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14 CFR Ch. I (1–1–24 Edition)
§ 33.84
(b) The surveys shall cover the
ranges of power or thrust, and both the
physical and corrected rotational
speeds for each rotor system, cor-
responding to operations throughout
the range of ambient conditions in the
declared flight envelope, from the min-
imum rotational speed up to 103 per-
cent of the maximum physical and cor-
rected rotational speed permitted for
rating periods of two minutes or
longer, and up to 100 percent of all
other permitted physical and corrected
rotational speeds, including those that
are overspeeds. If there is any indica-
tion of a stress peak arising at the
highest of those required physical or
corrected rotational speeds, the sur-
veys shall be extended sufficiently to
reveal the maximum stress values
present, except that the extension need
not cover more than a further 2 per-
centage points increase beyond those
speeds.
(c) Evaluations shall be made of the
following:
(1) The effects on vibration charac-
teristics of operating with scheduled
changes (including tolerances) to vari-
able vane angles, compressor bleeds,
accessory loading, the most adverse
inlet air flow distortion pattern de-
clared by the manufacturer, and the
most adverse conditions in the exhaust
duct(s); and
(2) The aerodynamic and
aeromechanical factors which might
induce or influence flutter in those sys-
tems susceptible to that form of vibra-
tion.
(d) Except as provided by paragraph
(e) of this section, the vibration
stresses associated with the vibration
characteristics determined under this
section, when combined with the ap-
propriate steady stresses, must be less
than the endurance limits of the mate-
rials concerned, after making due al-
lowances for operating conditions for
the permitted variations in properties
of the materials. The suitability of
these stress margins must be justified
for each part evaluated. If it is deter-
mined that certain operating condi-
tions, or ranges, need to be limited, op-
erating and installation limitations
shall be established.
(e) The effects on vibration charac-
teristics of excitation forces caused by
fault conditions (such as, but not lim-
ited to, out-of balance, local blockage
or enlargement of stator vane passages,
fuel nozzle blockage, incorrectly sched-
ule compressor variables, etc.) shall be
evaluated by test or analysis, or by ref-
erence to previous experience and shall
be shown not to create a hazardous
condition.
(f) Compliance with this section shall
be substantiated for each specific in-
stallation configuration that can affect
the vibration characteristics of the en-
gine. If these vibration effects cannot
be fully investigated during engine cer-
tification, the methods by which they
can be evaluated and methods by which
compliance can be shown shall be sub-
stantiated and defined in the installa-
tion instructions required by § 33.5.
[Doc. No. 28107, 61 FR 28433, June 4, 1996, as
amended by Amdt. 33–33, 77 FR 39624, July 5,
2012; 77 FR 58301, Sept. 20, 2012]
§ 33.84
Engine overtorque test.
(a) If approval of a maximum engine
overtorque is sought for an engine in-
corporating a free power turbine, com-
pliance with this section must be dem-
onstrated by testing.
(1) The test may be run as part of the
endurance test requirement of § 33.87.
Alternatively, tests may be performed
on a complete engine or equivalent
testing on individual groups of compo-
nents.
(2) Upon conclusion of tests con-
ducted to show compliance with this
section, each engine part or individual
groups of components must meet the
requirements of § 33.93(a)(1) and (a)(2).
(b) The test conditions must be as
follows:
(1) A total of 15 minutes run at the
maximum engine overtorque to be ap-
proved. This may be done in separate
runs, each being of at least 2
1
⁄
2
minutes
duration.
(2) A power turbine rotational speed
equal to the highest speed at which the
maximum overtorque can occur in
service. The test speed may not be
more than the limit speed of take-off
or OEI ratings longer than 2 minutes.
(3) For engines incorporating a reduc-
tion gearbox, a gearbox oil tempera-
ture equal to the maximum tempera-
ture when the maximum engine over-
torque could occur in service; and for
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Federal Aviation Administration, DOT
§ 33.87
all other engines, an oil temperature
within the normal operating range.
(4) A turbine entry gas temperature
equal to the maximum steady state
temperature approved for use during
periods longer than 20 seconds when op-
erating at conditions not associated
with 30-second or 2 minutes OEI rat-
ings. The requirement to run the test
at the maximum approved steady state
temperature may be waived by the
FAA if the applicant can demonstrate
that other testing provides substan-
tiation of the temperature effects when
considered in combination with the
other parameters identified in para-
graphs (b)(1), (b)(2) and (b)(3) of this
section.
[Doc. No. 2007–28502, 74 FR 45310, Sept. 2, 2009]
§ 33.85
Calibration tests.
(a) Each engine must be subjected to
those calibration tests necessary to es-
tablish its power characteristics and
the conditions for the endurance test
specified § 33.87. The results of the
power characteristics calibration tests
form the basis for establishing the
characteristics of the engine over its
entire operating range of speeds, pres-
sures, temperatures, and altitudes.
Power ratings are based upon standard
atmospheric conditions with no
airbleed for aircraft services and with
only those accessories installed which
are essential for engine functioning.
(b) A power check at sea level condi-
tions must be accomplished on the en-
durance test engine after the endur-
ance test and any change in power
characteristics which occurs during the
endurance test must be determined.
Measurements taken during the final
portion of the endurance test may be
used in showing compliance with the
requirements of this paragraph.
(c) In showing compliance with this
section, each condition must stabilize
before measurements are taken, except
as permitted by paragraph (d) of this
section.
(d) In the case of engines having 30-
second OEI, and 2-minute OEI ratings,
measurements taken during the appli-
cable endurance test prescribed in
§ 33.87(f) (1) through (8) may be used in
showing compliance with the require-
ments of this section for these OEI rat-
ings.
[Doc. No. 3025, 29 FR 7453, June 10, 1964, as
amended by Amdt. 33–6, 39 FR 35468, Oct. 1,
1974; Amdt. 33–18, 61 FR 31328, June 19, 1996]
§ 33.87
Endurance test.
(a)
General. Each engine must be sub-
jected to an endurance test that in-
cludes a total of at least 150 hours of
operation and, depending upon the type
and contemplated use of the engine,
consists of one of the series of runs
specified in paragraphs (b) through (g)
of this section, as applicable. For en-
gines tested under paragraphs (b), (c),
(d), (e) or (g) of this section, the pre-
scribed 6-hour test sequence must be
conducted 25 times to complete the re-
quired 150 hours of operation. Engines
for which the 30-second OEI and 2-
minute OEI ratings are desired must be
further tested under paragraph (f) of
this section. The following test re-
quirements apply:
(1) The runs must be made in the
order found appropriate by the FAA for
the particular engine being tested.
(2) Any automatic engine control
that is part of the engine must control
the engine during the endurance test
except for operations where automatic
control is normally overridden by man-
ual control or where manual control is
otherwise specified for a particular test
run.
(3) Except as provided in paragraph
(a)(5) of this section, power or thrust,
gas temperature, rotor shaft rotational
speed, and, if limited, temperature of
external surfaces of the engine must be
at least 100 percent of the value associ-
ated with the particular engine oper-
ation being tested. More than one test
may be run if all parameters cannot be
held at the 100 percent level simulta-
neously.
(4) The runs must be made using fuel,
lubricants and hydraulic fluid which
conform to the specifications specified
in complying with § 33.7(c).
(5) Maximum air bleed for engine and
aircraft services must be used during
at least one-fifth of the runs, except for
the test required under paragraph (f) of
this section, provided the validity of
the test is not compromised. However,
for these runs, the power or thrust or
the rotor shaft rotational speed may be
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