Aerotow ropes: short or long, breakable or unbreakable?

The reality is there have indeed been fatalities due to over-strong tow ropes, and one of the preventative measures is to use a rope designed to break in case of over-stress.

The load on the rope is relatively light and can be figured using the L/D of the glider.

The "L" is the lift required to make the glider fly, which equals the weight of the glider.

Dividing the glide ratio into the weight equals the drag, or load on the tow rope.

A gllder with an L/D of 30, weighing 900 pounds would have a load on the tow rope of only 30 pounds.

Since the glider is being towed uphill, the load is slightly more. (Towed by the space shuttle, straight up, the load would equal the weight of the glider, disregarding acceleration forces.)

Anyway, the load on the tow rope is small. This load can be simulated by pulling the glider by the rope by hand on a smooth surface.

Typically, we use a tow rope with a breaking strength of 1,200 pounds, (regulated by the rules - weight of the loaded glider) or a much stronger, more durable rope with a much higher breaking strength with complying weak links on both ends of the tow rope.

The weak links can be the mechanical types made by Tost. These are expensive and weigh enough to cause the tow rope to fly very low behind the descending towplane.

The weak links can also be made from smaller tow ropes that comply with the strength requirements. The rope manufacturer must be trusted to conform to the requirments.

Bottom line is weak links are an important, regulated safety requirement. They rarely are needed, but there are occasions when they can save lives.

Finally, pilots and line crews need to be vigilant about the condition of launch equipment, glider and towplane.

Tom Knauff