Fuselage Bulkhead Construction

by Frank Justice

There are detailed instructions in the construction manual for some of the bulkheads. These instructions will tell you more or less the same thing but in different words, so it will be helpful to read both. They will also tell you to do more than just form the basic bulkheads in some cases; the extra tasks called for can be performed more easily on the bench than in the fuselage and there is little likelihood of doing something that will be out of alignment. You do not have to prime or rivet any bulkhead pieces before all are formed; you can just as well make all of them, then prime and rivet them in one big batch. There are detailed riveting instructions here for some of the bulkheads included with the preparation instructions, so if you hold this until the end make sure you mark them to go back to later.

Firewall Instructions

Engine Mount Note:
The engine mount comes with the finishing kit, but the holes to mount it are made as part of the fuselage kit construction. It is worthwhile to obtain an engine mount early from Vans so you can get these holes drilled in just the right location since there have been reports of up to 1/8 error in mount hole locations.

Prop Governor/Oil Filter Clearance Cutout
If you plan to use a constant speed prop you will need to make a cutout in the firewall and cover it with a box. This is necessary to allow room for the prop governor which is mounted on the rear of the engine. The box also allows easy access to change the engine-mounted oil filter even if you dont have the constant speed prop. It is much easier to mount this box while building the firewall rather than waiting until later.

Recent Kit Improvement/ Firewall
  1. Vans has recently changed the amount of work done for you on the firewall in that all of the little gussets and angles are precut and enough holes are drilled in the firewall and these pieces to allow you to cleco everything together and start drilling. This change will save you on the order of 20 hours of work and insure that everything lines up properly. The firewall has an opening already cut in it for the Prop Governor/Oil Filter Clearance Box. If you do not want to make this provision you must use a piece of stainless steel to block the hole. If your kit has this improvement, skip down to the Dual Brakes Mod section (if it applies to you) or to the Finishing and Riveting the Firewall section just below that. If you received your kit before this change was made, continue on from here.
  2. The easiest way to make the prop governor/oil filter clearance box to buy the box from Van's. Before the finished box was available Vans sold a precut piece of metal that was easily bent up and riveted. As supplied, this kit made a box 8 wide which would not fit properly between two of the firewall stiffeners which are located 8 apart. It would be easier to make the stiffeners a little farther apart than to make the box narrower, but the battery box (drawing 48) would then not fit well without shimming. Construction of the box from the kit is covered near the end of the firewall section.The pre-made box was also too wide for a time but this has been corrected.
  3. The construction manual calls the firewall the "most difficult" bulkhead to build. It certainly takes the most work, but it is not difficult. You might even call it fun if you enjoy working jigsaw puzzles with no picture on them. A number of dimensions are given in these instructions; don't just use them blindly, check the drawings to see where they came from and to insure that Van's has not changed any recently. You may also find that the plan dimensions for the main firewall piece (F-601A) do not match the piece you have exactly. This should not cause any problem.
  4. The only really critical part of the firewall construction is the location of the engine mount bolt holes; these must line up with the engine mount that you will be getting with your finishing kit. The next most important thing is that the engine mount support brackets WD-602 and WD-603 are placed so that longerons attached to them will line up with the side skin surface, and also that the engine mount bolt heads will clear the arms of the support brackets. Stiffener placement in itself is not critical; however, if not properly placed, it will be necessary to do some unscheduled trimming of the engine mount support brackets.
  5. The firewall is somewhat hard to handle while building because the main part is not rigid and the flanges are on the bottom side for most operations. You will find it is worth the trouble to make a wooden addition to your work surface that is 3/4 thick and shaped to fit just inside the flanges of the main firewall piece.
  6. Hang up drawing 25 and open the construction manual to the photos on page P (8-1) to aid in identifying parts.
  7. Gather all the parts you will need, preferably while you do your inventory. The main part of the firewall, F-601A, is stainless steel with some flanges. F-601B is aluminum and looks like a very heavy empenage rib (you split it to make the two sides). Paper bag 671 has the small gussets and spacers F-601C thru H. Plastic bag F-654 P contains F-695. The piece of angle 2" x 2 1/2" x .187" is what you make F-601J out of. If you are doing the trigear version, find F-6122, which is a piece of 3/4" x 1" angle, bent up instead of extruded, 7" long and cut diagonally on both ends. The WD-602 and 603 engine mount supports are small welded steel assemblies. You will also need 3/4" x3/4" x .125 (1/8)" and .062 (1/16)" angle stock. Put the F-672 forward bottom skin (with the turned-up edges) where you can get at it easily later for a measurement.

Make the right and left F-601J gussets out of the heavy 2 x 2 1/2" angle.
  1. Locate and mark the four engine mount bolt holes on the flange side of the F-601A firewall. Use the section of drawing 25 that shows one half of the basic F-601A. The bolt hole locations are indicated by the small crosses. Note that the distance between the top and bottom pairs of holes is not quite the same. Two holes are already made but they may or may not be in the correct positions. Verify their distance apart and their distance from the bottom of the F-601A (it may not be exact). The important dimensions are the spacing between the holes since they must match the engine mount which you do not have now. Locate and mark the bottom holes using the top holes for reference points. Drill these holes #40 or 3/32".
  2. Mark the outer edges of the outer rectangle of stiffeners on the flat side of the firewall (F-601A). It is 39" by 21 7/8". It is important that this rectangle is centered on the bolt holes especially side-to-side at the bottom.
  3. Mark the outer edge of the two inner rectangles (that is, the two lines shown 8" apart on the plans). As previously stated, you may have a pre made prop governor/oil filter clearance box that is a little too wide. Measure the width of your box and mark two points on the firewall about 3/16 farther apart than the width of your box at its lower edge (the end that is more boxy and less tapered) corresponding to where the lower edge of the box will sit. This point is approximately 10 up from the bottom of the firewall. Mark another pair of points 8 apart at the bottom of the firewall. Draw your inner rectangle edges lines using these points; this will make the stiffeners here slant slightly if your box was too wide. The stiffeners need to be exactly 8 apart at the bottom of the firewall so the battery box will fit and to allow the two heavy engine mount support gussets there to be in the right place, but they need to be far enough apart to allow you to get the cutout box in and out through a hole between the stiffeners.
  4. Do the following to indicate where you don't want to drill rivet holes in the stiffeners and as an aid in trimming flanges: Lay an F-601D gusset where it will end up on the upper-inside corner of the inner rectangle and mark its outline. Mark the outline of the F-601J pieces on the lower inside corner of the inner rectangles. Mark the outlines of the WD-602 and -603 engine mount support brackets (location doesn't need to be precise, it's just to guide making rivet holes and trimming angles).
  5. Cut the angles for the outer rectangle. The top is 36 3/4" long, 3/4 x 3/4 x .125 (1/8)" angle. The bottom is the same material, but 38 3/4" long. The sides are different material, 21" long, 3/4 x 3/4 x .062 (1/16)" angle.
  6. Locate these pieces on the firewall with flanges toward outside and drill them to it #30 with 2" spacing. Do not drill any rivet holes that would be underneath the WD-602/WD-603 engine mount support weldments or gussets whose outlines you marked.
  7. Hold the engine mount supports in their proper locations and mark the upright parts of the side stiffener angles for trimming to clear them (top and bottom stiffeners don't need any). Remove the stiffeners and trim.
  8. Cut the F-601B piece in half to make the two firewall side pieces. Clamp these on the firewall on the flat side but with their flanges pointing the same way as the firewall flanges. At the top end the sides should form a smooth curve with the flange on the firewall. At the bottom end they should be located so that at a point 3 1/4" up from the bottom of the firewall the outer edges are 3/16" out from the side stiffener. They may not line up with the firewall edges. Verify that the bottom skin F-672 fits properly at this point; the side pieces may be moved outward 1/8" or inward by 1/16" if necessary since it is difficult to reshape the bottom skin. Drill the side pieces through the holes in the firewall.
  9. Reattach the side angles over the side pieces to the firewall. Attach the bottom angle to the firewall. Trim the angles where they hang over the edge of the firewall.
  10. Cut two pieces of 3/4 x 3/4 x .062 (1/16)" angle for the inner rectangle sides and drill them to the firewall #40 with 1 1/4" spacing, avoiding the gusset locations. Flanges toward each other.
  11. Place an F-601C gusset inside each upper-outer corner of the main rectangle. Cut two pieces of 3/4 x 3/4 x .062 (1/16)" angle about 22 5/8" long for the upper-outer to lower-inner corner diagonals, and then trim the ends to fit the firewall. Also trim the flange off a little more than where the outline of the gusset F-601J hits it at the lower corner so the engine mount support will not hit it. Drill to the firewall #40 with only one hole at each end for now. Mark the outline of these stiffeners on the firewall . Remove these stiffeners.
  12. Lay a piece of angle on the other diagonal (upper inside to lower outside of inner rectangle) and mark the edge where the flange will be; note that it is different for the top and bottom half of this stiffener. Lay the F601F gusset in the lower outside corner (next to, not on, the stiffeners) and mark the notch you will cut in it (size and shape not critical), Cut out this notch.
Note: The half-diagonal piece that goes from the crossing to the lower outside corner must be riveted to the full diagonal that goes from lower inside to upper-outside. The drawing shows this being done with a bent piece of aluminum strip used as a splice plate. You can also cut the lower outside diagonal piece an extra 3/4 inches longer, cut off one flange even with the other diagonal, and bend the upright part of the flange around to lay on the other diagonal. This is described below; either way works.
  1. Cut a piece of 3/4 x 3/4 x .062 (1/16)" angle about 10 1/2 inches long for each lower diagonal. Note that they are a little longer than the space between the notch in the F-601F gusset and the other diagonal; this is so you can bend down some of its flange and rivet it to the other diagonal. Trim this stiffener to length and bend the flange to mate with the other diagonal. Also trim off the flange at the other end to just outside the area of the notch in F-601J so the engine mount support will not hit it.. Drill this stiffener to the firewall #40, 1 1/4" spacing; none of the holes should be inside the area of the notch in the F-601F gusset. Drill the bent over flange to the other diagonal #30.
  2. Cut a piece of the angle about 11 1/2" long and trim it to fit between the long diagonal and the upper inside corner. Drill it to the firewall #40, 1 1/4" spacing, with the hole at the lower end about 2" from its end. Cut another piece of angle about 2" long and trim it to fit snugly over the diagonal and the longer diagonal. Drill this piece to both diagonals and the firewall #40, then you can take it off and drill its flange to the flange of the short diagonal.
  3. With all the stiffeners clecoed on, place the F-601E gusset on the thin stiffeners at the top inside corners. Place the F-601D gusset on top of that and the top stiffener as well. Drill these to the firewall #30.
  4. On the lower-inside corner put the F-601H on the firewall, then the F 601G on that and the thin stiffeners, then the F-601J on top of these and the bottom stiffener. No, it won't look exactly like the picture. Drill all these to the firewall #30.
  5. Place the notched F-601F on the firewall and the plain one on top of that in the lower outside corner. The top one should be lined up with the bottom one as follows: the diagonal edges (toward the inside of the rectangle) are lined up, and the edge toward the outside goes against the side angle; any gap should be along its bottom edge.
  6. Place the WD-603 engine mount support on top of this, lined up so that the outer edge of a piece of .0125 (1/8)" angle placed upright on the support corner will line up with the firewall flange. The longerons (fore-aft structural angles) will go here later and you want them placed so that the skin lies smooth over them and the firewall flange. Also, drawing #31 detail E (lower right corner) as well as a recent revision to drawing #25 show the placement of gusset F-684 (found in bag F-654 but not installed at this time) on the outside of the stiffener and inside the WD-603 arm; modify the placement of the WD-603 as necessary to allow this. You will also need to round the corner of the engine mount support in the weld area to match the radius of the inside of the longeron angle so it will lay flat against the support arms. Drill all these to the firewall #30, making sure you don't get close to where the engine mount bolt will go.
  7. Place two of the F-601C gussets in the upper-outside corner and place the WD-602 engine mount support on top as above. Drill these to the firewall #30.
  8. Drill 17/64" or 9/32" at the engine mount bolt hole locations through everything including the WD-602 and -603 engine mount supports. These holes are used later with 1/4 bolts to mount the firewall to the fuselage jig. It is preferable but not essential to get your engine mount early and used it to locate these holes. If you do not have your engine mount you can make the holes 3/16 instead to allow more room for moving the holes later when they are drilled out to 3/8.
  9. If you have the tri-gear version place and drill the F-6122 angle approximately where shown and drill it #40 to the firewall. Then mark two points on the upright side of the angle 7/16 each way from the center and about 3/8 from the edge of the flange; drill these out to 7/16 (these hold fittings for the brake lines; see drawing #49).
  10. Remove all the pieces that go on the firewall. As you remove them mark the side of each piece that sits directly on the main firewall piece for countersinking.
  11. Dimple all the holes in the firewall (male die on side with flanges) and countersink all the corresponding holes in the stiffeners and gussets as previously marked. You will be using flush rivets with the flat head on the engine side of the firewall.

Firewall Cutout Box Kit
(This section applies only to the box kit sold for a time around 1994 consisting of a precut flat piece of steel that you bend up and rivet)

When making the box, bend the small tabs first, then the box sides. Make the bends such that the box is no wider than 8 at any point and a little narrower at the flange. On the sides of the box where the flanges overlap after bending, cut off part of one of the flanges so you don't have two thicknesses of metal there. Drill the holes #40 for the rivets that tie the box sides together. Dimple the holes from the outside. Put Pro-Seal or an epoxy structural adhesive on the box to seal it from fumes and rivet the sides together.

Firewall Cutout Box Opening
Make the opening in the firewall large enough for the box to fit through the hole; the box flanges will be on the engine side. The top edge is even with the lower edge of the top stiffener. Drill the box to the firewall. Remove the box and dimple the holes.

Dual Brakes Mod
If you ever plan to have brakes on the right side (an optional kit you order from Vans) you should put in some brackets to hold the two cross-over brake lines now. See drawing #49; detail A shows a bracket for one line, but you can make them for two lines by cutting the material 1 1/2 X 1 1/2 and drilling two holes 7/16 for the bushings. Drill these brackets to the center firewall stiffeners approximately where shown, or just under the firewall cutout box if you have one.
Finishing and Riveting the Firewall
  1. Deburr, clean, and prime all the aluminum pieces and the engine mount support brackets. The firewall itself is stainless steel and may be left unpainted.
  2. Rivet everything together except leave out all the rivets that attach the firewall cutout box (if used) to the firewall. It is recommended that this be done by backriveting using the Avery tool and the firewall fully supported and level with the bottom die in the tool. Many rivets in the minimum length will be too long and this method is the only way you can avoid cutting them or suffering bent rivets. Put Pro-Seal or structural adhesive between the side pieces and the main firewall piece to seal the joint against fumes.

F602 Bulkhead
The F602 bulkhead is just two side pieces. Trim the ends of these pieces and drill the holes as shown in drawing #25. These cutouts are to clear the 1/8" thick longeron angles. Do not cut the notches in the sides or bend the flange over at the top until later in assembly. Drawing 31 shows how this bulhead fits in the fuselage just behind the firewall.

F604 Bulkhead
  1. This is the bulkhead at the main spar, part of which was supplied in the wing kit.
  2. Collect all the pieces called out on drawing 15 and assemble them with a few clecoes and clamps. Make sure every hole is lined up. This insures that you have the right pieces and that you will be countersinking on the correct side. The F-604C uprights attach to the flange side of the F-604A main piece; the F-604D side pieces attach to the F-604C uprights, and the F-604B fatter uprights are attached only to the F-604D side pieces.
  3. Remove the F-604B fatter uprights from the F-604D side pieces. Circle all the smallest (1/8") holes in the F-604A main piece where the F604C uprights attach. The drawings only show 13 rivet holes per side but the bulkhead pieces in the kit normally have 15 holes; do all 15 holes. Just dont do anything to the larger holes which are for bolts. Remove the clecos holding the F-604C pieces to the main piece.
  4. Mark the 5/8" hole for the rudder cables in both F-604B pieces.
  5. Countersink at all the circles on the F604A main pieces.
  6. Clamp each F-604B and F-604C pair together with the two large holes lined up. Drill 5/8" through both at the location marked previously on the F-604B.
  7. Deburr all holes, rub out scratches, clean, and prime.
  8. Rivet the F604C pieces to the F-604A main piece with AN426AD4-5 flush head rivets.
  9. Make two spacer blocks approximately 7 1/4" x 7 1/4" , and 1 1/4" thick to simulate the main spar in this area. Place the blocks so they do not extend beyond the outside edge of the bulkhead, and leave a gap of about 3/8 between the top of the block and the top of the opening in the side piece F-604D. Put about four bolt holes accurately placed in each one by marking the locations through the holes in the main part of the bulkhead and then drilling the holes to the exact size (no larger than what is needed to be able to get #3 bolts in) in the drill press. This is necessary later for properly aligning the forward half with the rear half for riveting on the bottom skins.
  10. Clamp the F-604D side pieces to the F-604A/F-604C assembly and the F 604B with the spacer blocks in between. Put #3 bolts in through the spacer blocks. If not already done in your kit, drill a few holes #40 through the side pieces and the rest of the assembly as shown in the drawing. Clecos in these holes will hold the assembly together for now; they are not riveted because other pieces will be added later in this area.
  11. Find F-604E and F-604F channels (in the fuselage kit) and prep them as required in drawing #28. The open end of the F-604F channel may not be exactly 1 5/16", but don't bother with it now.
  12. Finish making the F-633 Control Column Mounts shown in drawing #47, except do not drill the 3/16 holes. Find the Wd-610 Control Column (a T shaped welded tube assembly shown on drawing #41). Clamp the Control Column Mounts to the flange side of F-604A covering the seventh holes from the center, with the flanges of the angles toward the center, and the bearing in the mounts closer to the top of the bulkhead. See drawing #40 for the proper orientation. Use the Wd-610 Control Column to get the proper spacing between the two mounts; the center of the mounts should be the same distance apart as the center between the two brackets on the column. Drill the mounts through the existing holes in the F-604 and set them aside for later priming and installation.

F605 Bulkhead (Seat Back and Wing Rear Spar Attach)
  1. Refer to drawing #26 and #33, and do read this section in the construction manual. Also get out drawing #32; it shows more clearly than the others how some of the pieces fit at the top of the bulkhead.
  2. Tweak the flanges on the F-605A bulkhead bottom pieces to 90 degrees and flute the curved flange to get the bow out of them (1 1/4" centers for flutes).
  3. Lay the F-605A bottom pieces flange side up with the large ends together and a straightedge along their straight edges. Trim the large ends if necessary to make them butt properly together and then trim the small ends to get the proper length of each (21"). Trim all of the flange off the straight edges for 3" from the small ends as shown in the basic fabrication illustration for these pieces (top of the drawing).
  4. Make the splice plate for the bottom pieces out of 0.032 (1/32") trim or scrap material as shown at the top of the drawing. The height should be about 3 3/8,not 3 1/8, and the top edge needs to be positioned right up to the bend in the flanges of the F-605As. Drill only the top and center pairs of holes, not the bottom pair, making sure you don't get them too close to where you will be cutting out the square hole in the middle later for the elevator push rod (see the main assembly picture).
  5. Clamp or tape the two bottom pieces to the worksurface flange side up with the straight edges aligned along a straightedge and drill the splice plate to the bottom pieces.
  6. Trim the F-605B long curved bar (flange strip) to the proper length and mark its center. Trim and taper the shorter F-605C strips to the correct length, measuring both the overall length and the distance from the first bend to the end.
  7. Lay the bottom piece assembly flange side down on the table, clecoed together, and place the bar in position on it. (This is just so you can use the straight edge of the F-605A pieces as a reference for measuring positions and vertical lines on the bar.)
  8. Mark and drill the bar as follows to avoid interferences:
  9. Mark the ends of the F-605A pieces on the bar. Mark the outline of the inboard tip and the inboard bend of the short bars onto the long bar. Mark the positions of the rib webs onto the bar using drawing #33. Mark the rivet positions on the bar using drawing #25, making sure that the ones that correspond with the tips of small bars will not be too close to their edges, and that none go past the point of the bend in the short bars. Mark the positions of the bolt holes at the outer ends, making sure that they are far enough in from the F-615 rib webs to allow access to the #3 nut that will be there (about 3/8" in from the ends of the F-605A's should do it).
  10. Hold the seat belt anchors approximately in position on the long bar using drawing #33. Move any of the previously marked rivet holes if necessary to get them away from future seat belt anchor bolt holes. You will not mount the seat belt anchors at this time because it is easier to get the right placement later.
  11. Drill the long bar #12 or 3/16" for the bolt holes near each end.
  12. Drill the bar #30 for the rivets that hold it to the F-605A bottom pieces. Mark the rivet holes where the ribs go to prevent riveting them during bulkhead assembly.
  13. Make the spacers that go between the F-605B and C strips at the end bolts. Glue them in place to the long bar. Clamp the short strips to the long bar and match drill the rivet and bolt holes. Countersink the rivet holes in the short bars that will be underneath the outboard seatbelt anchors. Check to see if you need to round off a corner of the spacer to prevent it from digging into the short bar.
  14. Clamp the long bar to the F-605A bottom pieces and splice plate and match drill the rivet and bolt holes. Countersink the rivet holes that will be under the two seat belt anchors near the center of the fuselage.
  15. Mark the rectangular cutout in the bottom pieces and splice plate for the elevator push rod with the dimensions shown (1 5/8 x 1 1/4), but make the lower edge of it 3/8 above the bar rather than right above it. Remove the bar and make the cutout. Drill the 5/8 round hole next to it.
  16. Rivet the two bottom pieces and the splice plate together at the upper four holes only. Put the manufactured (round) head on the side opposite the flanges. It is better to do this now rather than waiting.
  17. The only easy and sure way to get the rest of the F-605 bulkhead aligned properly is to draw its outline on a work surface you can drill into and build it over that. You can see the dimensions that follow on drawing #26. Draw a line 42 1/2 inches long representing the top of the top piece and mark its center (21 1/4" in). Then draw a fuselage centerline down perpendicular to that one at its center and 22 13/16 long. Draw another line centered on and perpendicular to that one, 42 inches long (21" to center); this line does not follow an edge, but its ends mark the location of the outer lower corners of the F-605A pieces. You have now drawn an "H" laying on its side. Verify that the lines are exactly square with each other by comparing diagonal measurments from one side to the other (for example, is the distance from an upper line end to the corner between the lower line and the center line the same for both sides?) .
  18. Secure the bottom piece to the work surface with clecos, flanges up, with the lower corners at the ends of the 42" long line.
  19. Lay the F-605D side pieces on the pattern and modify their lower ends so they fit the bottom pieces. Make the two large holes in each of the side pieces only if you are doing manual flaps, they are not used with the electric flap option. If you are going to install electric flaps, drill the plastic blocks for the endes of the control arm to the F-605 now.
  20. Lay the F-605F top piece in place on the pattern, with the 2 wide side down and the 3/4 flange pointing toward the bottom of the bulkhead. See the side view of the bulkhead over on the left side of drawing #26 and remember that the F-605 hangs off to the rear of the bulkhead. Mark the flange toward you as rear. Mark the top also. Several people have put this piece on backwards even after they figured out the right way for it to go, so be careful. The F-605F should stop at least 1/8" short of the ends of the 42 1/2" line (trim if necessary). Mark and cut off the flange on the short side of the top piece to clear the F-605D side pieces. Modify the upper end of the side pieces so they will fit properly to the top piece and if necessary to obtain the overall side height. They should not dig into the bend at top or bottom.
  21. Overbend the flange on the outside edge of the side pieces by about 4 degrees so they will follow the skin line. Then place the side pieces for the following drilling steps so their outside edge lines up with the ends of the top and bottom pieces. Drill four of the six upper holes through the side pieces into the bottom piece; do not drill the two at the outside edge. Make sure none will be under or too close to where the long bar will interfere with driving the rivets later.
  22. Cut off about 1/2" (plans say 3/4") of the outside edge flange of the side pieces at the top, just over 1/8" deep. This is to clear the longeron angle which will be added later; see detail A of drawing #26.

Make the F-605G heavy angles.
  1. If you are doing a tip-up canopy, you must add in the F-605E channels and the F-605H and I spacers. These are not needed for the sliding canopy, so if you want to save some work you can leave these pieces out. There is 1/2" wide material in the kit for the spacers. There is an adequate description of this part in the construction manual. There is a bracket that will later be installed with four bolts on the front (non-flanged) side of this area; see drawing #51, view D-D' . Do not put any rivet holes in this area to avoid having to remove some later. Also note that there are no rivets holding the F-605G angle to the top piece; two bolts will go through this area later. At its full length the F-605E channel and possibly the associated spacers will interfere with the attachment of the F-622 side ribs (see drawing #32). To avoid this, cut the pointed end of the F-605E channel off so it will be no more than about 9 long.
  2. Drill the side pieces to the top piece with the F-605G angle included (and the tip-up canopy extra pieces).
  3. Take the assembly off the work surface and turn it over. Drill the lower edge rivet and bolt holes through the bottom piece into the side pieces. Drill another rivet hole through both between the outer bolt hole and the other rivet hole. Disassemble and modify (cut, bend down) the flange on the side pieces if necessary to allow a proper seat for the bolts that will hold the seat belt anchors on later.
  4. It is probably best to rivet this assembly together now while the work surface is still handy. Deburr and prime at least the mating surfaces. Leave the bars off to start. Drive one rivet at each corner, then put the assembly back on the work surface to get it lined up right. Then drive the rest of the rivets, moving the assembly back to the work surface after the first few to insure that it has not shifted. Verify that the long bar won't hit any rivet heads and then rivet it on , making sure you don't put in any rivets that will also go through the short bars or the seat ribs. Make sure you put a rivet in the last hole before the outer bolt hole on each end. Then rivet on the short bars.
  5. The drawings you have been using show the F-657 gusset but not clearly. Its placement over the top piece and under the longeron is shown more clearly on drawing #32. The shape shown there is for the tip-up canopy. If you are doing a sliding canopy, see drawing SC3 for the proper shape. The blanks for the F-657s are in plastic bag 654P with a bunch of other small pieces. Trim it to size and form the curved edge, but do not drill it or trim the edge that goes against the longeron at this time.

Electric Flap option

(Questions on this go to Gil Alexander, gil@rassp.hac.com)
  1. Attach the EF-661 mounting blocks to the aft side of the F-605 bulkhead, using the Wd-631 flap control weldment as a spacing guide. Pre-drill the EF-661 mounting blocks (preferably in a drill press), and then use these holes to locate the #12 holes in the F-605 bulkhead for the AN3 bolts. The vertical positioning of the weldment can be fixed by clamping the F-680 central bearing block on the flange of the F-605B crosspiece, 2 inches left of the centerline (this is it's actual location).
  2. NOTE: Production parts have shown a tight fit of the EF-661 mounting blocks against the skins, and several builders have had to cut away a portion of these mounting blocks in the area of the skin/F-605 rivets. Check that the EF-661 blocks will clear the final fuselage skin location and bulkhead flanges.
  3. Mark the EF-661 mounting blocks left and right, and store them away until the later fitting of the flap actuating mechanism. You will be glad at that time that you drilled the mounting holes for the EF-661 now.

F-606 (Baggage Compartment Rear)
  1. Hang up drawing #27, also #33. The construction manual states that you can align these bulkhead pieces using only the tooling holes; that may not be true for the pieces in your kit.
  2. Look at SK-47 in the construction manual for a diagram of the proper alignment of the bulkhead pieces. You can do this easily using the lines that you drew on the worksurface for the previous bulkhead (F-605). Make two lines parallel to the perpendicular line and 18" away from it on each side. Lay the F-606B bulkhead bottom piece flange-up on the worksurface with its flange toward you, with the bottom line centered in its tooling holes and its center at the perpendicular line on the worksurface. Drill 3/16" through the tooling holes into the work surface. Secure the bottom piece to these holes with bolts or clecoes.
  3. Make a mark on the perpendicular line 35.21 (35 7/32)" up from the bottom of the bottom piece. This mark and the two other lines you have marked define the top and side edges of the bulkhead; the dimensions are taken from drawing #24. Make a horizontal line (perpendicular to the perpendicular line) at a point 21.44 (21 7/16)" up from the bottom; this indicates where the top of the main longerons should lie, taken from drawing #22.
  4. Secure the F-606A side/top pieces underneath the bottom piece using the tooling holes. Align the top and side edges with the marks on the worksurface and secure them with tape or small clecoes near the inside edges. If you cannot make the edges line up properly or the bulkhead does not appear to be square in shape try misaligning the tooling holes to see if you can make it better. Mark the horizontal line onto the bulkhead sides. If the hozontal line does not show in the slot, mark an area for cutting out later so the longeron can be located properly.
  5. Drill rivet holes #30 as shown in drawing #27, except do not drill the upper two at each end of the bottom piece. At the top center, the uppermost hole should be at least 3/8" below the main flange line and the lowermost one as low as it can be placed. F-687 (the top rib that goes rearward from here, see drawing #32) attaches with the upper three rivets.
  6. Find an F-627 baggage floor rib and the three-foot long piece of 0.032" x 3/4" x 1" angle (the plans may still show one angle dimension as 5/8", not 3/4") Using drawing #33 place the rib in position against the F-606B bottom piece two inches from its center, bottom flange aligned beyond the bottom flange by 0.025" (the bottom skin in this area sits on top of another skin which goes on the flange of F-606 first; see drawing #36), and mark where the top side of the rib falls on it. Draw a horizontal line through this mark all the way across the bulkhead. Trim the angle to fit and place it with the short side of the angle against the F-606B and the long side aligned with the line for the top of the ribs. The top side of the angle should line up approximately with the upper edge of the bulkhead bottom piece. Drill the angle #40 to the F-606 assembly using 1 1/2" spacing with the first hole in the center, but do not actually drill the hole to your left of the center one because it may interfere with F-628 later. Dimple the angle and F-606 in from the flange side (so the rivet heads won't interfere with placing the baggage compartment back panel). Also dimple the holes at the top of the bulkhead.
  7. If not already there, cut out the trim cable and elevator push rod holes in the F-606 pieces. If present, cut off any flanges along the inside edges of the F-606 pieces. It is not necessary to try to eliminate any of the wavyness in the flat areas of these pieces; the baggage compartment back panels will hold them flat enough.

Elevator Bellcrank Support Ribs F-628 and F-629
  1. Locate the F-628 and F629 ribs and verify that the 84 degree angle shown in drawing #30 is correct; if not the flanges must be tweaked or the bottom skin will be distorted. Cut the large hole in F-629 as shown in drawing #30 revision 6.
  2. Drill the F-628 rib and angle as shown in drawing #30, but do not drill any rivet holes in the area where the elevator bellcrank will be supported later (see drawing #32); this is approximately 4 1/4" above the base (fat end) of the piece. Do the same for F-629 except do not drill near a point 3" from the fat end. On F-629 the angle should go past the bend at the fat end so that its end is even with the flange; also, be sure the angle edge is not below the rib web at all at the fat end.
  3. The holes for the aileron bellcrank bolt in F-628 and F-629 must be lined up carefully or one of the pushrods may hit the structure. Make a pattern out of construction paper for about the first six inches of the fat end of the F-629 rib. Make it on the side with the attached angle, with the edge going to the inside bend of the angle. Mark the bulkhead edge (the fat end) and the bottom skin edge (the long edge with the bent-up flange) on it, as well as a line that follows the centers of the rivets along the added angle. Put this pattern on the non-flange side of the F-628 rib; the bottom skin edge lined up with the flange at the fat end and the bulkhead edge lined up with the long edge with the bent-down flange. Draw a line along the centerline of the angle rivets where it crosses the existing line. This is the location of the bolt hole in both ribs. Mark this location on both ribs and drill a 1/4" hole there.
  4. Lay the F-606 bulkhead assembly flange down on the worksurface and locate the position of the F-628 vertical rib on it. Drawing #33 shows it looking down from the top, with the web 1" from the centerline. At this position it is offset enough from the F-627R baggage floor rib that you cannot attach both with the same rivets. Later you may have to notch the flange of the baggage floor rib to clear the F-628 attach rivets. Mark the position of both edges of the F-628 on the bulhead, remove it, and drill mounting holes for it in the bulkhead. Reattach it to the bulkhead and drill it through the bulkhead. Dimple all the holes in the same direction as the baggage floor support rib holes (this is so they will not interfere with the placement of the F-627R floor rib as well as the baggage compartment back and the support angle F-632B (tip-up canopy only).
  5. Clamp the F-629 rib to the bulkhead with its web 1" from the centerline. Use section G-G' of drawing #32 for the correct orientation. Note that this view hows how it should look from the front just a little bit aft of the forward flanges of the F-628 and F-629 ribs. Drawing #33 does not show F-629 properly except for the location of the rib web. Drill it the same way as the F-628 was drilled. The flange of F-629 that goes against the bulkhead points away from the F-627L rib so there is no interference between the two in attachment. Mark any area of its flange which must be trimmed so it won't block the elevator pushrod access hole. Disassemble. You will probably only have to dimple the one hole which is also in the baggage floor support angle. Trim the flange of F-629 if necessary.
  6. Find the piece of 0.032 x 2 3/4 x 5 3/4" plate in bag F-654P. This is used to make F-630, which is shown best on drawing #33 section A-A'. Align it to go underneath the flanges of F-628 and F-629 on the bulkhead bottom so that those holes drilled through it will not be too close to its edges. Drill holes in it through the bulkhead. Mark the outline of the elevator pushrod access hole on it. Remove it and make the cutout and dimples as appropriate.
  7. Reattach the F-630 plate as well as the F-628 and F-629 ribs to the bulkhead bottom. Cut the piece of angle that secures the F-630 plate to the F-629 rib, clamp it in place, and drill it #30 as shown in section A-A' and J-J' of drawing #33. Also drill the upper end of F-630 to the F-628 rib and the lower end in the center to the bulkhead. The angle does not attach directly to F-628.
  8. Disassemble, dimple the new holes in the plate and rib, and countersink the appropriate rivet holes in the angle.

Top Gusset (F-688)and Rib (F-687)
  1. Assemble everything and stand the bulkhead upright. Find F-688 and drill it to the top of the bulkhead as shown in drawing #32 The top of the bulkhead should be clamped to hold it straight while doing this, and F-688 should be exactly centered and aligned with the web of the bulkhead. You can then drill the rest of the holes shown in the drawing.
  2. Mark rivet centerlines aligned with each other along the flanges at the end and the upper side of rib F-687. Clamp the rib to the bulkhead and gusset using the centerlines as a guide. Drill it through the bulkhead, but drill only the first hole next to the bulkhead in the gusset to it.
  3. Rivet the F-630 reinforcing plate and the bulkhead sides to the bulkhead bottom, making sure you do not put in any rivets that also attach the F 628 and F-629 ribs or the baggage floor support angle. Rivet only the bottom hole where the sides of the bulkhead join at the top. Rivet the angles to the F-628 and F-629 ribs; it is probably easier for you to rivet the angle to the F-628 support before mounting it on the bulkhead, but that may mean that you will have to use one or more pop rivets to attach the assembly to the top end of the bulkhead (no big deal). Mark the baggage floor support angle "rivet on after bottom skin" and cleco it to the bulkhead.

Rear Panel Preparation
Refer to drawing #37 and do the initial trimming of the F-652 and F-651 baggage bulkhead pieces. This consists of rounding the top of F-652, cutting away the upper flange of F-651 to clear the F-628 upright and the sides of F-606, and making the slots for the shoulder harness anchor cables as shown in detail A (a dimension is missing; make the top panel overlap the bottom one by 3/4). Mark but do not drill the mounting holes.

F-607 and F-608 Bulkheads
  1. Verify that the proper holes are present for the trim and rudder cables. Flute as necessary to get them flat but do not try to make the flanges perpendicular to the webs. Deburr the edges. Where there is a notch and an indentation in the flange next to it is the place where the main longeron will go; make sure that the indentation is deep enough for the 1/8" thick longeron outside edge to line up with the rest of the bulkhead flange.
  2. Connect the two halves together by lining up the tooling holes. Measure the width and height using drawing #24. Note that an extra 0.125 (1/8") must be added to the width for these two bulkheads; this was a change made to give a slight outward bow to the sides to help the skins lie better. Also note that the numbers on drawing #24 do not agree exactly with the ones on drawing #22, but that the difference is not enough to cause any problems. If height or width is incorrect by more than about 1/8", ignore the tooling holes and clamp the halves to a width such that the error in the height and width are approximately the same.
  3. Drill the bulkheads #30; on F-607 do not make any holes closer to the top than 1 1/4" (the rib from F-606 attaches here).
  4. Lay a straightedge across the bulkheads at the top of the slots for the longerons and measure the distance from it to the top and bottom of the bulkhead. If these numbers do not agree with the values on drawing #22, mark the proper position for the longeron top on the bulkheads. If necessary enlarge the slot to allow the bulkhead to be positioned properly on the longerons.
  5. Rivet together.

F-609 through F-612 Bulkheads
  1. Use drawing #28.
  2. Cut the lightening holes and control cable holes as shown in drawing #28 for F-609 and the lightening hole in F-610.
  3. Verify the heights of F-610, F-611, and F-612 using drawing #22 or #23 which show the distance from the top of the longeron to the bottom of the bulkhead (upside down in the case of drawing #23). Your bulkheads should be no longer than the number shown less the longeron thickness (1/8"); if not you will have to trim the corners to clear the side of the longeron that points inward as well as its inside corner radius.
  4. For a tailwheel airplane cut out the large notch in both F-611A's. If you are building a tri-gear RV-6A, cut the notch out of F-611A and F-611B.
  5. Make the proper bars for the F-611 bulkhead (straight for tailwheel and tapered for tricycle gear) and drill them to the F-611 main pieces.
  6. Rivet the bars to both of the F-611 main pieces except do not do the top two holes.
  7. If you are building a tailwheel airplane join the two F-612 bulkhead pieces as shown.

Ready to Jig Up
  1. To make later steps go easier, modify the angle of the flanges of F-606 through F-612 to about 8 degrees outward on the sides and 5 degrees on the bottom and top; on the F-611 this is the side with the bars on it. On F 611 (and F-612 if tailwheel) the reaward flange must be bent inward; try to grip it up in the bend with the seaming pliers so that the extra bend tends to occur on the web side of the factory bend, thus narrowing the skin line here so it matches the front flange. Flatten out the web of F-612 as much as possible.
  2. After all the pieces are primed and riveted you are ready to start jigging the fuselage.

fusebulk.doc 2/10/96 Frank Justice

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