RU2536361C1 - Antenna dome - Google Patents

Abstract

FIELD: radio, communication.

SUBSTANCE: antenna dome comprises a ceramic shell, a metallic attachment frame and the heat-insulating ring located between them, connected to the shell and the frame with the heat-resistant adhesive. The ring is made of heat-resistant glass-plastic composite based on aluminium-chromium-phosphate, polyimide, organic-silicon and phenol-formaldehyde binders.

EFFECT: improvement of impermeability and stability of the antenna dome to the effects of dynamic loads under conditions of prolonged thermal-power exposure.

2 cl, 1 dwg

Description

The invention relates to the field of aviation-rocket technology, mainly to the designs of nasal radiolucent fairings, which are a shelter from aerodynamic impact for antenna devices of homing heads (AU GOS).

The main problem of creating a workable design of the antenna fairing, in addition to providing the specified radio technical characteristics (PTX), is the creation of a reliable connection between the fairing and the adjacent compartment of the aircraft (LA), in particular rockets. The complexity of the constructive solution to this problem is often due to the problematic direct connection of the radiotransparent fairing shell made of brittle ceramic material with a metal frame connecting the nose compartment with the adjacent rocket compartment.

Ceramic dielectric materials used for the manufacture of radiotransparent shells of fairings have a low temperature coefficient of linear expansion (TEC) in the entire range of operating temperatures, and the metal materials used for the manufacture of frames are initially high (except for some invar alloys in the range -60 + 300 ° C ) and increasing with increasing heating. In the process of aerodynamic heating of the fairing when the shell and the frame are directly connected, tensile stresses arise in the ceramic shell caused by the radial expansion of the frame exceeding the radial expansion of the shell. Due to the low tensile strength of the ceramic material, these stresses reach the ultimate strength of the ceramic and lead to destruction of the shell.

At the same time, in modern missiles, the outer surface of the ceramic cowl shell in the connection zone with the adjacent compartment is heated to 1000-1200 ° C with a total duration of the regime of 10-15 minutes, which leads to heating of the frame to temperatures of more than 300-350 ° C. Such heating of the frame leads to the destruction of a brittle ceramic shell having a limited thickness determined by the electrical calculation of the wall thickness, even with some thickening (up to 30% of the nominal wall thickness) in the non-radio-transparent zone (zone of the junction site). A significant increase in the wall thickness of the shell in this zone in order to reduce spacer tensile stresses is most often impractical for technological reasons.

The known design of the antenna cowl (RF patent No. 2209494, IPC 7 H01Q 1/42, 2002), comprising a ceramic shell and a metal frame connected by a heat-resistant adhesive, in which a slight decrease in the heating of the frame and hardening of the shell is achieved by the fact that the shell is made in one piece from an internal power element made of porous ceramic and impregnated with polymer, and an external heat-shielding element. The main disadvantage of this design is the lack of strength of the internal power element for the perception of prolonged heat force effects on the structure, leading to the heating of the frame over the maximum temperature compatibility for thermal expansion of the shell materials and the frame.

The closest device in terms of features selected as a prototype is an antenna cowl according to US patent No. 4520364, IPC 6 H01Q 1/28, 1/42, 1985, including a radiolucent sheath, a heat-insulating section in the form of a ring made of composite material on a polyimide binder, metal butt frame and elements of their connection. The ceramic shell is connected coaxially with the heat-insulating section and the butt frame on tapered mating surfaces with heat-resistant adhesive and using standard fasteners. The introduction of a heat-insulating section into the fairing design allows to reduce the temperature of the metal frame to acceptable values.

Reasons limiting the use of this invention are:

- the use of heat-insulating sections in this design allows to reduce the temperature on the frame for a short time and can not ensure the performance of the structure in conditions of increased heat power, because all structural elements are spaced along the longitudinal axis and are interconnected only by adhesive, and the entire external load of the adhesive is perceived, excluding the structural elements themselves from the “work”; when the adhesive bond between the elements is weakened, the structure catastrophically collapses;

- prolonged heating of the structure, even with a slight external force, weakening the adhesive bond between its elements, helps to reduce the tightness of the internal volume of the fairing and reduces resistance to dynamic loads (vibration, vibration, linear acceleration, etc.), which also leads to structural failure;

- to strengthen the adhesive bond between the elements, the radial movement of the frame during heating is not used.

The objective of the present invention is to ensure the operability of the antenna fairing under conditions of increased heat load of structural elements caused by the long duration of the aerodynamic impact on the fairing.

The problem is solved by the fact that the proposed:

1. Antenna fairing containing a ceramic shell, a metal butt frame and a heat-insulating ring located between them, characterized in that the ring is made of heat-resistant fiberglass with a normal elastic modulus in tension 2-2.5 times less than the normal elastic modulus of the ceramic shell, and the thickness rings selected from the ratio:

$${\alpha }_{\mathrm{about}b}\cdot E_{\mathrm{about}b}\cdot {\delta }_{\mathrm{from}\mathrm{to}}={\alpha }_{\mathrm{from}\mathrm{to}}\cdot E_{\mathrm{from}\mathrm{to}}\cdot {\delta }_{\mathrm{about}b}\left(\text{one}\right)$$

where α _about - TECL shell;

α _SK - TECL fiberglass ring;

E _about - the modulus of normal elasticity of the shell;

E _SK - the modulus of normal elasticity of the fiberglass ring;

δ _about - the wall thickness of the shell;

δ _ck is the thickness of the fiberglass ring.

2. The antenna fairing according to claim 1, characterized in that as a heat-resistant fiberglass selected fiberglass based on chromium-phosphate, polyimide, organosilicon or phenol-formaldehyde binders.

The drawing shows a longitudinal section of an antenna cowl in the area of the node connection with the adjacent compartment.

Antenna fairing includes a ceramic shell 1, a metal butt frame 2 and a heat-insulating layer 3 made in the form of a ring coaxially connected by heat-resistant adhesives 4 and 5 with a shell and a frame. The ring is made of heat-resistant fiberglass, the normal tensile modulus of which is much lower than the modulus of the shell material in the range of operating temperatures. The necessary modulus of normal elasticity of fiberglass is provided by the regulation of the porosity of the material of the ring.

While the heating of the frame occurs in the range of relative compatibility of the thermophysical characteristics of the shell materials, the insulating layer and the frame, the joint is not in a state of mutual constraint of deformations caused by the difference in thermal expansions of these structural elements.

As the frame warms up, the system leaves its relatively equilibrium state, a gradually expanding spacing of the ceramic shell with a heat-insulating fiberglass ring appears, since the thermal expansion coefficient of its material is higher than the thermal expansion coefficient of ceramic and the fiberglass ring itself with a metal frame. At the same time, softening of the binder in the fiberglass ring begins, which contributes to the deformation of the ring under the influence of the spacer forces of the frame.

Since almost all heat-resistant fiberglass has a compressive strength significantly lower than the tensile strength, tensile stresses arising in the ring do not lead to destruction of the ring from thermal expansion by the frame, since the expansion of the frame is neutralized by the deformation of the collapse of the ring and the sealing of its wall. The ceramic shell and the fiberglass ring are made of materials that are relatively compatible for thermal expansion coefficient, but the shell has a higher modulus of normal elasticity of the material and a greater wall thickness, therefore, deformation of the ring under the influence of the expansion of the frame does not cause significant tensile stresses in the shell, leading to its destruction. Thus, the ring between the shell and the frame is in a complex stress-strain state, and there is reason to believe that the thermal expansion of the frame is suppressed by the deformation of the fiberglass ring and adhesive and enhances the direct connection between the structural elements; the possibility of transferring the external power load perceived by the shell to the frame through fiberglass depends on the thermal strength of the fiberglass, its geometrical parameters and the magnitude of the external load on the fairing, as well as the degree of its preload by the frame to the ceramic shell. During long-term flight conditions of the rocket, the external load on the fairing reaches its maximum in the active part of the trajectory, when significant connection node heating has not yet occurred, in the marching part of the trajectory the load is relatively low, but can significantly increase at the end of the flight, therefore, the heat resistance and thermal strength of fiberglass are of decisive importance .

The operability of the design of the connection unit is ensured as long as the adhesive strength of the shell with the fiberglass ring is maintained, and the circumferential tensile stresses arising in the fiberglass ring from being expanded by the frame do not exceed the permissible ones. The choice of heat-resistant adhesives for connecting structural elements to each other is due to the level of temperature along the length of the joint. For example, a fiberglass ring and a frame can be connected with a Vixint U-2-28 elastic sealant, and the connection of the shell and the ring, as the most heated, can be made with hard heat-resistant adhesive, for example VK-58 or VK-15.

It has been calculated and experimentally established that in order to ensure the operability of the fairing structure and to exclude the occurrence of tensile stresses in the ceramic shell caused by expansion of the frame that exceed the permissible limits, it is necessary that relation (1) is satisfied, from which

$${\delta }_{\mathrm{from}\mathrm{to}}={\alpha }_{\mathrm{from}\mathrm{to}}\cdot E_{\mathrm{from}\mathrm{to}}\cdot {\delta }_{\mathrm{about}b}\text{/}{\alpha }_{\text{about}}\cdot E_{\text{about}}\left(\text{2}\right)$$

, тогда $$к={\alpha }_{ск}\cdot E_{ск}/{\alpha }_{об}\cdot E_{об}\left(\text{3}\right)$$

Denote $${\delta }_{\mathrm{from}\mathrm{to}}/{\delta }_{\mathrm{about}b}=\mathrm{to}$$

then $$\mathrm{to}={\alpha }_{\mathrm{from}\mathrm{to}}\cdot E_{\mathrm{from}\mathrm{to}}/{\alpha }_{\mathrm{about}b}\cdot E_{\mathrm{about}b}\left(\text{3}\right)$$

where k is the coefficient of proportionality.

In the manufacture of a heat-insulating ring from a material whose normal elastic modulus is 2-2.5 times less than the ceramic shell material module, the developed antenna cowl design allows the cowl to be operable when the frame is heated to temperatures of 400-500 ° C (the restriction is due to the heat resistance of the fiberglass material of the ring) ; the ratio of the thicknesses of the ceramic shell and the fiberglass ring corresponds to the proportionality coefficient k = 0.4-0.5.

This design of the antenna cowl can be implemented with ceramic shells and fiberglass rings, the materials of which even have low strength characteristics, provided they are highly heat resistant and have sufficient building height to organize the connection.

Achieved technical result of the application of the invention is the ability to create workable designs of antenna fairings under conditions of prolonged aerodynamic exposure, creating heat fluxes that lead to heating of the heat-insulating layers in the joints with the shell to 600-650 ° C and metal frames to temperatures of 400-500 ° C.

Claims (2)

1. Antenna fairing containing a ceramic shell, a metal butt frame and a heat-insulating ring located between them, connected to the shell and the frame by heat-resistant adhesive, characterized in that the ring is made of heat-resistant fiberglass with a normal elastic tensile modulus of 2-2.5 times less modulus of normal elasticity of the ceramic shell, and the thickness of the ring is selected from the relation

where α _about - TECL shell;
α _SK - TECL fiberglass ring;
E _about - the modulus of normal elasticity of the shell;
E _SK - the modulus of normal elasticity of the fiberglass ring;
δ _about - the wall thickness of the shell;
δ _ck is the thickness of the fiberglass ring. 2. The antenna fairing according to claim 1, characterized in that as a heat-resistant fiberglass, fiberglass based on aluminum-chromate-phosphate, polyimide, organosilicon or phenol-formaldehyde binders is selected.