GB2153982A

GB2153982A - Flight body

Info

Publication number: GB2153982A
Application number: GB08502392A
Authority: GB
Inventors: Walter Diesinger
Original assignee: Dynamit Nobel AG
Current assignee: Dynamit Nobel AG
Priority date: 1984-02-02
Filing date: 1985-01-31
Publication date: 1985-08-29
Also published as: GB8502392D0; IT1182164B; IT8547626A0; DE3403508A1; FR2559256A1; IT8547626A1

Abstract

A flight body which normally possesses a tail unit with three or four laterally projecting fins has, according to the invention, a maximum of only two fins (13, 14), thereby reducing its cost. A rotation is imparted to the tail unit (11) together with or separately from the fuselage (10), so that the direction of instability of the flight body constantly changes. However, the rotational frequency is essentially greater than the inertia-subject pitching or yawing frequencies generated by the asymmetry. <IMAGE>

Description

SPECIFICATION Flight body This invention relates to a flight body of the type which comprises a tail unit arranged at the rearward end of its fuselage, which tail unit provides, at least during the flight, laterally extending stabilising fins which rotate together with or relative to the fuselage.

Tail units of guided and unguided flight bodies are generally equipped with three, four or even more, laterally projecting fins, the preferred number of fins being four. The fins are uniformly distributed around the tail of the flight body, in order that the stabilising effect of the tail unit should vary as little as possible with the rotational position of the flight body.

It is to equalise asymmetries which can be generated for example by non-uniform distribution of the thrust of the propulsion unit when the flight body possesses its own engine, or by unequal mass distribution of the flight body, that it is the practice to allow the flight body to rotate its longitudinal axis during the flight. This rotation is achieved in such a way that the laterally extending fins are hardly tilted at all so that the air streaming along the fuselage turns the tail unit and with this the entire flight body. As a rule 2 to 3 rotations per sec are sufficient to compensate for the asymmetries. The maximum rotational speed is occasionally chosen to be even higher, however, for example 1 6 rotations per second, because it is necessary, among other reasons, to guarantee a sufficient rotation over the entire range of speeds of the flight body.

Finally it is a known practice to so arrange the tail unit on the fuselage of the flight body as to be rotatable around the longitudinal axis, whereby the fuselage rotates relative to the tail unit.

The mounting of several fins on the flight body entails high production and mounting costs. As a consequence of the relatively high requirements, which are placed on the fins withs respect to strength, aerodynamic shape, sizing accuracy and the like, the fins cannot be produced by cheap mass production techniques. Their production is moreover is very expensive on account of the required high quality.

According to the present invention there is provided a flight body of the type which comprises a tail unit arranged at the rearward end of its fuselage which tail unit provides at least during the flight a maximum of two laterally projecting stabilising fins which rotate together with or relative to the fuselage, which fins are such as to provide a rotational velocity which is essentially greater than the pitching or yawing frequencies generated as a result of inertia due to rotational asymmetries.

A flight body according to the invention possesses, instead of the usual three or four fins, only a maximum of two fins. In comparison with a four finned tail unit, this means that two fins are spaced to lie opposite one another and the fins which are retained are correspondingly enlarged. The stabilising effect of the tail unit is increased in the one direction in which drift at right angles is eliminated. By choice of a suitable rotational speed of the tail unit around the axis of asymmetry of the flight body, what is achieved is that the flight body flies stably because the rotation is so rapid that the stability changes cannot noticeably be produced mechanically during flight. What remains is an intermediate stability.

In a surprising way it has been established that a flight body with less than these fins has the necessary flight stability although no stabilisation by fins takes place in at least one place of symmetry. It is presupposed that the stability changing frequency is greater than the pitching or yawing frequency of the flight body to an extent and such that the flight body therefore possesses too much inertia about the cross-sectionai axes in order to react aerodynamically and/or mechanically in flight to the changes in stability which occur with time. Practical experiments have shown that this principle functions very well and it is possible in such a way to reduce costs to two fins (or even to one fin).

According to a preferred embodiment, two fins are precisely arranged lying opposite one another. These fins should provide balanced mass distribution, i.e. be equal in size, so that, on rotation of the flight body, no unbalance exists. The fins are arranged in a common plane passing through the longitudinal central axis of the flight body and achieve a stabilisation across this plane. Since the rotational speed in this plane is essentially greater than the frequency of the instabilities dependent on the inertia of the flight body, the instabilities cannot lead to a change of course of the flight body.

For a better understanding of the invention and to show how the same can be carried into effect, reference will now be made, by way of example only to the accompanying drawings, wherein: Figure 1 is an elevation of a first form of flight body embodying this invention; Figure 2 is a perspective view of the tail unit of a second form of flight body embodying this invention, and Figure 3 is a plan view of the tail unit from the direction of the arrow Ill of Fig. 2.

The flight body shown in Fig. 1 possesses a longitudinally extending cylindrical fuselage 10 which forms a motor housing and is connected at its forward end to an ogive 10'.

A nozzle 1 2 whose internal cross-section increases rearwardly is connected at the rearward end of the fuselage 1 0. The nozzle 1 2 is surrounded by the tail unit 11 which likewise is fixed to the rearward end of the fuselage 10. The tail unit 11 possesses two fins 13,14, projecting in oppositely set directions and which are pivotally supported on longitudinal extending spindles 1 5. The forward ends of the spindles 1 5 are fixed to the fuselage 10 and the rearward ends to a ring 21 surrounding the nozzle 12.The fins 1 3 and 14 consist of segments which can be retracted around the spindles 1 5. They consist of a rigid part (inner) on which a spring metal plate (outer) is riveted so that the fins do not project above the contour of the fuselage 10 in the retracted condition. This makes possible the launching of the flight body from a cylindrical firing tube. After leaving the firing tube, the fins 13,14 project laterally under the action of combined compression/tension springs 1 6 which surround the respective spindles 15 and lock rearwardly. In the extended condition, the fins 13,14 project according to Fig.

1 over the contour of the fuselage 10 in oppositely set directions. The two fins 13,14 are set at 180 to one another. The fins are inclined to the longitudinal direction of the flight body 10 in known manner about a small angle (adjustment angle) so that the flight body executes in its flight a rotation about its longitudinal axis. The rate of rotation depends on the mass inertia and the magnitude of the instabilities occurring. It lies preferably in the range of 1 5 to 30 Hz.

In the embodiment according to Figs. 2 and 3, the two fins 1 3 and 14 are curved in known manner corresponding to the circumferential curvature of the fuselage so that they match the contour of the fuselage in the withdrawn state (in the firing tube).

Each of the fins 1 3,14 is connected over a spindle 1 7 with a control lever 1 8 whose other end is hinged to a longitudinally extending spindle 1 5. The levers 1 8 are so biassed by the torsion springs seated on the longitudinally extending spindles 1 5 that after leaving the firing tube they then project radially, with the fins 13,14 being inclined to the torsion springs 1 9 seated on the spindles 1 7 up to a (not shown) detent and are locked in place.

During the flight the fins 13,14 assume the condition shown in Figs. 2 and 3 with-in the horizontal orientation of the flight body shown in Fig. 3-the one fin 1 3 being curved downwardly and the other fin 14 upwardly. Because of the setting angle of the fins, the flight body rotates in the direction of the arrow 20 in Fig. 3 about its longitudinal axis.

As a consequence of the configuration of the flight body tail region and the stability requirements placed on the two finned tail unit, fin 14 and lever 18 can form a unit so that the spindles 1 7 and the torsion springs 1 9 can be dispensed with. In such a case the part cylindrical segments 1 3 and 14 must either be smaller-with a fixed constructio nor the curvature of the segments must be enlarged.

Claims

1. Flight body of the type which comprises a tail unit arranged at the rearward end of its fuselage which tail unit provides at least during the flight a maximum of two laterally projecting stabilising fins which rotate together with or relative to the fuselage, which fins are such as to provide a rotational velocity which is essentially greater than the pitching or yawing frequencies generated as a result of inertia due to rotational asymmetries.

2. Flight body according to claim 1, which comprises two said fins disposed diametrically opposite one another.

3. Flight body according to claim 1 or 2, wherein the fin or fins is/are set inclinedly on the fuselage with respect to the flight direction for achieving a combined rotation of fuselage and tail unit.

4. Flight body according to any one of claims 1 to 3, wherein the fins are pivotable relative to the fuselage.

5. Flight body according to claim 4, wherein the fins are curved in accordance with the outer contours of the fuselage.

6. Flight body according to claim 4, wherein the fins comprise an inner portion which is rigid and an outer portion of spring sheet metal capable of curving to the outer contours of the fuselage.

7. Flight body, substantially as hereinbefore described with reference to and as shown in Fig. 1 of the accompanying drawings.

8. Flight body which comprises a tail unit, substantially as hereinbefore described with reference to and as shown in Fig. 2 or 3 of the accompanying drawings.