Electric R/C Flight
Part 1: Introduction
My name is Heather Mardon, I am a fairly new club member but have been flying electric powered R/C planes for about two years. As there seems to be a reasonable level of interest in this field I thought I would write a column to try and explain some of the technical jargon and dispel some popular mythís about electrics.
Why I fly electric
In essence Electric models are mostly the same as their IC counterparts. The following is a comparison of the two.
|Powerplant||Internal combustion||Electric motor|
|Fuel||Glowfuel/Petrol||Nicad or NiMh Batteries|
|Throttle||Server connected to carb||Electronic Speed Controller (ESC)|
Typically the construction of an electric powered model can be made lighter due to far less vibration from the motor and it does not need to be fuel proofed. With electrics there is not an unlimited amount of power on tap so you need to be mindfull of weight at every step of building. A good saying to remember is "itís hard to save 100grams in one place, but easier to save 1 gram in 100 places". The cost of smaller radio gear and servos has dropped over the years so try and use the lightest you can. Eg GWS Naro Pro-BB servos have plenty of power, only weigh 13grams and cost about $50.
"Electrics are only for indoor/parkfly models"
Wrong! Electric powered models range from 50g feather weight indoors up this Ĺ scale Klemm L-25 (6.5m span)
The hardest part of making an electric is knowing what motor/gearbox/battery/prop combination to use. There are far more variables involved than just being able to say "requires a .40 - .46 2 stroke"
The easiest method is to copy off somebody else who has already done the homework! (As long as there plane is similair in weight, flying speed etc). I will be going into much more detail on power plant selection in future articles.
An electric model peforms best when it is designed for this power plant from the start. Then the design can accommodate the different motor mounting, a place for the battery pack and preferably a hatch to allow access to the battery so the wing does not have to be removed as well as lighter weight construction.
It is possible to do IC to E power conversions of existing kits and plans. Some are better suited than others, for example most of the SIG Kadet and Senoirita designs convert easily as they are lightly built to begin with. Many IC powered ARF kits are too heavy for successful conversion although there are a few exceptions. A future article will cover a conversion I am currently undertaking of an Airsail Volksplane.
Hereís the business end of a SIG LT-25, Itís powered by a Kyosho "Magnetic Mayhem" reverse motor on a 3.5:1 Master Airscrew gear box on 10 cells and a 12 * 8 prop. The motor has been wrapped in a ply tube and fitted to the original kit motor mount.
There are several Electric designed kits that have been around for a long time eg Great Planes ElectriCub & Electrostreak. These models perform poorly on there bundled motors and recommended batteries. By changing the motor, increasing the number of cells and in the case of the Cub adding a gearbox these models can be totally transformed.
Next month Iíll be talking about the types of electric motors and going over a few "rules of thumb" for choosing a power plant.