an Arimid$^{®}$ fiber and the outer sheets are coated Phenolic$^{®}$  is common as well. In fact, a myriad of other material  combinations such as those using fiberglass, plastic, Nomex$^{®}$,  Kevlar$^{®}$, and carbon fiber all exist. Each honeycomb  structure possesses unique characteristics depending upon  the materials, dimensions, and manufacturing techniques  employed.  Figure 1-39  shows an entire wing leading edge  formed from honeycomb structure. Nacelles (sometimes called “pods”) are streamlined  enclosures used primarily to house the engine and its  components. They usually present a round or elliptical  profile to the wind thus reducing aerodynamic drag. On  most single-engine aircraft, the engine and nacelle are at the  forward end of the fuselage. On multiengine aircraft, engine  nacelles are built into the wings or attached to the fuselage  at the empennage (tail section). Occasionally, a multiengine  aircraft is designed with a nacelle in line with the fuselage aft  of the passenger compartment. Regardless of its location, a  nacelle contains the engine and accessories, engine mounts,  structural members, a firewall, and skin and cowling on the  exterior to fare the nacelle to the wind. Some aircraft have nacelles that are designed to house the  landing gear when retracted. Retracting the gear to reduce  wind resistance is standard procedure on high-performance/ high-speed aircraft. The wheel well is the area where the  landing gear is attached and stowed when retracted. Wheel  wells can be located in the wings and/or fuselage when not  part of the nacelle.  Figure 1-40  shows an engine nacelle  incorporating the landing gear with the wheel well extending  into the wing root. Nacelles Figure 1-37.  The honeycomb panel is a staple in aircraft construction. Cores can be either constant thickness (A) or tapered (B). Tapered  core honeycomb panels are frequently used as flight control surfaces and wing trailing edges. A B Skin Skin Core Core Skin Skin Constant thickness Tapered core 1-19