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project pattern


T


Redux Last month, you met Yuri, star of the Pro-


ject Pattern Redux series. Next up is a look at how it’s manufactured, a far cry from the materials and methods used in the EU-1A of the original Project Pattern.


he general steps described below convey a sense of the production process. Plenty of pictures are in- cluded as in this instance they eas-


ily convey the process more efficiently than words. The initial step is the application of wax to


the female molds, followed by the application of the base color coat (typically white). In the case of fully painted models (such as Yuri), paint masks are applied to the mold for each paint color/pattern. To ensure symmetry, masks are produced by a vinyl cutter. Once the painting is completed, a layer of fiberglass cloth is placed into the mold, fol- lowed by a layer of airex foam, and then a fi- nal layer of fiberglass cloth. Carbon fiber cloth is added to the layup in areas of high stress (nose and firewall, landing gear mounts, wing tube mount, etc.) and in the ailerons, elevators, and rudder to assure they remain true under aerodynamic loads. Lay- ers of cloth are placed in the mold at biased


by dave lockhart with algirdas ungulaitis You can reach Dave Lockhart via e-mail at davel322@comcast.net


angles to achieve the greatest strength. After all the materials are laid into the


mold, the whole assembly is “bagged” and a vacuum is applied to ensure uniform adhesion of all materials and removal of excess epoxy. The composite layup is given 24 hours to


cure, and then the edges of the molded parts are trimmed flush. The next step is the in- stallation of internal structures/reinforce- ments; fuselage formers, wing/stab spars and ribs, and control surface facings. All in- ternal structures are cut to within 1mm ac- curacy using a CNC mill. Templates are used to ensure accurate placement of all in- ternal structures. The final step involves joining the mold halves, which are bolted to- gether, and then allowed to cure for six days. After curing, the wings, stabs, and fuselage


are removed from the molds. The chord-wise edges of the ailerons are cut, and two cuts are made spanwise on the bottom of the ailerons to create a gap between the wing and aileron leading edge approximately 5⁄8 inch wide and allow the top skin hinges to flex freely. These gaps are then “sealed” with curved carbon fiber hinge seals attached to the bottom edges of the aileron leading edges. With the control surface at neutral, the seal extends into the wing, to the void space between the wing


trailing edge and the aileron leading edge. As the control surfaces move, the hinge seals maintain very small gaps between the wing skins and aileron leading edges. Similar treatment is given to the elevators.


For the rudder (molded as one piece with the fuselage), a similar width of material is re- moved, and essentially a half-round fiber- glass tube is attached to the leading edge of the rudder, and the hinges are recessed with- in the half-round fiberglass tube. This type of “pocket hinge” reduces turbulence at the hin- geline and presents a clean appearance. The next step of construction completed


by RC-Composit was the installation of the wing and stab tubes with incidence adjuster mechanisms. With any aerobatic aircraft, alignment of the wing and stab to the fuse- lage is critical for good flight performance. Alignment will be furthered discussed later in this series, but for now, suffice to say Yuri left RC-Composit in very good alignment. The last construction steps completed by RC-Composit were the installation of the motor battery tray and the rudder servo tray. The typical construction time at RC- Composit ranges from four weeks to seven weeks, depending on the level of the kit (ba- sic or custom).


PHOTOGRAPHY: ALGIRDAS UNGULAITIS


Producing symmetrical paint lines in the mold (above left) is ensured with the use of masks cut on a vinyl cutter. Carbon fiber cloth reinforcement (above right) is added to the nose of the composite layup. With all materials placed in the molds (below left), the fuselage molds are “bagged” and a vacuum is


applied for a 24-hour cure period. The composite skin structure is very strong and requires minimal internal structure. The needed structural pieces (below right) are CNC cut to a tolerance of less than 1mm. These will be added once the composite parts are fully cured.


52


JUNE 2012


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