Dorsal Fin

This blog covers the dorsal fin install

Overview
The fin installation was covered in the blog on Stab Faring leaving the final task of securing the fin to the air-frame.

Installation
The holes drilled in the previous blog that secured the dorsal fin with 3/32'' clecos were all enlarged to 5 mm and fitted with Countersunk thin sheet M3 rivet nuts. These allow the dorsal fin to be screw flush with the skin of the aircraft unlike the large flange type supplied with the kit.

Note: All these specialized items were purchased from Fastener Kits Online in Australia

Rivet Nuts installed in previous 3/32'' holes

Note: the large head rivet nut was installed in error and replaced

Fixing

M3 Wafer Screw

Fixing is always a issue with cheese head screws chunky, countersunk are not a practical option and the fin has to be removable for heavy maintenance, pop rivets are not a option.

Having used wafer washers previously, a quick search on the net located a supplier in China who supplies these screw in a bag of a 1000 M3 x 12 for $24 with free but very slow postage.

Wafer head screws fitted to port side

The screws have a profile similar to a 3.2 mm pop head rivet and using a 3.5 mm mounting hole allowed the dorsal fin to be secured tightly to the fuselage skin.

Profile Modification
The top edge of the dorsal fin had a flat edge and while filling the side faring with dry macro the excess was applied to the top edge and once it reached the plastic stage the application was adjusted by hand to resembled a radiused edge. Once cured a combination of 80 / 120 / 240 grit aluminium open cut paper were used to achieve a final profile. The rough edges were filled with blade putty and sanded with 120 / 240 aluminium open cut paper to a smooth profile.

Comment
Happy with the final result with the screws working as well as hoped.