1. Title of the invention
Method of Manufacturing Composite Torque Plate for Helicopters

2. Introduction
The Torque plate is an element designed to transmit the torsion load from Main Gear Box (MGB) Housing to the structure through Anti Resonance Isolation System (ARIS). It provides an anti torque arrangement and is interposed between the ARIS and MGB. The constituents of Composite Torque Plate are bi-directional carbon epoxy prepreg and foam core. The quasi-monolithic construction at the attachment portion, as well as the design features call for an unconventional technique for manufacturing a composite torque plate. The construction of Composite Torque plate is shown in fig.l.

3. Field of invention
The invention relates to the field of Composites manufacturing, specifically for the Helicopters. The method of manufacturing composite Torque plate is a unique process that requires sophisticated tooling and equipments along with skilled manpower.

4. Use of invention
The invention deals with a modern method for manufacturing of composite Torque Plate for Helicopters, with the use of advanced materials. The manufacturing of Torque plate in stages ensures an uncomplicated, robust and reliable method for the purpose. The resultant composite component manufactured by the method provides distinct advantages like reduction in weight with increased reliability and service life.

5. Prior art
Patent no. US2388653 A - Helicopter; It discusses about an anti torque mechanism for use with helicopter machines having single lifting propeller.
There is very limited literature available on the torque plates for application in helicopters. Moreover, no literature/patents, are available on the art of manufacturing Composite Torque plates.

6. Draw backs of prior art
Drawbacks of the above referred patents are as follows:
a) US2388653 A - Deals, with .the anti torque mechanism of helicopter which counters the torque generated by the rotor and loss of lift during the rotor movement in backward direction.

7. Comparison between prior art and present invention
S/N 1 PRIOR ART 1 CURRENT INVENTION "
Patent US2388653 A is applicable to anti torque It deals with the
1 mechanism of helicopter. Does not deal with manufacturing process of
composite torque plate. composite torque plate.
Table 1: Comparison between prior art and present invention
Prior art does not deal with composite material application and the concept of application is different.

8. Aim of the invention
The aim of the invention is to provide a modern method for manufacturing of composite torque plate for Light weight helicopters, wherein a pre-impregnated Carbon BD fabric and high density foam are processed in stages.

9. Summary of the present invention
The usage of prepregs and foam for the fabrication of composite torque plate offers some challenges in the form of defects, like
> Prepreg layer folds
> Foam crush
> Layer sliding and foam dislocation
It is an invention of developing the method to manufacture defect free composite torque plate for helicopters, overcoming the above challenges. The major stages of this invention are:

a) Development of the prepreg layers as per the design requirement.

b) Machining of high density foam to the requirement (detail, 1 number required per torque plate).

c) Manufacturing of flange (detail, 2 numbers required per torque plate).

d) Manufacturing of foam assembly (detail, 1 numbers required per torque plate).
e)- Manufacturing of torque plate.The Multi-stage process, metallic tools/mould and proven cure cycles are the special features of the invention.

Manufacturing of Composite torque plate in stages provides the following advantages:
>.. Control of defects, as the product can be inspected stage wise
> Control of Exothermic reaction, as the cured part thickness gets divided over the number of cures in stages
> Simplicity of tooling, as the complicated tooling for single stage curing is avoided

10. Brief description of drawings and tables
Fig. 1 shows the construction of Composite Torque plate
Fig. 2 shows the cut carbon BD layers for Flange lay-up
Fig.3 shows the Flange detail
Fig.4 shows the cure cycle for Flange
Fig.5 shows the Foam Assembly detail
Fig.6shows the Hot Platen Press used in the curing of Foam assembly
Fig.7 shows the Cure cycle for foam assembly
Fig.8 shows the Torque plate.
Fig.9 shows Torque plate lay-up in Split mould in open and closed condition
Fig. 10 shows Lay-up scheme for Composite Torque Plate
Fig.l 1 shows the Cure cycle for Torque plate curing
Table 1 shows Comparison between prior art and present invention

11. Statement of invention
This invention specifically focuses on manufacturing method of Composite Torque Plate wherein advantages of high modulus carbon prepregs with foam as filler materials is harnessed.

12. Detailed description of invention
Composite torque plate is manufactured in five stages and provides anti-torque to the torque generated by the rotor and transmission system of the helicopter. It also an integral part of the vibration isolation system of advance light helicopter.
Composite torque plate is manufactured using following raw materials:
i) Carbon Bi-directional pre-pregs ii) High density foam

The stage wise sequence of the method is provided below:

a) The optimally developed layers are cut using automated prepreg cutting machine an kitted as per the layup sequence. These layers are preserved at -18 deg. C till usage The cut layers for Flange detail are shown in Fig.2 before start of the lay-up process.

b) Foam machining:
Machining of high density foam is carried out using 3/5 axis machining centre as pe requirement. Proper care is taken to avoid moisture contamination (detail, 1 numbe required per torque plate).

c) Manufacturing of flange (detail, 2 numbers required per torque plate) [Refer Fig. 3] :
The cut and kitted carbon prepreg material is laid up on the lay-up tool after adequat tool preparation. A total of 21 layers are laid up, one after the other, as per the correc orientation* Debulking of the layers is carried out after the lay-up of every 4 layers a room temperature to avoid any air entrapment and achieve proper compaction. Th layup is then vacuum bagged and cured in an Autoclave as per the cure cycle referre< in fig. 4.
The cure cycle represents the pressure, temperature and vacuum controls required t< be exercised over the curing time. For curing of flange, the temperature rise of \-\ °C/minute is maintained starting from room temperature up to 75±5°C. A dwell o 40+5 minutes is maintained at this temperature followed by temperature rise up t< 135±5°C. Again a dwell of 60+15 minutes is maintained at this temperature followec by cooling at the rate of 1-3°C.
Pressure of 2.5 bar is maintained up to 75±5°C. With the start of first dwell, th< pressure is raised to 5 bar and maintained throughout the curing. The lay-up i; subjected to vacuum minimum 0.2 bar gauge pressure during the entire curing.
The cured flange is then demoulded, finished and subjected to ultrasound check fo bond quality and defects, if any.

b) Manufacturing of foam assembly (detail, 1 numbers required per torque plate) [Refe fig.5]..
The machined foam is wrapped with six carbon layers using adhesive film.
The layup is positioned in the foam assembly tool and cured in hot platen press [refe
fig.6] as per cure cycle [refer fig.7],
Temperature rise up to 3°C/minute is maintained from room temperature till 135±5°(
followed by dwell of 60+15 minutes, after which cooling is carried out at 2
3°C/minute. Pressure of 500KPa is maintained during the entire period.
The cured foam assembly is demoulded and finished to dimensions.

c) Manufacturing of torque plate [refer fig. 8],
The cut and kitted layer are laid up as per the layup in the split lay-up mould. In either split mould, 17 layers are laid up with intermediate debulking at room temperature for minimum 30 minutes after every 6 layers, These block of layers in either mould undergoes debulking at room temperature for 4-6 hours. Subsequently, foam assembly wrapped with adhesive film is positioned with 3 more bi-directional carbon layers [Ref. fig. 9]. Pre-compacted filler material is positioned on the edges of triangular foam to create a smoothly flushed surface. Fig. 10 shows the final lay-up scheme for the Composite Torque plate.
Vacuum bagging is then carried out and it is cured in autoclave as per the cure cycle [refer fig. 11],
The heating rate of l-2°C/minute is maintained from room temperature till 75±5°C followed by dwell of 40+5 minutes. Again heating rate of l-2°C/minute is maintained from 75°C to 135±5°C followed by dwell of 60+15 minutes. After the second dwell, cooling is carried out at the rate of 0.8-3°C/minute.
Pressure of 0.5 bar is maintained before the beginning of first dwell, 4 bar is maintained during the first dwell and pressure of 8 bar is maintained after finishing of first dwell. The lay-up is subjected to vacuum minimum 0.2 bar gauge pressure during the entire curing.
The part is then subjected to nod-destructive testing i.e. ultra sound test and CT-Scan. After due clearance of the cured component, drilling of holes is carried out as per design requirement.
The parts manufactured using this method, have been subjected to adequate tests in rig and in helicopter, and the outcome meets the design requirements.