Frequently Asked Questions - 2008/03 | Model Aviation Library

Author: Bob Aberle

Edition: Model Aviation - 2008/03
Page Numbers: 89,90,91

Electric indoor CL flying

Q336

"I've seen references in your column to electric powered control line flying and the successes Bob Hunt has had with such planes. But I heard recently that there is now a move towards indoor electric powered control line flying. What can you tell me about this and whom might I contact for more details?"

A336: One of the people actively developing this concept is Bob Wilder of Colleyville, Texas. He has been known for years for his many indoor RC endurance records, but Bob has always been fond of control-line (CL) flying. Last year he applied his talents to new concepts for indoor CL flying.

Bob's approach involves flying electric-powered CL models from 27- and 32-foot lines in school gymnasiums and similar indoor facilities. The beauty of this is that the airplanes are constrained by the lines; they cannot go astray and hit walls, ceilings, or basketball hoops. School gyms are much more available to modelers than large inflatable sports domes.

The type of aircraft Bob is developing tends to weigh 6–8 ounces and is powered by brushless motors with input power of 30–50 watts. The models are mostly made from Depron foam sheet material, often reinforced with carbon-fiber tape.

I had been following Bob's design progress for the past year, but I didn't fully understand everything until I saw his demonstration at the JR Indoor Electric Festival in Columbus, Ohio, last November. He aims to develop indoor CL designs for categories such as scale, racing, combat, carrier, speed, stunt, and general sport.

Bob has developed two interesting concepts. The first employs conventional two-line control with a standard bellcrank operating the elevator (and sometimes coordinated flaps). In this configuration the brushless motor is controlled by an ESC that is connected to a special Multiple Function Electronic Timer device that Bob offers.

The timer can be programmed to time your flight and cut off power before the battery is depleted. It also allows the user to adjust motor speed. The timer weighs only 3.2 grams and is inexpensive.

Some people have difficulty flying CL because turning rapidly in circles can cause nausea. Watching gymnasium walls flash by might even exaggerate this condition. To cope, Bob developed a single-control-line aircraft tethered to a centrally located pylon.

In that setup the timer is unplugged and replaced with an RC receiver (much like replacing a module) and an RC servo. The pilot stands outside the circle, holding an RC transmitter that remotely controls the motor (via the ESC) and the elevator (via the servo). I witnessed several flights and found the concept fascinating.

To make loops even tighter for CL combat, Bob devised a gimbaled electric motor mount. As elevator control is applied, the motor pivots up and down, which greatly tightens loop maneuvers. The airplane almost pivots as if held at both wingtips. I’ve seen photos of Bob flying combat with a friend, and it looks like a lot of fun. I would guess this gimbaled technique could work with single- and double-control-line setups.

As for where to buy these airplanes and the timer/control systems: Bob has several hobby manufacturers interested in the designs and would like to sell production rights. In the meantime, he’d love to hear from anyone interested in this type of indoor flying. Bob prefers phone calls; his number is (817) 498-6316. He wants to assess market potential, so please call if you have an interest.

Q337

"I own several six-meter (50 MHz) RC receivers and have used them successfully for several years now. Recently I went to buy several more 50 MHz RC receivers and found they were no longer available. Can you recommend any suppliers that I may have missed?"

A337: First, a note on sources of supply; then some additional information about six-meter (50 MHz) RC operation.

To my knowledge, Futaba and JR still sell RC transmitter modules and receivers intended for 50 MHz operation. The 50 MHz transmitter modules can plug into most of their transmitters. You can purchase receivers separately; they are not the smallest or lightest by present-day standards.

FMA Direct offered its tiny M5 dual-conversion receivers on 50 MHz several years back, but the supply has dried up. The company was accepting special orders for a remaining batch of 50 MHz receivers, but that offer ran out November 30, 2007. I apologize for not passing that information along sooner. You might still contact FMA Direct as a courtesy.

On the RC Groups forum, Jim Cob posted an article titled "Mini-HowTo—Castle-Berg 50 MHz conversion" describing his successful conversion of the Castle Creations Berg four-channel MS4L receiver to the 50 MHz ham band. You must know what you are doing to accomplish this conversion and be aware that modifying the receiver voids the factory warranty. Still, the reference is available for those inclined.

The best news is that a Canadian manufacturer has been offering several types of 50 MHz RC receivers. Sombra Labs Inc. of Ottawa, Ontario, indicated it still has the Lepton 5 single-conversion (crystal) receiver at 6.8 grams (0.24 ounce) total weight and the SL-8 synthesized dual-conversion receiver at 9 grams (0.32 ounce) total weight. Both operate on the Amateur Radio Service six-meter band (50 MHz). I believe the company also has receivers on the original 53 MHz RC channels.

I also understand that West Mountain Radio, maker of the CBA II battery tester, will be distributing Sombra Labs receivers in the U.S. West Mountain Radio’s website showed only 72 MHz receivers at the time, but the 50 MHz receiver should be added.

With many users moving to 2.4 GHz spread-spectrum systems, one might wonder why anyone would pursue six-meter RC flying. Although you share 50 MHz frequencies with other amateur operators ("hams"), I have used the band since 1957 (my call is W2QPP) and have never had a model shot down or interfered with.

To legally fly RC on six meters you must hold a valid Amateur Radio Service license. Until several years ago, obtaining that license required knowledge of Morse code at five words per minute; that requirement no longer applies. Now you must pass a written test of roughly 35 questions.

You can learn about license requirements, see sample tests, and find test locations by contacting the American Radio Relay League (ARRL) in Newington, Connecticut. There are also online resources to help you get a ham radio license. If you’re interested in pursuing six-meter RC operation, look up both ARRL and the online license-help resources.

For those properly licensed and regularly using the six-meter amateur band, your license is valid for 10 years. Check your expiration date. I found my general-class license expires in May 2008. If your license expires, you cannot legally use the six-meter band to fly RC or enter sanctioned AMA flying activities—licenses are checked at these functions.

If your license needs renewal, you can download FCC Form 605. It can be submitted only 90 days before your license expires or up to two years after its expiration. You can renew online. If you are beyond two years, contact the ARRL for further instructions.

Q338

"Now that we are seeing so many inexpensive micro-size brushless electric motors, what do we do for micro-size scale aircraft?"

A338: I expect many micro-size ARF and even RTF models will soon appear on the hobby market. For now I recommend the laser-cut kits from Dumas Products, available with wingspans of 17, 24, and 30 inches.

For plans, I strongly recommend the micro rubber-powered designs from Bill Schmidt, a noted modeler. Bill has had many construction articles published in Flying Models magazine over the years, and you can purchase plans for those airplanes from Carstens Publications. Bill also sells plans direct; I recently bought micro-size scale plans for an Aeronca 7AC Champion, a Piper PA-11 on twin floats, and a Piper PA-16 Clipper. All of Bill's plans can be easily converted from rubber-powered free flight to electric-powered RC. Write or call Bill Schmidt and request a catalog listing of his micro-scale plans.

Please write in with your questions; that is the only way we can keep this column format going. When referring to published Q-and-As (for follow-ups), provide the question number as a reference. — MA