Chpt 7 - Fuselage Exterior

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updated: 09/05/2022

 

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Step 1 – Building the NACA Scoop

Step 2 – Contouring the Bottom

Step 3 – Glassing the Bottom

Step 4 – Contouring the Sides

Step 5 – Glassing the Sides

01/07/2006 – In this chapter the outside of the fuselage is rounded and finished off and the sides are tapered back to the firewall and the NACA scoop is built as per drawing M-16.  Hard points are installed for the landing gear door and reinforcing is added where the step attaches.  Carving out the fuel gauges and cutting out the area where the canard attaches and installing the Nav antenna before applying the glass for the  outside skin.

Before I started with Chapter 7, I removed the aluminium trestles from my work table , which act as the legs for the table and lowered the table top onto the floor. I then made some wooden clamps for F22 and the Firewall, so that the complete Fuselage was supported in-between the trestles.  This placed the fuselage at a nice height for working on the bottom and also allowed me to position the fuselage as required.          

Step 1 – Building the NACA Scoop

I started with cutting out the NACA template from drawing M-16 and then transferred the shape of the scoop onto the fuselage bottom.  The foam pieces were cut out as per plans from one sheet 2" thick x 24" x 48”, white 2lb density Poly Foam - Wicks part No. F100-035 and one sheet 1" thick x 24" x 48”, white 2lb density Poly Foam - Wicks part No. F100-025.

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I decided to follow suggestions from other builders and extend the 1" foam further out to allow a better transition from the fwd landing gear bulkhead to the fuselage bottom. Unfortunately I had already cut the 1" poly foam as per plans, so I just added an extra 38" x 6" piece of poly foam, as per the 3rd photo above. The foam was microed into place, weighted and left overnight to dry.

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I then moved onto making the plywood pieces A, B, and C and floxed them into position on the lower longeron. The bevelled edges are sanded to match the curve of the bulkheads.  I used mixing sticks taped to the inside of the fuselage as a guide to hold the plywood pieces flush with the 6 layers of BID done at the end of chapter 5.  I" foam pieces were then cut slightly oversize and microed against the plywood.

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Here is plywood piece D floxed into place. The bevel matches the curve of the bulkhead and lines up with plywood piece C. I couldn't get piece C and D to line-up properly and at the same time keep it level.  Drawing M-8 and M-9 show piece D as being square to the sides and level. Eventually I decided to go with a nice fit between C and D with a silent slope fore and aft on D.  I hope this doesn't cause any problems with fitting the lower engine mounting bolts later on?  After applying the 2 ply BID lay-up to plywood piece D, I added the 2" block of urethane foam. 

I used left over pieces of 3/8” H45 Blue PVC Divinycell foam (Wicks Part No.F500-030) from Chapt 5 & 6 to make the inserts in the scoop between the aft bulkhead and the firewall.  I ended up with small gaps between the 2" piece of white urethane foam and the 3/8" PVC insert and think that I could have got a better fit, if the 3/8" PVC was fitted first before the urethane foam.  A photo in the plans on Chapt 7 page 6, actually shows that Nat fitted his this way, which is different to the instructions on page 2?

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I have decided not to follow the plans method for securing the Landing gear cover which is made in Chapter 9 and have omitted making the "Dreaded Joggles", instead I will be following the method detailed on Wayne Hick’s  website.   I had some difficulties sanding down the NACA scoop foam as pieces of micro kept breaking off from the join between the 1" and 2" foam pieces and scoring deep grooves into the soft white urethane foam.  I think I should have only microed the bottom and NOT the sides.  I will have to fill these with micro just before glassing the bottom. 

The NACA scoop was then glassed with 2 plies of Bid as per plans.  I rounded off allIMG_1358.JPG (88579 bytes) edges and tight corners with micro before glassing. IMG_1369.JPG (88299 bytes) After cure I trimmed off the excess glass using the FEIN master and carefully smoothed out the edges with a flat file.

At this point I stopped everything and took a little time to read up and make sure I was 100% sure about how to start profiling the sides.  I updated my plans with the Chapter 7 corrections, published in Cozy Newsletter #78 from July 2002.IMG_1357.JPG (113605 bytes) IMG_1359.JPG (105591 bytes)

This is how I removed the foam from the Fuselage aft ends as stated in the corrections:-   

 

Step 2 – Contouring the Bottom

I started with sanding the fuselage back sides from a point on the upper longeron, 25"IMG_1370.JPG (116258 bytes) forward from the firewall, gradually tapering the foam from this point back to the firewall in an arc.  Refer to the Cozy Builders Site  - Q&A's on Chapter 7.  The corners were removed as per plans using a Jig Saw set at 45Ί.  I used a normal short blade and then followed through with a hacksaw blade to complete the rough cutting.  

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I then cut out the template shown on the large M-16 drawing and made a sanding jig out of 2 plywood ends & polystyrene, covered with 2 layers of Bid.IMG_1379.JPG (93804 bytes)  I glued a piece of 36 grit sandpaper onto the jig and started carefully profiling the corners down, until I had a 0.25 in flat on the bottom wooden longeron.  I carried this through to about the middle of the landing brake and then shaped the aft section to pick-up the radius on the landing gear bulkhead.  Little bits of dried micro kept breaking off and scoring the white foam, making it very difficult to get a nice smooth finish. After about 3hrs of sanding I got a reasonable profile and decided to stop before I messed it up.

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The next step is to prep the landing brake by sanding a 1/16" deep depression 1" wide fwd of the brake and 2" wide along the sides and the aft edge. 

1/02/2007 - Building started again on chapter 7 this month, after almost 6 months of inactivity. Family visits, overseas holidays, Christmas and a general lack of motivation all tributed to the numerous excuses I had for not continuing with the project on a regular basis. Well I hope I have overcome this hump in the road and am back into the building frame of mind again.

Before glassing the bottom of the fuselage, I completed the preparation on the landing brake by cutting the 1/16” recess all the way around the flap with my RouterIMG_1778.JPG (83719 bytes)IMG_1777.JPG (76300 bytes) and used duct tape for the 1” build up on the sides and back edges. At the same time I also cut the 1” recess around the front sides & bottom edges of the fuselage, including F22, for the nose cone, which is made and fitted later on in the building process.

After talking to a number of flyers / builders down at the SAAA club, I decided not to install any aerials into the bottom of the fuselage. The general consensus is that VOR & NDB is almost obsolete in Australia and a good GPS is going to provide me with all the navigation needs I require for VFR flying. I also decided not to install the wooden block for the step as I don’t like this design and will be considering something else along the lines of what Marc Zeitlin has installed into his Cozy IV - http://www.cozybuilders.org/chapters/Retract_Step.html 

Step 3 – Glassing the Bottom

I marked and cut all the UND cloth required for the 2 bottom lay-ups, including the extra reinforcing lay-ups used on the landing gear and firewall bulkheads. With the help of my better half, we started at 6:00pm in the evening and finished about 5 hours later. I used the slow MGS 287 hardener for these lay-ups to ensure that I had plenty of working time. I battled to get the cloth to lie down in the landing brake recess and in the end; I cut the cloth with a sharp blade at the edge of the 1” duct tape as suggested by other builders who had the same problem.

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I peel plied the complete fuselage bottom to ensure a good finish. I hope this doesn’t add too much weight to the finished job, but I’m sure I will use far less micro when I get onto the finishing section.

Step 4 – Contouring the Sides

After cure I trimmed and removed the excess cloth on the edges of the fuselage and within the NACA scope and I was very happy with the general quality of the overall job. I then turned the fuselage right way up and placed it back onto the aluminium stands, with polystyrene underneath to protect the fuselage bottom from any damage, whilst working on the next step.

I started by cutting out the area forward of F-28 for the canard installation later. Once this was done I then cut out the templates A, B, C & D from drawing M16, which are used for profiling the fuselage top edges. I then glued the cut outs onto Ό” plywood, which I then cut out using the Bandsaw. For template “C”, I cut out 2 sections and made a sanding block about 4” wide.

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The fuselage sides were then marked, using the measurements as stated in the plans for each template. I found the shaping / sanding of the top edges far easier than the bottom edges and completed both sides in about an hour. The plans are not clear on how far back you can go when transiting from “C” to “D”, so at the end of the day I went with what looked good and also assumed that the Turtle-back and wing section would cover most of this any way.

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 Next the fuel site gauge area was prepared as per plans.  I will be using the Vance Atkinson Fuel gauges.

Step 5 – Glassing the Sides

I then re-fitted the turning trestles I made earlier on, to the front and back of the fuselage and rotated the fuselage so that the side lay-ups could be completed. I marked and cut all the UND cloth required for the 3 side lay-ups, including the extra reinforcing lay-ups used at the top of the fuselage edges. With 2 pairs of hands this again progressed well and each side took about 4 hours to complete. I used a 50/50 mix of slow and fast hardener for these lay-ups, which gave me more than enough working time. Again I peel plied both sides to ensure a good finish.

 

                   

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Onto Chapter 8    

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