1. Title of the invention

Improvement in design of Cockpit Floor Side member for supporting Engine Truss mount loads of a turboprop trainer aircraft.

2. Field of invention
It is an aircraft structural design used for transferring Engine truss mount loads through Longerons(primary bending member) to the fuselage structures of a basic turboprop trainer aircraft.

3. Use of invention
This improved design will effectively transfer the engine mount loads to the fuselage in addition to serving as a Cockpit floor side member. A single machined member is also used to establish web to web connection between top & bottom frames and for providing continuity between skin and Covers.

4. Prior art
Longerons supporting the cockpit floor is usually made with C-cross section and an additional bath tub fitting is used as an interface for transferring engine mount loads to the fuselage.

5. Draw backs of prior art

1) Limited access for fastening the C-cross section Longeron with the typical bath tub fitting.
2) Additional angles are required to establish web to web connection between frames.
3) Additional splice members for establishing 'skin to skin' or 'skin to cover' continuity.
4) Difficult to establish modular-construction and hence more assembly time.
5) Load transfer depends on the strength of various connections on the Longeron and hence one should go for more margin of safety(extra material).

6) Increased Weight due to extra parts and fasteners.

6. Comparison between prior art and present invention

The improved design is a single machined member whereas the prior art is a sheet metal buildup or structural assembly. The design can be directly assembled to major assembly unlike the prior art which requires a separate subassembly and hence tooling. In prior art, the continuity between frames and skin are established through additional angles and fittings. The new design directly integrates all these members. The improved design is interchangeable and helps in modular construction. As it is a single machined member, Manufacturing time is greatly reduced by the use of CNC machines. The no. of fasteners coming on the Longeron can be greatly reduced and hence the reliability and safety of the structure is improved.

7. Aim of the invention

Aim of the invention is to eliminate the draw backs of the conventional design and to improve the structural integrity of fuselage .

8. Summary of the present invention

a) Longerons are the major bending members of the fuselage. Engine truss mounts are generally connected to Longeron so that the engine loads are diffused effectively to rest of the fuselage structure.

b) The present design of Longeron applies to the bottom portion of the engine truss mount starting from the firewall where there is an additional requirement of supporting cockpit floor.

c) The Longeron incorporated in the design is of T-cross section. Center flange of the T-section supports the cockpit floor whereas the contour side webs helps in maintaining the skin to skin & skin to cover continuity.
d) Additional ribs are provided at various stations to connect the top and bottom frames maintaining the web continuity in them.

e) The Longeron section is sized up locally where the engine truss mount load of 4.4 ton(resultant) and 16 Nm(moment) is coming as reaction at the firewall juncture.

f) The Longeron has a hole in its front face where the truss mount is attached through firewall with a single bolt. Bushes are provided at the juncture to improve the bearing strength.

g) The reason for incorporating a T-cross section is due to its easy access for fastening inside the
fuselage on either side of the cockpit floor. This avoids the use of blind fasteners which
compromises strength, h) Appropriate steps are given in the Longerons where there is a requirement to accommodate doors and covers, i) For Easy removal of bolts in order to separate the Truss mounts, a pocket of adequate width(85mm) is provided at the firewall juncture, j) The length of the Longeron designed is just 1.7 m and hence machining it as single piece does not call for sophisticated CNC machines, k) Apart from the single bolt for engine truss mount attachment, the design calls for only rivets for establishing connections with other members of the fuselage. I) Inspection of cracks in the Longeron is easy as it is of T-cross section and does not require high cost equipments. m) This longeron is made with ICY points for easy interchangeability with other series of aircraft, n) This is an universal design which can be adopted to transfer loads at interfaces where it is desirable to use T-cross sections eg.

Fuselage transport joint.

9. Brief description of drawings
Fig-l Prior art showing the conventional Longeron design for connecting engine truss mount
Fig-2 Improved Longeron design proposed with T-cross section for connecting engine truss mount.
Fig.-3. Attachment schemes with adjacent structure

10. Statement of invention
The improved design applied to this turboprop trainer aircraft effectively transfers the engine truss mount loads to the fuselage structure. This Design can be applied to all aircrafts with nose mounted Engines. The key feature of the design is it is a single machined part and it also serves as a support for cockpit floor and cockpit frames.

11. Detailed description of invention
The improved design consist of a T-cross section with an integrated fitting in the front. The integrated fitting which look like a box with one side open, connects the engine truss mount with the fuselage structure. The integrated fitting transfers the loads from the attachment point to the rest of the T-cross section. The Thickness of the Longeron face where the engine truss mount bolt is picked up is increased to cater for bearing strength. The Thickness of the cross section is smoothly varied from the mounting point to avoid unnecessary stress concentration in the Longeron member. The cross section has top and bottom ribs at every frame station of the fuselage. These ribs allow web continuity between top and bottom frames. Skin continuity on the contour side is established through the flange members on the contour side of the longeron. Steps are given on the contour side flanges of the longeron to allow the attachment of Access panels and for attachment with other structural members of the fuselage. Sufficient blend radius of 8mm is given in the region of fitting and 4.5mm in the rest of the areas to account for smooth stress flow and fatigue resistance.

Claims

1. This improved design will effectively transfer the engine mount loads to the fuselage in addition to serving as a Cockpit floor side member.

2. This improved design can be implemented in any aircraft where the forward engine mount loads are to be transferred to the fuselage structure, especially to the members of the cockpit region.

3. A single machined member is used to establish web to web connection between top & bottom frames and for providing continuity between skin and Covers.

4. It also acts as an edge member for the cockpit floor supporting it on either side of the aircraft center line.

5. The Machined member comes with ICY point for connecting the engine truss mount and hence can be interchangeable to different aircrafts.

6. The improved design has the minimum weight with no extra parts and eliminates the tooling time and cost required to form the extensive sheet metal build up structure.

7. The single component design makes inspection and maintenance easy.

8. The proposed design is just a scheme for transferring engine mount loads with a T-cross section. Detail design will yield the exact dimensions required to carry the applied loads.