Larry Kruse's Lippisch P.13B
Lippisch Construction Notes
Construction of the Lippisch P.13B begins by transferring the parts from the template plans to the foam board. That is best accomplished by backing the templates with a heavier material such as poster board, carefully cutting them out, and then tracing them onto the foam board using a pencil. It is better to use a pencil than a pen in case you have to erase, or you accidentally stray from a line in the cutting process.
Note that the front and main wing templates are drawn showing only half of each in order to fit onto a single page. It’s a simple matter to mark a centerline on the foam board, trace around one of the templates, and then flip it over to draw the other half.
I used a self-healing cutting mat under the foam board and a disposable scalpel with a #11 blade to cleanly cut out the pieces. A hobby knife with a sharp pointed blade will also work, but be sure to keep the blade sharp to avoid tearing the foam board’s paper backing.
I left the paper backing on for added strength, and I think it was a good decision. Although it’s inexpensive, the Dollar Tree foam board is rugged and resistant to damage compared to Depron or similar products. Cut out all parts, including the 3/32-inch plywood motor mount before beginning assembly.
If you’ve never used hot glue, be prepared to work quickly before it sets up. Hot glue was the main adhesive used on the model and greatly speeds up the assembly process. Having stated that, and as a safety note, prepare some scrap pieces of foam board or balsa with a rounded end if you are persnickety about smoothing out or removing the excess hot glue used to reinforce the joints. Do not use your index finger to quickly wipe the excess away. (Don’t ask me how I know that.)
To keep the assembly process moving along quickly and efficiently, the following assembly steps will help you complete your Lippisch P.13B in a short time:
1. Place the bottom front plate flat on the work surface and cut out a scrap piece of foam board 3/38 inch narrower than the width of the plate. This scrap piece will be used as a spacer to keep the fuselage sides parallel as they are glued to the bottom front plate. Apply hot glue to the top of one outside edge of the bottom front plate. Stand one of the fuselage side rails on edge and attach it to the bottom front plate at the notch. Hold it upright and at 90° until the glue cures. Repeat for the other side rail, positioning the scrap piece of foam between the rails to keep them parallel at the aft end.
2. Laminate the two bottom fuselage pieces using five-minute epoxy and keep them pressed together as the epoxy sets up. Spread the epoxy thinly on one side using foam board or balsa scrap before pressing the other side in place. Wipe off any excess that squeezes out of the sides with a dry paper towel.
3. Joining the two wing pieces is next. Place a piece of waxed paper longer than the joint between the front wing piece and the main wing flat on your work surface. Spread a narrow bead of five-minute epoxy on the rear of the front wing piece and slide it into place against the shallow “V” cut in the front of the main wing.
Check to see if any epoxy is seeping out between the two surfaces, and if it is, wipe it off immediately with a paper towel. Weigh the two pieces down flat and keep them pressed against each other until the epoxy sets up.
4. Using a long straight edge, mark a vertical centerline with a pencil on both the top and the bottom of the wing. These two lines will be the reference guides for joining all of the remaining pieces to the completed wing panel. If you need to enlarge the motor mount/motor/propeller cutout to accommodate the power combination you have chosen, now would be the time to do it.
5. Glue the laminated fuselage bottom to the bottom centerline of the wing with hot glue, reinforcing the joint with additional beads of hot glue on either side.
6. Position the fuselage side rails and bottom front plate unit over the bottom of the wing using the centerline you have drawn on the wing as a reference point. Adjust the fuselage rails until they are evenly spaced and parallel to that line. Mark the position of each rail and draw a line the full length of each rail on the wing to guide your application of the hot glue.
7. Glue the fuselage side rail/bottom front plate unit in place by running a bead of hot glue down each of the lines you marked and place a heavy bead of glue in the notch of the laminated fuselage former. Be prepared to work quickly to get everything straight and pressed into position. Re-glue the side rail joints inside and out for additional strength.
8. Turn the assembly over so the top of the wing faces up. Taper the bottom of the leading edge of each elevon by sanding it to a wedge shape for clearance when down-elevator is needed. I waited to hinge the elevons until after I had airbrushed the top surface of the airplane, but I think that either before or after painting would be fine, given the results I had.
9. Hinge each elevon with one long piece of Blenderm (or similar) tape placed over the top seam of each elevon/wing joint and press down. Now fold the elevon back flat against the wing surface and place two pieces of tape at right angles to the elevon/wing seam on the bottom (now facing up), spacing the tape out for strength and flexibility and pressing it into position.
10. Glue the top fuselage (cockpit piece) in place, reinforcing it with additional beads of glue on both sides. The twin rudders can also be glued in place. Make sure they are both straight and vertical. Extra glue on each side of both rudders is required, as was the case with the top fuselage piece.
11. The tip winglets can be sanded to an angle to slightly cant outward, and then pinched into a curved shape to match the outline of the wingtip. Attach them with hot glue, and then run a bead of hot glue on the bottom side of the joint to provide a supporting fillet.
12. The final item to glue in place is the motor mount. I found it easiest to bolt the motor to the motor mount and then install it against the cruciform-mounting surface provided by the juncture of the wing and the two fuselage pieces.
Five-minute epoxy is the best choice for adding both the required strength and allowing the assembly to be tweaked as it cures to keep it at a 0-0 thrustline. After the first epoxy coat cured, I added a second coat to build up fillets between the back of the motor mount and the foam board cruciform.