EP0078921B1 - Tail unit with reduced ground wind sensitivity - Google Patents

Description

The invention relates to an empennage of the type specified in the preamble of claim 1.

Tail units cause the longitudinal stability of unguided missiles. In the case of guided missiles, generally only a low level of longitudinal stability is sought in order to facilitate longitudinal control. However, there is also the possibility of artificially stabilizing an unstable guided missile using a controller built into the control.

The stabilizing effect of an empennage arises from the fact that when the missile rotates out of the direction of flight, the empennage generates a turning moment that continues until the missile is turned back in the direction of flight. This turning back, eliminating the disturbance moment about the center of gravity of the missile comes about because the tail unit is attached behind the center of gravity of the missile and acts as a wing due to the deflection from the flight direction. Is the buoyancy, i.e. If the stability is high, the disturbance is eliminated quickly; if it is small, the disturbance is only slowly compensated for. If the tail lift is insufficient, the deviation from the flight direction increases until the missile "breaks out" after a certain time and the missile longitudinal axis is rotated by 90 ° to the flight direction.

With high longitudinal stability, a momentary deviation from the direction of flight is quickly eliminated, but disadvantageously also with ground wind, i.e. here with wind components that do not work in the direction of flight. This should be illustrated using the example of a crosswind acting from the left when viewed in the direction of flight. This wind causes the missile to no longer flow axially, but at an (usually small) angle from the left at the resulting speed. Due to the above-described mode of operation of the tail unit, the missile is now turned into the wind until the crosswind component has become zero. But this means a deviation from the direction of launch. Only weak stabilization reduces the sensitivity to cross winds.

For aerodynamic reasons, the effectiveness of wings in subsonic flow increases with increasing flight speed, but decreases in supersonic. In the case of unguided supersonic missiles, the tail unit must therefore be at least large enough that it is also sufficient for stabilization at the maximum speed, which then results in a high sensitivity to ground wind in the known tail units.

It is known to reduce the sensitivity to ground wind by a high take-off acceleration because the over-stabilization phase is short, or by tail units that remain completely closed after take-off or in accordance with DE-A-2045687 until the missile breaks out due to instability begins. Combinations of both methods are also known.

In the first case, structural and / or rocket-related problems as well as a reduced flight distance are disadvantageous because the highest flight speed near the ground, i.e. with a correspondingly high air resistance, and in the second case the necessary installation of an opening delay, which can only be optimized on a side wall of certain intensity and duration.

The invention has for its object to design a tail so that it is particularly effective at the highest airspeed in comparison to the take-off speed in order to be able to use a fixed tailplane or a tailplane that opens immediately after takeoff.

This object is achieved in accordance with the characterizing part of claim 1. To reinforce the pressure equalization, the fins of the tail unit can be provided with openings or recesses in their fully flowed area outside the contour of the missile. For example, these can be designed as perforations which are arranged in the region of the end of the fins facing the missile fuselage. This pressure equalization has the consequence that the lift and thus the stabilizing effect of the tail are reduced. Since the pressure equalization is stronger for aerodynamic reasons at low airspeed after takeoff than at supersonic speed, the measure according to the invention has the consequence that such an empennage also works worse at high airspeeds than a conventional one, but particularly poorly at low airspeeds works. However, this means that it is less sensitive to cross winds.

Another particularly advantageous measure to achieve pressure equalization between the top and bottom of the fin is specified in claim 1. The term "stretching" is understood to mean the ratio of the square of the span of the fins to their plan area. The pressure difference between the top and bottom that balances out at the free fin ends leads to a reduction in buoyancy, and the greater the smaller the stretch is. This influence also depends on the airspeed, in such a way that at the intended maximum supersonic speed, the lift reduction associated with the reduction in the stretch is relatively small, whereas it is comparatively large at the low airspeeds after takeoff. In order to achieve the same stabilizing effect at the final speed, the area of the tail unit according to the invention must therefore be increased accordingly compared to a conventional one. Because of the much stronger one Buoyancy reduction at low flight speeds is still a considerable reduction in wind sensitivity. Tail units with an aspect ratio of less than 1 have proven to be particularly advantageous, whereas conventional tail units generally have an aspect ratio of approximately 2.5 to 3.

The reduction of the influence of wind by using tail units with a small extension can be difficult with conventional construction, since this leads to tail units whose depth or axial extension is large compared to their wingspan. This requires a correspondingly long tail of the missile or results in tail units, the wingspan of which would disappear within the caliber and can therefore no longer be implemented.

According to the invention, the formation of the tail unit according to claim 2 can be provided in these but also other cases. The tail unit is then broken up into individual wings, each of which can easily be designed as a wing with a small extension. The individual wings are not attached to the fuselage as usual, but at such a lateral distance from it that their inner ends facing the fuselage are also fully exposed to the air flow. This not only results in pressure equalization over the outer ends, but also over the inner ends of the wings. The latter is, however, reduced by the web-shaped mounting of the wings and the certain width of the intermediate space compared to the theoretical value, so that the effective extension of the individual wings is greater than their geometric, which must be taken into account in their design.

The reduction in the effectiveness of an empennage, namely more with subsonic flow than with supersonic flow, can also be achieved by means of slot-shaped recesses within the fin plan area. Another possibility is specified in claim 3.

• Fig. 1 ein konventionelles Leitwerk,
• Fig. 2 ein Leitwerk kleiner Streckung,
• Fig. 3a und b Leitwerke mit Einzelflügeln,
• Fig. 4a bis e Leitwerke mit Durchbrechungen,
• Fig. 5a und b Leitwerke mit perforierten Einzelflügeln und
• Fig. 6 ein Leitwerk mit gekippter Flügelanordnung.

The invention is shown schematically in the drawing in exemplary embodiments and is explained below with reference to this. They each show in the view

• 1 is a conventional empennage,
• 2 an empennage of small extension,
• 3a and b tail units with individual wings,
• 4a to e tail units with openings,
• 5a and b tail units with perforated individual wings and
• Fig. 6 is an empennage with a tilted wing arrangement.

Fig. 1 shows the tail 1 of a missile with a conventional empennage of great extent. The fins 2 have a rectangular plan with the span b and the depth I, where b = 3 I. This gives the extension as a square of the span, divided by the floor plan, the factor 3.

2 shows a tail unit according to the invention, in which the aspect ratio is small in contrast to this. Small is understood to mean an extension of less than 1.5. It is preferably less than 1. In the case shown, it is just 1 when b = I.

In the tail unit shown in FIG. 3a, the fins 2 are designed as single wings with a small extension, which are connected to the fuselage 1 via a web 3 in each case. The fins 2 are arranged at a distance a from the fuselage 1 and thus outside the contour of the missile in the region of its tail so that they extend in their entire extent, i.e. are also fully exposed to the flow according to arrow A with their inner end 2 '. The extension is reduced b = 0.5 I to a factor of 0.5.

The tail unit otherwise corresponds to the conventional structure, i.e. it consists of at least three, preferably four but also more than four fins 2, which are firmly connected to the fuselage 1 in flight. The trailing edge of the fin and the trailing edge of the fuselage do not have to lie in one plane. In the case of folding stabilizers, the holder 3 can be fastened to the fuselage 1 in a known manner so that it can be rotated and locked. A corresponding mechanism can also be present at the interface of the holder 3 and fin 2. For aeroelastic reasons, it is advantageous if the holder 3 is fastened to the front of the fin 2 so that it is more or less turned into the wind by the buoyancy and resistance forces acting on it, with corresponding deformation of the holders, i.e. their angle of attack is reduced.

Fig. 3b, which, like the other figures for the sake of simplicity, only shows a partial view of the tail units, shows one with two retaining webs 3 on the fuselage 1 at a distance a, i.e. fin 2 fastened while leaving the gap or space 4.

In the variant shown in Fig. 4a, the pressure compensation is achieved by an axially extending perforation 5, which is preferably arranged in the area of the fin-fuselage transition, but also in other areas of the fin plan, albeit with a reduced effect can be. This perforation, which extends over the entire depth of the fins, advantageously advantageously approximately divides the entire tail unit into individual wings with a small extension. In this way, existing conventional tail units can also be modified with relatively little effort.

FIG. 4b shows a version in which instead of the perforation according to FIG. 4a, a longitudinal slot 6 open at the rear is provided, which instead could also be open at the front or, according to FIG. 4c, can also be designed as a slot 6 'closed at both ends . Here too, an approximate division into single wings with a small extension is achieved, which can also be applied to existing conventional tail units.

4d and e show variants with a similar pressure-equalizing effect, in which the slot-like or triangular recesses 7, 7 'are essentially transverse to the longitudinal axis of the missile, ie extend in the span direction of the fins 2.

The various possibilities of pressure equalization can also be combined with one another, as shown in FIGS. 5a and b with individual wings 2, webs 3 and perforations 5, if e.g. in the course of the design of a tail unit should show that the brackets 3 hinder the lateral pressure compensation too much.

6 finally shows a tail unit with fins 2 turned forward, in which these can be rigidly attached to the fuselage 1 with their one corner 8. This corresponds to FIG. 3a if a smooth transition between fin 2 and holder 3 is provided in this. However, it is also possible to design it as a folding tail unit with the turn-tilt bearing 9, in which, in a known manner, the fins 2 are first opened up about an axis parallel to the longitudinal axis of the missile and then tilted forward or, depending on the arrangement, also backwards . This results in a tail assembly that is aerodynamically favorable in terms of reducing the effectiveness of the tail unit by the exhaust gas jet.

The fins shown in Figs. 2 to 6 have a rectangular plan, but this is not a requirement. In the case of folding stabilizers in particular, other layouts may also arise for structural reasons. The effect of the tail units according to the invention, the reduction in ground wind sensitivity, does not change as a result.

For the sake of simplicity, the rigid tail units according to the invention that are shown or that open up at the start do not change their configuration during the flight. However, more complicated tail assemblies are also possible with an effort comparable to the known late-opening tail assemblies, which enable a further reduction in the sensitivity to ground wind. For example, in the variant shown in FIG. 3a, the fin 2 is mounted so as to be resiliently rotatable about the axis of the web 3. As a result, the position of this fulcrum - viewed in the direction of flight - before the point of application of the lift force on the fin 2, its angle of attack is smaller than that of the fuselage, which means an effective reduction in the effectiveness of the tail unit.

Non-guided missiles are designed to rotate to compensate for asymmetries. The speed of rotation around the longitudinal axis increases with the airspeed. The centrifugal force or the dynamic pressure can be used to to lock. Correspondingly, perforations can be sealed or tail fins e.g. 6 are rotated on the fuselage in order to reduce the stability-reducing influence of the small aspect ratio or to eliminate it, if necessary, with increasing flight speed.

Claims (3)

1. Fixed or hinged tail unit for guided or unguided supersonic missile, characterised in that the fins (2) of the tail unit are formed for reducing their effectiveness at the beginning of the flight phase so that a reinforced pressure equalisation between their upper and lower sides is possible by the fins (2) exhibiting a small elongation, in particular an elongation less than 1, and/or the fins (2) being provided externally of the contour of the flight body in the region of their end directed to the flight body with perforations, slits (5, 6, 6') or the like extending in the longitudinal direction.

2. Tail unit according to claim 1, characterised in that the fins (2) are formed as separate wings acting independently of one another, which are arranged spaced apart from the tail of the flight body (1) while retaining an intermediate space (4) lying outside the contour of the flight body and are connected with this by means of at least one web (3) bridging over the intermediate space (4).

3. Tail unit according to claim 1, characterised in that the fins (2) are inclinedly arranged and are only connected at one corner (8) with the tail (1) of the flight body.

Images