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Old Jun 15, 2012, 09:13 AM
Motors beat engines!
Milwaukee Wisconsin, United States
Joined Feb 2001
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Parkzone Stinson on 4 cells

After reading a post on RC Airplane World Forum where someone offhandedly mentioned that they were running their Parkzone Stinson on 4 cells ( instead of the recommended 3 cells) with no modifications since the stock speed control is the switching type and allows this, I decided to give it a try myself.
In theory, adding a 4th cell will give about a 77% power ( watts) increase, ( 1.33 x 1.33 = 1.77 ), but in the air it felt like WAY more.
Previously on 3 cells, the plane had adequate power, enough to fly easily, do reasonably large loops ect, but was certainly no powerhouse. On 4 cells, its a whole different animal, climbing at a high rate of speed nearly straight up out of sight, making loops as large as you care for them to be, and able to penetrate fairly high winds effortlessly. I am now able to do some more advanced aerobatics that previously it just didnít have the steam to accomplish.
The battery Iím using is about the biggest that could be fit into the battery bay, a Hobbyking Zippy 2650 pack. Using this pack requires you to push the battery wires into the fuselage access hole after connecting, and the battery door will still barely close. Surprisingly, the plane still balances perfectly with the much heavier battery in place, not even requiring a trim change afterwards.
As a caveat to anyone considering trying this mod out, this does push amps and watts up past what the motor is rated for, and can only work if full throttle is used for fairly short bursts to allow the motor to cool back down between bursts of power. This is a 105 gram motor which would imply a max continuous rating of around 300 watts, and we are now drawing 500 plus at full power. While this gives us a very nice 165 watts/lb rating it will also melt this partially plastic motor if your not careful.
That being said, the plane is now much more fun to fly and Iím having a ball with it.

Dean
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Old Jun 15, 2012, 09:44 AM
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E-Challenged's Avatar
United States, CA, Garden Grove
Joined Oct 2000
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I had a suspected brownout crash with my Hitec Optima receiver, stock built-in 700mah switch mode BEC in the stock E-Flite speed control and five servos including flap servo. I added a Park BEC and have had no further problems. It sounds like you have been lucky so far with 4S and stock setup. Why you would want to over-power a scale-like 30's classic and use it for "advanced aerobatics" is beyond me. On 3S 30C I can do consecutive loops from level flight, outside loops, inverted, slow rolls, etc. and get duration well over ten minutes. Also with flaps there is a lot of fun doing touch and goes, slow fly byes, and short take-offs and landings.
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Old Jun 15, 2012, 06:17 PM
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Lnagel's Avatar
Moab, Utah, USA
Joined Apr 2003
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Quote:
Originally Posted by DeaninMilwaukee View Post
In theory, adding a 4th cell will give about a 77% power ( watts) increase, ( 1.33 x 1.33 = 1.77 ), but in the air it felt like WAY more.
That's because it is way more. Current increases with the square of the voltage increase. Power increases with the cube of the voltage increase. So by going from 3s to 4s current increases by 1.77 and power increases by 2.37.

Larry
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