SECTION 7: BUILDING THE WING
WING JIG
Because the RV-6/6A wing has a constant chord with no twist (wash-out) or taper, it can be constructed with the use of relatively simple jigging fixtures. The recommended jig consists of two vertical posts, preferably running from floor to ceiling. If the ceiling is out of reach, it is possible to build a free standing rigid jig that will do the job. Horizontal arms of steel angle or wood support the main and rear wing spars during construction A jig of this type is illustrated in Fig. 7-1 , and uses the same posts used for the construction of the horizontal and vertical stabilizer. The exact size of the posts and arms is not important, but they must be sufficiently strong and rigid to support the wing during construction. What is important is that proper alignment be maintained. This jigging concept uses horizontal and vertical lines for alignment so plumb lines and a carpenters level are adequate instruments to establish and maintain alignment.
MAIN SPAR
The main wing spar is the single most important structural component in the RV-6/6A. It carries the entire lifting load of the wings. NO compromises should be considered in its materials or construction accuracy.
Much effort was devoted to making the spar drawings and instructions thorough, accurate, and easy to read.
PLEASE READ AND RE-READ the plans and instructions until you are certain about the construction procedure before starting.
NOTE: Standard RV-6/6A Wing Kits are supplied with pre-drilled wing spars which require assembly, if you are building pre-drilled spars from the kit, see the section ASSEMBLING THE MAIN SPAR for appropriate instructions. If you have selected the optional ore-assembled ("Phlogiston") spar, move ahead and beam at "REAR SPAR".
ASSEMBLING THE MAIN SPAR
The standard spar provided in the RV-6/6A wing kit has been aligned and drilled at the factory. The F-604 fuselage bulkhead has been aligned and drilled in assembly with the spar components to insure the proper fit when the airplane is finally assembled. The spar/bulkhead assembly also includes the four W-620 heattreated steel splice plates and the close-tolerance NAS bolts. Drilling the spar and bulkhead "in assembly" assures that all the components will match one another, but these components are NOT truly interchangeable from one airplane to the next. If, for instance, a spar flange strip or splice plate is damaged, another part must be fabricated and drilled to match-a tedious and difficult chore. Therefore, it is even more important than usual to work carefully and avoid damaging parts.
Factory identification of components
The individual bars, flange strips and other spar components are punch marked so that they can be correctly relocated. The spar serial number and "R" or "L" (denoting the right or left wing) markings are engraved on the spar web and flange strips. Small dots are punched into the butt ends of the flange strips; the single dot marks the top and the double dot the bottom. (Remember: Think of top, bottom, left, right, etc., as if you were in the pilot's seat, facing forward.) Spreader bars have engraved numbers, starting with 1 at the inboard end and going up to 15 at the outboard end. These numbers are marked on the top aft surface. NOTE that these numbers and punch marks are made by humans, and could be wrong. Double check.
Measurement Reference
The inboard end of the spars are cut on an angle to allow dihedral. The reference point for spanwise measurement is LOWER INBOARD END, marked "0" on DWGs 12 and 13. It is a good idea to mark thiscorner of the spar and double check that all measurements are made from it-measuring from the upper corner will result in errors of almost half an inch.
Disassembling the Spar
The spar is temporarily assembled for shipping. It is held together with several rivets and lockwashers whichmust be removed so the spar can be taken apart and the components prepared for final assembly.
Protect the spar with electricians tape and use a thin screwdriver to twist the lockwashers up and away fromthe spar. Clip them off the rivets with sidecutting pliers. Now the rivets can be driven back out of the sparwith a drift punch.
PREPARING THE SPAR COMPONENTS
Sand or file away all cutting and milling marks on the edges of the spar flange strips. These bars should be finished just like the HS-409 bars used in the horizontal stab - remember? Break the edges, round the tips, smooth all surfaces to a satin finish.
Deburr the lightening holes. The fastest way is with a small Scotchbrite wheel in a die grinder, but wet-and-dry sandpaper and some patience will do the job as well.
Prepare the W-422 tie-down bracket by drilling bolt holes as shown on DWG 20.
Deburr all the pre-drilled rivet holes in spar components. This tedious chore can be made to go a bit faster by using the deburring bit in a slow turning electric screwdriver.
Clean all components with a solvent and a Scotchbrite pad. The resulting surfaces should have a satinsheen, with no scratch marks or pits. If the primer you are using requires etching, an inexpensive etchingtrough can be made from a length of plastic roof gutter.
When all the components are dean and dry, use a Sharpie to mark the position and part numbers. The inkin Sharpies will bleed through most primers and this can be used to advantage here. It is very easy toobscure all the small position numbers etched into the components with a coat of primer, and then waste a lot of time trying to find where each piece goes.
Finally, prime all the components,
ASSEMBLING THE SPAR FOR RIVETING.
The first step is to install the spreader bars on the W-606B Spar Web Doubler. The spreader bar positioning should be carefully done to avoid mis-aligning holes. Each spreader bar is marked; the number "1" is the inboard most bar and the number "15" the outboard most. The bar is also marked with the last two digits of the spar serial number of your assembly, followed by an "R" or "L" as appropriate to the right or left spar assembly. All of the markings are on the top aft surface of the bar and must be assembled correspondingly to the spar.
Attach the bars with clecoes, two per bar, through the Web Doubler and into the bar. It is important that thebars be quite secure, for if they come loose after the main spar web and laminations have been riveted, it willbe nearly impossible to re-locate them. An alternate method of holding them in place is to slip AN-47GAD4 rivets into the holes and hold the rivets in place with masking tape until driven. In any case, be certain that at least an alignment rivet or cleco is in place at all times to prevent "losing" the bar inside the spar. Some stiffener bars overlap the edge of lightening holes at some locations; this is normal.
Now you are ready to add the longest spar flange strips (W-606C & W-606D) to the assembly across the tops and bottoms of the spreader bars.
We've found the best procedure is to pre-assemble the spar with six long AN3 bolts installed through thespar web doubler in the bolt positions at station 23.50, 34.375 and 43.625, {see DWG 12} in both the top andbottom flange strips. Slip the various components over these bolts for initial location and install washers and
nuts loosely. (It is a good idea to use hardware store nuts or wing nuts for temporary fitting and save theexpensive nylon stophuts for actual installation).
Special attention must be given to riveting the five inner most spar web stiffeners to the spar. Because this inboard portion of the spar is to slip in between two fuselage bulkheads, the surfaces must be flat. Thus, flush head rivets must be used on ail five stiffeners, and the shop heads are to be on the rear side of the spar. For the fifth stiffener, the %" wide one, both the factory and shop heads must be flush. The required procedure is machine countersinking the stiffeners and dimple countersinking the spar webs. This is illustrated in Fig. 7-2.
Now slide two of the top and two of the bottom close tolerance bolts into the drilled and reamed holes in thesplice area. Alignment of these holes is, of course, of utmost importance for easy, final assembly of theaircraft. Use the inboard most reamed holes and the % inch reamed holes, being careful to hold thelamination lightly in contact with each other to prevent any particles from getting between the strips.
It is not necessary to install the splice plates now, but be certain that the shank portions of the bolts passentirely through all of the laminations, so that the full diameter of each bolt extends through the spar. All of the threads of the bolt should be visible.
The rest of the spar components are "stacked" onto the assembly. Place AN3 bolts along the length of thespar, in the appropriate holes as shown on the blueprints. You will have to select bolts of the proper length toallow tightening for this preliminary assembly. In most cases, these will not be the same length bolts used inthese holes as you assemble your wing later. Do not tighten these bolts at first.
Fit and drill the 0.063 spreader angles shown in DWG 13 (see Sect. C-C) as you pre-assemble the outboardportion of the spar. We suggest you clamp these in place being careful that the 3/16 rivet holes will fall in thecenter of the angle flange. Protect the spar with a drill bushing {any small piece of tube with a 3/16" o.d. thatwill guide a drill bit accurately) and back drill the 3/16 holes through the angles. Temporarily install bolts or clecoes to hold the angle to the spar, then drill the 1/8" rivet holes. Disassemble for de-burring before final assembly.
Insert every 5th or 6th rivet to assure best alignment of the rivet holes before clamping the assembly together with the bolts, using washers under the nuts. Be sure to use rivets of the proper length for each location. Any more than the standard "1-1/2 D" extending out of the holes is asking for trouble when driving them especially the AN470AD6 rivets. Several of the inboard spreader bars use rivets of the -1 1 length. These rivets are difficult to obtain, so -12 rivets are provided in the kit. Use a rivet cutter to cut 40 AN426AD4-12 and 1 00 AN470AD4-12 rivets to -1 1. Check that the ends are dressed off fairly square and round.
All surfaces in the spar should be well primed before assembly. This is a permanent sub-assembly that cannot practically be inspected during its service life, so more than perhaps anywhere else in the airplane, it is important to protect the parts against corrosion. The close tolerance bolt holes in the center of the spar should be cleaned with solvent after the spar is assembled. These bolts fit so closely that even a film of primer makes it very difficult to install them.
Now go ahead and install the remainder of the rivets. We find it convenient to lay riveting tape, (available in Van's Accessories Catalog) down the row of rivet heads to keep them from vibrating or falling out as we work. The tape can be peeled off of each rivet head as you come to it during the rivet driving operation.
SETTING THE RIVETS IN THE SPAR
Before you begin riveting, be especially careful that no chips or debris are lodged between the various pieces.
it is not likely you will have any serious hole alignment problems, but should you need to pass a drill through the pre-drilled rivet holes, be certain that no chips or scrapings collect between laminations. Likewise, if you force a rivet into a mis-aligned hole you may roll a burr up on the rivet which can get between laminations or under the rivet head. Clamping the lamination tightly together adjacent to the hole to be re-worked will prevent the accumulation of chips.
The small 2x or 3x rivet gun used for the rest of the airplane is not powerful enough to drive 3/16" rivets this size easily, so you must use an alternative method.
Perhaps the easiest is to rent a pneumatic rivet squeezer from Van's. The charge is nominal and the squeezer handles the big rivets easily and quietly. Unfortunately, Van's has a limited number of these expensive tools, so it may not be available exactly when you want it. See Fig. 7-3.
If you choose to use the squeezer, clamp it securely to a bench and devise a method of running the spar past it. It is easier to keep the tool stationary and move the spar. There are a couple of things to watch closely when squeezing: the protruding rivet head must be very close to the nominal 1.5d. Squeezers are very intolerant of over-long rivets and tend to "cleat" or "hobnail" them. Also, the spar and the rivet being set must be absolutely square to the plunger on the squeezer. If they are at even a slight angle, the powerful squeezer will drive them sideways, again resulting in a cleat.
The spar should be fed level through the throat of the squeezer, and held as firmly as possible while the squeezing action is applied. If the spar and squeezer are permitted to tilt with respect to each other, the shop head will buckle sideways and be unacceptable. It is also important to adjust the squeezer stops so that the shop head is not flattened excessively. The best procedure for this is to progressively decrease the gap between the setting dies until the desired head height is attained. The squeezer will have to be re-adjusted for each of the rivet lengths used in the spar.
Starting with the shorter rivets near the outer end of the spar, the builder can become proficient with the operation of the rivet squeezer or heavy duty gun before setting the longer and more difficult rivets near the root. Another alternative is find, beg or borrow a larger rivet gun. A 5x or 6x gun is about right Used in conjunction with a 5 to 7 pound bucking bar, a gun this size works easily and well. Fig. 7-4 shows a convenient way of setting the spar on the table and shooting the rivets with the gun. Although one person can drive these big rivets with a gun, it is very fatiguing and two should be used if at all possible. The pounding action of the gun may tend to separate the bars of the spar before setting the rivets. If the rivet is set so that it holds the bars apart, rather than together, it compromises the strength of the spar and repair is very difficult. Use padded C-clamps on each side of the rivet being driven to prevent the bars from being separated.
Probably the simplest method of setting spar rivets is to use a deep throat dimpling arbor with a rivet set and a two to three pound hammer. At first glance, this seems pretty crude, but it actually works quite well. Think of it as a rivet gun in slow motion. The center channel of the arbor should be reinforced below the anvil to resist the blows of the rivet set. When setting the rivets this way, be sure that the arbor is exactly square to the spar and use clamps as described with the rivet gun.
Work carefully to insure that the rivets are properly set. Drilling out long rivets is very difficult to do without damaging the spar. If an occasional rivet is mis-set, consider leaving it in place. Experience has shown usthat the damage caused by trying to drill the rivets out is often worse than leaving it in. If you have any doubts, contact Van's for assistance.
F-604 BULKHEAD ASSEMBLY
Your bulkhead has been pre-assembled in a fixture to hold dimensions and alignment as accurately as possible. The various components were then pre-drilled and dimpled to assure accurate assembly by the builder. The bulkhead pieces have been marked with "AFT", "FWD", "RA" (right aft), etc., as they came out of our drilling fixtures. It is important to match up these marks as you assemble them to keep accurate alignment in your pre-drilled bulkhead assembly.
We recommend that you prepare and prime all of the pieces of your bulkhead as the last step before riveting it together. Place the 1/4 close tolerance bolts through the matching bolt holes in the side and bottom pieces of the bulkhead for added insurance of alignment during the riveting.
The F-604E side plates are fitted in the assembly fixture at our plant so that they are accurately positioned.
When you install your bulkhead assembly in your fuselage jig, you can set the dihedral relative to your fuselage by laying a level in it. Your wing will come out with the dihedral angle set "in rig" with the fuselage as accurately as can be accomplished without jigging up the entire airplane.