Description:1 Title of invention
Engine drain collector tank for a fighter aircraft

2 Field of invention
The present invention relates to mechanical engineering in general and particular to design of engine drain collection devices as a part of aircraft structural engineering in fighter aircraft with buried engines. The present invention is used to store and dispose engine drain fluids that get discharged, when the engine is shutoff after flight or after engine ground run or after a false start.

3 Background of invention
In a typical fighter aircraft, engine drain fluids are discharged by aircraft engine, when the engine (100) stops after Engine Ground Runs (EGR) or after false starts or after the end of routine flights. These engine drain fluids used to be disposed with help of a drain pipe (103) as shown in Fig 1, which extends outside the aircraft outer contour. A compressible bellows (101) seats between the engine which is in a compressed state between the drain pipe (103) and the engine (100) as shown in Fig 1.
Whenever, the engine (100) is shut off as mentioned in the above cases, the discharged hot engine drain fluids from aircraft falls on the runway and react with the bitumen of the aircraft runways. If parked in the hanger, it reacts with epoxy based floor paints of Hangar floors causing damage to them. The spillage of these fluids may also cause safety hazard to maintenance personnel, when spilled on the aircraft hangar floors as the fluids cause slippery floors and small fumes due to their reaction with epoxy paint of the floors. The practice is not environmental friendly as these fluids gets discharged without any control on disposal.
In the prior art as shown in Fig.1, Engine drain pipe (103) extending out of aircraft engine bay door (102) has the following drawbacks:
i. Damage to floors, aircraft runways and hangars.
ii. Safety hazards to the aircraft personnel.
iii. Environmental hazards.
iv. Increased aerodynamic drag due to extended drain pipes (103) out of aircraft contour.

4 Summary of the present invention
The primary objective of the present invention is to provide a means to collect drain fluids that are drained from aircraft engine (100) when shut off after engine ground runs, false starts or after completion of flight. The present invention facilitates periodic disposal of collected engine drain fluids without adversely affecting the life of the runways or creation of oil puddles & potential fumes on the hangar floors. It also ensures the safety of maintenance personnel by prevention of skidding due to spillage of fluids in hangars and exposure to hazardous fumes.
The design of an engine drain collector tank (104) to collect and dispose the engine drain fluids varies depending on the type of aircraft whether it is a commercial or a military aircraft, based on type of engine, whether it is turboprop or turbofan. The present invention of engine drain collector tank (104) is specific to a typical Military fighter aircraft, where the turbofan engine (100) is buried in the aft fuselage. The volume of the engine drain collector tank varies based on requirements and is determined by multiplying the “maximum volume of the engine drain fluid collected per flight” and the “Number of flights before disposal” as per maintenance requirements of customer.

5 Brief description of drawings
Fig.1 illustrates the prior art of the invention with typical location of an engine drain pipe (103) along with compressible bellows(101) between the engine(100) and engine bay door(102) as used in a fighter aircraft.
Fig.2 illustrates the present invention of engine drain collector tank (104), which is located between the engine (100) along with compressible bellows (101) and the engine bay door (102) in a fighter aircraft.
Fig.3 illustrates a typical engine drain collector tank (104) fabricated with formed top and bottom corrosion resistant steel alloy sheets (105), (106). It comprises of flanged drain pipe with internal threads (107) at the top, drain plug bracket with internal threads (108) at the bottom and flanged over flow pipe (109). Corrosion resistant steel brackets (110) at the forward and rear sides of the engine drain collector tank (104) with counter sunk bolts & nuts (111) used to install the engine drain collector tank (104) between the compressible bellows (101) and the engine bay door (102).
Fig.4 illustrates the cross sectional details of the engine drain collector tank (104) showing all the components along with flush drain plug valve(112) at the bottom, which is used to drain the engine drain fluids from the bottom and plurality of hexagonal head bolts(113) to connect engine drain collector tank (104) to compressible bellows(101).

6 Detailed description of invention
Refer Fig.2 for the location of the engine drain collector tank (104) between the engine (100) along with compressible bellows (101) and engine bay door (102) in a fighter aircraft.
Refer Fig.3 for the details of the present invention of engine drain collector tank (104) which comprises of formed top and bottom corrosion resistant steel alloy sheets (105), (106), flanged drain pipe with internal threads (107), drain plug bracket with internal threads (108), flanged overflow pipe (109) and plurality of corrosion resistant steel brackets (110).
Refer Fig.4 for the cross sectional details of the engine drain collector tank (104) along with view –AA taken from Fig.2 and sectional views in the interface areas of the engine drain collector tank (104) with compressible bellows at the top and spring loaded flush drain plug valve (112) at the bottom. Section view BB shows the detail of the interface of drain plug bracket with internal threads (108) with flush drain plug valve (112) at the bottom of the tank. Section view CC shows the detail of the interface of flanged drain pipe with internal threads (107) with compressible bellows (101) at the top of the tank. View DD shows the flush drain plug valve (112) at the bottom of the tank.
Engine drain collector tank (104) is fabricated from appropriately formed top and bottom corrosion resistant steel alloy sheets (105), (106) and welded at the top and bottom along the edges to create the sealed enclosure of the drain tank of required volume. Welding fabrication method minimizes the probability of leakage as there are no holes as in alternative joining methods of riveting or bolting which act as potential sites for leakage. Flanged drain pipe with internal threads (107) is welded to the top corrosion resistant steel alloy sheet (105). Flanged overflow pipe (109) and drain plug bracket with internal threads (108) are welded to the bottom steel alloy sheet (102) before welding of the bottom sheet (106) to the top corrosion resistant steel alloy sheet (105), which form the engine drain collector tank (104).
The function of flanged drain pipe with internal threads (107) at the top of the engine drain collector tank (104) is to ensure a fluid tight passage to the drain fluids from compressible bellows (101) to the inside of the engine drain collector tank (104) without spillage at the interface of compressible bellows (101) and the top face of the engine drain collector tank (104). The function of drain plug bracket with internal threads (108) at the bottom of the tank (104) is to provide a fluid tight connection to spring loaded flush drain plug valve(112) at the bottom of the engine drain collector tank (104) from where the drain the fluids are periodically collected by maintenance personnel. The function of flanged over flow pipe (109) is to spill the fluids out of the tank after reaching a specified level in the tank (104) after of specified flights in cases where maintenance personnel overlook the disposal of the engine drain fluid. This over flow is only a mechanism not exercised often but only in case of a rare maintenance oversight. The flanged drain pipe (107) and drain plug bracket (108) are machined members made of corrosion resistant steel whereas the flanged over flow pipe (109) is a corrosion resistant steel pipe with a welded steel flange. The Plurality of corrosion resistant steel brackets (110) are welded to the collector tank (104) at the forward and aft sides which are then connected to the engine bay door (102) through removable bolts & nuts (111). Corrosion resistant steel brackets (110) are fabricated by welding of formed corrosion resistant steel sheets.
A unique feature of the tank is the flanged drain pipe with internal threads (107) which is connected to the flange of the compressible bellows (101). This flanged drain pipe with internal threads (107) is machined out of corrosion resistant steel alloy billet and threads are cut in the flange to match with the pitch of the fastener hole locations existing in the compressible bellows (101). Drain plug bracket with internal threads (108) mounted at the bottom of the engine drain collector tank(104) has the similar advantage of preventing leakage on to the engine bay door(102).
This type of connection using internal threads in flanged drain pipe (107) at the top of the tank (104) and internal threads in drain plug bracket (108) at the bottom of drain collector tank (104) at the interface regions is significant as it prevents the possible leakages near fastener joints. In prior art, a plurality of sealed anchor nuts is used in drain pipes connecting to compressible bellows (101), which leads to the leak at their lug areas and the use of a sealant is mandatory to avoid leakage. High temperature resistant sealants or gaskets are to be used in these cases for arresting the leakage as the location of the engine drain is a high temperature zone. Further, when the sealed anchor nuts installed inside the tank are damaged, the welding of the top corrosion resistant steel alloy sheet (105) and bottom corrosion resistant steel alloy sheet (106) has to be removed for repair and to be re-welded, which is cumbersome and not advisable.
The present innovation of drain collector tank (104) uses a unique and innovative feature of parts with Internal tapped threads at interfaces which addresses the problems of potential leakages into the engine bay area without the use of these high temperature resistant sealants or gaskets. Further it stores the engine drain fluids and allow these fluids to be disposed safely during servicing after flight without any causing environmental or safety hazard.

Drawing Numerals:
Sl.No. Description
100 Engine
101 Compressible bellows
102 Engine bay door
103 Drain pipe
104 Engine drain collector tank
105 Top corrosion resistant steel alloy sheet
106 Bottom corrosion resistant steel alloy sheet
107 Flanged Drain Pipe with internal threads
108 Drain plug bracket with internal threads
109 Flanged over flow pipe
110 Corrosion resistant steel brackets
111 Countersunk bolts & nuts
112 Flush drain plug valve
113 Hex head bolts , C , C , C , C , Claims:We claim:
1. An engine drain collector tank (104) for a fighter aircraft that consists of an engine (100) with compressible bellows (101) and an engine bay door (102), characterized in that, the tank (104) is designed for storage and disposal of the engine (100) drain fluids, the tank (104) is located between the engine (100) with the compressible bellows (101) at the top and the engine bay door (102) at the bottom with a plurality of counter sunk bolts & nuts (111) at the compressible bellows (101) attachment and a plurality of hex head bolts (113) at the engine bay door (102) attachment, and the engine drain collector tank (104) is comprising:

a top corrosion resistant steel alloy sheet (105) and a bottom corrosion resistant steel alloy sheet (106) that are welded at the top and bottom respectively, along the edges to create the sealed enclosure of the drain collector tank (104) of required volume;

a flanged drain pipe with internal threads (107) that is welded to the top corrosion resistant steel alloy sheet (105) to ensure a fluid tight passage to the drain fluids from compressible bellows (101) to the inside of the engine drain collector tank (104) without spillage;

a drain plug bracket with internal threads (108) that is welded to the bottom steel alloy sheet (102) to provide a fluid tight connection to a spring loaded flush drain plug valve (112) at the bottom of the engine drain collector tank (104), from where the fluids are drained periodically and collected by maintenance personnel;

a flanged over flow pipe (109) that is welded to the bottom steel alloy sheet (102) to spill the fluids out of the tank (104) after reaching a specified level in the tank (104), if the maintenance personnel overlook the disposal of the engine drain fluid after specified flights; and

a plurality of corrosion resistant steel brackets (110) that are welded to the collector tank (104) at the forward and aft sides which are then connected to the engine bay door (102) through removable bolts & nuts (111).

2. The engine drain collector tank (104) for storage and disposal of engine drain fluids, as claimed in claim 1, wherein, the flanged drain pipe with internal threads (107) is machined out of corrosion resistant steel alloy billet and threads are cut in the flange to match with the pitch of the fastener hole locations existing in the compressible bellows (101) to prevent leakage on to the engine bay door (102). ; similarly the drain plug bracket (108) at the bottom of drain collector tank(104) at the interface regions is significant as it prevents the possible leakages near fastener joints.

3. The engine drain collector tank (104) for storage and disposal of engine drain fluids, as claimed in claim 1, wherein, the type of connection using internal threads in flanged drain pipe (107) at the top of the tank (104) and internal threads in drain plug bracket (108) at the bottom of drain collector tank (104) at the interface regions are preventing the leakages near fastener joints.