These requirements were adhered to for many years. Today,  containers achieve the required holding and deployment  needs through design tailoring. The bottom corners of the  reserve container are designed so that the bag is held in place  while the pilot chute and bridle deploy and then releases the  bag, rotating it out of the container top to bottom into the  airstream. At the same time, the bag can still deploy quickly  in the event of a horseshoe-type malfunction.  The main container is less restrictive than the reserve in  holding the main canopy in place during deployment. This is  important so that there is no tendency for the bag to twist or  be unstable on deployment. With many of the main canopies  used today, if the bag is unstable, it results in the main  canopy opening unevenly and causing spins and possible  malfunctions. Along with the main bag, the main risers must  be able to deploy evenly for the same reasons. In the early days of skydiving, the primary body position  was a stable, face-to-earth position. This resulted in the main  container being behind the parachutist out of the airflow. One  of the primary problems faced during those days was the high  incidence of pilot chute hesitations. This was the result of poor  training and lack of understanding of that air flow. Eventually  skydivers learned to sit up during deployment causing the air  to flow over their back sweeping the pilot chute into the main  stream. Hand deployed pilot chutes were developed to make  packing easier and eliminate the need for a metal ripcord. Figure 2-13.  Modern aerodynamic container design.  container. This contributes to higher reserve bag release  forces. In severe cases, this can result in a reserve pilot chute  in tow with potential serious consequences. The balance  between sufficient main riser protection and the requirement  for unhindered reserve deployment is a critical design feature. In the face-to-earth position, the primary purpose of the  container is to hold the canopy and pilot chute closed, and  then allow it to open during deployment. Today, body  positions experienced during free fall range from head-down  to feet-to-earth and everything in between. Where speeds  formerly experienced ranged from 110 miles per hour (mph)  to maybe 140 mph, today speeds in a head-down position can  exceed 200 mph. This has changed the container dynamics to  ensure a more secure system and increased protection from  the wind blast. These changes have resulted in more secure  and streamlined configurations to accommodate these new  requirements.  Figure 2-13  shows a modern container design  shaped to meet the high-speed airflows of today. Most modern sport parachute containers have housings of  some sort to accommodate ripcords and riser release cables.  These flexible metal conduits come in 3 basic types in varying  diameters: non-compressible, relaxed, and non-extendable.  The housing type is critical to provide proper protection  and function for the usage. Non-extendable is used for most  ripcord housings, except on Navy seat packs. Relaxed refers  to the ripcord housing that is not completely compressible.  Non-compressible housing is the correct type to use for 3-ring  cutaway systems so the compression does not cause the sides  to release unevenly. An additional area that needs to be addressed when designing  piggyback systems is the main riser covers. In the early days  of sport piggyback designs, the main risers were held in  position by webbing keepers. As the sport progressed, the use  of fully enclosed main riser covers became the norm. In their  attempt to protect the main risers during high-speed free fall,  some designs tend to restrict the deployment of the reserve  container in the event of a “total” main pack malfunction.  When this happens and the main container remains closed,  the main riser covers do not open. Because of this, there is  additional restriction over the upper corners of the reserve  According to Poynter’s Parachute Manual, “the harness is  an arrangement of cotton, linen, nylon, or Dacron$^{®}$ webbing,  which is designed to conform to the shape of the load (usually  the body), to be carried in order to secure it properly so that  the opening forces and the weight of the load are evenly  distributed during opening and descent.” Harness Design 2-9