FireFlys' Cozy Mark IV, #1500

Dedicated to those that lost their lives on 9/11


Chapter 8 

Headrest, heat duct, seat belts, & step


Chapter 8 Research Summary (PDF Document) - Please contact me if you have tips/FAQ's that should be added


Step 1 - Carving the Foam Pieces  

Step 2 - Glassing the Inside Surface for Wet Layup

Step 3 - Glassing Outside of Shoulder Support 

Step 4 - Glassing and Installing Headrests

Step 5 - Installing Shoulder Harness Attachments

Step 6 - Installing Outside Seatbelt Attachments/Step

Step 7 - Center Seatbelt Attachment


  • I ommited the plans style step - I plan on installing a retractable version.
  • I added flox behind the rear seat inserts to reduce the "pocket" created between the insert and the longeron doubler.
  • Clamped a straight board onto seatback support, then used compass to create a template for the rear heat duct.
  • Made the transition piece using a wooden (vs. foam) core...DO NOT FOLLOW MY LEAD!

Step 1 - Carving the Foam Pieces  

8.1.1 Layout headrest pieces then 1 ply BID, one side. (1st paragraph Step 1)

8.1.2 Cut out headrest pieces, then assemble with flox. (1st paragraph Step 1)

8.1.3 Cut out and trial fit shoulder support pieces. (2nd paragraph Step 1)

8.1.4 Cut out, and epoxy plywood inserts into shoulder support. (2nd paragraph Step 1)

8.1.5 Install Canopy Hinges (Refer to Chapter 18). (3rd paragraph Step 1)


Step 2 - Glassing the Inside Surface for Wet Layup  

8.2.1 Epoxy shoulder support together. (1st paragraph Step 2)

8.2.2 Cut out holes for canopy lock push rod in Shoulder Support and SB. (1st paragraph Step 2)

8.2.3 Make foam jigs to hold shoulder support in place. (1st paragraph Step 2)

8.2.4 1 ply BID layup on inside surface, let tack, then attach to seatback. (1st paragraph Step 2) - 


Step 3 - Glassing Outside of Shoulder Support 

8.3.1 Radius edge, bevel edges at inserts, and 12 ply BID buildup on inserts. (1st paragraph Step 3)

8.3.2 Prep shoulder support, and 2 ply BID. (2nd paragraph Step 3)

8.3.3 Add 3 ply UND reinforcement over shoulder supports. (Fig. 7, notes Step 3) - 


Step 4 - Glassing and Installing Headrests

8.4.1 Radius edges, 2 ply BID front and back of headrest. (1st & 2nd paragraph Step 4)

8.4.2 2 ply BID on sides, with 3 ply BID reinforcement over top. (2nd paragraph Step 4)

8.4.3 Later on, Flox right headset in place, with 2 ply BID at joint. (3rd paragraph Step 4)


Step 5 - Installing Shoulder Harness Attachments

8.5.1 Measure and drill holes for harness, flox nut plate in place. (1st paragraph Step 5)

8.5.2 Touch up nut plate access hole, notch headrests if necessary. (1st paragraph Step 5)





Step 6 - Installing Outside Seatbelt Attachments/Step

8.6.1 Make inserts and brackets. (2nd paragraph Step 6) - Carved wood inserts to fit.  Requires contours on bottom to fit space, and on top to remove sharp angles (for BID layup).  Plans did not specify the size of the inserts - I made mine approximately 3"x3".  

8.6.2 Install inserts with flox, cover with 7 ply BID. (2nd paragraph Step 6) - Pretty straight forward.  On rear seatbelt inserts, I added flox to minimze the "pocket" created between the insert and the longeron doubler.  You can see this better in the Step 7 pictures.   Step Done

8.6.3 Install 3 brackets. (2nd paragraph Step 6)

8.6.4 Install bracket/step combo. (2nd paragraph Step 6) Will be installing a retractable step vs plans method.

Added Step -- 8.6.5 Apply 2ply BID over foam inserts at bottom of front seat (aft side) - Applied micro over foam, then taped joints in same fashion as bulkheads.   Step Done








Step 7 - Center Seat Belt Attach

8.7.1 Make template for aft heat duct. (1st paragraph Step 7) - I clamped a  piece of 1/4" plywood onto the seatback support so the bottom (straight) edge "continued" the top line of the foward heat duct to the foward LG bulkhead.  I then set my compass to the widest distance between the fuselage bottom and the bottom edge of the plywood piece.  Once set, I used the compass to trace the fuselage curve onto the piece of plywood.  Then, without changing the setting, I ran the compass along the bottom of the plywood to transfer the proper gap.  Connected the lines with vertical marks and added a 45 degree riser in the back.  Once finished, I layed paper over the plywood and traced the drawing.  Then used the paper template on the foam.  Step Done

8.7.2 Cut foam for aft heat duct, cover 2 ply BID, 2 ply UND. (1st paragraph Step 7) - As with the forward duct, glassed the pieces that would be on the interior of the finished duct.   Step Done

8.7.3 Cut out and assemble duct. Test fit. (1st paragraph Step 7) - Per plans.   Step Done

8.7.4 Cut Aluminum tube and install with flox. (1st paragraph Step 7) - No changes from front heat duct.  Used flox vs. plans instruction to use 5 min epoxy. (Newsletter #82)  Step Done

8.7.5 7 ply UND and 2 ply BID over rear seat belt attach. (1st paragraph Step 7) - Fig 16 showed the 7 ply UND layup going down after the transition tube was in place.  I followed the written instuctions and did it now (as was done in Ch. 6).  The layup climbed the 45 degree riser.  As with the front heat duct, I glassed each side separately with reinforced floxed corners at the glass-to-glass joints, rather than rounding edges to apply BID on the exterior of the heat duct per plans.  Probably a small weight penalty for this, but I preferred the crisp edges on these parts.  Step Done

8.7.6 Carve transition piece, cover with tape. (2nd paragraph Step 7) - I planned on avoiding the problems of dealing with the easily damaged foam, by using carved wood covered with electrical tape.  It worked, but I wouldn't recommend it to others.  My thought was that if properly laid out I would be able to easily knock out the wooden core.  My thought was wrong... The electrical tape offers a wonderful release, but there is still too much resistence to easily remove the core.   Step Done  

8.7.7 2 ply BID over transition piece. (2nd paragraph Step 7) - In my second mistake on this part, I decided to wet out lengths of 2" BID tapes (Which I purchased from Wicks, but have yet to find a suitable use for...) then wrap the mold like putting an ace bandage on an arm.  This turned out to be a mess and a waste of time.  On my second effort I supported the mold from each end so I could spin it (rotisserary style).  I then epoxied the mold, then layed dry BID (cut from the cloth..not the tape) onto the wet surface allowing it to adhere as I went.  Continued to rotate the part laying the dry BID onto the wet surface until I made a few revolutions.  This worked great.  Repeated the process with the peel ply.   Step Done

8.7.8 Carve out transition piece mold, cut holes, and flox in position. (2nd paragraph Step 7) - This is where I paid the price on the wooden core.  Using a 1.25" drill bit, wood chisels, and patience, I was able to remove the core without damaging the transition piece.  The plans do not offer any specifics on where to cut the hole and place the transition tube.  I placed the transition piece to allow ~1/4" gap between the outside surface of the transition tube, and the forward surface of the 45 degree riser.  My thought is that this should offer enough clearance to connect a hose to the transition piece.   Step Done

8.7.9 Flox rear heat duct in place, tape joints with 2 ply BID. (2nd paragraph Step 7) - Floxed in place, and peel plied joints.  Allowed to cure before putting BID tapes down.  While reading through the plans, realized that I did not apply the UNI plies called out for in step 8.7.2.  Prior to taping seams, I reinforced the exterior of the rear heat duct with the UNI plies.   Step Done

8.7.10 Reinforcement layup (7 ply: 4 BID, 3 UND, alternating) over front/rear center seat belt attachments. (3rd paragraph Step 7) - Completed the layup by making a 4" x 19" 4-ply tape (BID, UND, BID, UND) and a 5" x 19.5" 3-ply tape (BID, UND, BID).  Due to the bump created by the insert, this may have been a little easier to lay each ply directly in position rather than make tapes.  But, with a little effort, got all the plies to lay down nicely without large air pockets.   Step Done

8.7.11 Open up holes in front and rear seat belt tubes. (2nd paragraph Step 7) - 


Chapter 7    Chapter Index    Chapter 9

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