Here I am assuming weight on a slightly higher side.
motor=40g, esc=25g, prop+adapter=10g, 2S-battery=75g, 3-servos=15g, rcvr=20g, connectors(motor->esc,esc->battery,etc)=15g, pushrod+controlhorns=20g
total electronics weight=220
Airframe weight=250
Total AUW=470gms
Assuming this is your motor:
http://www.rcgroups.com/forums/showthread.php?t=5702077x3.5 GWS HD
@10.9v, 18.66oz, 529gm of thrust - 10.9 as this is the maximum stated.
@7.9v, 10.6oz, 300.5gm of thrust - 7.9v as (4.2v/cell *2 = 8.4v. Nearest minimum volt reading is for 7.9v)
The power to weight ratio 300/470 = 0.64.
This may not give enough thrust to your airplane. You may try with your 2S battery but if the airplane does not takeoff or does not exhibit enough power during it's flight, then I am of the opinion that you move to a 3S battery or change the motor which can provide a higher thrust @2S. Can't tell you off hand which motor would be better. You can probably try and increase the prop to 7x5 or 7x6 but not beyond that and I won't even suggest looking for 8x(*) props, else you risk burning your motor. Even with your entire electronics assembled do a test @home itself by doing a step increase of 10sec,20,30...60sec at wide open throttle (WOT) and see that the motor does not turn too hot to touch. If its to hot, step down on the prop and re-test after motor has cooled down to room temp. Similarly check ESC & battery if they are becoming warm during each temperature test after you have motor has come to complete halt.
Would suggest the following battery:
ZIPPY Flightmax 1000mAh 3S1P 25C:
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=6470Reason:1) 3S, 2) 1000*25 = 25000/1000=25A of max discharge/min. your motor is max hungry for 16A, so there won't be strain on your 25A battery as it exceeds more than 30% of motor's max current demand.
ESC is 18A which is very near to motor's max 16A current usage and may burn out at continous WOT. Either don't go for a continuous WOT or migrate to a 25A ESC for piece of mind.
Ashutosh.
Print
