Chpt 6 - Fuselage Assembly



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updated: 09/05/2022


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Step 1 – Fuselage Assembly

Step 2 – Centre Keel and Seatback Brace

Step 3 – Installing the Fuselage Bottom 

28/02/2006 – I have decided to follow recommendations from other builders and will be assembling the Fuselage sides and bulkheads upside down on my workbench.  I will be following the method detailed on Wayne Hick’s website.  The trestle legs are adjustable on my workbench, so I will be lowering the table to a suitable height to make the whole jigging operation easier.  If required I can remove the legs completely and drop the tabletop onto the workshop floor.  The jigs used for the making of the fuselage sides were easily removed with no damage to the top of the workbench and any remaining hot glue was easily removed using a scraper.  I remarked the centreline down the middle of workbench as I will be using this as a reference to the centrelines already marked on all the bulkheads.

Step 1 – Fuselage Assembly
After marking the bulkhead locations on the workbench, I then cut a 2” slot in workbench top for the Instrument panel and I also drill 4 x ¾” holes in my bench top for adjustable clamps, which I intend to use for clamping the top longerons securely down onto the bench top, aft & fwd.  I then used my new Digital laser level to ensure the workbench was level in all directions.

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The temporary firewall took a bit of fitting & filing in order to get the longerons to fit through the holes.  Once fitted I then secured the temporary firewall to the end of the workbench with a plank and a couple screws, ensuring that it was perfectly lined up with the centre line, horizontal and 90° to the bench top.  The F22 bulkhead was fitted and secured with a couple screws into the longerons and the overall length of the fuselage was checked to ensure that it was correct at 101.75”.

The front seat back bottom corners, cut during Chapter 4, did not fit properly into the bottom longerons, as I had removed too much material when trying to cut the corners as per plans to 45°.  I had to repair the corners by sticking about 3/4” of extra blue foam onto the corners and reshaping using a profile gauge.  Once I was happy with the fit I then re-glassed the extra pieces of foam as per plans for the front seat.  I would recommend other builders not to cut the bottom corners in Chapter 4 as stated in the plans, but to wait until Chapter 6 when you can obtain the exact shape from the fuselage sides using a profile gauge and get a perfect fit.

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After the Instrument Panel and Front Seat back had been trail fitted, checking for a good fit on the sides, perfectly horizontal and 90° to the bench top, I then made fitting marks along the fuselage sides with a black marking pen and drilled pilot holes for the locating screws.  This will ensure that I can easily install the 3 bulkheads and reproduce the good fit I had obtained, before removing them for the final installation.

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In preparation for the final installation I removed all the bulkheads, sanded the sides of the fuselage panels as well as the bulkheads, after removing the peel ply applied during Chapter 4.  I started floxing in the Front Seatback first and then moved onto the IP, finishing with F22.  Using the Smart Digital Level I managed to get readings of 0.0° to 0.1° along the top of the front Seatback, Instrument Panel and F22 bulkheads, with the vertical measurements coming out between 89.9° and 90°.

The front seatback was 47.3°.  I was very happy with these readings and my final setup.  Generally I achieved a good fit between all the bulkheads and the fuselage sides and very little force was required to squeeze everything together.  As can be seen in the above photos I used stop blocks screwed into the workbench to hold vertical batons in place, whilst being pulled together at the top with a threaded rod or nylon straps.  Before moving onto the aft bulkheads I taped the corners of the seatback, IP and F22 using the Bid tape method detailed in the plans.

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I didn’t want to cut another slot in my work table, so I have left the fitting of the F28 bulkhead until the fuselage can be moved or turned over and have proceeded with fitting the landing gear bulkheads.  I started with removing the peel ply on the edges and completely sanded both sides of the 3 landing gear bulkheads.  I then made the 8”x8” plywood corner fitting guides as per plans, used for setting up the fwd bulkhead and also as a drilling guide for the ¼” pilot hole.  The hot glue method recommended in the plans for securing the guides onto the surface of the bulkhead wouldn’t stick properly, so I resorted to using 5-minute epoxy.

To get the aft Bulkhead setup accurately, I used 1”x1” wooden batons, clamped to the inside of the fuselage and used the digital level to ensure it was perfectly vertical.  I then trial fitted the aft bulkhead and used a second set of clamps to clamp the bulkhead to the wooden batons.  The initial fit was pretty good and I didn’t need to file too much, in order to get the bulkhead nice and level.  I then floxed the bulkhead into place and used a nylon strap over the wooden batons, to apply a little inward pressure against the aft bulkhead.  In the 2nd & 3rd photos you should be able to the red laser light, spot on the centre line.

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The lower half of the fwd bulkhead was fitted and floxed in using the 8” plywood corners to ensure that the bulkhead was square and spaced correctly.  After the flox had dried the ¼” holes were then drilled through to the aft bulkhead, as per plans.  The 8” plywood corners were then removed and the top half of the fwd bulkhead was fitted and floxed into place.  I used box tape to hold the outside edge together and only floxed the inside, where the top half joined with the bottom bulkhead.   When it was dry I removed the box tape and applied more flox to round off the corner.  I then taped all the inside corners with 2 plies of bid tape.

The fuselage was then turned over and re-levelled in preparation for the additional lay-ups on the top half of the fwd bulkhead as per drawing M-5 and the fitting of the F28 bulkhead.  The temporary firewall was removed and the position of the longerons, stringers and cable channel holes were transferred to the bottom half of the permanent firewall and cut out.  The bottom firewall was then floxed into place using 5” plywood corners to ensure that the firewall was square with the fuselage sides and the correct distance from the aft landing gear bulkhead.

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The weight of the Fuselage at this point was approx. 20kg

Step 2 – Centre Keel and Seatback Brace

When marking out the pieces for the seat brace as per the drawing in Chapter 2, page 5, I noticed that the 2 braces and the 2 duct side pieces were not laid out as opposite to each other, as stated in Chapter 6, page 4.  I ended up cutting out all the pieces and glassing the 2 triangles together with bid and all the straight duct sections together with uni.  After cure I cut all the pieces out with the Fein.  I cut out the ¼” birch plywood insert with the band saw and removed the foam from the 2 triangles with the blade of a utility knife.  I found that the dimensions given for the placement of the braces, which formed the map pocket weren’t even close and I ended up placing the braces to suit the hole I had cut in the seat, back in Chapter 4.

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My first attempt at making the fuel valve-mounting bracket failed with the one side snapping clean off, when I tried to bend it around a 4mm radius using the Vice.  My second attempt using the Wicks supplied 2024 T3 aluminium also cracked.  After reading the many issues other builders have had trying to bend this stuff, I decided to use 6061 T6 instead.  I adapted a door hinged screwed down onto a wooden block as a temporary bending brace and my 3rd attempt was successful.

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When I made the instrument panel in Chapt 4, I made it about ¼” deeper and now needed to trim off the excess, so that the bottom of the IP was level with the bottom longerons.  The air duct and seat brace were trail fitted, checking alignment with the bottom of the IP and the front seat.    I had to trim about a 5mm off the bottom of the seat brace to match the slope to the front seat and to get a good fit onto the air duct, keeping everything straight and level with not gaps.  I also marked the front seat for the extra cut away required for the removal of the fuel valve.  Once I was happy with the fit I rounded all corners, applied the 7 uni lay-up over the seat belt securing point as per plans and then completed the 2 bid lay-up, on both the air duct and seat brace.  When everything was dry I joined them together and floxed the unit into place on the IP and front seat, finishing with the 2” bid tapes.

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Test fitting the Centre Keel and Seatback Brace and the finished product.

 Step 3 – Installing the Fuselage Bottom

The fuselage bottom is made from 3 sheets of 3/8" thick x 32" x 48”, blue low-density H45 PVC Divinycell Foam.  Wicks part No. F500-030.

The 3 sheets were placed over the fuselage bottom and trimmed to fit between F22 and the Fwd bulkhead.  I climb underneath and marked with a pencil along the bottom longerons and all bulkheads.  The foam was then placed onto the workbench, joined with 5-minute epoxy and trimmed to size.  The foam bottom was then placed back onto the fuselage and the wooden support frame was made up using 1"x2" pine strips. When everything was shimmed correctly, the strips were screwed together and the frame was glued onto the foam using small amounts of 5-minute epoxy. 

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Back on the workbench the Speed brake was marked and cut out using a Jig saw set at 45º.  The tapered spacers used to give the fuselage bottom depth and contour are made from a single sheet of 3/4" thick x 24" x 48, 4.5lb Last-A-Foam and left over foam from when the fuselage sides were constructed in Chapter 5.  Wicks part No. F400-045.  The inside edges were all cut at 30º.  The section covering the speed brake was profiled out of the single sheet and the off-cuts were joined together to make up the rest of the tapered spacers.  Once all the spacers had been cut and test fitted they were microed into place and small nails used to hold them down.  The next day the fuselage bottom was test fitted onto the fuselage to ensure a good fit and all the top edges on the spacers were lightly sanded to round off the corners before glassing.  

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I did not follow the suggested plans method of glassing the fuselage bottom, floxing and taping to the fuselage all in one operation. This sounded too much like a marathon exercise to me and I did not like the idea of waiting 4 hours for the lay-up to "tack", before turning it over and placing it onto the fuselage, with the possibility of the lay-up coming loose and dropping onto the floor. Instead during the evenings I worked on preparing the foam for glassing as well as measuring and cutting the 2 plies of Bid cloth required for the interior bottom (cut at 45" fibre orientation, with the 2nd ply laid in a crossed direction to the 1st ply). I also cut the extra piece of Bid cloth required to strengthen the floor area behind the front seat, when the back passengers are climbing in and out of the aircraft.

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On Saturday morning with the help of my better half, we made an earlier start with applying the micro slurry and laying up the 3 pieces of Bid cloth. This took about 4 hours to complete, at which point I then applied peel ply to all areas that would be floxed onto the fuselage longerons and bulkheads. I was tempted to peel ply the complete internal floor area using one length of peel ply off the roll, but decided against this as I was concerned about the extra weight I might be adding, as well as the difficulties I might have getting the peel ply to follow the numerous contours across the fuselage bottom.

The layup was left overnight to cure and the following day I then proceeded with trimming, sanding and floxing the bottom onto the fuselage, which took another 4 hours to complete. Before I started I double checked the fuselage with the laser digital level to ensure that it was still level in all directions. With the bottom fitted, floxed and weighted, I climbed underneath the fuselage and removed any excess flox and filled any gaps. I have found that by sanding a radius onto the ends of a mixing stick makes a very nice tool for getting the joints and gaps floxed just right. I normally make 2 different sized radiuses on each end of the mixing stick, one left and one right handed (See picture above). 

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This was left to cure for a further 2 days before I removed the weights and wooden frame from the fuselage bottom, and lifted the completed fuselage back onto my work table. I rechecked for level and looked for any signs of twisting and couldn't find anything that was out of place.  With the fuselage laying on its side, on the work bench, I then proceeded to tape all the joints at my own leisure.

Chapter 6 was finally completed on 28th June 2006, with a total of 104 hours worked over nearly 4 months. I feel I could have finished this chapter a lot sooner than I did, but due to work commitments, the odd dose of flu and cold wet winter evenings, I just didn't put in the hours per week that I should have. Now that winter has set-in I seriously need to consider installing a Reverse Cycle Air-conditioning unit into the garage, if I hope to do any work at all during the next 4 months of winter.

I thought I would mention that at this stage I have used up about half of my original  35Kg L285 MGS Epoxy kit, about half a packet of Micro and a quarter packet of Flox. 

Chapter 7 here I come -