Chapter 4

Fuselage Bulkheads

Larry Wimble's "Cozy Mark IV" Site
Chapter 4 - Fuselage Bulkheads

Postdate: 2003-11-23

I started on my first actual plane part today: The front seatback bulkhead. It went reasonably well.

The seatback is 28.8" tall, requiring that you "glue" two pieces of foam together. I used the radial saw at my office with a metal cutting bit on it to cut and taper the foam pieces. I then used the "hinge" method of "gluing" the pieces together with 5-minute epoxy. Watch out for this stuff. I mixed a batch larger than what I needed, and you guessed it, exotherm city.... I then spent 20 minutes peeling off cured 5-minute epoxy so that I could try it all over again. This time I mixed it up on my scale and poured it on right out the 3oz dixie cup I mixed it in. This worked much better. Now off to epoxying....

The layup is two pieces of UND on opposite biases. I asked Susan to cut two pieces, 48" in length. They turned out too short, so we ended up piecing them together. The layup looks to have turned out OK, despite the error.

The only thing that annoys me is that there is some shadowing in the layup. It makes it look like there are areas which are resin-lean, but no amount of epoxy or stippling would make a difference. I then realized that these darker areas were where I had poured the micro on in the beginning. Perhaps I'll post a message to the group and ask anyone else if they get this.

Cutting 45 degree taper	ready to 5 min epoxy.	ready to glass.
Closeup of the taper.	Frontside yayup completed.

 

Entry #: 6
Postdate: 2003-12-09

Alas, there comes a time when one must finally give up on something. The seatback bulkhead is considered a failure piece, and I've decided to redo it over the objections of some of the Cozy group.

Why?

After the front-side layup cured, I noticed a bunch of small air bubbles in the layup. Not a big deal, these can be repaired. Then, when I went to trim the fiberglass flush to the foam, I noticed some "waves" in the fiberglass along the tapered edge where the fiberglass ends at the point. The glass had basically seperated from the foam in places and it was going to look terrible from the back seat.

At this point, I endevoured to repair the waves by using a heat gun. This probably would have worked with a little more experience, but I ended up making matters worse. In an attempt to repair this, I decided to cut off 1/4" of the taper, and round it off. This way, I could do the backside layup "all the way around" to the front side. This was coming along beautifully (and would have looked really cool) until the weather turned cold. Yes, it gets cold in Florida. Coincidently, I found myself in a position of having to shut off the heat in the shop while the backside layup was curing as I had to leave the house and I don't exactly trust the kerosene heater. As a result, my layup was not fully cured in the morning. This brings question to the curing ability of the epoxy and the overall long-term strength of the piece.

Given all of the above evidence, I am scrapping the piece and starting over.

This is by no means, a failure in all respects. I have learned a great deal and will probably produce a new seatback in half the time I spent on the first one, and it will be of far superior quality.

 

Entry #: 7
Postdate: 2003-12-28

After regrouping and changing a few things, I have remade the seatback. I did a few things different this time.

First, I prepared for low temperatures by building an "oven" out of some insul-board that I bought from Home Depot. It fits "around" my layup table I also bought a small ceramic type heater to place at the end of the oven to keep the temperatures up inside.

Second, I prepared for the layup by purchasing the foam from Aircraft Spruce this time. ACS stocks a piece big enough for the seatback without having to combine two pieces.

Then, the work begins. I tapered the edge as I did before, and glassed in the front side. Upon cure, I find no bubbles or waves. It looks good. A keen-eyed person who looks at the pictures below will notice that it looks a little bigger than your average seatback. It is. I have decided to make the fuselage 3" bigger (more on this later).

After the front side cured, I trimmed it, and prepared for the backside layup of a single layer of BID. After having made all my flox corners, I layed it up. Everything came out well.

I think the biggest lesson I have learned here is: Don't rush! Use the slow hardner liberally (speaking in terms of MGS epoxy). There's nothing wrong with a four hour pot life.

Laying up the peel ply.	The "oven" keeps the layup warm.	Preparing the back side for layup.
A friend stoped by and got put to work.	Layup completed but not trimmed.	The finished product.

 

 

Entry #: 8
Postdate: 2004-01-26

The two forward bulkheads are now complete. I have to say that the foam used in this step is incredibly difficult to cut with a knife. I was actually tired after cutting it all out. I think I'm going to use a saber saw when I cut out the instrument panel.

Due to the size of the foam stock (12" x 48"), one must "glue" the pieces together with 5-minute epoxy to form the bulkhead.

Both sides went well. After doing the first layups (the aft faces of F22 and F28), I spent the better part of 6 hours with a dremyl tool trimming away the excess glass flush with the foam. There *must* be a better way. Once again, I made my way down to Home Depot and looked through their router bit selection. Aha! The same bit that's used for formica trimming can be used to cut the glass flush with the foam. Used with my router table, the trimming of the front side layups happened within about 45 minutes vs. 6 hours. The only drawback to this is that fiberglass shavings go EVERYWHERE! Wear an appropriate dust mask, long-sleeved shirt, a pair of goggles, and do it outside if you can.

 

Getting ready to 5 min epoxy the upper and lower pieces.	Ready to glass the aft faces and the F22 doubler.	Oh the messes we make.
The glass cuts for the forward faces	Aft face done.	F22 done (minus center column channel).
F28 done.

 

 

Entry #: 9
Postdate: 2004-04-19

Just got back from Sun N' Fun with some renewed vigor for the Cozy project. I met Mark Zeitlin, John Slade, and a few others. The Cozy BBQ was a great deal of fun.

Still doing a lot of traveling, but I managed a little time today to trim thr instrument panel. I'll hopefully be glassing the aft side upon my return from Washington on the 26th. Stay tuned............

 

Entry #: 10
Postdate: 2004-05-31

I took the day off today (yeah, I know it's a holiday, but when you're self employed, there's really no such thing) and glassed the other side of the instrument panel. Except for the stiffeners, the IP is done. I also took the opportunity to do the 22-ply layup for the main landing gear hardpoints. It took about 2.5 hours to do this layup. I also did some things a bit differently as I find cutting glass at 45 degrees irritating. I traced the 4 hardpoints onto a piece of 11x17 paper at 45 degrees, and then cut rectangles from my roll of BID at 90 degrees rather than 45. When I cut the hardpoints out of the cured layup, the fibers will be oriented at 45 degrees for installation into the bulkheads.

One thing I did do right before I started this layup was to put some pumps on my MGS containers. If you're using MGS epoxy and not using a pump, this should be required. See my Misc and Rants page.

Also, note my red face in the layup below? That's my alergy to the epoxy. It makes my face turn red, gives me a sunburn feeling, and my eyes dry out. Still haven't quite figured out if the problem is contact or inhalation, but at this time it's more of an annoyance than anything else.

Instrument panel both sides layed up.	Laying up the L/G hardpoints.	The blob finished but not trimed.
Another hardpoint layup pic.	IP and hardpoint blob ready to be trimed.

 

Entry #: 11
Postdate: 2004-08-05

I've now glassed one side of the forward landing gear bulkhead set. Unfortunately, I've run out of both peel ply and UNI, so I'm stuck at the moment. Supplies are enroute.

 

A friend stoped by and got put to work.	After epoxing the hardpoint in place on the fwd L/G bulkhead.	Preparing to epoxy the hardpoints in place on the aft L/G bulkhead.
Ready to glass the forward bulkhead pieces

 

 

Entry #: 12
Postdate: 2004-10-18

I took Saturday morning and straightenend up the shop since it became a storage locker while the hurricanes passed through Florida. With a newly cleaned up shop, there's only one thing to do....

I glassed and peel-plied the forward side of the aft landing gear bulkhead. The forecast temperature was going down to 53, so I fired up the kerosene heater at about midnight to keep it toasty in my shop while the layup cured.

Sunday, I trimmed that up, and proceeded to glass the forward sides of all three L/G bulkhead pieces. I have to say that UNI is very difficult stuff to work with. On the aft L/G bulkhead, you're supposed to add 8 plies of UNI to the ends of the bulkhead for strength. I was trying to make a nice neat "edge" and the stuff kept fraying all over the place. I finally just decided to do the best I could, and cover the nastiness with the last layer of UNI.... It seems to have turned out nice.

All that's left in Chapter 4 is the firewall, which I intend to do this week :-)

 

Stiple, stiple, stiple.	The aft LG bulkhead (fwd face)	All three bulkheads glassed and peel-plied.
Trimming up the bulkheads.

 

 

Entry #: 13
Postdate: 2004-10-22

A couple days ago, I took M-7 and M-8 to a blueprint shop and asked them to make a copy of each, and a mirrow of each. This way, I would have all four quadrants to lay on the plywood in order to cut the temporary firewall.

Unfortunately, the blueprint shop's copier seems to distort things, making it nearly impossible to line up. There was a 3/16" problem no matter what.

A friend suggested we take the DXF file on Marc Zeitlin's site down to the office and cut the quads out of adhesive material using the laser table at my office. A couple hours later, we had perfect quads that adhered straight to the board. It was late, and not wanting to annoy my neighbors with a running saw and vac, we decided to call it a day.

Last night, with a little assistance, I cut the temporary firewall out. It has turned out quite nice.

The birch needed for the permanent firewall is enroute. Should have it by the beginning of next week

Adhearing the quads to the plywood.	Ready to cut out.	I'm definately on top of my work.
All it needs is some of the holes cut.