GB2181848A

GB2181848A - Indicating glide path direction of parachutes

Info

Publication number: GB2181848A
Application number: GB08525608A
Authority: GB
Inventors: Trevor Kirby-Smith
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1985-10-17
Filing date: 1985-10-17
Publication date: 1987-04-29
Also published as: GB8525608D0; GB2181848B

Abstract

A device for use with parachutes comprises mounting means (14) attachable to a rigging line (12) of a parachute (10), an aerodynamic drag element (15) pivotally connected by an arm to the mounting means, the drag element taking up a line of flight parallel to the glide path of the main parachute, and means detecting the angle between the rigging line and the line of flight. The angle may be indicated visually by moving a fixed arm over a scale (14) or detected electrically by sensing the bending of a flexable arm. In the latter case velocity may also be measured. <IMAGE>

Description

SPECIFICATION Drive ratio measuring device The present invention relates to devices for measuring the drive ratio of a parachute. The drive ratio is here defined as the ratio of horizontal to vertical speed relative to the local wind vector.

When a parachutist descends from a high altitude he has not hitherto been provided with means for easily checking his drive ratio, and in some circumstances he may wish to try and optimise this so that he covers the maximum distance across the ground for a minimum loss of height taking due account of the local wind vector. It is an object of the present invention to provide a device to enable the drive ratio to be monitored by the parachutist or to be relayed to a remote ground station.

According to the present invention there is provided a drive ratio indicator comprising mounting means for attaching the indicator to a rigging line or riser of a load carrying parachute, a flexible arm connected at its first end to the mounting means, and at its second end to an aerodynamic drag element, guide means for guiding the arm over the drive ratio indicating scale, when deployed the aerodynamic drag element taking up a line of flight parallel to the glide path (relative to the wind vector) of the load carrying parachute and the arm moving over a scale to thereby indicate the drive ratio of the load carrying parachute.

An advantage of the present invention is that it may be easily attached to a rigging line or riser of a main parachute to provide a simple method of determining the drive ratio of the parachute. The device may be conveniently carried in a small bag by the parachutist and easily attached to a rigging line or riser of the main parachute when deployed, or in some way attached to the parachute prior to deployment. The device may be conveniently stored in folded manner and the cruciform parachute will rapidly open when introduced into the airstream. The aerodynamic drag element is the cruciform parachute, chosen because it flies at nominally zero angle of attack to the airflow, especially if it spins. A swivel is incorporated at the rigging line confluence to facilitate spin motion without rigging line twisting and canopy collapse.

According to a second aspect of the present invention there is provided a drive ratio indicator in which the aerodynamic drag element is a parachute connected to the second end of the flexible arm by connector means.

An advantage of the use of a parachute as an aerodynamic drag element is that it may be conveniently folded and stored in a compact form prior to deployment.

According to a further aspect of the present invention there is provided a drive ratio indicator in which the mounting means is a mounting rod attachable to a rigging line of a load carrying parachute.

A rod may be advantageously used to provide support for the flexible arm and calibrated scale giving indications of drive ratio because it is easily stowed in compact form and still capable of providing rapid and rigid support to the scale and flexible arm when attached to a rigging line.

According to a further aspect of the present invention there is provided a drive ratio indicator having a flexible strip pivotally mounted between two guide walls, the guide walls having markings on them to provide a visual indication of the drive ratio of the load carrying parachute.

According to a further aspect of the present invention there is provided a drive ratio indicator in which the guide walls are in the form of quadrants and flexible arm is longer than the radius of the guide wall quadrant so that the flexible arm extends beyond the guide walls to provide the visual indication of the drive ratio.

An advantage of the present invention is the flexible arm is allowed to rotate freely in the space between the guide walls the flexible strip effectively acting as a pointer on the quadrant scales.

According to a further aspect of the present invention the guide walls are translucent and the flexible arm is visible through the guide wails.

Advantageously the guide walls are made from a translucent or even transparent material such as polythene, thereby enabling the flexible marker strip to be easily seen through the quadrant and provide a bigger area for reading drive ratio values.

According to a further aspect of the present invention there is provided a drive ratio indicator in which the flexible arm is securely held onto the mounting rod, the deflection of the flexible arm detectable by transducer means on the arm, the transducer adapted to provide a signal, the signal usable to indicate drive ratio of the load carrying parachute.

An advantage of this aspect of the present invention is the provision of means for determining the drive ratio electrically, so enabling a remote readout of the drive ratio to be obtained, this being particularly useful for unmanned loads attached to a parachute or for experimental purposes, such as the early testing phases of a new parachute when the parachute would normally be dropped with a dummy load.

According to a further aspect of the present invention there is provided a drive ratio indicator in which the flexible strip has strain gauges mounted on the surface of the strip, the strain gauges producing a signal on deflection, the signal useable to determine the drive ratio of the main parachute.

Advantageously the flexible strip is fitted with strain gauges in the form of, for example, a four legged bridge, to enable easy determination of the extent of the deflection.

According to a further aspect of the present invention there is provided a drive ratio indicator in which the flexible strip is provided with means for determining the strain on the strip exerted by the drag force of the cruciform parachute, the strain determining means adapted to provide an indication of the wind relative speed of the load carrying parachute.

Advantageously this aspect of the present invention provides means for determining the speed of the parachute and its associated load by measurement of the drag forces exerted on the cruciform parachute.

According to a further aspect of the present invention there is provided a drive ratio indicator in which the flexible strip is made from an elastic material, the elastic material having speed calibration markings on it, the markings passing a fixed marker point to thereby indicate the speed of the load carrying parachute.

Advantageously the present aspect of this invention provides for a simple and reliable means of determining the speed of the parachute assembly, such a speed measuring system also being easily foldable for stowage prior to deployment on a rigging line.

According to a further aspect of the present invention there is provided drive ratio indicator in which a split tube is fixed between the flexible strip and the small aerodynamic drag parachute swivel in a direction stibstantiaily perpendicular to the longitudinal axis of the tube, the tube split to define a longitudinal aperture, the parachute exerting a force on the tube and strip and causing the shape of the tube to alter, strain gauge means attached to the tube to determine the changes of shape and thereby provide an indication of the strain on the tube and hence the speed of the parachute.

An advantage of this aspect of the present invention is the provision of an electrical means of detecting speed, which may be conveniently coupled to the electrical method of determining drive ratio.

In order that the present invention may be more easily understood it will now be described with reference to the following drawings of which: Figure 1 shows a general arrangement of a drive ratio/speed indicator according to the present invention.

Figure 2 shows a drive ratio speed indicator for use with a manned parachute assembly.

Figure 3 shows a similar device adapted for use with an electrical detection system and suitable for use with an unmanned parachute.

Figure 1 shows a main parachute (10) having rigging lines (11) leading down to risers (12), the risers (12) attachable to a load (13).

The load or store (13) may be either a person or equipment, or both. The device (14) may be attached to a riser (12) or rigging line (11).

It may be adapted for providing a visual readout or an electrical output convertible to a drive ratio value either on the parachute or at a remote location. The device (14) has attached to it a cruciform parachute (15). The cruciform parachute (15) is chosen because it is aerodynamically stable, particularly if it is allowed to spin about its longitudinal axis.

This is achieved by use of a swivel connector (16).

Figure 2 shows an embodiment in which the device is adapted for the visual mode of operation. The device is attachable, as before, to a riser (20), (or rigging line, not shown). The mounting rod (21) is attachable by clip means (22) to the riser (20). A pair of calibrated side walls (23) are securely connected to the mounting rod (21), the guide walls are spaced sufficiently far apart to permit a flexible strip (24) to be pivotally mounted between them.

A first end of the flexible strip (24) is mounted at a pivot point (25), the second end connected to a swivel connector (26), the swivel connector (26) being used to join the confluence point of the rigging lines of the cruciform parachute to the flexible strip (24).

The swivel connector permits the cruciform parachute to rotate about its longitudinal axis (an axis perpendicular to the plane described by the ends of the cruciform arms). In operation the cruciform parachute will take up a line of flight parallel to the glide path of the main parachute (relative to the wind vector).

The cruciform parachute which is attached to the flexible strip will exert a drag force on the flexible strip and maintain it in a taut position extending from its pivot point. The flexible strip is longer than the radius of the quadrant and so extends beyond it, the drive ratio can be determined with reference to the calibration marks (23) on the quadrant. The quadrant is adjustable and will have been calibrated for a particular parachute by previous measurements. To aid visibility the marks could be painted in various different colours or use could be made of fluorescent or luminous paints.

Figure 3 shows an alternative embodiment of the present invention which is adapted for providing an electrical readout of the drive ratio. The device is attached to a riser (30) or rigging line by clips (31). The mounting rod (32) has secured to it the first end of a flexible strip (33). The second end of the flexible strip (33) is connected to a split tube (34) by a iabric tag which is secured to the inside of the tube and thence attached to the confluence point of the rigging lines (35) of the cruciform parachute (not shown) via the swivel (36).

On the surface of the flexible strip are transducer means (37,38) for detecting the bending movement of the flexible strip (33). The transducer means may be used to determine the drive ratio of the main parachute. The transducer means may conveniently be strain gauges or the like. It may be convenient to double the number of transducers by having a pair on each side of the flexible strip connected in such a way as to form a bridge network.

A further feature of the present embodiment is the provision of the facility to measure the drag force of the cruciform parachute and thereby determine the speed of the main parachute. This is the split tube (34) which is secured to the flexible strip, the slit defining a longitudinal aperture in the tube. The tube (34) may be made of metal or other relatively stiff material and has secured to its surface a plurality of transducers (39). In operation the drag force exerted on the flexible strip and split tube by the cruciform parachute will cause the tube to be distorted by enlarging the slit, this distortion being detected by transducers, for example strain gauges (39) secured to the outside of the tube. The device may thus be used to simultaneously provide both drive ratio and air speed measurements.

In an alternative embodiment the flexible strip shown in Figure 2 may be made of an elastic material, the flexible strip extending with increasing drag force exerted by the cruciform parachute. The flexible strip could be marked with transverse markings along its length to provide an indication of air speed.

Alternatively it could be equipped with a pointer or marker which could move past a pointer or a graduated scale on the guide walls.

Alternatively the device could be attached to a nominally vertical surface of the torso of the parachutist, (or dummy), spaced a short distance away and to the side of the torso by a rigid, articulated arm.

This avoids the prior need to ascertain the side view geometry of the parachute in a steady glide since an approximate "vertical" for the mounting rod can be achieved".

The aerodynamic drag element is shown as a cruciform parachute, this particular arrangement works well because the cruciform parachute will fly stably, particularly if it is allowed to spin freely. Other 'arm type' design parachutes, such as triform or five arm parachutes should function satisfactorily. The aerodynamic drag element need not be limited to just parachutes of known form but could be rigid or semi rigid cones for example. A cone supported at its apex and flying apex first could, if allowed to spin, provide the required aerodynamic drag.

Claims

1. A drive ratio indicator for use in conjunction with a load carrying parachute comprising mounting means for attaching the indicator to a rigging line of a load carrying parachute, a flexible arm connected at its first end to the mounting means and at its second end to an aerodynamic drag element, guide means for guiding the arm over the drive ratio indicating scale when deployed the aerodymic drag element taking up a line of flight parallel to the wind relative glide path of the load carrying parachute and the arm moving over a scale to thereby indicate the drive ratio of the load carrying parachute.

2. A drive ratio indicator according to claim 1 in which the aerodynamic drag element is a parachute connected to the second end of the flexible arm by connector means.

3. A drive ratio indicator according to claim 1 or 2 in which the mounting means is a mounting rod attachable to a rigging line of the load carrying parachute.

4. A drive ratio indicator according to any preceding claim in which the flexible arm is pivotally mounted between two guide walls, the guide walls having markings on them to provide a visual indication of the drive ratio of the load carrying parachute.

5. A drive ratio indicator according to any preceding claim in which the guide means are in the form of quadrants and the flexible arm is longer than the radius of the guide means quadrant so that the flexible arm extends beyond the guide means to provide the visual indication of the drive ratio (speed).

6. A drive ratio indicator according to any preceding claim in which the guide means are translucent and the flexible arm is visible through the guide means.

7. A drive ratio indicator according to any of claims 1 to 4 in which the flexible strip is secured to the mounting rod, the deflection of the flexible strip detectable by transducer means on the arm, the transducer adapted to provide a signal, the signal usable to indicate drive ratio of the load carrying parachute.

8. A drive ratio indicator according to claim 6 or 7 in which the flexible arm has strain gauges producing a signal on deflection, the signal useable to determine the drive ratio of the main parachute.

9. A drive ratio indicator according to any preceeding claim in which the flexible strip is provided with means for determining the strain on the strip exerted by the drag force of a drag parachute, the strain determining means adapted to provide an indication of the speed of the load carrying parachute.

10. A drive ratio indicator according to claim 9 in which the flexible arm is made from an elastic material strip, the elastic material having speed calibration markings on it, the markings passing a fixed marker point to thereby indicate the speed of the load carrying parachutes.

11. A drive ratio indicator according to claim 9 in which the flexible arm is secured to a tube in a direction substantially perpendicular to the longitudinal axis of the tube, the tube split to define a longitudinal aperture, the drag force on the tube causing the shape of the tube to alter, strain gauge means attached to the tube to detect the changes of shape and thereby provide an indication of the strain on the tube and hence the speed of the parachute.

12. A drive ratio indicator substantially as hereinbefore described with reference to the accompanying figures.

13. A drive ratio indicator incorporating a parachute speed measuring device substantially as hereinbefore described with reference to the accompanying figures.