An unmanned helicopter, comprising a nose, a fuselage and a tail, wherein the fuselage is formed by enclosure of a first side, a second side, a third side and a fourth side, an engine fixed in the fuselage and located between the second side and the third side, a main rotor for the flight of the unmanned helicopter is arranged on the first side, an undercarriage for the landing of the unmanned helicopter is arranged on the fourth side, the second side and the third side are symmetrically distributed on both sides of the first side and the fourth side; wherein the unmanned helicopter further comprises: an air inlet system, the air inlet direction of which faces to the direction of the nose so that the airflow flows into the engine through the air inlet system to be burnt and as the air inlet direction of the air inlet system faces to the direction of the nose, the air inlet direction corresponds to the flow direction of airflow that flows reversely relative to the unmanned helicopter and which is backward relative to the fuselage, so that the airflow smoothly flows into the air inlet system under the action of its own flow velocity relative to the unmanned helicopter, an exhaust system to discharge the tail gas generated by the combustion in the engine; a cooling system, which is fixed on the first side, so that external cold air is sucked into the fuselage via the cooling system to cool the fuselage the air inlet direction of the air inlet system is parallel to the exhaust direction of the exhaust system, the exhaust direction of which faces to the direction of the tail to discharge the tail gas generated by the combustion in the engine through the exhaust system, a dynamic balance system is rotationally fixed on the tail, and a rotation plane of which is vertical to the rotation panel of the main rotor, so as to control the dynamic balance degree of the unmanned helicopter in a flight process through the rotation of the dynamic balance system, characterized by: the air inlet system is only fixed on the second side; the exhaust system is only fixed on the third side. an air inlet system, the air inlet direction of which faces to the direction of the nose so that the airflow flows into the engine through the air inlet system to be burnt and as the air inlet direction of the air inlet system faces to the direction of the nose, the air inlet direction corresponds to the flow direction of airflow that flows reversely relative to the unmanned helicopter and which is backward relative to the fuselage, so that the airflow smoothly flows into the air inlet system under the action of its own flow velocity relative to the unmanned helicopter, an exhaust system to discharge the tail gas generated by the combustion in the engine; a cooling system, which is fixed on the first side, so that external cold air is sucked into the fuselage via the cooling system to cool the fuselage the air inlet direction of the air inlet system is parallel to the exhaust direction of the exhaust system, the exhaust direction of which faces to the direction of the tail to discharge the tail gas generated by the combustion in the engine through the exhaust system, a dynamic balance system is rotationally fixed on the tail, and a rotation plane of which is vertical to the rotation panel of the main rotor, so as to control the dynamic balance degree of the unmanned helicopter in a flight process through the rotation of the dynamic balance system, characterized by: the air inlet system is only fixed on the second side; the exhaust system is only fixed on the third side. the air inlet system is only fixed on the second side; the exhaust system is only fixed on the third side.