The Balance of Weight, Battery Capacity, and Flight Time
In remote-controlled aviation (including FPV drones, quadcopters, and fixed-wing airplanes), flight duration is governed by a fundamental trade-off: battery capacity versus vehicle weight. Adding a larger battery increases stored energy, but it also increases weight. This extra weight requires the motors to spin faster, drawing more electric current just to maintain hover or level flight. Eventually, the weight penalty surpasses the energy gain, causing flight time to decrease.
Calculating flight time begins with battery chemistry. Lithium Polymer (LiPo) batteries are standard due to their high discharge rates and energy density. Stored energy is measured in Watt-hours (Wh) and is calculated as: \(Wh = \frac{\text{Capacity (mAh)}}{1000} \times \text{Voltage}\). The nominal voltage of a LiPo cell is 3.7V. Thus, a 4S battery (4 cells in series) has a nominal voltage of 14.8V, while a 6S battery has 22.2V.
To model flight duration, we must estimate power consumption. At hover, the power (P) required in Watts is determined by the model's total weight (W) and motor efficiency (measured in grams of thrust per Watt, or g/W): \(P_{\text{hover}} = \frac{W}{\text{efficiency}}\). Current draw in Amperes is then: \(I_{\text{hover}} = \frac{P_{\text{hover}}}{V_{\text{battery}}}\).