Flat Foamie Series

Depron Build Instructions

The Latest Version is Available Online at http://www.racores.com/FlatFoamieDepronInstructions.htm

(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


Items required to build the plane:

A Hobby knife and replacement blades or Snap Knife

A cork backed metal ruler, 18Ó recommended

Foam Safe CA Glue and kicker

Blenderm or equivalent hinge tape

A piece of fine sandpaper to roughen the pushrod pieces for gluing

Optional: four .032Ó EZ-Connectors for your pushrod attachments


1.           Remove the parts from the foam sheets gently with an X-Acto blade around the edges where they are attached to the sheets and place them on a flat building surface. If you will paint the plane you might leave the fuselage pieces in the sheet. You may want to build on top of plastic or wax paper to avoid gluing the plane to the surface. Select the slotted elevator and the 8Ó flat piece of Carbon Fiber that matches the slot. Using Foam Safe CA glue, glue the strip into the slot with it flush with the surface.

2.           The next step is to bevel both sides of the elevator hinge joints. Lay the hinge area of the elevator against the edge of the work surface or any straight edge. Place a metal ruler on top of the elevator the same distance from the edge as the thickness of the foam. Using a new X-Acto blade or snap knife, trim along the edge/ruler at a 45 degree angle the length of the edge. If the foam starts to drag and rip, use a new blade. Cut the stabilizer in the same manner.

3.           Continue cutting bevels in the aileron and wing control surfaces being careful to make left and right ailerons and the matching surface on the wings.

4.           Working in an area large enough that the entire outline of the plane can lay flat, take the two wing panels and test fit them together with the long flat piece of carbon fiber in the slot. Wick thin foam safe CA into the joints and spar and spray with kicker. Flip the wing over and add glue to this side also.

5.           Locate the horizontal front (motor mount area) of the fuselage and fit it to the front of the wing. Wick CA glue into this joint also.

6.           Attach the rear horizontal fuselage piece to the rear of the wing in the same manner.

7.           Take the stab/elevator assembly and making note of the wing hinge bevel (we consider the side with the smooth joint the top and the side with the bevel to be the bottom), attach it to the rear fuselage piece in the same way with the hinge bevel facing the same side as the wing (both up or both down).

8.           There is a third piece of flat carbon strip in the kit which can be optionally be used to further reinforce the nose of the plane. Just cut the carbon in half and cut slices into the nose area as shown and CA in place.

9.           You should now have an outline of the completed plane. This is a good place to paint the plane before you hinge the surfaces and attach the fuselage pieces.

10.       Once your paint is dry, remove the fuselage halves from the foam sheet and bevel the rudder hinge joint. Make sure that you bevel the same sides of the rear fuselage and rudder. Do not hinge the rudder at this time. Check the elevator horn position and with the hinge on top, hold the rudder upright and you want the point of the bevel on the side opposite the elevator horn. This allows for your rudder servo to be on the side opposite the elevator servo.

11.       Holding the elevator and stabilizer together so that the points of the hinge line are together, tape over the hinge line and smooth out the tape fully. Fold the surface down so the bevel touches together and tape the opposite side of the surface. Flex the elevator fully to make sure you have good movement of the hinge. Continue in the same manner with the hinging of the ailerons.

12.       Place the wing with the smooth hinge joint down on the building surface so the V bevel is facing up. Find the fuselage bottom and test fit it into the notches on the outline. Smear glue on the two pieces and attach the fuselage bottom in place making sure it stands perpendicular to the horizontal surface and the motor mount notch faces forward.

13.       Find the two thin (3mm) wedge shaped tail stiffeners. These 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 in the bottom fuselage and rear horizontal tail. You can put round toothpicks into these holes to help align where the corners of the tail stiffeners should go. The large end of the wedge should face the front/wing end. Dry fit the wedge in place and wick the joints with foam safe CA. Attach one of the thin wedge shaped pieces to each side of the rear fuselage.

14.       Take the plywood aileron servo bellcrank (bowtie shaped) and glue it to the existing nylon servo arm using CA. Rough the surface of the nylon servo arm with sandpaper first. Position/align the center hole of the plywood bellcrank concentric with the screw hole in the nylon servo arm. If you are using the 9 gram HXT900 servo included in our completer kit you will find alignment holes in the bellcrank that either the .032Ó z-bend rods or #1 screws can be used to align the bellcrank. We have cut the center hole to be snug on the servo arm and attach under the arm.

15.       With the aileron servo bellcrank mounted as shown, install the 9 gram aileron servo in the precut hole in the front of the plane. Note that the servo output shaft is towards the rear and the flat side of the bellcrank is also. Tack glue the servo in place with your preferred method, I use CA glue on the mounting ears but other people use low temperature hot glue.

16.       Take your motor and mount it to the plywood disk provided being careful not to block the notches. Set it so the wires arenŐt in the notches either. Remove the motor and using CA glue, glue the disk onto the front of the plane built thus far. If you are using the hexTronics 2730 motor from our completer kit the firewall has pilot holes to match the mount.

17.       Using the notch in the disk as a guide, glue the fuselage top onto the plane, aligning it with the slots. Cut the servo hole out if necessary to allow clearance over the servo arm.

18.       Using CA, glue the small foam quarter circles (gussets) to the back of the motor disk so the curvature matches the motor mount and the fuselage to provide more contact surface to secure the motor disk. Two sets of gussets are provided for additional glue area.

19.       Glue the fuselage doublers to the underside of the fuselage to further reinforce this area to protect it during landings.

20.       Insert  the aileron control horns into the precut slots in the top of the ailerons so they are flush with the bottom of the aileron slot and the holes are aligned over the hinge line. (Note: the elevator horn has a notch in it to step over the elevator spar and is different than the rudder and aileron horns. Be sure to not use it for the ailerons. Glue in place with CA along the entire length. These longer horns provide support to the control surfaces.


21.       There are two ways to make the control linkages adjustable. With the materials provided you can bend a V into the z-bend rods which can be pinched or spread to adjust the control centering. This is generally good enough since the alignment is only necessary when you set the plane up initially. The second method that can be used is to buy optional mini (to fit .032Ó wire) EZ-Connectors and cut the z-bends off the end of the pushrod wires. Either of these methods work and only needs to be done at the servo end of the pushrod.

22.       Find the aileron pushrod materials. You will need 4 pieces of shrink tubing, 4 Z-bend wires and the two short pieces of carbon rods. Use a piece of sandpaper to gently rough up (remove the gloss) the ends of the carbon rods and the straight ends of the Z-bend wires. Put two of the pieces of heat shrink onto a carbon rod. Place the Z-bend wire into the middle hole on the control horn and slide the shrink tubing over the wire and rod to hold it in place. Put the other Z-bend wire in the hole shown on the  bellcrank and slide the heat shrink over this end. Using a pin or clamp or clothespin, center the aileron surface to the fuselage. Adjust the carbon rod so it has equal gaps on both ends and carefully CA the wire to the carbon rod to secure it. Follow the same procedure on the opposite aileron linkage. Wiggle the sticks to see that the controls move freely.

23.       Locate the elevator horn that is notched to step over the carbon strip that is already in place. Glue the horn in place using CA so the holes are aligned over the hinge.

24.       Hinge the rudder to the rear of the fuselage using tape as done on the other control surfaces.

25.       Glue the rudder horn in place so that it is on the side of the fuselage opposite the elevator horn.

26.       Now we will roughly balance the plane to find the best position for the tail servos. Install the motor and propeller and position the ESC on the front of the plane. Position the receiver also.

27.       Put the elevator and rudder servos on the top of the horizontal fuselage near the wing and holding the plane above the wing spar, slide them front or back in order to balance the plane. You may find that you need to also move the ESC and receiver forward to make it balance. Balancing without the battery means you will be able to use different size batteries at the CG point without affecting the balance. (These servo positions will depend on the equipment you have chosen to use.) Glue the servos in place. CA can be used, some people prefer hot glue or you can use contact glue. You want them firmly attached.

28.       Connect the servos to the receiver and center the rudder and elevator servos. Put a long control arm on each servo so that it is pointed straight up. Using the two long carbon rods, create the rudder and elevator pushrods in a manner similar to the aileron pushrods. Before you complete both servo ends be sure to slip the provided pushrod supports over the carbon rod. Use EZ Connectors or the V notch method to make them adjustable. Depending on the position of your servos you may need to shorten the rods. When your servo rods are in place, push the supports into the  horizontal and vertical surfaces midway down the pushrod to keep it from flexing in the middle. Trim the supports so they donŐt extend beyond the back side of the fuselage and glue them in place with CA, being careful not to get any near the pushrod to glue it to the supports.

29.       Using Velcro, attach the receiver and ESC to the positions you determined to have the best balance. Put a long strip of Velcro below the wing spar in order be able to move the battery forward and back to fine tune your balance.

30.       The plane is now completely assembled. Route the servo wires through a slot in the foam to the receiver side of the fuselage and connect everything in place. Use tie wraps to gather the wires in a neat bundle.


31.       Control throws are a matter of personal preference. Some people want lots of surface movement to do 3D maneuvers while other people like a more docile handling plane. The Yak responds very well to rudder movement and throws up to 45 degrees in each direction are often used. You can add exponential to your controls to calm down the center portion of the travel. If you are going to go for this type of aggressive throws, you might want to start with 50% exponential until you get a feel for the plane. DonŐt be afraid to challenge yourself and learn new things. Get out and enjoy flying.

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