After reading a post onRC Airplane World Forumwhere someone offhandedly mentioned that they were running theirParkzone Stinsonon 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 didn’t have the steam to accomplish.
The battery I’m using is about the biggest that could be fit into the battery bay, aHobbyking 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 I’m having a ball with it.