GUY FORSHEY’S AERONCA CHUM
By Sal Calvagna | rcgiants@optonline.net
WELCOME BACK. Hopefully, you were productive this past winter. It’s now time to show off your latest and greatest build at the local field or flying event.
Featured in this month’s column is a one-off variant of a well-known classic and a short how-to on painting a canopy frame. Enjoy!
Scratch-Built Aeronca Chum
Guy Forshey, of Hollidaysburg, Pennsylvania, scratch-built this very unique Aeronca Chum 1/4-scale model from factory drawings. He has always been drawn to aircraft from the 1920s to 1940s time period, and he discussed building the 1/4-scale version of the Chum with his son, Brenton, who is an aerospace engineer for Boeing.
One day, a tube arrived at his home with factory drawings of the Aeronca Chum that were dated 1947. The fuselage drawing was a nearly perfect 1/4 scale, but the wing drawing was much larger. He reduced the wing to 1/4 scale and plotted the fuselage cross sections so that the fuselage sheeting would contour smoothly from one former to another.
The model was built similarly to any other scratch-built project, with time set aside to make a fiberglass cowling using the Styrofoam mock-up and plaster method.
The windshield and side windows feature compound curves that were heated and pressed over carved basswood molds. The biggest challenge was covering the model with 4-mil aluminum. The balsa skin was covered with .75-ounce fiberglass cloth that was bonded with Z-Poxy finishing resin, followed by two coats of water-based sanding sealer. After being fine-sanded, the aluminum panels were applied one at a time. The cockpit detail was straightforward because it sported few instruments and a wide bench seat. Guy recommends to anyone who is considering building an aluminum-clad model to take the time to add rivet detail using a small-diameter brass tube or other homemade device.
Of special note, take a look at the photo of the fixture that was used to support the fuselage formers. It is Guy’s own design that was built in the 1980s to keep a Waco cabin fuselage in perfect alignment. He has been using it ever since and is not aware of anything like it that is commercially available.
At 1/4 scale, the model spans 86 inches, with a fuselage length of 60 inches. The all-up weight is approximately 12 pounds, and Guy reports that it flies like an absolute dream on a Rimfire .80 electric motor and a Castle Creations 90 ESC using a six-cell LiPo battery pack.
As some information about the full-scale aircraft, the first Ercoupe was flown in 1937 and was touted as the safest fixed-wing aircraft of the time. It was certified by the Civil Aeronautics Administration as being incapable of spinning. Aeronca obtained a license to produce the Engineering and Research Corporation Ercoupe under the designation of 12AC Chum. Shortly after the end of World War II, Aeronca built two prototypes; the second one was fitted with a single, large vertical fin and rudder. However, it never went into production.
Guy is a member of two clubs, the Altoona RC Club in Duncansville, Pennsylvania, and the Cove RC Flyers in Woodbury, Pennsylvania. Nice work, Guy, on this one-off, unique model and your equally impressive fuselage fixture.
How to Paint a Canopy Frame
Painting the frame on a multifaceted canopy is not my favorite part of the building sequence, but it is necessary. Aircraft such as the Mitsubishi Zero, Junkers Ju 87 Stuka dive bomber, North American AT-6, and others have lots of framework that must be masked off before being painted. It requires some patience and a steady hand.
For this demonstration, I’m using a Nick Ziroli Plans Zero canopy that was made
from polyethylene terephthalate glycol, commonly known as PETG. This is the material from which all of Ziroli’s clear “glass” parts are made.
Once the canopy has been cut to size and trimmed to fit, I only use one tool and two different types of tape to mask off the individual panels: a new X-Acto #11 blade, 1/4-inch fine line tape, and masking tape. Masking tape does not contour well, so with a frame that has a curve, I use the fine line tape because it can follow a curve extremely well. Once the curved part of the framework is taped off, I follow up with the standard masking tape. The tape needs to be trimmed carefully with the #11 blade.
First, you want a nice, even paint line that accentuates the framework. Second, you need to only cut the tape and not cut into or score the clear PETG. The reason is that vibration from your engine will finish the job and your canopy will start to fall apart. Practice on a scrap piece of PETG with some masking tape; you’ll soon get a feel for the proper pressure. Take your time! Remember the old saying, “Rome wasn’t built in a day.”
Once it’s painted, use the #11 blade to gently pick at the tape corners to remove it. This is the most satisfying part because your finished canopy and frame become exposed. Good luck!
That’s all for this month. I hope to see you at an upcoming event.
SOURCES:
Nick Ziroli Plans
(631) 467-4765
www.ziroligiantscaleplans.com
Castle Creations
(913) 390-6939
https://home.castlecreations.com
