a similar tractor type. Modern aerodynamic knowledge and construction methods may reduce but never eliminate the difference. A remote or buried engine requires a drive shaft and associated bearings and supports, torsional vibration control, and adds weight and complexity. Center of gravity and landing gear considerations To maintain a safe center of gravity (CG) position, there is a limit to how far aft an engine can be installed. The forward location of the crew may balance the engine weight and will help determine the CG. As the CG location must be kept within defined limits for safe operation load distribution must be evaluated before each flight. Due to a generally high thrust line needed for propeller ground clearance, negative (down) pitching moments, and in some cases the absence of prop-wash over the tail, a higher speed and a longer roll may be required for takeoff compared to tractor aircraft. The Rutan answer to this problem is to lower the nose of the aircraft at rest such that the empty center of gravity is then ahead of the main wheels. In autogyros a high thrust line results in a control hazard known as power push-over. Aerodynamic considerations Due to the generally high thrust line to ensure ground clearance, a low wing pusher layout may suffer power change induced pitch changes, also known as pitch/power coupling. Pusher seaplanes with especially high thrust lines and tailwheels may find the vertical tail masked from the airflow, severely reducing control at low speeds, such as when taxiing. The absence of prop-wash over the wing reduces the lift and increases takeoff roll length. Pusher engines mounted on the wing may obstruct sections of the wing trailing edge, reducing the total width available for control surfaces such as flaps and ailerons. When a propeller is mounted in front of the tail, changes in engine power alter the airflow over the tail and can give strong pitch or yaw changes. Propeller ground clearance and foreign object damage Due to the pitch rotation at takeoff, the propeller diameter may have to be reduced (with a loss of efficiency) and/or landing gear made longer and heavier. Many pushers have ventral fins or skids beneath the propeller to prevent the propeller from striking the ground at an added cost in drag and weight. On tailless pushers such as the Rutan Long-EZ the propeller arc is very close to the ground while