US3224193A

US3224193A - Anisotropic heat shield construction

Info

Publication number: US3224193A
Application number: US290395A
Authority: US
Inventors: Joseph F Loprete; Arthur D Cangialosi
Original assignee: Curtiss Wright Corp
Current assignee: Curtiss Wright Corp
Priority date: 1963-06-25
Filing date: 1963-06-25
Publication date: 1965-12-21
Anticipated expiration: 1982-12-21

Description

Dec. 21, 1965 J. F. LOPRETE ETAL ANISOTROPIC HEAT SHIELD CONSTRUCTION Filed June 25, 1965 5 Sheets-Sheet 1 INVENTORS .JUEJEFH F. LE] ETE. R DCANBI EIEI WEQ L ATTEIRNEY Dec. 21, 1965 J. F. LOPRETE ETAL 3,224,193

ANISOTROPIC HEAT SHIELD CONSTRUCTION 3 Sheets-Sheet 2 Filed June 25, 1963 ATTI'JRNEY Dec. 21, 1965 J. F. LOPRETE ETAL ANISOTROPIG HEAT SHIELD CONSTRUCTION Filed June 25, 1963 3 Sheets-Sheet 5 INVENTORS LJEIEIEFH F. LDF'RETE QYRTHLIR QEANEIIALEIEII ATTEIR NEY 3,224,193 Patented Dec. 21, 1965 Fice 3,224,193 ANISOTROPIC HEAT SHIELD CONSTRUCTIQN Joseph F. Loprete, Wayne, and Arthur I). Cangialosi, Clifton, NJ, assignors to Curtiss-Wright Corporation, a corporation of Delaware Filed June 25, 1963, Ser. No. 290,395 18 Claims. (Cl. (SO-35.6)

This invention relates to heat shield structures and is particularly directed to a novel construction for heat shield structures utilizing anisotropic materials.

Although the invention described herein relates to exhaust nozzles of jet engines or the like, it is not intended that the invention is so limited. Thus, the invention is also applicable as a heat shield for aircraft, missiles, space vehicles, atmosphere re-entry vehicles and other devices intended to travel through space or the atmosphere or any part thereof which may be exposed to high temperatures for a limited period of time.

It is known in the case of rockets and jet engines to use a special means for cooling the exhaust nozzles, such as for example, a liquid coolant. In planning for higher thrust devices the problem arises that the propellants used in such devices burn at higher temperatures which may be in excess of 6000 F. Accordingly, it follows that exhaust nozzles capable of withstanding these higher temperatures must be provided. It is a prime object of the present invention to provide a novel exhaust nozzle construction which is capable of withstanding relatively high temperature conditions while avoiding the serious problem of erosion of the gas wall at the nozzle throat area.

The invention makes use of the relatively unique properties of a known form of graphite called pyrolytic graphite. The pyrolytic graphite material is normally deposited on a substrate layer which usually is a conventional graphite. As the pyrolytic graphite is deposited, it forms a layer having marked anisotropic properties. Along the plane of deposit or in other Words along a plane parallel to the deposited layer, the pyrolytic graphite is highly thermally conductive and has a relatively low coefficient of thermal expansion in this direction while in a direction perpendicular to the plane of deposit the material is highly non-conductive but with a relatively high coefficient of thermal expansion in this direction. The heat conduction characteristics of pyrolytic graphite are particularly significant at high temperatures because of the high temperature properties of graphite. In addition the heat insulating property of pyrolytic graphite increases with increase in temperature. The present invention utilizes the above properties of pyrolytic graphite in providing a novel exhaust nozzle construction with a nozzle heat sink with sutficient capacity to substantially eliminate erosion of the nozzle gas Wall and particularly in the nozzle throat region wherein temperatures are relatively extreme.

The construction of the present invention generally comprises a plurality of circumferentially disposed wedges of pyrolytic graphite which extend axially in a direction parallel to the nozzle axis. The orientation of each of the pyrolytic graphite wedges is such that with respect to the nozzle axis thermal conduction will be relatively high in an axial and radial direction while in a circumferential direction the construction will be relatively highly thermally non-conductive. With this construction the heat will flow from the normally hotter regions of the gas wall of the nozzle to portions having relatively cooler temperatures thereby lowering the nozzle throat gas wall temperatures. A pyrolytic graphite layer or layers may be provided around the outer surface of the wedges with the planes of said layer being oriented so as to act as a heat insulator at the radially outward portions of said wedges and thereby form a heat shield for the supporting outer structure of the nozzle. The invention will be pointed out in more detail in the following detailed description. Reference may also be made to co-pending application Serial No. 125,253 filed July 19, 1961, invented by George Kraus, now Patent No. 3,156,091 issued on November 10, 1964, for a dilferent configuration of a jet engine nozzle utilizing pyrolytic graphite.

Accordingly, it is an object of the invention to provide a novel and improved heat shield structure for aircraft subject to high temperature operation.

It is another object of the invention to provide a novel and improved heat shield construction having anisotropic heat properties.

It is still another object of the invention to provide a novel and improved heat shield construction for an aircraft exhaust nozzle.

It is a further object of the invention to provide a novel and improved heat shield construction for an aircraft exhaust nozzle which prevents excessive heat and erosion in the region of the nozzle throat.

It is an additional object of the invention to provide a heat shield construction for an aircraft exhaust nozzle having anisotropic properties and wherein novel means are provided in said construction for conduction of heat and relief of compression stresses.

Other objects and advantages of the invention will become apparent upon reading the following detailed description with the accompanying drawing wherein:

FIG. 1 is a sectional view of an exhaust nozzle embodying the invention and taken along line 11 of FIG. 2;

FIG. 2 is a sectional view of the exhaust nozzle of FIG. 1 taken along line Z2 of FIG. 1;

FIG. 3 is a perspective view of one of the anisotropic elements of the nozzle of FIG. 1;

FIGS. 4-7 are diagrammatic views of a portion of an exhaust nozzle showing modifications for varying the heat conduction in the nozzle throat region; and

FIGS. 4A-7A are sectional views of one of the anisotropic elements of the nozzle taken along lines A-A of each of said FIGS. 4-7, respectively.

In FIG. 1 there is illustrated a multi-layer exhaust nozz-le 10 which may for example, be provided for a rocket, said nozzle 10 having an outer housing or load carrying member 12 which is suitably connected to the casing 14 of a rocket as by bolts 16 or other suitable means. A seal means 18, as for example an O ring may be provided between the casing 14 and housing 12 for preventing any gas leakage between said members. The nozzle 10 has an inner surface 20 with a convergent-divergent profile, the throat region of which is indicated at 22. As indicated in FIG. 1 the exhaust gases flow from the rocket in the directions of the arrows shown in FIG. 1 and are expanded out the rear end of the nozzle 10 opposite from the end of said nozzle attached to the rocket casing 14. The inner layer of the nozzle 10 is formed from a pinrality of abutting wedges of pyrolytic graphite in a manner which will be more clearly explained below. As shown in FIG. 1 the wedges indicated at 24 extend substantially the entire length of the rocket nozzle in the direction of the axis aa of said nozzle.

As stated, the wedges 24 are preferably formed from pyrolytic graphite which material has definite anisotropic characteristics. The pyrolytic graphite is obtained in a furnace by vapor deposition from carbon bearing vapor. The wedges 24 are formed by depositing pyrolytic graphite on a flat surface, the graphite being deposited on said surface to form a sufiicient thickness for obtaining the desired size wedges to be used in said nozzle 10. It is known that the thickness to which pyrolytic graphite can be deposited is limited and therefore the wedge size is likewise limited. The pyrolytic graphite wedges are then formed by cutting and machining such a deposited layer of pyrolytic graphite such that a median plane between the sides of the wedge is substantially parallel to the plane of deposit of the pyrolytic graphite. The nozzle inner surface or layer is built up from a plurality of such wedges disposed in a circle to form a substantially annular ring shaped nozzle layer about the nozzle axis aa. If it is found that the pyrolytic graphite can be deposited in greater thickness, then of course, thicker wedges and therefore a lesser number may be used.

The wedges 24 of the invention have their layer or deposited plane disposed so that said plane substantially includes the axis a-a of the nozzle and about which said wedges are circumferentially arranged to form a circle coaxial with said axis.

In other words, each wedge member 24 is made up of a layer plane of pyrolytic graphite which extends along the length of said wedge and the nozzle is constructed so that each layer plane lies in a plane passing through the axis a-a of said nozzle 10.

As already stated, pyrolytic graphite has very pronounced anisotropic properties in particular with respect to heat conduction and insulation. In directions parallel to the plane of deposit, the pyrolytic graphite has excellent heat conduction properties while in a direction perpendicular to said plane the pyrolytic graphite is an excellent heat insulator. With reference to FIG. 3 wherein there is shown one of the Wedges 24 of the invention, from the discussion above, it will be seen that, in directions longitudinally and radially relative to the nozzle axis as well as in any other direction parallel to the surfaces or median plane of each of the wedges, there will be good heat conduction while in a direction substantially perpendicular to the median plane of each of said wedges 24 there will be little heat conduction. From the illustration of FIG. 3, it will be apparent that when a plurality of wedges 24 are disposed in the manner shown in FIGS. 1 and 2 to form the nozzle interior, the nozzle will have high heat conduction in directions axial along the axis aa and radially from said axis. However, in a circumferential direction with respect to said axis aa, that is in a direction from one wedge to the adjacent wedge, the nozzle will have high heat insulating properties with little heat being conducted around the nozzle in said circumferential direction. It will be apparent therefore that as the hot combustion gases flowing through the nozzle 10 from the rocket, the heat will be relatively rapidly conducted away from the inner surface of the nozzle throat region 22 and since the heat transfer from the exhaust gases to the nozzle is a maximum in the region of the nozzle throat, there will be a flow of heat longitudinally and radially outwardly in each wedge 24 from the nozzle throat region. As stated, the heat conduction will be radially away from the nozzle throat 22 and axially along said nozzle so that the heat is conducted from the area of said nozzle exposed to extreme temperatures to regions of said nozzle which are relatively cool. Thus, it will be seen that heat saturation in the nozzle throat area is delayed by allowing the heat to flow into portions of the nozzle which are relatively cool thereby forming a very efficient heat sink. As is well known in rocket nozzles, erosion of the nozzle throat area is a major problem which is caused by the region of a nozzle throat area becoming heat saturated and rising to a temperature wherein this region may decompose. In the present invention erosion is completely eliminated since the heat is conducted away from the nozzle throat area so that said nozzle throat area does not reach a temperature wherein decomposition may take place. Also, as explained above, pyrolytic graphite has relative high rate of thermal expansion in the direction of good heat insulation. In the present invention however, since good heat conduction is providid in axial and radial directions with relatively low thermal expansion in these directions, a problem in prior rocket nozzles of thermal expansion in the axial direction is substantially eliminated. This eliminates the need for providing bulky expansion joints to compensate for said thermal expansion. However, as a safely factor a slight annular space 26 is provided at the axial end of the nozzle adjacent the rocket engine to provide for any axial expansion that might take place. The axial expansion is relatively low in the present invention and has been found to be in the neighborhood of 0.004 in./in. of length.

As also explained above, pyrolytic graphite has good heat insulation properties in a direction perpendicular to the plane of deposit which in the orientation of the wedges 24 illustrated in FIGS. 1 and 2 is a circumferential direction with respect to the nozzle axis 41-41. In this direction however, each of the wedges is subject to relatively high thermal expansion. In order to compensate for the thermal expansion in the circumferential direction, each of the wedges is undercut along a substantial portion of one of its faces as indicated at 28. A small portion of each said undercut faces is not undercut so that when the wedges 24 are placed in position as illustrated in FIGS. 1 and 2, each of said Wedges will abut against the adjacent wedge in the region of the gas wall to prevent gas leakage into the undercut region. The amount of the undercut is set to limit contact between the wedges due to the circumferential thermal expansion of the pyrolytic graphite but also assures contact between the adjacent wedges at the gas wall. The undercut minimizes the amount of restrained material thereby minimizing the wrap thickness required to restrain the thermal expansion and makes the required restraining loads uniform over the length of the wrap thereby eliminating the complication of a wrap of non-uniform thickness. Due to this construction, the nozzle suffers substantially no deformation due to thermal expansion during operation and is capable of cold restarts from operation to operation. It should be understood that, in lieu of the undercuts in each of the Wedges 24, spacers may be provided between the wedges which would. permit expansion between the wedges while maintaining a gas tight seal at the inner surface of the nozzle.

An intermediate layer 20 of pyrolytic graphite which may take the form of a sleeve or a plurality of sleeves (three as illustrated) is placed in surrounding engagement with the wedges 24 with the plane of deposit of said intermediate layer 29 being disposed to provide heat insulation in a radial direction with respect to the nozzle axis a-a. As shown in FIG. 2 each of the sleeves of the intermediate layer 29 is preferably formed from a plurality of sleeve segments, there being four illustrated for each sleeve, in order to provide for slight circumferential expansion of the nozzle. The intermediate layer 29 forms a heat shield around the outer diameter of the wedges 24, as illustrated, to protect the housing or load carrying layer 12 from the heat conducted radially outwardly from hot exhaust gases passing through the; nozzle. Radially outwardly of the sleeves of the inter-- mediate layer 29 and in tight surrounding engagement. therewith is a wrapping which may comprise a tight fiting sleeve, bands or filaments made of various materialssuch as steel, plastic, glass fiber or other metals. The wrap or outer layer 30 is fit in tight engagement with the intermediate layer 29 and serves to maintain gas tight contact between the wedges 24 and to minimize the throat area change due to thermal expansion. This is achieved by pre-loading and restraining the heat sink, thereby inducing high but allowable compressive stresses between adjacent wedges. Supported at each axial end of the nozzle are a ring member 32 and a ring member 34, respectively, said rings 32 and 34 being formed from pyrolytic graphite and having their plane of deposit oriented so that said rings are non-conductive or highly heat insulating in the axial direction with respect to the nozzle axis a-a. The function of the rings 32 and 34 is similar to that of the intermediate layer 28, that is to function as a heat shield for the load carrying member or housing 12 at its axial ends as well as for the adjacent end of the rocket casing 14 so that these members are protected from the heat of the hot exhaust gases.

It will be apparent from the above detailed description that a novel nozzle construction has been provided for high temperature operation. Due to the radial and axial heat conducting characteristics of the nozzle construction, the heat will be relatively rapidly carried away from the nozzle throat region wherein temperatures are most extreme and thus prevent the possibility of erosion of the gas wall at said nozzle throat region. The heat is conducted away from the above mentioned highly-heated region to other regions of the nozzle that are relatively cool, thus preventing heat saturation of the heat sink in the highly heated regions. Further, the construction substantially eliminates axial thermal expansion of the heat sink so that cold restarts are permitted without the use of bulky expansion joints. It has also been found that the novel construction of the invention increases the critical depth of the heat sink, or outside radius, to which heat reduction can be obtained with increases in depth in the nozzle construction. It is known that the critical depth decreases with increasing convective heat transfer coefficient which is highest in the region of the nozzle throat. The invention keeps the nozzle throat relatively cool by conducting heat into portions of the heat sink where lower temperatures exist.

Erosion of the gas wall immediately forward and aft of the nozzle throat region has relatively little effect on the nozzle performance as compared to erosion in the throat region itself. It has been found that further decreases in the nozzle throat temperatures can be had in the nozzle construction of the invention at the expense of increasing the temperature forward and aft of the throat by modifying the heat sink formed by the wedge construction. In FIGS. 47 there are shown diagrammatic views of a portion of a wedge construction nozzle with the heat conduction paths being indicated by the arrows therein for the various modifications with FIG. 4 illustrating the heat conduction for a nozzle having wedges without modification. For purposes of illustration, the arrows shown in said figures only purport to show the heat conduction in a substantially radial direction with respect to the nozzle axis. It will be seen in FIG. 4 that the radial heat conduction in the nozzle 10a illustrated therein flows in a direction substantially perpendicular to the inner surface a toward the outer surface of the nozzle 10a and tends to flow toward the center portion of the nozzle throat region. As seen in FIG. 4A, wherein one of the wedges 24a is shown, the heat may be conducted radially through the wedge 24a without any substantial interruption. Therefore, it will be apparent that the heat conducted through the wedges 24a has a tendency to concentrate at a region above the nozzle throat area thus limiting the heat that can be conducted from the nozzle throat. The modifications in FIGS. 57 and 5A- 7A serve to control the flow of heat from the region of the nozzle forward and aft of the throat region into the heat sink region of the nozzle throat area and increase the heat capacity characteristics in said nozzle throat area.

In FIGS. 5 and 5A there is shown a nozzle 1% with the wedges 24b of said nozzle 10b having radiation gaps 36 and 38 formed therein to isolate the heat sink in the nozzle throat region. The radiation gaps are formed by cutting a portion through each wedge 2412 as shown in 6 FIG. 5A which upon assembly of the wedges into the nozzle forms the radiation gaps 36 and 38 illustrated in FIG. 5. Due to the orientation of the radiation gaps 36 and 38 a substantially trapezoidal-shaped heat sink is formed in the nozzle throat region. As seen from the radially heat conducting arrows of FIG. 5, the heat conducted at the gas wall forward and aft of the nozzle throat region is prevented from flowing into the nozzle throat heat sink region which, therefore, limits the amount of heat conducted into this region. As stated above, the heat conducted into the region forward and aft of the throat region is not critical to the operation of the nozzle and, therefore, heat saturation at these points in itself is not detrimental. However, due to the fact that less heat is conducted into the nozzle throat heat sink region from the region fore and aft of said nozzle throat, this permits a greater amount of heat to be conducted from the nozzle throat region itself into its heat sink before heat saturation will occur thereby permitting the nozzle throat to operate a substantially longer period before the decomposition temperature will be reached.

In FIGS. 6 and 6A there is shown a second modification wherein there is provided in the nozzle 10c two cone members 40 and 42 formed of pyrolytic graphite and having their plane of deposit disposed to insulate against heat conduction in a substantially axial direction. The heat flowing from the regions fore and aft of the nozzle throat in this embodiment cannot flow into the nozzle heat sink region adjacent the throat area due to the insulating properties of the cones 40 and 42 although heat will be conducted in a substantially radial direction along said cones 40 and 42. This embodiment functions in a similar manner as that of FIGS. 5 and 5A in that the heat sink in the nozzle throat area is not saturated with heat from the regions fore and aft of said nozzle throat area, thus increasing the capacity of the heat sink in this region for cooling the nozzle throat gas wall.

FIGS. 7 and 7A show a third embodiment of the invention wherein a portion along each longitudinal face of the wedges 24a. is cutout as illustrated in FIG. 7A to form a heat choke. As illustrated in FIG. 7, when the wedges are placed together in the nozzle a heat choke is formed at the regions forward and aft of the nozzle throat area with said heat choke extending substantially parallel to the gas wall in these regions. Each

heat choke

44 and 46 serves to bring about an abrupt reduction in the heat flow area from the region forward and aft of the nozzle throat area to block the heat flow into the interior of the heat sink forward and aft of the throat region. The function of this embodiment, therefore, is similar to that of the embodiments described above.

The invention has been illustrated and described in connection with a rocket engine exhaust nozzle. As previously stated, however, the invention has other applications particularly where a part is exposed to high temperatures for a limited period of time. For example, it may be used as a heat shield to protect the load carrying structure of other aircraft parts from the high tem peratures which exist at the external surface of those parts exposed to supersonic flow of the surrounding atmosphere thereover. The construction of the invention is applicable not only for high temperature usage on the inner surface of aircraft parts, but may be used for high temperature operation of external parts of aircraft.

While the invention has been described in detail in its present preferred embodiment it will be obvious to those skilled in the art, after understanding the invention, that various changes and modifications may be made therein without departing from the spirit and scope thereof. For example, in the region forward and aft of the nozzle throat area other materials may be substituted for the pyrolytic graphite since the temperature conditions in these areas are not as critical as in the nozzle throat area. Also, the members maybe shaped with arcuate sides instead of flat sides, as illustrated or with the plane of deposit other than substantially parallel to the median plane of each wedge member. It is intended in the appended claims to cover all such modifications.

We claim:

1. An exhaust gas nozzle construction for jet engines or the like comprising a nozzle having a substantially annular housing; a layer coaxially supported in said housing and having an inner surface which substantially conforms to at least a portion of the inner nozzle surface, said layer being composed of an anistropic material oriented so that said material is relatively highly thermally conductive in planes substantially including the nozzle axis and relatively highly thermally non-conductive in a circumferential direction about said axis.

2. An exhaust gas nozzle construction as recited in claim 1 wherein said layer comprises a plurality of substantially wedge-shaped members composed of pyrolytic graphite, said wedge-shaped members being disposed adjacent each other in a circle about the nozzle axis with the sides of each wedge-shaped member tapering toward the nozzle axis and said layer having a substantially annular cross-section.

3. An exhaust gas nozzle construction as recited in claim 2 wherein said wedge-shaped members extend axially along the nozzle axis with at least a portion of each side of each said Wedge-shaped members being placed in tight operative engagement with an adjacent wedge-shaped member.

4. An exhaust gas nozzle construction as recited in claim 3 wherein each of said wedge-shaped members has a portion of at least one of its sides cut back for providing a circumferential spacing between adjacent wedge-shaped members such that said spacing permits thermal expansion between adjacent wedge-shaped members in a circumferential direction relative to said nozzle axis.

5. An exhaust gas nozzle construction as recited in claim 4 wherein each wedge-shaped member has an undercut portion over a substantial portion of one face thereof and at the radially inner portion thereof having a land on said one face for abutting an adjacent wedgeshaped member .to provide a substantially gas tight structure for the radially inner surface of said layer.

6. An exhaust gas nozzle construction as recited in claim 3 wherein each wedge-shaped member has a plurality of gaps formed therein extending between the sides thereof; and said gaps of each wedge-shaped member being aligned with the gaps of adjacent wedgeshaped members to form a plurality of radiation gaps in said layer, said radiation gaps being inclined from the nozzle throat with respect to the inner surface of said nozzle and extending from a region adjacent the nozzle throat substantially into the regions of said layer forward and aft of the nozzle throat for limiting the conduction of heat into the region of said layer adjacent the nozzle throat from the regions of said layer forward and aft of the nozzle throat.

7. An exhaust gas nozzle construction as recited in claim 3 wherein said wedge-shaped members are of multi-par-t construction; said layer further comprising at least two facing cone-shaped members composed of pyrolytic graphite spaced between adjacent parts of each of said wedge-shaped members with said cone-shaped members separating the nozzle throat region of said layer from the regions of said layer forward and aft of said nozzle throat region; and said cone-shaped members being oriented in said layer for relatively high heat insulation in a direction substantially parallel to the direction of gas flow through said nozzle such that heat is substantially prevented from flowing into the region of said layer adjacent the nozzle throat from the region of said layer forward and aft of said nozzle throat.

8. An exhaust gas nozzle construction as recited in claim 3 wherein each wedge-shaped member has a channel cut in each said side thereof and said channels of each wedge member being aligned with the channels of adjacent Wedge-shaped members to form at least two heat chokes in said layer, said heat chokes extending substantially parallel to the inner surface of said nozzle from the region adjacent the nozzle throat into the regions of said layer forward and aft of the nozzle throat to the region adjacent the axial ends of said layer for limiting conduction of heat into the region of said layer adjacent the nozzle throat from the regions of said layer forward and aft of the nozzle throat.

9. An exhaust gas nozzle construction as recited in claim 1 comprising; an intermediate layer of anistropic material in surrounding engagement with said firstmentioned layer; and said intermediate layer having an orientation such that it is relatively highly thermally non-conductive in a radial direction with respect to the axis of said nozzle for forming a heat shield around the radially outer surface of said first-mentioned layer.

10. An exhaust gas nozzle construction as recited in claim 9 wherein said intermediate layer includes an annular sleeve member comprising a plurality of circumferentially-spaced sleeve segments for permitting circumferential expansion of said segments.

11. An exhaust gas nozzle construction as recited in claim 9 wherein said nozzle has a convergent-divergent flow path for the exhaust gases flowing therethrough; and the radial depth of said first-mentioned layer being substantially greater than the radial depth of said intermediate layer at least in the region of said nozzle throat.

12. An exhaust gas nozzle construction as recited in claim 9 further comprising an outer layer surrounding said intermediate layer with said outer layer in tight fitting engagement with said intermediate layer for supporting said first-mentioned and intermediate layers in said nozzle housing and said outer layer extending substantially the entire length of the inner surface of said nozzle housing.

13. An exhaust gas nozzle construction as recited in claim 1 further comprising a ring member composed of anisotropic material supported at each axial end of said nozzle in engagement with said layer with said anisotropic material of said ring members being oriented for relatively high thermal non-conduction in a direction substantially parallel to the axis of said nozzle for providing a heat shield at said axial ends of said layer.

14. An exhaust gas nozzle construction as recited. in claim 13 wherein said ring member at the axial gas receiving end of said nozzle is spaced from the axial end of said nozzle housing for permitting slight axial thermal expansion of said nozzle construction.

15. An aircraft part or the like having a surface exposed to high temperature gas flow thereover, said part having structural load carrying means; an intermediate layer of heat insulating material disposed over said load carrying means; a layer of material disposed over said intermediate layer and having its surface remote from said intermediate layer exposed to said high temperature gas flow, and said layer being composed of an anisotropic material with said material being oriented so that at least at its surface remote from said intermediate layer has its relatively high thermal conduction in a first direction substantially parallel to the direction of gas flow and a second direction substantially perpendicular to the direction of gas flow and having relatively high thermal non-conduction in a third direction perpendicular to said first and second directions.

16. An aircraft part as recited in claim 15 wherein said anisotropic material is pyrolytic graphite.

17. An aircraft part as recited in claim 16 wherein said intermediate layer is composed of pyrolytic graphite 9 it} With said pyrolytic graphite being oriented so that it is References Cited by the Examiner relatively highly thermally non-conductiye in a direc- UNITED STATES PATENTS tion substantlally perpendicular to the direction of gas flow for providing good heat insulation between said 3,137,132 6/1964 Turkat 60-355 second-mentioned layer and said load carrying means. 5

18. An aircraft part as recited in claim 17 wherein the thickness of said second-mentioned layer is substantially greater than the thickness of said intermediate MARK NEWMAN Prlmmy Exammer' layer. SAMUEL LEVINE, Examiner.

Claims

1. AN EXHAUST GAS NOZZLE CONSTRUCTION FOR JET ENGINES OR THE LIKE COMPRISING A NOZZLE HAVING A SUBSTANTIALLY ANNULAR HOUSING; A LAYER COAXIALLY SUPPORTED IN SAID HOUSING AND HAVING AN INNER SURFACE WHICH SUBSTANTIALLY CONFORMS TO AT LEAST A PORTION OF THE INNER NOZZLE SURFACE, SAID LAYER BEING COMPOSED OF AN ANISTROPIC MA-