Thread: Discussion Conver a balsa stick 40 plus
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Old Aug 20, 2012, 12:31 AM
wizard of odd is offline
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Australia, WA, Kalgoorlie
Joined Apr 2011
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Welcome to RCG!

The Stik is a perennial favourite amongst sport models and will fly well on electric power.

Some things need to be considered:
1. Weight of model ready to fly. Since you have the model already it would be easy to weigh it without the power system installed. The projected weight will determine what power plant will be required. If your model is for instance going to be around 5 pounds, and you want at least a power to weight ratio of 100W/lb, you will be in the market for a 500W+ power system.
Power (Watt)= current (Amp) x Voltage. The battery supplies the voltage to the motor via an ESC, and the motor will draw current depending on the load applied to the motor. The ESC needs to be able to handle the amount of current required (usually specified by the manufacturer), and so does the motor. A rule of thumb is 3W/gram for an average outrunner (though a decent quality motor will be able to perform well above this)- so for 500W power consumption, you will need a motor in the 160-180g weight class at least. Since W=AxV, your required power level can be reached by either lower cell count (voltage) at higher current draw, or higher cell count at lower current draw. Another frequently touted rule of thumb would be IC engine size in cubic inch x 1200, which in the case of a .40 size engine would be 0.40X1200=480W. Online propeller calculators like this one http://www.ecalc.ch/motorcalc_e.htm?ecalc can be handy to get you in the ball park, so to speak.

2. Wing loading. For a model like a Stik, you will probably aiming for a wing loading in the range of 15-18Oz/Sq.ft. If you can work out the wing area of the model, you can determine what a realistic AUW should be for the flight envelope you desire. Refer back to point 1. above. You can for instance have a power system weighing lets say 1lb, producing 500W at a power to weight ratio of 100W/lb, or a power system weighing 2lb, but with the increased weight still only producing 100W/lb (or maybe more), at the expense of a higher wing loading and poorer flying characteristics. You need to take this into consideration when choosing your power system- bigger motors and more cells are not necessarily desirable, unless you plan on flying a very high powered brick! It will still fly like a brick though....

Anyway, you must be tired after reading all that rubbish, so: Not knowing the details of your model, my guess would be a motor of between 200 and 250g, with a kV (r.p.m. per Volt) rating of 650-950, ESC of around 60A, spinning a 12x8-14x7" prop at an Amp draw of around 50A off a 4 or maybe 5 cell Lipo pack.

Hope that helps

Odd
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