A hybrid helicopter includes a rotary wing, two half-wings with respective propellers, and an engine installation continuously driving the rotary wing and the propellers by meshing with a mechanical interconnection system. A piloting assistance device for the hybrid helicopter is configured to determine maximum mean pitch (βmax) applicable to the propellers without exceeding the power available for the propellers. The piloting assistance device is configured to determine the maximum mean pitch (βmax) as a function of the current mean pitch of the blades of the propellers as measured in real time, a maximum power that can be delivered by the engine installation, a current power being delivered by the engine installation, and a relationship determining a power gradient (GRD) as a function of pitch for the propellers.