GB2045704A - Deflecting a rocket exhaust stream - Google Patents

Abstract

Rocket propulsion unit for guided missiles, with a jet deflection system for vectored thrust, wherein the thrust nozzle 8 has an extension bell 12 immediately following the outlet mouth 10 of the nozzle and extending beyond the expansion ratio corresponding to ambient pressure. To effect jet deflection control impulses are arranged to take effect in a desired direction of deflection and are fed through control apertures 24B, 28A distributed around the periphery of the nozzle. The control apertures feed into a marginal zone at the outlet end 10 of the nozzle and are connected to an injection system 14 which provides the apertures with pressure gas or liquid (e.g. a refrigerant) as a control fluid. Fins 16, 18, 20 may be provided between two closely adjacent nozzles whereby roll control may be effected through differential feed of control fluid to each nozzle. <IMAGE>

Description

SPECIFICATION Rocket propulsion unit primarily for guided missiles This invention relates to a rocket propulsion unit primarily for guided missiles, having a deflection system for the thrust exhaust stream and wherein the thrust nozzle has an extension immediately following the divergent outlet of the nozzle and extending beyond that ratio of expansion which corresponds to ambient pressure. Control impulses which take effect in selected directions of deflection being fed to control apertures distributed around the periphery of the nozzle.

For thrust vector control of rocket propulsion units systems are known in which a control fluid is injected at high excess pressure points into the thrust nozzle in order to effect a jet deflection and to thus produce lateral components of thrust in desired directions. Thrust vector control systems of this kind are only effective in yaw and pitch and do not provide control of roll about the longitudinal axis of the propulsion unit. For the deflection process considerable quantities of control fluid are required in relation to the mass throughput of the thrust nozzle and correspondingly large throughflow cross sections are used for the injection apertures, resulting in undesirably long response times and bulky construction and excessive weight for the control fluid system.

In propulsion units in which the deflection is effected by Coanda effect, a number of selectively controllable air inlet apertures are provided distributed around the nozzle periphery in the thrust nozzle extension part at the outlet of the nozzle. These produce control impulses by virtue of ambient air being drawn in for a short period of time or, if the jet does not automatically attach to the thrust nozzle extension by the Coanda effect, for the whole duration of the deflection process. This results in an asymmetrical distribution corresponding to the desired direction of deflection into an under-pressure zone in the thrust nozzle or in that part of the thrust nozzle extention which is adjacent the outlet of the nozzle.A deflection system of this kind using controlled suction intake of ambient air suffers from the disadvantage that considerable through-flow areas for the air suction apertures have to be opened and closed and undesirably long switching times for the deflection or reversal of the jet and also a bulky air control structure are required. Control or stabilizing the missible as regards roll is not possible. In addition, the position of the under-pressure zone depends on the ratio between the combustion chamber pressure and the ambient pressure, so that if the ratio changes during flight the under pressure zone may move and the emission of a control pulse through the air suction intake apertures and the entire thrust vector control will be impeded or even nullified.

An object of this invention is to provide a rocket propulsion unit with thrust vector control which will, if required, prove effective in a roll direction, with short response times, a limited rate of mass throughput and limited through-flow cross sections for the control apertures.

According to this invention there is provided a rocket propulsion unit with a deflection system for the thrust exhaust jet and wherein the thrust nozzle has an extension immediately following the divergent outlet of the nozzle and extending beyond the point where the expansion ratio produces ambient pressure jet deflection control impulses each taking effect in a certain desired direction of deflection being fed to control apertures distributed around the periphery of the nozzle, the control apertures opening into a marginal zone at the outlet end of the nozzle and connected to an injection system which supplies the said apertures with pressure or liquid as a control fluid.

In the invention, using injection of a control fluid of high density, preferably a cooling fluid under pressure, into a marginal zone having good jet deflecting action through constructionally simple fluid injection system which may be built with small volume and weight in the zone of the control apertures, the control impulses and control impulse changes are moderate in relation to the volumetric and quantitative throughput and thus provide short response times. Reliable thrust vector control is provided even when the pressure at the control apertures, as a result of fluctuations in the pressure ratio, temporarily rises above ambient pressure.By means of fins or spoilers used in conjunction with the injection of control fluid roll control is effected, in addition to which the thermal stress undergone by the fins or spoilers, apart from the cooling action of the control fluid, is considerably reduced mainly due to their position in the thrust nozzle. This provides a considerable advantage for those parts of the fins or spoilers which extend into the thrust nozzle jet.

Control fluid impulse may be fed in through one or through a number of simultaneously operative control apertures for a short time until the jet is deflected or, in the case of a less distinct Coanda effect, for the duration of the jet deflection operation. The remaining control apertures are kept closed.In order to simplify the control impulse production the control fluid injection process may take place subject to a pulsating through-flow but with a pulse duration which is varied in accordance with the particular lateral thrust or roll desired at the time, in such a way that in the event of a change in the thrust vector the difference between the quantity of control fluid injected through one control aperture and that injected through the aperture acting in the opposite direction is altered by regulating the respec tive impulse durations of these control aper tures in opposite sense.

The invention is further explained in more detail by reference to an embodiment shown as example in the accompanying drawings. In the drawings: Figure 1 shows a schematic longitudinal section through a rocket propulsion unit in accordance with the invention, and Figure 2 shows a section on line 2-2 of Fig. 1 to a larger scale.

The rocket propulsion unit 2 shown in the drawings is for a guided missile and has a combustion chamber 6 with a solid propulsive charge 4 and a convergent/divergent thrust nozzle 8 following the chamber and having a divergent thrust nozzle extension 1 2 which immediately follows the outlet end 10 of the nozzle and which extends beyond that ratio of expansion corresponding to the ambient pres sure. In the thrust nozzle 8 a narrow reduced pressure zone is created at the outlet end 10 of the nozzle and in that part of the thrust nozzle extension 1 2 which is adjacent to the said end.Into this zone measured quantities of cooling fluid under pressure, such as freon, are injected by an injection system 14 at points in the thrust nozzle prolongation 1 2 distributed over the periphery of the nozzle, so that by making use of the Coanda effect a jet deflection is obtained in the thrust nozzle extension 1 2 and thus pitch and yaw control is effected as well as roll control.

For roll control the part of the extension 1 2 which is adjacent to the end 10 of the thrust nozzle has four rib-shaped fins 16, 18, 20, 22, directed radially inwards and located in diametrically opposed pairs mounted rigidly 90 apart. The injection or control apertures 24A, B, 26A, B, 28A, B, of the injection system 14 are situated on the sides of each fin at the upstream end and are connected through an electrically actuated control valve 32 to an annular conduit 36 supplied from a tank 34 with cooling fluid under pressure.

As the fins 16-22 are subject to the flow of the cooling fluid injected through the control apertures 24-30 and are of comparatively thin section as well as being situated in a zone in which the reaction gases generated in the combustion chamber have already expanded with a corresponding reduction in temperature, they are protected against unacceptably high thermal stresses.

For the pitch and yaw control, diametrically opposed control apertures act in opposite directions to one another so that the decisive factor for the control effect is the difference between the quantity of fluid injected through one control aperture and the quantity injected through that aperture situated opposite thereto. Referring to Fig. 2 when the quantity of cooling fluid injected through the control apertures 24A and B totals more than that injected through the control apertures 28A and B then the jet is deflected downwards. By appropriate control of the individual quantities injected through the control apertures immediately adjacent to each jet fin, therefore, it is possible to regulate the lateral thrust component which takes effect about the pitch and yaw axis.

The injection of cooling fluid also produces a local cooling front which attaches to that wall of the fin which is immediately adjacent to the injecting control aperture and this produces a roll moment about the longitudinal axis of the propulsion unit. If the individual quantities of cooling fluid injected on the two sides of each fin are equal, then the forces acting in the roll direction will cancel. In the event of an increase in the amount injected through the control apertures with suffix A the jet propulsion unit will be subjected to an anticlockwise roll moment. In the event of an increase in the amount injected through "B" apertures the roll moment will be clockwise.

The quantities of liquid supplied through the individual control apertures are regulated by a control means 38 through which electrically operated valves 32 are provided with inphase pulsation with an individual impulse duration selectable in each case. The quantity of cooling fluid injected through all control apertures together is mainly constant, and the magnitude and direction of the control moments generated about the three principal axes of the propulsion unit are dependent on the one hand on the subdivision of the overall quantity of cooling fluid between the four jet fins 16-22 and on the other hand on the way in which each individual quantity is then subdivided between the control apertures on the two sides of each fin.

Claims (6)

1. A rocket propulsion unit with a deflection system for the thrust exhaust jet and wherein the thrust nozzle has an extension immediately following the divergent outlet of the nozzle and extending beyond the point where the expansion ratio produces ambient pressure, jet deflection control impulses each taking effect in a certain desired direction of deflection being fed to control apertures distributed around the periphery of the nozzle, the control apertures opening into a marginal zone at the outlet end of the nozzle and connected to an injection system which supplies the said apertures with pressure or liquid as a control fluid.

2. A rocket propulsion unit in accordance with Claim 1, wherein the control fluid injection is pulsed with a selectively variable impulse duration at the control apertures which are provided in the thrust nozzle extension in the vicinity of the outlet of the nozzle.

3. A rocket propulsion unit in accordance with Claim 1 or 2, wherein the control fluid is a pressurised fluid.

4. A rocket propulsion unit in accordance with any preceding claim, wherein fins extend into the thrust jet and are positioned to be cooled by the control fluid in the thrust nozzle extension in the vicinity of the outlet end of the nozzle.

5. A rocket propulsion unit in accordance with any preceding claim, wherein pairs of fins are positioned opposite one another and directed radially inwards in the thrust nozzle extension, control apertures being provided on the two sides of each fin.

6. A rocket propulsion unit substantially as herein described with reference to the accompanying drawings.