Self-Retracting TieDowns

By Bob Reed

The MyMods/TieDown shown is for the tail mount. The photos show a top view, extended side view, trial fit into opening, and an installed views. The MyMods/TieDown is mounted on a 1/4" phenolic plate which was shaped so that the bottom fit the cutout opening as tightly as possible.

The metal retractor is set down into the phenolic a little over 1/16" in order to have the bottom edge of the retractor perfectly flush with the bottom edge of the fuselage after installation. The mounting screws are all countersunk and bonded into the phenolic prior to installation. The size of the plate was picked to spread the load over a large area of the fuselage. The forward portion is a little longer than needed but I used that area to drill and shape a nice water drain hole after installation. The whole thing is placed just a couple of inches behind the rear bulkhead before installation of the bulkhead.

Prior to installation, the opening in the fuselage was cut and cleaned out. A wet Micro/Flox was spread across the bottom in a thin layer and the edges filled. A two ply bid was then placed so that it overlapped the top by two inches all around. The phenolic plate was then put into place and pressed down to ensure that no air bubbles were caught between the bid and the fuselage. This was weighed down until cured. Once cured, the space around the phenolic was filled with a micro flox and an additional two ply bid applied with 3 inch overlap onto the fuselage. While wet, the metal frame and hold downs which had been covered with tape to make them easy to remove, were bolted down as tightly as possible. This pressed the glass down under the retractor while curing. After this cured, I cut the opening for the MyMods/TieDown retractor through all the glass bids and the bottom of the fuselage and trimmed it out. The retractor mechanism was then bolted down fully assembled. The bottom edge of the retractor is flush with the bottom edge of the fuselage and is self retracting.

The extra holes in the sides of the retractor are simply to lighten the mechanism some. The screw shown in the side view is there to keep the counterweight from going beyond the balance point for self retraction. The top view shows the nylon spacers which help keep the retractor from wobbling back and forth and keep the operation smooth. It also shows all the screws for holding the mechanism to the plate. It might be a slight over kill but I wanted to spread the load evenly over a wide area.

If I were to do it over again, I would move the main pivot hole in the retractable portion up about 3/16 inch. This would eliminate the need to counter sink the whole mechanism in the phenolic block and possibly eliminate the need for the stop screw.