SECTION 8: THE FUSELAGE
The RV-6/6A fuselage is a monocoque or stressed-skin structure. The strength of a fuselage is very similar to nature's most perfect monocoque structure, the egg. Like the egg, the fuselage can withstand tremendous loads when properly applied, but yet is prone to localized failure when subjected to concentrated loads. The skin shape is determined and maintained by web-like frames or bulkheads and also by longeron angles and skin stiffener strips. The longerons and bulkheads also provide localized strength for the attachment of wings, empennage, controls, canopy, etc. When the skins are riveted in place, the fuselage becomes very rigid and self-supporting.
There are some variations in constructing the fuselage, depending on whether the builder has chosen the RV-6 or RV-6A, and which canopy, sliding tilt-up, is to be installed. BE SURE THAT THE INSTRUCTIONS
YOU ARE FOLLOWING APPLY TO THE AIRPLANE YOU ARE BUILDING.
JIGGING
The recommended jig for RV-6/6A fuselage construction is detailed on DWG 23. This jig could be referred to as an "inverted bed" or "horizontal ladder" jig. It consists of two longitudinal beams with perpendicular crossmembers and legs for supports. It is cross-braced, so it is rigid in all planes. Since the top longerons are horizontal over most of the fuselage length, they can be directly supported on the top of the jig, using a horizontal level plane as a jigging reference. A firm centerline can be marked on the jig, independent of the straightness of the main beam side-members. Since the fuselage has a large opening for the canopy, and horizontal top longerons, it is logical that the fuselage be jigged and constructed in the inverted position.
JIG CONSTRUCTION
The RV-6/6A fuselage jig shown on DWG 23 is relatively inexpensive and easy to construct. Materials and tools available to certain builders may permit the fabrication of a different, perhaps superior, jig, but the design shown is a good compromise of simplicity, cost and quality.
Lumber used in jig construction should be as straight and dry as possible. Drying, shrinking lumber may disturb alignment. Assembly of the jig with 8d and 16d nails is sufficient: however, for maximum rigidity, the use of glued joints and lag or drywall screws are recommended. If the jig is intended for use in the construction of several fuselages, these added steps in jig construction will pay long term dividends. Leg lengths should be uniform and can be nailed on irregularly if the shop floor contours dictate. Shims can be used under the legs if necessary during final leveling. It is a good idea to attach the legs to the shop floor. If your floor is concrete, a structural adhesive like Liquid Nails works well.
Once the jig is leveled both longitudinally and laterally, establish a centerline with a taut string or wire. As mentioned before, this centerline is independent of the straightness or waviness of the edge beams. The horizontal crossmembers of the jig are shown with beveled edges to permit maximum access to the structure while being drilled and riveted. The position of these crossmembers should correspond to both the dimensions listed on DWG 22 and DWG 23. However, individual aircraft vary slightly and it is possible that bulkheads may need to be shifted slightly to support a smooth skin, especially bulkheads F-607 and F-608.
Fasten the crossmembers that support these bulkheads with screws, so they can be repositioned if necessary.
BUILDING THE BULKHEADS
Most RV-6/6A bulkheads and fuselage ribs are formed in two or more pieces and then riveted together to form the complete bulkhead ring. The smaller bulkheads in the rear of the fuselage are formed in one piece.
Fabrication and assembly of the bulkheads is detailed on DWG 23 through 23.
THE FIREWALL
The F-601 firewall bulkhead comes from the factory partially pre-drilled and clecoed together. The remaining holes punched in the stainless steel panel must be continued through the aluminum angle reinforcements and WD-602/603.
Determine the hole sizes and finish drill the reinforcing angles and weldments. Label all parts so they can be easily relocated, then disassemble the firewall, deburr and prepare all the parts for riveting. Take the time during disassembly to study the firewall and learn how the components fit together -- having a good mental picture will be a big help when it comes time to put all the parts back together. Prime the steel and aluminum components before riveting -- the stainless, of course, needs no priming.
If you are building an RV-6A, you must fabricate and drill the F-6122 angle oh the left side
For the RV-6, these holes may simply be filled with rivets or a thin strip of aluminum may be riveted to the inside of the firewall.
The rectangular opening in the center of the firewall must be filled. Use the F-601K recess if you are installing an engine with a prop governor or a spin-on oil filter (new engines from Van's require the recess) or a flat sheet of stainless steel if your engine does not require a recess.
When the parts are completely prepared, rivet the firewall together. Note the rivet call-outs carefully. The RV-6/6A firewall uses flush rivets with the heads forward. The resulting smooth surface on the engine side of the firewall makes cleaning and mounting accessories much easier.
One of the objectives of the firewall is to keep fumes and liquids in the engine compartment from entering the cabin. Some of the folded and bent corners have unavoidable openings; around the lower corners of the firewall and the bends of the firewall recess, for instance. These should be sealed with tank sealant or Hitemp RTV (available in auto parts stores) during construction.
THE BULKHEADS
Bulkhead F-602 is constructed per DWG 22 and DWG 25, and there is no assembly required prior to fitting into the fuselage framework.
F-603
Bulkhead F-603 (tip-up canopy) or F-6103 (sliding canopy) is the instrument panel. Construction of the panel is best left until the fuselage is upright and off the jig.
F-604
The construction and assembly of wing attach bulkhead F-604 is covered in Section 7. Now that you have the parts, there are a few other things that can be done before the bulkhead is installed in the jig. The control stick assembly shown on DWG 41 may be prepared and assembled, at least temporarily. Clamp the F-633 control column mounts to F-604 and double-check their position by fitting the control stick assembly.
Mark and drill the F-663s for the bolts that will attach them to the bulkhead.
While the sticks are mounted, you may mark and cut the flange of F-604 to allow full control movement, as shown on DWG 37.
A "spar substitute" spacer is needed in bulkhead F-604. This spacer serves several purposes. First it maintains the position the side flanges relative to each other, so they cannot be pinched together during assembly. Second, it helps keep the bulkhead flat. The bulkhead should be as flat as possible when the floor ribs and bottom skins are drilled to it. If it curves, it will be difficult to align the holes in the spars and get the bolt through them.
Use a piece of lumber, or laminated plywood and/or lumber, equal to the spar in cross section, damped or bolted to the forward face of F-604A. It should several inches wider than the bulkhead, so it protrudes out each side of the fuselage, and as wide as the spar. Make cutouts where the seat ribs join the bulkhead, so the ribs can be ciecoed on when the time comes.
Another method of keeping the bulkhead straight is to install small wood spacers at the outboard ends, to maintain the proper gap between F-604A and F-604B, then bolt the W-620 splice plates against the fore and aft faces of F-604. Use temporary hardware store bolts.
F-605
Bulkhead F-605 consists of many parts which must be accurately positioned, drilled, and riveted together.
However, most components are straight sided, brake-formed parts that are easy to jig and fit. The F-605B Center Section Bar has been formed to the specified curvature and conforms to the F-605A Bottom Bulkhead. The two F-605C Bars should be cut to the specified length and taper in preparation for assembly.
F-605 assembly begins by splicing together of the right and left halves of F-605A as shown at the top center of DWG 26. The two parts are (aid flat side down on a flat surface and the straight upper F-605 flanges are clamped to a straight angle or board. Then the 0.032 splice plate is placed over the butt joint at the center (rear side of spar; between the flanges), and drilled per DWG 26. Note that a hole will later be needed in the center of this splice, so this should be marked and rivet holes spaced accordingly.
While ciecoed together, the F-605A is turned over face up so the F-605B and F-605C bars can be positioned
and drilled. The F-605B bar should be centered on the bulkhead with its ends 1/8" up from the bulkhead channel bottom. Use DWG 26 and DWG 33 to locate the seat ribs, baggage ribs and seat belt anchors.
Carefully mark the rivet holes on the F-605B and F-605C. The locations may be adjusted slightly to center in rib flanges. Clamp F-605A, B and C firmly together and drill the rivet holes. The bars can be removed to make further assembly of the bulkhead easier.
Layout of the major parts of the F-605 assembly should be done on a flat tabletop covered with a sheet of thin plywood or particleboard which can be drilled.. At a glance, the bulkhead appears square, but it is not. The bottom width is 1/2" less than the top width. Recommended procedure is mark out the outline on the jigging surface, starting with the flat top surface, along a straight edge of the particleboard sheet. Measure and mark the ends and center of the top width. Then, using a carpenters square or equivalent, draw a light line square (perpendicular) to this edge from each mark down to the bottom of the bulkhead. Measure outward from the center to locate each of the bottom corners. Cross check these points by measuring inward 1/4 inch from the light square lines. Once the corner points are verified, draw in dark side lines. Now you can overlay this pattern with parts F-605A and F-605F, front side down, followed by the F-605D side channels. These four primary bulkhead members can be held in place with clamps or nailing blocks.
The lower corner intersections of F-605A and F-605D can be marked and drilled, placing several clecoes in
each intersection to further secure it to the jig. However, be careful not to drill any holes in the area covered by the F-605B bar, Finish the F-605D side channels by using the Unibit to drill the 5/8" rudder cable holes and cutting the openings for the manual flap arms.
NOTE: DO NOT cut the flap arm holes if you are installing electric flaps.
While the Unibit is out, you can also drill the trim cable hole (manual trim only) and the corners of the pushrod opening in F-605A.
If you are installing a sliding canopy, the side channel reinforcement parts F-605E, H, and I can be omitted. If you are installing a tip-up canopy they can be positioned now. Before drilling, check that they all fit together such that the top fuselage longeron, an AA6-125 3/4 x 3/4 aluminum angle extrusion, will fit into the upper comer notch as shown in detail "A". Note that the thickness of spacers F-605H and I in conjunction with the flange of channel F-605D are approximately equal to the 1/8" thick longeron angle. If additional spacers are needed for a snug fit of F-605E, they should be installed in the inboard side of the channel.
Cut and position F-6Q5G. Be sure that it is snug up against the top of Channel F-605F by clamping them together. Now, this corner assembly can be drilled and clecoed to the jig. The side spacer strips can be held in place with tape, because they will eventually be riveted in conjunction with the fuselage skin.
Disassemble the entire bulkhead, deburr the holes and edges, remove scratches, and prepare for priming.
The bar and angle components are not Alclad material so must be primed. After priming, reassemble and check for proper alignment. Then rivet the major components together. Note that DWG 26 shows the location where seat and baggage ribs will later be attached, and shows these holes with circles denoting that they are to be left open at this time. Cover these with tape to avoid accidental riveting.
Before riveting on the F-605B & C bars, refer to DWG 33, section E-B which shows the attachment of the F 634 Seat Belt Anchors to the forward face of this bulkhead assembly. Clamp the anchors to the F-605 bulkhead temporarily and look for any interference between them and the rivets that will join F-605 A &B.
AN3 bolts are used to attach the anchors to the bulkhead. The position of these bolts in the flanges of the seat belt anchors may be adjusted slightly to maximize the distance between bolt holes and rivet holes.
Machine counter sink F-605B&C and use AN426AD4-6 flush head rivets where the flanges of the seat belt anchors cover the rivet holes. Pre-drill the anchor flanges for AN3 bolts, then clamp the two anchor halves to the F-605 with a 1/8" spacer between them and drill 3/16" holes through them and the bulkhead. Position the outboard anchors. You will find that one of the existing rivet holes coincides with the bolt hole in the anchor.
Enlarge this hole in the bulkhead to 3/16", (this rivet will be replaced with a bolt) then complete the drilling of all the other anchors. The steel anchor parts can now be removed, primed, and stored until they will be needed for final assembly. The remainder of the bulkhead can now be riveted. Remember to leave holes used to attach seat and baggage ribs.
F-606
Bulkhead F-606 consists of three primary segments which can be accurately jigged simply by aligning the tooting holes with 3/16" bolts or 3/16" clecoes. However, because of the possibility of free-play in the holes, the alignment can be checked by taking accurate square measurements as shown in Fig. 3-1. Because of variations in production, the F-606A bulkheads sometimes have a slight flange on their inner edge. This should be trimmed off because the inner edge of the bulkhead web must be flat so the baggage bulkhead can be installed later as shown in DWG 37. A fourth member, F-606C, is riveted to F-606 as shown in DWG 33. The forward facing leg of the F-606C angle will be used for attaching the baggage floor. Position this so it will be level with the baggage floor, if you choose to install F-606C along with the initial assembly of this bulkhead, you should check its position by fitting the baggage floor ribs in place on the lower portion in the positions given on DWG 33. The option is to delay installing F-606C until the basic fuselage assembly is underway, at which time it can be installed along with the baggage ribs.