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Post by JimCasey on Jul 2, 2005 19:31:30 GMT -7
For Father's day, I got a note that I will soon be the proud owner of s SpeedyBee 25 ARF. WHat electric package would I use to power this little gem? Engine, batteries, esc....I have flown a long time but haven't delved into electrics since my Great Planes Spectra with an O5 can and a 7x1200mah car pack.
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Post by ctdahle on Jul 14, 2005 22:58:56 GMT -7
Jim, the problem is that there is not a straightforward answer. Determining the motor/prop/gear ratio/battery/voltage combination for an electric powered model requires a lot more brainwork than the TLAR approach we are used to in the glow fuel world.
Generally, it is done with software. There is a program out there called "motor calc", I think, and what you do is input things like the wing area and weight of the model, the type of performance you expect, the stall speed of the model and other factors, and the program then allows you to "try out" different prop/motor/battery combos to see which ones fit your parameters. Battery selection is an issue because you have to have a setup that will deliver enough current to spin the motor fast enough to fly the plane, but that will not overheat the motor and not drain so fast that you don't have any flight time. You have to make tradeoffs between weight, voltage and mAH capacity. This affects charge time, the rating of your speed control and the type of battery charger you have to use.
You have to have a way to figure out how much power, in watts and amps that you need to get the performance you want. Then you have to experiment with different power plant combinations to determine how to efficiently transfer that power to the air, via a propellor.
Honestly, I am cluless about how to go about it. I just surf the forums until I find a discription of a plane that seems comparable to what I want to fly and that also contains a listing of prop/motor and battery combinations. Then I try to figure out if I have the equipment to support that combination and can afford.
I think that there are two kinds of e-flyers, one kind buys the popular package deal and doesn't think much about the technical aspects of what he is buying, relying on the retailer to have put together a good combination. The other kind builds completely from scratch and designs the airplane as an integrated system of powerplant, prop, control system and power supply. This is an ambitious challenge.
With a glow model, you want more power, you bolt in a bigger motor and know that you will get a bit less flight time unless you also add a bigger tank. You know that this will increase wing loading and make the plane fly faster and more responsively.
With electric, you can add a pitchier prop which may give you faster shorter flights, or slower, longer ones, a bigger motor may mean slower flights, or shorter ones, or it may make no difference at all. Changing batteries may increase speed, or duration, or both, or neither, but in any event you have to have done your math in order to even predict.
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