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. 
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. 
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. 
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. 
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. 
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