Description:1. Title of the invention
Title of Invention: Stiffened slat assembly of an aircraft.

2. Field of invention
This invention relates to aircraft structural engineering in general and more particularly to design of aircraft wing slat assembly and associated stiffening.

3. Background of Invention
Slats are high lift devices that are used for achieving improved low speed characteristics of the aircraft. They are fitted on the leading edge of wing on fixed wing aircraft. The classical structural design of the leading edge slats consists of ribs (101) for giving the shape to the slat surface and wrapped around skin (102), the whole assembly resists the bending of the slat due to high aerodynamic forces. The slats are deployed on circular profile by means of slat tracks (103). The slat tracks are generally two in number, typically positioned close to the edges of the slat. The slats are actuated by means of an actuator typically mounted close to the center of the slat. Hence, slat can be treated as an over hanged beam supported on slat tracks close to the ends. The typical advantages of this kind of the design is its simplicity in manufacturing and assembly as it involves less number of parts. However, when the spacing between the slat track increases, the following are observed:
- the deflection of the slat due to aerodynamic forces increases;
- the skin thickness increases to reduce the deflection which increases the slat assembly weight;
- forming difficulty of thick skins;
- waviness of the skin during fastening; and
- increase in the skin stresses;

4. Brief Summary of invention
The primary objective of the present invention is to increase the stiffness of the slat of an aircraft and in the meantime reduces the overall weight of the slat assembly. The spar is at 30% from the leading edge of the slat where maximum web height is available. The spar is oriented along the surface of the top skin. This increases the bending stiffness of the slat and hence reduces the overall slat deflection. This also avoids unnecessary increase in the slat skin thickness and also reduces the stresses on the slat skin.
The present invention, i.e., stiffened slat assembly of an aircraft, comprises of a spar which provides the required additional stiffness, it comprises multiple ribs which give aero foil shape to the slat and multiple slat skins which close the skeletal structure and assures smooth airflow on the slat surface with a minimum drag. The wrinkling of the skin during assembly is prevented by the introduction of spar. The overall shape distortion of the slat assembly is also significantly reduced by the introduction of spar in the slat assembly

5. Brief description of drawings
Fig-1, shows the schematic of the present invention, i.e., stiffened slat assembly of an aircraft.

6. Detailed description of invention
Refer Fig-1. Slats are high lift devices that are used for achieving improved low speed characteristics of the aircraft. They are fitted on the Leading Edge of wing on fixed wing aircraft. The classical structural design of the leading edge slats consists of ribs (101) for giving the shape to the slat surface and wrapped around skin (102), the whole assembly resists the bending of the slat due to high aerodynamic forces. The slats are deployed on circular profile by means of slat tracks (103). The slat tracks are generally two in number typically positioned close to the edges of the slat. The slats are actuated by means of an actuator typically mounted close to the center of the slat. Hence, mathematically, slat can be treated as an over hanged beam supported on slat tracks close to the ends. The typical advantages of this kind of the design is its simplicity in manufacturing and assembly as it involves less number of parts. However, when the spacing between the slat track increases, the deflection of the slat due to aerodynamic pressure also increases. This non-linear deflection degrades the aircraft performance, as well as making the skin to take all bending loads. This behavior of the slat leads to increase in skin thickness to reduce deflection, with significant weight penalty. In the present invention, a spar (104) is introduced within the available aero foil thickness of slat (100), which increases the strength and stiffness of the slat (100) with reduced weight than the slat currently in use. The waviness of the skin (102) during manufacturing and assembly is prevented by the introduction of spar (104)
Fig-1 shows the construction details of the present invention, i.e., stiffened slat assembly (100)of an aircraft, used for achieving improved low speed characteristics of the aircraft. They are fitted on the leading edge of wing on fixed wing aircraft. The structural design of the leading edge slats consists of ribs (101) for giving the shape to the slat surface and wrapped around skin (102), the whole assembly resists the bending of the slat due to high aerodynamic forces. The slats are deployed on circular profile by means of slat tracks (103). The slat tracks (103) are generally two in number typically positioned close to the edges of the slat (100). The slats (100) are actuated by means of an actuator typically mounted close to the center of the slat. Hence, the slat (100)is treated as an over hanged beam supported on slat tracks (103) close to the ends. The typical advantages of this kind of the design is its simplicity in manufacturing and assembly as it involves less number of parts.
The stiffened slat assembly of an aircraft(100)comprises of a plurality of ribs (100). These ribs (100) are C cross sections, machined from light aluminum alloy which is anodized and coated with primer to avoid corrosion.
A spar (104)of Z cross section is positioned at 30% from the leading edge of the slat where maximum web height is available. The spar (104) is oriented along the surface of the top skin (102). The spar (104) increases the bending stiffness of the slat (100) and hence reduces the overall slat deflection. This avoids unnecessary increase in the slat skin (102) thickness and also reduces the stresses on the slat skin (102). The spar (104) is machined from light aluminum alloy bar stock which is anodized and coated with primer to avoid corrosion.
A plurality of metallic skins (102) is provided to close the skeletal structure and it assures smooth air flow on the slat surface with a minimum aerodynamic drag. The skins (102) are sheet metal parts which are stretch formed from light aluminum alloy sheet which is anodized and coated with primer to avoid corrosion.

7. Drawing Numerals:

Sl. Nos. Name of the Part Description
100 Slat assembly
101 Slat ribs
102 Slat skin
103 Slat tracks
104 Spar
, Claims:We claim:
1. A stiffened slat assembly (100) of an aircraft, comprising:
- a plurality of ribs (101)that gives aero foil shape to the slat assembly (100);
- two slat tracks (103) to deploy the slats (100) on a circular profile, such that each track (103) is positioned close to edges of the slat (100); and
- a plurality of metallic skins (102) to close the skeletal structure of the slat assembly (100) and to assure a smooth air flow on the slat (100) surface with a minimum aerodynamic drag, characterized in that, a spar (104) is introduced within the available aero foil thickness of the slat (100) to provide additional strength and stiffness to the slat assembly (100) without increasing the slat skin (102) thickness, the spar (104) reduces the stresses on the slat skin (102), the spar (104) prevents the wrinkling of the skin (102) during manufacturing and assembly, and thereby, overall distortion of the slat assembly (100) is avoided.

2. The stiffened slat assembly (100) of an aircraft, as claimed in claim 1, wherein, the spar (104) is placed in the slat assembly (100) at30% from the leading edge of the slat where maximum web height is available, the spar (104) is oriented along the surface of the top skin (102) required stiffness, and the spar (104) is made of a Z cross section machined from light aluminum alloy that is anodized and coated with primer to avoid corrosion.

3. The stiffened slat assembly (100) of an aircraft, as claimed in claim 1, wherein, the skins (102) are sheet metal parts which are stretch formed from light aluminum alloy sheet that is anodized and coated with primer to avoid corrosion.