Author: Paul Bradley
Edition: Model Aviation - 2011/02
Page Numbers: 88,89,90
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Making foam skeletons without a laser

Paul Bradley | [email protected]

Light is right. Since we are in the middle of the traditional building season, I'll lead off with construction ideas from Gordon Johnson. He is from the Boston, Massachusetts, area and is fairly well known within the indoor micromodel world.

Although Gordon builds airplanes that Joe Malinchak normally covers in MA's "Micro-Flying" column, he has developed some construction methods that can be applied to slightly larger aircraft that are flown indoors and outside—or small-field models.

For several years Gordon has worked with and developed approaches for structures that have frames covered with a membrane. You may ask what is so new about that; we have had stick-and-tissue construction methods almost since the first model airplane was built. Where Gordon departs from long-established methods is in his mix of new materials with the old concept of a membrane-covered framework.

The standard approach for a membrane-covered structure is to build the framework from sticks. This involves gluing joints and learning the tricks associated with assembling a set of stick frames. It is not hard to do or to learn, but it does require an investment of time.

These days we see many, if not most, small models made from sheets of thin, lightweight foam. Using sheet foam normally translates to a drastic reduction in build time with equal or lighter flying weights than those of comparable built-up, balsa-frame, membrane-covered aircraft. Because sheet foam is becoming such a popular construction material for micromodels, Gordon thought he could take it to a new level. One reason for building a frame-based model rather than one made from solid sheets of the construction material is lighter weight. Even with lightweight sheets of foam, removing a large portion would mean an overall weight savings.

Foam skeleton technique

Gordon has been making foam framework covered with light plastic film. The big change is that he cuts the frames from foam sheets rather than assembling them from foam strips. Cutting the frames from sheet eliminates most of the glue joints and means that he doesn't have to deal with slicing and fitting strips.

Look at the photo that Gordon provided of his Airbender. You can see the film-covered foam framework cut from sheet stock and a wing frame.

Cutting such frames is easy with a sharp blade, straightedge, and sharpened brass tubing. Gordon uses the brass tubing to cut the corners of a frame area. Once the corners are "drilled," he simply cuts straight lines between the holes and then drops out the material to be removed. It does not take long for him to complete a frame.

When the frames are cut, you can apply some color and then apply the covering material. The resulting structure is incredibly light and surprisingly strong. As is the case with almost all aspects of building model airplanes, the only limitation is your imagination.

Small-field designs from recent magazines

The December 2010 Flying Models magazine featured two great construction articles about airplanes that are perfect for small-field flying. One of those was Robert Dance's cool-looking Firefly. I presented Robert's lovely Piper Pacer in the August 2010 column. He is multitalented, which is evident in his Firefly design. He provided a nice photo of it for me to include here.

The 45-inch-span, 14.5-ounce aircraft is covered with yellow silk and trimmed in blue dope. Most electric-power modelers choose brushless motors, but Robert's Firefly uses the tried-and-true brushed 6-volt Speed 400. Not long ago the mighty Speed 400 was the dominant motor for electric-powered small-field flyers. Although it is a bit old school, the battery pack is a modern two-cell Li-Poly of roughly 1350 mAh capacity. The Firefly has captured my fancy.

The other design in Flying Models that caught my small-field eye was a nice 26-inch-span L-19 Bird Dog by Pat Tritle. He supplied me with a nice photo of it. Although Pat designed the L-19 for rubber-powered free flight, it would make a great conversion to small-field RC using components from the ParkZone Micro P-51 or HobbyZone Champ. The FF Bird Dog weighs 45 grams, or roughly 1.6 ounces. Its weight as an RC model would probably be close to 2 ounces. Pat is selling laser-cut kits for the L-19 through Pat's Custom Models. See the "Sources" listing for contact information.

New small models from BSD Micro RC

While I was at the KIEF (Keystone Indoor Electric Fly) gathering in October, I had the opportunity to examine and fly several new models that Bob Selman is selling through BSD Micro RC. An accompanying photo shows the George Harris designs: a 20-inch-span twin called the "L-TX," a 14-inch-span Smith Miniplane, and an 18-inch-span Ercoupe.

The twin uses two brushed motors with the Gary Jones 4:1 gear drive, and the other airplanes are intended for the small AP03 brushless motor. The models are in the 1.25- to 1.75-ounce weight range. They work well indoors or in small outdoor spaces. Check out these designs on the BSD Micro RC website. The address is in the "Sources" listing.

Throttle-only outdoor pusher

Not long ago I shared with you a No-Cal (profile) Hughes racer that John Krouse built. The model was unique in that it used only throttle control; no flight control surfaces were active. John built his airplane for indoor use. Flying inside with no rudder control would be challenging enough—there are no wind gusts but there are walls—but John took the throttle-only concept one step further. Enter his outdoor pusher design with throttle-only control.

The outside environment presents a major challenge: wind. I would think that keeping a throttle-only model upwind would be fun. John's design is up to that challenge. He constructed it from balsa, and it uses a single-surface 1/32-inch-thick cambered wing with an 8%-thick airfoil.

The pusher has an 18-inch wingspan and weighs 34 grams. Power is provided by a Gary Jones 4:1 gear drive turning a GWS 5x3 propeller, energized by a single 130 mAh Li-Poly cell. The receiver is a Plantraco 900 MHz unit that includes a built-in speed control. The equipment is available from BSD Micro RC.

You've devised another interesting project, John.

Clear canopies and pilot figures for ParkZone models

ParkZone has provided us with some fantastic small-field RTFs in recent years, and they generally have opaque windshields or canopies. The downside of that kind of enclosure is that you can't see the pilot. This is especially troubling with models such as the ParkZone Micro P-51 and T-28, which have nice bubble-type canopies. I like scale models with visible pilots.

Enter Keith Sparks, who is a well-known scale modeler and the proprietor of Park Flyer Plastics. He has developed aftermarket clear canopies for the Micro P-51 and Micro T-28. He also sells terrific pilot figures that are sized to work with those models. The photo that Keith provided of the T-28 dressed up with a clear canopy and pilot figure is striking. If you would like to give your ParkZone Micro P-51 or T-28 a plastic greenhouse canopy, take a look at Keith's website. The address is in the "Sources" listing.

200-square-inch reduced-size old-timers

During the past year or so, MA Technical Editor Bob Aberle has been on a mission to generate interest in an old-timer/vintage event for reduced-size models. His idea is to fly designs with 200 square inches of wing area. To underscore Bob's proposed event, he has developed several sets of plans and corresponding models. His latest is the Ray Heit Scram from 1937.

The built-up, stick-style fuselage gives the airplane character. Bob powers his with a Lazertoyz 10-gram 1811-20 brushless outrunner motor. Energy comes from a two-cell, 800 mAh Li-Poly battery pack. The all-up flying weight is 7 ounces.

As is the case with Bob's other 200-square-inch old-timers, you can get plans for the Scram from the RC Micro World online magazine. That publication has been undergoing some changes; one is that its content is now free to everyone. A subscription gets you all of the plans featured on the site in a full-size digital format. Contact information is in the "Sources" listing.

The space meter tells me we have run out for this issue. As always, I look forward to hearing from you regarding your latest small-field modeling project. MA

Sources

Transcribed from original scans by AI. Minor OCR errors may remain.