SYSTEM OPERATION

• Document Type: FOIA
• Collection: FOIA Collection
• Document Number (FOIA) /ESDN (CREST): 06535942
• Release Decision: RIFPUB
• Original Classification: U
• Document Page Count: 16
• Document Creation Date: December 28, 2022
• Document Release Date: August 10, 2017
• Case Number: F-2014-00925

Approved for Release: 2017/07/25 C06535942
Approved for Release: 2017/07/25 C06535942
Approved for Release: 2017/07/25 C06535942
Al2 Section VII
YSTEMS OPERATION
TABLE OF CONTENTS
Page
Engine
7-1
Engine Trimming
7-1
Normal Trim Operation
7-2
Trimming with Surge Sensitive Engines
7-5
Inlet System Operation
7-5
Spike and Bypass Control
7-5
CIP Indications
7-7
Fuel System Operation
7-7
Normal Fuel Tank Sequencing
7-7
Jet Puma System
7-11
Tank 4 Ullage System
7-11
Fuel Tank Empty Light Sequence
7-11
ENGINE
ENGINE TRIMMING
On many engines, engine trim adjustment
can be accomplished only on a test stand or
while the aircraft is on the ground. One of
the features affecting operation of these
aircraft is an engine trim device which is
operated from the cockpit. The trimmer is
normally used to maintain EGT within a re-
Page
In-Flight Refueling 7-11
Fuel Management Prior to
Refueling 7-12
Fuel Management During
Refueling
Subsonic Cruise Fuel Management
Flight Control System
Brake System Operation
7-12
7-12
7-13
7-14 I
commended operating range in flight when
at or near Military thrust or when the after-
burner is operating. It modifies the turbine
inlet temperature vs compressor inlet tem-
perature scheduling characteristics of the
main fuel control. Changes in engine trim
are indicated by the EGT gage. Trimming
has little direct effect on afterburner op-
eration, but the trimmer is the only main
engine control available to the pilot when a
throttle is set in the afterburner range.
Changed 15 March 1968
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7-1
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SECTION VII
A-12
NORMAL EXHAUST GAS TRIM TEMPERATURE
KC-135A GAGE O.A.T. AT TRUE MACH 0.80 -�C
-40 -30 -20 -10 0 10
850
800
700*
650
600
r CAUTIoN
,a
: �Engine surge may be encoun ered
above the nominal operating bane
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550 t
"414t-14-:{1,11441 -1-",
-60 -40
20
4
-.4
Note: Applicable to YJ and YJ-1 wig nec.
Basis. PAW preliminary 0.1. Curve F4000 ,11,
Dated 5-20-66 Revised 6-12-67
�T C.I T. �C (F.A.T. ON THE GROUND
9 -10 0 j '10:
-20 0 20 40
C.I.T. -�F (F.A.T. ON THE GROUND)
Figure 7-1
NORMAL TRIM OPERATION
The following describes the normal use of
trim capability at the present time.
Prior to Takeoff
A trim run is usually made on the end of the
runway prior to takeoff using the following
procedure:
4
60 80
1. Wheels - Check chocked.
30
� If
100 120
2. Throttles - MILITARY momentarily
then IDLE.
This serves to unload the trimmer and
reduce hysteresis.
3. Throttles - MILITARY until EGT sta-
bilizes.
7-2
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SECTION VII
A-12
4. EGT trim switches - As required per
figure 7-1.
5. Throttle - IDLE rapidly.
This throttle chop serves to check the
proper sequence of bleed operation by
the absence of compressor stall.
Climb and Cruise
Trim as necessaq after takeoff and while
accelerating to 60 C CIT to maintain EGT
less than 845oC. EGT must be maintained
below 805oC when above 60oC CIT. It is
recommended that the EGT be maintained
between 7750C and 8050C during cruise.
Subsonic Operation
The engine fuel control is scheduled to re-
duce turbine temperature rather rapidly as
compressor inlet temperature falls below
5oC to preclude the possibility of engine
stall. The EGT trim may be used in this
operating regime to up trim the engine if
required. It may be possible to increase
the EGT more than 50 C but in most cases
the increase will be less since the uptrim
range is a function of the original trim
setting.
WARNING
Uptrimming in the low temperature
area can cause over temperature
during subsequent aircraft accel-
eration or above 5 C CIT unless
the EGT trim is reset to nominal
schedule prior to acceleration.
Effect of Engine Thrust Variation with EGT
Figure 7-2 illustrates the typical variation
of engine thrust with EGT at scheduled rpm,
Mach 3.2 and 80,000 feet. For a given level
of thrust, higher throttle settings and in-
creased fuel flow are required as EGT is
decreased. Full throttle ceilings in cruise
and while turning are reduced; this occurs
because combined burning efficiency of the
engine and AB decreases with lowered EGT.
The degradation in thrust for all throttle
settings, at Mach 3.2 and 80,000 feet, is
approximately 1.3 percent per 10 C of EGT
decrease. Although only one flight condition
is illustrated, the trend is the same for
other flight conditions.
Effect of RPM Suppression on MAXIMUM
THRUST
As EGT decreases, the engine nozzle opens
to maintain scheduled rpm. At high Mach
number and maximum power, low EGT may
cause the nozzle to open fully and any further
EGT decrease will result in rpm suppres-
sion below schedule. When this condition
occurs the engine speed will supopress ap-
proximately 50 rpm for each 10 C of EGT
decrease. The airflow through the engine
decreases due to the suppressed rpm, lead-
ing to a higher inlet duct bypass require-
ment and opening of the forward bypass
doors. At Mach 3.2 this results in a thrust
degradation and drag increase of approxi-
mately 3.5 percent per 10 C of EGT de-
crease for each affected engine. If Mach
number decreases as a result of the change
in thrust and drag, the spikes schedule
more forward and the forward bypass doors
open further. Performance will deterio-
rate rapidly under these cumulative effects
and it is recommended that cruise EGT be
maintained between 775�C and 805�C to
avoid the possibility of this situation oc-
curring.
After Air Refueling
The KC-135 crew can advise the pilot of the
proper engine trim to be set when the air-
7-3
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A-12
TYPICAL THRUST VARIATION WITH EGT
12
11
10
9
8
7
6
5
TYPICAL THRUST VARIATION WITH EGT
UN INSTALLED
NOTE
CONDITION
SCHEDULED
MACH 3.2 80,000
1
SHOWN AT
RPM
FT.
q:.
't
EXAMPLE:
9180 lb to
reduction
at constant
8590 lb - 1.3%
per 10�C of EGT
throttle setting.
decrease