A dump gate system for a fluid hopper in a firefighting aircraft. A gate sealably engages a gate opening in the hopper at a closed position. The gate is hingedly connected about the gate opening, and a drive shaft is supported within the hopper. A crank arm is fixed to the drive shaft and is further coupled to the gate by a connecting link. The crank arm and the connecting link define an over-center geometry while the gate is at the closed position, such that weight of the fluid on the gate induces torque on the drive shaft in a gate-closing direction. An electric motor is selectively coupled to rotate the drive shaft in a gate-opening direction to thereby enable control of the fluid flow from the hopper according to an angular position of the drive shaft.