Simplify the following text for a Grade 10 native English-speaking person.
Original: The feathers not directly employed in the biplane wing structure , like those on the tibia and the tail , could have been used to control drag and alter the flight path , trajectory , etc. .
Simplified: The feathers not directly employed in the biplane wing , like those on the tibia and the tail , could have been used to control and alter the flight path .