13-7 Figure 13-12.  The retractable gear of a Boeing 737 fair into recesses in the fuselage. Panels attached to the landing gear provide smooth  airflow over the struts. The wheel assemblies mate with seals to provide aerodynamic flow without doors. Figure 13-14.  Rigid steel landing gear is used on many early  aircraft. Figure 13-13.  Non-shock absorbing struts made from steel,  aluminum, or composite material transfer the impact forces of  landing to the airframe at a non-damaging rate.  Figure 13-11.  Wheel fairings, or pants, and low profile struts reduce  parasite drag on fixed gear aircraft.  it. Landing gear struts of this type made from composite  materials are lighter in weight with greater flexibility and  do not corrode.  of many individual small strands of elastic rubber that must  be inspected for condition. Solid, donut-type rubber cushions  are also used on some aircraft landing gear.  [Figure 13-15] Before the development of curved spring steel landing struts,  many early aircraft were designed with rigid, welded steel  landing gear struts. Shock load transfer to the airframe is direct  with this design. Use of pneumatic tires aids in softening  the impact loads.  [Figure 13-14]  Modern aircraft that use  skid-type landing gear make use of rigid landing gear with  no significant ill effects. Rotorcraft, for example, typically  experience low impact landings that are able to be directly  absorbed by the airframe through the rigid gear (skids).  The use of bungee cords on non-shock absorbing landing  gear is common. The geometry of the gear allows the strut  assembly to flex upon landing impact. Bungee cords are  positioned between the rigid airframe structure and the  flexing gear assembly to take up the loads and return them to  the airframe at a non-damaging rate. The bungees are made  Rigid  Bungee Cord