Cowls - Part 3

This blog covers the fitting the lower cowls cheeks

Overview
With the top cowls ready to be installed the lower cowls now had to be fitted in a similar  manner to the top.

Installation
The starboard side was fitted back into the flange jig and clamped to the side rail of the upper cowl attachment. A digital protractor was zeroed on the fuselage side, placed on the flange of the cowl and leveled.

With the cowl located a light was placed on the inside and the edge of the fuselage marked on the outside face of the cowl. 

With the edge marked a offset line of 2 mm was added and the waste trimmed using a Dremel motor tool fitted with a thin cutting disc.

The next task was to fit a fastener mounting to for the lower cowls. With the experience  from the upper cowls a aluminium angle was machined using the proven pattern.

With the sides trimmed a series of slots was filed to expose the fuselage edge as outlined in Part 2 of the cowls.

With the edge adjusted to fit the first mounting point was drilled 45mm [1.75''] down from the last mount for the top cowl. Six [6] more were added pitched at 90mm [3.5''] as per the suppliers recommendations.

First lower cowl attachment with
lower flange attachment fitted

Next task was to install the lower top cowl attachment that will tie the two assemblies into one unit. 

The Tucano cowls have a flange on the side supported by a integrated angle, to use the Skybolt fasteners requires an aluminium support to achieve the required strength, so the flange above the angle was removed with a Dremel Motor tool.

Cowl after trimming shown in insert above
Aluminium mount shown in o/a imiage

Next a new aluminum angle was machined by notching with the 10mm ball mill pitched at 45 mm along the full length of the lower flange. This was fixed using 3mm pop rivets fitted with 3mm brass washer on the underside to prevent the rivets pulling through.

Aluminium angle trial fit before riveting

The same techniques were applied to the port side and when the level across the two cheeks was checked it is was less than 0.5 degrees.

Comment
When a little smoother for the firewall angles while the cowl top edge was as we say "a drop kick". The way the aluminium flanges met were the hand of God as no one was more surprised than me..!

Next job is to glue the lower cowls and to trim and install the top cowl