FireFlys' Cozy Mark IV, #1500

Dedicated to those that lost their lives on 9/11


Chapter 7 

Fuselage Exterior
This is the chapter where you complete the outside of the fuselage. 

Chapter 7 Research Summary (PDF Document) - Please contact me if you have tips/FAQ's that should be added



  • I would make the NACA template out of paperboard vs. paper.  It will be easier to trace with less movement.
  • Add ~ 6 inches of 1" urethane foam during Step 7.1.1 to avoid creating dip in fuseage bottom 
  • I added 1/8" foam extensions to LG bulkheads to account for NOT using joggles
  • Recommend "honey-like" micro on urethane foam.  Also, I would try to limit micro between urethane blocks to the minimum needed (or none), to reduce gouges during contour.  You should be able to fill any gaps before glassing the fuselage bottom.  Alternatively, you may want to consider using a more durable foam to build the NACA scoop.
  • Used the Fein tool to cut through micro before chiseling away the foam around the spar cutout.
  • Rather than hunt down the Tim Lumpp tool, I made my own sanding block out of 4 pieces of 1" MDF cut to the template and glued/screwed together.
  • Used the two Perma-Grit blocks to remove the 1/16" depressions (see step 7.2.4).
  • Order your antenna kit early in the process (it may take a few weeks to get...).  I would recommend not using RST (I used an Amateur Radio supplier and a Stained Glass Supply company).
  • If you are not familiar with soldering, refer to "How-to" videos on YouTube.
  • Don't forget to round off F-22 prior to glassing bottom.
  • Made "tapes" to reinforce landing gear and engine mount hardpoints in Step 7.3.4.
  • When contouring foam - spend most time on shaping the blue foam first with very few and light passes on the yellow/tan foams.



Building the NACA Scoop  

7.1.1 Trace NACA Scoop template, cut foam, and micro to bottom. (1st paragraph Step 1) - Used paper to make template, but if I did it again would use paperboard.  NOTE- Ended up creating a new template out of paperboard, cutting both sides at same time for uniformity.  Transfered template to fuselage.  To avoid a "dip" in the fuselage bottom, I added a line at ~30" ahead of forward landing gear bulkhead as guide to extend foam to (this will require some larger urethane pieces than the plans call out for - see 7.1.3). To accomodate the template, the NACA scoop cutouts in the LG bulkeads (more so in the forward LG bulkhead) had to be widened equally. With foam pieces rough cut (see 7.1.3), it was time to make the scoop shape cut-outs.  I did this by first transferring the template drawing on top of the foam, then used a hacksaw blade to get with 1/8" to the line.  Once that was done, I put the piece back in its original position (on top of the paperboard template) and weighted it down to keep it from moving.  Then, with the Perma-Grit blocks on their sides (to create a 90 degree edge), I slowly worked the curve to match the template below; repeating the process for the other side.  Also, since I am planning to use Wayne Hick's LG Cover method, I took this time to "add" 1/8" back to the LG Bulkheads that are no longer needed as joggles.  Prior to microing, used duct tape to protect areas from run off.  Microed all the foam from steps 7.1.1, 7.1.3, and 7.1.5 at the same time.  Initially I made the micro a little too wet for the process, then I settled into the more "honey-like" consistency that seemed to work best.  I tried to limit the amount of micro between the urethane blocks to the minimum, in order to make contouring the foam easier in step 7.1.7.  From my experience of fitting the foam, I was skeptical of the amount of weight that some builders said they needed to make the pieces conform to the bottom.  As you can see from the picture to the left, I am now convinced...    Step Done 

7.1.2 Cut out plywood pieces and flox them to LG bulkheads. (2nd & 3rd paragraph Step 1) - Hot glued sticks in place (covered with packing tape) to rest pieces against while the flox cured.  Did not bevel the edge as shown in the drawing, opting instead to trim the piece when contouring will take place.     Step Done 

7.1.3 Micro foam to outside of plywood. (3rd paragraph Step 1) - The foam parts layout in Chapter 2, Page 5 did not show the suggested pattern for the pieces described in 7.1.1, 7.1.3, and 7.1.5.  I made the layout shown in the picture to the left.  Rough cut the pieces first, then shaped them to position.  Actually "Rough" is a bad word to use when dealing with the urethane, this stuff breaks up when you look at it funny...handle with care!  Used clamps to hold foam against "A" and "B".  The foam against "C" seemed to hold in place without pressure, so I left it alone to cure.     Step Done 

7.1.4 Cut plywood to fit between aft LG and FW, and flox in place. (4th paragraph Step  1) - Shaped and cut pieces.  Glued and clamped short boards (with packing tape) to hold pieces in the proper position during cure. My interpretation of the drawing for part "D" was to keep the piece perpendicular to the FW, and adjoining to part "C" at the FW as well.  Thus when the fuselage is shaped, "C" and "D" should appear as one piece at the firewall, requiring no foam fill.  When I floxed "D" into position, I went ahead and added a rounded filet (and peel plied) at the corners where the glass ply will bend.    Step Done 

7.1.5 Cut foam for between LG and FW, and flox in place. (4th paragraph Step 1) - Pretty straightforward, just be careful that you don't disrupt the 2 ply BID layup while pressing in the foam.  Weighted foam down until cured.    Step Done 

7.1.6 Cut and flox in place foam to finish NACA scoop. (5th paragraph Step 1) - I chose to do this step ahead of 7.1.3 and 7.1.5 to prevent damaging the fragile urethane.  Cut pieces to fit, and floxed into position per plans (1/8" above the rear LG Bulkhead NACA cutout).  Again, I hot glued boards covered with packing tape to hold pieces in place.  Covered pieces of foam with duct tape to keep clean, then removed the tape after pieces were in place and excess epoxy wiped away.   I also added foam on NACA cutout of both LG bulkheads to make up for the 1/8" "joggles" that won't be needed for the alternate gear cover method.  Once cured, I sanded the additional foam to be flush with the surrounding foam.   Step Done 

7.1.7 Contour the NACA foam. (7th paragraph Step 1) - NOTE- the plans don't mention anything about contouring the urethane between the LG and FW, but it seems appaerent that this is the time to do that...I did.  Made a 33" sanding stick vs. 22" described in the plans.  Other than that step was pretty straightforward.     It appears to be commonplace for micro fragments to cause gouges in the urethane.  I thought I had found a way to avoid this by not using sandpaper more aggressive than 80 grit, and continually cleaning surface after each pass with the sanding stick. I think that worked very well, however, I did end up with one gouge that will need to be filled.    Step Done 

7.1.8 Insert aluminum for LG cover.  (8th paragraph Step 1) - SKIPPING; WILL USE THE HICKS METHOD.   Step Done 

7.1.9 Glass inside of NACA Scoop (9th paragraph Step 1) - My friend Glen gave me a hand glassing the inside of the scoop.  Standard procedures used (i.e. Rounded corners where glass would bend, templates, and "wax paper layups") and added peel ply at end.             Step Done 


Contouring the Bottom  

7.2.1 Taper sides from ~25 forward of firewall back to the firewall. (1st paragraph Step 2) - Removed foam from around spar cutout per plans.  Used Fein tool to make clean cut through the micro that connects the blue foam to the yellow. Followed up with a chisel to remove material, then sanded smooth and rounded edges for glassing.  I used the NACA scoop template to draw a "carving" guideline along the side from the corner of the spar cutout to the mid-landing brake transition area.  Many builders reported sanding into their electrical channels when taking too straight of a taper.  To avoid this, I was a little more conservative with my taper - creating a more gentle, and slightly rounded, taper.  Step Done 

7.2.2 Contour corners 1st cut at 45 degrees. (2nd paragraph Step 2) - Drew guidelines along bottom and sides"a la Sui(Bernie)" - however rather than cutting a piece of wood, I just clamped a straight board onto my large Perma-Grit Block at 90 degrees (so the smooth side of the block could ride against the side) then clamped a marker to the board.  Used the Jig Saw with 5.5" blade to make first cut to about the middle of the landing brake, then used the belt sander to take down the rest.  Step Done 

7.2.3 Contour corners Finishing cuts and shaping. (3rd paragraph Step 2) - I made a contour tool by cutting four pieces of 1" MDF using the template in the "M" drawing, then glued them together to make a 4" sanding block.  Coated the block with extra micro and epoxy from step 7.1.9 for added strength. NOTE- the template in the plans doesn't match the curvature of my F-22...I decided to use the template tool I made from mid-brake forward, then tapered to match F-22.  Also, if I were to do it again I would round off the ends of the tool that contact the bottom and side (I did for the second side) because I was a little overaggressive, or careless, and ending up sanding a gouge in the bottom that will have to be filled.  Finished shaping using a variety of sanding tools, and being very careful about keeping the sanding tool perpendicular to the hard surfaces (wood, flox, micro, etc.), otherwise the foam along side the surface would wear away unevenly.  As others have done, I took a few passes (from aft to front) with a sanding belt cut in half to finish off.  NOTE - At this time I left the single piece of foam that covered pieces "A" and "B" (at the landing gear opening) intact, and following the contour of the rest of the bottom.  When I install the landing gear, I'll shape the piece for best fit.   Step Done...sort of  While waiting for my antenna kit from RST, decided to micro the fuselage bottom to help the copper tape adhere better and to protect the urethane until I'm ready to lay down the UNI.  Afterwards, I ended up reshaping the transition from the firewall to the middle of the landing brake because I was unhappy with the way I had it.  Then, more micro put down on the newly exposed foam.  Now, Step Done    

7.2.4 Sand depressions around Landing Brake and F22, and tape build-up around LB  (4th and 5th paragraph Step 2) - Note reference Chapter 9, Step 6 (my step 9.6.1) before beginning.  Now there is no getting around the fact that I butchered the cutting of the landing brake in Chapter 6, I knew it at the time...fortunately you can always fix something; it may just take more work.  To begin the fix, I very carefully measured and sanded the 1/16" depressions based on what the brake cutout should have been.  My trick was to use the two Perma-Grit blocks for most of the work.  To do this I put the long block (smoother side down) along the outside of the line I wanted to sand, then butted the small block against the larger one over the area to be sanded.  I could then slide the small block back and forth to remove the foam.  It worked very well and went quickly.  Used the small hand files to finish the corners and where the micro from the added urethane foam in step 7.1.1 protruded into the depression outline.  Then I used sandpaper to make a smooth transition from the fuselage bottom into the depression so the glass would conform easily.  To finish the fix, I reshaped the landing brake opening to the plans specifications, added foam to the landing brake then cut to match the new opening.  Again, I plan on having the landing brake hinge extend the full length of the brake rather than the shorter plans length.  Step Done 

7.2.5 External step reinforcement. (6th paragraph Step 2) - SKIPPING; I plan on doing a retractable version and will update when I get there.

7.2.6 Nav Antennas. (7th paragraph Step 2) - Let me preface this step by saying if you have waited until the start of this chapter to order antenna supplies from RST, then don't bother -- seek alternate sources.  While Jim Weir is highly respected, their service level does not meet modern standards - according to builders, product will come when it is ready to ship.  Don't expect confirmation that your order is being prepared nor email or phone calls to be returned.  After several weeks, I cancelled my order (via Paypal) and found local sources (all had product in stock, and were within 20 miles of my house) -- wish I had done that from the start...I probably would have been done with this chapter by now!  I chose the layout many builders are currently using with the marker beacon running fore to aft along the pilot side (each arm 34.3"), the nav antenna forward of the landing brake with the vee open toward the passenger side (and each 22.8" arm @ 30 degrees), and a glide slope forward of the landing brake with the vee open toward the firewall (and each 7.5" arm @ 20 degrees).  Drilled 3 cable holes, at ~30 degree angles rearward, just forward of the IP.  2 were below the pilot side vertical electrical channel, 1 below the other side.  After tracing out pattern on bottom, routered channels from the exit point of the drilled holes to each antenna.  To finish the channels, I widened areas for the 3 Anidon FB-43-2401 torroids, created slopes at the base of each arm to allow solder joint to be covered by micro, and used the flexible grinder on the Roto-Zip to soften the bend into the cabin.  Stripped and tinned coax leads, then soldered each to their matching copper arms.   Note - Remember to maintain < 1/2" space between each arm.  After checking continuity on each arm, moved completed antenna to its position (didn't want to expose foam to heat), peeled backing from tape and secured it in place.  Used small foam "wedges" to keep cable below surface, sealed cable exits at IP, then potted channels with micro.  Once cured, I sanded micro potting flush with the surface and confirmed the continuity again.  Step Done  

7.2.7 Loran Antenna. (8th paragraph Step 2) - SKIPPING; No Loran to be installed.  Step Done 


Glassing the Bottom  

7.3.1 Prep and flox vertical corner of NACA scoop. (1st paragraph Step 3) - Did this step at the same time I microed the bottom in step 7.2.3.  After cure sanded in preparation for laying the glass.   Step Done

7.3.2 Trim bottom longerons flush with Firewall, prep bottom for layup. (1st paragraph Step 3) - Fein tool and sanding...   Step Done

7.3.3 2 ply UND on bottom, 30 degree orientation. (1st paragraph Step 3) - As usual, Glen (or "Mr Epoxy") stepped in to give me a hand on this layup.  I thought this step would have gone a little quicker since I microed everything in advance of laying the antennas - it didn't.  There is nothing particularly hard about this step, but it is a little tedious.  In preparation for this step, I rolled up the UNI needed onto two rolls (one for each ply).  This way I could check the glass and tape the salvege.  I also drew 30 degree guidelines onto the bottom of the fuselage.  Then when we laid the glass, we could just roll out the UNI directly on the fuselage.  This worked out really well, and required very little work to remove wrinkles and air bubbles.  Once the glass was wet, I cut of the masking tape that held the salvege - still had some problems with "strands" coming off the edge, but it was the best I could do.  Since I skipped the "LG Joggles" I didn't have the problems many builders encounter of getting the glass to conform.  Also, since I took the edges down on the LG and F22 depressions (see Step 7.2.4), I had no problems with glass conforming there as well.  However, I forgot to round the edge of F22 prior to glassing, so I did have some trouble bringing the glass over and probably will have to address some air bubles after cure..     Step Done

7.3.4 Install engine mount reinforcement layups Two 3-ply UND (6 plies total) both sides. (2nd & 3rd paragraph Step 3)  - This too was a little tedious.  Drew a guideline onto bottom so I could center reinforcements above the 1/4" LG holes.   Then made tapes for each section.  During layup, I had to notch the pieces so the would conform around the contoured bottom without wrinkling.  I notched by cutting parallel with the UNI from the ends into the bulkhead, this allowed me to keep the fibers straight and not compromise their strength.  I think this will make some attach points uneven (since some fibers had to overlap others) - if it creates a problem, I plan on filling the low points with flox and covering with BID.   Step Done

Contouring the Sides

7.4.1 Remove portions of sides forward of F28. (1st paragraph Step 4) - Per plans    Step Done

7.4.2 Make templates for contours. (2nd paragraph Step 4) - Per plans    Step Done

7.4.3 Contour corners. (2nd paragraph Step 4) - Used the "Cheese Grater" to rough out the shape, then finished with the PermaGrit Blocks.  As with contouring the bottom, 99% of the work is shaping the blue foam first - the yellow foam only requires a few very light, and careful, passes to complete.    Step Done

7.4.4 Clean outside area for fuel sight gauge. (3rd paragraph Step 4) - - SKIPPING; HAVE NOT DECIDED TO USE   Step Done

7.4.5 Sand depressions at F22. (4th paragraph Step 4) - Completed during Step 7.2.4    Step Done


Out of Order - Landing Gear Reinforcements - Moved from Chapter 9 - Wanted to get this done while fuselage was right side up in order to build the "rotisserary" support in the next section.

Moved 9.1.4 2 ply BID over NACA scoop (3rd paragraph Step 1) - Prepped area by shaping corners and microing around all corners to insure glass would conform, then glassed per plans (sandwich between wax paper and cut notches at intersection of corners).   Step Done

Moved 9.1.5 3 ply BID over Rear LG Bulkhead, Side, and Firewall. (4th paragraph Step 1) - Per plans - Make a good template, then sandwich plies between wax paper and cut.  Place into position starting from center of side and working out towards Firewall and LG Bulkhead.   Step Done

Moved 9.1.6 3 ply BID from LG hardpoint to Firewall hardpoint. (5th paragraph Step 1) - Per plans, similar to 9.1.5.    Step Done

Glassing the Sides  

7.5.1 Build A-Frame rotisserary. (1st paragraph Step 5) - Used my existing frames as the foundation for the rotisserary.  Started by "sandwiching" F22 between two pieces of 3/4" inch plywood, with 1/4" plywood cut to fit on the center of each leghole.  Then I removed a wheel from a caster, and attached the assembly to a 2x4.  Connected this piece to the F22 "sandwich" and the sawhorse frame so the fuselage would rotate at ~25" above the ground.  That would provide an acceptable working height when the fuelage is as at 90 degrees, yet allow the fuselage to rotate fully without hitting the ground.  At the rear of the plane, I cut 2x4 pieces to fit between the NACA scoop on the bottom, and the interior of the rear landing gear "compartment", then I enclosed these pieces in a frame that encompassed the entire rear LG bulkhead and the FW.  Then with a 3/8" hex bot, connected this frame to a post that I attached to the other sawhorse.  This set-up seemed to work well, but I find it best to tighten the rear bolt/nut and then use a screw ( at the rear turning assembly) to prevent the fuselage from spinning.    Step Done

7.5.2 UND layups on first side, plus reinforcement layup at Upper Longeron. (2nd & 3rd paragraph Step 5) - To prepare for this layup, I rolled out 105" of the UNI to cut my 3rd side ply (parallel to the longerons), top longeron reinforcements, and rear engine mount reinforcements (which will be prepared as a tape).  I also drew 30 degree + other reference lines on the side, and prepped the spar cutout area for a flox corner at the glass-to-glass joint.  Following that, a pretty straight-forward layup...just takes a little while if you're alone.    Step Done

7.5.3 Engine mount reinforcement layup on first side. (4th paragraph Step 5) - Made a tape, then layed from the side toward the FW.  Had to make 3 relief cuts (parallel with UNI fibers), so I could bring the reinforcement over the FW without creating bubbles.  This causes an uneven buildup over the engine mount hardpoints.  I'm planning to create a small buildup to "smooth" out this uneveness without adding a lot of extra weight.    Step Done   

7.5.4 UND layups on second side, plus reinforcement layup at UL. (5th paragraph Step 5) - Per plans, similar to 7.5.2    Step Done

7.5.5 Engine mount reinforcement layup on second side. (5th paragraph Step 5) - Per plans, similar to 7.5.3    This concludes Chapter 7 - I'm unsure whether I'll take the obligatory "Chapter 7 first flight" pictures (with vroom vroom noises, of course)...  And now the rest of the story: I promised my wife I would move the plane so she could have the hangar (or as she likes to call it, "the garage") for the winter; something about ice, snow, and windshields...blah, blah, blah.  So during the move, put some soft foam down on the floor and boarded for my first flight.  A stupid grin and vroom vroom noises soon followed.     Step Done 

Chapter 6    Chapter Index    Chapter 8

N911HF - No 911 Heroes Forgotten