Cable Wiper Assembly

Airborne sonar systems include a hoist mechanism carried in a helicopter, a storage drum and drive means therefor which operate to lower a sonar transducer into the water and raise it out of the water. When raised, the transducer is carried snugly against a conical seat which prevents it from swinging or moving during flight. Older types of airborne sonar use comparatively heavy transducers with large, thick cables having many strands and are limited in the depth to which the transducer is operated. Although the hoist mechanism is operated at limited speeds, there are problems connected with various aspects of the retrieval. The force required to pull the transducer through the water is greater than that required in air; hence, there is a danger that the transducer may tend to jump out of the water and swing in an uncontrolled manner for a time, which complicates operation of the helicopter. Further, means must be provided to insure that the transducer does not hit against the seat with excessive force. A further problem is that the cable tends to carry a substantial amount of sea water with it as it is reeled in. Since the hoist is within the helicopter and since the water tends to be sprayed all around as the cable passes over the guide sheaves, it has been found necessary to provide a cable wiper between the seat and the guide sheaves to prevent excessive amounts of water from being carried on board the helicopter.

With the advent of later types of airborne sonar, transducer operating depths have become much greater, and cable speeds upon deployment and retrieval have also become much greater. While the cables themselves are smaller in diameter, the greater speed to which they are subjected results in their carrying even greater quantities of water, at least on a per-unit-of-time basis. With the greater reeling speed and the quantity of water carried it was found that, in the absence of a cable wiper, the spray of sea water as the cable made contact with the guide sheave was intolerably heavy. It soon became apparent that the type of wiper used on the earlier, larger cable was inadequate also, primarily because the higher cable speeds used brought on disproportionately greater amounts of water. Thus, to accommodate the smaller, faster moving cable, more needed to be done than simply to decrease the diameter of the hole in the wiping elements to match the diameter of the smaller cable.

FIG. 1 is a side view of a hoist used for high speed airborne sonar systems including a cable wiper according to my invention.

FIG. 2 is a sectional view taken along line 2--2 of FIG. 1. FIG. 2A is an exploded view, partly in section, of a single wiper and spacer as shown in FIG. 2.

FIG. 3 is an enlarged sectional view of the spacer of FIG. 2A.

FIG. 4 is a plan view of the spacer of FIG. 3 as seen along line 4--4 of FIG. 3.

FIG. 5 is a plan view of the spacer of FIG. 3 as seen along line 5--5 of FIG. 3.

FIG. 6 is a sectional view of the housing for the wiper structure shown in FIG. 3.

Referring now to FIG. 1, a hoist frame is shown generally at numeral 10 which stands on the floor of an airborne vehicle such as a helicopter. Carried near the top of frame 10 is a sheave 12 which is mounted to swivel in three dimensions. As the sheave pivots, rotary transformers 14 and 16 sense movement around each of two axes and provide electrical signals to the controls or autopilot of the helicopter. At the rear of the frame is a guide sheave 18 which may be used in association with a level wind structure to cause a cable 20 indicated by dash-dot lines to be wound evenly on a storage drum, not shown, but which is driven and controlled by hydraulic means shown generally at numeral 22.

Suspended from the pivot structure which supports sheave 12 are support members 24 which carry a cable wiper assembly 26. Attached to the frame 10 below the cable wiper assembly 26 is a funnel or seat structure 28 against which the transducer is held when being transported.

FIG. 2 is a sectional view taken along line 2--2 of FIG. 1. In this view it will be seen that the support members 24 are pivotally carried in the frame 10 by means of a cross-member 30 supported in frame 10 by means of bearings 32. The cable wiper structure 26 is, in turn, pivotally supported on members 24 by means of bolts 34 which pass through the housing of cable wiper assembly 26 and support members 24. Carried inside of assembly 26 is a sleeve 36 including are a ports 37 and a flange 38 which holds a retainer 40 for a spring 42. Within sleeve 36 is a generally cylindrical cable wiper housing 44 shown in a greater detail in FIG. 6. Housing 44 has a number of radial ports 45. A frusto-conical transducer stop member 46 holds a hat-shaped retainer member 47 tightly against the bottom of housing 44. Spring 42 is held under compression, and it absorbs some of the shock when a transducer strikes the rubber bumper 49 forming part of member 46. Carried within housing 44 and pressed tightly together by retainer 47 are plurality of wipers 48 interleaved with wiper spacers 50. Details of wipers 48 and spacers 50 are somewhat more clearly FIGS. in FIG. 2A, 3, 4 and 5. In FIG. 2A an individual wiper and spacer are shown enlarged. The wiper 48 is essentially a rubber washer which has a cut through from outside to inside to facilitate getting it around the cable. Once so located, its edges are firmly secured between two spacers or between a spacer and one end of housing 44. The inside diameter of the wiper 48 is slightly smaller than the diameter of cable 20 so that contact with the cable is assured. It will be observed that as cable 20 moves downward, the wiper members will deflect into spacer wells 52, and no significant resistance or force against the cable 20 is exerted. When the cable 20 is being retrieved, it moves rapidly upwardly, carrying a substantial volume of water with it. The wipers press snugly around the cable and are prevented from deflecting significantly in the direction of the cable by the flat adjoining surfaces 54 of the spacers 50. The resulting wiping action causes the water on the cable to be deflected into the wells 52 from whence it is drained through radial ports 56, through ports 45 in housing 44, and out of ports 37 in sleeve 36. Of course, the greatest part of the water is deflected by the lower wiper which is adjacent retainer 50 and caused to flow straight down and out of the bottom of transducer stop member 46.

The number of wiper stages required for any particular application will depend largely upon the speed of deployment and retrieval of the cable. The faster the cable moves, the more water it will tend to carry. Making the wipers fit more tightly around the cable will simply result in wearing on the inside edges of the wipers. This inside diameter should preferably be smaller than the average cable diameter by only a matter of about 0.004 inch.