FireFlys' Cozy Mark IV, #1500

Dedicated to those that lost their lives on 9/11


Chapter 6 

Assembling the fuselage


This is the chapter where you build the sides to the fuselage. 

Chapter 6 Research Summary (PDF Document) - Please contact me if you have tips/FAQ's that should be added



  • Trial fit all bulkheads in fuselage side jigs.  Note - Make sure that bulkheads stay plumb in two planes (fore-to-aft, top-to-bottom) during fitting, AND if you think you're taking too much off - you probably are...(stop, and check everything again!).  
  • Using a compass makes it easy to trim bulkheads to the proper shape.
  • Plastic sandwich bags (with duct tape reinforced corners) really does work nicely to dispense flox.
  • Like many, I built a low table with adjustable feet and assembled the fuselage upside down.  Note: If you build a table, leave an opening for F-28 as well as the IP.
  • Used drywall screws, and wooden stops to secure the fuselage components.
  • I channeled out the foam along the sides of the IP, Seatback, F-22 doubler, and landing gear bulkheads, to allow the flox to have a "bite" on the bulkhead.  In addition, I channeled out the exposed foam around the inside leg holes of F-22 and the IP to fill with excess flox from attaching the sides.  
  • Put packing tape on the table surface where flox may come in contact with it (no need to glue the fuselage to the table!).   Also taped off areas of the sides and bulkheads where I didn't want flox and epoxy, making it easier to prep for the tapes later.
  • Used a board spanning the LWX's, to hold the upper forward LG in place during cure.
  • Made the fuel selector valve bracket out of glass (8 ply).  Did not cut out the 4 side holes at this time (can't determine why they are there).
  • Used a combination of weighted blocks to hold the seatback brace spacers in place and a simple jig to form the heat duct.
  • Used "hinge method" to join fuselage bottom foam pieces.
  • Added foam to bottom of the rear side of the seatback to "cut off" angle created when bottom goes on.
  • Drew guidelines on the fuselage bottom to assist me while laying the glass.
  • Saved and reused fuselage side jigs to hold fuselage in place while taping interior seams. 
  • Glassed the map pocket while working on the tapes.  Also, I channeled out the exposed foam around the inside leg holes of F-22 and the IP to fill with excess flox from attaching the sides.  When cured, I sanded them back to shape to form a more durable edge.
  • Taped the interior seams in 3 stages.  Also, taped the long side-to-bottom and center keel seams (front of plane to firewall) that weren't shown in Fig 33.











Fuselage Assembly - Done  

Began the trial fitting of all the bulkheads while the sides were still in their jigs - making small adjustments at a time.  Unfortunately, I didn't head my advice of small adjustments when I fit the instrument panel.  When I fit it to the second side, the bulkhead wasn't held plumb from top-to-bottom and it caused me to take off too much material.  Put that under the category of measure twice, cut once (...dumbass!).  The error can be fixed well enough, but just adds time to the build and should have easily been avoided.  Given that the gap was ~ 1/8", I probably could have gotten away with just putting in extra flox, but it just didn't feel right to "short-cut it".  Also, maybe the extra step will keep me focused on avoiding this type of mistake in the first place!  Fixed the mistake by: putting the IP in the correct position; tracing a new line 1/2" from the side with a compass; epoxying on a new piece; glassing over the extension; tracing a new line 1/2" outward from the first line; and trimming to fit.  Perfect (mistake, what mistake?).   

Decided to assemble the fuselage upside down like many others - it just seems to make more sense to me and hopefully will make installing the landing gear bulkheads easier as well.  Now at first I planned on only building a simple elevated jig, but after futzing around for too long, I went ahead and made my jig into a table.  The table surface is 102" long, with a cutout at 82.5" from the aft end.  These measurements allow me to attach the temporary firewall at the rear, rest F-22 at the front, and align/clamp the IP against the table cutout.  Used carriage bolts and nuts to adjust the table (as I did with the work table), and set them in the concrete relief cuts of my hangar (read "garage") floor to keep the table from moving.  Then with the help of daughters Jillian and Katherine, roughly laid out the sides and bulkheads.

After getting everything where I wanted and verifying measurements, I secured wooden stops to the table (interior to each side, just behind F-22, IP, and Seatback) so I could return both sides to the same position.  F-22 was secured at the corners (per plans), with drywall screws vs nails.  The IP was secured along the sides (per plans) with drywall screws plus 2 additional screws at the top of the IP that attached it to the table. The Seatback was also held in place along the sides with screws, and a wooden strip that kept it perpendicular to the centerline. Like Wayne Hicks, I was fortunate that everything fit together snugly and was appropriately plumb and level with little more needed than the drywall screws to keep it in proper position.  Then I began the disassembly process.

Once taken apart, I channeled out the foam along the sides of the IP, Seatback, and F-22 doubler, to allow the flox to have a "bite" on the bulkhead.  (I think I got this idea from the Cozy Girls.)  {In addition, I channeled out the exposed foam around the inside leg holes of F-22 and the IP to fill with excess flox from attaching the sides.  When cured, I sanded them back to shape to form a more durable edge.  I don't recall reading this in the plans, but I'm assuming that those areas will need to be addressed during finishing, and now seemed like an easy time to address it.}  After everything was cleaned up, I taped off (with clear packing tape) all areas I wanted to keep clean and began putting the fuselage together with assistance from my youngest daughter Katherine.

With the temporary firewall and the IP attached to the table and sides removed, I started by applying a thin layer of raw epoxy on all joints.  Then, I put flox on the sides of the IP, seatback, and their respective positions on each sides.  The sides were placed into the firewall and kept outward.  Once the seatback was put into position, the sides were brought in and the seatback attached with the screws.  The IP and F-22 followed accordingly.  I used a small piece of wood to keep the 3/8" foam on each of the sides (near F-22) from bowing outward during cure.  Cleaned all excess flox from each joint, leaving a nicely rounded seam, then removed the packing tape protecting the areas around the joints.   Confirmed everything was level and plumb, then REPEATEDLY told everyone to stay out of the hangar for the next day!  As anxious as I was about the whole process, everything went together smoothly and quickly.  

After prepping and taping the foward bulkheads (F-22, IP, & Seatback(aft side only, I will complete forward tape when fuselage is flipped over)), moved on to the landing gear bulkheads.  Started with the rear LG bulkhead and followed the plans method by attaching a block to the fuselage side.  However, first I rounded the corner of the block where it contacts both the side and the bulkhead, then wrapped the block in saran wrap and peel ply, respectively.  Then prepped the area by applying epoxy, and "packing" the corner with flox, in addition to the normal bulkhead preparation (including channeling out the foam like the foward bulkheads).  I also went ahead and taped the front side corners of the rear LG bulkhead while the flox was still uncured.

Made wooden 8" spacers per plans and clamped into position (added "tabs" on the blocks, so I didn't have to glue the spacers into position), then epoxied the foward LG bulkhead into place following the same preparation as the other bulkheads.  After cure, I drilled the 1/4" holes through the rear LG bulkhead and attached the upper half of the foward LG bulkhead.  Now when I first trial sized the part I was concerned that it was going to come up ~1/8"-1/4" too short at the rear tip (the edge that faces the spar cutout), but after fine tuning the fit it worked okay.  After the fit was right, I attached the part.  To do this, I cut a piece of 1"x 6" to span between the two LWX's, put on packing tape wherever the board may contact epoxy, put the bulkhead in place, then screwed the board to each LWX.  Once the part was in the proper position, I clamped it to the board, then unscrewed the board, prepped the surfaces, and reinstalled the board (with the attached part), and let everything cure.  Once cured, removed the board and installed the aft side 6 ply and seam reinforcements.

Removed the temporary firewall and floxed the lower firewall into place per plans.


Center Keel and Seatback Brace - Done  

Drew the keel and seat back parts on the foam "roughly" following the suggested foam pattern from the plans.  I made sure to check that I had opposite pieces so when I glass the foam, I will have glassed only the interior sides.  I've read about numerous builders who end up glassing an exterior side on the first layup(usually the seat back brace), and think that most occur because the natural tendancy is to draw out a rectangle split diagonally.  This gives you two equal triangles, but presents one interior and one exterior face.  Afterwards, I microed and glassed the parts per plans.  That should have been the end of that section, but it wasn't.  In an inexplicable bonehead move, I weighted down the parts without puting plastic between the peel ply and the flat board used to press everything down.  TIP - Don't do this!!!  What a pain in the neck getting the parts out, and once I did, there were several dry spots.  Repairs not a problem, just frustrating.  I did go ahead and glass the spacers on both sides while I was fixing things (I couldn't see any penalty for having these rigid).

Following the lead of others, I made the fuel selector valve bracket out of glass.  I made a form out of wood, covered it with box tape, then laid 8 plies (2 BID, 1 UNI, 2 BID, 1 UNI, 2 BID), covered with peel ply and plastic, then weighted down the top and clamped sides during cure.  After cure drilled the top holes and epoxied on the nut plates.  When cured, put rivets in place then put 1 ply BID on the top and floxed around plates with a single BID ply covering the bottom.  At this point I did not drill the side holes in the bracket.  It seems from the plans that these holes are no longer used (At least that what it appears like to me...hopefully I won't regret this later).  Also, while I was looking over the plans, I began to question the seatback cutouts.  It looks like I will have to widen (to 2") the opening at the fuel valve to allow for installation/removal.  I'll wait and see once I'm about to install the brace.  

Made plywood parts as detailed in plans, although left out the 3/8" hole since I plan on using an electric landing brake actuator like others.  To install in the seatback brace, I removed the foam as specified, then covered the exterior faces of the plywood with packing tape (to prevent sticking).  Once that was done, I mated the two pieces (with the exterior sides facing each other) and secured the outside edges with packing tape (trimmed to leave no overhang) to hold them together. Placed one brace foam side up and put protective tape along the vertical cut line (same for the other brace), floxed the plywood into place, then floxed the top of the plywood and put the other brace on top, foam side down.  This allowed me to verify that I hade a "mirror image" of both sides.  Once assured, weighted parts down and let cure.  When done, the parts came apart cleanly.

During this section of the build, I took a short vacation with the family to Maine.  Although I lost build time, the lake is one of my "Main...e" inspirations for building an airplane; making the trip more reasonable for long weekends.  When I returned I finished prepping the heat duct and seatback brace spacers.  For the heat duct, I made a simple jig that allowed me to put the top down first, insert a temporary spacer (2" x 3" wrapped in wax paper), then flox the sides in place.  Rather than using nails,  I used a combination of weighted blocks to hold the seatback brace spacers in place.

Rather than rounding edges to apply BID on the exterior of the seatback brace and heat duct, I glassed each side separately with reinforced floxed corners at the glass-to-glass joints.  Probably a small weight penalty for this, but I preferred the crisp edges on these parts.  Like others, I chose to install the heat duct first, then mate the seatback brace to it.  After trial fitting the heat duct, I floxed it into position, and peel plied the floxed joints. I think it is real easy to make nice seams if I shape the flox, peel ply and allow to cure, then go back and tape the joints.  By doing so, I get a firm radius that is prepped for, and won't "move" when working, the glass.

Once the heat duct was in place, I trial fit the seatback brace.  The fit was fairly close, requiring only some minor adjustments on the edge that connects to the heat duct.  Before attaching the brace, I worked on the "hole" in the seatback to make sure that the fuel selector valve would be removable.  From the plans, it appears that the opening is designed to be 1.5", but the part is 2".  Since I plan on using an electric landing brake actuator, I decided to close the vertical opening in the seatback.  I had kept the pieces I had originally removed, so I shaped and microed the patch in place.  Then glassed the interior, making sure to put flox at the glass-to-glass joints. I also measured and cut out the map pocket opening.  I'll finish that surface once everything is in place.

Floxed the seatback brace in place using blocking to hold the bottom (or the 'actual' top of the brace) in place and weighing down the heat duct at the top (or, more correctly, the bottom).  Taped all seams with 2 plies BID at 45 degrees.



Installing the Fuselage Bottom  

Yea... I finally got started on the bottom.  Traced, cut, joined the 3 sheets of foam per plans.  Used ripped plywood and 1x2's to make frame, and attached to the foam.  Then measured, drew, and cut out the speed brake.  If I were to do this again, I would have cut the brake out before attaching the 3 pieces of foam together.  I think it would have been easier to cut without handling the larger "combined" piece.  

Next you start the giant jigsaw puzzle of making the spacers to give the fuselage bottom some "depth".  I was worried that I would not have enough of the spacer foam, but I took my time, making sure my cuts were right, and everything turned out okay.  Once I had the rough shapes cut, I began sanding down the slopes.  I  left myself a little "margin of error" when sanding the slopes.  Once I have the spacers micro'd in place, I'll trial fit and remark the bottom.  Then I can fine tune the sanding prior to the bottom layup.  

Micro'd the spacers in place, using drywall nails to hold pieces in place.  Since the blue foam is fairly flexible, it would bow from side to side between the frame rails.  By using the drywall nails (I think it was Wayne Hicks that dubbed the drywall nails "Composite Clecos"), I was able to draw the blue foam to the spacer for cure.  Also made a slight change in plans by adding some foam (double thick 3/4" spacer foam) to the lower back side of the seatback.  I did this by fitting and microing one "row" in place.  Then I fitted and microed the second "row" to the first.  My hope is that I can make a more aesthetic seam when the bottom is installed, and to make taping the joint easier (although the plans show just the front side getting taped, I know some builders have done the back as well - Obviously, I'm planning to do so as well). 

Fine tuned and rounded spacers, cleaned off, filled holes, and completed layup of fuselage bottom.  And (like the plans) while that may be a short sentence, it is a pretty stout event.  Enlisted some help from the family, primarily my youngest daughter Katherine (who was an epoxy machine...), and toiled away.  Drew some guidelines onto the bottom to help direct me while laying the glass.  Spewed handful of explatives while working the glass up and down the various contours to avoid getting ulcers.  Then repeated the process 3 more times (3 plys BID, plus the peel ply layer), although I lost Katherine somewhere along the way...maybe too many explatives(oops).  One thing that stood out for me was that this was the same layup I had helped another builder, Nate Wolfe, with when I was considering building.  I remember thinking at the time how far along he seemed, and how great it would be when I got there too.  So, although it was a bear, at least it felt like a bit of a milestone.  (Nate's story HERE)  If you've not checked out Nate's site, it is worth a look, particularly the Building Blog -- He has a good sense of humor, and I always seem to get a chuckle out of his stories.  

Like many others, I chose to wait until the bottom cured before attaching it to the fuselage.  Checked level and prepped surfaces, including channeling IP and heat duct bottoms, then went about making flox.  Buttered parts with flox then joined the two pieces together with the help of my wife.  I also floxed F-28 in place at the same time.  Weighted the bottom down with bricks to keep it in place.  Then cleaned up the joints.  Unfortunately, I didn't have enough peel ply to cover all the joints, so I'll have some crappy sanding ahead of me before I can tape them.  Moved the cured fuselage onto the work table, setting them into the appropriate side jigs (which I kept around for this purpose) to work on taping the interior seams.

NOTES - If you are planning to use Wayne Hick's alternate Landing Gear Cover (as I am), then in Chapter 6 (Fig. 32) you will need to relocate your block to 3/8th inch below the scoop cut out to insure that the fuselage bottom mounts flush to the cutout.  In Chapter 7, you'll find that the bulkheads are designed to be below the fuselage bottom to create "joggles".  Wayne's method does not require joggles, so the 1/8th will need to be added then if you don't correct it now.   

Due to the winter months, I was a little slow finishing up this chapter.  I taped the seams in 3 stages.  First, I taped all the "gravity friendly" horizontal seams with the plane resting on it's left side.  More specifically: the left side-to-bottom joints between F-22 and IP, IP and Seatback, & Seatback and Firewall; and the right side of the center keel fore and aft of the Seatback. NOTE - The plans don't specify that these joints are to be taped in Fig. 33, I'm just assuming that it is implied.  I also taped the joint between the front of the seatback and the left side at this time (I waited until now to complete this step from the fuselage assembly so I wouldn't have to perform it with the fuselage upside down).   After cure, I taped the vertical seams (with the fuselage on its side) that are depicted in the plans (Fig. 33).  I have to wait to complete my modified aft Seatback joint until I get some micro from Wicks.  The third stage involved taping the remaining horizontal seams - opposite of the 1st stage.  While I was taping, I also glassed the bare foam at the map pocket; which included floxing the corners facing the seatback.

Chapter 5    Chapter Index    Chapter 7

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