I have been busy, and the well-traveled sailplane aficionado, Gordy Stahl, offered to contribute some good content for my “RC Soaring” column. Read on to learn about electric-launch sailplanes.
Gordon Buckland and I have been Soaring pals from roughly the first day he decided to get back into RC Soaring in 2009. He had emigrated from Australia 10 years before that to pursue a career in the US, and hadn’t flown an RC sailplane for more than 20 years.
We met at the Orlando Buzzards club flying site in Florida and he was full of enthusiasm, excitement, and memories of skills long since rusted. I helped him get started again and I’m proud to call him my friend and very proud of his growth in the RC Soaring hobby.
He mentioned to me that he was swamped with life and that his column deadline was coming up, so I asked if he’d like for me to write something about electric-launch sailplanes. I have been playing with various motors, gearboxes, and other doodads because it’s clear that Altitude Limited Electric Soaring (ALES)/F5J Lite will be a busy part of RC Soaring. Electric launch is “RC Soaring Lite,” because it loses a third of the experience of flying sailplanes.
There are three components to an RC sailplane flight: the launch, the flight, and the landing. With winch launching, the pilot must study, work on programming settings, and practice launches to optimize his or her technique to achieve a safe, high launch.
As the modeler approaches the winch his or her mind reviews a checklist of possibilities. The pilot feels some fear and elation while hooking up to the line, tapping out the line slack, and building tension, then feels the pull increase on his or her shoulder/arm and hand. When he or she calculates that it is right, the pilot throws the aircraft!
Time slows as this person watches the sailplane rise upward. Many thoughts and calculations are processed, then the model hits a spot roughly 75 feet up. The wing suddenly grabs the air, stuttering for a minute to decide whether it’s going to continue onward. The pilot is focused to avoid chaos. He or she taps the pedal to avoid taking in too much line, yet maintaining speed for the “ping” release at the top. Then there is the elation of seeing that the aircraft is highest in the group, or sometimes the frustration of being lowest!
With electric launch, the pilot is cheated out of that part of the Soaring experience. New pilots starting with electric-launch models may never learn or feel the exhilaration that comes from launching. I’m not implying that electric launch isn’t fun or challenging or that there is nothing to learn about electric-launch strategies, but using an electric motor and propeller does have a price beyond the cost of the components.
Because electric launch is quickly gaining popularity, is accepted by the League of Silent Flight (LSF), and many contests use it (specifically ALES-class competitions), I have been busy learning about its launch strategies and equipment. It uses LiPo batteries for the motor, and the same pack powers the receiver via the BEC. Did you know that you need to storage discharge LiPo motor packs? If you don’t, they can swell up while waiting to be used.
At the first ALES contest I attended, the horn sounded and I turned on the motor. The airplane went up approximately 30 feet, leveled off, and floated down in front of me, out of control. The battery I chose was dead! I almost lost an expensive airframe! That’s when I started looking for alternative receiver power sources for the BEC.
I tried using a receiver battery pack instead of the BEC, but accessing and charging it in the skinny fuselages was a hassle. I needed a smart backup receiver battery system. A smart electric-launch sailplane pal, John Lueke, told me about the Scorpion Backup Guard for $24.99 from Scorpion Power Systems. I purchased it from Graves RC.
It’s tiny. At only 38 grams and 5 x 31 x 15mm, it comes complete with a two-cell 500 mAh LiPo battery with 5 volts at 10-amp peak. It’s approximately the price of a NiMH battery receiver pack! The BEC still powers the receiver and the Scorpion is plugged into any open receiver servo slot. When the circuit inside the Scorpion senses a voltage drop below 5 volts from the BEC, the backup battery takes over!
If front-end components of your expensive electric-launch sailplane died, you would still have control. Upon landing, you would hear the Scorpion beeping, bragging that it saved your model!
Just Short of Perfect
You have to connect the motor battery so that the BEC can power the system. A small switch on the Scorpion engages it. To ensure that the Scorpion’s battery doesn’t get used except for during an emergency situation, you need to switch it off before disconnecting the motor battery.
Don’t store it fully charged. You must do storage discharging between flying days. It needs an adapter to charge its battery, so it must be accessible in the fuselage.
If your BEC has a short-term voltage drop, the Scorpion will turn on and remain on. It doesn’t hurt anything, but you likely would prefer that it all be there if you need it. Its battery doesn’t need to be charged after setting for long periods, and a red light will flash to indicate low voltage.
One consideration is your choice of ESC. Many come set at 5 volts. That’s a problem because of voltage drop spikes. You should look for an ESC with 5 volts plus BEC output or one that is programmable such as the inexpensive ZTW Mantis series, also available through Graves RC.
So, if the Scorpion isn’t everything we want, what is? After using the system for more than a year at contests, I’ve learned that a backup system should have:
• A small size and weight.
• No need to charge or maintain its LiPo. (It acts as a charger, drawing energy from the motor battery to ensure it is always ready.)
• An automatic on/off. On when the BEC’s voltage drops, but off when it goes above what’s needed. Also, a range of voltage output to match the high-voltage systems used today.
• An inexpensive price.
OptiPOWER Ultra Guard 430
Jeff Sanford posted information on the RC Soaring Society’s Facebook page about the Ultra Guard system—a backup battery system that appeared to have all of my dream features!
The device is plugged into a free port on your receiver system. When you power up it waits, monitors your system’s set voltage (5 to 9 volts), then arms at that voltage minus 0.5 volts. The device is then armed and monitors the system voltage and the state of its backup pack.
If the backup pack needs topped off, it will draw from the motor pack and stop when it gets to 8.1 volts. It samples the system voltage every 2 milliseconds and if the system voltage drops below the armed set voltage, the buffer pack steps in. If the system voltage recovers, it drops out.
The Ultra Guard system is 17 x 50 x 30mm and weighs 39 grams, including the 430 mAh LiPo. It is available through Experience RC for $39.There’s a button on the board that allows you to manually put its LiPo in discharge mode, or set the system to hibernate while it’s in your shop drawer!
The Ultra Guard is software based and is fitted with a micro USB port so that as firmware features are upgraded, you can update your Ultra Guard 430. Some very cool features are in the works! If you have more questions, check out the websites listed in “Sources” or contact me via email.
I’m excited! Are you?
Thank you, Gordy, for your contribution. Until next time, go downwind and soar.