Building with an open door and window requires a little modification to the airframe. The modification can be made easily while building the plane but can also be made on a pre-built plane with a little more work. First part of article will talk about it as you build and at the last part will be for a built plane. This is based on the ¼ scale SIG Cub but can be adapted to work with other models.
As you build Please read the complete article before you start. In step 1.A disregard the ½ by 15/16 notches. You will need to cut 1/8 inch off the bottom of F5 former top. You will need to cut the notches 3/8 by 7/16. In step 1.B assemble parts with CA not epoxy, former side will need to be shortened 3/8 inch. Later you will remove all of F5 excluding top former. Skip step 1C. After completing step 2.C trace the door outline from the plans to the right side of the fuse. and cut the door out. You will need to outline both the door and the door opening with 5/15 balsa. Step 2.D change the balsa and spruce laminate to a 3/8 x 7/16 spruce and cut a 5/32 x 5/32 grove down the bottom inside of both sides. Step 2.E will be skipped and on 2.F you will install F5 and F7. Tack glue the F5 in place as it will be removed after the fuse is built. Step 2.G do not add the left cabin top piece. Step 2.H, this is a critical step. Due to the lack of formers F6 you will need to use a square to get the fuselage straight.
With the plans plat #1 in front of you, you will need to make two cabin reinforcement rods out of 5/32 music wire. Allowing the wire to extend ½ out of former F7 bring the wire alone the bottom inside of the cabin top piece then bend down to follow the windshield brace. Extend the wire down even with the cabin wire in the side of the fuse. Note: the wire will need to be bent in a little where it enters the sides of the fuse. Sand the wires down this is for better gluing. Step 3.G do not glue the wire. Skip Step 3.H through 3.K for now, you will come back later to finish them. Section (4) Cabin Area, do the following before you start section 4.A. Lay the plane on its side down on the plans. Epoxy (I use and recommend the two-ton epoxy from Wal-Mart) the right and left Cabin top piece in place being careful not to get clue in the 5/32 grove. Remember the grove will be on the bottom inside edge of the pieces. Let it dry overnight. Insert the two 5/32 reinforcement rods in the groves allowing ½ inch past former F7. Front part of the rods should line up with the grove in the nose section and fit beside the 5/32 cabin wires. The rods might need small adjustments to fit.
Flip the plane upside down and work one side at a time. Remove the rod and apply epoxy (just enough to coat the area between the rod and the 5/32 groove) to the grove in the top piece reinsert the rod. Remove any epoxy the squeezes out. Apply epoxy to the grove on the nose and insert both 5/32 wires. Let dry for a few hours and repeat to other side. Make two windshield braces from 5/16 spruce cutting a 5/32 grove in the top inside edge. Apply epoxy and install. Let set over night. Using light cloth wrap the cabin top piece and windshield brace twice using epoxy. Sand and smooth after epoxy has cured Now go back to step 3.H and continue through 4.B. Skip down to 4.G make F5G out of ¼ ply and epoxy in place. After epoxy has cured remove the bottom part of F5 that was tacked glued in. Now go back to step 4.C and apply sticks where F5 and F6 would have been. Step 4.F has already been done. By removing F5 all the stress is now applied to the reinforcement rods.
Built as an afterthought. With the plans plat #1 in front of you, you will need to make two cabin reinforcement rods out of 5/32 music wire. Allowing the wire to extend ½ out of former F7 bring the wire alone the bottom inside of the cabin top piece then bend down to follow the windshield brace. Extend the wire down even with the cabin wire in the side of the fuse. Note: the wire will need to be bent in a little where it enters the sides of the fuse. Sand the wires down this is for better gluing. Remove the cabin tope pieces, and windshield braces. You will need to drill 5/32 holes as deep as you can beside the 5/32 cabin wire. Trace the door outline from the plans to the right side of the fuse. and cut the door out. You will need to outline both the door and the door opening with 5/15 balsa. Now change the balsa and spruce laminate that you removed early to a 3/8 x 7/16 spruce and cut a 5/32 x 5/32 grove down the bottom inside of both sides. Trim the rod according to the depth of the holes drilled. Apply epoxy in the hole and insert the rod. Now apply epoxy (just enough to coat the area between the rod and the 5/32 groove) to the grove in the top piece epoxy the top pieces to former F5 and F7. Remove any epoxy the squeezes out. Let epoxy cure. Make two windshield braces from 5/16 spruce cutting a 5/32 grove in the top inside edge. Apply epoxy and install. Let set over night. Using light cloth wrap the cabin top piece and windshield brace twice using epoxy. Sand and smooth after epoxy has cured. Replace F5G with ¼ ply and epoxy in place. After epoxy has cured remove the bottom part of F5 along with all of F6. Apply ¼ x ½ sticks where F5 and F6 would have been. Add ¼ x ½ window brace and sand.
Window Using the plans build the window out of ¼ spruce to fit inside the window area of the plane Make the window braces out of ¼ spruce. Glue together with epoxy. On the bottom drill two 1/16 holes in the bottom of the wind frame. Insert 1/16 brass rod in the holes, and trim them allowing 1/8 inch protruding from the bottom. Bend a section of 1/16 rod to make a handle and apply to inside bottom of window. Apply clear plastic to the side.
Door Refer to drawing below for help. Although a cub did not come from the factory with a handle on the outside mine dose. The door handle and latches are made from 1/16 brass rod. Drill a hole in the door for the handle. Solder a washer to the handle and the insert it in the door. Take a strip of brass 3/16 by 5,8 and drill four 1/16 holes in it. Solder the strip on to the handle at the second hole from the top. Attach the spring to the bottom hole, and the latches to the other holes. When you turn the handle down the latches should retract in. Cover the inside of the door with 1/32 balsa and screw in place
Installing Hinge the door and window with typical hinges. With the door open apply black paint to latches, turn handle, close door, and release handle. This should transfer the black to the sides of the fuse. Open door and drill holes inside of opening to receive the door latches. Bring door and window together and transfer the location of the pines from the window to the door and drill. The close door and window bring window and door together by aligning the pins in the window to the holes in the door as you turn the handle to close the door. If you have questions about this article fill free to email me.
In the drawing the gray is existing on the planes, Green is the new window frame that is made. Dark Blue is existing door frame, purple/blue is door frame that has been added. Light purple/blue is existing wood removed. Orange is cabin door frame that is added. Yellow rods are the latches.
