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Building technique: Utilizing a Wing-Jig, Scale P-51 "Speed Wing"

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Building technique: Utilizing a Wing-Jig, Scale P-51 "Speed Wing"

Old 02-27-2015, 10:40 PM
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Iron Dog
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Default Building technique: Utilizing a Wing-Jig, Scale P-51 "Speed Wing"

Over the years that the Warbird Racer Trinity-build thread has been going on, some questions I have been asked, regarding the building methods I've incorporated in that thread, were mainly from those who have yet to use a wing jig. A couple have asked how I design and scratch-build my wings, such as those used on both my P-39 and P-51; and a found the prospect interesting and specifically asked if I would "please explain how to build wings using a wing jig."


Addressing this seems timely in that "Bulldog" just picked one of the second run (or 2nd prototype version) of my P-51 "Speed Wing" laser-cut short-kits, has never used this method, and wants to start it soon; and, two others still have my 1st-prototype wing kits won as prizes at my VALLEY OF SPEED warbird race. From the feedback I have received, so far, none of those receiving these kits have jig-built a wing before. As I will be giving three more kits away as prizes to contestants at this year's VALLEY OF SPEED II, on August 2nd at SAMs, and want everyone to have a rewarding experience with them, it would likely be helpful to explain this process sooner, rather than later.


I thought it would be better to do so on a separate thread so that these builders can more easily access the information and refer to it as an on-line construction manual, rather than have it buried within the other rather large thread; while hopefully simultaneously answering the questions for any others that want to know more about this construction method.


If you have interest in this method, please read on.


As with the composite construction methods I detailed in the Trinity-build, I am self-taught. I learned by buying a Great Planes wing jig and trying it out on my own. I liked it so much, I kept building in this manner, and have built my own style of wing jigs; but do not claim to be an expert. I merely want to support my friends’ efforts, and hope to cut their learning-curve a little by sharing the mistakes I’ve made in the past, and those techniques that have worked well for me, thus far. Feel free to ask questions or add your expertise . . . sharing and improving our knowledge and skills-sets is what this is all about!


(I realize that this thread could also be placed in the Kit-building Forum, but the subject I will be using as an example is a wing custom-designed to complement what is currently the most commonly used ARF in scale warbird racing; and, those asking me to explain this process are scale warbird racers more commonly frequenting this forum, so its placement here seems more appropriate to me.)


If you’re still with me, let’s get started!
Old 02-27-2015, 10:49 PM
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This build thread will use the Iron Dog Air Racing, Scale P-51 “Speed Wing” short-kit as an example of building using a wing jig. I want to thank Tim Stafford (of 8th-Scale Aviation) for all his help with the CAD work that made this design a reality.


Packaged Short-kit balsa and ply laser-cut pieces


Built and Solartex-covered initial prototype, built as the clipped-wing version.



"Galloping Ghost" fuse sitting on completed wing.



The next few posts will be initial setup questions primarily unique to this design. For those just curious about building with a wing-jig (not as specifically to this kit) please bear with me.
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Last edited by Iron Dog; 02-28-2015 at 01:07 AM.
Old 02-27-2015, 10:58 PM
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Iron Dog Air Racing
Scale P-51 “Speed Wing”
Assembly Guidelines

Notes to builder: This wing was designed with the intention that assembly would utilize a wing jig. There are no tabs for building on a flat surface. Assembly guidelines demonstrate use of the Great Planes wing jig, merely because it comes complete, and is likely to be the most readily available version for the average modeler.



The intent of this design was to improve scale fidelity by incorporating a truly scale wing outline/plan-form, given the length of the World Models P-51 ARF and original Great Planes P-51 kit/ARF, while introducing an airfoil design that was capable of higher racing speeds and slightly improved low-speed stability, when compared to the stock wing – especially if the stock wing was clipped.
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Old 02-27-2015, 11:19 PM
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Sample view of wing plans, left panel


Ribs laid out on wing jig.

Initial planning stages:
Make some decisions regarding which version is to be built:
  1. Scale 55 5/8” full-span at 555”[SUP]2[/SUP] wing area; or, Reno race-modified clipped-wing 50 3/8” version at 519”[SUP] 2 [/SUP]wing area (“The Galloping Ghost”, “Stiletto”, or similar)
  2. With, or without, flaps.
  • Either way, do NOT remove the servo cut-out, as the rear drill rod/carbon fiber rod must pass through the hole located near the center of the cut-out (see picture below). If flaps are used, the cut-out is removed only after sheeting the wing.
  • If scale flaps are desired, they will cut into the 1/8” birch ply wing bolt base, at the root of the wing. The ends of this bolt base would need to be shortened so that it does not extend to the scale outline of the flap; and to secure it, scrap balsa would need to be incorporated, attaching it to the top sheeting of the wing, rather than to rib W2. (Or some other preferred method for wing attachment incorporated.)
3. Are the aileron servos able to fit within the cutouts of plywood rib W7, and mount directly to this rib? Or, will larger servos be installed within the bay W7-W8, and attached to aileron hatch doors?
  • Plans show the latter method, with servo arm opening more towards the center of the control surface.
  • If the servo is to be mounted directly to the plywood rib, the hatch orientation shown on the plans will likely have to be reversed, with the opening for the servo’s output-arm oriented towards the root of the wing (and perhaps some minor repositioning of the ply hatch mounts may be necessary to better align the hatch with various servos’ output arms). Additionally, if this mounting method is chosen, it is much easier to mount the servo to the rib nowprior to construction of the wing. Taking this step now eases both the mounting of the servo, and the running of the servo wires through the wing panel.
4. Will scale dihedral be used?
Shear web W1 and the dihedral brace were designed with scale dihedral built into the wing. Some racers prefer to sacrifice the stability of scale dihedral in favor of other perceived benefits of a wing with less dihedral. (Some racers argue that a wing, so designed, “carries more speed through the turns”; but I have yet to find a study by a degreed aerodynamicist that verifies this.)
If you decide you want less dihedral, you will need to lessen the angle in both SW1s equally, and then lay them together to trace out and cut a new 1/4" thick, plywood dihedral brace.
Please note:
The dihedral brace is 1/2" less in height than the shear webs to accommodate fitting between the two 1/4" top and bottom spars. For a proper fitting dihedral brace, you will need to subtract 1/4" from both the top and bottom of the pattern. When completed the new dihedral brace would appear as if vertically centered between the shear webs. (Accompanying picture is only for illustration purposes and therefore utilizes the unmodified dihedral brace and shear webs.)
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Last edited by Iron Dog; 02-27-2015 at 11:59 PM.
Old 02-28-2015, 12:06 AM
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Make some decisions regarding strength vs. weight, cost, and preferred construction methods:


  1. Will both carbon rods be used, and glued permanently within the structure of the wing?
  2. Will the drill rod(s) that come with the wing jig be used during construction, and slid out after sheeting the wing? If so, be very careful not to get any glue on the drill rods. Otherwise, when removing the drill rod, ribs may be split/damaged when drops of hardened glue are forced through the holes that have no additional clearance for this increased mass that must pass through.
Old 02-28-2015, 12:15 AM
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Prepare parts for wing assembly:
  1. Carefully remove balsa wing ribs from sheets – especially the smaller, more fragile ribs W8 – W10. Slicing through the retaining tabs with an Exacto[SUP]®[/SUP] knife or single edge razor blade is recommended, over forcibly “punching them out.” (There may also be later benefits of saving at least one of the scrap “cut-sheet” material pieces for use as patterning templates, as may later be needed. (See “General Wing Assembly”, Step #17 as a potential example.)
  2. Similarly, cut retaining tabs in ply parts to remove these parts from the cut-sheets. Servo cut-outs in W4 and W7 intentionally have thicker retaining tabs that are harder to cut through. This is intended as a reminder to the builder so that the cut-out in W4 is not accidentally removed until after general construction and sheeting of the wing is completed – and in most cases, will be removed only if flaps are employed. (see picture below)
  3. Remove the 1/4" diameter circular material remaining within the cutouts for the rods of the wing jig to pass through. It is recommended to save the balsa circles to use as convenient spacers between the plywood Washout Jigs, as detailed in the following section.
  4. Remove balsa shear webs from sheets. Any remaining material from retaining tabs on shear webs may need to be removed with a quick swipe with sanding block – just enough to “true” the edge, without risk of altering the angles. This ensures direct wood-to-wood contact along the entire edge surface when gluing.
  5. Please note that W10a and SW9a are used exclusively for the clipped-wing version. Similarly, W10 and SW9 are used exclusively for the full-scale wing. (The appropriate wing tip blocks also come pre-cut and included for either desired version; as well as “Galloping Ghost”-style wing-tip strakes for the race-modified version – these can be sanded down for “Stiletto,” or similar racers.)

Note differences in thickness of the retaining tabs between these two cut-outs.


Shear webs removed from cut-sheets. Note that there are 3 sets: 1 for each wing panel, and a third set to be used as temporary rear rib "spacers" for quick and accurate alignment of ribs on the jig. (Saved 1/4" circular balsa material is visible, as well.)
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Last edited by Iron Dog; 02-28-2015 at 01:23 AM.
Old 02-28-2015, 01:02 AM
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Prepare the plywood Washout Cradles:
  1. Line up the two root (straight) Washout Cradle pieces, and the two tip Washout Cradle pieces (angled forward at negative 3-degrees). Each is marked “front” and “back.”
  2. Glue four ¼” diameter balsa circles fairly evenly spaced along the length of each type of the jig pieces, each with a drop of medium CA. (Do not place any in the dead-center of the cradle pieces, as the bolt and wing-nut will pass approximately through the center of the cradle.)
  3. Glue a second circle directly on top of the first.
  4. Put a drop of CA on top of the second circle and carefully, but relatively quickly align the front edges so that the assembly is “square” and the ¼” cradle cut-outs for the jig rods are properly aligned.



Note: This particular CAD-designed, laser-cut, wing short-kit comes with a matched pair of laser-cut secondary jigs (I refer to them as "cradles") that hold both rods at the correct washout angle so when built as suggested on a wing jig, there is no variance from one wing panel to another. (My goal has been to learn from every mistake I have made over the last 20 years of building, and incorporate these lessons into improving my designs towards approaching making everything relatively "idiot-proof.") The cradle at the root is level; but the one at the tip is angled, holding the rods at 3 degrees washout.

These washout cradles are potentially unique to this design. I've not seen any other kits come with them; but, it just makes sense to do it this way, so someone else has probably thought of it, too. So, when building any other wing, without custom washout jigs, one can use a scrap piece of 1/8" (or thicker) plywood as a spacer under the rear jig rod at the tip section of the wing jig. This is a quick and easy way to add a very gradual twist to the wing ribs from root to tip, and build in washout into any wing. One could use a bigger spacer, to increase the washout, as desired.
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Old 02-28-2015, 12:54 PM
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Wing Jig Set-up:
  1. This particular wing was built with the outside edge of the uprights of the aluminum jig brackets moved in 2 ¼” from each end of the two wood mounting rails (or “base” rails of the jig). This is done by drilling holes 3 1/4" in from the outside edges of the wood base rails of the jig.



The left edges of the wood mounting rails are shown with both the "standard" hole drilled 1" from the outside edge, and the 3 1/4" from the outside edge more appropriate for accommodating washout in this design's wing panels.

Notes for general building of wings (not specific to this kit):
When setting up the wing jig for a wing with no washout, the position of the aluminum brackets really doesn't matter. They can be aligned with the outer edges of the wood base rails of the jig assembly, giving plenty of room for larger/longer wing panels, longer stick sheet and stock, etc., without having to continually re-drill holes to mount the aluminum brackets. This would be accomplished by measuring in 1" from the outside edge of the base rails to drill the standard mounting hole.

However, in wings in which washout is desired, the degree of washout would diminish the longer the distance between the brackets. The brackets were moved in for construction of this wing design in order to maintain the full 3 degrees, while still giving enough room on each side of the panel to measure angles, and slightly overhang the edges of stick and sheet stock during assembly.
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Last edited by Iron Dog; 02-28-2015 at 05:55 PM.
Old 02-28-2015, 06:01 PM
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Wing Jig Set-up: (continued)

2. Square the aluminum brackets to the wood base rails, and tighten the wood screws enough to hold this orientation accurately.

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Last edited by Iron Dog; 02-28-2015 at 06:07 PM.
Old 02-28-2015, 06:32 PM
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Wing Jig Set-up: (continued)

3.
Set the plywood washout cradle assemblies on the aluminum jig brackets, at each end of the wing jig. Run the bolt through the center of each cradle and screw on the wing nut only enough to retain the bolt from falling out.
Remember that the washout is negative 3-degrees at the tip; so the trailing edge of the tip is angled up, and the leading edge is angled down.


4. Align the wing ribs in mirror images so there is one left, and one right, wing panel. Ensure that the ribs are clustered in ascending/descending order such that the root rib (W1) is at the same end as the straight cradle, and the tip rib (either W10 or W10a, depending on the version being built) is at the same end as the angled cradle.


5.
If CF rods are being used, sand a bevel into each end of the rod to eliminate burrs and ease sliding of the ribs onto the rods.



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Old 02-28-2015, 06:42 PM
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Wing Jig Set-up: (Continued)

6. With the wing ribs loosely clustered together, gently slide the carbon fiber rods (or drill rods) straight through the holes in the ribs. Be careful not to expand the diameter of the holes, or break the smaller, more fragile ribs towards the tip of the wing. I recommend applying pressure to the center of the ribs, just outside of the rods.

It was discovered that the front rod hole in rib W4 was positioned approximately 1/16” too far rearward. The purpose of building prototypes is to discover any such inaccuracies so they can be corrected so that customers are not made to suffer any “head-scratching.” I merely took a Dremel[SUP]®[/SUP] with a narrow, pointed grindstone and carefully extended the front of the hole by 1/16”.

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Old 02-28-2015, 07:52 PM
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Wing Jig Set-up: (Continued)

7. Place the jig over the plans on an appropriate warp-free building surface.

8. Place the rods in the washout cradles, ensure the rods are centered in the jig and loosely snug the wing nuts. Sight along the rods and the wood base pieces to ensure that the wing assembly will be square to the wing jig. Double-check to ensure the jig itself (aluminum brackets to the wood base rails) is still “square.”


In the first two pictures, note that the CF rods run parallel to the wood base rails of the jig, and the entire assembly remains "square." Picture 3 shows the 3-degree negative washout of the cradle at the tip.

9. Align the inside edge of the aluminum bracket of the jig with the plans. More specifically, the bracket near root rib W1 should be aligned with the center section of the wing plan.


Note that rib W1 is slid out of the way, the aluminum bracket is aligned with the wing center, and rib W2 is lined up over its position on the plans.

10. Gently slide the ribs apart. Align W2 with its location on the plans. Move W1 further away from W2 (over the aluminum jig bracket), and the other ribs to generally be just outside of their location shown on the plans.

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Last edited by Iron Dog; 02-28-2015 at 07:59 PM.
Old 02-28-2015, 09:52 PM
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General Wing Assembly:
  1. Prepare main spruce spars, labeled “Spar A” on the plans. A total of (6) 1/8” x ¼” x 36” spruce spars are needed. (2) more will be used later as rear spars, for a grand total of (8).
Sight down the length of each when purchasing to ensure they are as warp-free as possible. It is recommended that any warps or bows are “opposed” – and therefore “negated”, as much as possible. [Picture these parentheses () as bowed spars. Opposite bows can largely cancel one-another out, once glued. Spars glued bowing the same direction . . . (( . . . are more likely to introduce a warp.]

a. Cut four of them to a length of 28”. This will shorten them enough to fit within the confines of the wing jig, yet give enough extra length to serve as a “fudge factor. (If one end is more warped, remove 8” from this end.)

b. Cut two of the remaining 36” lengths in half. Glue each 18” half (opposing any potential bows) to one of four 28” full-length spar pieces. These pieces should be aligned at one edge, not centered (Example: –––––––––); and should now be free from warps and bows.



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Last edited by Iron Dog; 02-28-2015 at 09:55 PM.
Old 02-28-2015, 10:06 PM
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General Wing Assembly:

2. Perhaps the most critical single step towards assuring success in the accurate assembly of the wing is this one. The goal now is to ensure that rib W2 is absolutely square to the rest of the assembly. Rib W2 serves as the reference to which all other parts will be aligned.


a. Double-check that rib W2 is still directly above where it is drawn on the plans.

b. Set one of the laminated spruce spars (Spar A) on top of the ribs, with the shorter length on the bottom, and such that the shorter section extends between 3/8 – 1/2” beyond where rib W7 is drawn on the plans. (This will allow a similar 3/8 – 1/2” extension beyond rib W1 at the wing centerline.) Therefore the laminated 1/4 x 1/4" section runs from beyond W1 through beyond W7, and the 1/8 x 1/4" section runs from just outside W7 through W10 (or W10a).



c. From the front, insert a small carpenter’s square, or similar tool. Rest this as vertical as possible against the front jig rod and vertically align W2 to the wood base rails of the jig. Take small aluminum triangle square (or similar tool) and ensure that the length of the rib is 90-degrees to the jig rods. You can also sight the side of the rib to the reference lines on the plans. When satisfied that W2 is true, fully seat Spar A into the cutout for W2. Only seat the Spar into the other ribs partially, as you will still need to move them into position, and do not want too much friction – either making it difficult to do so, or causing you to crack a rib. Double-check that W2 is still accurately aligned. When satisfied, apply a drop of thin CA on each side of the spar and rib. If carbon fiber (CF) rods are used, apply CA to bond the rib to the CF rods.



d. Repeat procedures a through c similarly for the bottom Spar A. (Please note that the shorter length of this bottom, laminated spar will be facing up.)
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Last edited by Iron Dog; 02-28-2015 at 10:19 PM.
Old 02-28-2015, 10:54 PM
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General Wing Assembly:

3. When satisfied that W2 is secure, move rib W1 so it is seated within the top and bottom spars, but do not glue it yet.

4. Insert (shear web) SW2 against W2, centered on the spars and slide rib W3 snugly against the opposite end. Use a second SW2 as a rear spacer, and snug the rear section of the rib against this second spacer, as well. Then insert SW3 against W3, centered on the spars; and using a second SW3 as a rear spacer, snug the rib against the shear web. Repeat this process consecutively for each shear web and rib, working out towards the tip of the wing.



5. When done, fully seat both the top and bottom spars (Spar A) into each rib. To do this, make sure the rib cut-out is aligned with the spar, then gently pinch the spars together at the rib. Double check that each rib remains square – vertically to the jig base, and lengthwise to the jig rods.
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Old 02-28-2015, 11:47 PM
  #16  
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General Wing Assembly:


6. When satisfied with the accuracy of the rib orientations, and the alignment of the shear webs’ centering on the spars and the ribs, you are ready to begin applying thin CA to properly glue each joint. Please read the notes below, and steps 7 and 8, before doing so.

Additional Notes
:

  • If using CF rods that will be glued permanently, don’t forget to CA the ribs to the rod, as well, to increase the rigidity of the entire structure. If using removable drill rod, be very careful not to allow CA to accidentally wick into the hole. Otherwise, the rod will be very difficult to remove, and may potentially cause some damage upon removal. Having a couple squares of toilet paper or a paper towel handy to immediately absorb unwanted CA is recommended, prior to gluing.
  • Similarly, stray drips of CA on a CF rod in-between the ribs are essentially a non-issue if gluing them in. But, as stated earlier, would effectively enlarge the mass (diameter) of the rod that must pass through the hole when the rod is later removed – potentially damaging any ribs this extra mass must pass through.
  • The speed and accuracy of quickly laying out all the ribs and shear webs and so rapidly gluing them down is one of the great advantages of this building method. But, one can get a little carried away in the heat of the moment. Do NOT accidentally glue rib W1 at this stage.

7. If using CF rod(s), glue the front CF rod to the ribs at this time. Skip this step for any drill rod(s).

8. Back the shear web that is against the spruce spars slightly away from them, so that wicking CA will not accidentally glue them before more accurately centering them from top to bottom. Doing so with an earlier shear web may prevent the spar from properly being seated at the next rib.

9. Due to the double-tapered nature of the P-51 wing planform and the “fatter” airfoil used by the stock wing, ribs W1 and W2 are significantly “fatter” than those used throughout the rest of the wing. This causes a necessary curvature in the spar as it approaches the root ribs. Therefore, carefully pinch the top and bottom spars together at rib R3 to fully seat them, and hold while gluing. (Pinch them just outside of the rib to avoid accidentally gluing your fingers.) Often, excess CA will run down and pool at the bottom of the rib/spar joint. Have something handy to absorb/wipe away this CA immediately – otherwise, it will have to be sanded off later, resulting in additional work, and/or could result in changing the shape of the airfoil.
Excess CA pooled at bottom of airfoil absorbed by paper towel

10. Do the same at ribs W4 and W5. In fact, be prepared to hold the spars for a longer amount of time and/or use a little extra glue, as the plywood ribs are more stubborn in their absorption of the CA and seem to take longer for proper curing.


11. Continue in this manner, working out towards the tip.

12. Carefully remove the extra rear shear web spacers and glue each rib to the rear CF rod. (Assuming this rod is used, and will be left as part of the wing structure.)





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Old 03-01-2015, 12:00 AM
  #17  
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General Wing Assembly:

13. It is at this point that the dihedral-angled shear web SW1 and root rib W1 can be aligned and glued:


a. Insert both SW1 and the rear SW1 spacer so that the square (or right-angled) side of each is against rib W2. (Unlike the other spacers, due to the dihedral angle, this particular rear spacer shear web will need to be inserted vertically.) For proper dihedral it is important to note that the longest side is oriented at the bottom of the wing, and the shortest side is at the top.

b. Then slide the root rib W1 against the shear webs. Lay a straight-edge across the top of the rods to ensure that the rib is perfectly straight, with no warping, prior to gluing. (Any warps would likely cause gaps at the centerline when later gluing the wing halves together. This could affect the integrity of the glue joint.)






c. Very carefully move the straight-edge away and CA the inside (towards the W2 side only) of the rib to the front and rear CF rods (if used). Because of the complex curves in this section of the wing, you will need to gently, but firmly pinch the spruce spars to seat them in the spar cut-outs of the rib. Ensure the dihedral-gauged shear web is away from the spars, then glue spars to rib W1. When the glue is dry, with one hand, continue holding the spars in place, while the other hand slides SW1 back against the spars. Center the shear web perfectly on the spars and glue. Once this glue joint has set, you can release the spars without worry that the spar will pull away from the rib.

(Pull straight-edge away before actually gluing.)



d. Remove the rear SW1 spacer.
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Old 03-01-2015, 12:07 AM
  #18  
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General Wing Assembly:


14. One at a time, properly center the remaining shear webs and glue each to the spars and ribs. (I skip every-other-one so I can still work relatively quickly without worry that the CA will wick through from one shear web – through the rib – and accidentally glue the neighboring shear web before I have it positioned properly.) If you prefer, you can tip the jig on its side to better check the orientation of the shear webs, to ensure they truly are centered perfectly. I like to tip it so it just barely hangs over the edge of my workbench so I can look down at the front section of the wing. Just take care to ensure that the fragile trailing edges of the ribs are not damaged.



15. Glue in the 1/8 x 1/4" spruce Spar B to the top, rear section of each rib.


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Old 03-01-2015, 12:47 AM
  #19  
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General Wing Assembly:


16. Using a small razor saw, trim down much of the excess overhanging spar material extending beyond the root and tip sections of the wing. It is recommended to leave just a slight amount of material overhanging the root and tip ribs. In other words, do not attempt to cut the spars completely flush, or you may slice into the ribs and/or leave a gap in the spar material when the center sections are later glued together. (This material will be sanded flush when the panel is eventually removed from the jig.)

17. If excess glue was not appropriately wiped from the joints, or spars were not carefully seated during the gluing process, some minor sanding of the spar-to-rib joints may be necessary, prior to sheeting the wing. Be very careful during this process. Because the glue and spruce material is much harder than the thin balsa ribs, it is far too easy to accidentally sand the ribs and alter the shape of the airfoil. (I have accidentally done this, many times over the years, and will illustrate the consequences, here.)
To better avoid this situation, sand very lightly and carefully with a finer grade of sand paper. If using a sanding block, be sure to move it from front-to-back, rather than side-to-side, and try to utilize the harder plywood ribs (W4, W5, and W7) as a guide, as much as possible. In some cases, it may be better to lightly sand with a folded piece of sandpaper, instead.
If the worse happens, and you accidentally alter a rib’s shape (especially critical with rib W2, which needs to match the wing saddle of the fuse), remember you have a back-up copy of the pattern of each rib from the original laser-cut sheets. A small section with the original airfoil shape can be traced and/or cut out using the original rib pattern from one of these cut-sheets, and this small “repair piece” can then be glued to an inside edge of the altered rib – thus restoring the airfoil’s proper shape.

An example of airfoil's shape being altered due to "less than careful" sanding at the spar.


Use saved cut-sheet to trace/cut section from scrap balsa. Remaining tab from spar cut-out is a handy reference.
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Old 03-05-2015, 04:53 PM
  #20  
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Sheeting the Top of the Wing:
If you wish to order 30” length pieces, you may do so. This assembly guide will assume that the more easily obtainable 36” sheet materials are being used.


1. For each panel, cut two 3/32” x 4” x 36” sheets somewhat diagonally, leaving 3 9/16” on one side and 1 7/16” on the other side. This piece will become the top trailing edge sheet. (Set the leftover angled 2 9/16” x 7/16” piece aside.)

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Old 03-05-2015, 05:09 PM
  #21  
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Sheeting the Top of the Wing:


2. Trim each end so the sheeting still slightly overhangs the root and tip ribs by at least 1/8”. (You might want to give yourself a little extra material as a “fudge factor.”)


3. Measure and mark 5/8” up across each end of the trailing edge of the piece, and using a long straightedge, draw a line. Use a sanding bar, held at a slight angle to the edge of the sheeting, taper (or bevel) this 5/8” section of the sheeting at the trailing edge, as shown in Figure 1:1 on the plan sheet. With each top and bottom piece beveled in this manner, the sheets can later be glued together to a relatively sharp edge without causing under-camber or similar deviations from the fidelity of the shape of the airfoil.

Left edge is tapered, beginning 5/8" ahead of trailing edge to a sharp point at the trailing edge.


Above picture did not focus well enough to show appropriate detail, so another picture is shown. Pictured is the bottom trailing edge sheet, tapered in the same way. (If you are noticing the background, please note that at this stage in the directions, the top sheet has not actually been glued down, yet.)
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Old 03-05-2015, 05:13 PM
  #22  
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Sheeting the Top of the Wing:

4. Draw a centerline down the middle of Spar B and add a bead of thick CA on the half towards the trailing edge. Align the front edge of the top trailing edge sheeting and gently hold it in place until the CA sets. Do not press down on the top, or a warp in the trailing edge could be induced. Simply pinch the sheeting and the spar together and hold momentarily. If a denser balsa sheet is used, clothespins could be utilized without damaging the sheeting; otherwise scrap wood sheet or stick material could be used to protect softer balsa sheet material from being dented by the clothespins, if desired.
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Old 03-05-2015, 06:24 PM
  #23  
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Sheeting the Top of the Wing:

5. Turn the entire wing jig – with the wing assembly still attached – upside-down and wick thin CA to glue this piece of sheeting to the rear section of each rib.
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Old 03-05-2015, 10:22 PM
  #24  
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Sheeting the Top of the Wing:

6. Set a piece of 3/32” x 6” x 36” sheet on top of the wing panel, directly in front of the rear sheeting piece you just glued down, with just a slight amount of overhang beyond the tip rib, and most of the extra sheet extending well beyond the root rib. Center the leading edge of the sheeting at the very center (or “midline”) of Spar A, and mark the point that this sheeting meets the rear sheeting at the tip of the wing panel. Measure and mark 25” towards the opposite end.* Line up your straight-edge diagonally from your mark at the tip, such that the straight-edge runs off the other edge of the sheeting at the 25” mark, leaving the full 6” at this end. In other words, once the overhanging 11” x 6”* piece is eventually removed, you will have a mid-wing sheeting piece that measures 6” at the root, and between 2 3/4 - 2 7/8”* at the tip. The grain should be oriented at a 90-degree angle to the wing centerline, running straight out to the tip; and should span the distance from the mid-line of Spar B up to the mid-line of Spar A across the length of the panel. When satisfied the fit and alignment will be correct, use your Exacto[SUP]®[/SUP] knife to make the diagonal cut. Once cut, place the angled sheeting piece in-position and remove the 11”x 6” rectangular overhang at the root with a razor saw. (* Please note that these dimensions are for the clipped-wing version being modeled and shown in the pictures. The piece needed for the full-span version will likely be 27 1/4” long and approximately 2 5/8” in chord at the tip, with only about an 8 3/4” x 6” rectangular shaped overhang at the root.) Spray the back side of this wing center sheeting with CA Accelerator if desired, apply medium CA to the rear edge of Spar A, the front edge of Spar B and the top of the rib sections in-between. Carefully align this sheeting piece (ensuring a slight overhang at both the root and tip) so that it is flush against the rear sheeting and gently press it in place, from the rear forward, until the glue is set. As much as possible, pinch the sheeting together at the spars or otherwise support the structure from underneath to avoid inducing a warp.

At the tip rib, mark the cut line where the center sheeting meets the rear sheeting (at the centerline of rear Spar B).


The mark at 25" is long enough to meet the edge of the rear sheeting, also overhanging slightly beyond the root rib.


I'm not "a lefty"; would never try to make my cut without holding the knife perfectly vertical, and firmly holding the straightedge in-place; etc. Picture for illustration purposes only.


Center sheeting glued in-place.
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Last edited by Iron Dog; 03-05-2015 at 10:24 PM.
Old 03-09-2015, 07:52 PM
  #25  
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Sheeting the Top of the Wing:

7. When finishing the forward section, I foresee different builders having different preferences, but I would like to share some previous experience to consider before you start. When I built the very first prototype, I glued the 1/8" by 1" leading edge doubler to the leading edge before sheeting and beveled the doubler to the contour of the ribs, prior to sheeting. I then used one long, wide 3/32" sheet in one piece to sheet the remaining forward section of the wing, because I wanted the extra rigidity from having that sheet run the full span of the wing. I was not happy with the result. This final sheeting piece had to be forced to take too many compound curves, and even with relief cuts and wetting it down, it still resisted conforming well enough. Pressing so forcefully onto the wing jig to try to keep the tension from popping the sheeting off of the ribs while the glue set was not exactly conducive to keeping the entire assembly straight and true. Because of the strength of using both carbon fiber spars and the three spruce spars running the full span of the wing, I realize the relatively minute amount of extra strength from the sheeting is not worth the trouble, so I decided to try a different approach this time – and am pleased with the results. If you are leaving in the CF rods, the following steps (A - G) would be my recommendation:


Jumping ahead in the construction a little, this view gives an idea of the complex curvature that the front sheeting must conform to as it progresses from the extra-tapered root section. It is caused by the substantially elongated and therefore much larger root ribs, compounded by the thicker airfoil used by these root ribs of the stock World Model and Great Planes wings, which must be used to fit the saddle of stock fuses without having to build a crutch system (ribs W1 and W2 are visible on left), as it progresses to the thinner airfoil and more"normal" length standard taper section (ribs W3 and W4 are visible to the right). This complex curvature makes gluing a wide, one-piece sheet across the full length of the panel, without unintentionally causing a warp or bow, a very challenging undertaking.)
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Last edited by Iron Dog; 03-09-2015 at 09:31 PM.
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