Frequently Asked Questions
Bob Aberle | [email protected]
This is the 22nd monthly column in which I try to give the best possible answers to questions you have written or E-mailed to me. Each new inquiry has a sequential number for identification purposes.
Because publication space is limited, part of this month’s material will be published here, and you can find the column in its entirety on the AMA Web site at www.modelaircraft.org/mag/faq/index.asp. All questions and answers are posted there.
Once the material is posted to the Web site, you must access particular questions and answers by subject matter or categories. This is done to help you retrieve data for particular subjects. When you call up a question, it reads “Answer …” Double-click on that word, and that information, along with any related photos, will appear.
Let’s get started!
Q174 — Is electric-powered CL really viable?
“I attended the AMA Nationals competition held in Muncie, IN this past July primarily to observe the Control Line Stunt (Precision Aerobatics) event participants. While walking around and talking to the experts I learned that several of the top fliers were thinking of using electric power instead of glow, and that two of the Advanced class entrants had electric-powered models entered.
“Is this a viable idea? Since you are so involved in electric-powered flight, can you give me your thoughts on this new thrust?”
A174 — Answer
You asked the right person — I’m quite aware of this trend in electric-powered CL models. At least 10 years ago I witnessed a modeler fly an electric-powered CL model while attending the old KRC (Keystone Radio Control club) Electric Fun Fly in Quakertown, Pennsylvania. I even remember Model Aviation’s Aeromodeling Editor Bob Hunt taking a flight with his modified RD-1 model back then; he had converted it from glow to electric. At that time the best that electric power could offer was a cobalt, geared motor and Ni-Cd batteries. That combination was inefficient and somewhat heavy. A timing device (made by SR Batteries, I believe) was set to cut off the motor rather than let it “slow out.”
Unknown to me, many top CL Stunt competitors have been experimenting with electric power since that time. Recently I learned that Model Aviation Hall of Famer Windy Urtnowski is offering a DVD documenting much of the progress in electric-powered CL models up to the present. You can obtain this video from Windy by E-mailing [email protected] or calling (201) 896-8740 before 6 p.m. EST.
With the more recent progress in brushless motors and Li-Poly batteries, electric CL models are getting a real lift. Immediately after the 2005 AMA Nats, Bob Hunt (another Model Aviation Hall of Famer) decided to retrofit his Genesis Extreme design with electric power. That model was originally designed for .40-size glow power. Bob decided to use the electrified Genesis to try to win a spot on the U.S. F2B (CL Stunt) team that would compete at the FAI CL World Championships in Spain, July 16–23, 2006. He made this decision after watching the successes Mike Palko had with his Silencer (featured in the March 2005 Model Aviation—the electric-power theme issue).
Equipment used on Bob Hunt’s retrofit:
- AXI 2826/10 brushless outrunner motor (provided by Hobby Lobby International)
- Thunder Power 4S2P Li-Poly battery pack made from 2000 mAh cells (nominal 14.8 V, capacity 4000 mAh)
- Castle Creations Phoenix-45 speed control
- Bill Lee 11.5 x 4.1 carbon-fiber three-blade propeller
- Maximum motor current recorded: 39 amps
Because an electric-powered CL model cannot use radio control to operate the ESC, a solid-state timer/controller is required. Sergio Zigras (of Z Tron) designed a new timer distributed by Windy Urtnowski; it costs $30. Learn more at www.windyurtnowski.com.
Z Tron CL ESC Controller and Timer highlights:
- Size: 1 x 3/4 x 1/2 inch
- Weight: 2 grams
- Timable flight period: 0.5 to 8.0 minutes, in programmable 30-second increments
- Motor speed is adjustable during the timed flight
- Optional arming feature: push-button arm gives you 30 seconds to walk out to your control handle before the motor starts
The prescribed maneuvers in the AMA Precision Aerobatics pattern are completed in approximately 5.6 minutes, so the timer is commonly set to 6.0 minutes — roughly equivalent to running a glow tank dry.
One of the biggest benefits of electric power is the low noise level. You can fly at sunrise at a local athletic field and be largely unnoticed (though it’s best to get permission in advance).
Flying his electric-powered Genesis Extreme, Bob Hunt earned one of the three team spots — the first U.S. team member to fly CL with electric power at Worlds. He will join Paul Walker (first place) and David Fitzgerald (second place). Best of luck to Bob and the rest of the team!
Q175 — Will FMA Direct add a meter to the 6s Skyvolt charger?
“I read your review article on the new FMA Direct Skyvolt balanced battery-charging system that appeared in a recent Model Airplane News. I noticed in the photos that the FMA Direct 6s Skyvolt charger has only LED indicators and no meter.
“I'm kind of disappointed since I've been used to the LCD screen on my AstroFlight 109 Lithium charger. Is there any chance that FMA may add a meter at a later time?”
A175 — Answer
I’ve been using two different FMA Direct Skyvolt batteries, the 6s charger, and both types of DPMs (Discharge Protection Modules) for the past three months. I’m thoroughly satisfied with the total performance of this integrated Li-Poly cell-balancing concept.
The 6s charger has six separate outputs built into one case, so each cell in your Skyvolt battery pack is individually charged to the same maximum voltage and the cells are balanced after each charge.
I was also disappointed about not having an LCD screen with metered outputs on the 6s charger. In discussions with FMA Direct engineers I learned they may offer a deluxe version of the 6s charger with an LCD display in the future.
In the meantime, FMA Direct has upgraded its Viewer Software (normally supplied with its FS5 and FS8 receivers) to include the 6s charger. You can download the program from the FMA Web site (www.fmadirect.com) under "Service & Support" → "Downloads." Download "Dot.Net Framework Update" and then "Charger 6s Viewer."
If you don’t already have FMA Direct’s interface cable, you will need the Flight Systems PC Serial Interface Module (sells for $19.95). Plug the servo-connector lead from this module into the 6s charger, and plug the serial connector into a serial port on your PC — or use a serial-to-USB adapter to connect to a USB port.
I downloaded the viewer software to my laptop and connected the interface cable and adapter to a USB port. When you open the software you get a neat data sheet that displays:
- The voltage of each cell in your Skyvolt pack
- The ampere-hours (Ah) put back into each cell during charging
- A digital readout of the set charge current
- A graphable data display and a "Save As" option for filing data
I took my laptop to the flying field and left it next to the 6s charger. If you expect to be out for a long time, bring a power inverter to operate your laptop because its battery may not last that long. I’m enjoying this feature — it’s actually better than having an LCD screen built into the charger.
Q176 — Should I time full motor runs on the ground to avoid ESC low-voltage cutoff in flight?
“I have had my electric motor stop abruptly in flight when the ESC low-voltage cutoff operated. I ended up almost losing my aircraft because I was quite far from the runway when that happened. A friend told me I should time the full motor run on the ground as a guide and then keep track of that flight time while flying so I can shut down the motor before it cuts off by itself. Does that sound right?”
A176 — Answer
No — that is not the right approach. You should not run a motor statically on the ground for long periods. Without the benefit of the natural airflow a model gets while flying, you can easily overheat the motor, the ESC, and even the battery. A quick motor-current check on the ground is fine, but long static runs are risky.
Many modern ESCs have a "slow cutoff" setting that gives you some warning before the motor stops completely. If a sudden cutoff bothers you, consider using an ESC with a slow-cutoff feature.
— MA
Transcribed from original scans by AI. Minor OCR errors may remain.
