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An Introduction

to

Radio Control Electric Flight

by

Phil Langton

 

 

 

Information and Guidelines

for entering the exciting world of

 
 

Electric Powered R/C Flying

 

This document is broken into 5 parts

Part 1 - Introduction
Part 2 - Understanding power requirements & motors
Part 3 - Understanding batteries
Part 4 - Construction considerations
Part 5 - Conclusions

 

 Part 2

 

RULES OF THUMB & GOOD IDEAS:


The following guidelines will help the reader arrive at a satisfactory beginning in the exciting and challenging new field of Electric Model Flying. We’ve tried to use everyday language where possible, but the units of “Power” “Pressure” and “How much Fuel there is in the tank” end up being expressed as Watts, Volts and Amp Hours or derivations   thereof; Sorry!

1.    How much Power do I need for a given model?

Response: There are many ingredients in this equation, but here are a couple to get us started. 
Power, is expressed as Watts and when related to the weight of the model can give the modeler their first check on whether a certain electric power combination will achieve the flight performance they expect.  So, here are some statistics that are  somewhat universally accepted.
        50 to70 watts per pound  for a slow hand launch floater.
        70 to 100 watts per pound for fun aerobatics & ROG.
        100 to 150 watts per pound to easily ROG off grass.
        150 and above for competition, prop hanging etc
        200 to 250 watts per pound for electric flan jet models.

 

2.    Current limits for typical ‘can’ type brushed motors.

These are guidelines not rules. The following suggestions are MAXIMUM Amps that should be used by each motor, if you want to get a reasonable life out of your motor. Please appreciate that electric motors powered by DC will try to perform to the load placed on them, even if it means destruction!! They can be exceeded but there are consequences! For example the Speed 400 motor is quite good for a class of pylon racing and some pilots are quite happy to burn up a motor like this in one days racing. (After all, as the cost only $12 – 18 it’s not a big expense.) But to apply this approach to everyday sport flying will only result in disappointment.



So, here are my suggestions for sensible upper limits for some of the popular ‘can’ type motors:-
        Speed 400        10 Amps
        Speed 540        20 Amps
        Speed 600        25 Amps
        Speed 700        30 Amps
Other brush type motors, especially those with adjustable timing etc can be run at much higher currents but mostly the manufacturers of these motors will give relevant instructions.

3.    Current checks for typical brushless motors.

Brushless motors have introduced efficiencies in energy usage some say from as much as 10 to 20%! This is an enormous benefit to the quest for satisfactory electric flight. To give an idea of how important this is, take the simple 380 can motor, now generically known as the Speed 400. One can buy a outrunner brushless motor that will give the output of the Speed 400 but is 20% more economical to run and may be even 20% lighter as well.
Alternately, A motor of similar physical proportions to a Speed 400 motor can give the output of a 480 can motor, also without much of a weight penalty.
Rules of thumb are not so appropriate here as there is so much variation in brushless motor construction and performance, e.g. They can be “inrunner or outrunner” type motors and each of particular flight performances.
The wisest course of action here is to consult the makers data either from original instruction manuals or by searching the world wide web. You can, of course copy the combinations of your modeler friends who have successfully done exactly what you propose to do. AND,  this vital:-
Always, yes, always make up a testing stand and set up your propeller/motor/battery/speed controller combination and do actual amps/volts/watts checks before even thinking of bolting the gear in you model.   

Obviously, then compare your results against the requirements of your model, always keeping within the parameters of your equipment.
Most “would be” electric flyers’ errors occur because they short circuit this checking. They do so often at some considerable expense and grief!!!!
 

 

Disclaimer:  To the reader... please feel free to download, use and copy this Treatise on the understanding that it is for 'private' use only and must not be used in any way for commercial purposes without the writers permission. 
 
Note also, that the information is a work in process and may be amended at any time should the writer or the Club decide so to do. No responsibility or liability is expressed or implied with respect to the information contained in the Introduction to Electric Flight material.

A copy of this article is also available in pdf format below.

Files:
Name Created Size Downloads    
O.S. Engines 2008 Flyer 2008-10-18 104.47 KB 317 Download

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