Trim Tab - Part 4

The next task is to fabricate the braces for the stiffener installed in Part 5. A MAC trim is capable of a 40 lbs of thrust and the thrust is transferred to the rear spar via the ribs as per the factory installation.

A motor mount Z profile was folded from 0.025'' 2024-T3 aluminum - 60 mm wide with 10 mm flanges. Two lighting holes were created because a suitable flaring tool was on hand.

Z frame trim mount

Two angle mounts were fabricated and fitted at each end after a series of trial fittings ensuring that the second rib was maintained in its correct location relative to the mounting holes in the skin. Brackets were fixed with 3 x 1/8'' pop rivets to the face of the Z as shown above.

#3 Rib mount 

The cover plate was now slotted to accept the trim motor link.

Trail fit of MAC drive

The motor center line was located on the face of the Z and the first two mounting holes were marked with a felt pen - both holes were drilled and the motor mounted with cleco's then refitted, position checked and the rear holes marked.

On this install the rear two holes were moved up to provide improved access from the available opening.


All holes were fitted with 3 mm riv-nut's at the motors mounting points then refitted to determine the best angle to suit the available opening. 

The #3 rib the center hole was drilled, clecoed and repeated at the other side using one of the mounting holes for the new rib foot. Once the most suitable angle was determined using the trim motor the other holes were drilled and pop riveted.

Mounting Z Bracket at #3 rib

The motor was re-installed using four [4] M3 x 12 pan head screws then the stainless steel clevis attachment was fitted to the tab with 1/8'' pop rivets.