Radio Control: Scale

Radio Control: Scale

Bob and Dolly Wischer

Installing Equipment

Adding seats, upholstery, and controls for even spartan interiors used to be rare. Today some interior detailing is common, although a truly complete cockpit is still not often seen. The degree of completeness depends on the modeler's desire to reproduce the prototype and on access to the full‑size aircraft for measurements. Photos help, but direct measurements of the original are best.

Space and layout

• Servos, receiver, and batteries often occupy the space normally used by passengers in civil‑type models. Military types, with relatively small cockpits and larger overall fuselage volume, are less likely to be cramped. Builders of large aircraft have the advantage of more internal space, and modern high‑torque servos are smaller than they used to be.
• Hiding servos and the receiver beneath a cabin seat is simple and effective.

Servos and engine proximity

• To avoid running a throttle pushrod through the cabin, the throttle servo can be mounted just behind the engine. Using a .60‑size two‑stroke or a twin/four‑stroke engine, vibration problems with a servo mounted close to the engine are often minimized. We have mounted a Kraft 15 servo about an inch behind the engine; in several models these servos have required no service for ten years and hundreds of flights.
• The real enemy of a close‑mounted servo is an unbalanced propeller. Vibration from a .90 or 1.20 four‑stroke single‑cylinder engine can be severe; in those cases place the throttle servo farther away. Balsa wood is a good absorber of vibration.

Throttle pushrod routing

• If the throttle pushrod must pass across the cabin, bury it in a side wall: use a heavy flexible cable encased in a plastic tube and epoxy it into a groove cut in the cabin wall; the cable exits the firewall behind the engine.
• Where the cable exits the firewall, cut it off and join it to the throttle lever with a music‑wire extension connector—a short length of soldered brass tube. Wherever a flexible cable is unsupported, a music‑wire extension provides rigidity.
• We have tried stiffening flexible cable by flowing solder into the strands; this helps only for very short lengths. Over distances of more than about two inches the cable may buckle under compression, and when the servo arm moves the throttle will not open.

Switches and canopy

• Concealing the on‑off switch is a common problem for scale appearance. On open‑cockpit airplanes, consider installing the switch so it can be operated by moving the pilot's throttle lever or a small push knob.
• Locating the switch inside a cockpit with a sliding or hinged canopy is undesirable unless the canopy has a secure latch. Otherwise the canopy may open unexpectedly during flight, or the canopy will need to be tied down for safety. Some modelers use a bit of transparent tape to seal the canopy latch after the switch is set—this is a nuisance because the tape must be peeled away after landing.
• In cabin‑type models the switch can be hidden under a seat or behind a cabin door. If the door must be opened for ground handling, it will have to be opened before and after each flight; this creates a risk that the door won't be latched before takeoff. The latch should be substantial—preferably a copy of the full‑size latch—and the door must be secured in the open position while the model is on the ground to avoid being blown shut by prop blast.

Cabin doors and actuators

• On some cabin models, the doors can be operated by a servo mounted on the spar inside the fuselage. A lever projects through the fuselage side to operate the door. Use a strong hinge and a good counterbalance or spring to hold the door against prop blast. On small models, simple wire hooks or latches may be sufficient.
• If doors are made removable for ground handling, reinforce the door opening, fit small dowels to locate removable doors accurately, and support hinges with small blocks. Small screws accessible from inside the cockpit often suffice to fasten doors securely.

Pilot figures and access

• Scale pilot figures must be secured well or they will be blown out or rattle. Fasten the pilot with a screw or small bolt from beneath the floor. If the pilot is removable, provide a convenient access panel beneath the fuselage.
• Receivers can sometimes be hidden beneath the cockpit floor—a section of floor can be held by a wooden cleat and a single wood screw for access. Another method for 1/5‑scale or larger models is to place the receiver inside a dummy pilot: wrap the receiver in foam and hold it with the seat belt. A disadvantage is the pilot must remain inside, and it may be preferable to remove the pilot for static judging at contests to show cockpit detail.

External pushrods and concealed linkages

• One of the best methods for a concealed control connection is a wire pushrod that extends outside the fuselage in a concealed location, such as the open rear end of a radial‑engine cowl. Another successful method is to use an existing cowl opening (for example an oil fill tube opening) and run a tiny bent wire through it—barely visible.

Switch harnesses and wiring

• The standard switch harness supplied with radios often has wires that are too short for hidden switch locations. Hobby shops commonly stock extension cords and connectors for modifying switch harnesses. It may be better to buy a new switch and make a custom harness to fit exactly.
• Scattering batteries, switch, receiver, and servos around the interior for concealment usually means extra wiring and extensions. Plan a wiring path through the structure during construction to keep wiring out of sight and tidy. This requires forethought but is not particularly difficult.

Receivers and equipment concealment

• Receivers, being flat, will sometimes fit beneath the floor; servos can be hidden beneath seats. Because of our insistence upon concealment, very few of our scale models use factory switch harnesses.

Historic note and wiring lessons

• Early RC scale models carried large batteries, tube‑type receivers, multiple switches, and escapements. Wiring then was often a tangled mess—jokingly compared to a Brillo pad.
• Never coil the antenna inside the fuselage. We once coiled the antenna out of sight and flew the model; it crashed. Lesson learned.

Antenna installation

• Stretch the antenna loosely rearward inside the fuselage. If the wire is long enough, let it protrude through a tiny hole near the tailpost and tie a knot to prevent retraction. For longer fuselages, tape the antenna at intervals to a length of 1/8‑inch square balsa, then insert the balsa into the fuselage rear; a bit of masking tape at the front end keeps the balsa from coming adrift.
• On our recent models the rudder is operated by a pair of tightly stretched steel cables and the antenna parallels this cable path. The antenna can contact the cables without reducing radio range because the cables are anchored to plywood bellcranks. If bellcranks are metal, check range with the antenna inside the fuselage to be sure there is no loss.

Grain Filler

Within the past two years, Hobbyponx introduced a Fast Fill product for filling balsa grain. It worked well for filling, but was hard to sand. Hobbyponx has recently improved the product and introduced a new Fast Fill that now sands away easily and performs as expected.

Hobbyponx Colors

Hobbyponx has released camouflage color formulas covering U.S. Navy fighters from the 1930s into early WWII and the three colors used in British Royal Air Force insignia.

• For U.S. Navy fighters during the 1930s:
• All‑metal surfaces (top and bottom): gloss light gray ANA 512.
• Fabric surfaces: yellow.
• Upper wing (on biplanes) top surface: orange yellow (chrome yellow).
• Prototype/early Grumman F4F Wildcats and Brewster Buffalos used this scheme.

• Shortly before the war: overall matte light gray ANA 602 was adopted for some aircraft (later F4Fs and Brewsters).

• With the outbreak of war: a two‑color scheme was used — matte blue‑gray ANA 603 on top with matte light gray undersurfaces (used in 1942 on Wildcats, Hellcats, and early Corsairs). On early Corsairs the lower surface of folding wing panels was painted in the upper surface color.

• In 1943: a three‑color scheme of sea blue, intermediate blue, and matte white was adopted.

Navy formulas (Hobbyponx epoxy paints):

• Gloss light gray: 9 parts H70 gray, 5 parts H10 white, 1 part H55 cream. For gloss finish mix one‑to‑one with H02 gloss or H06 quick spray hardener.
• Matte light gray: 50 parts H10 white, 21 parts H70 gray, 2 parts H66 dark red, 1 part H49 Cub yellow. For matte finish mix one‑to‑one with H05 flat hardener.
• Matte blue‑gray: 10 parts H70 gray, 3 parts H81 black. For matte finish mix one‑to‑one with H05 flat hardener.

RAF insignia colors (use H05 flat hardener with these mixes):

• RAF red (dull rust‑red): 20 parts H65 bright red, 3 parts H66 dark red, 2 parts H57 orange, 1 part H81 black, 1 part H10 white.
• RAF blue: 11 parts H24 dark blue, 5 parts H81 black, 1 part H65 bright red.
• RAF yellow: 9 parts H49 Cub yellow, 7 parts H47 bright yellow, 3 parts H55 cream, 2 parts H66 dark red.
• White: Hobbyponx H10 white (straight).

Notes:

• These formulas are correct only when Hobbyponx epoxy paints are used.
• During 1942–43 there was some variation in the red used on U.S. insignia (bright red versus the dull rust‑red). Use reference material to choose the appropriate shade.

Bob and Dolly Wischer S‑221 Lapham Peak Rd., Delafield, WI 53018.

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