attack for the rotating blade with a subsequent 
increase in pressure rise. Of course, if the 
change in angle of attack or pressure rise is 
beyond some critical value, stall will occur. 
While the stall phenomenon of a series of 
rotating compressor blades differs from that 
of a single airfoil section in a free airstream, 
the cause and effect are essentially the same. 
If an excessive pressure rise is required 
through the compressor, stall may occur with 
the attendant breakdown of stable, steady flow 
through the compressor. As stall occurs, the 
pressure rise drops and the compressor does not 
furnish discharge at a pressure equal to the 
combustion chamber pressure. As a result, a 
flow reversal or backfire takes place. If the 
stall is transient and intermittent, the indica- 
tion will be the intermittent “bang” as back- 
fire and flow reversal take place. If the stall 
develops and becomes steady, strong vibration 
and a loud (and possibly expensive) roar 
develops from the continuous flow reversal. 
The increase in compressor power required 
tends to reduce RPM and the reduced airflow 
and increased fuel flow cause rapid, immediate 
rise in exhaust gas temperature. The pos- 
sibility of damage is immediate with the steady 
stall and recovery must be accomplished 
quickly by reducing throttle setting, lowering 
the airplane angle of attack, and increasing 
airspeed. Generally, the compressor stall is 
caused by one or a combination of the fol- 
lowing items: 
(ti) A malfunctioning fuel control or gov- 
erning apparatus is a common cause. Proper 
maintenance and adjustment is a necessity for 
stall-free operation. The malfunctioning is 
most usually apparent during engine 
acceleration. 
(6) Poor inlet conditions are typical at 
high angles of attack and sideslip. These 
conditions reduce inlet airflow and create 
nonuniform flow conditions at the com- 
pressor face. Of course, these conditions are 
at the immediate control of the pilot. 
NAVWEPS 00-801-80 
AIRMANE Pl?RFORMANCE 
(c) Very high altitude flight produces low 
compressor Reynolds numbers and an effect 
similar to that of airfoil sections. As a 
decrease to low Reynolds numbers reduces 
the section c&, very high altitudes reduce 
the maximum pressure ratio of the com- 
pressor. The reduced stall margins increase 
the likelihood of compressor stall. 
Thus, the recovery from a compressor stall 
must entail reduction of throttle setting to 
reduce fuel flow, lowering angle of attack and 
sideslip and increasing airspeed to improve 
inlet condition, and reducing altitude if high 
altitude is a contributing factor. 
(3) While the j7ameout is a rare occurrence 
with modern engines, various malfunctions 
and operating conditions allow the flameout to 
remain a possibility. A uniform mixture of 
fuel and air will sustain combustion within a 
relatively wide range of fuel-air ratios. Com- 
bustion can be sustained with a fuel-air ratio 
as rich as one to five or as lean as one to twenty- 
five. Fuel air ratios outside these limits will 
not support combustion due to the deficiency 
of air or deficiency of fuel. The characteristics 
of the fuel nozzle and spray pattern as well as 
the governing apoaratus must insure that the 
nucleus of combt .,on is maintained through- 
out the range of engine operation. 
If the rich limit of fuel-air ratio is exceeded 
in the combustion chamber, the flame will 
blow out. While this condition is a pos- 
sibility the more usual cause of a flameout is 
exceeding the lean blowout limit. Any con- 
dition which produces some fuel-air ratio 
leaner than the lean limit of combustion will 
produce a flameout. Any interruption of the 
fuel supply could bring on this condition. 
Fuel system failure, fuel system icing, or pro- 
longed unusual attitudes could starve the flows 
of fuel to the engine. It should be noted the 
majority of aviation fuels are capable of 
holding in solution a certain small amount of