Author: B. Kopski
Edition: Model Aviation - 1995/10
Page Numbers: 80, 82, 83, 84, 85
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RADIO CONTROL ELECTRICS

Bob Kopski, 25 West End Drive, Lansdale PA 19446

THIS MONTH'S TOPICS include a reminder ("Club Call"); an October meet; tiny R/C Electric gear; Master Airscrew product use and modifications; prop balancing; and follow-up on the electrified Sig Wonder.

Club call

  • All-electric clubs (or clubs with significant electric participation looking to grow) are invited to write for listing in the early 1996 column.
  • Clubs with electric newsletters that are available to anyone should indicate availability and how to obtain a subscription.
  • Please include a SASE with correspondence for which you'd like a reply.

October meet — Gulf States Electric Fly-In

  • Dates: October 21–22.
  • Sponsored by: Ozone R/C Club.
  • Location: Louisiana Polo Field ("America's Finest Electric Flying Field").
  • Events: All-day fun flying, several contest-style events, Cajun cookout, and more.
  • Contact: Ben Mathews, 101 Mulberry, Metairie LA 70005; Tel.: (504) 833-5589.

Tiny R/C Electric (CETO system)

  • Cloud Nine RC (John Worth) is marketing a very small RC system by CETO — about 1/2 ounce airborne weight.
  • John Worth (former AMA Executive Director) has described several indoor projects using this tiny system and is expanding its applications.
  • Contact: Cloud Nine RC, 4326 Andes Dr., Fairfax VA 22030; Tel./fax: (703) 273-0607.

MASTER AIRSCREW POWER SYSTEM AND MODIFICATIONS

System description

  • Master Airscrew economy electric power package typically includes:
  • "Can" motor
  • Gear drive
  • 12 x 8 folding prop
  • Spinner
  • Available gear ratios: 2.5:1, 3:1, and 3.5:1.
  • Typical price: often discounted under $30 (suggested retail $39.95).
  • Operates well on 6–7 cells and offers good value for the money; used successfully in sailplanes (e.g., Electra) and some profile models (Mirage, PT Electric).

Issues encountered

  • On some models the landing gear does not provide clearance for the supplied 12-inch folding prop, requiring hand launches.
  • Folded blades can hang up on fuselage protrusions and fail to reopen.
  • In raffle/ready-to-fly applications (Showvolt/profile Revolt type), fixed-blade wood props (11 x 7 to 12 x 8) perform well but are often stronger than the supplied gearbox, resulting in damaged gearboxes after impacts.

Motor mounting modification

  • Purpose: let the motor assembly give under impact to reduce gearbox breakage.
  • Change: retain original fuselage location and V-block, but replace the "golden inner rod" clamps with ordinary rubber bands to allow some movement.

Folding-prop modification (prop-specific)

  • Purpose: make folder blades springy, less likely to hang up, and able to yield on impact.
  • Parts required:
  • 1/4-inch length, 6-32 machine screw (quantity as needed for hub)
  • 6-32 split-ring lock washer(s)
  • Formed piece of .025" x 1/4" K&S brass strip
  • Hardware-store O-ring (approx. 3/8" I.D., .1" thick — often labeled "#10")
  • Small drop of thin cyanoacrylate (CyA)
  • Steps (summary):
  1. Drill 7/64" holes centered on the brass strips, 1/8" from the ends.
  2. Pass 6-32 screws through these holes; place the lock washers between screw heads and brass strips.
  3. Thread the screws into the hub holes originally used for the spinner. Put a tiny drop of CyA at the screw head/brass interface.
  4. Bend the brass strip so the upturned ends are even with the hub ends; upturn only about 1/16" to capture the O-ring.
  5. Fit the O-ring over the upturned ends to hold the blades in the open position under light tension; blades gain a springy give on impact.
  • Notes:
  • This modification can be done with simple tools and supplies.
  • The original spinner may still be usable by fitting the brass strips between spinner and hub with the spinner screws holding both.
  • In sailplane installations where folded hangup is unlikely, this modification may be unnecessary or counterproductive.

PROP BALANCING

  • Method (from Keith Shaw):
  • Tools: prop, prop balancer (e.g., Du-Bro), thin clear plastic packing tape.
  • Procedure:
  1. Mount prop on balancer and determine the light blade.
  2. Apply a piece of tape to the back surface of the light blade, trimmed to the blade outline.
  3. Recheck balance. If the treated blade becomes heavy, remove small amounts of tape starting near the hub and recheck until balance is achieved.
  • Advantages:
  • Quick, neat, clean, no sanding or paint required.
  • Tape is nearly invisible and won't ruin decorated props for scale models.
  • Caution:
  • For "wet" (fuel) applications, tape may be attacked by fuel and is not recommended; traditional sanding/filing is probably best for fuel engines.
  • The editor also questions tape use for high-rpm or wet props from a safety standpoint.

SIG WONDER ELECTRIFICATION — FOLLOW-UP

Conversion details

  • Noted at LVRCS '94; became a popular wet-to-electric conversion.
  • My installation:
  • Motor: geared Cobalt .05
  • Prop: 12 x 7 Sonic-Tronics folding prop
  • Batteries: seven 1700 mAh SCRC cells
  • Control: two channels; throttle via Flighttec SP with BEC
  • All-up weight: 44 ounces
  • Comments:
  • The electrified Wonder is not for beginners — it is responsive and can be touchy.
  • Built from the kit with minor changes: wingtip plates and cowled motor (required recutting fuselage sides), and substituted sheet balsa for the stab where kit material was heavy.
  • Battery pack velcroed to the fuselage floor.

Cooling and battery-pack issues

  • After several flights the pack ran hot; added air intakes (cut from plastic spoons) on each side and atop the motor cowl. Air exit was at the elevator pushrod opening.
  • Cooling was only partially effective because the pack is nested; rear cells did not benefit as much.

Cell surface temperature tests

  • Setup: LM34DZ sensor attached to a front cell and a rear cell; recorded surface temperatures.
  • Results (rear cell / front cell):
  1. Ambient air: 81°F
  2. Before charging: 79° / 78°
  3. After peak charging: 95° / 94°
  4. After "full power" 5:58 flight: 151° / 133°
  5. 15 min. of blower air via motor compartment: 109° / 90°
  6. Remove wing, blow air into fuselage: 80° / 77°
  7. After peak charging (second measurement): 99° / 97°
  8. After 5:33 flight with air intakes blocked: 146° / 146°
  • Observations:
  • Cooling airflow as implemented may carry heat from the front toward the rear, making rear cells hotter.
  • This does not compare with installations where airflow is planned from the start and is more effective.

Recommendations and notes

  • Consider an E-configuration with a removable bottom hatch for cooling and easier recharging of the pack.
  • Balance point is sensitive; honor the plan location. On mine the balance point is 5/8" forward of the plan location to calm the model. Do not balance rearward of the plan location.
  • The Velcroed pack allows easy fore/aft adjustment for trimming.
  • Reinforce the twin-fin attachment joints with triangle gussets where the fins meet the fuselage; the stock joints can break easily due to limited glue area and ground contact.

CLOSING

  • Please enclose a SASE with correspondence for which you'd like a reply.
  • Meanwhile, enjoy the clean, quiet, and powerful joy that electric flight brings — and the flying fields you don't lose because of it.

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