How To Make a Sailplane Tow Release
by Stephane Ruelle
Many modern scale sailplanes use a commercially available tow release that mounts in the center of the nose. In some cases, an under the nose tow line attachment is used and some manufacturers build a tube in block release into their models (ie. Horizon Hobbies Blanik and ASW20 models). Here is a step-by-step way to fabricate such a tow release.
The necessary components can be fabricated by using several pieces of scrap plywood and a length of tubing with a solid pushrod. Here, three pieces of plywood are sandwiched together to form a slot for the pushrod tubing.
Glue assembly together
Use epoxy to glue the parts together. Wood block is approximately 30mm long, 15mm wide, and 25mm high.
Make a slot
Using a router or Dremel tool with a round bit, cut a horizontal slot through the wood block and nylon tube (obviously with metal pushrod removed). This can also be done by making two cross cuts with a razor saw, breaking out the section and rounding out the slot with a round file.
Glue the block into the fuselage
Make a slot in the bottom of the fuselage nose where you tow line to attach. Glue the slot in the block of wood that you just made over this slot in the fuselage. Use a piece of fiberglass tape to strengthen the attachment of the block to the fuselage.
Make a servo mounting tray
Again, scrap pieces of plywood and hardwood can be used to fabricate a servo mounting tray. Attach the top strap of plywood with screws making the servo removable for servicing if needed.
Complete the installation
Glue the servo tray to the fuselage so that the metal pushrod moves freely through the tubing and slot in the plywood block. Although the tow line does not put direct strain on the servo, it is best to use a servo with significant torque to easily pull the metal pushrod through the slot against the side load of the tow line. Using a servo with metal gears is also a good idea.