GB2162623A - Aerodynamic deceleration mechanism - Google Patents

Abstract

A mechanism for the aerodynamic deceleration of the rotational motion w of a submunition body 1 ejected from its carrier has braking surfaces 2 which can be swung out. The braking surface 2 is flexible or resilient at least in the direction of the curvature of the body wall 4 and can additionally be provided with a centrifugal-force mass 7. The hinge or pivot 5 is stressed practically exclusively in tension and can be a reinforced edge portion of a flexible surface 2 or a pliant intermediate piece between the surface 2 and the wall 4. <IMAGE>

Description

SPECIFICATION A mechanism for aerodynamic deceleration and a body including such a mechanism This invention relates to a mechanism for aerodynamic deceleration of rotational motion of a body, for example a submunition body, and to such a body including the mechanism.

Such a submunition body is described in German Offenlegungsschrift No. 27 57 141. There it is shown that the practical realisation of radially braceable or spreadable braking surfaces is hampered by critical constructional constraints more especially since the wall of the cylindrical body encloses a live charge; and effective use of the body against a target seemingly allows no construction of a kind that would be necessary for the retention of rigid braking flaps, along with the formation of frictional moments for the abatement of the rotational energy upon folding out (spreading) of such braking surfaces.On the other hand, the measures proposed in that prior publication, for circumventing these difficulties, for decelerating the rotational motion of the projectile, tend to be disadvantageous with respect to production and assembly expenditure; and the displacement of the proposed braking surfaces into their effective positions does not appear to be sufficiently insusceptible to trouble.

An object of the present invention is to provide a mechanism which is distinguished by relatively simple, thereby space-saving construction with good reliability.

According to the present invention there is provided a mechanism for the aerodynamic deceleration of the rotational motion of a body, for example of a submunition body ejected from its carrier, by means of braking surfaces hingable or pivotable to the walling of the body so as to be swingable outwardly from the body, in which the braking surfaces are inherently flexible and represent centrifugal-force masses opposite their hinging or pivotal connection.

Further according to the present invention there is provided a body including a mechanism in accordance with the immediately preceding paragraph.

Such a flexible braking surface may be realised simply as a metal sheet or cloth (fabric) which can be wound or coiled, tightly, and therefore not very bulkily, around the wall of the body; on the other hand, however, through its (the braking surface) mass (and possibly through a centrifugal-force mass mounted additionally at its end, it unfolds reliably and rapidly when locking in the initially rolled-up state is released, for example because the body has been ejected from its engagement position in a carrier.With somewhat greater constructional expenditure, possible flutter phenomena of the braking surfaces are avoidable or at least may be alleviated, by being equipped with rod-shaped centrifugal-force masses or by being designed so as to be flexurally pliant only in the peri'pheral direction yet flexurally stiff transversely thereto (in other words in the direction of the body axis). This design results for example in the type of construction of hollow cylindrical shells made of resilient material, for instance spring plate. In this case it can be expedient to equip the free end of each braking surface with a displaying bias which deviates from the wall arching (curvature of the body wall); this promotes initiation of the display motion after release of the braking surfaces, which is then completed by the centrifugal-force.

Since, as can be shown (see below), the braced or spread angular position of each braking surface when displayed and tautened under the influence of the centrifugal force stands, relative to its hinging at the wall of the body, in torque equilibrium with the aerodynamic braking force, the hinging at the wall does not need to absorb any kind of supporting moments, it is stressed solely in tension.

Therefore, any constructionally expensive troubleprone measures for the design of hinges designed for the absorption of braking or supporting moments are rendered superfluous. On the contrary, it may be sufficient, for the connection of the braking surface to the body wall, to provide the hinging by way of a simple swivel hinge or even only by way of a flexurally plaint intermediate piece, which can be designed integrally with the material of the braking surface itself (for example as a reinforced piece of fabric) or else be interpolated separately for example in the form of a flexible leather strip.

Also the hinging of the braking surface to the wall of the body is thus not bulky, so that in the carrier, beyond the space requirement for the body itself, there is only a seemingly minimum additional space requirement for the accommodation of the braking surfaces in their wrapped-up state. Possible additional space is not required for the accommodation of damping and retention components, for an interception or restraining of the swing-out motion of the braking surfaces and the display retention thereof, after release of the braking surfaces as a result of ejection from the carrier; because such measures, on account of the hinging, stressed solely in tension, of the braking surface to the body and on account of stable braking-surface orientation under the influence of the torque equilibrium, are now superfluous.

Still further according to the present invention there is provided a body including a mechanism for the aerodynamic rotational deceleration thereof, said mechanism comprising braking surfaces which spread out from the body under the action of centrifugal force, said braking surfaces being pivotally connected on walling of the body and being inherently flexible.

An embodiment of a mechanism for aerodynamic deceleration in accordance with the present invention will now be described, by way of example only, with reference to the much simplified drawings in which: Figure I shows, in front view, a cylindrical body in accordance with the present invention with braking surfaces still abutting along its wall; and Figure 2 shows the body in accordance with Figure 1 with the braking surfaces swung out and arched under the influence of aerodynamic inci dent-fl ow.

The body 1, shown in Figure 1 in front view, preferably represents a submunition body which can be ejected, for example from a spin-stabilised, carrier (not taken into account in the drawings) fired above a target area. The packing in which the body 1 is arranged in its carrier prior to the ejection requires flexible braking surfaces 2, which are hinged or pivoted, parallel and symmetrically to the axis 3, to the cylindrical outer wall 4, which surfaces initially butt against, and conform to the contour of, this wall 4. The free ends 6, opposite to the hinging or pivotal connection 5, of the braking surfaces 2 (for simplification only two braking surfaces are shown, but several more can also be arranged peripherally which are mutually staggered symmetrically to the axis 3) are additionally equipped with centrifugal-force masses 7.These masses may, for example be bar-shaped (i.e. extending parallel to the axis 3) and be enclosed or held in quivers or slings 8 at the braking-surface ends 6. However, discrete individual masses 7 may be provided which are arranged in a mutually staggered manner along the edge of the free brakingsurface ends 6; unless, in a particular case, even the mass distribution in the braking surface 3 (with a resulting centre-of-gravity lying sufficiently remote from the hinging or pivotal connection 5) yields an adequate centrifugal force.If the region of the hinging or pivotal connection 5 relative to the thickness of the flexible braking surfaces 2 is made more bulky (Auftragen), the peripheral length of the braking surfaces 2 is advantageously, as shown in Figure 1, so designed that similarly more bulky additional masses 7 at the braking-surface ends 6 do not come to rest straight up, but rest (considered peripherally) in front of or behind a hinging 5. The hinging 5 itself may be designed as a swiveljoint folding hinge; however, as shown, a coupling-up or attachment of the braking surfaces 2 by way of flexurally pliant intermediate pieces 9 is sufficient; for instance pieces 9 may be in the form of a leather strip which is fastened on the one hand (for example by rivetting or bonding) to the wall 4 and on the other hand along the edge 10 of the associated braking surface 2.If the flexible braking surfaces 2 consist of material I for example of metalised sheet or gauze, textile cloth or plastics, they may in the region of their edge 10 also be designed directly as the flexurally pliant intermediate piece 9, for example by a fabric strip reinforced in the region of the connection to the wall 4.

The flexible braking surfaces 2 do not however have to be designed as material or fabric surfaces which are flexurally plaint in any direction (for example sail cloth). It can also - which will be gone into more below - be advantageous to use flexible braking surfaces 2 which are flexurally resilient flexurally-pliant in the direction of the course of the curvature of the wall 4, but on the other hand are relatively flexurally stiff transversely to this direction, i.e. the surfaces 2 may be realised for example as hollow cylindrical shells made of spring plate.In this case, too, it is advantageous to equip the free end 6 with a centrifugal-force mass 7, and the transitional region in front thereof, as indicated in dot-dash lines in Figure 1, with a bias or initial tensioning (pre-load) away from the wall 4; so that the braking surfaces 2 are then displayed in the region of their ends 6, lifting off rapidly from the wall 4, in this direction as soon as they are freed from their (assumed in Figure 1) packing constraint position by emergence from their carrier.

After ejection from the carrier, a rotational motion w of the body 1 is to be abated as rapidly as possible down to a residual magnitude, so that the body moves in an aerodynamically stable manner, but low in rotation. The flexible braking surfaces 2 serve for that aerodynamic deceleration of the initial rotational motion w.

Each flexible braking surface 2 is displayed laterally in that - after release of the locking in the carrier - the centrifugal force Fz acting substantially on its mass 7 leads to the braking surfaces 2 being radially stretched, as indicated in Figure 2 by the broken-line orientation. This ray-shaped display is, however, not achieved if any aerodynamic braking force Fa (which is directed tangentially opposite to the direction of the rotational motion w) becomes effective, as illustrated symbolically in Figure 2, as a force integral over the attack surface in the effective braking-surface centre-of-gravity 11.

This braking force Fa leads to the arching (shown in an exaggerated manner in Figure 2) of the braking surface 2, and to an effective swivelling of the chord or fibre over (or by way of) this arching (relative to the radials indicated by broken lines) by a small swivel angle s in the attack direction of the braking force Fa. This swivel angle s is, however, negligible (in the order of magnitude below 10o), especially if by appropriate dimensioning of mass 7 (and on the other hand of the surface extent over which the braking force Fa acts on the braking surface 2) it is ensured that the centrifugal force Fz, tautening the braking surface 2, is large relative to the braking force Fa. The torque equilibrium (balance) (indicated beside Figure 2) applies about the braking-surface hinging 5.Since the rotational motion w enters with the same power both into the centrifugal force Fz and into the braking force Fa, the geometrical shape and angular posiiton of the braking surface 2 once achieved along with the formation of the torque equilibrium is maintained over the desirably occurring reduction in the rotational motion w. This system, too, is kinetically stable insofar as for example a rise, (caused by the ambient air factors) in the braking force Fa leads to a more severe buckling (bending or straining) of the braking surface 2, in other words to a displacement of the braking-surface end 6 closer to the hinging 5 and thus to a reduction of the effective aerodynamic attack surface, in other words again to a reduction of the previously rising braking force Fa. If, on the other hand, an ambient air flow counters the recorded braking force Fa, in accordance with the rotational motion w, the buckling of the braking surface 2 becomes less. The end 6 (here additionally loaded by the mass 7) thus moves outwardly, and the effective attack surface for the reduction in spin of the body 1 is enlarged; with the consequence of an again enlarged effective braking force Fa and enlarging braking action by reason of the pirouette effect, which is further reinforced by an outwardly shifting additional mass 7.

In the event of particularly unfavourable dimensions and ambient influences it cannot be completely precluded that the braking surfaces 2 are acted upon by ambient air flows in the direction of the axis 3 or at a small angle to this axis 3; which with small dimensions of the surfaces 2, (in other words slight centrifugal-force tension forces, in the case of a braking surface 2 which is flexurally pliant in any direction) can lead to flutter phenomena, and thus to unstable motional behaviour of the body and aerodynamic losses. If necessary, such phenomena can be nullified simply by the braking surfaces 2 not being designed for example from cloth, but being such as to be flexurally stiff in the direction of the axis 3 (in other words for example as already mentioned above as cylindrical shells made of spring sheet). Then the desired bending or flexure under the influence of the aerodynamic braking force Fa, of each braking surface 2 is furthermore possible; but transverse incident flows (for instance in the direction of the axis 3) do not lead to deformation of the braking surface 2 relative to the direction of the axially-parallel hinging 5; in other words flutter phenomena may be reliably avoided.

Claims (11)

1. A mechanism for the aerodynamic deceleration of the rotational motion of a body, for example of a submunition body ejected from its carrier, by means of braking surfaces hingable or pivotable to the walling of the body so as to be swingable outwardly from the body, in which the braking surfaces are inherently flexible and represent centrifu gal-force masses opposite their hinging or pivotal connection.

2. A mechanism as claimed in Claim 1 in which the braking surfaces are fastened to the wall paral lel to the axis of the rotational motion and which in themselves do not absorb considerable bending moments in any direction.

3. A mechanism as claimed in Claim 1, in which the braking surfaces are fastened to the wall paral lel to the axis of the rotational motion and which in themselves absorb bending moments transversely to the direction of the axis of the body.

4. A mechanism as claimed in Claim 3, in which each braking surface is designed as a hollow-cylin drical shell made of material which is flexurally elastic (resilient) in the direction of the arching (curvature) of the wall, and is equipped in the re gion of the free end with resilient bias which is di rected oppositely to the direction of curvature of the wall.

5. A mechanism as claimed in any one of the preceding claims, in which the hinging is fashioned as a flexurally pliant intermediate piece between the body wall and adjoining braking-surface edge.

6. A mechanism as claimed in any one of Claims 1 to 4, in which the hinging is designed as a reinforced edge region of flexible braking surface consisting of fabric or material.

7. A mechanism as claimed in any one of the preceding claims, in which the braking surfaces are equipped at their free ends with additional centrifugal-force masses.

8. A mechanism as claimed in Claim 7, in which the masses are rod-shaped and are arranged at the braking- surface ends parallel to the body wall.

9. A mechanism for the aerodynamic deceleration of the rotational motion of a body substantially as herein described and illustrated in the accompanying drawings.

10. A body including a mechanism for the aerodynamic rotational deceleration thereof, said mechanism comprising braking surfaces which spread out from the body under the action of centrifugal force, said braking surfaces being pivotally connected on walling of the body and being inherently flexible.

11. A body as claimed in Claim 10 and substantially as herein described and illustrated with reference to the accompanying drawings.