NO855162L - COVER FOR FLIGHTS REFERENCE UNIT IN AIR. - Google Patents

Description

Technical field of the invention

The invention relates to an enclosure for receiving an inertial reference unit (IRU) (hereinafter referred to as IRU unit) for aircraft and, more particularly, it relates to a dip-bnazed IRU enclosure having a rigid chamber with shock-isolating mounting means to receive an inertial sensor unit (ISA)

(hereinafter referred to as ISA unit) and a chamber which includes a thermal mass for cooling electronics belonging to the IRU unit.

Background for the invention

An IRU unit is an instrument on board an aircraft -•'.or other means of access, where the instrument produces output signals relating to the position of the aircraft. The position-related output signals from the IRU unit can be used in connection with the aircraft's flight, either for direct flight of the aircraft to a new destination, or to provide information about the aircraft's position to the flying personnel.

In practice, the IRU unit is contained in an enclosure or box, which can be removable mounted to the aircraft's... The box provides space for both the inertial sensors that are used to register position changes, as well as for associated electronics for processing the sensor signals and providing navigation signals. Typically, the inertial sensors include a group of three gyros, each of which is placed in relation to one of three mutually right-angled axes. The output signal from each gyro is a signal that is related to the angular displacement of the gyro around its respective axis. In modern applications, conventional mechanical gyros, of the rotating wheel type, are being replaced by ring laser gyros. Linear acceleration is registered by a triad of three accelerometers, each of which is aligned in relation to one of the three coordinate axes. Each accelerometer produces an output signal that corresponds to the aircraft's acceleration along its respective axis.

An enclosure for an IRU must provide shock isolation for the inertial sensors and component cooling. The mounting device for the inertial sensors must be designed so that shocks or other vibrations applied to the IRU housing are not transmitted to the sensors, thereby avoiding incorrect sensor signals and possible destruction of the sensors. The electronics connected to the IRU unit generate heat during operation and must be cooled. For the IRU using ring laser gyros, additional cooling must be provided to remove heat radiating from the laser units.

The conventional method of providing an enclosure for aircraft inertial reference systems is to place the inertial sensors and associated IRU electronics in a standard size box. The Aeronautical Radio Incorporated (ARINC) standard enclosure size for an IRU unit is currently a 10 MCU (modular concept unit). Standard sizes for the MCU unit are in reality identical to the previous ATR (Air Transport Radio) standards. An MCU unit is effectively equal to a small size 1/8 ATR package, so a 10 MCU box corresponds to a small size 1 1/4 ATR package. Accordingly, a standard IRtJ unit of 1 1/4 ATR size has the dimensions: width = 32.23 cm, height = 194 cm, and depth = 32.4 cm. A 1 1/4 ATR size box has been found to be of sufficient size to contain the shock-isolating mounting device for the inertial sensors as well as to provide adequate space for the various electronic circuit boards to allow convection cooling of the boards by means of ventilation holes in the housing and , if necessary, pressurized air cooling.

While commercial and certain military aircraft have sufficient space set aside for electronic instrumentation to accommodate a 1 1/4 ATR size IRU enclosure, space in smaller aircraft is very limited and cannot accommodate such a large enclosure. Moreover, it is the case that while commercial aircraft usually use fans for to cool the electronic instrumentation by means of convection, such cooling fans are not usually provided in smaller aircraft.

A requirement for correct performance of the IRU unit is that the reference coordinate axis of the inertial sensors is exactly in line with corresponding axes in the aircraft. This instrument/aircraft alignment has conventionally been provided by mounting the IRU enclosure to a tray section which in turn has been attached to, and aligned with, aircraft equipment. Such tray sections typically include two alignment pins placed far apart and which engages with alignment holes provided at the rear of the IRU enclosure. A third alignment pin is provided at the front of the drawer section and this engages a hole provided in a flange attached to the front of the lower surface of the IRU enclosure. The large distance between the two rear pins ensures the necessary alignment of the casing in relation to the aircraft through the alignment of the drawer section. An airtight air passage is provided between the upper surface of the drawer section and the lower surface of the IRU enclosure to allow cooling air to flow through the enclosure vents.

Summary of the invention

The present invention relates to an improved enclosure for an IRU unit for aircraft. The enclosure can be designed in a size that is significantly larger than a standard-sized 1 1/4 ATR box, and can still provide sufficient shock insulation for the inertial sensors and sufficient cooling for the associated IRU electronics.

The improved IRU enclosure mounts to a mounting tray section in an aircraft train has uniquely positioned alignment pins to ensure a firm alignment of the enclosure. The tray section is designed to facilitate heat flow from the enclosure to the tray section and from the tray section to the exterior of the aircraft.

Briefly described, according to the invention, it is provided

an enclosure to accommodate an aircraft IRU. The IRU unit includes an ISA unit which comprises position sensors, and an electronic circuit module for processing data from these position sensors and providing navigation signals. The enclosure includes a dip-soldered framework. The framework includes a chamber to accommodate the ISA unit and a chamber to accommodate the electronic module. The walls constituting the ISA chamber have a predetermined stiffness to maintain the ISA chambers in a predetermined alignment in response to forces acting on the framework. For-

step by step, the chamber for the ISA unit, which is provided for in the framework, is pentagonal in that it has an open surface that is used for the ISA unit to be accessible;-. A cover plate is fitted over and covers the open face and is attached to the framework by removable fasteners designed to secure

a predetermined stiffness of the cover plate to the ISA chamber interface.

The ISA is mounted to the walls of the ISA chamber by means of a plurality of shock-absorbing mounting devices, each shock-absorbing mounting device having a predetermined elasticity so that the ISA is truly isolated from shocks to which the framework is subjected. The shock-absorbing mounting means are preferably located so that the center of elasticity of each shock-absorbing mounting means is aligned with the center of gravity of the ISA unit. In the preferred con- . construction, the shock-absorbing mounting devices are located at opposite corners of the ISA unit.

It is preferred that the displacement of the ISA unit relative to the ISA chamber is controlled by a caging device. This suspension device includes a pair of pins where each pin is attached to and protrudes from opposite sides of the ISA unit. Each pin is received inside

in the hole of an elastic eyelet attached to a wall of the ISA chamber, and where the pins and eyelet holes are sized and aligned to form a predetermined "clearance" between the surface of each pin and the eyelet hole so that when a predetermined shock is transmitted to the ISA unit at least one of the pins engages its corresponding eyelet to thereby limit the movement of the ISA unit relative to the ISA chamber.

It is also preferred that the surface of each eyelet is predetermined distance from the surface of the side wall of the ISA chamber opposite the eyelet so that predetermined displacement of the ISA unit relative to the ISA chamber along the longitudinal axis of the pin causes the eyelet surface to engage with the opposite surface of the ISA unit, thereby on the same means of limiting the movement of the ISA unit relative to the ISA chamber.

The module space for electronics in the dip-soldered framework preferably includes four side walls where at least one of the side walls has a heat-dissipating mass designed as an integral part of the wall. The electronic module is mounted to the heat-dissipating mass in order to thereby promote conduction transfer of heat from the electronic module to the heat-dissipating mass.

For the preferred embodiment where the electronics module consists of a plurality of individual circuit boards, opposite side walls of the electronics module chamber are provided with parallel heat dissipating flanges which are integral with the side walls. The heat-dissipating flanges are designed so that the circuit boards are supported between opposite heat-dissipating flanges. The circuit boards are mounted so that they rest against opposite heat-dissipating flanges so that heat from the circuit boards is transferred by wire to these.

Preferably, the component side of each circuit board is equipped with a thermally conductive surface, such as a metallic copper overlay, and with this thermally conductive surface mounted so that it rests against the heat dissipating flanges.

For the preferred embodiment, the electronics module includes a plurality of circuit boards which are electrically interconnected by means of a mother panel or backplate. A back plate is fitted to the enclosure by means of a recessed lip-shaped edge formed integrally with the framework around an open surface thereof. The recessed lip-shaped edge is designed so that the support edges of the back plate rest against the lip-shaped edge. A panel covers the open face of the enclosure, and fasteners attach the panel to the enclosure. A soft pad, preferably formed of rubber, is shaped so that it can be placed between the panel and the backplate so that when the panel is attached to the housing, the soft pad presses the backplate into contact with the connection ends of the circuit boards. The soft cushion insulates the back plate from impacts on the housing.

The enclosure can be combined with a mounting tray section where the mounting tray section is adapted for predetermined alignment with, and attachment to, an aircraft. The tray section is preferably L-shaped when viewed from the side, and has a horizontally arranged portion and a vertical portion sorrv extending from one end of the tray section. The vertical part has two alignment pins that protrude above the horizontally arranged part. The housing includes a rear end portion which is provided with two holes, the holes being located and sized to receive the alignment pins when the housing is mounted to the drawer section. The alignment holes are placed in diagonal corners of the enclosure to thereby ensure rigid alignment of the enclosure in relation to the drawer section and the aircraft.

The drawer section preferably includes a plurality of heat-conducting soft fingers which protrude so that the fingers rest against predetermined locations on the housing when the housing is mounted to the drawer section, thereby facilitating heat transfer from the housing to the drawer section. The drawer section is in turn preferably equipped with thermally conductive feet to conduct heat from the drawer section to the aircraft. The walls of the electronics module chamber are preferably equipped with heat-reflecting surfaces to minimize the radiation of heat from the walls of the electronics module. All other wall surfaces in the enclosure are equipped with heat-radiating surfaces to thereby facilitate heat radiation from the enclosure to the surroundings.

Cartoon characters.

Figure 1 is a perspective drawing showing the assembly of the preferred enclosure for the IRU unit and the matched relationship between the enclosure and the aircraft tray section. Figure 2 is an exploded perspective drawing showing the component parts of the IRU framework before dip soldering. Figure 3 is a side section showing a partially assembled IRU enclosure. Figure 4 is a side section showing the shock mounting system and suspension system associated with the ISA unit. Figure 5 is a side cross-section showing the ISA unit's suspension system.. i Figure 6 is an expanded side cross-section of the IRU enclosure's electronics module chamber and which illustrates how the mounting of the back plate (motherboard) is shock-insulated. Figure 7 is a detailed vertical drawing showing the assembly of the circuit boards in the electronic module.

Figure 8 is a front view showing the IRU enclosure.

Figure 9 is the IRU enclosure seen from behind.

Detailed description.

Figure 1 is a perspective drawing showing the assembly of the IRU unit generally indicated at 10, and the matched relationship between the IRU housing and the associated mounting drawer section 12 for mounting to aircraft.

The principal mounting structure for the IRU unit is a dip-soldered framework 14. The dip-soldered framework 14, the construction of which is described in detail with reference to Figure 2, is generally rectangular in shape and has a rectangular planar top surface 16, a rectangular planar bottom surface 18 and a rectangular planar back surface 20. The front surface 22 of the framework 14 includes vertically aligned heat dissipating ribs 24

and a recessed surface 26 provided with pairs of brackets 28, 30 to receive alignment pins. Figures 8 and 9 are floor plans of the front surface 22 and the back surface 20, respectively.

Different partitions delimit different chambers in the dip-soldered framework 14. A relatively thin vertical wall 32 separates the power supply chamber, indicated generally at 34, from a chamber for signal processing circuits, indicated generally at 36. A relatively thick vertical wall 38 separates the chamber 36 for the signal processing the circuit from the chamber 40 of the ISA unit, which is shown receiving the ISA unit 42.

A vertical relatively thick wall 44, which has a Lf.-shaped top bracket part 44a, separates the ISA chamber 40 from the chamber for pins and receiver holes, indicated generally at 46.

The bottom surface 18 of the framework 14 is designed with a relatively thick, raised floor part 48 through the ISA chamber 40 and the chamber 46 for pins and receiver holes.

As discussed in greater detail with reference to Figure 3, the relatively thick side walls 38, 44, and the thick raised floor portion 48 form a rigid ISA chamber 40 that accommodates the ISA unit 42.

A pair of holes 50, 52 are formed through the top surface 16 of the framework 14 and, as described in greater detail with reference to Figures 3nqg 4, provide a means of securing the ISA assembly 42 within the ISA chamber 40. A corresponding pair mounting holes (not shown) are made through the bottom surface 18 of the framework 14.

The signal processing electronics for the inertial reference system are provided on eight circuit boards, designated collectively at 60. The circuit boards are conventionally constructed and have components on one side and interconnecting metal strips on the opposite side. To facilitate the cooling of the components, the component side is equipped with a thermally conductive surface, preferably copper. Integral with the lower surface of the signal processing circuit chamber 3 6 is a plurality of heat dissipating flanges, collectively designated at 62. Integral with the upper surface of the signal processing circuit chamber 3 6 is a set of heat dissipating flanges, collectively designated at 64. The lower and upper heat dissipative flanges 62, 64 are aligned perpendicular to the longitudinal axis of the framework 14, and are vertically aligned relative to each other so that the circuit boards 60 can be received within the slots formed between adjacent heat dissipative flanges 62, 64 for vertical support inside the chamber 36 for the signal processing circuit. A plurality of mechanical circuit board guides 66 associated with the lower heat dissipative flanges 62 and a corresponding plurality of circuit board guides 68 associated with the upper heat dissipative flanges 64 secure the circuit boards 60 within the signal processing circuit chamber 36, with the thermally conductive surfaces of the circuit boards 60 resting on the opposite surfaces of the heat-dissipating flanges 62, 64. In this way, the heat-dissipating flanges 62, 64 form a thermal mass that allows heat conduction away from the circuit boards 60.

The discussion with reference to Figures 3 and 7 illustrates the manner in which the circuit board guides 66 and 68 press the thermally conductive surfaces of the circuit boards 60 against opposing surfaces of the heat dissipative flanges 62 and 64.

The interconnections between the circuit boards 60 are provided by a mother panel or back plate 70. The back plate 70 is attached to the open surface furthest away from the chamber 36 for the signal processing circuit by means of a cover plate 72 which is designed to cover the chamber 3 6 for the signal processing the circuit and the open face of the chamber 34 for the power supply. Screws fix the cover plate 72 in position on the framework 14. A soft shock-absorbing pad 74 is placed between the cover plate and the back plate 70. In this way, shock and vibration energy applied to the back plate 70 through the framework 14 is dissipated in the pad 74. The assembly of the back plate 70, the cover plate 72 and the soft pad 74 is shown in greater detail with reference to Figure 6.

In a similar way is a soft pillow. 75 placed between the cover plate 102 and the open ends of the circuit boards 60 to provide shock isolation for the circuit boards 60. The circuit boards 60 are equipped with connector ends 60a (or connector pieces as can be better seen with reference to Figures 3 and 7), which are adapted corresponding connector pieces (shown with reference to figures 3 and 7) on the surface of the back plate 70. Metallic circuit strips on the back plate 70 form the electrical connections between corresponding connector pins.

A slot 80 is formed through the wall 38 which allows a cable to be connected between the chamber 36 for the signal processing circuit and the ISA chamber 40, which can be better seen with reference to figure 3.

The circuit for the power supply for the IRU unit is provided on a pair of printed circuit boards, indicated collectively at 90. A pair of lower heat dissipating flanges 92 are integrally formed with the framework 14, transverse to the longitudinal axis thereof, on the lower surface of the chamber 34 for the power supply. A pair of aligned heat dissipating flanges 94 are integrally formed with the framework 14

on the upper surface of the chamber 34 for the power supply.

The power supply circuit boards 90 are conventionally designed with the components on one side and metallic circuit strips on the opposite side. As with the circuit boards 60, the component side of the power supply circuit boards 90 includes a thermally conductive surface, preferably a metallic copper overlay, which is used to conduct heat away from the components. The lower and upper heat-dissipating flanges 92,

•in

94 is arranged so that the circuit boards 90 for the power supply can be vertically supported inside the chamber 34 for the power supply. A pair of lower circuit board guides 96 adjacent to the lower heat-dissipating flanges 92, and a pair of upper circuit board guides 98 adjacent to the upper heat-dissipating flanges 94 are used to hold the circuit boards 90 in position, so that the thermally conductive layer on the component side of the circuit boards 90 rests against opposite surfaces of the heat-dissipating flanges 92, 94. Thus, the heat-dissipating flanges 92, 94 form a thermally conductive mass which is used to dissipate heat from the components on the circuit boards 90.

In the same way as with the circuit boards 60, interconnections have been provided between the circuit boards 90 for the power supply at the back plate 70.

A transverse channel 100 is formed below the chamber 34 for the power supply. The transverse channel 100, which is better shown with reference to Figure 3, provides a cavity and through this a cable can be passed to connect the chamber 34 for the power supply and the chamber 36 for the signal processing circuit.

The circuit boards 60 for the signal processing and the circuit boards 90 for the power supply are held in position by means of a cover plate 102. The cover plate 102 is designed to cover the open surface of the chamber 3 4 for the power supply, the chamber 3 6 for the signal processing circuit, the ISA chamber 40 and. the chamber 46 for the pin and receiver hole. The cover plate 102 is held in position by means of a plurality of screws, such as screw 104, which are received inside threaded holes (not shown) in the framework 14. A very short distance between these screws, such as screw 104, is used around the ISA -the chamber 40 to ensure a rigid connection between the cover plate 102 and the ISA chamber 40 to improve the structural integrity and rigidity thereof.

A cover plate 110 is mounted over the bottom surface 18 of the framework 14, which is better seen in Figure 3. A gap between the cover plate 110 and the bottom surface 18 allows a connecting electrical cable to be drawn between the ISA chamber 40, the chamber 46

for pins and receiver holes and the chamber 3 6 for the signal processing circuit.

A handle, indicated generally at 120, includes a hand grip 122 and projecting arm portions 124, 126. That is. provided for holes 128, 130 in the angular parts of the arms 124, 126. The handle 120 is mounted by means of holes 128, 130 in the handle and rotatable pins (not shown) to the corresponding pin bracket pairs 28, 30, whereby the handle 120 is rotatably mounted to the framework 14 .A pair of locking arms, such as locking arm 131, are rotatably mounted to the arm portions 124, 126 and include gripping portions, such as gripping portion 131a, which snap together with receiving surfaces formed in the front surface 22, thereby locking the housing 10 to the drawer section 12.

The receiving tray section 12 is generally L-shaped, as can be seen from the side view, and has a generally horizontal support surface 130 and a vertical standing surface 140 projecting from the rear end of the tray section 12. On each side and in close proximity of on the horizontal support surface 130 are flanges 132, 134 spaced to accommodate the width of the housing 10 for the inertial reference system. Protruding upward from the horizontal support surface 130 is a plurality of soft thermally conductive fingers, such as fingers 136. The fingers, preferably formed of beryllium cups, are arranged in rows perpendicular to the longitudinal axis of the horizontal support surface 130" and are positioned to contact selected portions of the bottom surface 18 of the enclosure 10, thereby providing a path for heat to flow from the enclosure 10 through the fingers 136 to the drawer section 12. A pair of U-channel shaped feet 140, 142 are mounted to the bottom surface of the drawer section 12 The feet 140, 142 are formed of a thermally conductive material, such as aluminum, and are designed to transfer heat from the mounting tray section 12 to the adjacent aircraft surface (not shown).

From the vertical surface 140 of the drawer section 12, a pair of alignment pins 150, 152 protrude. The alignment pins 150, 152 are aligned in parallel, and protrude above the horizontal support surface 130. Alignment holes (shown in Figure 9) which are provided in the rear surface 20 of the housing 10, the alignment pins 150, 152 are fitted on the housing 10 and slide into place on the drawer section 12.

To ensure that the housing 10 is held rigidly in a fixed aligned position with the tray section 12, the alignment pins 150, 152 and corresponding alignment holes in the housing are spaced as far apart as possible in diagonal corners of the rear surface 20.

A female connector 160 is mounted to the vertical surface 140 in line with a protruding male plug (not shown) which projects from the lower rear surface 20 of the enclosure. Electrical connections between the aircraft and the enclosure are provided through connector 160.

An eyelet 162 is provided through a:!:flange 164 projecting from the side flange 132, and this makes it possible to extend a cable (not shown) from the aircraft to the female connector 160.

A projecting arm 166 from the front surface of the drawer section 12 includes a cross pin (not shown) which is adapted to the handle 120, which is better shown with reference to Figure 3.

To further increase the cooling of the components. in the IRU unit, and with reference to Figure 1, the inner walls of the chamber 36 for the signal processing circuit and the chamber 34 for the power supply are coated with bright metal color which is heat reflective. In this way, the heat in the walls of the chamber 3 6 for the signal processing circuit components and the chamber 3 4 for the power supply is not radiated back to the electronic components on the respective circuit boards 60, 90. All other surfaces of the enclosure for the IRU unit are otherwise painted black. These black surfaces promote the radiation of heat from the enclosure to the surroundings.

As discussed above, the framework 14 is a whole unit, formed by dip soldering. Figure 2 is an exploded drawing of the framework 14, showing the individual component parts before the dip soldering is carried out.

Referring to Figure 2, the individual component parts of the framework 14 include a top surface part 16 and a bottom surface part 18, both of which are substantially rectangular plates. A raised floor 48' projects upwards from the lower surface portion 18. The raised floor 48 defines the bottom of the ISA chamber (42 in Figure 1). A central cutout 201 through the raised floor 48 allows connection cable to be fed in and out of the ISA chamber.

Holes 205, 206 are provided through the raised floor 48 and these allow the mounting of shock absorbers to support the ISA unit, which is better shown with reference to

figures 3 and 4.

A lower set of parallel heat dissipating flanges 62 is formed in the chamber portion of the signal processing circuit which constitutes the bottom surface 18. A transverse channel 208 separates the heat dissipating flanges 62 from the raised floor 48, and this channel 208 is constructed to receive the lower portion 38a of the wall 38. The lower part 38a of the wall 38 includes a transverse slit, indicated generally by arrow 210, which is used to pass an electric cable (not shown) through a hole in the chamber part for the signal processing circuit which constitutes the bottom plate 18.

A transverse slot 210 separates the raised floor 48

in the ISA chamber from the raised floor of the chamber (46 in Figure 1) for pins and receiver holes. This slot is constructed to receive the bottom edge of the wall 44 which separates the ISA chamber from the pin and receiver hole chamber. A cut-out 212 in the central rear part of the bottom surface 18 and the raised

floor 48 provides clearance for the electrical connector (not shown) mounted there. Clearance for this contact is also provided by a rectangular cut-out 214, which is provided in the side wall 44.

The rear surface part 20 is provided with a cut-out 130, together with mounting hole pairs 131, 132, for mounting and securing the electrical contact. A pair of diagonally positioned alignment holes 134, 136 in the rear surface portion 20 are designed to mate with the alignment pins (150,152

in figure 1) which protrudes from the mounting drawer section (12 in figure 1).

Aligned with the alignment hole 136, a hole (not shown) is formed in the opposite face 220 of the raised floor portion 48 of the bottom surface 18. A hole, (not shown) is formed

in

in a block 222 which is attached to the bottom surface of the top surface portion 16, and is aligned with alignment hole 134.

A top wall 230 for the ISA chamber projects downward from the top surface 16. In addition, parallel heat dissipative flanges 64 are formed on the lower surface of the top surface 16 and these flanges 64 are aligned with the lower heat dissipative flanges 62. A slot 234 separates the top wall 230 for The ISA unit from the heat dissipating flanges 64. The width of the transverse slot 234 is designed to receive the top surface 38b of the side wall 38. Centrally located in the side walls 38, 44 are provided holes 240, 242 which, as will be more clearly understood with reference to Figure 4, receive eyelets which form part of the suspension system for the ISA unit.

The rear or fifth wall of the ISA chamber is formed by a generally rectangular plate 244. The plate 244 also covers the fifth side of the chamber (46 in Figure 1) for pins and receiver holes.

A wall 32 separates the chamber (36 in Figure 1) for the signal processing circuit from the chamber (34 in Figure 1) for the power supply. A lower L-shaped bracket 250 forms the transverse channel (100 in Figure 1) and has a front surface which includes the recessed portion (26 in Figure 1) in the front surface 22. Two pin receiving bracket pairs 28, 30 are formed in the recessed the front surface 26 of the bracket 250 and, as described above, provides a means for mounting a handle to the framework 14. A hole 252 through the recessed surface 26 allows an external electrical cable to be passed into the framework 14. Mounting holes, such as mounting holes 253 , allows hole 252 to be covered by means of a screw-on cover (not shown).

The top of the channel (100 in Figure 1) is provided by a generally rectangular shaped member 260 which has a heat dissipating flange 92 attached to its top surface. A slot 262 through the heating flange 92 and rectangular part 260 allows a cable to be fed from the power supply chamber (34 in Figure 1) into the transverse channel 100.

A generally rectangular portion 270 supports the remaining lower heating flange 92 for the power supply chamber.

In the assembled state, the non-rectangular shaped part 270 separates the bottom of the heat-dissipating rib part 224 from the recessed front surface 26.

A bracket 272 is connected to the bottom surface 18 and projects downwards from this. A hole 274 in bracket 272 receives the third alignment pin (not shown) of the mounting tray section.

The various components of the framework 14, as shown in Figure 2, are preferably made of aluminium. The process of using a chemical melt bath to perform dip soldering, which bonds together the various component parts of the framework 14, is conventional and well known, and as such this process will not be described in detail here. In general, the component parts shown in figure 2 are held in the final desired position by means of a suitable tool. The parts are dipped into a flux bath with the filler metal pre-placed in the joints to be soldered. On removal from the flux bath, the unit is cooled and then removed from the tool.

The dip-soldered IRU framework 14 of Figures 1 and 2 realizes many advantages over other inertial reference system enclosures previously known in the art. Dip soldering forms rigid connections between the five walls

38, 44, 48, 230 and 244 of the five-sided ISA chamber. This rigidity helps not only to isolate the inertial sensors from shocks to which the framework 14 is subjected, but also to ensure constant alignment of the ISA unit in relation to the mounting tray f the six ion and the aircraft.

In addition, the various joints in the dip-soldered framework provide low thermal resistance. Therefore, the entire framework 14 for the inertial reference system serves as a thermal mass for the purpose of cooling the heat-producing components of the inertial reference system.

In addition, the use of dip brazing of an inertial reference frame allows the relatively thick walls such as walls 38, 44, 48 and 230 to be formed near relatively thin walls such as wall 244. If such a construction were attempted by conventional metal casting techniques , cracks will form in the interface between thin and thick walls. Thus, dip soldering allows thick walls to be designed where rigidity is required, and thin walls to provide maximum space for enclosure of the relevant components in the inertial reference system. This makes it easier to design the entire inertial reference system in a smaller package than previously known.

Figure 3 is a side view showing the IRU enclosure 10 shown mounted to the mounting drawer section 12. The side cover (102 in Figure 1) has been removed to illustrate the location of various components inside the enclosure 10.

Shown is the power supply chamber 34 formed at the front surface 22, a portion of the top surface 16, the vertical wall 32 and portions 260, 270. A pair of honor/heat sinks 92 are aligned with a pair of upper heat sinks 302. The circuit boards 90 for the power supply is secured against heat sinks 92, 302 by means of lower and upper clips 96, 98. As shown in greater detail with reference to Figure 7, the copper clad component sides of circuit boards 90 abut the lower and upper heat sinks 92, 30 2 , whereby heat dissipated<->from the<n>circuit board components is conducted over the copper-clad surface and

into heat sinks 92, 302 to provide cooling by conduction for the power supply circuit components.

A transverse channel 100 is formed under part 260 and can be used to carry electrical connection cables (not shown). A front cover 101 covers an inspection hole (252 in Figure 2)

and can be removed using retaining screws (not shown) to

lead test leads into the housing.

Chamber 3 6 for the signal processing circuit is defined

of side wall 32, side wall 3 8 and portions of top surface 16 and bottom surface 18. A series of heat sinks 62 project upwardly from the floor of signal processing circuit chamber 36 and are aligned with downward heat dissipating flanges 64 extending downward from top surface 16. The heat sinks 62, 64 form slits to receive circuit boards, such as the circuit boards 60, with lower and upper card guides 66, 68, respectively, and are used to fix the circuit boards 60 in position. Figure 7 is a detail that better shows the boundary conditions between the thermally conductive surface of the component side and circuit-i

the cards 60 and the heat-dissipating flanges 62, 64.

Shown in front view is a drawing of the front surface of the backplate 70. The backplate 70 is provided with a plurality of female connectors, such as connector 310, which are designed to mate with corresponding male plugs, such as male plug 312, mounted to each circuit board 60, 90. In this way, as the circuit boards 60 are inserted into the chamber 36 for the signal processor ■■

then the circuit and circuit boards 90 are inserted into the chamber 34

for the power supply, electrical connections are established from each board 60, 90 directly to the backplate 70. On the opposite side (not shown) of the backplate 70, conventional metallic circuit strips are used to interconnect the circuit boards 60, 90.

There is shown a partial drawing of a cable 320 which is shown as it extends towards the back plate 70. This cable, coming either from the ISA chamber 40 and/or from the chamber 46 for pins and receiver holes, is passed through a hole, (210 , in Figure 2) and the slot (80 in Figure 2).

ISA chamber 40 is defined by the top wall 230, the raised floor 48 and the side walls 38 and 44. The ISA unit 42 is shown mounted in the ISA chamber 40. The ISA unit 42 is generally rectangular in shape and has recessed opposite corners 42a, 42b. A pair of elastic insulators 330, 332 are shown mounted to the recesses 42a, 42b. In reality, two spaced elastic insulators are used at each recessed corner 42a, 42b. The elastic isolators 330, 332, which are described in greater detail with reference to Figure 4, help to isolate the ISA unit 42 from vibrations to which the enclosure 10 is exposed.

From opposite sides of the ISA unit 42 protrude a pair of pins 340, 342 which are used in the suspension system for the ISA unit, which is described in detail with reference to figures 4 and 5.

An electrical cable 320 is routed to the ISA unit 42 by means of the cutout 201 provided through the raised floor 48.

Chamber 46 for pins and receiver holes is defined by side wall 44, end surface 20 and portions of raised floor 48 and part of upper wall 230. Pins 150, 152 from tray section 12 are drawn and project into holes provided in the block 222 and through the front surface 220 of the raised floor 48. The drawing also shows the female connector 160 from the tray section 12 in full engagement with the male plug which is fixed in chamber 46 for pins and receiver holes.

The drawer section is shown partially in cross-section to allow the guide rails 132 to be omitted. The tray section includes the horizontal support surface 130 and the vertical portion 140, to which are attached first and second alignment pins 150, 152. A side bracket 164 includes a grommet 162, which allows an electrical cable to be routed from the aircraft to the connector at the connector 160.

A pair of U-channel-shaped thermally conductive feet 140, 142 are shown attached, e.g. by rivets, to the bottom of the horizontal support surface 130. Protruding upward from the upper horizontal support surface 130 are rows of fingers 136. The fingers are made of a soft thermally conductive material, such as beryllium copper, and are designed so that when the enclosure 10 is mounted to the drawer section 12, the fingers are arranged in contact with various parts of the housing 10. In this way, heat flow is aided from the housing 10 through the fingers 136 to the drawer section 12, and then from the drawer section 12 through the U-bracket-shaped feet 140, 142 to the mounting surface of the aircraft, indicated generally at 350. The indicated positions of the fingers 136, such as at the central and right edge portions of chamber 36 for the signal processing circuit and at the central and right edge of ISA chamber 40 is carefully selected to maximize heat flow from enclosure 10 to tray section 12.

A third alignment pin 360 is mounted via the block 362 and jam nut 364 to a beveled lip-shaped edge 365 at the forward portion of the horizontal support surface 130

of the drawer section. The third alignment pin 360 engages the hole in the bracket 272 which extends downwardly from the front part of the enclosure 10.

The front arm 124 of a handle 120 is shown attached to a pin receiving bracket 30 projecting from the recessed portion 26 of the front surface 22. A projecting detent 370 at the end of the arm 124 engages a cross pin 372 which is enclosed within the projecting arm 166 from the drawer section 12. A locking arm 131 pivotally mounted to the projecting arm 124 has a hook 131a which engages a lip-shaped edge 271 formed in the lower surface of the plate 270. A similar locking arm (not shown) is pivotally mounted to the other protruding arm (126 in figure 1). In this way, the enclosure 10 is locked to the mounting drawer section 12. Release of the enclosure 10 from the drawer section 12 is accomplished by rotating the locking arms (such as arm 131) out of engagement with the lip-shaped edge 271 and then rotating the arm 124 by means of the grip 122 .This forces the detents 370 out of engagement with the pin 372 and allows removal of the inertial reference system.

Figure 4 is a plan view from the side showing the ISA chamber

4 0 with the ISA unit 4 2 installed. The ISA chamber 40, as formed in the dip-soldered framework 14, is a five-sided enclosure that includes a back wall 244, side walls 38, 44, a top wall 230 and a bottom wall 48. The chamber 40 is designed to provide a very rigid housing for the ISA unit 42, thereby maintaining the ISA unit 42 aligned with the ISA enclosure, mounting drawer f the six ion and the aircraft to ensure correct registrations from the sensors.

The ISA unit 42 is mounted inside the chamber 40 using

of elastic insulators, such as insulators 330, 332. Each insulator 330, 332 has a foot piece 333 formed of an elastic material, such as silicon rubber, with a metallic base plate 335 and a threaded central bushing 337 of metal. The base plate of each insulator 330, 332 is placed flush with the recesses 42a, 42b, respectively, which are formed in diagonal corners of the ISA unit 42. Mounting screws, such as screws 331;. secures each insulator 330, 332 to the ISA unit 42^A cutaway of insulator 330 shows a mounting screw 402, the head of which is accessible through a manufactured opening 52 in upper wall 230 and which is screwed into bushing 337 and is used to secure iso- lator 330 in place and equalize the voltage to which insulator 330 is exposed. Although only two insulators 330, 332 are shown, another pair of insulators is mounted on spaced portions of recesses 42a, 42bJ

The natural frequency of the insulators 330, 332 is designed for

to be much higher than the frequency of the shocks that can be applied to the ISA unit 42. In addition, the natural frequency of the isolators 330, 332 is designed to be much lower than the frequency of the vibrating motion that is applied to the laser gyros. The centers of elasticity 330a, 332a of the insulators 330, 332 are also positioned to be in line with the center of gravity 410 of the ISA-

the unit. The resulting construction is particularly effective in minimizing the vibrations that occur on the framework 14 when connected to the ISA unit. 42 and introducing potential errors in the signals produced by the position sensors in the ISA unit.

Insulators, such as insulators 330, 332, are commercially available from Barry Controls, Inc., Burbank, Calif.

To protect the sensitive sensors located inside the ISA unit 42, a suspension system is used that limits the movement of the ISA unit 42 relative to the chamber 40. The suspension system includes two pins 340, 342 which are attached to and protrude from, opposite sides of the ISA unit 42 near the midpoints of the side walls such that the longitudinal axes of the pins 340, 342 pass through the center of mass of the ISA unit 42. The pins 340, 342 are received inside the holes in the eyelets 420, 422, respectively, which are fixed respectively in holes 240, 242 in the side walls 38, 44.

Figure 5 is a detailed cross-sectional view showing the pin 342 which is received within the hole in the eyelet 422 secured within the hole 242 of the side wall 44. With the ISA unit 42 in its rest position, the pin 342 is aligned so that it is centered within the the hole

in the mesh 422. The diameter of the pin 342 is adapted to the diameter of the mesh 422 in such a way that a predetermined distance is provided between the outer surface of the pin 342 and the diameter of the hole in the mesh 422. In addition, the distance between

the sidewall of the ISA unit 42 and the surface 440 of the mesh, set to a predetermined value.

For forces acting on the ISA assembly 42 that exceed a predetermined level, the pin 342 engages the eyelet 422, or the sidewall of the ISA assembly 42 engages the surface 440 of the eyelet 422, thereby establishing a limit to the movement of The ISA unit 42 in relation to the ISA chamber 40. Due to the compliance of the mesh 422, the ISA unit is not suddenly decelerated in relation to the chamber 40 and thereby the load on the sensors in the ISA unit is reduced.

By placing the longitudinal axes of the pins 340, 342 through the center of mass of the ISA assembly 42, the pins 340, 342 will engage their corresponding eyelets, 420, 422 respectively, in a symmetrical manner, ensuring comparable suspension conditions on both sides of the ISA unit 42.

In one construction of the invention, the diameter of the pin 342 was chosen to be 0.635 cm with the diameter of the hole in the eyelet 422 being 1.27 cm. The distance between the surface of the side wall of the ISA unit 42 and the surface 440 of the mesh 422 was chosen to be 0.3 cm.

It should be noted that in alternative constructions of the framework 14, insulators such as insulators 330, 332 may be placed in place of the suspension pins 340, 342 and eyelets 420, 422. However, the suspension system described above was used in the preferred construction due to space limitations .

Figure 6 is a cross section showing the IRU enclosure 10 from the end and showing the assembly of the back plate and circuit boards. Upper and lower framework surfaces 16, 18 are shown. By means of circuit board guides 66, 68, a circuit board 60 resting against heat dissipative flanges 62, 64 is locked in position.

A male connector 312 is attached to the contact side of the circuit

card 60. Various electrical circuit points on circuit card 60

are connected by pins inside connectors 312. A cover 102 is attached over the open right side of the housing 10 by means of screws, such as screws 602, 604.

From the back plate 70, a female contact"310 i protrudes

a direction to mate with connector 312. Backplane 70 includes a corresponding contact, such as contact 310, for each of the various circuit boards 60 with which it mates. Metallic circuit strips (not shown) provided on the surface of the backplate 70 form interconnections between various connectors on the circuit boards 60.

The outer dimensions of the back plate 70 are such that it is adapted to come flush against an inner lip-shaped edge 610, 612 which is integrally formed with the housing 10. The back plate 70 is held in place by a cover 72 and a plurality of screws, such as screws 606, 608, which are screwed into threaded holes (not shown) provided in the housing 10. Between<:>the cover 72 and the back plate 70 is placed a soft pad. 74. The soft pillow'774,

which is preferably made of an electrically insulating material,

provides shock-absorbing mounting to the backplate 70. Similarly, a soft pad 75, which is placed between the cover plate 102 and the edges of the circuit boards 60, acts as shock insulation for the circuit boards 60.

Figure 7 is a side view into chamber 36 for the signal processing circuit. Here, a circuit board 60 is shown in place against a lower heat-dissipating flange 62. The circuit board 60 has a component side 60a and from this protrudes various

electronic components, such as component 702. On the component side 60a of the circuit board 60, a heat-dissipating surface, preferably copper, is provided. Heat dissipated by the electronics components, such as component 702, is conducted through thermally conductive layer 60a and to heat sinks, such as heat sinks

flange 62.

The circuit board 60 is held in place with its component side thermally conductive layer 60a abutting the heat dissipative flange 62 by means of a support clip for circuit leads. A handle 66a on the clip device 66 can. is pulled outward to release each card 60 and, when a card is seated, the handle 66a is rotated to its locking position, as shown in Figure 7, forcing a leaf spring (not shown) to bear against the rear surface of the card 60, thereby forcing the thermally conductive surface 60a to abut the heat dissipative flange 62. Support clips 66 for card leads of the type used in the present enclosure are commercially available from Birtcher Corporation, El Monte, California.

Figure 7 also shows the front surface of the connector 312 attached to the circuit board 60 which fits together with a corresponding contact, on the back plate 70. Such a contact is shown at 310.

The circuit boards 90 for the power supply mate with the backplate 70 in a similar manner.

Preferably, heat dissipating components (such as component 702) are placed on the circuit boards 60, 90 so that they are

as close to the heat dissipating flanges (such as flange 62) as possible,

thereby providing a short thermal path for the heat flow from the circuit boards 60, 90 to the framework 14. The vertical position of the back plate 70, in the preferred embodiment (rather than a more conventional horizontal position) facilitates this purpose.

Figure 8 is a drawing seen from the front of the enclosure 10. The front surface 22 includes the vertically spaced heat dissipating ribs 24 which radiate heat from the enclosure to the surroundings.

A recessed portion 26 includes an opening 252 from which electrical cables can be routed to test the enclosed electronics. A cover plate (not shown) is secured over opening 252 by means of screws (not shown) which are screwed into threaded holes, such as hole 253.

Protruding from the lower left and right portions of the front surface 22 respectively are pin receiving brackets 28, 30. These brackets, which are described more fully with reference to Figure 3, provide a means for mounting a handle (not shown).

Downward from the housing 10, a bracket 272 with an alignment hole 274 projects. The third alignment pin (Figure 3) on the mounting drawer section is received inside the alignment hole 274 when the housing 10 is mounted to the drawer section.

Figure 9 is an end drawing of the rear surface 20. A cut-out 130 is provided for contact in the lower, central part of the rear surface 20 with mounting holes 131, 132 which are used to fix the contact (not shown) in place. The bracket 272 projecting downwardly from the lower surface of the housing includes the alignment hole 274, as described above.

Alignment holes 174, 176 are provided in diagonal corners of rear surface 20. As described with reference to Figure 1, these alignment holes accommodate alignment pins (150, 152) projecting from the vertical surface of the mounting drawer section. In previous constructions, such alignment holes were provided with a predetermined de-

•in

stand on a horizontal line at the back of the enclosure. Because the present inertial reference system enclosure is considerably smaller than those previously known in the field, a unique feature of the present placement of the alignment holes 134, 136 is that they are spaced by a maximum possible distance S,, on a diagonal , thereby providing maximum rigidity of the enclosure 10, and maintaining a correct in-

straightening ay the casing 10.

In one construction of the present inertial reference system, the total length of the top surface is 1.6 (figure 3). '38.56 cm. The width of the enclosure, W (Figure 9), is 12.42 cm. The height, H (figure 9) of the enclosure 10 is 19.33 cm. In this construction, the alignment holes 134, 136 are spaced apart by a distance,

S (figure 9), of 20 cm. The horizontal distance, HS (Figure 9),

of the alignment holes 134, 136 is 10.16 cm, while the vertical distance, VS (Figure 9), is 17.26 cm.

In order to provide rigidity for the ISA chamber 40 in the above-described construction of the invention, and referring to Figure 4, the side walls 38, 44 and the top wall 230 are designed with a thickness of 0.635 cm, while the raised floor 48 has a thickness of 1.77 cm.

The described inertial reference system enclosure occupies a volume less than half the size of a standard 1 1/4 ATR box and, as such, is less than half the size of aircraft inertial reference system enclosures previously known in the art. This size has been achieved while maintaining rigidity for the ISA chamber through proper dimensioning of the ISA unit walls and dip brazing construction. In addition, the ISA unit is isolated from shocks to the enclosure due to carefully engineered shock-absorbing mounting and suspension systems.

The considerable attention paid to heat dissipation from the various heat-dissipating components used in the inertial reference system has made convection cooling, which has been necessary in previous designs, unnecessary. By carefully constructing the heat flow paths from the heat-producing components in the IRU to the IRU enclosure, and then through the mounting tray section

to the aircraft, there is no need for convection holes in the enclosure, and thereby foreign matter is prevented from penetrating. The IRU will also, in certain mounting contexts, be used at high pressure altitudes where there is little or no convection cooling.

To further increase the cooling of the IRU components, and with reference to Figure 1, the inner walls of chamber 36 for the signal processing circuit and chamber 34 for the power supply are given a glossy metallic color which is heat reflective. In this manner, the heat in the walls of chamber 3 6 for the signal processing circuit components and chamber 34 for the power supply is not radiated back to the electronic components on the circuit boards 60, 90 respectively. All other surfaces of the IRU enclosure are otherwise painted black. These black surfaces promote the radiation of heat from the enclosure to the surroundings.

In summary, an improved IRU enclosure for aircraft has been described. While the preferred embodiment of the invention has been described in detail, it must be understood that many modifications and variations are possible, all of which fall within the spirit and scope of the invention.

Claims (34)

1. Enclosure for accommodating an inertial reference unit, for an aircraft, where the inertial reference unit includes an inertial sensor unit (hereinafter referred to as ISA unit) consisting of position sensors, and an electronic circuit module for processing data from the position sensors and producing navigation signals, characterized in that the enclosure includes: a dip-soldered framework including a chamber for receiving the ISA unit and a chamber for receiving the electronics module, the walls forming the ISA chamber providing a predetermined stiffness to maintain the ISA chamber in a predetermined alignment under the influence of forces acting on the framework. 2. The enclosure according to claim 1, characterized in that the dip-soldered framework for the ISA chamber includes a five-sided, open enclosure, where the ISA unit is accessible through the open surface, and a cover plate for mounting above, and which covers the open surface, the cover plate is attached to the framework by removable fasteners to ensure a predetermined stiffness of the resulting cover to the ISA chamber interface. 3. Enclosure according to claim 1 or 2, c a r a c t e r i i ss. characterized in that the ISA is mounted to the walls of the ISA chamber by means of a plurality of isolators, each isolator exerting a predetermined compliance so that the ISA is effectively substantially isolated from shocks applied to the framework. 4. Enclosure according to claim 3, characterized in that it includes a first insulator attached to the top surface of the ISA unit towards a first end thereof and a second insulator attached to the bottom surface of the ISA unit at one end thereof which is diagonally opposite the first the end. 5. Enclosure according to claim 3 or 4, characterized in that the insulators are predetermined in relation to the center of gravity of the ISA unit. 6. Enclosure according to claim 5, characterized in that the insulators are positioned so that the center of elasticity of each insulator is in line with the center of gravity of the ISA unit. 7. Enclosure according to any one of the preceding claims, characterized in that it includes a suspension device for predetermined limitation of the movement of the ISA unit in relation to the ISA chamber. 8. Enclosure according to claim 7, characterized in that the suspension device includes a pair of pins, each pin is attached to and protrudes from opposite sides of the ISA unit, each pin is received inside the hole in an elastic loop which is fixed inside a wall of the ISA chamber, the pins and eyelet holes are sized and aligned to form a predetermined clearance between the surface of each pin and eyelet hole so that when a predetermined force is applied to the ISA assembly, at least one of the pins will engage its corresponding loop, thereby limiting the movement of the ISA unit in relation to the ISA chamber. 9., Enclosure according to claim 8, characterized in that the surface of each eyelet is positioned at a predetermined distance from the surface of the side wall opposite the eyelet, so that a predetermined movement of the ISA unit in relation to the ISA chamber along the longitudinal axis of a pin causes that the eyelet surface contacts the opposite ISA surface to thereby limit the movement of the ISA unit relative to the ISA chamber. 10. Enclosure according to claim 1, characterized in that the dip-soldered framework for the chamber for the electronics module includes four side walls, where at least one of the side walls has a heat-dissipating mass that is shaped in one with the wall, and where the mounting device mounts the electronics module to the heat-dissipating mass for to conduct heat away from the electronics module to the heat-dissipating mass. 11. Enclosure according to claim 10, characterized in that the electronics module includes a plurality of individual circuit boards, and where opposite side walls of the chamber for the electronics module are equipped with parallel heat-dissipating flanges that merge with the side walls, the heat-dissipating flanges are designed so that the circuit boards can be supported between opposing heat dissipating flanges, the enclosure further including circuit board mounting means for mounting each circuit board so that it rests against opposing heat dissipating flanges so that heat from the circuit boards is transferred by conduction to the heat dissipating flanges. 12. Enclosure according to claim 11, characterized in that each circuit board includes a component side for mounting electronic components and a contact side for forming electrical connections between the components, and where each component side of the circuit board includes a thermally conductive surface, and where each circuit board is mounted inside in the chamber for the electronics module so that the thermally conductive surface rests against the heat-dissipating flanges, whereby heat from the circuit board components is conducted over the thermally conductive surface to the heat-dissipating flanges. 13. Enclosure according to claim 11, characterized in that the electronics module further includes a back plate to form electrical connections with the contact ends of the circuit boards, and where the heat-dissipating flanges and circuit boards are designed so that the contact ends of the circuit boards are accessible through an open surface in the dip-soldered framework, the housing includes further means for mounting the back plate to the housing so that the back plate forms the electrical connections to the circuit boards. 14. Enclosure according to claim 13, characterized in that the device for mounting the back plate to the enclosure includes a recessed lip-shaped edge formed in one piece with the framework around the open surface of the framework, the recessed lip-shaped edge is designed so that predetermined support surfaces allow the backplate rests against the lip-shaped edge, a panel to cover the open face, means for removably attaching the panel to the enclosure, and a soft pad designed to be placed between the panel and the backplate such that when the panel is attached to the enclosure, the soft pad the backplate in contact with the contact ends of the circuit boards, the soft pad ensures that the backplate is isolated from impact on the enclosure. 15. Enclosure according to claim 1, 10 or 12, in combination with a mounting drawer section, characterized in that the mounting drawer section is adapted to be pre-determined arranged with, and attached to an aircraft, the enclosure and the drawer section are pre-determined designed so that the enclosure can be mounted to the drawer section in a predetermined alignment in relation to this. 16. Enclosure according to claim 15, characterized in that the drawer section is generally L-shaped when viewed from the side, and has a horizontally placed part and an upright part projecting from one end of the drawer section, the upright part having two alignment pins projecting over it the horizontally disposed portion, and the housing includes a rear end portion with two holes, these holes being located and sized to receive the alignment pins when the housing is assembled to the tray section. 17. Enclosure according to claim 16, characterized in that the rear end part is generally rectangular in shape and where the holes are placed in diagonal corners of the rear end part. 18. Enclosure according to claim 17, characterized in that the alignment holes are separated by approximately 20 cm. 19. Enclosure according to claim 16, characterized in that: the drawer section includes a third alignment pin, this third alignment pin is parallel to the two alignment pins, the third alignment pin protrudes from the opposite end of the horizontally placed drawer section part from the two alignment pins, and the enclosure includes a bracket projecting downwardly from the front end portion of the housing, the bracket including an alignment hole to receive the third alignment pin when the housing is assembled to the tray section. 20. Enclosure according to claim 15, characterized in that the drawer section includes a plurality of heat-conducting soft fingers which protrude so that the fingers rest against the enclosure when the enclosure is mounted to the drawer section to thereby conduct heat from the enclosure to the drawer section. 21. Enclosure according to claim 20, characterized in that the fingers are positioned to contact predetermined parts of the enclosure to maximize the heat flow from the enclosure. 22. Enclosure and drawer section in combination according to claim 20, characterized in that the fingers are made of beryllium copper. 23. Enclosure according to claim 20, characterized in that the lower surface of the horizontally placed drawer section part is equipped with thermally conductive feet to conduct heat from the drawer section to the aircraft. 24. Enclosure according to any one of claims 10 to 12, or 20 to 23, characterized in that the walls of the chamber for the electronics module are equipped with a heat-reflecting surface to minimize the radiation of heat from the walls of the electronics module. 25. Enclosure according to claim 24, characterized in that all wall surfaces, apart from the walls around the electronics module, are equipped with a heat-radiating surface to promote radiation of heat from the enclosure to the surroundings. 26. Device for attachment of and heat dissipation from one inertial reference unit (IRU unit) to an aircraft characterized in that it includes: an enclosure for the IRU unit, the enclosure includes a thermally conductive mass and a device for mounting heat-producing parts of the IRU -the assembly of the thermally conductive mass, a mounting tray section adapted to be predetermined aligned with and attached to the aircraft, a device for mounting the casing of the tray section in a predetermined alignment therewith, a device for conducting heat from the thermally conductive mass to the tray section, and a device for conducting heat from the tray section to the aircraft. 27. Device according to claim 26, characterized in that the device for conducting heat from the thermally conductive mass to the drawer section includes a plurality of heat-conducting soft fingers that protrude from this so that the fingers rest against the thermally conductive mass when the enclosure is mounted to the drawer section . 28. Device according to claim 27, characterized in that the fingers are positioned to contact predetermined portions of the thermally conductive mass to maximize the flow of heat from the enclosure to the tray section. 29. Device according to claim 27 or 28, characterized in that the fingers are made of beryllium copper. 30. Device according to any one of claims 26 to 29, characterized in that the device for conducting heat from the tray section to the aircraft includes thermally conductive feet which are mounted to the tray section, the feet being in contact with the aircraft when the tray section is attached to the aircraft. 31. Device for attaching an inertial reference unit (IRU unit) to an aircraft in a predetermined alignment with the aircraft, characterized by: an enclosure for receiving the IRU unit, the enclosure having a generally rectangular rear end surface with two alignment holes predetermined located at diagonal corners of the rear end surface, and a mounting tray section including means for mounting the enclosure to the tray section, the tray section adapted to be predetermined aligned with and attached to the aircraft, the tray section is generally L-shaped in side view and has a horizontally located portion and an upright portion projecting from one end of the tray section, the upright portion having two alignment pins projecting from the portion above it horizontally positioned portion, the alignment pins engage the alignment holes when the housing is mounted to the drawer section so that the housing is secured in predetermined alignment with the drawer section. 32. Device according to claim 31, characterized in that the drawer section includes a third alignment pin, the third alignment pin is parallel to and protrudes from the opposite end of the horizontally arranged part from the two alignment pins, and the enclosure includes a bracket that protrudes downward from the front end of the enclosure, the bracket has an alignment hole to receive the third alignment pin when the enclosure is assembled to the drawer section. 33. Device according to claim 31 or 32, characterized in that the alignment holes have a distance of approximately 20 cm. 34. Device according to claim 31 or 32, characterized in that the alignment holes have a distance of approximately 10 cm horizontally and 17.3 cm vertically.