Steady-state engine windmilling and engine speed decay characteristics of an axial-flow turbojet engine Page: 4 of 22
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NACA RM E51I0O
Accessory horsepower _ Generator voltage72
(0.141)(746)
The generator voltage regulator maintained approximately constant voltage
(and therefore power) at engine speeds above 4000 rpm. At engine speeds
below 4000 rpm, the voltage decreased with engine speed. Because the
generator was designed for use on an engine of lower rated speed, a con-
tinuous operation of the engine at engine speeds above 8000 rpm was not
possible.
The engine was mounted on a wing in thbe test section of the altitude
wind tunnel (fig. 1). Dry refrigerated air was supplied to the engine
through a tunnel make-up air system. The air, approximately at sea-level
pressure at the entrance of the make-up air system, was throttled to a
pressure at the engine inlet corresponding to the desired flight con-
ditions. Engine inlet temperatures correspond to NASA standard altitude
conditions except for conditions requiring temperatures below -200 F,
which could not be obtained.
To record the transient condition of the engine during an engine
speed decay run, oscillograph instruments were used to record engine
speed, indicated air speed, and accessory generator voltage. Conven-
tional forms of instrumentation were also used to calibrate the oscillo-
graph data and to determine the steady-state engine windmilling
performance (fig. 2).
A list of the symbols and methods of calculations used in this
report are presented in appendixes A and B, respectively.
PROCEDURE
The steady-state engine windtmilling data were obtained without the
accessory load at altitudes from 5000 to 50,000 feet and over a range of
flight Mach numbers from 0.19 to 1.06.
All engine speed decay data were obtained by simulating combustor
blow-out by closing a solenoid operated valve in the engine fuel line,
when the engine was in steady-state operation. Because of the accessory
design limitation, as mentioned earlier, an initial engine speed of
approximately 8000 rpm was used for the main portion of the engine speed
decay runs. Data were taken at altitudes of 5000, 10,000, and 40,000 feet
at several -flight Mach numbers, with and without an accessory load. The
only data obtained with an initial engine speed of 12,000 rpm were taken
at an altitude of 5000 feet and a flight Mach number of 0.27, with and
without an accessory load.3
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Sobolewski, A. E. & Farley, J. M. Steady-state engine windmilling and engine speed decay characteristics of an axial-flow turbojet engine, report, December 5, 1951; (https://digital.library.unt.edu/ark:/67531/metadc59134/m1/4/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.