2 of figure 2.12. Curve 2 of this illustration 
defines an upper limit of fuel flow which can 
be tolerated within stall-surge and tempera- 
ture limits. The governing apparatus of the 
engine must limit the acceleration fuel flow 
within this boundary. 
To appreciate the governing requirements 
during the acceleration process, assume the 
engine described in figure 2.12 is in steady state 
stabilized operation at point A and it is desired 
to acceler&the engine to maximum RPM and 
stabilize:at point C. As the throttle is placed 
at the position for maximum RPM, the fuel 
control will increase the fuel flow to point B 
to provide acceleration fuel flow. As the 
engine accelerates and increases RPM, the fuel 
control will continue to increase the fuel flow 
within the acceleration boundary until the 
engine speed approaches the controlled maxi- 
mum RPM at point C. As the engine speed 
nears the maximum at point C, the fuel contrcl’ 
will reduce fuel flow to produce stabilized oper- 
ation at this point and prevent the engine 
overspeeding the commanded RPM. Of course, 
if the throttle is opened very gradually, the 
acceleration fuel flow is barely above the steady 
state condition and the engine does not ap- 
proach the acceleration fuel flow boundary. 
While this technique is recommended for 
ordinary conditions to achieve trouble free 
operation and good service life, the engine must 
be capable of good acceleration to produce 
rapid thrust changes for satisfactory flight 
control. 
In order for the powerplant to achieve mini- 
mum acceleration times, the fuel control must 
provide acceleration fuel flow as close as 
practical to the acceleration boundary. Thus, 
a maximum controlled acceleration may pro- 
duce limiting turbine inlet temperatures or 
slight incipient stall-surge of the compressor. 
Proper maintenance and adjustment of the 
engine governing apparatus is essential to 
produce minimum acceleration times without 
incurring excessive temperatures or heavy stall- 
surge conditions. 
NAVWEPS 00-8OT-30 
AIRPLANE PERFORMANCE 
During deceleration conditions, the mini- 
mum allowable fuel flow is defined by the lean 
limit to support combustion. If the fuel flow 
is reduced below some critical value at each 
RPM, lean blowout or flameout will occur. 
This condition is illustrated by curve 3 of 
figure 2.12 which forms the deceleration fuel 
flow boundary. The governing apparatus must 
regulate the deceleration fuel flow within this 
boundary. 
To appreciate the governing requirements 
during the deceleration process, assume the 
engine described in figure 2.12 is in stabilized, 
steady state operation at point C and it is 
desired to decelerate to idle conditions and 
stabilize at point E. As the throttle is placed 
at the position for idle RPM, the fuel control 
will decrease the fuel flow to point D to provide 
the deceleration fuel flow. As the engine 
decelerates and decreases RPM, the fuel gov- 
erning will continue to decrease the fuel flow 
within the deceleration boundary until the idle 
fuel flow is reached and RPM is established at 
point E. Of course, if the throttle is closed 
very slowly, the deceleration fuel flow is barely 
below the steady state condition and the engine 
does not approach the deceleration fuel flow 
boundary. The fuel control must provide a 
deceleration flow close to the boundary to 
provide rapid decrease in thrust and satisfactory 
flight control. 
In most cases, the deceleration fuel flow 
boundary is considerably below the steady 
state fuel flow and no great problem exists in 
obtaining satisfactory deceleration character- 
istics. In fact, the greater problem is con- 
cerned with obtaining proper acceleration 
characteristics. For the majority of centrifu- 
gal flow engines, the acceleration boundary is 
set usually by temperature limiting conditions 
rather than compressor surge conditions. Peak 
operating efficiency of the centrifugal com-