Chpt 4 - Bulkheads



Cozy Build Project
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Pre - Chpt
SAAA - Chapter 24
Project Costs

Working on Chapter 19

updated: 09/05/2022


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Step 1 – Front SeatBack

Step 2 – Forward Bulkheads

Step 3 – Instrument Panel

Step 4 – Landing Gear Bulkheads

Step 5 – Firewall

01/11/2005 – Whilst waiting for my shipment to arrive from the States I decided to make a start with cutting out the Firewall Templates and making the Temporary Firewall.  I decided to cut the templates from the extra M drawings I purchased, instead of tracing them out and I will be doing this for all the templates required through out the various Chapters.  If I need to refer back to anything I will still have the original M drawings supplied with the plans.  I used 6mm plywood to make the temporary Firewall template, just pinned the cut-out onto the board and cut it out with the Jigsaw.  I will do the same for the Birch permanent Firewall.

Step 1 – Front SeatBack
The front seat is made from 2 sheets of 0.75in thick x 24” x 48”, blue low-density H45 PVC Divinycell Foam.  Wicks part No. F500-035.

I followed the plans instructions to the tee and used the cutting attachment on my Dremel to cut the corners, edges and cutouts (must remember to put the Fein MultiMaster on my Christmas shopping list).  I also cut the map pocket hole undersize as suggested, so that it can be trimmed to size later in Chapter 6 when fitting the Map Pocket.  I made an early start with using the Plastic Peel Ply method as described on John Slade’s website and Wayne Hick’s Hinge method for joining the foam, I was very happy with the results.  I had no real problems with the actual making of this piece, even though it was my very first attempt at working with glass and epoxy, but I did battle with my first attempts at reading the instructions and drawings.

I found that the instructions and drawings were not very clear about whether the sides of the seatback and corner cut-outs were to be glassed or not.  After checking on the Internet and forums I was even more concerned that I was reading the instructions incorrectly, as no one else seemed overly concerned about the Seatback and nothing was mentioned about the sides.  After seeking reassurance from another Cozy builder in Sydney, I proceeded with making the Seatback and did NOT glass the sides or cutouts.

Update (10/03/2006) – See comments in Chapter 6 regarding cutting the Front Seat back bottom corners and map pocket.  I would recommend leaving the corners until Chapter 6, so that they can be cut accurately, taking the shape from the fuselage sides using a profile gauge.  Also leave the map pocket slot about 1” shorter at the top and the bottom and cut to size when you fit the Seat Brace.

I did use peel ply before laying down fibreglass cloth on the front section of the Seatback, in the area were flox was required, along the top and bottom edge.  This is done before glassing the front, so that when you turn the Seatback over to glass the back, you can just remove the 6mm peel ply strip and fill the edges with flox, no sanding required.  If I hadn’t watched Burt Rutan’s videotape, I would have missed this trick.  I also peel plied around the edges of the Seatback, front and back, after completing the lay-ups.  This will make fitting the Seatback to the fuselage sides in Chapter 6 easier.

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Final Weight of SeatBack = 2.5kg

To help stop the UNI cloth from fraying, I used masking tape along the cutting line.  The tape stays on the cloth edges until the sides are knife trimmed at the end of the lay-up (Thanks Chris, this tip helped a lot).  The UNI cloth is not wide enough to cover the whole Seatback at 45º so two pieces of UNI cloth are used.

Step 2 – Forward Bulkheads
The forward bulkheads consist of 3 pieces – the F22, F22-doubler and F28 and they are all made from 2 sheets 0.2in thick x 12” x 48” 18lb, white high density Last-A-Foam.  Wicks part No. F400-085.

I used a Dressmakers serrated-edged tracing wheel to transfer the cutting lines from the M4 drawing onto the foam.  This was far easier than tracing the cutting lines with a pencil.  Last-A-Foam is quite hard and not easy to cut with a Stanley knife or any other knife for that matter and I wasn’t doing very well with the Dremel either.  So after a frustrating afternoon I finally buckled and went down to the local tool shop and bought the Fein MultiMaster - WOW what a difference.  The Fein is expensive, but well worth the amount of time and frustration it is going to save you.

When cutting the BID cloth at 45º for F22 and the Instrument panel keep the triangular shaped off-cuts.  They can be used later on F22 and the Landing Gear Bulkheads.

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F28, F22 & F22 Doubler cut out ready for Glassing. F22 & F22 Doubler Glassed together. The green area is the 11 lay-ups
of Bid and Uni.  Final weight of F22 was 1Kg and F28 was 292Kg.

Step 3 – Instrument Panel
The Instrument Panel is made from 2 pieces of 0.2in thick x 12” x 48” 18lb, white high density Last-A-Foam, glued together with 5 minute epoxy.  Wicks part No. F400-085.  By joining a couple off-cuts I managed to save a full sheet of 0.2in foam.

The instrument panel is pretty straightforward to make and was completed over a single weekend.  I only cut out the leg holes before glassing and did the smaller holes on the sides and bottom after cure.  To cut out the smaller holes I drilled the corners with a 12mm drill bit and either used a hacksaw blade or the Fein to cut between the holes.  A medium half round file was used to dress to the final size.  As recommended by other builders I did increase the bottom dimension by 1/4" to improve the fit when installing the fuselage bottom.

To do the cable channels on the fwd face, I glued together, using 5-minute epoxy, some 0.2in thick foam off cuts to make the 1in wide strips.  These strips were glued onto the fwd face of the Instrument panel with 5-minute epoxy, the corners rounded and filled with Dry Micro before glassing.  To get the correct channel shape I used a 1” thick piece of wood wrapped in Cling wrap as suggested by other builders.

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Final Weight = 1.9kg           Aft Side                     Fwd Side

Step 4 – Landing Gear Bulkheads
The Fwd Bulkhead is made in 2 pieces, which are joined later in Chapter 6.  The Aft Bulkhead is made in one piece.  Both Bulkheads are made from 0.25in thick; tan medium-density H100 PVC Divinycell Foam.  Wicks part No. F500-055.

I found that the M drawings M5 – M6 for the Landing gear bulkheads were once again difficult to interpret as the left half of the drawing (normally the detailed section) showing the cutting lines and the 0.25” holes in the hardpoints, different to the right hand half of the drawing.  I used the measurements from the right hand half of the drawing as correct for cutting and as recommended in the FAQ, I will drill the 0.25” holes in the FWD bulkheads 1.2” from the top.  For ease and convenience I only cut the 45º taper shown on the drawing for one of the FWD bulkheads after all glassing was completed and cured on both sides.

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As recommended by most builders I increased the plans recommend 22 layers of BID for the hard points to 24 layers.  This worked perfectly for me and all 4 pieces measured exactly 0.25in thick.  Most of the cloth required for making the hardpoints was cut out of the off-cuts saved from Step1 to 3.  Cutting the 96 pieces of cloth before starting was a real pain in the butt.

I started by making a paper template of the size of the hardpoint I required and taped it to the workbench.  I then covered the template with cling wrap and started the lay-up by first laying down the Peel ply, 24 layers of BID and then finished with another layer of Peel ply.  The completed lay-up was then covered with more cling wrap and weighted down using a flat plank and lots of lead.  I used 0.25” thick foam off-cuts as spacers to ensure that I didn’t flatten the lay-up by more than 0.25”.  I used the Fein to cut out the hard points to the required shape to fit into the pre-cut foam Bulkheads.

NB: - Remember to remove the Peel Ply on the hardpoints before starting with the remaining overall layups on the Bulkheads.  I forgot to do this on one hardpoint, fortunately I released what I had done in time, whilst still applying the last layer of BID and was able to remove the Peel Ply before continuing with the final layup.

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Aft Bulkhead Final Weight = 1kg                      Fwd Bulkheads Final Weight = 0.7kg and 0.5Kg

Step 5 – Firewall
The permanent Firewall is made in 4 pieces from 0.25” thick Birch Plywood.  Wicks part No. 6mmx2x4B.  I received 2 pieces of Birch Plywood in my order from Wicks 1 x 24”x48” and 1 x 24”x24”.  The following photo shows how I laid out the 4 sections of the Firewall before cutting.  The temporary Firewall is made in one piece, from any cheap plywood that you might have lying around.

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Due to Christmas holidays I didn’t get this section finished before the end of the year as hoped.  The cutting out of the Firewall templates and the temporary Firewall was completed back in November 2005, so it shouldn’t take too long for me to complete the 4 sections, which make up the Permanent Firewall.  It has been reported by most builders that the plans recommended method for securing the 4 Blinds screws for the control wire pulleys is not good enough and they start turning after a while.  I filed the screw heads into a + sign and lightly sanded the head and shaft before floxing them into place, which hopefully should stop them from turning.  Only time will tell whether I have made the right decision in doing it this way?

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Floxing in the Blind Screws. Firewall Final Weights - Top = 1.5kg, Middle = 145g ea, Bottom 1.25Kg

To stop getting epoxy and flox on the threads of the screws I inserted the screws into the holes first and then squeezed flox into the countersink recesses using a sandwich bag with the corner removed, similar to icing a cake.  I have not drilled or cut any holes in the Firewall at this stage and have left the holes for the longerons until Chapter 6, just in case I’m a little off with some of my measurements.

Well that completes Chapter 4 and I must admit it took longer than I thought it would - a total of 71 hours.  I learned a hell of a lot and was maybe a little over cautious to the point of being anal with ensuring that everything measured and looked exactly right before moving onto the next piece.  Cutting out all the Bulkheads was a little fiddly and things got much easier after I purchased the Fein Multi Master, can’t imagine doing this project without it.  I’m now looking forward to moving onto bigger things and putting it all together.