With the improvements in available equipment flying electric no longer means compromising duration, performance or restriction to lightly loaded designs. There is a plethora of electric designs available many exceeding the performance of fuel powered equivalents. In addition it is feasible to power models designed for glow power with an electric setup.
- No fuel mess to clean up resulting in longer airframe life due to covering staying attached and no fuel soaked timber.
- Field equipment reduced to Transmitter, Battery(s), Charger and Model.
- Quiet operation (Outrunner designs)
- Reliable operation (less dead stick landings)
- Time taken to refuel (recharge batteries)
- Throttle management required for extended flights
- Additional initial investment in charger etc.
An electric model must consist of the following carefully considered components as each component will affect the performance of the whole system. It is worthwhile following model manufacturers recommendations, advice from those with a history of success or personal research. I would recommend a computer program such as motocalc to assist with decisions. www.motocalc.com
40 size conversion
Looking at all possible aircraft is beyond the scope of this article so let’s look at the conversion of a 40 size sports aircraft designed for glow power. In this case we are looking for spirited performance with a duration of at least 8 minutes consuming less than 80% of battery capacity. Although larger than required a 50mm dia x 55mm long outrunner is chosen producing 600 revs per volt. As this will draw under 50amps a 60amp speed control is chosen. This system could be powered with 4 cell lipo of 4000 to 5000 mah or 5 cell of 3200 to 4200mah capacity. I have chosen a 5 cell as the amp draw will be less and the prop smaller for clearance. More importantly I had the 5 cell battery. Propellers play a huge role with electrics and on this occasion I chose APC 12x8 electric. Receiver and servo’s are powered by a separate ubec ( a regulator to provide constant 5v power to the receiver and servos) however a receiver pack could have been used.
This results in a model around 2oz heavier than 2 stroke glow equivalent at 5lb 10oz
with the following specifications:
- 23mph stall, 36mph optimal, 67mph maximum
- 46 amp static current draw
- 6lb 11oz thrust @ 10000 rpm
- 812 watts input @ 86% efficiency
- Flight times of 10 minutes
This is similar performance to an OS 55ax (700 watts = aprox 1hp)
Batteries & Chargers
Quality batteries are essential to achieving strong performance and savings in this area will probably cause disappointment. To maintain batteries a quality balancing charger is essential. Try to choose a charger that is upgradable as new battery chemistries are introduced.