Q-44: I’m an experienced modeler who has flown strictly glow-fuel-powered aircraft. I always knew what displacement engine would power a particular size and weight aircraft. Now I’m entering electric power and I’m having trouble relating motor designations, motor current, number of battery cells in a pack, propeller size, and whether or not I should use direct or gear drive. Can you steer me in the right direction?
A-44: This is the biggest concern of all electric-power enthusiasts. Before getting frustrated you should first go by the manufacturers' recommendations. Ready-to-fly (RTF) models come with the motor mounted in the aircraft. All the choices have been made for you. Almost-ready-to-fly (ARF) models will either include the motor with the kit or will at least specify all the necessary electric-power equipment to make that specific airplane fly.
Construction kits intended for electric power will usually specify motor, propeller, battery, speed controller, etc. The problems begin when you attempt to convert a model intended for fueled power into electric power. Problems also can occur when you decide to improve the performance of your electric-powered model by going to alternate size motors and batteries. Motor and battery distributors can usually point you in the right direction by suggesting components that meet your needs. But what can you do on your own?
Two excellent computer programs are available from Sid Kauffman (ElectriCalc)
(www.slkelectronics.com/ecalc/)
and Stefan Vorkoetter (MotoCalc) (www.motocalc.com/). These programs are not
expensive, however, they do require current motor data to continue to be useful.
In other words as each new electric motor is introduced into our hobby, the data
must be posted into these programs. Regular updates are made available and that
is highly recommended. In both of these programs you can vary motor types, motor
current, number cells in a battery, propeller size, etc. Each time you change a
parameter, the program is smart enough to recalculate the effect on your model.
In addition to these motor calculation programs, there are several Web sites
that I can recommend that will provide much electric motor application data. One
is the Great Electric Motor Test (data) from Fredrik Wergeland that can be
accessed at this Web site: www.flyingmodels.org/motortest/pdf/TheMotortest_4.pdf.
Application data can be found for many current brushless motors as well as some
ferrite motors. A total of 82 pages are presented in this pdf file.
Another valuable motor data source is Dick Miller’s Motor Characteristics, which
can be found on his personal Web site: http://home.ptd.net/~rcm65/. For many
years, Dick was the Electric Columnist for Flying Models magazine. His
data is sorted by motors as well as by wing area of the aircraft. When you open
his Web site, first click on “Motor Data Motor Suppliers,” then open the pdf
file for “Sort by Motor” or “Sort by Area,” You will be amazed at the amount of
data Dick has accumulated, all of which was based on his own motor testing. He
didn’t just use manufacturer-provided data.
One other excellent source of motor data comes from the folks at Grand Wing
Servo (GWS). For the past couple of years I have used these 21 pages of data
that were made available on the GWS Web site (www.gws.com.tw/english/product/powersystem/lps.htm).
After calling up this Web site, you can select any one of the motor types
printed across the top of the Web page. Unfortunately, in recent months that
data has been somewhat difficult to access. One of the major GWS distributors in
the USA—Balsa Products Inc.—is attempting to retrieve that GWS motor data and
place it on its own Web site: www.balsapr.com. I suggest you keep a watch for
it. If you plan on seriously pursuing electric power, these computer programs
and data Web sites are must reading.