With these and subsequent rigging lines the following technique was used: on all lines a strength test was made and a safety factor of at least ten to one was demanded. Most of the lines used are of braided or woven nylon, chosen for its low weight-strength ratio. To facilitate handling of the line segments each length is prepared with a small hook on either end. The knots employed are double carrick bends.
The total length of the early trains reached as much as eight hundred feet, making them extremely difficult to release. A system of restraining the load line was evolved with two winches paying out restraining lines while balloons and equipment were added to the load line. In this way the pull of the balloons themselves and the much greater strain caused by even light winds was held by winches. When the final piece of equipment was clear of the ground (or when the entire flight line was under tension with the lowest element being held back) a gunpowder squib was electrically fired to sever the restraining lines near the bottom of the balloon. Figure 27 shows the aluminum "cannon" holding the gunpowder, the two winch lines and a light line used to pull the restraining lines away from the load line after firing. The load line has not yet been attached in Figure 27, but will be fixed just above the "cannon".
When the restraining line is severed, there is danger of a pendulum swing of the train causing the lower components to be dashed into the ground. To avoid this action, the lowest piece of equipment is usually held by a member of the crew on the back of a truck. By driving downwind faster than the surface wind speed, the pull of the balloon can be resolved into only a vertical component and the equipment may be safely released when the truck gets under the balloon.
With later plastic cell flights, this method of launching was also used in cases of light wind. When winds of about 5 knots are encountered,