Flat Foamie Series

Mini P-51D Build Instructions

This version dated May 18, 2021
The Latest Version is Available Online at http://www.racores.com/MiniP51DInstructions.html (click on the pictures to expand) We suggest that you read through the instructions once before starting to build to become familiar with the sequence of steps and the flow of construction.

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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 (Beacon Foam-Tac)
A piece of fine sandpaper to roughen the pushrod pieces for gluing.
Velcro for attaching the ESC, Rx and battery.
A .050" Allen wrench for removing and tightening the motor mount grub screws.
Optional: four .032" EZ-Connectors for your pushrod attachments

Kit Parts Layout.
  1. Grab Sheet A from the kit which has the fuselage and tail pieces and lay it on the building board. Leave the parts in the sheet for this step.

    With your Xacto blade, separate the 4 spar slots. Gather the following strips of 5mm carbon fiber from the bundle. Main fuselage spar 345mm, Lower front fuselage spar 155mm, Fuselage tail spar 170mm, and Elevator spar 145mm and lay them out as shown.

  2. Smearing glue (Foam-Tac) on both sides of each spar, place it into its slot. For the 170mm fuselage tail spar, don't spread glue the full length on the side that faces the parts sheet at the tail. That spar should slide snuggly forward in the slot, leaving about a 5mm section at the rudder with no carbon fiber (for the rudder bevel later). Lay the sheet aside flat for the carbon fiber to dry.

  3. Cut the wings and ailerons out of sheets B and C. Spread glue on the center wing joint and press the two wings together. Lay flat to dry.

  4. Before you throw the scraps of sheets B and C away, it would be useful to take the scraps from above the two wings and practice cutting bevels and hinging with only a little glue to avoid too stiff hinges. You need to remember that hinges will continue to stiffen over the first 24 hours. You can always smear a little more glue on later if they are too weak. That is the beauty of glue hinges in that they are easy to maintain and repair.

  5. Cutting bevels video
    Gluing the hinge video
  6. With your Xacto blade, separate the 2 wing spar slots. Gather the two longest pieces of flat 5mm carbon fiber, the rear wing spar 500mm and the front wing spar 400mm and lay them out in place.

    Smearing glue (Foam-Tac) on both sides of each spar, place it into its slot and lay the wing flat to dry.

  7. Remove the A2 stabilizer and A3 elevator from sheet A at this point and bevel the hinge line. DO NOT GLUE THE ELEVATOR HINGE AT THIS POINT!

  8. Remove the A1 fuselage and A4 rudder from sheet A at this point. Hold the elevator up to the rudder area of the fuselage with the point of the bevel towards the bottom. The side of the elevator that has the horn slot is the opposite from the pointy side of the rudder bevel. Cut the bevel of the fuselage hinge line. Cut the rudder bevel to match, noting that the top of the rudder is skinnier than the bottom and hinge the rudder. Smearing a minimum amount of glue on the bevel points, hinge the rudder and fuselage together.

  9. Insert the elevator into the slot in the tail of the fuselage so the center indent is in the half circle opening at the rear making sure that the point of the bevel is towards the bottom. Slide the stabilizer into the slot in front of the elevator with the bevel point to the bottom as well. Smearing a minimum amount of glue on the bevel points, hinge the stabilizer and elevator together. Do not glue this assembly into the fuselage at this point.

  10. Gather the wing and the ailerons and cut the bevels in the hinge joints being careful to make a left and a right aileron. Smearing a minimum amount of glue on the bevel points, hinge the ailerons to the wing and set aside to dry.

  11. Find the two 40mm stabilizer stiffeners in the small parts baggie. Find the 9mm alignment gauge in the kit bag. Smear glue on the section of the stabilizer between the cuts, top, bottom and front and then center it in the fuselage slot pushed all the way forward. Smear glue on the 40mm stabilizer stiffeners on the side toward the fuselage, and on the back half of the outer side of the stiffener. Then slide them into those cuts in the stabilizer, against the fuselage on both sides. Take the alignment gauge and slip it over the fuselage below the stabilizer placing it against the stabilizer Pin the stabilizer to it from the top. This will hold the stabilizer at 90 degrees to the fuselage while the glue dries.

  12. Find the lite-ply firewall in the parts baggie as well as the 2 firewall supports (A5) on sheet A. Put glue on the front of the fuselage, skipping the very center where the firewall hole goes, and put the firewall between the two notches. Smear glue on the flat edges of the Long gussets and glue them in place over the long fuselage spar and against the firewall to keep it square. Make sure everything is pressed together tight and the firewall is perpendicular to the fuselage (no right or down thrust). Allow the glue to dry before continuing.

  13. While waiting for the glue to dry, now might be a good time to solder the 2mm bullet connectors onto the motor wires

  14. With the stabilizer glue dry, unpin the alignment gauge from the stabilizer. Slip the wing into the wing slot with the aileron hinges facing up, the bevels facing down, and smear some glue on the center section of the wing between the leading and trailing edge tabs. Center these tabs in the wing slot. From the bottom, slip the alignment gauge over the fuselage and, like the stabilizer, pin the wing to the alignment gauge. This procedure will give you good alignment between the wing and stabilizer and make the plane fly true.

  15. With the firewall glue dry, Glue the 8 quarter circle gussets (A6) in two layers matching the firewall shape and press it onto the fuselage and against the back of the firewall. Repeat for the other 7 gussets (two in each quadrant). Make sure everything is pressed together tight.

  16. Find the small plywood sheet of horns in the parts baggie and pop the 4 horns out. Notice that one of the horns has a flat front to the glue area. That is the elevator horn and the flat fits against the spar. Spread glue on both sides of the diagonal lines section of the bottom of the horn and glue this horn into the slot on the underside of the elevator so the front of the horn meets the hinge line. The 2 of the other horns have 4 pushrod holes. Those are for the ailerons and they go on the top side and the remaining 3 hole horn is for the rudder and goes on the side opposite the elevator horn.

  17. The airframe is now complete. If you are going to paint it, this is the time to avoid getting any on the electronics. If you do paint it, use very light coats as EPP is a sponge and you can add a lot of weight very quickly. Another good option is to use colored sharpies to personalize it with minimal weight. This is also a good time to go over all the joints and make sure the glue is solid. Also check both sides of all the spars as sometimes putting a spar into the slot can wipe the glue off as it slides in and the bottom has less glue. Once you are done with any gluing and painting, continue on with the electronics installation.

  18. Open the servos and insert them into the appropriate slots. The 5g (aileron) servo goes into the hole in the fuselage in front of the wing and the 3.7g tail servos go into the holes in the wing on either side of the fuselage. Glue the tail servos in place, but do not glue the aileron servo. (I use Foam-Tac, but some people like using hot glue) All servos mount with the splined shaft towards the tail. Whichever side the aileron servo wire is on will be the side you mount your Rx so put the wire from the tail servo on the other side through the passthru hole in the fuselage so they are all on the same side.

  19. Remove the mount from the motor and attach it to the firewall using the predrilled holes. I prefer to mount it so the grub screws point side to side for ease of access. The grub screws on the mount are 1.3mm and near invisible if you drop them. I don't have any replacements.

  20. From the small plywood sheet, carefully remove the aileron anti-differential bellcrank (bowtie shaped) and find the 5g four sided servo arm in the accessory bag. Cut the two longest arms off. Slide the servo arm hub through the hole in the bellcrank and secure from the bottom with screws. (I use the mounting screws from the 3.7g servos)

  21. Measure the 4 carbon fiber pushrods to be 1/2" smaller than the distance from the servo arm screw to the surface hinge line at the control horn. Be aware that the elevator and rudder pushrods are different lengths.

  22. Take the two short carbon fiber rods and attach the z-bend wires to the two ends using the small pieces of heatshrink tubing. The z-bend wires and heatshrink is in the small parts baggie. Shrink the heatshrink in place to hold the wires but DO NOT GLUE THEM AT THIS TIME.

  23. Put the z-bends of the aileron pushrods through the top hole on the aileron horns and then through the holes shown on the bellcrank (farthest forward one in from edge). Attach the servo arm on the aileron servo and adjust it so it is aligned straight across, Now adjust the ailerons so they are level by sliding the wires under the heatshrink tubing. Once you have everything perfectly aligned, glue the wires to the carbon fiber using cyanoacrylate glue being careful to not glue them to the plywood horns or bellcrank.

  24. Find the two single side servo arms for the two 3.7g servos to prepare for the tail pushrods.

  25. Take the two longer tail pushrods and on one end attach a z-bend wire with the heatshrink tubing like before. Remove the pushrod guides from the small plywood sheet and slide half of them over each pushrod (BEFORE you do the second end). Now put the second z-bend wire on the other end.

  26. Put the z-bend wire through the top hole in the rudder/elevator horn and then put the second end through the innermost hole on the servo arm. Attach the servo arm to the servo so that it is sticking out perpendicular to the fuselage. Adjust the pushrod so the surface is straight and the servo is perpendicular and then glue the wire in place with cyanoacrylate glue being careful not to get any glue on the dangling pushrod guides or control horns.

  27. At two equidistant points along the pushrods, push the guides into the fuselage to keep the pushrod as straight as possible. Clip off any excess that pushes through the back side and glue in place being careful not to get glue on the pushrod so it can slide through.

  28. Mount the motor into the mount already attached to the firewall and plug the ESC into the motor leads. Tighten the grub screws. Locktite is optional but not a bad idea. I mount the motor so the wires are on the side opposite the servo wires. Run the ESC servo connector through one of the pass through holes to be on the same side of the fuselage as the servo wires. Note that the propsaver has two different faces and put the one forward that best fits the back of your prop.

  29. Plug all the controls into your receiver of choice and bind to a fresh model on your transmitter using an appropriate flight battery. Make sure all your trims are centered and no subtrims are set. Verify all the servos are moving in the correct direction and reverse as needed. Move the servo arms so they are as perpendicular to the fuselage as possible (servos are always half a spline off) and adjust it to be perfect using the subtrim settings on your transmitter. As you finish each control, put the servo screw in place. When you get the aileron servo adjusted and have the screw in the arm, glue the servo into position. (getting the screw in the arm is why we left the servo unglued)

  30. Attach a prop to the motor with the propsaver o-ring and while holding the model at a safe distance, blip the throttle to see if the motor is turning the correct way (pulling the plane forward) and if it is backwards, swap any two ESC/motor wires to reverse it.
  31. Adjust the control throws and exponential as you like being careful to keep the rudder throw lower so it doesn't interfere with the deflection of the elevator. Unplug the flight battery and turn off the transmitter. Your plane is now set up. Using velcro and cable ties, neaten up the wires under the plane. I put a longer piece of velcro for the battery on the ESC side of the fuselage so you can move the battery front to back for balance. The CG of the plane is about even with the front of the tail servos. You will have best luck of you mount the Rx and battery even with the rear of the wing.