Question: why is fiberglass and carbon composite material in the Saqr models stealthy?

Saqr (meaning: "Falcon") is the name of a line of Unmanned aerial vehicles produced by the King Abdulaziz City for Science and Technology for the government of Saudi Arabia.  s of 2014 , three models had been developed: Saqr 2, Saqr 3 and Saqr 4.  The Saudi government has developed the craft for research purposes, and the units are equipped with cameras for aerial photography.  According to Prince Turki bin Saud bin Mohammed, the Saqr-1 has a range of more than 2,500 km and can remain airborne for more than 24 hours.  The UAV flies at an average altitude of 20,000 feet.  All three models are manufactured from fiberglass and carbon composite material, making them lightweight and stealthy. <SEP> Fiberglass reinforced plastic grating (also known as FRP grating, glass reinforced plastic grating or fiberglass grating) is a composite material manufactured by combining a matrix of resin and fiberglass.  Fiberglass grating does not corrode like steel grating and is therefore used in corrosive environments to reduce maintenance costs.  It is used in a variety of applications including walkways and overhead platforms.  FRP grating is a structural product that can be weight-bearing between spans. <SEP> Stealth aircraft are designed to avoid detection using a variety of technologies that reduce reflection/emission of radar, infrared, visible light, radio-frequency (RF) spectrum, and audio, collectively known as stealth technology.  Development of stealth technology likely began in Germany during World War II, the prototyped Horten Ho 229 was designed for twin BMW 003 jet engines but finally powered by twin Junkers Jumo 004 jet engines being described as the first stealth aircraft.  Well-known modern examples of stealth of U.S. aircraft include the United States' F-117 Nighthawk (1981–2008), the B-2 Spirit, the F-22 Raptor, and the F-35 Lightning II. <SEP> A void is a pore that remains unoccupied in a composite material.  A void is typically the result of an imperfection from the processing of the material and is generally deemed undesirable.  Because a void is a non-uniformity in a composite material, it can affect the mechanical properties and lifespan of the composite.  Voids can act as a crack nucleation site as well as allow moisture to penetrate the composite and contribute to anisotropy of the composite .  This is an issue because crack formation and propagation can create unpredictable behavior in the laminate.  For aerospace applications, a void content of approximately 1% is appropriate for performance while other grades of composites can have between 3%-5% void content.  A small change in the percentage of void content may not seem like a large problem however for a loaded carbon fiber laminate composite, a 1%-3% increase in void content can reduce the mechanical properties of the composite by up to 20% Void content in composites is represented as a ratio, also called void ratio, where the volume of voids, solid material, and bulk volume are taken into account.  Void ratio can be calculated by the formula below where e is the void ratio of the composite, V is the volume of the voids, and V is the volume of the bulk material.