Electric Flight in Australia

 

How can I keep my battery cool in flight?

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If you are drawing a reasonable amount of AMPS your battery pack will become warm, even hot, during flight. Some aircraft designs show cooling ducts to allow air to flow over the cells during flight. A scoop collects the air forward of the cells and you must also have exit holes behind the cells. If you do not have exit holes you will cause excess drag as air enters your fuselage and cannot escape. One principle you must be aware of is that the area of the exit holes must be greater than the inlet holes to allow adequate airflow. Having said that, I must point out that I believe, and it is commonly accepted by many, that it is not possible to achieve any appreciable cooling of your cells by this method. The cells are such a solid mass of matter, and the heat is so deep-seated, I believe that cooling ducts are not worth the trouble.

Similarly, there have been some efforts to cool the motor by drilling holes through the spinner and in the front former to allow air to pass through the motor. I do not believe that this works either. The spinning prop is hard pressed to collect air through the hub, and the clearance between armature and magnets is so small that negligible air can pass through.

It is accepted, though, that if you can cool the brushes and commutator of your motor (if you are running a brushed motor), it will run more efficiently. A scoop on one fuselage side opposite one brush, and a larger hole opposite the other, may help in cooling this area. A scoop which projects from the fuselage side can prove a hazard for folding props, though, and result in a burnt electric system (in the absence of overload protection) if the scoop fouls the prop when you switch on. I believe that some attempt at cooling should be made if you have an aircraft in which the motor runs continuously at relatively high amperages for, say, more than 45 seconds at a time. If you are using low amperages (15A and less), or if you only run your motor for short periods at a time (as in electric glider competitions) I again feel that cooling efforts are not worth the trouble.

It is better to have your motor mounted with free air space around it – not in a tube – but with a small, removable wooden block under the rear of the motor to take landing shocks. Also, have your battery pack removable so that you can take it out and cool it in the shade and in the breeze after flying (blowing air is the best form of cooling, which is why some fliers make up a cooling tube with a little fan to blow air over the pack). You will find that the battery pack becomes warmer to the touch after the flight as the heat from inside the pack dissipates.