Estes Advanced Target Drone, Kit #1913, Build, Part 4, Engine Mount

The 20/50 rings were rough. I sanded the flat sides with some 400 grit on a block.

On the right - a 1/8" notch was cut for the engine hook relief. 

On the other side of the engine hook notch, a smaller notch was cut for the Kevlar line.

Notice the Kevlar line under the top bend of the engine hook.

The upper centering ring also goes over the top bend and the engine hook slit. This locks and strengthens the engine mount.

Tie a small square knot. There isn't much room between the BT-20 and BT-50 tubes. Keep the knot small.

On the right, I've tucked the loose end under the looped Kevlar line into the glue fillet.

A engine block is glued into the top of the mount against the upper bend of the engine hook.