Overview The original plans method of constructing the Center Section Spar does not lend itself well to vacuum bagging techniques. While I was building the jig, I could not help but think that I was extremely close to actually building a mould. After working out some of the dimensions in AutoCAD, I came up with a method to construct a jig/mould that would allow me to build the CS Spar from the outside in. As you will see, vacuum bagging techniques can be applied through 90% of the fabrication.

	I started on Chapter 14 (Center Section Spar) to fill time while I'm waiting for Chapter 10 tasks to cure. The table is big enough to enable me to do this so I'm going to step it up a notch.
	Building the Jig I spent the weekend building the jig for the spar. Pretty tedious stuff when you start talking about hundredths of an inch. I measured and set up a strip of MDF to act as a nailer for the deck portion of the jig. This assures that the deck will be at 6.12 inches on the main portion and accurately slopes to 6.05 inches where it tapers to the ends.
	In place of 'sticks' to support the bottom foam for the spar, I constructed another side of 3/4 MDF. I used the triangular scraps as nailers on the sloping ends (to secure the deck) to insure accuracy. A straight piece ripped from more scrap facilitated nailers for the flat runs.
	Because this is reversed construction, there are two areas I need to address at this time: The bevel/twist for the outboard 32 inches on what will end up being the top. The bevel (.5" x 1.0") on what will become the rear top and bottom corners.
	The bevel is formed using plaster. I tacked a scrap of .75 MDF on the ends set to the proper rise. I calculated this to be .32 inches based on the templates. I next used a straight edge to screed the plaster to the desired profile and let it setup. After a couple of sand and fill steps, I had a good shape to work with.
	The 'leading' edge is created by ripping a piece of Last-a-foam to the .5" x 1.0" dimensions (27 degrees) and secured it to the MDF with brads and glue.
	The inside surface was covered by vacuum bag film (to act as a release) follow by peel ply.

	My project will use the Infinity Retractable Landing Gear (mains.) This requires some additional steps. A crush plate of 16 plies of BID will be fabricated. Towards the end of the spar construction an internal layup of 13 plies of UND will be applied to the internal (outboard) top, forward ond bottom surfaces as an additional reinforcement. This actually ties into the shear web layup to form a solid box beam which will support the landing gear assembly.
	Its a lot of cutting but the use of masking tape to control the edges did help control the fabric. I marked out the pieces a bit larger than I needed and made both sides in this single layup. After the cure, it will be cut into two pieces that measure 5.4 x 19 inches. I vacuum bag everything I can to get the best epoxy to glass ratio and eliminate any bubbles. Thick layups like this are prone to generate bubbles between layers as the temperature increases in the curing part. While vacuum bagging is not a substitutefor good technique, it is a valuable tool and is well worth the investment.
	I have all of the layup complete and in the bag. I started with a 15 x 24 scrap of MDF and put a piece of poly over it. I followed that with a piece of peel ply of roughly the same dimensins. I used a sharpie to mark out my pattern on the peel ply matching the dimensions to the 11.5 x 20 measurement I used on the fabric. Add 16 plies of BID and I'm ready to close it up. Peel ply, perf ply, bleeder/breather layer and a layer of poly. I put another piece of MDF on top and ran a small piece of duct tape in a couple of areas to secure the works and popped the whole thing into the vacuum bag. JD used a heavy metal plate for this but I'll let the atmospheric pressure do the work for me.
	A couple of days have passed and I took the package apart and it looks great. Very consistant in appearance and thickness. Next it's out to the radial arm saw and cut this to an oversized dimensions of 6 x 22. I  peeled back enough of the peel ply so I could get hold of it before I cut them to size.When I put the interior skin (BID) on the forward face material of the spar (top as it sits in the jig) I will cut out the area that the crush plates fit into and laminate it to the glass that will become the interior face of the spar. I talked with JD about this as it does deviate slightly from the 'New Construction' segment in the plans but the number of plies and position of the plies will work out to be the same so I got his okay.
	The plans method has you lay a piece of peel ply over the outboard 19 inches of the spar and then glass over that. After assembly, the foam is cut down to the peel ply and then your additional 10 ply wrap and crushplate are installed. While you are working with this area, you only have the single ply of BID supporting the area. This would require installing some type of support on the interior to avoid any distortion of the area while you work with it. Instead of this, I integrated the crush plate into the .25 inch foam. I traced the interior profile onto the crush plate and fitted a half inch border of foam on the long sides. There is more on this later on.
	I had to wait for my Aluminum  stock to arrive but it's here and I'm ready to go. I cut the aluminum parts on the band saw to the dimensions called out in the plans. Previously I had cut out the spar trough templates but because of the change in my approach to building this part, I will need them only as a reference. Bandsaw: Good investment!

	Step 1: Outside Layup The center section spar mold is positioned with the forward face up and the top edge nearest to you. Make a 4 ply UND layup with the fiber orientation at 45 degrees, alternating the direction with each layer. Now flox in place the two shoulder harness hard points. Cover the entire layup in peel-ply, perf-ply, breather/bleeder and vacuum bag. This will end up being the exterior face of the spar. TIP: I added a 3/4 lip on the top of the mold to enable the glass to continue outside the finished product mold to help hold everything in alignment. You may need to take some additional measures to prevent the material from pulling away and falling back into the mold while you wrestle with the peel ply and other layers, in preparation for bagging.
	Step 2: Spar Caps I tipped the mold onto the top (facing you) and install the temporary spar dam with brads. I wrapped the pine pieces that I used for the dam, with celophane packing tape to prevent the layups from bonding to the dam. Beginning with the longest tape, begin laying up the spar cap. Be generous with the heat gun to assist in wetting out the tapes as there are no foam parts to damage. Once this is complete, I set it aside to cure. I vacuum bagged this layup and packed it with electric blankets to get the best part possible. I had to draw down the vacuum as I manipulated the bag to get a good fit into the inside corners. At one point I had to disconnect the vacuum, adjust some more and then reconnect. It is very important to get a good fit here. The bottom spar cap is done in the same manner. NOTE: Even though I'm doing these layups in the summer months, I always use the electric blankets for additional heat. The extra heat thins the epoxy and allows more of the excess to flow into the bleeder/breather layer. It also provides a preferable environment for a good cure.
	Step 3: Shear Web The shear web layup consists of a 4 ply UND layup with the fiber orientation at 45 degrees, alternating the direction with each layer. This layup will span the three sides made up of the two spar caps and the aft face between. The spar cap dams need to be removed at this time to ensure complete contact throughout the layup. Before applying the shear web, run a bead of flox along the two inside corners to provide a smooth transition curve for the fabric to follow. I trimmed the shear web to the edges of the spar cap and then added the peel ply (etc.) and put it in the vacuum bag to cure. The mold was again packed with the electric blanket to keep the part toasty and facilitate as much excess epoxy as possible to transition into the bleeder/ breather layer. (There are scraps of trimmed glass in the picture.)
	Step 4: Mid Level Hard Points Trim the CS1 foam so that it will fit into the cavity between the top and bottom sides. Hardshell both sides and allow to cure. Sand the CS1 foam and fit into place. Mark several points to assure proper alignment later. Remove the CS1 and mark the placement of the hardpoints. Remove the foam in these areas. Apply micro to the inside face of CS1 and press into place being careful to properly align to your marks and avoid pressing so hard that micro leaks into the hardpoint areas. Apply flox to the face of the aluminum hardpoints and run a bead around the edges of the foam where it will seat and press into place. Secure the foam on place with duct tape to preserve the alignment and vacuum bag the part to eliminate any air gaps and to assist in pressing the part into place. A piece of MDF cut to fit the area can be added to assist in applying an even pressure throughout the area until the micro and flox cure. Once the micro has cured fit the center portion of CS1 and micro into place using the same technique.
	Step 5: Build spar trough (Foam) Cut and fit the one inch DIVINYCELL foam to 2.75 inches and bond to the inside of the shear web. For the infinity landing gear, the outboard 20 inches needs to be left bare to expose the interior surface of the shear web for a later step. Because of this the edge should be beveled to transition to the surface of the shear web. Bond the foam to the interior surface with micro. I vacuum bagged this step to eliminate any voids as well as clamping it to insure a good bond. After that is cured, cut several additional strips 2.75 inches in width. I cut off a the portion at the inside top to form a 27 degree bevel (.5 inches x 1.0 inches) to match the inside bevel of the glass. Again these are bonded using the same method as before. After this has cured, you will have a mismatch of the inside surface resulting from the thickness of the spar cap itself. With the inside surface as a guide, shave the extra foam flush using the flush cut blade of the Multimaster. For the last step, I added a waste piece .5 x .75 to the top of the foam to bring it flush with the top of the mold. I also rounded the edge to assist in holding the layup in place. The waste are will be cut off in a later step.
	Step 6: Interior Layup Apply plies of BID in a 45 degree orientation across the three faces of the interior. Now, apply the local reinforcements (layup 3) at the inboard wing attach hard point areas (Fig. 5, see also section B-B and H-H). and place in the vacuum bag to cure. Once cured, remove the top waste portion (.75 inch strip) of the mold. Cut the part flush with the new edge you are presented with. (see picture) Cut two oversized bulkheads and apply 2 plies of BID on each side and allow to cure. While that was curing, I taped in place (in the bottom aft corner) some pieces of .5 inch PVC conduit. I covered this with peel ply and poly and applied a 2 ply tape of BID, peel ply and poly, then placed it in the vacuum bag to force the layup to conform to the profile of the corner and conduit.
	After the cure, I trimmed these to size and cut them to form a chase on either side of the bulkheads. Affix the two bulkheads in place with flox and 2 inch BID Tapes where contact is made with the spar. The electrical chase is attached once the bulkhead tapes have cured with two inch BID tapes.

	Step 7: Forward Face In Preparation for this step I removed the .75 inch waste trim and (using a Multimaster flush cut blade) I trimmed the entire top (forward face) of the part flush with the remaining surface of the jig. )
	Lay the three pieces of ¼ in. PVC foam that make up part CS4 (center section spar forward face) down on your table with the inside face up. Take two pieces and cut to fit the profile that make up the forward outside sections leaving it short by 21 inches. The Last 21 inches is made up of the crush plate with a .5 inch border of .25 inch foam. This matches the exposed foam area that makes up the top and bottom of the spar. When viewed from the inside, you should only see the crush plate excluding the cutback areas on the outboard 3.5 inches (to access the outboard wing attach bolts.)
	The best way to do this is to butt the crush plate against the straight (this will end up being the top side of the part) and trace the inside profile onto the crush plate. After you do that, mark it as a straight line and cut it to that dimension. Don't worry about the slight dip in the outboard 3.5 inches. Micro a .5 inch boarder of .25 inch foam on both of the long sides and and attach to the remaining piece to make up the outboard forward face. ) The method of integrating the crush plate as part of the foam helps to maintain the rigidity of the part. Lay up 1 ply of BID (each side) at 45 degrees orientation (layup 1). After applying the BID, I added a piece of peel ply and flipped if on it's face onto a piece of 3/4 mdf (protected by vacuum bag film) and slipped the entire piece into a vacuum bag to cure. The forward/outside face is down so the inside ply will form to the slight recess formed by the thinner crush plate compared to the .25 inch foam) The center section forward face is pretty straight forward. Lay up 1 ply of BID (each side) at 45 degrees orientation. Peel ply and allow to cure. Knife trim at the appropriate time. ) After cure, remove the peel ply and bond the three forward face pieces in place with wet micro to complete the box. Butt together. It is not required to lap glass across this internal joint
	Step 9. Exterior Hardpoint and Reinforcement With a file, radius the top edge of LWA2 (section B-B) and the top and bottom edges of LWA3 (section C-C) to a 1/8 in. radius. Clean and sand them and install them with flox as shown in the section views. After cure, make flox comers, and lay up (layup #7) 3 plies UND 3 in. wide centered over LWA2 and LWA3 as shown (Fig. 16), lapping onto the top and bottom at the outboard hard point, and onto the top at the inboard hard point. Now add 1 ply BID 5 in. wide at 45 degree orientation, centered over the UND strips, only on the aft face. Do not lap this BID layer onto the top or bottom of the spar box. Peel ply edges for a good transition and allow to cure.
	Step 10: Installing the crush plate. You’ll need some poly sleeves or some kind of protection for your arms because you will need to reach inside the end of the spar to facilitate this layup. Secure the spar in a position where the forward face will be facing down. On another table, layup 11 plies of UND at a 30 degree orientation over a piece of poly. Once these are completed, prepare the forward, top and bottom inside faces to accept these layers by priming the interior with epoxy. Run a bead of flox in both inside corners and form a curve transition area in the corner. Lay another layer of poly over the top of the 11 plies, squeegee well and trim to size. Roll up the plies in the direction of the fiber orientation, while removing the bottom poly. Starting in the Aft-upper corner, begin applying the 11 plies to the interior top, forward face and bottom of the spar, Once this is worked into place the poly can be carefully removed. The crush plate is now primed with epoxy and inserted into place on the interior facing edge. This layup can be vacuum bagged by inserting a bag slightly larger than the part, securing to exterior of the spar and applying a vacuum. The bag should be sealed to the inside of the spar to avoid pulling a vacuum against the bulkhead. I highly probable that the bulkhead would fracture under such forces.
	Step 11: End Caps Using your dremel, make a small flox corner all around the two outboard bulkheads, CS5 and CS8, and then lay up 1 ply of BID at 45 degree fiber orientation on both bulkheads. See section E-E. Cut a 2-1/4 in. diameter hole through the bottom (not the top) of the spar box at B.L.65.5 (2 in. from the end) and forward of the spar cap as shown in section C-C. Do not cut through the spar cap! This will be your access to the outboard wing attach bolts. After cutting the hole, remove a small amount of foam around the edges of the hole and trowel in dry micro to protect the bare foam. This is layup #9, and completes construction of the center section box spar.