether work is done or not by the molecule:

(a) a small percentage of the kinetic energy of the molecule is transformed and radiated out as heat energy in all directions.

Greater is the slowing down and or change of direction (greater is the acceleration) greater is the amount of kinetic energy transformed and radiated out.

It means that greater is the angle of collision lesser is the amount of heat energy radiated because lesser is slowing and the change of direction; greater is the kinetic energy and velocity of the molecule after reflection.

(This occurs according to Maxwell's law of electromagnetic radiation. The law: When an electric charge is slowed down (not when speeded up) and/or changed direction the kinetic energy of the charge is radiated out as electromagnetic energy; greater is the slowing and/or change of direction greater is the radiation of the heat energy. And neutral bodies contain electric charges. An exception to this law occurs when an electron revolves in certain orbits (Bohr's orbits) around the nucleus of atoms).

(b) another small percentage may be transformed and radiated out as sound energy in all directions. Greater is the angle of collision lesser is the quantity of sound energy radiated. [0022] Taking the two kinds of radiations together: Greater is the angle of collision,

(i) lesser is the amount of kinetic energy transformed into heat and sound energy; so greater is the kinetic energy and velocity of the molecule after reflection. (ii) lesser is the force of collision.

[0023] There are three ways by which lift arises in aerodynamic lift, each in a particular circumstance. 1. Reaction force lift or Newtonian lift 2. Unbalanced force lift or Shape lift. 3. Action force lift

[0024] Reaction force (Newtonian) lift: (Fig.lf)

Fc: Net force of collision the undersurface applies on the air reflected downward and forward.

Cv: Vertical component of F_RC FRC: Newton's reaction force to Fc CH: Horizontal component of FRC + ΘA: Positive angle of attack. Mp. Direction of motion of the structure and the horizontal

This lift occurs when a surface is moved forward (in one horizontal direction MD) at a positive angle of attack (+Θ_A) in static air. The surface works on the air molecules which collide on it and get reflected. The force of the work (for linear motion) on an air molecule is directed downward and forward [0020]. So, the net force F_c of the work is directed downward and forward. So, the Newton's reaction force F_RC to Fc is directed upward and backward on the body. This force (F_RC) or its horizontal, backward component (C_H) cannot act because the body is moved forward overcoming the backward component. But its vertical component (Cv) is fee to act.

If Cv is directed through the centre of gravity (eg) of the structure of the surface and is in the line of gravity and is greater than the weight of the structure then the net upward force lifts the structure.

If it is directed through the eg but is not in the line of gravity, then the component of Cv in the line of gravity acts. Then the net force of this component and weight lifts the structure.

If it is not directed through the e.g. then it will only cause torque around the e.g., clockwise or anticlockwise depending on the location of e.g.

Since the lift occurs due to the reaction force of Newton's third law's this lift is called 'reaction lift' or "Newtonian lift'. (Explanation for observations 15 and 18)

[0025] Newtonian 'push down' at negative angle of attack:

When a surface is moved similarly forward but at negative angle of attack the surface applies a net force of collision on the air molecules. The air molecules apply a net reaction force on the upper surface. This reaction force is directed downward and backward. It or its horizontal backward component can not act because the surface is moved forward against the backward component. Its vertical component, directed downward will push the structure of the surface downward. (Observation 20)

[0026] Unbalanced force lift or Shape lift (Fig.lg): Lift of airfoil at zero angle of attack:

Qcυ'. Average angle of collision of upper reflected air molecules on the upper up sloping surface.

Feu: Net force of collision by upper up sloping surface on air molecules F_DR: Air's force on the upper surface; Reduced FD CHU: Horizontal component of FRCU F_RCU'. Newton's reaction force to Feu Cvu. Vertical component of FRCU Gc: Centre of gravity of airfoil. F_UR: Air's force on lower surface: Reduced Fu C_HL Horizontal component of FRCL

Fci.: Force of collision by lower down sloping surface on an air molecule Θ_CL: Average angle of collision of lower reflected air molecules at lower down sloping surface

CVL: Vertical component of FRCL F_RCL Newton's reaction force to FC_L M_D-. Direction of motion of the airfoil and horizontal.

Note: Whether the airfoil is stationary or is moving air, air molecules will be colliding on the leading sloped surfaces from different directions [0018] at various angles of collision and get reflected in various directions e.g.

(i) From the upper up sloping surface molecules are reflected upward, upward-forward and upward-backward, downward-forward. Let the molecules reflected in all upward directions be called 'upper reflected molecules '.

(ii)From the lower down sloping surface molecules are reflected downward, downward- forward and downward-backward, upward-forward. Let the molecules reflected in all downward directions be called 'lower reflected molecules '.

1. When the airfoil is stationary at zero angle of attack:

[0027] When the asymmetric airfoil or the symmetrical structures are stationary in air, pressure on the upper and under surfaces are equal and opposite. So, air's downward force (F_D) (Fig. Ia) on the upper surface is equal to air's upward force (Fu) (Fig. Ia) on the under surface. F_n = Fu. They are balanced forces.

2. When the airfoil is moved at zero angle of attack:

[0028] The airfoil is moved in one direction, the horizontal. Then, the leading sloped surfaces do work on the air molecules colliding on them at different angles of collision. Then: (i) The work done is great; so the kinetic energy and so, the velocity of the reflected molecules are much higher than the kinetic energy and velocity (free stream velocity) of the surrounding air molecules.

(ii) Greater is the angle of collision of the air molecule greater is the kinetic energy and the velocity of the reflected molecules. [0022]

At the upper surface:

1. Reaction force of work: θcu is the average angle of collision of upper reflected air molecules on the upper up sloping surface. Let Feu be the net force of work by the upper up sloping surface on 'upper reflected molecules'. Note that it is directed upward and forward [0020]. So, the net reaction force F_RCU to Feu is directed downward and backward in the airfoil. It or its horizontal backward component C_HU cannot act because the airfoil is moved forward against the backward component. Its vertical component Cvu is directed downward. It is free to act.

The line of action of Cvu is generally located in front of centre of gravity of the airfoil. So Cvu tends to cause mainly torque. In the fig. it will cause anticlockwise torque.

2. Upper reflected molecules: They collide on and deflect away some of the molecules coming down to cause the downward force F_D on the upper surface. They in turn will get deflected. Note that a reflected molecule can deflect more than one molecule because it has much higher kinetic energy.

(i) So, F_D, on the upper surface gets reduced to F_DR.

(ii) Consider the molecules reflected upward-backward in the upper reflected molecules and all molecules deflected backward and backward-downward. They form the upper airflow very near the upper surface (Explains observation 2)

(iii) The upper airflow velocity is greater than the free stream velocity because of the higher kinetic energy of the molecules reflected from the upper up sloping surface. (Explains observation 3) At the lower surface:

1. Reaction force of work: Θ_CL is the average of the angles of collision of lower reflected molecules. Let F_CL be the net force of work by the lower down sloping surface on 'lower reflected molecules. It is directed downward and forward. So, the reaction force F_RCL to FcL is directed upward and backward. It or its horizontal backward component cannot act because the airfoil is moved forward against the backward component. Its vertical component C_VL is directed upward. It is free to act.

The line of action of C_VL is generally located in front of centre of gravity. So, CVL tends to cause mainly torque. In the fig. it will cause clockwise torque.

2. Reflected molecules: The lower reflected molecules collide on and deflect away some of the molecules coming up to cause the upward force Fu on the lower surface. They in turn will be deflected. Note a reflected molecule can deflect more than one molecule because it has higher kinetic energy.

(i) So, Fu on the lower surface gets reduced to F_UR.

(ii) Consider the molecules reflected downward-backward in the lower reflected molecules and all molecules deflected backward and backward-upward. They form the lower air flow very near the lower surface. (Explains observation 2)

(iϋ) The lower airflow velocity is also greater than the free stream velocity because of the higher kinetic energy of the reflected molecules. (Explains observation 3)

[0029] Even though the number of the upper reflected molecules is much greater

(because of much greater area of the upper up sloping surface) than the number of the lower reflected molecules Cvu and its torque are very comparable to the opposite C_VL and its toque. Reasons: 1. The average angle of collision θcu on the upper up sloping surface is greater, so force of the collision is lesser. 2. Lines of actions of the two forces are not at the same distance from the centre of gravity of the airfoil.

So, net torque is zero or insignificant.

[0030] But F_D gets reduced very much more than Fu i.e. F_DR becomes much smaller than

Reasons:

(i) The number of upper reflected molecules is much greater than that of the lower reflected molecules because the area of the upper up sloping surface is much greater than that of the lower down sloping surface.

(ii) Because of the curvatures of the leading sloped surfaces, the number of molecules reflected more backwardly in the upper reflected molecules is much greater than that in the lower reflected molecules. So, the number of molecules, causing part of F_D on the 'upper back surface' (4 in fig. Ia), deflected off is much greater than that, causing part of

Fu on the 'lower back surface' (7 in fig. Ia).

(iii) The kinetic energy of upper reflected molecules is greater than that of lower reflected molecules because the average angle of collision θcu on the 'upper up sloping surface¹ is greater than the average angle Θ_CL on the 'lower down sloping surface'.

[0031] F_D gets reduced so much that net downward force (F_DR + Cvu) on the upper surface is much lesser than the net upward force (FU_R + CVL) on the lower surface. So, the pressure on the upper surface is much lower than the pressure on the lower surface.

(Explains observation 6)

So, a net upward force of these two forces, FL = (FUR + CVL) - (FD_R + Cvu) results; if it is greater than the weight of the airfoil it lifts the airfoil. (Explains observation 1)

[0032] Since the lift is mainly due to unbalancing of the two balanced forces F_D and Fu the lift is called 'unbalanced force lift'. Since the unbalancing in turn occurs due to the shape of the airfoil we can call this lift as 'shape lift'.

[0033] Explaining other observations:

Observation 4: Differently shaped airfoils have difference in areas and curvatures of the leading sloped surfaces.

Observation 5: Since upper airflow's average angle of collision is greater than that of the lower airflow its velocity is greater than that of the lower airflow. Observation 7: Reason: Absence of lower down sloping surface. So, lower reflected molecules are absent. So, Fu is not reduced as much. So, F_UR is now greater. So, F_L is greater. Ground effect:

Observation 8: Action force lift

The air molecules reflected mainly in the forward and downward direction from the lower down sloping surface matter here.

Initial production: (Fig. Ih). These molecules send pressure waves in this direction. Note that the pressure of these waves is higher than that of the surrounding air because the reflected molecules have higher (kinetic) energy. The waves get reflected from the ground. When the airfoil comes over these reflected waves, after traveling a distance d, the higher pressure of these waves gives the additional lift, the ground effect. Note that the ground effect is absent in the distance d.

Later on: The pressure waves are continuously produced, so are continuously present (including in the distance d). So, continuous ground effect is present. The additional lift is due to the (action) force of the pressure waves on the lower surface; so, the lift is called action force lift.

Observation 9: 1. Presence of the additional pressure waves sent from the time the airfoil is just above the height until it becomes horizontal 2. Increase in the average angle of collision of molecules responsible for the pressure waves (due to the orientation of the lower down sloping surface due to the small negative angle of attack of the airfoil). Observation 10: As velocity increases work done by the lower down sloping surface increases; so, the pressure of the waves increases.

Observation 11 : The nearer the aircraft is to the ground lesser is the distance the pressure waves travel; so lesser is their leak in other directions and also lesser is the dissipation of their energy as sound and heat energy; so greater will be their pressure. Observation 12: When the airfoil turns acutely the pressure waves are now sent fresh in this changed direction i.e. it will be in the phase of initial production. So, it has to travel the distance d in the changed direction where reflected pressure waves are absent; so, ground effect is absent at the acute turn.

Observation 13. The pressure waves reflected from the ground and directed upward and forward, deflect some of the molecules in front of the airfoil away from the foil. Observation 14: Symmetry is the cause.

Observation 15: The reaction force (Newtonian) lift is added to the shape lift. Observation 16. 1. The average angle of collision θcu on the upper up sloping surface increases; so, the reflected molecules have higher kinetic energy; so, F_D is reduced more. 2. The average angle of collision Θ_CL on the lower down sloping surface decreases; so, the reflected molecules are less energetic; so, Fu is less reduced.

Observation 17: 1. Above the stall angle, the upper airflow gets separated from the upper back surface due to its direction of flow. Into the space between the upper flow and the upper back surface normal air and vortices of air flow and accumulate, which increases the pressure on the upper back surface. So, the lift decreases. More is the angle beyond the stall angle more is the separation more is the flow and accumulation, so more is the decrease of lift. 2. The effective area of the lower surface for molecules to hit upward to cause Fu goes on decreasing; so, Fu goes on decreasing. In other words the Newtonian lift goes on decreasing.

Observation 19: Up to this angle the shape lift remains greater than the "Newtonian push down'.

[0034] Note:

1. The shape lift is similar to the lift of a 'held drooping paper¹ when air is blown on to its upper up sloping surface in the required direction and force. Then the upper surface of paper is similar to the bent upper surface of airfoil. The difference: In case of paper, the higher energy of the upper reflected molecules comes from the energy that blows the air. In case of the airfoil, the higher energy of the upper reflected molecules comes from the energy that moves the airfoil.

2. C_HU and C_HL together form the resistance, called in aerodynamics as 'induced drag', to the motion of the airfoil.

3. When conducting wind tunnel experiments with airfoil at zero angle of attack the wind must be blown exactly onto the leading sloped surfaces. Wind blown higher and/or lower to these surfaces will remove molecules causing F_D and Fu, which will give wrong results.

[0035] So, the factors for lowering of pressure on the upper surface:

1. Areas of the upper up sloping and lower down sloping surfaces. Greater the upper up sloping surface greater is the pressure reduction. The areas are determined by respective bend distance and height.

2. Curvatures of the two leading sloped surfaces. Greater is the average angle of collision on the upper up sloping surface (i) greater is the kinetic energy of the upper reflected molecules and (ii) greater is the number of molecules deflected more backwardly; so greater will be the reduction of pressure on the upper surface.

The inventor's theory is based on mainly collision laws. So, his theory can be called 'collision theory¹. [0036] Explanation of venturi effect with inventor's collision theory: The molecules reflected off the curved venturi surfaces collide against the molecules flowing through the venturi in the direction of flow and so make them flow faster. Narrower is the venturi greater is the number of molecules reflected off the venturi surfaces. This greater number collides against lesser number of molecules now flowing through the narrower venturi; so make the lesser flow still faster.

[0037] The inventor's collision theory can explain the 'lift of a rotating cylinder in a smoothly flowing fluid', which is also not explained so far.

Consider the fluid flowing from the reader's left to right across a cylinder rotating clockwise and placed with its longitudinal axis perpendicular to the direction of the flow. The leading upper half of the cylinder, the half facing the incoming fluid, does work on the fluid in the direction of flow where as the leading lower half of the cylinder, the half facing the incoming fluid, does work on the fluid against the direction of flow. So, the number of molecules reflected off backwardly and upwardly from the leading upper half is much greater than that reflected off backwardly and downwardly from the leading lower half. This similar to what happens in the 'shape lift' of the airfoil. So, the net upward force that results lifts the cylinder.

Object of the invention

It is to structure the airfoil such that wing vortex is significantly reduced and still the aerodynamic lift is achieved.

Statement of the invention

Present day means to reduce wing vortex try to reduce the vortex after it has formed i.e they do not deal with the cause of vortex formation, so fail. The inventor's invention reduces the cause of the vortex, so, reduces the vortex significantly.

Detailed description (Fig.2)

Parts: 1: Leading edge; 2: Curved upper up sloping surface; 3: Upper bend; 4: Upper back surface; 5: Trailing edge; 8: Upper bend height; 10: Lower bend; 11: Lower down sloping surface; 13: Upper bend distance; Po: Outer portion; Pi: Inner portion. Principle: Divide the airfoil into two portions: 1. Outer portion (P₀): Extends from the tip (T) up to a small convenient distance towards the root (R). 2. Inner portion (Pi): Extends from the outer portion up to the root. The shape and size of the outer portion are such that as the airfoil moves at zero angle of attack (i) the pressures on the upper and lower surface remain equal or the pressure on the upper surface is only insignificantly reduced (ii) the vacuum left behind is as small as possible. This prevents the formation of vortex at the tip and outer portion. The shape and size of the inner portion are such that, when the airfoil moves at zero angle of attack:

(i) The pressure on the upper surface becomes gradually lesser as one goes towards the root; so, the amount and strength/velocity of airflow (part of vortex that can form) from over the upper surface of the outer portion towards the root will be very small, (ii) Vacuum left behind gradually increases as one goes towards the root from the outer portion; so that the amount and strength of downward flow (into this vacuum) of the above flow (the rest of the vortex that can form) only gradually increase, (iii) Still the needed aerodynamic lift of the airfoil occurs. Accordingly as one goes from the tip towards the root:

1. The structure of outer portion: (i) Symmetrical (ii) The upper and lower bend distances and heights are as small as possible (reduces volume) (iii) As thin as possMe. (reduces volume) (iv) The length of the chord as small as possible (reduces volume) and (v) The span of the outer portion is conveniently chosen. The type of symmetry depends. Or the features in (ii), (iii) and (iv) may gradually increase insignificantly from the tip. 2. The structure of the inner portion: If the inner portion is not flat bottomed: In upper half:

(i) gradual increase in the upper bend's distance (13) and height (8) such that the area of the upper up sloping surface (2) gradually increase and are greater than the area of the lower down sloping surface

(ii) gradual change in the curvature of the upper up sloping surface so that the average of the angles of collision of air molecules on this surface gradually increases but still remains greater than that of the lower down sloping surface

(iii) gradual increase in the chord length to the necessary extent to get the necessary lift. In the lower half:

(iv) keep the lower bend distance and height of the lower down sloping surface same or only slightly increase such that they are smaller than those on the upper half. (v) keep the curvature of the lower down sloping surface same or only insignificantly change

If the inner portion is flat bottomed the only half, the upper half has same features given above.

Scope of the invention

The invention is to reduce wing vortex of airfoil structures significantly. This description is not meant to be construed in the limited sense. Various modifications of the disclosed embodiment as well as alternate embodiments of the invention will become apparent to persons skilled in the art upon reference to the description and to inventor's theory of airfoil lift. It is therefore contemplated that such modifications can be made without departing from the spirit and scope of the invention as defined.

Claims

Claims:I claim

1. an airfoil structure comprising an outer portion and an inner portion. As one goes towards the root from the tip, the features are:

2. The said outer portion in claim 1 is characterized by having the following features: (i) It is symmetrical (ii) Its upper and lower bend distances and heights are as small as possible, (iii) It is as thin as possible (iv) Its chord length is as small as possible, (v) Its span from the tip to the inner portion is conveniently chosen.

3. The quantities in (i) (the symmetry), (ii), (iii) and (iv) of the outer portion in claim 2 may remain constant or gradually increase or change insignificantly.

4. The said inner portion in claim 1 if not flat bottomed is characterized by having the following features in the upper half: (i) Gradual increase in the upper bend's distance and height such that the area of the upper up sloping surface gradually increase and are greater than the area of the lower down sloping surface (ii) Gradual change in the curvature of the upper up sloping surface so that the average of the angles of collision of relevant air molecules on this surface gradually increases but still remains greater than that of the lower down sloping surface (iii) Gradual increase in the chord length..

5. The said inner portion in claim 1 if not flat bottomed is characterized by having the following features in the lower half: (i) The lower bend distance and height of the lower down sloping surface remain same or only slightly increase such that they are smaller than those on the upper half, (ii) The curvature of the lower down sloping surface remains same or only insignificantly changes such that the average angle of collision of relevant air molecules is lesser than that on the upper up sloping surface.

6. If the inner portion is flat bottomed the only half, the upper half has same features said in claim 4.