Cozy Mark IV Chapter 4, Fuselage Bulkheads

Exciting stuff... in chapter 4 we now actually start building airpane parts!

These first parts are mostly big flat pieces of foam covered with fiberglass on both sides. The plans are carefully written to start you off on the easiest sections, namely big flat pieces like the seats and other bulkheads.

This is an aircraft built entirely from plans. That's right... just a big book of instructions, diagrams, and a stack of large drawings. It is common for builders to make copies of the large drawings by tracing them onto large sheets of paper for transfer onto the foam where it will be cut.

In the photo below, you can see that I have taped the some of the large drawings that come with the plans onto a large window and then covered them with paper for tracing with a 0.5mm pencil. These particular drawings depict the landing gear bulkheads on the left, and two of the bulkheads in the forward portion of the aircraft on the right. The idea here is to duplicate the drawings so that I can transfer them onto foam and fiberglass without destroying the original drawings.

Cozy Mark IV drawings, Tracing the bulkhead drawings in the window


Early on in the building process I learned the lesson to carefully read and understand the instructions given in the plans. Would you believe that after all of this work, I ended up manufacturing a forward landing gear bulkhead in one great big piece instead of three pieces. (In other words... I did not read the plans properly. If you are building this aircraft, read the plans five times before you start building, and then check websites of other builders to see their pictures and comments.)

The most difficult, time consuming, and expensive (glass+epoxy without any foam) part of this particular bulkhead is the dark area in the lower left corner of the drawing that you see taped to the window (actual piece ready to install shown also). This hardpoint area made from 25 plies+ layer of glass was easily salvagable. It is strange to start off with cloth made of glass, add epoxy, and stack up 25 layers to end up with something that actually is rigid like glass and sounds like glass when you hit it with something.

Cozy Mark IV, Landing Gear Hardpoints

The photo below shows the LG bulkhead after I cut off the faulty portion. Even the part that I cut off wasn't right. I didn't properly interpret the plans, and ended up with a mistake.

This photo (below) is how NOT to do the landing gear bulkhead. Luckly I only had to do the top portion later. I can still use the scraps for other parts of the airplane.
Cozy Mark IV landing gear

I started doing vacuum bagging early on in the project, adopting a technique presented by the Cozy Girrrls on their website (referenced elsewhere in this site). This particular layup is the correction to my landing bear bulkhead error. This is the upper portion of the forward landing gear bulkhead. I should have done it this way in the first place. I guess the old-sock is a bit of an inelegant solution for the absorbant material at the end of the vacuum hose, but it works just fine and goes right into the trash afterwards. Can you spot the old sock?
Cozy Mark IV forward landing gear bulkhead, curing under LoVac vacuum bagging

This is the (upside down) photo of the very first part constructed that will become part of the aircraft. This is the backrest for the front seats. It is constructed of one large piece of foam with multiple layers of fiberglass. (Mine has an extra layer of fiberglass on one side. I guess my seat will be stronger than any Cozy out there, but I doubt anyone will ever be impressed.) The top and bottom of the seatback is carved to perfectly match the contour of the fuselage sides. The holes and notches in the sides are for control systems and rigging that must attach to the ailerons and rudders. The seating position in the Cozy Mark IV is quite reclined. This seatback will be installed with a recline angle of about 45 degrees for pilot comfort. Once installed, it will not be adjustable like your car seat... it doesn't slide forward and back, and it doesn't recline up and down. Think of it more like a park bench going 150-200 MPH. Later, in Chapter 5, the big curved fuselage sides will be constructed and in Chapter 6, the sides will be put together with the bulkheads to form something that looks like an odd rowboat. This seatback is structurally important to the airframe just like any other bulkhead.
Cozy Mark IV seatback

The firewall is made from some very fine quality Finnish birch plywood. (Woodworkers would be envious of the quality of this wood although I have heard of other builders getting warped pieces. Note to new builders getting warped pieces... you will cut this down into four separate firewall pieces.) After cut into shape (4 pieces), aluminum hardpoints are embedded into the plywood along with some screws for mounting pulleys and brackets that will be part of the rudder and aileron system. These aluminum hardpoints provide a drillable (or for some tappable), and high-compression-strength area to accept the load. weight, and vibration of the engine and mount as well as the compression exerted by the bolts.

Once all of the metal pieces are properly embedded into the firewall plywood, the firewall is then given a good coat of epoxy and covered with fiberglass all over. It was only after completion of my firewall that I read suggestions from other builders that it is a good idea to acid wash and alodine treat all aluminum parts on the airplane. Some say that it is not necessary. For the few cents it would cost, I wish I alodine treated my aluminum hardpoint inserts in my firewall. Note to new builders: treat your aluminum parts before embedding in layers of fiberglass.

The hardpoints that I have added to the firewall are about twice the size of the plans. I can accept this slight weight penalty in exchange for the peace of mind that it will give me when installing my engine mount. More treatements will be done to this area prior to engine installation, including an additional aluminum sheet and a layer of fire and heat resistant materials. At the time of this writing, I have not decided on the engine type for my Cozy Mark IV.
Cozy Mark IV, Instrument Panel, pre-glassInstrument Panel Hardpoints, Cozy Mark IV

This is my instrument panel under construction. The instrument panel is made of 1/4 inch dense foam and covered by glass. The panel is reinforced by ribs made of the same material that double as areas to run wires, pitot-static hoses, vacuum lines, etc. It took a lot of patience to cut this dense and brittle foam into just the right shape. Holes on the sides are for control cables and/or torque tubes.  

The two lower center holes are for the heat vent, and the two large holes on either side of center are where the pilot and copilot put their legs. The first photo shows the instrument panel before any glass or epoxy, and the second shows some of the glass treatments on the stiffener ribs going in.

As the months and years go by, tthere will be many more photos of the Cozy Mark IV instrument panel bulkhead.
instrument panel foam, cut and ready for glassing glassing the instrument panel

My good friend Dave P. doing an inspection on my landing gear bulkheads and my Lo-Vac (vacuum bagging) technique. Dave is an aerospace quality engineer, so I guess that finger poking into my layup is ok. After all, he is a degreed professional! I am glad I didn't get a bill for this inspection.

Dave is a future canard-builder who is currently working on construction of the dream-workshop/hangar on a 5 acre parcel near the Aqua Dulce airport in California. Oh yeah... he is working on construction of a home at the same time.
Quality Inspector David Petrovich examining the LoVac technique

I learned early on that it pays to have all of the glass cloth pre-cut, labeled, and ready to go before a layup. I was glad that I took this advice because it made my chapter 4 work go very smoothly. Unfortunately, it wasn't until later that I learned that a beginner really should be working with slow epoxy hardener. The stack of glass cloth were prepared, pre-cut, marked, and organized before getting started on some of the Cozy Mark IV landing gear bulkheads where there are many layers of glass laminated onto the foam core.
Cozy Mark IV, Chatper 4 glass ready for layup

This is my F22 bulkhead after the layup has cured. A lot of glass needs to be cut away. The Fein tool makes quick and easy work of this task. The plans tell you to wait for the "knife-trim stage" when the layup has gotten a bit leathery and can be cut with a utility knife. The Fein tool works so much better. Besides, a utility knife is not a power tool... what fun is that?

Cozy Mark IV, F22 bulkhead construction

In this photo, you can see my F-22 bulkhead complete and ready for timming with the laminate trimmer. This is a Porter Cable Laminate Trimmer with a top-bearing flush cut bit. On top of the cured bulkhead that I made about 1/4 inch to 1/2 inch oversize, you will see a plywood template that is the exact size. The laminate trimmer makes nice work of cutting the bulkhead to perfect dimensions. The results look great.
Cozy Mark IV, F22 bulkhead ready for trim with a Porter Cable laminate trimmer

It is worth noting that the trick to effective use of luan plywood templates and a laminate trimmer is to avoid making the tool do too much work. The idea is to trim the edge rather than cut the edge. This is what happens when you try to cut a recently cured composite sandwich panel a little deeper than the laminate trimmer can handle.

As you look at the picture, imagine smoke, and the worst smell you can possibly imagine. Dont try this at home... it really produces an unforgettable odor.

Yes, that is smoke, and it smoked for a long time before stopping. The heat created by cutting, and well insulated by the fiberglass and foam on all sides of the cutting bit caused the epoxy to break down and smolder. It is a smell you won't ever forget.

Believe it or not, the part was not damaged whatsoever. Only the portion going into the trash as scrap suffered from the little thermal overload experiment. (This area is part of the "ears" on bulkhead F22. This part of F22 gets cut off and thrown in the trash after it's usefulness as an alignment piece is done later on in construction.)
composite construction mishaps, Cozy Mark IV F22 Bulkhead smokes and burns during router trim.  Exotherm?

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