Ch 6: Heat Duct & Seat Back Brace (Part 2 of 3)

Heat Duct Assembly
The heat duct goes together pretty easy however it was a little unwieldy while floxing the 3 parts together.  They are 40.75" long and when you assemble them they are only glassed on one side with 2 ply UND...they are kinda floppy at this stage.  I used the nail method in the plans as well as some spacers for the open bottom for holding it together nice and square during cure.  For the curve at the front of the heat duct, I used some slight clamp pressure against two large craft sticks (tongue depressor, epoxy stirring stick) to hold it in place while curing...worked perfectly.

Safety Belt Attach Point
Before glassing the exterior of the entire part, a 5/8" AL tube is installed with flox and will provide one side of the safety belt attach point.  I floxed in the tube and then performed the 7 ply reinforcement immediately following.  This allowed me to make a nice smooth rounded top over the tube.

Seat Belt Attach Point Installed into Heat Duct

Glassing the Heat Duct
When glassing the exterior of the heat duct, I measured out a rectangle of 2 ply BID about 10" x 43" on aluminum foil.  I supported the heat duct off the table using a 2x4 turned on it's side and inserted into the bottom of the heat duct.  That way I could let the glass on the sides hang while curing.  After wet out, I back rolled the glass and foil onto an old cardboard roll (like what the glass cloth comes rolled on) and then rolled it out on top and down the middle of the heat duct.  I made the width of the glass so it would drape down each side and be easy to glass the entire piece at one time.  It worked pretty good...better I think than trying to put resin on  the vertical sides of the duct or turning the duct from side to side.  I had a few dry spots I had to fix but I'm sure that was because I wet out the 2 plys of glass at the same time and clearly missed some air.

Joining the Heat Duct to the Seat Back Brace

Heat Duct with extra .75" of
last-a-foam on each side

In the previous post I widened the seat back brace to get a larger map pocket.  My map pocket is now 3" wide which makes the total width of the seat brace 3.5"...too wide to fit on top of the 2" heat duct per plans.  So, I needed to widened the heat duct aft of where it passes through the seat.  I had some left over .75" last-a-foam which was perfect so I cut pieces to fit on each side and floxed them in place.  Be sure to trial fit all this in the airplane.  I must have went back and forth to the plane a dozen times making sure everything was right before I did anything permanent.

The pictures show the added foam with beveled front ends to match the seat back and how the seat brace will install on top when done.  The added foam will get glassed over before attaching the heat duct and seat brace together.  Time to do the final glassing and joining the two parts.

Seat brace as it would be installed
on the heat duct width extensions

Onward,
cab