tintinthepirate

Hi folks,
I am building a kit build Carl Goldberg Tiger II (5Lb or so low wing trainer, slightly modified to be a tail dragger with dual aileron). It's now 80-90 percent done and I need to get motor/ESC/LiPo pack to decide the modification to fuselage. I have zero experience with electric motors so I got most ideas from this article:
http://www.flyrc.com/glow-to-electri...n-tips-part-i/

Based on this article I have decided to get the following:

Golden Power A4120-7 530KV 530kv 1200w 55A max 300g $45.00
http://www.buddyrc.com/golden-power-...ess-motor.html

ZIPPY Compact 4000mAh 4S 25C Li 370g $34.00
http://www.hobbyking.com/hobbyking/s...lipo_pack.html


TURNIGY TRUST 55A SBEC Brushless Speed Controller $24.00
http://www.hobbyking.com/hobbyking/s...ontroller.html

Could someone with experience confirm if this is an reasonable setup?

Another motor I considered was
Turnigy Aerodrive SK3 - 4250-410kv Brushless Outrunner Motor
http://www.hobbyking.com/hobbyking/s...ner_motor.html

but based on my limited undersanding of electric motors this one requires bigger prop which might not be ideal for the Tiger 2

Thank you!

jester_s1

The motor should be fine, but if you prop the plane for the recommended 800 watts you'll be right at the top of what the speed controller can handle. Doing that will cause your speed controller to prematurely fail, so I'll suggest going up to a 75-80 amp unit to allow some headroom.

I don't recommend Zippy batteries for anything you'll fly much. There are guys who say they are the best value out there, but that's only true is by "value" they mean "cheapest." Spending a bit more on Gens Ace (my fav) or Power Wing batteries will get you a tad more power and considerably longer life. To make the plane useful for a day of flying, you'll need at least 2 batteries and preferably 3 along with a charger that has the power for a 1C charge. That's a touch under 60 watts, so any of the 80 watt chargers on the market will do nicely.

So is this your first plane or just your first electric?

tintinthepirate

Thank you jester_s1, I will look into the battery pack you recommended. As to ESC, seems most article I read recommend 100w/lb that's 500-600w for my 5-6lb Tiger 2. Would a smaller motor give longer fly time? I don't plan to use the motor/ESC on a different plane. This will stay as a low wing trainer.

This isn't the first plane, I have flown glow engine planes before. I am mostly looking forward to flying tail dragger(my first) and low wing(my first).

jester_s1

The link you provided to the motor recommended propping it to get around 800 watts. That's just a touch over 1 hp which is what an actual real world .46 engine will give you. I think your 5 lb flying weight estimate is a bit on the ambitious side. I haven't had a Tiger 2 (flew one once while training and loved it) but most .40 size sport planes wind up at 6-7 pounds. So yes, your ESC will probably be fine if you keep it at 600 watts or less, but you might also find that the prop that gives you the 600 watt ceiling just doesn't have the pull that you want it to. It's nice to be able to get the performance you want for only a $4 prop change.

As for you question about flying time, that's all related to how many amps you draw. Going to a smaller prop on a given motor will reduce the amp draw and the power, giving you longer flight times. Of course, throttling back will do that for you too. The other motor you listed is a lower Kv rated motor, so it won't turn as fast or draw as many amps with a given prop. But then, of course, you might find that you don't like how it flies either. With the Golden Power motor, you still won't even hit 10k rpm with a fully charged battery, so it'll be more like flying with a .60 four stroke than a .40 2 stroke. That can be a good thing, but I wouldn't want to go any lower unless you're wanting stump pulling torque for big vertical performance and/or 3D flying.