Flat Foamie Series

40" EPP Yak55 XL Build Instructions

This version dated June 14, 2021
The Latest Version is Available Online at http://www.racores.com/FlatFoamieEPPXLInstructions.html (click on the pictures to expand) We suggest that you read through the instructions once before starting building to become familiar with the sequence of steps and the flow of construction.

Do not remove the parts from the sheets before instructed. Some steps are done with the parts in the sheets.

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Items required to build the plane:
A Hobby Knife and replacement blades or Snap Knife
A cork backed metal ruler, 18" recommended
CA Glue (regular or foam safe) and kicker
EPP Contact Glue (UHU por, Beacon Foam-Tac or Welders)
A piece of fine sandpaper to roughen the pushrod pieces for gluing
Velcro for attaching the ESC, Rx and battery.
Optional: four .032" EZ-Connectors for your pushrod attachments
Kit contents as it comes out of the box

Remove this page from the instructions and refer to the diagrams on the back (Page 2) to locate the parts as you build.

Kit Contents as it comes out of the box.

  1. Please note, the ordering of these steps is such that subassemblies will dry while you do the following steps in preparation for their use. Do not remove the parts from the sheets before instructed. Some steps are done with the parts in the sheets.

  2. Remove the front wing KF bottom pieces (D1 and D2) from the sheet and glue them at the center with Foam-Tac and set aside to dry.

  3. Leaving the parts in sheet F, glue the 333mm piece of flat carbon fiber into the slot in the elevator (F1) with Foam-Tac and set aside to dry.

  4. Find the ailerons (C2 and E2) and remove them from the sheets leaving the other parts in the sheets. Remove the L shaped scrap foam piece from the aileron position against the rear wing pieces (C3 and E3). Bevel this edge of the rear wing pieces (C3 and E3) from the bottom using a new sharp blade and the cork-backed ruler supported by the surrounding foam (C1 and E1). Bevel the corresponding edge of the ailerons (C2 and E2). With the bevels cut, remove parts (C3 and E3) from the sheet. Using a fine bead of Foam-Tac, hinge the ailerons to the rear of the wing. Use less glue for the hinge than you think you need as it will stiffen over the first 24 hours. You can always smear additional glue on the hinge at a later point. Repeat for the second wing half.

  5. Glue the two wing halves (C2+C3 E2+E3) together at the center section and set aside to dry.

  6. Remove the front wing KF top pieces (C1 and E1) from the sheets and glue them together at the center and set aside to dry.

  7. Making sure the center joint is dry, glue the 750mm piece of flat carbon fiber into the slot in the front wing KF bottom pieces (D1 and D2) subassembly and set aside to dry.

  8. Remove the Fuselage Top Front (A3) and Rear (A2) parts and glue them together. The joints are asymmetrical and the pieces need to flip over so they match each other. Do the same with the Fuselage Bottom Front (A1) and Rear (B2) and set aside to dry. Note: do not discard the 4 quarter round gussets (A4) from the remaining Sheet A foam.

  9. From Sheet F, remove the 4 fuselage jig pieces (F4), the horizontal fuselage rear (F2) and the Stabilizer (F3). Leave the trapezoidal scrap piece of foam attached to the rear of the Elevator (F1). Removing the scrap foam from the front of the Elevator (F1) and using the trapezoidal scrap of foam as a resting point for the cork backed ruler, bevel the elevator hinge on the bottom (the spar should make this process easier).

  10. Bevel the rear edge of the Stabilizer (F3) and hinge with the Elevator (F1) using a fine bead of Foam-Tac. You can now remove the trapezoidal foam piece from the rear of the Elevator (F1). Glue the small end of the horizontal fuselage rear (F2) to the tab on the front of the Stabilizer (F3), making sure the paint side is correct and set aside to dry.

  11. Find the plywood sheet with the 40" XL Leading Edge Jig on it and carefully pop the pieces loose. Press the legs into the slots so they are all facing the same way and flush with the bottom. The leading edge foam will rest on this in the following steps.

  12. Place the rear of the wing subassembly (parts C2, C3, E2 and E3) on your build surface. Take the front wing KF top subassembly (C1 and E1) and place it on top of the rear subassembly so that it overlaps and hides the rib notches in it. Spreading glue on the front top area of the rear of the wing subassembly (parts C2, C3, E2 and E3) between the rib notches, reposition the front wing KF top subassembly (C1 and E1) on the glue. Align the paint and the wingtips. Use the 4.5mm leading edge jig to hold the leading edge up off the build surface and let dry.

  13. Remove the five triangular wing ribs (B4) from Sheet B.

  14. With the glue dry, flip the wing assembly over on the build surface and using the 9mm fuselage jigs (F4), support the rear portion of the wing and ailerons subassembly off the build surface. Use the 4.5mm leading edge jig to hold the leading edge up off the build surface. Glue the five wing ribs (B4) into the notches and onto the inside of the front wing KF top (C1 and E1), paying attention that the longest one goes in the center and the two shortest ones near the wingtips.

  15. Spread glue on the inner surface of the wing assembly from the above step along the leading edge, across the top of the ribs, and across the front of the wing rear pieces and put the front wing KF bottom pieces (D1 and D2) subassembly with the carbon spar in it on the glue and align the leading edge, wing tips and paint at the rear edge and let dry. Press the piece into the glue a few times over the first few minutes. This subassembly needs to dry well for the following steps.

  16. Remove the horizontal fuselage nose (B1) from Sheet B and with the paint side down (the top of the plane is currently against the building board) glue it to the tab on the front of the wing assembly. Supporting the nose with the 6mm fuselage nose jig (G2), align the wing leading edge top/bottom seam in the center of this piece and let dry. Note: the leading edge of the wing is 18mm thick and this nose piece is 15mm so there will be a slight step. 1.5mm of this step should be on each side of the wing so that the center line of the nose (B1) matches the center line of the wing assembly.

  17. Using the four 9mm fuselage jigs (F4), glue the Stabilizer/Elevator subassembly (F1, F2 and F3) to the notch in the rear of the wing assembly. Support the pieces with the 9mm fuselage jigs (F4). You now have the complete horizontal outline of the plane assembled.

  18. With the Rudder (B3) on the table with the top counterbalance towards the left, bevel the hinge line.

  19. Using the Rudder (B3) as a guide, cut the corresponding bevel at the rear of the top (A2 and A3) and bottom (A1 and B2) fuselage subassemblies. Do not hinge these pieces at this time. It is simply easier to cut the bevel now before the vertical fuselage parts are installed.

  20. After allowing sufficient time for the fuselage nose and tail assembly attachments to dry, take the fuselage bottom subassembly (A1 and B2) and dry fit the tabs into the associated slots to verify fit. The critical alignment here is the cutout for the firewall in the nose to maintain a proper thrust line. Trim the tabs if necessary to get the proper fit. Remove from the slots and spread glue on the flat portions between the tabs (not on the tabs at this point) and reinsert and realign it. Making sure you have a good glue fit, support the fuselage bottom (A1 and B2) vertical with construction squares and let dry.

  21. From Sheet G, remove the two rear fuselage stiffeners (G1) and bevel both of the long edges.

  22. The two rear fuselage stiffeners (G1) are glued to the bottom of the fuselage at a 45 degree angle to form a triangle cross-section with the fuselage bottom and horizontal outline and even with the rear fuselage bevel. This will prevent the tail from twisting in flight, so it is important to complete this step flat on the building board to maintain the alignment. There are small alignment holes and slightly larger ones paired in the rear of the wing and stabilizer. You can put round toothpicks into the smaller holes to help align where the edges of the fuselage stiffeners should go. The ends of the stiffeners should position between the larger holes. The large end of the fuselage stiffeners (G1) should face the front/wing end. Dry fit the fuselage stiffeners (G1) in place before spreading glue on both the beveled edges and attach one of the fuselage stiffeners (G1) to each side of the rear fuselage.

  23. It is important to let the glue dry as this is your tail alignment and the plane will be removed from the building board next step.

  24. With the current assembly dry, lift the plane from the building surface and lift the main assembly off the build table and turn it upright. Dry fit the Fuselage top (A3 and A2) into the slots. The critical alignment here is the cutout for the firewall in the nose to maintain a proper thrust line. Trim the tabs if necessary, to get the proper fit. Spread glue along the bottom of the fuselage top, including the tabs this time, and glue it into the slots. Align the front of the fuselage in the firewall area so the edges all match and be sure the fuselage is perpendicular to the horizontal plane surfaces. Let this dry and check to be sure the glue joints remain tight and vertically aligned.

  25. Find the two plywood firewalls and notice the grain on them. Matching the screw pattern, glue the firewalls together so the grain is 90-degrees to each other for added strength. Spreading glue on the fuselage foam pieces, glue the firewalls in place in the nose, being careful to align them perpendicular to the fuselage. This is your thrust line so be sure it's aligned.

  26. Using a thin bead of Foam-Tac, hinge the Rudder to the rear of the fuselage.

  27. Find the quarter round gusset pieces (A4 and B5) and glue them in place as shown behind the firewall. This is important as it gives the firewall more glue surface and prevents the motor breaking off as easily. Use all 8 pieces, 2 per quadrant.

  28. Find the plywood control horn sheet and remove the 4 horns. Notice that one of them has a right-angle front on it. This is to go up against the Elevator carbon fiber spar. I recommend you install this one first to avoid it being installed in the wrong slot. I find spreading glue on the horns and squeezing some into the horn slots gives a strong attachment. The front ear of the horn should match the hinge joint so the pushrod holes line up over the hinge for optimum geometry. Install the other 3 horns in the same manner. All horns mount on the top surface with the Rudder horn installed on the opposite side from the Elevator horn.

  29. Install the 9g servos in the holes provided. If the wing servos don't sit flush with the top of the wing you might need to remove some foam from inside the wing to allow it. The wing servos have the splined post towards the front of the plane and the tail servos have the splined post towards the tail. Route the wires down to a common area where your Rx will be located. There are pass-thru holes provided. Do not install the servo arms at this time.

  30. Measure and cut the pushrods to be the distance from the servo splined post screw hole to the hinge line at the horn, minus 1/2". Clean the Z-bend wires and ends of the carbon rods with the sandpaper or alcohol to remove any possible oil.

  31. Assemble the pushrods with the Z-bend wires and heat shrink tubing. Do not glue the Z-bend wires at this point. For the tail servos, install half of the pushrod supports on each pushrod before putting the second Z-bend in place.

  32. Assemble the firewall mount on the motor as per the manufacturer's instructions. Bolt the motor to the firewall (without the prop) positioning the wires so they point to the side chosen for the radio installation. Connect the ESC and route the servo wire to the Rx area and pass the battery wire through the fuselage hole to the opposite side.

  33. Connect all the servos/ESC to the Rx being aware that you will need to set up dual aileron servos in the programming (which is dependent on your choice of radio). Plug in a battery to the ESC and bind your radio to the plane. This will also center your servos. Be sure you don't have any trim/subtrim set up at this point. Unplug the battery and turn off the radio. Remove the bind plug from the Rx, if necessary.

  34. Pick a surface and install the appropriate pushrod in the control horn. Take a servo arm and install it on the opposite end of the pushrod. With the surface held at neutral, install the servo arm on the splined shaft so that it is at a 90-degree angle to the pushrod. The splines seldom line up perfectly so just find the closest one. This will be adjusted using the subtrims on your radio. Slide the Z-bend wires under the heat shrink as needed for alignment. Do not install the servo arm screw at this point. Repeat for the other 3 servos.

  35. Turn the radio on again and verify the servo directions and reverse any as needed. Using the subtrim feature for each channel, set the servo arm perfectly 90-degrees to the pushrod. Verify the control surface is set to neutral and with a piece of paper towel protecting the paint, put CA on the Z-bend at one end of the pushrod. Verify the surface is neutral again and CA the other end of the pushrod. On the tail pushrods be careful not to drip any CA onto the pushrod supports. Install the servo arm screws, unplug the battery and turn off the radio.

  36. Install the propeller on the motor at this time and power up the plane again. Holding the plane securely away from yourself, give it a small amount of throttle to verify direction. If the motor is running backwards, swap any two motor connections to the ESC and retest. Unplug the battery and turn off the radio again.

  37. At regular intervals on the tail pushrods, stab the pushrod supports into the foam and glue in place with Foam-Tac. Sight down the pushrods to make sure there are no bends or kinks to cause binding. Make sure the supports are perpendicular to the pushrods to avoid binding.

  38. If you have chosen to install our optional landing gear set, now is the best time to install the plywood mounting plates using the pass-thru holes on the fuselage as a positioning guide. Follow the instructions provided with the Landing Gear set. The gear struts can be put on and off in the future using the two screws provided with the gear set.

  39. Attach the Rx and ESC to the fuselage using Velcro. Using cable ties, gather up the excess servo leads to neaten the installation. I like to have all the components on one side of the fuselage and then use a long piece of Velcro on the other side for battery attachment. This allows you to position the battery forward or back to fine tune your CG. Tail heavy will hover a little better for example.

  40. Initial CG should be set to approximately the wing spar position and then adjusted through flight testing to your personal preference.