airspeed. In this flight maneuver, the aircraft is in a steep  climbing turn and almost stalls to gain altitude while changing  direction. A lazy eight derives its name from the manner in  which the extended longitudinal axis of the aircraft is made  to trace a flight pattern in the form of a figure “8” lying on  its side. It would be difficult to make a definite statement  concerning load factors in these maneuvers as both involve  smooth, shallow dives and pull-ups. The load factors incurred  depend directly on the speed of the dives and the abruptness  of the pull-ups during these maneuvers.  Generally, the better the maneuver is performed, the less  extreme the load factor induced. A chandelle or lazy eight  in which the pull-up produces a load factor greater than 2 Gs  will not result in as great a gain in altitude; in low-powered  aircraft, it may result in a net loss of altitude.  The smoothest pull-up possible, with a moderate load factor,  delivers the greatest gain in altitude in a chandelle and results  in a better overall performance in both chandelles and lazy  eights. The recommended entry speed for these maneuvers  is generally near the manufacturer’s design maneuvering  speed, which allows maximum development of load factors  without exceeding the load limits.  All standard certificated aircraft are designed to withstand  loads imposed by gusts of considerable intensity. Gust load  factors increase with increasing airspeed, and the strength used  for design purposes usually corresponds to the highest level  flight speed. In extremely rough air, as in thunderstorms or  frontal conditions, it is wise to reduce the speed to the design  maneuvering speed. Regardless of the speed held, there may  be gusts that can produce loads that exceed the load limits.  Each specific aircraft is designed with a specific G loading  that can be imposed on the aircraft without causing structural  damage. There are two types of load factors factored into  aircraft design: limit load and ultimate load. The limit load  is a force applied to an aircraft that causes a bending of the  aircraft structure that does not return to the original shape.  The ultimate load is the load factor applied to the aircraft  beyond the limit load and at which point the aircraft material  experiences structural failure (breakage). Load factors lower  than the limit load can be sustained without compromising  the integrity of the aircraft structure.  Speeds up to, but not exceeding, the maneuvering speed  allow an aircraft to stall prior to experiencing an increase in  load factor that would exceed the limit load of the aircraft.  Most AFM/POH now include turbulent air penetration  information, which help today’s pilots safely fly aircraft  There are two other points of importance on the Vg diagram.  One point is the intersection of the positive limit load factor  and the line of maximum positive lift capability. The airspeed  at this point is the minimum airspeed at which the limit load  can be developed aerodynamically. Any airspeed greater than  this provides a positive lift capability sufficient to damage  the aircraft. Conversely, any airspeed less than this does not  provide positive lift capability sufficient to cause damage  from excessive flight loads. The usual term given to this speed  is “maneuvering speed,” since consideration of subsonic  aerodynamics would predict minimum usable turn radius or  maneuverability to occur at this condition. The maneuver  speed is a valuable reference point, since an aircraft operating  below this point cannot produce a damaging positive flight  load. Any combination of maneuver and gust cannot create  damage due to excess airload when the aircraft is below the  maneuver speed.  If the aircraft is flown at a positive load factor greater than the  positive limit load factor of 4.4, structural damage is possible.  When the aircraft is operated in this region, objectionable  permanent deformation of the primary structure may take place  and a high rate of fatigue damage is incurred. Operation above  the limit load factor must be avoided in normal operation.  The lines of maximum lift capability (curved lines) are the  first items of importance on the Vg diagram. The aircraft in  Figure 5-53  is capable of developing no more than +1 G at  64 mph, the wing level stall speed of the aircraft. Since the  maximum load factor varies with the square of the airspeed,  the maximum positive lift capability of this aircraft is 2 G at  92 mph, 3 G at 112 mph, 4.4 G at 137 mph, and so forth. Any  load factor above this line is unavailable aerodynamically  (i.e., the aircraft cannot fly above the line of maximum lift  capability because it stalls). The same situation exists for  negative lift flight with the exception that the speed necessary  to produce a given negative load factor is higher than that to  produce the same positive load factor.  The flight operating strength of an aircraft is presented  on a graph whose vertical scale is based on load factor.  [Figure 5-55]  The diagram is called a Vg diagram—velocity  versus G loads or load factor. Each aircraft has its own Vg  diagram that is valid at a certain weight and altitude.  capable of a wide range of speeds and altitudes. It is important  for the pilot to remember that the maximum “never-exceed”  placard dive speeds are determined for smooth air only. High  speed dives or acrobatics involving speed above the known  maneuvering speed should never be practiced in rough or  turbulent air.  5-37  Rough Air  Vg Diagram 