FR2551619A1 - HEAT PROTECTED MEMORY UNIT FOR AN AIRCRAFT FLIGHT DATA RECORDER - Google Patents

Abstract

THE INVENTION CERNEES A HEAT PROTECTED MEMORY UNIT FOR AN AIRCRAFT FLIGHT DATA LOGGER. ELECTRONIC MEMORY DEVICES IN THE SOLID STATE 26 ARE EMBEDDED IN SYNTHETIC ORGANIC WAX 28 WHICH SHOWS A SOLID-LIQUID TRANSITION AT A TEMPERATURE ABOVE THE NORMAL OPERATING TEMPERATURE OF THE MEMORY UNIT AND LESS THAN THE ACCEPTABLE MAXIMUM TEMPERATURE FOR MEMORY DEVICES 26. WAX 28 IS SURROUNDED BY A THERMAL SEAL 18 CONSTRUCTED OF A SOLID THERMALLY INSULATED MATERIAL. A METAL ENCLOSURE HOSTS AND PROTECTS THE INSULATION ASSEMBLY AND MEMORY DEVICES 26. APPLICATION TO THE PROTECTION OF THEFT DATA IN THE EVENT OF ACCIDENT AND FIRE.

Description

The present invention relates to heat-protected enclosures

  to protect and retain a device or assembly from a high temperature environment that would otherwise destroy them, especially heat protected enclosures where dimensions and weight are important parameters In the embodiment of the present invention as disclosed, it is a lightweight compact memory unit for use in an aircraft flight data recording device 10 capable of surviving in an accident, the memory unit being designed to withstand an aircraft crash with subsequent fire without losing or losing very little

stored data.

  Although there are many situations in which it is necessary or desirable to protect a device, element or set of exposure harmful to a high temperature environment, the protection of a system's memory device Aircraft flight recorder has extremely severe design constraints in the event of an accident or fire In this regard, in order to be able to preserve flight data supplied to the memory unit by the data acquisition unit For a flight data recorder, for a predetermined period immediately prior to an aircraft accident, the memory unit must be designed and arranged to withstand temperatures above 1100 C, which are experienced during a fire while being constructed. simultaneously to withstand crushing and penetration forces that may

  occur either during an impact or during a secondary shock with other parts or parts of the aircraft.

  In addition, the memory unit of a flight data recording system is subject to additional design constraints imposed by considerations generally applicable to aircraft equipment and systems including dimensional, weight, cost, ease of maintenance and reliability. Technical advances in various solid-state electronic device technologies have led to high capacity electronic memory devices for nonvolatile storage of digitally encoded data with programmable transistors

  field and read-only and memory devices 10 which are the two types of memory in question.

  Since these devices are small and lightweight and have high reliability, there has been an important tendency to replace the magnetic stripe transports used in current models of flight recorder systems with solid state memories.

  In view of the increased demands for protection against heat, the commonly used technique of mounting a tape conveyance or other flight data recorder memory device within a cavity which is formed by packing the device The solid memory which is relatively good as a thermal insulator and surrounding this assembly with a protective metal enclosure does not make it possible to achieve the desired overall size and weight reduction of the memory units which could be obtained in recording systems. of flight data using semiconductor memory devices such as programmable memories

  and erasable ROM (ROM).

  In accordance with the present invention, a relatively compact and lightweight heat shield is achieved by using a thermal insulator which has a solid to liquid phase transition in the form of at least a portion of the heat protection structure which recesses. or surrounds the device to be thermally protected The temperature at which the solid to liquid phase transition takes place is chosen to be:

255161-9

  (a) above the peak temperature encountered under normal operating conditions and (b) at or below the peak temperature corresponding to the device to be protected. When subject to a fire or other high temperature environment, the material having the solid-liquid phase transition (and any other thermal insulator used) initially serves as a conventional heat shield with relatively high thermal inertia. When the fusible material reaches the melting point, it actually serves as a heat sink because the thermal energy reaching that material is then used to convert it from a solid state to a liquid state (heat of fusion). maintains the maximum temperature reached during exposure to a temperature environment

high, to an acceptable level.

  The presently preferred embodiments of the present invention are provided for maintaining solid-state electronic memory devices of a flight data recorder at a maximum temperature of 200 C or below thereof when the memory unit of the flight data recorder 25 is exposed to a fire which produces temperatures of 1100 C for a period of 0.5 hours and that the unit of memory is left undisturbed for 4 additional hours In these forms In one embodiment, the currently preferred fusible material is a synthetic organic wax defined chemically as N, N'-ethylenebis-stearamide (or by its N, N: -distearoylethylenediamine synonym) having a chemical configuration of H 2 C 17 COHNC 2 H Where the alkyd radicals extend linearly from the amide bonds on each side of the

molecule.

  With respect to the physical configuration, the flight data recorder memory unit disclosed in accordance with the present invention includes an outer casing constructed of a metal having high thermal conductivity and high crush and bead strength. An intumescent coating or paint is generally applied to the exterior surfaces of the outer casing to provide additional thermal insulation. An insulating layer of solid material having relatively low thermal conductivity has each inner surface of the outer casing to form a cavity. rectangular

  which is placed in the center inside this box.

  One or more printed circuit boards which include the solid-state electronic memory devices to be protected are mounted within an internal metal box which is housed inside the box.

  central cavity, the synthetic wax type material surrounding and coating the printed circuit boards.

  An electrical connection between the solid state electronic memory devices and a remotely located flight data logger data acquisition unit is facilitated by a flexible ribbon type multi-conductor cable which interconnects the printed circuit board with an electrical connector that is mounted

  on the outside of the outer casing.

  Other features and benefits

  of the present invention will result from the following description of several embodiments which are given by way of example with reference to the drawings,

  wherein: FIG. 1 is an exploded view of a flight data recorder memory unit designed in accordance with the present invention; Fig. 2 is a partial cross-sectional plan view of the flight data recorder memory unit of Fig. 1; Figure 3 shows a phase diagram of the synthetic organic coating wax used in the embodiment of Figures 1 and 2; and FIG. 4 shows the temperature versus time characteristics of an embodiment of the present invention as well as the temperature versus time characteristics of flight data recorder memory units of the same size using any conventional solid insulation material. The memory unit of a thermally protected flight data recorder system 10 and designed in accordance with the present invention is illustrated in FIGS. 1 and 2 and is generally designated by the reference numeral 10. As known from the prior art such a memory unit is provided to provide recording of various important parameters of aircraft performance for a predetermined period which takes place immediately before each time the flight data recorder is deactivated (including deactivation During operation, the information stored inside the memory unit is continuously supplied by additional components of the flight data recording system such as an acquisition unit. data that receives input signals from various detectors and systems the aircraft and processes these signals to produce signals c compatible with the recording or storage medium used by the flight data recorder memory unit In the case of the embodiment disclosed in accordance with the present invention which uses a solid state electronic device such as electronically erasable and electronically erasable semiconductor (ROM) memory circuits as an information storage medium, the data acquisition unit periodically provides digital signals which are written

  sequentially in semiconductor memory circuits

$ 551619

  conduct so that the memory circuits store a sequence of digital words, i.e., a representation of sampled data in time of the history of each monitored parameter. Typically, with respect to commonly used techniques, data compression is generally employed to allow the storage of digital signals representing a descriptive period of 15 to 30 seconds.

  minutes for each monitored parameter.

  As shown in FIGS. 1 and 2, the presented embodiment of the memory unit of the flight data recorder system of the present invention comprises an outer metal casing 12 which has a substantially rectangular cross section when The flanges 14 extend orthogonally from oppositely disposed edges of the base of the outer casing 12 to facilitate mounting of the memory unit 10 to an appropriate location within the housing. the aircraft by means of bolts or other conventional fasteners A substantially rectangular cavity 14 extends inwardly from one of the faces of the outer casing 12 to the base of the memory unit 10, so that the most of the outer casing 12 has the configuration of a substantially rectangular shell The outer casing 12 is constructed of a titanium alloy or other material which has a relatively low density, a relatively high thermal conductance and a relatively high resistance to crushing and penetration, the wall portions which are defined between the cavity 16 and the external surfaces of the outer casing 12 having dimensions allowing To Withstand Crushing and Penetration for the Accident Case A shell-type heat seal 18, housed within the cavity 16 of the outer casing 12, provides a first thermal barrier to protect components that are The heat seal 18 is substantially rectangular in cross-section with respect to each of its major axes and forms a cavity in the internal regions of the memory unit 10 of the high temperature fires that may occur during an aircraft accident. extending inwardly 20 which is coaxially placed inside the cavity 16 of the housing The heat seal 18 is preferably a unitary structure which is formed of a solid material which constitutes a good thermal insulator (i.e., has a low thermal conductivity K) and a relatively low density of materials. Suitable materials include thermal insulators which are protected combinations of fibrous materials and very fine particulate materials, the MIN-K 2000 and MICROTHERM brand names representing two satisfactory materials which are manufactured by Johns-Manville Co of Denver, Colorado and by Micropore Insulation, Ltd. of UptonWirral Merseyside, Great Britain, respectively. As they have a very low thermal conductivity, for example K = 0, 146 to 170 C, K = 0927 to 1100 C, the material sold under the trade name MICROTHERM is usually the preferred material for

supply the heat seal 18.

  As best shown in FIG. 1, a relatively thin-walled central shell 22 which accommodates in the cavity 20 receives and contains one or more printed circuit boards 24 which provide physical support for a number of memory storage devices. solid state 26 and an electrical interconnection therefor Although the arrangement of FIG. 1 shows a conventional printed circuit system

  wherein each solid state memory device is coated to form what is called a double in-line package, other configurations may be used.

  For example, in some embodiments of the present invention, it may be advantageous to bond semiconductor wafers which contain circuitry for a number of electronically erasable programmable ROMs directly to a ceramic substrate or other medium which includes electrical interconnects which In any case, the central shell 22 is preferably formed from a material such as stainless steel or another metal which has a reasonable value of the ratio of density to the thermal capacity (i.e., the product of the density of the material and the heat capacity is relatively high) and which can also be worked or easily formed In addition, each printed circuit board 24 is mounted in a central shell 22 so that each solid state memory device 26 is spaced apart. internal surfaces

of the central shell 22.

  In order to obtain the high degree of thermal protection achieved according to the present invention, the open regions between the inner walls of the central shell 22, the printed circuit 24 and neighboring memories in the solid state 26 are filled with a Fusible insulator (28 in FIG. 2) having a solid to liquid phase transition at the desired temperature limit for solid state memories 26 or below thereof. As shown graphically in FIG. such material is characterized by a first temperature range in which an increase in heat energy supplied to the material produces a corresponding linear increase in the temperature of the material (material below its melting point T in FIG. 3) and which is further characterized by a relatively constant temperature region or an increase in the supplied thermal energy melts the material as schematically shown in FIG. 3, a continuous increase in the thermal energy supplied to such a material after it reaches the molten state will generally cause a vaporization of the material, with additional increases in the heat energy supplied causing an increase in temperature in the steam produced. The latter feature is of importance to the present invention only in that the fuse insulator 28 which is used in practice for carrying out the present invention is chosen so that very little vaporization or no vaporization at all will occur. occurs when the memory unit 10 of FIG. 1 is subjected to a high temperature environment related to

to the fire of the aircraft.

  The heat insulating fuse material commonly used in the practice of the present invention is a synthetic organic wax defined chemically as N, N'-ethylenebis-stearamide (or by its N, N'-distearoylethylenediamine synonym) having a chemical configuration of H The alkyd radicals extend linearly from the amide linkages on each side of the molecule. Such synthetic wax is available from Glyco, Inc. of Greenwich, Connecticut under the US Pat. the brand name ACRAWAX C and it is commonly used in many

  commercial applications which do not relate to the present invention.

  With regard to the present invention, N, N'-ethylenebis-stearamide is advantageous in that various formulations which have different melting points are readily available. On the other hand, the material can be subjected to conventional methods of manufacture because is not toxic and is available

  according to different particular forms.

  Referring again to FIGS. 1 and 2 and the physical configuration of the memory unit 10, there is provided an electrical connection to the printed circuit board 24 by means of a flexible flat cable assembly 30 constructed from Polyimide tape or other material which includes a series of conductive spaced strips When the printed circuit board 24 is placed in the central shell 22, the cable 30 extends through a rectangular slot 32 which is formed in a This is then filled with a melted synthetic organic wax to coat the printed circuit board 24, the solid state electronic memory devices 26 and the cable 30. 34 which comprises a rectangular metal plate 36 and flanges 38 which extend at right angles from the plate so as to abut against the inner walls of the central shell 22 substantially closes the inner shell 22 for receiving a fuse insulator 28 (synthetic organic wax)

  which melts during an accident and a fire of the aircraft.

  Thermal insulation is provided for the face of the central shell 22 which is defined by a cover assembly 34 by means of a substantially rectangular thermal insulator 40 which is constructed from the same material which is used to form the thermal liner. 16 (for example, the above-mentioned "MICROTHERM" insulation) As shown in FIG. 1, the thermal insulation 40 is preferably covered with a fiberglass reinforced resin 42 (or

  another durable material) to protect the thermal insulation 40.

  A second substantially rectangular cover plate 44 which is constructed of the same material as the outer casing 12 covers the open face of this casing so as to completely enclose the memory unit 10 so as to substantially close the unit and provide a substantially identical thermal conductance with respect to the thermal energy that is coupled through each rectangular face of the unit

of memory 10.

  With particular reference to Figure 1, we see that the electrical cable 30 out of the cavity 16 of the outer casing 12 through a rectangular slot 46 which is formed in a wall of the outer casing 12 A connector 48 at the outer end of the cable It is connected to a connector 50 which is located on the printed circuit board 52. In the embodiment described, the printed circuit board 52 is mounted substantially parallel to the face of the outer casing 12 which has a slot 46. and contains conventional interface or control electronics (not shown in FIG. 1) for sequentially addressing solid state memory devices 26 during operation of the flight data recorder system. command 15 do not need to survive a fire for the preservation of the data stored in the solid state memory devices 26, they are of preferably mounted within the memory unit 10 to eliminate data errors that might otherwise be caused by electromagnetic interference and other transient signals encountered in systems

electric aircraft.

  To complete the memory unit 10 and provide an electrical connection between the data acquisition unit 25 of the system and the printed circuit board 52, the memory unit 10 comprises an electrical connector 54 which passes through the main face of the memory unit 10. A flange 56 is substantially U-shaped. As shown in FIG. 1, the flange 56 is mounted on the outer casing 12 with a connector 54 spaced from the printed circuit board 52. A form 58 ribbon cable assembly The present invention provides the electrical interconnection between the connector 54 and the printed circuit board 52. The degrees of thermal insulation achieved by carrying out the present invention are illustrated in FIG. 4, which shows the temperature characteristics as a function of time of a flight data recorder memory unit constructed in accordance with the present invention (curve 60 of FIG. 4) and the temperature characteristics in accordance with the present invention. two time-identical memory units without fusible insulation 28 but use substantially thicker heat seals 18 constructed with the aforementioned material which is marketed under the trade names MIN-K 2000 and MICROTHERM (Curves 62 and 64 of Figure 4, respectively) Each of the three memory units used to provide data of Figure 4 has a height of 7.62 cm, a length of 12.2 cm and a width of 11.4 cm, the wall thickness of the outer casing 12 being 0.32 cm Thus, the rectangular cavity inside the outer casing of the three memory units that produced the data shown in Figure 4 has a height of about 7 cm, a length of about 11.6 cm and a width of about 10.8 cm. In the two memory units which comprise the MIN-K 2000 or MICROTHERM isolator without inclusion of a fuse insulator, the thickness of the solid heat seal is about 2.3 cm. The memory made according to the present invention (curve 60) uses a thickness of 1.5 cm of MICROTHERM insulation as a heat seal 16 to thereby form a central cavity (cavity 20 of FIG. 5.5 cm, about 8.5 cm and about 7.6 cm larger. About 184 g of melted N, N'-ethylenebis-stearamide, which has a melting point of C are deposited in the central cavity to completely encase the circuit board 24 and the devices

  associated memories 26 in the solid state.

  The thermal performance according to the present invention is clear from FIG. 4 which shows the temperature reached in or near the solid state memory devices when the tested memory units have been subjected to a kerosene burner which produces temperatures of the order of 1100 C and a heat flux of the order of 157 500 W / m 2 for a period of 0.5 hours, being left undisturbed for 4 hours First, and this is of paramount importance, the maximum temperature achieved with the embodiment tested according to the present invention is about 176.6 C, while the memory unit using the MIN-K 2000 insulation 10 has reached a maximum temperature approximately 337 ° C and the memory unit using the MICROTHERM insulation reached a maximum temperature of about 318.3 ° C. In addition, the memory unit using a MIN-K 2000 insulation (curve 62) reached maximum internal temperature e about 39 minutes after ignition of the kerosene burner, the memory unit employing only the insulation

  MICROTHERM (curve 64) reaching the maximum internal temperature about 55 minutes after burner ignition.

  In contrast, the tested embodiment of the present invention has a thermal inertia exceeding that of the two memory units that utilize the solid insulator, reaching a maximum internal temperature

  approximately 68 minutes after ignition of the kerosene burner.

  Referring again to FIG. 4, it is noted that the temperature reached in the tested embodiment of the present invention at the end of the 30 minute burning period (137.8 C) is substantially less than the temperature. impairment in memory units using MICROTHERM 30 and MIN-K 2000 insulation (approximately 160.6 ° C) and approximately 204 ° C, respectively) Throughout the duration of the burning (period less than 30 minutes), and throughout the period In order for the tested memory units to reach the internal peak temperature, the temperature of the tested embodiment remains below that of the two memory units using only the MIN-K 2000 and MICROTHERM insulation. Like the synthetic organic wax used. in the tested embodiment of the present invention dissipates stored thermal energy at a slower rate than either MINK 2000 or MICROTHERM, the tested embodiment of the present invention is slightly higher than that of the other two memory units at the end of the test period shown in FIG.

  Figure 4 (the time is equal to 64.5 hours).

  The difference between the time temperature characteristic of the present invention and the memory units containing only a solid heat seal is especially important to preserve the digitally encoded information stored in the memory devices in the state of the present invention. In particular, the probability of destroying stored data bits is not only a function of the peak temperature attained but increases substantially in proportion to the duration of the storage devices at substantially higher temperatures. this can be seen from FIG. 4, and as can be appreciated from the foregoing discussion, the memory devices within the tested embodiment of the present invention are subject to less energy. tics than those inside memory units using fully MIN-K 2000 and M insulation In other words, since the area below the curve 20 is smaller than the areas below the curves 62 and 64, it can be seen that the temperature versus time characteristics presented by the invention substantially reduce the probability of loss of an unacceptable amount of stored flight data in comparison with a memory unit of

  same dimension using only solid thermal gaskets.

  Although the invention is described herein only in connection with a presently preferred embodiment of a flight data recorder system, those skilled in the art will recognize that various modifications, alterations, and substitutions may occur.

  be carried out without departing from the scope of this.

  For example, the invention, although described in terms of a memory unit for an aircraft flight data recorder system, may find applications in other situations requiring compact and lightweight thermal insulation. Situations of this type are likely to be more numerous especially for aircraft-type and spacecraft vehicles as more and more electrical systems which have been customarily made according to analog circuit designs are

  replaced by digital systems.

  In addition, the central shell 22 of the disclosed embodiment is not a necessary part of the present invention and may be removed if necessary or desired In this aspect, the presently preferred embodiments of the present invention use the central shell 22 to facilitate assembly and as a container for housing the portion of the flight data recorder memory unit to be retrieved to obtain the data.

registered flight.

1.6

Claims (8)

  An enclosure for thermally shielding one or more heat-sensitive elements of a high temperature environment, characterized in that it comprises an outer casing (12) having an internal cavity (16) containing one or more of said heat sensitive elements. the heat, a first thermal insulator in the form of a heat seal (18) which extends around the surface of the first internal cavity, and which defines a second internal cavity (20) with said sensitive elements which are spaced apart from the walls of the second internal cavity (20), the first insulator being a solid material and remaining solid when the enclosure is exposed to a high temperature environment, and a second thermal insulator (28) occupying at least a portion the second internal cavity (20), the second insulator (28) surrounding said sensing elements and having a solid to liquid phase transition at a temperature of predetermined ature, which is chosen to maintain the second thermal insulator in the solid phase when the enclosure is not exposed to the high temperature environment and to allow the conversion of the second thermal insulator (28) to the   liquid phase when the enclosure is exposed to a high temperature environment.   2 Enclosure according to claim 1, characterized in that the thermal insulation is a wax organic synthetic.   3. Enclosure according to claim 2, characterized in that the organic synthetic wax is chemically defined as N, N'-ethylenebis-stearamide.   and N, N'-distearoylethylenediamine.   4 Enclosure according to claim 3, characterized in that each of the sensitive elements is a solid-state electronic memory device for storing data which can be recovered from each of these devices after exposure of the enclosure   at a high temperature environment.   A memory unit capable of surviving after an aircraft accident and of the type comprising an enclosure (12) according to any one of the preceding claims, for enveloping one or more memory devices (26) and a thermal insulation layer ( 18) which encloses the walls of the outer enclosure to form a cavity for maintaining one or more of said devices (26) below a predetermined temperature limit when the memory unit   is subjected to both a normal operating temperature range and a high temperature environment, characterized in that it comprises a second thermal insulator (28) filling at least a portion 15 of the cavity (20) and surrounding each of the memory devices (26), the second thermal insulator (28) having a solid to liquid phase transition at a predetermined temperature which is not greater than the predetermined temperature limit of the memory device and which is larger than each temperature within the normal range of operating temperatures. Memory unit according to Claim 5, characterized in that the second thermal insulator   is an organic synthetic wax.   Memory unit according to claim 6, characterized in that the synthetic organic wax is chemically defined as N, N'-ethylenebisstearamide and N, N'-distearoylethylenediamine.   A memory unit according to claim, adapted to operate within a predetermined operating temperature range and to be capable of substantially retaining all data stored when exposed to a predetermined range of time. high temperature, characterized by comprising one or more solid state memory elements (26) for storing flight data information, an outer housing (12) having an internal cavity region (16) receiving the memory device, a heat seal (18) placed between one or more of the memory elements (26) and the walls of the inner cavity region (16), at least a portion of the heat seal (18) being spaced from each of the memory devices (26), and a thermal insulator (28) having a solid to liquid phase transition at a temperature that exceeds the range   predetermined operating temperature range, the thermal insulation (28) occupying at least a portion of the region defined between one or more of the memory devices (26) and the thermal liner (18) so as to envelop each of said devices of memory (26).   Memory unit according to Claim 8, characterized in that the thermal insulator is a organic synthetic wax.   Memory unit according to claim   9, characterized in that the synthetic organic wax is chemically defined as N, N'-ethylenebisstearamide and N, N'distearoylethylenediamine.