Quadcopter and UAV
A Quadcopter, also called a quadrotor helicopter, quadrotor, is a multirotor helicopter that is lifted and propelled by four rotors. Quadcopters are classified as rotorcraft, as opposed to fixed-wing aircraft, because their lift is generated by a set of rotors (vertically oriented propellers). Although it might be an oversimplification, in the UAV industry, weight is a disease and composites are the cure.
Because of scaling factors which limit fuel carrying ability, the flight duration of small powered vehicles is much less than that of larger craft. So, weight reduction becomes even more critical especially if payloads such as cameras or weapons are added in.
Balsa wood and Mylar film might seem to be about as light as you can imagine an airframe to be. However, balsa absorbs moisture and so its weight varies unpredictably. There are better materials now, such as carbon fiber laminates with an aramid honeycomb core.
Metals such as aluminum are generally too ‘heavy’ for UAVs at the smaller end of the spectrum.
So, composites are used in airframe components, structural members and wing coverings and for monococque structures as well
Composites are important too in propellers where angular momentum places load on bearings. Weight reduction here has payback in lighter, more durable bearing designs which increases maintenance intervals. Kevlar/epoxy composites are used in propeller construction, with properties being tailorable using mix and layup variations. Where a rotary wing UAV design may have as many as six or more propellers, weight savings are considerable.