Chapter 5 - Fuselage Sides

What's Up?

In this chapter, we will be building the fuselage of the aircraft. The parts will be BIG - since it take the full length of the plane except the nose and the engine compartment. In addition, it will be curved. That should be interesting. Quite a bit of wood working is required for this chapter - mainly for fixtures and stuff. By the end of the chapter, we will be doing a large layup - expected to take HOURS per the Cozy archives.


Making the Jigs (FJA to FJF)

The first part of this chapter requires some  wood working to prepare the jigs, but it is pretty straight forward. The FJA (with curved edge) requires a bit more attention than others. Since I wanted to make sure all 4 are exactly the same, I tried to make the first one as precisely as I could. That means tracing the curvature carefully, trimming close to the curvature with a band saw, then …. sand, sand and sand to the contour line. After I accomplished that, I trimmed and clamped all four FJA’s together, then sand, sand and sand some more! Here’s a picture how they turned out.






Mounting the Jigs on the Work Table

Once the jigs were made, I bolted them down on the worktable. The plan requires a ½”  gap at the tip of the two ends – a perfect application for a laser beam. I cut two 1”x½” wood blocks – one for each end of the jigs. I put a mark at the mid-point of the ½” sides of the blocks. Now, I placed these small blocks 102” apart (per plan) and ran the laser beam right down the center of these two blocks. The laser beam is the center line of the jig set up as shown.


Instead of using nails, I pre-drilled the wood jigs and screwed them down onto the work table. This way, I have less tendency to move them out of alignment while securing them in place. Don't forget to double check the dimensions once they are secured. Now I am ready to build the longerons.



Building the Longerons

The longerons were quite straight forward. Between clamps, nails and wedge blocks, I managed to secure the longerons in place to cure. I gave it 3 days to cure (while I built a local heat tent). They popped off quite readily and retained their curvature - I was impressed. The packing tape under the longerons did a great job in keeping the longerons from sticking to the work table - thanks to the friendly advice from the plans!


Preparing the Masonite Boards

First thing I noticed was that there wasn't quite enough material for a 2-piece per side set up as shown in the plans. Figure it is going to be another one of those 'creative' tight fit layouts (as we all experienced in the past), I measured, re-measured and re-measured some more... I finally gave up and ended up with 3-piece per side, 94"x21", 4"x21 and 4"x21". I was able to make both masonite sides with a single 4'x8' board though. I later found out from the archive, someone did mention briefly that there was not enough material for a 2-piece masonite per side - nothing specific though. Considered yourself FOREWARNED!


Making the Fuselage Sides

Foam for the fuselage sides was easy to cut with a razor blade. The curved edges at the bottom were not too bad either. Again, I completed one side first, then I traced out the second side using the first side as a template. This way, I should get two symmetrical sides or at least a pretty close pair.






Preparing Control Stick Clearance on Fuselage Sides

 I drew out the positions of the control stick clearance (with a compass and felt tip) on both of the fuselage sides and double checked its positions. I used a plunge router with a flush router bit and milled out about 6" diameter x .25" deep of  foam. Used various grit sand-paper and shaped a gradual slop that forms an 8" diameter clearance per plan.







Preparing Fuel Gauge on Fuselage Sides

Next I carved out the fuel gauge indentation for the right side according to plan - 19" from the rear edge... Marked out the pocket with a felt tip and start gouging with various grits of sandpapers. Looked good! Now do the left side. Fifteen minutes later ... done!

Stand back and admire my work of art and surprise.... they do not line up????!!!! A quick measurement revealed that the right side was 12" from the end instead of 19". How it got there ... I dunno. As warned by Mark Zeitlin - measure, measure and measure - well, now I know what you mean!

One of the wonderful things about foam structures is that you can easily fix your mistakes. I actually cut out the entire back panel (instead of filling up the indentation) and re-carved the fuel gauge indentation at the correct location. Scraping the back side of the panel makes Oops#2.

I later decided to use Vance Atkinson's LED fuel gauge indicator which requires a flat .25" indentation instead of the slope surface. Arrrrg... but I convinced myself that it will look pretty when its done!

Vance's fuel sight gauge arrived. It consists of a white plastic for the back with a clear cover & a little pea size float. The white part is about 7.5" tall, while the clear part is .25" wider all around. These dimensions are much larger than the plan dimensions. The obvious question would be - where should I carve the trough to accommodate these new fuel sight gauges?

I posted the question to Vance and was told to carve it with an extra .5" space all around such that I can adjust its position after the strake is installed. Well, I ended up carving a  trough the same size as the white plastic (7.5"x2.5"), with a .5" curvature starting 2.5" from the top edge of the fuselage, and added another .5" curvature from the bottom of the trough back to the top of the foam.   

Hopefully, the fuel sight gauge will be at the right place when it is ready to install them. Incidentally, there's wiggle room if I trim the fuel sight gauge to a smaller foot print as well. 





Setting Up the Fixtures for Fuselage Sides

This step requires the securing of the FJA - FJE fixtures at an upright position to shape the fuselage sides prior to glassing. With the help of a laser beam, I drew out the foot prints for the fixtures on the work table. Then I lined up the fixtures on the foot print. I noticed some warpages on a few fixture boards which I think needs to be corrected (I may be too picky on this one). I was concerned that Bondo (as recommended per plan) may not be strong enough to hold and correct the warpages in my fixtures. I decided to use Wayne Hick's approach by making fixture frames instead of gluing them on the table instead. I cut up a bunch of 2.5"x 14.5"x.75" plywood boards as spacers, screwed them to the fixture boards (5 places), forming a fixture frame (as shown).





There are two main advantages to this approach - 1) I can straighten out the warpages in the fixture boards, and 2) I can hold the foam boards onto the masonite with screws instead of 5 minute epoxy (per plan). This will eliminate the patch work later when the foam fuselage is separated from the masonite boards. 


Fast forward a bit here... the picture to the left shows the size of the hole left on the foam by the hold down screws after the fuselage is done. They are much smaller than the chunks of detached foam as described when using the 5-minute epoxy method. I filled them with micro before moving to Chapter 6. The thumb tack is just for size reference.   



I made a 7/8" thick block for lining up the fuselage foam sheets as I 'pulled' them down onto the masonite (with screws from the bottom side up). Surprisingly, the foam lays down on the masonite boards quite nicely even without any screws to begin with. Nonetheless, when it was done, they looked pretty good.








Shaping the Spacers

I followed the plans in forming the spacers. Two dimensions were missing from the plans but I found them in the Archives:


I used the same slope dimension (identified in C-C) for the large spacer at the aft end.


I started the heat duct slope 6" from the aft end of the fuselage and extended the slope for 3.75". I followed Rick Maddy's footstep on this one per his Web Site.

I set up my band saw for rough cutting the slopes for the spacer strips. I then sanded them to desired dimension with my HDSSS (Home Depot Sanding Stick Special). This foam is easy to shape, except it puts out lots of dust and they get into Every Where! I added a couple inches to the spacer strips when I shaped them because, I figure, when I attach them onto the curved fuselage sides, it will add a bit of length to it - it did. I cut the spacers strips to length before I was ready to micro them onto the fuselage. I used a lot of C clamps to hold the spacers in place during curing. 





Besides rounding the foam spacers, I learned (from other builders) that the longeron edges need to be rounded as well. Otherwise, the fiberglass will not lay down nicely. I used a router to put a 1/4" rounded edge along the entire length of the upper longerons. Initially, I was a bit concerned about the curved shaped longerons and that the router may not sit right, however, it worked out OK. Here's a picture of the longerons after I have the edges rounded. 







Applying UND onto Fuselage Sides 

This step requires 2 layers of UND glass at 30 degrees over the entire inner surfaces of the fuselage. If you have an opportunity to ask for a extra pair of helping hands - this will be a good time to ask! I got Susann (my better half) to help me lay out the UND on top of the fuselage so that I can pre-cut them for subsequent layup. The pre-cut UNDs were rolled up, marked and placed under cover to keep the dust out.


I microed both sides of the fuselage with Susann helping me by mixing the micro. It took us 2.5 hours - much longer than expected! I then proceeded to UND layup with Susann continuing on with epoxy supply. I took special care to push and pat down the glass at the stick control and fuel sight curvatures.  I was able to avoid the air bubble problems many builders experienced. We did both sides at the same time - without much of an air bubble problem - we were fortunate.


While the layup was still wet, I trimmed the glass along the upper edges of the fuselages per plan with my electric scissors. It was difficult to trim right up to the edges - I left about 1/16'' glass overhanging. We were at hour 7 since the beginning of this task, I was getting tired and did not pursue perfection - I should have. 


Spacer Board Preparation

Let me digress a bit and discuss how I prepared the spacer boards. The plan calls for 7/8" spacer. Well, most lumber does not come in 7/8" thickness. As you may recall, I have a neighbor that works for a lumber yard... A visit to the neighbor (with cookies) and I got myself a 6'x 1' board, planed to 7/8" thickness... the next day. I cut them into 8"x12" boards and wrapped them with packing tape. The reason for the packing tape is to make sure they do not stick to the flox that will ooze out between the longerons and the fuselage when they are clamped together (refer to longeron installation in this Chapter).


Installing the Longerons

After I trimmed the glass along the top edges of the fuselage sides, I slipped five (5) 7/8" spacer boards (prepared above) evenly between the fuselage sides. I brushed flox onto the mating surfaces of the upper longerons and upper edge of the fuselage and clamped them tight together. At this time, I was concerned about the 1/16" glass (I left un-trimmed earlier) because by pushing the spacer board down between the fuselage sides, I was shoving  the 1/16" glass (overhang) to fold down against the foam of the fuselage sides. I used lots of clamps to hold down the longerons onto the fuselage sides as well as to the spacer boards. Strips of peel ply were added per plan. This layup took us a total of 9 hours straight and we were exhausted when completed. My back was stiff for 3 days afterwards. 


After a 24 hour cure, I couldn't wait to remove the clamps to see the results. The folded glass at the upper fuselage did not cause any problem because I squeezed them so tight with clamps, they did not have any dimensional effect. The flox did not stick to the 7/8" wood spacers either because of the packing tape. With all the good news, I forgot to take pictures! The picture shows the aft spacers - cured with 2 layers of UND. You can see the fuel sight gauge and the electrical duct. The UND covering the electrical ducts needs to be trimmed - later. The light in the background is my heat source for my localized heat tent. I trimmed the glass overhang from the lower fuselage edges at this time. 



Applying the 4 layers of UND

The instruction (for this task) is contained in a 44 word sentence - it took me 8 hours from preparation to completion!


First, I un-rolled the UND on a long table making sure its straight and flat. I used 1" wide x 102" long strips of masking tape and taped along the full length of the UND. I repeated this every 5" apart. Once taped, I used my electric scissors and cut along the middle of masking tape - lengthwise. Since the UND cloth is 30+" wide, I can make six 5" wide strips of UND, each 102" long. I made a total of 8 strips - 4 for each longeron. The tape keeps the UND from fraying and allowed easy handling.


I decided to epoxy the 4 UND layers together first before applying onto the longerons. I cut a 6"x 105" 4 mil plastic strip and laid it down on a flat surface. I placed the 1st UND layer on it and wet it with epoxy, followed by the 2nd, 3rd and 4th respectively - adding epoxy on each layer as necessary. Once completed, I laid down another layer of 4 mil plastic on top (poor man's peel ply method) and squeegeed out the excess epoxy. When all the bubbles were removed, I used the electric scissors and trimmed off the rest of the masking tapes - leaving a 4+" x 102" strips of UND, sandwiched between 2 layers of 4 mil plastic. I then transported the strips to the longerons, peeled off the top layer of the plastic and laid it face down onto the longeron and spacer per plan. Don't forget to brush a layer of fresh epoxy onto the longeron before applying the UND though. Surprisingly, the UND laid down easier than expected. After removing the remaining 4 mil plastic from the UND, I peel plied the UND to ensure a smooth transition to the fuselage. After applying the peel ply, I re-laid the 4 mil plastic back on top of the UND strips and squeegeed some more to ensure the UND laid down nicely. I then covered it with the heat tent to help cure through the night.


My First Repair

Well, the bubble goblin made its first appearance overnight. I found a large bubble on the longeron after cure. This will be my first repair. I re-read Chapter 3 repair instructions and went for it. I ground out the 4 layers of glass where the bubble was. I then stepped outwards 1 layer less every inch. Since it was a 4 layer UND, I stepped out 4 inches - both directions. You can see the size of the bubble and the 4 layers of replacement UND - ready to be glassed in. Once I got the 4 layers done, I added on more layers of BID for the entire length (not shown). I then peel ply the entire repaired area. The result looked ok ... I hope it is really OK! I'll show the repair to an experienced builder next time when I get a hold of one.





Lower Triangular Longerons

Accordingly to the plans, I am suppose to check the dimensions in Fig 5 and mark the exact location of the lower longerons with a felt tip pen. With the white spacers and upper longerons installed and no access from the bottom side of the masonite, there's no way I can measure and mark the locations EXACTLY per fig. 5. I posted the question to the builder's group and got a few amusing responses. Basically, the distance between the lower longerons from the upper edge of the fuselage, should be close to the dimensions in Fig. 5. Most importantly, the dimensions should be equal on both sides. I laid a carpenter's square along the top edges of the longerons at designated locations per Fig. 5 and took measurements on opposite sides of the fuselage. Note that these dimensions will not be the same as the ones in Fig. 5 because the dimensions are no longer taken from a flat foam board as in the beginning. Here's the dimensions I got and the variances between the two sides:








































As you can see, most of the variance is within .05" with a maximum at 0.08". I can probably sand down the high side and fill the low side when installing the fuselage bottom. I decided to leave them as is for now and move on to the next step. 


I anticipated that the lower longerons would be a challenge due to the curvatures it has to conform to. I did a lot of reading on the Web and learned a few useful tricks. Instead of cutting relief cuts every 2 or 4 inches apart, I cut them every inch and some on the alternative edges as necessary. I think that will put less stress on the lower longerons during the curing process. You can see my clamp-de-thrifty in the  foreground. I found them on the Web - unbeatable price of $1.71 a piece. 






For curing, I cut up quite a few clamping blocks with 45 degree concave corners for holding the triangular shaped longerons in place for curing. Susann reminded me to wrap the face of the blocks with packing tape - what a life saver!  The holding clamps work very well and they popped off easily without sticking to the epoxy.


After the 24 hour curing, I cut up the 20 inch long doublers as well as the relief cuts to conform to the curvatures. Floxed in and clamped down, forming a square cross section per plan. You can see the result in later pictures.





Electrical Channels

I made the electrical channels using the male plug method as taught in the plans. They turned out reasonably well without too much of a challenge. The only difference I made (un-intentionally) was slanting the front tip to match the edge of LWY. It butts well against LWY when installed, but it created a lot more work for making the foam cover (fill) as directed in Fig. 17.








I cut up the stringers per Fig. 12. For the 1" wide LWX, I used the base dimension (15") and the two angles (45 & 35) respectively. As for the 2" wide LWY, I used the two dimensions (8.6" & 6.5") respectively. When I tried to line them up per Fig. 14 & 16, they weren't even close. I pondered over this more than I should have but come to the conclusion that the most important dimensions are the aft cutouts (5.5" x 8.7" per Fig. 16) and the 16.3" position for the LWX (Fig. 14).


If you make LWX and LWY as I described above, the short edge of LWX will be 12.57" instead of 12.7" - just a bit short AND the angle for LWY will be about 43.6 degrees.  To make the whole thing fit nicely per plan, I trimmed LWY to 45 degrees and extended the length of the LWX (look close at the picture).



After floxing in the LWX and LWY in place, I filled in the area bounded by the lower longerons, LWX and LWY with 3/4" Clark foam. I also embedded the electrical channel in place per plan. Clamps were used to hold the Clark foam in place during cure and were sanded leveled with the stringers. Filled the gaps with micro and laid 6 plies of BID per direction. You can see the filled area, trimmed glass and the embedded electrical channel (picture at left).







Trimming the Fuselage Sides

I made measurements to the fuselage sides using carpenter's square per plan. It turned out that the length of both fuselages are exactly 101.75" and square. I think I lucked out on this one. Only the vertical cuts on the foam need to be trimmed. Since the trimming requirement was minimal, I just sanded them down using the square as a guide. I did release the fuselage from the masonite boards by removing the anchoring screws. The size of the holes left on the foam by the anchoring screws were small and were patched up easily (refer to earlier picture). 






After the sides were trimmed, I marked the 5.5" x 8.7" area for the centerspar. I cut the cured glass first with the FIEN tool along the marked outline. Once the glass were cut, I took a jig saw to the rest of the foam. I then sand down the glass and foam edges smoothly and to exact dimensions. The two pictures to the right showed the cut out area as well as the completed fuselage.







Part Weight

Left fuselage                10 LB 15.4 OZ

Right fuselage              11 LB   0.6 OZ

1.2 Oz variance in weight between the two fuselage sides... maybe it will fly level!