Subsections

• 5.1 Dihedral braces
• 5.2 Wing bolt blocks
  • 5.2.1 Leading block
  • 5.2.2 Trailing block
  
  
• 5.3 Main wing construction
  • 5.3.1 Ribs to TE, spars and bottom sheeting
  • 5.3.2 Frontal webbing
  
  
• 5.4 Shaping wing trailing edges
• 5.5 Assembling two wing halves with dihedral brace
• 5.6 Adding half ribs and leading wing mount block
  • 5.6.1 First set of half ribs
  • 5.6.2 Leading wing bolt block
  • 5.6.3 Second set of half ribs
  
  
• 5.7 Adding top D box sheeting
• 5.8 Adding rear webbing
• 5.9 Adding Leading edge
• 5.10 Adding Wingtips
• 5.11 Adding wing gussets
• 5.12 Dihedral brace center sheeting and finishing
• 5.13 Applying Carbon Fiber tow to the wings
• 5.14 Drilling wing bolt holes
  • 5.14.1 Leading side wing bolt
  • 5.14.2 Trailing side wing bolt
  
  
• 5.15 Drilling fuselage wing bolt holes
  • 5.15.1 Primary hole in crossbeam F6
  • 5.15.2 Secondary hole in located in crossbeam F7
  
  
• 5.16 Finishing
  • 5.16.1 Shaping the leading edge

5. Wing

So much of the flight performance and longevity of the QFII DLG depends on a quality wing build. An incorrectly built wing can still fly but the level of performance will be reduced due to higher drag. A weakly built wing will not cope with the launch stresses of a strong launch.

5.1 Dihedral braces

Nearly all the forces that want to tear apart your wing will be focused down onto the dihedral brace, consequently the QFII has an over engineered brace which may appear to be bulky compared to other kits that you may have built. There are two main braces, each of noticeably different size.

• Obtain a 3.2mm and 2.4mm brace piece, they should overlay each other perfectly
• If you want to be extra sure about the strength you can apply a length of CF tow between the two pieces when they are glued together

• For gluing it is recommended that you use epoxy thinned down with some methylated spirits (denatured alcohol) in a 1:1:1 ratio (1 part of resin, 1 part of alcohol, 1 part of metho)
• Apply the thinned epoxy mix to one side of the dihedral brace. If you are adding CF tow then make sure that the CF is spread evenly and that there are no knots or lumps

• Clamp together the dihedral brace sandwich, don't worry if some CF tow protrudes from the assembly, this can be trimmed off later.

• Set assembly aside to cure. If you used thinned epoxy it will appear to be of rubbery consistency for a while and possibly even bubble a little. Due to the thinning it may not cure as quickly as the original epoxy (ie, 5 mins), again do not worry, give it a few hours.
• Repeat this process for the second dihedral brace.

5.2 Wing bolt blocks

The wing bolt blocks hold provide a secure area through which the 4mm nylon wing bolts will pass to bolt into the fuselage wing mount crossbeams.

5.2.1 Leading block

• Take the four pieces of 30 x 20 x 3.2mm balsa and glue together with white glue to form a block 30 x 20 x 12.8mm in size
• Clam and set aside

5.2.2 Trailing block

• Locate the two pieces of 30 x 58 x 3.2mm balsa, you will note that the grain orientation differs.
• Glue both pieces together with white glue to form a 30 x 58 x 6.4mm block

• Clamp and set aside

5.3 Main wing construction

It is important that your building surface is flat and clean. An uneven building surface will translate to a wing that is difficult to get straight afterwards. The wings are built in two halves which are later assembled together using the dihedral braces and wing mount blocks.

5.3.1 Ribs to TE, spars and bottom sheeting

• We use a building surface made from 3/4'' building ply laminated with 3~4mm cork. The plywood keeps flat even in varying humidity (so long as it is stored flat) and the cork provides sufficient grip for pins to be held securely.

• Lay the wing plan down on the cork. We like to use a copy of the wing plan that is disposable so that if glue gets on the plan or if it's torn we can simply throw it away.

• Start by dry pinning the two parts of the trailing edge (3.2mm) along the plan. Do not glue. Avoid putting pins through the wood, rather rely on adding pins all round forcing the wood to have no room for movement. Pinning through wood is not recommended because it crushes and creates weakness.
• Prepare the bottom D box sheeting by trimming it to a length between the final tip rib (R7) and center line of the wing plan.

• Trim away a portion of the bottom D box sheeting so that the dihedral braces and wing mount block can fit in when the two wing halves are finally assembled.

• To prevent the bottom sheeting sliding out of location while setting up the rest of the wing, you can chock it with a piece of scrap balsa and a couple of pins. The reason we use a piece of scrap balsa is to prevent the pins from crushing through the end grain of the bottom sheeting.

• The 10 x 2.4mm top and bottom spars must but cut to reach from the extreme tip of the wing to the center line of the wing, this means that the spars will protrude beyond the end of the final tip rib. We require this extension as it will hold the wing tips in and provide an unbroken link to the wing for inserting the launch peg.
• Insert one of the main wing ribs midway along the wing into the trailing edge slots by sliding it in horizontally ( do not attempt to push the rib end down into the TE slot as it will most likely snap). Do not glue. We do this so that we have a reference for where to locate the bottom sheeting and spar.
• Setup the 10mm x 2.4mm bottom spar and 50mm wide bottom 1.5mm sheeting to align with the inserted rib. Do not glue.

• Dry fit the remaining ribs to the wing (note how we have not yet glued anything).

• Check the following
  • Spar extends beyond R7 and slightly beyond the end of the wingtip
  • D box sheeting extends only to R7
  • D box sheeting has been trimmed away to allow for the leading wing mount block
  • D box sheeting and bottom spar are butted hard up against the rear of the ribs
  • Trailing edge is firmly pinned
• Commence gluing down the ribs with CA
  • Glue the ribs to the spar and D box sheeting, you may need to insert a piece of scrap 1.5mm balsa ad the leading edge (LE) of the ribs under the sheeting to make it meet with the rib.
  • Do not glue the spar to the D box sheeting between the spars, this will be done later when we add the shear webbing.
  • Glue the ribs at the trailing edge
  • To make alignment easier, you may want to make up some vertical alignment blocks with a 1.5mm slot. Use these to setup the rib as you glue it.

• Apply top spar, if the spar is not quite wide enough, make sure spar is aligned with the rear of the rib notch. This cannot be emphasised enough. If the spar is not flush against the rear of the notch then the dihedral assembly will not align correctly, subsequently causing potential twists in the wing later.
• Glue top spar to ribs

5.3.2 Frontal webbing

The use of webbing between the spars greatly enhances the stiffness of the wing. Without the webbing the wings will be inclined to bend and twist during launch causing spar compression which is often fatal.

• Note that with the laser cut kit from LaserArts, all the webbing is numbered. For each rib bay there will be four (4) pieces of webbing each (except for '1' which has quite a few more), one pair per wing half. The narrower pair of the four webbing's is intended for the leading side of the spar, this is what we will be using.
• There is a slight taper on the webbing for bays two (2) through to seven (7), it is important that you determine which way this taper is so that you orientate the webbing accordingly. The left hand wing will have the numbers facing towards the leading edge (the right hand wing will have the numbers facing towards the trailing edge).
• Insert the webbing between the ribs and apply a liberal amount of CA between the bottom D box sheeting and the webbing, this will allow for enough CA to wick behind the webbing and get between the 2.4mm spar and the D box sheeting (the area that we deliberately did not glue down when gluing the ribs).
• Do not yet install the rear webbing's, this will not be done until after the top sheeting is installed (much later)

• Repeat for the other wing, ensure that you build a mirror image wing, rather than two lefts or two rights, again this is something we have done in the past, it's really not fun, seriously.

5.4 Shaping wing trailing edges

The trailing edges as supplied in the kit are 3.2mm thick, these need to be shaped down using a balsa plane and/or sanding bar to provide the idea airfoil shape in the wing.

• You need to aim to get the TE down to a thickness of no more than 1mm. The thinner you can reliably get the TE the better your wing will perform because of the lesser losses from drag.
• Be very careful while you are planing/sanding down the TE that you do not pass the stresses into the ribs else they will possibly break off at the spar or the TE. The TE should be firmly secured to the bench either via clamp or other methods.
• Do not rush this stage, a simple slip could break a lot of your hard work.
• In order to assist preventing the planer or sanding bar from going too far, it's recommended that you temporarily attach some 0.6mm or 0.8mm wire to the edge of the TE, this stops the planer or sanding bar from going too far.
• Once the shaping is complete it's recommended that the fine edge is hardened by applying CA to it. A light sanding after the CA has cured is required to remove any small bubbling or such.

5.5 Assembling two wing halves with dihedral brace

• Take both cured sandwiched dihedral braces and mark their center lines on both sides

• Place the leading dihedral brace (with the narrower arms) in front of the spars, butted hard against the first rib and clamp
• Cut away the excess spars so that they now meet up with the center line on the dihedral brace
• Remove the clamp and dihedral brace
• Obtain two lengths of scrap 10 x 2.4mm spar off cut and insert between the two existing spars, this is done to help prevent the brace/spar join from collapsing under high loads

• Trim inserted lengths of spar off to match the lengths of the existing spars (which have been cut to length for the center of the dihedral).

• Obtain the larger dihedral brace (rear) and glue and clamp it to the rear of the spars
  • Make sure the brace is butted against the first rib
  • Make sure the brace is lying flat with the bottom sheeting (you will need to rest the brace over the edge of the workbench/board because of the extension under the brace).
  • Use epoxy, Weldbond, PU or other glue with very high lap shear strength

• Obtain the remaining dihedral brace (frontal), glue and clamp it to the front of the spars
  • Make sure the base of the brace is parallel to the base of the previously glued rear brace.
  • Make sure the center lines marked on the dihedral brace align

• Obtain and glue a single 30 x 15 x 3.2mm brace doubler and glue it to the rear dihedral brace. This is a spacer used to add yet more strength to the dihedral join and distribute the load.

• Obtain the 30 x 58mm rear wing mount block that we glued and clamped previously
• Glue this block to the brace doubler that was glued to the rear dihedral brace
  • Make sure that both ends of the block are flat and smooth to maximise adhesion surface area
  • Make sure that the wing mount block is flat and level
  • Make sure that the wing is lifted up at the correct angle (11 degrees or 112mm at R7)

• Obtain the trailing edge dihedral brace
• Glue the brace to the rear wing mount block
  • Make sure that the wing mount block and the brace are sitting flat and aligned
  • Do not yet glue the trailing edge to the brace

• Obtain the second wing half and prepare to join it to the first
• Trim the second wing spars to the center line of the dihedral brace as with the previous wing
• Fill the gap between the two spars as with the previous wing
• Trim the trailing edge to meet at the center line of the dihedral brace
• You will need to apply the glue for the two main braces before inserting the spars (highly recommended you use a slow setting glue for this operation as you will need to spend some time setting the wing up to be perfectly aligned.
• Setup both wing halves to be raised 112mm (11 degrees) at R7.
• Place flat blocks under the each wing at an arbitrary location to support the wing and keep the incidence of each wing the same. This is an important step, if the incidence of the wing halves differ it will cause the plane to roll. By placing a flat block for the spar and TE to rest on we are forcing the incidence to be constant on each side.
  • Check and double check the R7 tip height measurements
  • Check that the newly glued brace/spar is clamped and cannot drift out while setting
  • Check that the rear wing mount block is lying horizontally along the building surface (it may lift up a little from front to back, this is due to the built in incidence of the dihedral brace set)

• When the dihedral brace bond is dry you can proceed to glue the trailing edges to the TE dihedral brace (ideally they will already be well lined up with the brace).

5.6 Adding half ribs and leading wing mount block

Once the dihedral brace has been glued and the wing has formed one piece, we need to add in the half-ribs that will go in the region between the last full rib (that our dihedral braces are butted against) and the center.

5.6.1 First set of half ribs

• Obtain four specially laser marked ribs (they will have four additional vertical score marks near the spar notches)
• Cut the rib at the rear-most vertical score mark
• Cut the rib at the forward-most vertical score mark
• Discard the center section (containing the spar notches)
• Check for fit, trim the trailing edge of the rib as required
• Glue the half ribs in 50mm from the first full rib

• Repeat for both sides

5.6.2 Leading wing bolt block

• Obtain the 30x20x17.8mm block we created previously (Seesub:Leading-block)
• Glue block directly to the leading dihedral brace using Epoxy, Weldbond or other high lap shear glue
  • Make sure that the wings are resting level
  • The block should sit neatly between the two bottom sheets and be aligned with the center of the dihedral braces
  • Make sure that the rear wing mount block is lying flat, you should be able to make the wing move to the correct alignment simply by pressing down on the rear wing mount block to make it sit flat on the building board
  • To prevent gluing the wing to your building board, place a sheet of paper underneath the dihedral brace

5.6.3 Second set of half ribs

The second set of half ribs are prepared the same way as the first set

• Align the second set of ribs directly against the dihedral / wing mount blocks
• For the rear half of the ribs, align the ribs with the top of the dihedral brace (not the floor)

5.7 Adding top D box sheeting

• Place top D box sheeting butted against the rear spar notch of the ribs
• Check that the D box sheeting extends from the inner set of half ribs completely to tip rib R7
• If you wish to use CA to bond the top sheeting...
  • Tack down the D box sheeting onto the spar. Do not completely glue as we will do this when adding the rear webbing later.
  • Hold the wing with the ribs vertically orientated, LE facing up
  • Working from the dihedral brace out to the tips, grip the D box sheeting and press over each rib and dropping 2 ~ 3 drops of CA into the rib / D box join, the CA will run down this join and set within 5 ~ 10 seconds, repeat for all ribs. This is why we have not as yet applied the leading edge, else we would have no way of dropping in the CA.
• If you wish to use White glue to bond the top sheeting...
  • Apply white glue along the spar and all the ribs
  • Apply D box sheeting and hold down using sand bags or other method to ensure an even distribution of weight
  • Leave for several hours to cure

• Repeat for other half of the wing

5.8 Adding rear webbing

As with the leading side webbing, the rear spar webbing can now be applied using CA, again note that all the numbers on the webbing will be orientated the same way for each wing half, that is, on the left hand wing the numbers will face towards the LE, on the right hand wing they numbers face towards the TE.

5.9 Adding Leading edge

If all previous components of the assembly are aligned and correctly sized, the leading edge should apply with ease.

• Obtain 6mm square LE stock
• Place LE stock along the notches in the LE of the wing
  • The LE stock should rest at approximately 45 degrees
  • The LE stock should extend the same length as the D box sheeting (it can over extend but we will be trimming it back later)
  • The LE should be straight
• Glue down LE by either applying white glue into the notches before applying the LE stock or wicking CA after applying the LE stock.

• Repeat for other wing

5.10 Adding Wingtips

Each wingtip requires three precut components of 1.5mm.

• Insert the main wingtip between the two protruding spars from R7. It is quite likely that the fit will be tight, insert slowly
• Align the wingtip with the wing trailing edge
• Using 10 x 2.4mm spar offcuts, add support braces on either side of the main spar on both top and bottom sides of the wingtip

• Add wingtip doubler pieces to the underside of the wingtip

• Trim off excess 10x2.4mm doublers

5.11 Adding wing gussets

Gussets are small triangular pieces of wood which are used to spread load between two intersecting pieces of assembly.

• Glue gusset between the TE and the first full rib from the center of the wing

• Glue gusset between the TE and the last full length rib (R1's) before the start of the tapering tips

• Repeat for both sides of the wing

5.12 Dihedral brace center sheeting and finishing

• Glue a 30 x 15 x 3.2mm block 12mm forward of the TE dihedral brace.
  • This block provides extra support for the wing bolt.
  • The block should fit neatly and reach to both half ribs which were previously glued to the rear wing mount block.
• Apply 1.5mm sheeting from the TE dihedral brace through to the leading edge of the D box top sheeting.

• Trim the LE stock back to the inner most half ribs

• Insert a short length of LE 6mm square stock between the two half ribs

• Your wing should now appear similar to this

5.13 Applying Carbon Fiber tow to the wings

Carbon fiber has a very high tensile strength, meaning that it can endure a lot of pulling forces. To help prevent the wing from bending and flexing during launch we apply a strip of CF to both sides of the wing. With CF on both sides the wing can neither flex up nor down.

The exact method used to bond the CF to the D box sheeting will vary depending both on your preferred glue (CA or thinned epoxy) or the type of CF you're using (ie, Iron on CF tow will not require gluing). The process described here is for CF tow (12,000 strand) applied with CA.

• Sand down the D box sheeting with 150~300 grit paper to provide a smooth surface on which the CF can bond to
• Cut a length of CF tow extending from the dihedral center sheeting to the tip rib R7

• Flatten out and groom the CF tow until it is approximately 10~12mm wide, we need to get the CF tow this wide so that it remains as flat as possible against the D-box sheeting

• Weigh down the wing so that it cannot move about while setting the CF to the wing
• Tack down the tow at the wing center, ensure that it has cured sufficiently before proceeding.
• Grip the end of the tow (near the wing tip) and apply moderate tension to it keeping the tow both tight and flat. Keep the tow flattened against the D box sheeting
• Starting from the center, working in small 40~50mm lengths, apply several drops of fast CA to the CF tow, it will tend to pool at first and then commence to wick along the CF. Don't panic about the CA curing, because there is a lot of CA it will tend to stay wet for at least 10~20 seconds, more than enough time to do what is required
• Take a piece of scrap balsa with a straight edge (ie, a spar offcut) and smooth the CA along the CF towards the tip of the wing.
• Do try to smooth out the CA with too much pressure, we do require a reasonable amount of CA to be present in the CF to ensure it makes a good bond. If we apply too much pressure it will make the CF go 'dry'.
  • As you do this you will possibly notice that the CA begins to literally smoke, this is normal.
  • Never draw the smoothing in the opposite direction, if you do this the CF will lift up and create a dreadful mess
  • The CF should look shiny and flat
• Keep progressing until you reach the wing tip
• Give your completed strip several minutes to fully dry
• Do not touch the strip of CF, if you do there will be white fingerprints left after a few minutes.
• Repeat for both sides of the wing and both wings (4 strips in total)

• Check that the wing's LE is straight by placing the wing LE down onto a flat surface. The wing should sit very flat to the surface.

5.14 Drilling wing bolt holes

Setting the bolt holes can be a rather fiddly exercise as it's somewhat difficult to accurately align everything even with good workshop tools.

5.14.1 Leading side wing bolt

• Turn the wing upside down
• Support the wing from underneath with a narrow block (will need to be at least 112mm high)
• Drill a 1.5mm pilot hole 10mm ahead of the leading dihedral brace (the one contained by the D box sheeting) and 15mm in from the side of the wing bolt block

• Ensure that the drill bit is kept upright and that the wing is level during the drill process
• Drill out the pilot hole to the size required for the wing bolt (ie, 4mm)

5.14.2 Trailing side wing bolt

• Drill a 1.5mm pilot hole 20mm in front of the edge of the TE dihedral brace and 15mm from the side. This hole should pass directly through the additional 30x15x3.2mm block we added prior to covering the center section with sheeting (see ite:30x15x3.2mm TE Block).
• Ensure that the drill bit is kept upright and that the wing is level during the drill process
• Drill out the pilot hole to the size required for the wing bolt (ie, 4mm)

• Test fit the wing bolts in the holes
• Trim away the top 1.5mm sheeting to allow the heads of the bolts to recede beneath the sheeting and rest on the wing blocks
• Pin and CA around the bolt holes on both sides of the bolt blocks (you should be able to reach the blocks from above through the enlarged hole used to accommodate the bolt head). This process will make the balsa become a lot harder and resistant to crushing if the bolts slip a little
• Wait 5 to 10 minutes and drill the holes again to clear out any excess CA that may have built up from the pinning/CA.

5.15 Drilling fuselage wing bolt holes

It's important that the axis wing rests at exactly 90 degrees relative to the axis of the fuselage. If this isn't done then there will be varying strange flight characteristics which will prove hard if not nearly impossible to eliminate. Take your time with this stage, prepare to check and triple check everything. Drilling of the first hole is not as critical as the second hole since it will be the second hole that will commit the alignment.

5.15.1 Primary hole in crossbeam F6

• Insert the two fuselage crossbeam blocks that were made up earlier into the fuselage into the notches of F6 and F7.
• Mark on the blocks which one is which and mark the forward direction on each (orientation will matter once the holes are drilled)
• If the blocks do not sit flush with the sides of the fuselage and the formers then plane or sand down until flush, take care not to induce any 'rounding' of the surface.
• Hold down the fuselage onto the bench surface and make it as secure as possible
• Place the wing onto the wing saddle area
• Align the leading wing bolt block of the wing with the crossbeam of the fuselage in F6
• Place a pair of moderate sized solid cube of wood or metal with known good angles (ie, 90 degrees) on either side of the fuselage butted up against the LE of the wing. This sets up the wing to be aligned
• Check again that the wing leading bolt block is aligned with the crossbeam in F6
• With the drill bit you used for the holes in the wing, by hand insert into the leading wing bolt hole and turn several times to mark the crossbeam block while keeping pressure on the wing/fuselage to prevent the alignment from changing.
• Remove the wing away from the fuselage
• Remove the wing crossbeam from F6 and drill out at the mark indicated by the hand-turned drill bit
• Insert a blind nut or glue a nut on the underside of the crossbeam
  • Use the wing by putting the bolt through the wing and adding the crossbeam while tightening the bolt if required to pull in the blind nut or align the nut while being glued.
• The fuselage wing bolt holes will be completed later after the radio installation is completed

5.15.2 Secondary hole in located in crossbeam F7

The secondary hole is the one which needs to be done as accurately as possible to ensure the good alignment between the wing and the fuselage

• Reinsert the crossbeam for F6
• Reapply the wing
• Lightly bolt the wing down in the primary hole in F6 (don't do this bolt too tight else it may cause the wing to lift at the TE)
• Set up the wing and fuselage alignment again using the two cube blocks
• Measure the distance from the TE tip of R7 to the start of the horizontal stabilizer pylon standoff
• Do this for both sides of the wing, the distance should be equal
• Adjust the alignment of the wing until both distances are equal
• Now with great care, use the drill bit for the bolt hole through the existing hole in the wing and drill through the F7 crossbeam
• Take great care that you do not disturb the alignment
• Take great care that you do not drill excessively far and damage the CF boom
• If you wish to be extra safe, drill through only the first couple of mm and then remove the wing and cross beam, drilling the crossbeam separately.
• Once the hole is drilled through the F7 cross beam insert the blind nut or glue a nut to the underside.

5.16 Finishing

5.16.1 Shaping the leading edge

Use a balsa plane and sanding bar to shape the leading edge. It's suggested that you cut out a small template of the LE shape for the main wing section and use it as your guide for how to shape. The more accurately you can render the LE to the required shape the better your wing efficiency will be.