FLAT PLATE SPHERE SPHERE WITH  A FAIRING SPHERE INSIDE  A HOUSING Form drag Figure 2-9.  It is easy to visualize the creation of form drag by  examining the airflow around a flat plate. Streamlining decreases  form drag by reducing the airflow separation.  Drag Profile Drag Thrust 2-6 apparent gross weight increase is relatively small in banks up  to 30°. Even so, under the right set of adverse circumstances,  such as high-density altitude, turbulent air, high gross weight,  and poor pilot technique, sufficient or excess power may not  be available to maintain altitude and airspeed. Pilots must take  all of these factors into consideration throughout the entire  flight from the point of ascending to a hover to landing. Above  30° of bank, the apparent increase in gross weight soars. At  30° of bank, or pitch, the apparent increase is only 16 percent,  but at 60°, it is twice the load on the wings and rotor disk.  For example, if the weight of the helicopter is 1,600 pounds,  the weight supported by the rotor disk in a 30° bank at a  constant altitude would be 1,856 pounds (1,600 + 16 percent  (or 256)). In a 60° bank, it would be 3,200 pounds; in an 80°  bank, it would be almost six times as much, or 8,000 pounds.  It is important to note that each rotor blade must support a  percentage of the gross weight. In a two-bladed system, each  blade of the 1,600-pound helicopter as stated above would  have to lift 50 percent or 800 pounds. If this same helicopter  had three rotor blades, each blade would have to lift only 33  percent, or 533 pounds. One additional cause of large load  factors is rough or turbulent air. The severe vertical gusts  produced by turbulence can cause a sudden increase in AOA,  resulting in increased rotor blade loads that are resisted by the  inertia of the helicopter. and maintain lift. Many helicopter accidents are caused from  the rotor disk being overloaded. Simply put, pilots attempt  maneuvers that require more lift than the rotor disk can  produce or more power than the helicopter’s powerplant can  provide. Trying to land with a nose high attitude along with  any other unfavorable condition (i.e., high gross weight or  wind gusts) is most likely to end in disaster.  The tail rotor also produces thrust. The amount of thrust is  variable through the use of the antitorque pedals and is used  to control the helicopter’s yaw. The force that resists the movement of a helicopter through the  air and is produced when lift is developed is called drag. Drag  must be overcome by the engine to turn the rotor. Drag always  acts parallel to the relative wind. Total drag is composed of  three types of drag: profile, induced, and parasite. Profile drag develops from the frictional resistance of the  blades passing through the air. It does not change significantly  with the airfoil’s AOA but increases moderately when  airspeed increases. Profile drag is composed of form drag and  skin friction. Form drag results from the turbulent wake caused  by the separation of airflow from the surface of a structure.  The amount of drag is related to both the size and shape of the  structure that protrudes into the relative wind.  [Figure 2-9] Each type of helicopter has its own limitations that are based  on the aircraft structure, size, and capabilities. Regardless  of how much weight one can carry or the engine power  that it may have, they are all susceptible to aerodynamic  overloading. Unfortunately, if the pilot attempts to push  the performance envelope the consequence can be fatal.  Aerodynamic forces effect every movement in a helicopter,  whether it is increasing the collective or a steep bank  angle. Anticipating results from a particular maneuver or  adjustment of a flight control is not good piloting technique.  Instead pilots need to truly understand the capabilities of the  helicopter under any and all circumstances and plan never to  exceed the flight envelope for any situation.  Thrust, like lift, is generated by the rotation of the main  rotor disk. In a helicopter, thrust can be forward, rearward,  sideward, or vertical. The resultant lift and thrust determines  the direction of movement of the helicopter. The solidity ratio is the ratio of the total rotor blade area,  which is the combined area of all the main rotor blades, to the  total rotor disk area. This ratio provides a means to measure  the potential for a rotor disk to provide thrust and lift. The  mathematical calculations needed to calculate the solidity ratio  for each helicopter may not be of importance to most pilots but  what should be are the capabilities of the rotor disk to produce 