1. TITLE OF THE INVENTION

Structural Base Frame Interface for Starter Engine installation in a Transport Aircraft.

2. FIELD OF INVENTION

The invention relates to mechanical engineering in general and in particular to structural base frame interface for starter engine installation in military transport aircraft.

3. BACKGROUNDOF THE ART

The existing gas turbine electric generator which starts the main engine of the transport aircraft has been replaced with a new gas turbine electric generator in order to overcome the impending issues of obsolescence, supply chain and maintenance. The mounting points and centre of gravity (c.g.) of the new electric generator are different from the existing one. A structural base frame interface has been invented to take care of mounting loads and c.g. issues arising from new gas turbine electric generator. The structural base frame interface has to withstand and cater for the loads on account of the gas turbine electric generator weight, c.g. and aircraft manoeuvre loads like g-load, vibration load and shock load etc.

PRIOR ART / CITATIONS

The electrical power generated through gas turbine electric generator engine is used to start the main engine of the military transport aircraft. The aircraft engine mounts are used to connect the gas turbine engine with aircraft structural frame. The different type of link elements are used to connect the engine with airframe. A thrust mount arrangement is discussed in the patent number EP 2221249A2 titled "A thrust mount arrangement for an aircraft engine”. The thrust mount contains mounting bracket, fixed mountable pylon and pair of thrust links.

Another patent titled “Aircraft Engine Mount" US 6330995B1 discuss about an aircraft engine mount for mounting an engine to an aircraft which includes mounting frame, link
joints and ball joints. The engine is mounted at both forward and aft ends by corresponding forward and aft mounts which carries various load of aircraft. The load typically includes vertical loads such as weight of engine, axial loads due to thrust and lateral loads due to roll and yaw. The prime link joined between the aircraft and engine casing transfers tensile and compressive loads along longitudinal axis.

The patent number US7021585B2 titled “Aircraft Engine Rear Mount with thrust links and boomerang-shaped lever” describes a turbine engine mount to a pylon of an aircraft and includes bracket arrangement and lever attachment. The lever includes a central part with two arms, and the bracket includes an integral attachment lug. The function of mounting means is to ensure the transmission of mechanical loads between the engine and aircraft structure.

The aircraft engine assembly mounting is explained in the patent number US20050230532A1 titled “Aircraft Engine Mounting”. The aircraft engine mounting assembly comprises a bracket arrangement with two plates located either side of an opening in the structural bypass duct. According to this, the aircraft engine mounting assembly includes a pair of inclined links extending from spaced locations on the engine core casing to a bracket arrangement located in the bypass duct. The engine mounting bracket arrangement will engage with the structural bypass duct to transmit engine loads into the airframe via the structural bypass duct.

The Engine mount configuration ensures that the transmission of loads between the engine and the aircraft structure explained in the patent number US20090314881A1 titled “Engine mount system for a turbofan gas turbine engine". The typical loads include weight of the engine, thrust, aerodynamics side loads and rotary torque about the engine rotational axis. The engine mount configuration also should absorb deformations to which the engine is subjected during different flight operations and the dimensional variations due to thermal expansion and retraction.
The above patents discusses about the engine mounts for different types of gas turbine engine which caters to the direct installation of the engine to the aircraft structure. In the present case, the existing mounting structure is not suitable for the new gas turbine electric generator engine. Also, the fleet size of the transport aircraft being sizeable, the operationalization of the fleet with the new gas turbine electrical generator would have to be managed in a phased manner. This means that the original as well as the new engine would be interchangeably used by the fleet. Hence, necessitating the design of a structural interface base frame, which would be universal in nature, i.e that which allow for easy interchangeability and mounting of the original engine as well as the new gas turbine electrical generator.

4. SUMMARY OF THE PRESENT INVENTION

The main objective of present invention is to design a new structural interface frame which will connect the aircraft frame one side and the electric generator engine mountings on the other side while also taking care of mounting loads due to weight, c.g. and manoeuvres. The interface structural base frame is a light weight, integral structure with l-section as cross section and machined out from high strength aluminium alloy
plate. The aluminium alloy plate is solutionised and aged to achieve high material strength.

The objective of the invention is realized by the following technical scheme:

The structural interface base frame is designed with l-section as cross sectional bars. The l-sections has got better load bearing capacities and designed to resist bending, vibration, yield and helps to optimise the structural base frame weight. The base frame is designed to take care of the shift in weight and c.g of the new gas turbine electrical starter engine. The high strength aluminium alloy plate is machined with sectional cutouts to optimise the weight. It has been designed with required number of installation holes to attach into aircraft frame and required number of mounting holes for starter engine installation.

5. BRIEF DESCRIPTION OF DRAWINGS

Reference is now made to the accompanying figures in which:

Fig 1: is an isometric view of the structural base frame with Gas Turbine Electric Generator Engine

Fig 2: is an isometric view of the structural base frame along with aircraft frame Fig 3: is a detailed isometric view of the structural base frame

6. DETAILED DESCRIPTION OF INVENTION

Fig 1 illustrates the gas turbine electric generator engine (1)for starting the main engine of a military transport aircraft along with structural interface base frame. The power generated from gas turbine electric generator is used to start the main engine. The structural interface base frame (2) is used to mount the electrical generator engine using the bolt holes (4). The base frame is fixed on the aircraft frame (5) using another set of bolt holes (3).
Fig 2 illustrates the structural interface base frame (2) along with aircraft frame (5). The interface base frame is machined with cut-outs (6) to reduce the weight. The engine mount loads are transmitted to the interface frame through mount holes (4) and further it is transmitted to the aircraft frame through installation holes (3)

Fig 3 is a isometric view of the structural base frame. It is a symmetrical structural component with respect to the centre bar section (8), through which the engine mount loads are equally distributed to the mount holes (4) on both sides. The sectional cutouts (9) are equal and axi-symmetric with respect to centre bar section.

The structural geometry of the interface base frame with cut-outs, l-section, centre bar are optimised by carrying out structural analysis using finite element methods. The base frame is subject to engine mount loads, aircraft manoeuvre loads like g-loads, random vibration spectrum loads and shock loads. The newly designed interface base frame has been analysed for all type of operational load conditions. The structural frame is also rig tested for all load conditions. The geometrical and NDT tests have been carried out after the rig tests and found satisfactory.

BENEFITS

The following benefits are drawn from newly design structural interface base frame.

a) The newly designed structural base frame interface serves as an interface structure for the new gas turbine electric generator engine and aircraft frame.

b) The design allows for a universal engine mounting arrangement of the gas turbine electrical generator, i.e drop in replacement of the new gas turbine electrical generator can be realised in place of the old one, without modification on the aircraft.

c) With this simplified design, the main engine start with the new gas turbine electric generator became a feasible option and has been realised.
d) It takes care of weight, c.g. and lateral moment loads due to new gas turbine electric generator engine.

e) It takes care all mount loads and aircraft manoeuvre loads for all operating conditions.