NAVWEPS 00-SOT-80  OPERATING STRENGTH LIMITATIONS  The occurrence  of any one of these items could  cause structural damage or failure of the pri-  mary structure. A reasonable accounting of  these items is required during the design of an  airplane to prevent such occurrences  in the re-  quired operating regions. The limit airspeed  of an airplane may be any value between termi-  nal dive speedand 1.2 times the maximum level  flight speed,depending  on the aircraft type and  mission requirement. Whatever the resulting  limit airspeed happens to be, it deserves  due  respect.  the maximum positive lift capability of this  airplane is 4 “g”  at 200 knots, 9 g at 300 knots,  16 g at 400 knots, etc.  Any load factor above  this line is unavailable aerodynamically, i.e.,  the subject airplane cannot fly above the line of  maximum lift capability. Essentially 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. Gen-  erally, the negative CL,., is less than the posi-  tive CL,., and the airplane may lack sufficient  control power to maneuver in this direction.  Thus, the airplane in flight is limited to a  regime of airspeeds and g ’ s which do not  exceed the limit  (or redline) speed, do not  exceed  the limit load factor, and cannot exceed  the maximum lift capability.  The airplane  must be operated within  this  “envelope”  to prevent structural damage and ensure that  the anticipated service life of the airplane is  obtained.  The pilot  must appreciate the  V-n diagram as describing the allowable  combination of airspeeds and load factors for  safe operation. Any maneuver, gust, or gust  plus maneuver outside the structural envelope  can cause sttuctural damage and effectively  shorten the service.life, of the airplane.  If the subject airplane is flown at a positive  load factor greater than the positive limit load’  factor of 7.5, structural damage will be possi-  ble.  When the airplane is operated in this  region, objectionable permanent deformation  of the primary structure may take place and a  high rate of fatigue damage is incurred. Opera-  tion above the limit  load factor must be  avoided in normal operation. If conditions of  extreme emergency require load factors above  the limit to prevent an immediate disaster, the  airplane should be capable of withstanding the  ultimate load factor without  failure.  The  same situation exists in negative lift flight  with the exception that the limit and ultimate  load factors are of smaller magnitude and the  negative limit load factor may not be the same  value at all airspeeds. At speeds above the  maximum level flight airspeed the negative  limit load factor may be of smaller magnitude.  There are two points of great importance on  the V-n diagram of figure 5.4.  Point B is  the intersection of the negative limit  load  factor and line of maximum negative lift  capability.  Any airspeed greater than point  B provides a negative lift capability sufficient  to damage the airplane; any airspeed less  than point B does not provide negative lift  capability sufficient to damage the airplane  from excessive flight loads.  Point A is the  intersection of the positive limit load factor  and the line of maximum, positive lift capa-  bility.  The airspeed at this point is the  minimum airspeed at which the limit  load  can be developed aerodynamically. Any air-  speed greater than pomt A provides a positive  lift capability sufficient to damage the air-  plane; any airspeed less than point A does  not provide Positive lift capability sufficient to  The limit airspeed (or redline speed) is a de-  sign reference  point for the airplane-the sub-  ject airplane is limited to 575 knots. If flight  is attempted beyond the limit airspeed struc-  tural,idamage or structural failure may result  from a variety of phenomena. The airplane in  flight above the limit airspeed may encounter:  (u) critical gust  (6) destructive flutter  (c) aileron reversal  (d) wing or surface divergence  (e) critical compressibility effects such as  stability  and control  problems,  damaging buffet, etc. 