added the definition of this term at the end of the table in Section 33.77. For the typical turbotan engine, this is the bareengine inlet area calculated from De shown in Figure 1 (which follows paragraph 53j). Ds is the propulsion system feature that usually determines ingestion; that is, foreign object strikes outboard (relative to the duct centerline) of the highlight will usually be repelled, and strikes inboard of the highlight will usually be ingested. However, the nacelle design is not always known at time of engine certification testing and can change from one installation to another. Therefore, since De is a rough approximation of D for the typical turbofan engine, and since De is controlled by the engine manufacturer, it was chosen as the determinant of inlet area in the current rule.
Unfortunately, the definition in Amendment 33-12 is not without problems. For example, it is not clearly applicable to an aft-fan engine. Also, the nacelle inlet lip stagnation point area, As, (which as explained above, is the functional feature that normally determines ingestion, also known as the capture area) can be much larger than Ae, the bare-engine inlet area; and A is not particularly significant if the air inlet duct incorporates an inertial separator. Hence, judgement is required, and the following guidelines are recommended until a rule establishing an improved definition is promulgated.
Typical turbofan engines should use A, as defined herein and in Amendment 33-10 for calculating foreign object ingestion quantities. Other engines should use the capture area of the installed engine, if that area is known at the time of engine certification testing. If the nacelle design is not known, or if the manufacturer elects to do so, the engine inlet area, Ar historically. or estimated nacelle inlet, As, may be used, as has been done The TCDS or the FAA-approved engine installation manual (or similar document for non-domestic engines) should indicate which area was used for ingestion calculations. This area should be considered an installation limit. If a later engine installation results in a larger capture area, the foreign object ingestion test (quantities) should be re-evaluated for possible additional certification testing.
(3) In no case should the nacelle inlet throat area A{(f)D}, see Figure 1, be used for ingestion calculations as this may result in an invalid test.
h. The inlet area question is also most germane for the smaller mass-flow turboshaft (and some turboprop) engines. As in the turbofan engine case, the inlet area determinant for ingestion testing should be the free-stream capture area. This needs to be assumed as the front face area for the bare-engine case. If the engine design incorporates an inlet air separator system, then Chap 3 Par 53 77
engineering judgement will need to be applied to define the ingestion area for calculating ingestion quantities and for determining target areas.
i. The guiding principle should be the same in all cases; the induction air stream projected area exposed to the ingestion hazard should be the determinant area. This area must include the projected areas of spinners, inertial separator housings, starter housings, inlet nose cones, etc., if it is possible for the foreign object (s) to still be ingested after impacting such devices. One expected outcome of the ingestion test of such inlet configurations is to ensure that they are ingestion impact tolerant and do not, of themselves, become ingestion objects in the engine flow path.
j. The engine manufacturer may elect to require that the airframe manufacturer install the engine, such that it is impossible for free-stream ingestion objects to enter the engine inlet. In such a case, the TCDS and the installation instructions will need to specify this as an installations limitation. This approach has mostly been applied to rotorcraft engine installations wherein there is no direct line-of-sight between the ambient free-stream and the engine's front face. This arrangement effectively creates a zero ram-recovery plenum for the engine flow stream. The airframers would need to demonstrate that this produces no unairworthy or undesirable characteristic, in accordance with the certification rules for the installation.
Chap 3 78 Par 53
FIGURE 1. GENERIC TURBOFAN AND NACELLE CONFIGURATION Ds = nacelle inlet lip stagnation point equivalent diameter,
(a.k.a. highlight equivalent diameter).
D, = nacelle inlet throat equivalent diameter.
De = engine front face inlet equivalent diameter,
(a.k.a. bare-engine inlet equivalent diameter).
A = nD/¼, where n=pi.
Chap Par 53 . 79
54. Section 33.79, Fuel Burning Thrust Augmenter.
Section 33.79 Fuel burning thrust augmenter.
Each fuel burning thrust augmenter, including the nozzle, must--
(a) Provide cutoff of the fuel burning thrust augmenter:
(b) Permit on-off cycling;
Be controllable within the intended range of operation;
Upon a failure or malfunction of augmenter combustion, not cause the engine to lose thrust other than that provided by the augmenter; and
(e) Have controls that function compatibly with the other engine controls and automatically shut off augmenter fuel flow if the engine rotor speed drops below the minimum rotational speed at which the augmenter is intended to function.
*** Guidance. The INTENT of this section is to assure that the afterburner system is designed and constructed to function satisfactorily and not impair the functioning of the rest of the engine.
Incorporations: None.
References: None.
Chap 3 80 Par 54
SECTION 6. SUBPART F--BLOCK TESTS; TURBINE AIRCRAFT ENGINES
55. Section 33.82, General.
Section 33.82 General.
Before each endurance test required by this subpart, the adjustment setting and functioning characteristic of each component having an adjustment setting and a functioning characteristic that can be established independent of installation on the engine must be established and recorded.
*** Guidance. The INTENT of this section is self-evident.
Incorporations: None.
References: None.
Collectively, the results of the block tests, combined with the design and analytical substantiation data, form the basis for the engine type certificate data sheet and engine instruction manuals statements concerning: ratings, steady-state and transient operating limits, critical parts retirement life, environmental envelope, inspection requirements, maintenance/overhaul requirements, operational requirements, and engine/airframe interface requirements.
56. Section 33.83, Vibration Test.
Section 33.83 Vibration test.
establish the vibration characteristics of the rotor Each engine must undergo a vibration survey to discs, rotor blades, rotor shafts, stator blades, and any other components that are subject to vibratory exciting forces which could induce failure at the maximum inlet distortion limit. The survey is to cover the range of rotor speeds and engine power or thrust, under steady state and transient conditions, from idling speed to 103 percent of the maximum permissible speed. The survey must be conducted using the same configuration of the loading device which is used for the endurance test, except that the Administrator may allow the use of a modified configuration if that loading device type is incompatible with the necessary vibration instrumentation.
(b) The vibration stresses (or strain) of rotor and stator components determined under paragraph (a) of this section must be less, by a margin acceptable to the Administrator, than the endurance limit of the material Chap 3 Par 55 81
from which these parts are made, adjusted for the most severe operating conditions.
Each accessory drive and mounting attachment must be loaded, with the load imposed by each accessory used only for an aircraft service being the limit load specified by the applicant for the engine drive or attachment point.
*** Guidance. The INTENT of this section is self-evident.
Incorporations: None.
References: None.
a . The engine vibration survey should be conducted with a air distortion to be allowed by the engine installation distortion.
(1) The engine speed range to be surveyed is minimum idle speed to 103 percent of the maximum permissible speed.
maximum permissible speed is the highest rpm, including transients, for which the engine is to be approved.
(2) The principal result of the vibration survey is to demonstrate that an acceptable margin exists between the measured stresses and the endurance limit of the material being tested.
envelope of the engine, including the worst case inlet air distortion levels are found to be limiting, when correlated to ibratory stresses, then the engine installation instructions should specify those limits.
(3) Correspondingly, the recommended instrumentation, data acquisition and reduction methods, and coordination needs should also be provided in the engine installation instructions.
b. There are some engine designs which operate at such high rotor speeds and gas path temperatures that existing technology strain gages cannot survive this environment for very long. In such cases, the full stress survey should still be the goal and the test designed accordingly.
(1) If it becomes physically impossible to achieve the testing to 103 percent speed, then some form of analysis could be used to make up any difference.
Chap 3 82 Par 56
(2) Additionally, if any significant resonances are found in the operating range of the engine, then the engine should be run, at least, 10 million cycles at each resonant point and at points bracketing the resonances to assure the stress endurance limit is not exceeded. This is normally covered as part of the endurance test's incremental running.
57. Section 33.85, Calibration Tests.
Section 33.85 Calibration tests.
Each engine must be subjected to those calibration tests necessary to establish its power characteristics and the conditions for the endurance test specified in Section 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, pressures, 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.
accomplished on the endurance test engine after the endurance 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.
*** Guidance. The INTENT of this section is to determine the engine power characteristics by test calibrating the engine either before and during, or after, the endurance test.
Incorporations: None.
References: None.
The engine calibration tests, in combination with the other block est requirements, form the basis for the engine instrumentation statements to be included in the engine installation instructions.
These statements should encompass types, ranges, precision (readability), and accuracies of those parameters required for safe in-service engine operation, including reverse thrust operations, for each of the ratings.
Chap 3 Par 56 83
58. Section 33.87, Endurance Test.
Section 33.87 Endurance test.
(a) General. Each engine must be subjected to an endurance test that includes a total of 150 hours of operation and, depending upon the type and contemplated use of the engine, consists of one of the series oi runs specified in paragraphs (b) through (f) of this section, as applicable. For engines tested under paragraph (b),
(c), (d), or (e) of this section, the prescribed 6-hour test sequence must be conducted 25 times to complete the required 150 hours of operation. The following test requirements apply:
(1) The runs must be made in the order found appropriate by the Administrator 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 manual control or where manual control is otherwise specified for a particular test run.
Except as provided in paragraph (a) (5) of this seen de pe engine i at eat 10 percent de the value associated with the particular engine operation being tested. More than one test may be run if all parameters cannot be held at the 100 percent level simultaneously.
The runs must be made using fuel, lubricants and hydraulic fluid which conform to the specifications specified in complying with Section 33.V(c).
(5) Maximum air bleed for engine and aircraft services must be used during at least one-fifth of the runs. However, for these runs, the power or thrust or the rotor shaft rotational speed may be less than 100 percent of the value associated with the particular operation being tested if the Administrator finds that the validity of the endurance test is not compromised.
(6) Each accessory drive and mounting attachment must be loaded. The load imposed by each accessory used only for aircraft service must be the limit load specified by the applicant for the engine drive and attachment point during rated maximum continuous power or thrust and higher output. The endurance test of any accessory drive and mounting attachment under load may be accomplished on a separate rig if the validity of the test is confirmed by an approved analysis.
(7) During the runs at any rated power or thrust the gas temperature and the oil inlet temperature must be maintained at the limiting temperature except where the Chap 3 84 Par 58
test periods are not longer than 5 minutes and do not allow stabilization. At least one run must be made with fuel, oil, and hydraulic fluid at the minimum pressure limit and at least one run must be made with fuel, oil, and hydraulic fluid at the maximum pressure limit with fluid temperature reduced as necessary to allow maximum pressure to be attained.
(8) If the number of occurrences of either transient rotor shaft overspeed or transient gas overtemperature is limited, the number of the accelerations required by paragraphs (b), (c), (d), and (e) of this section must be made at the limiting overspeed or overtemperature. If the number of occurrences is not limited, half the required accelerations must be made at the limiting overspeed or.
overtemperature.
(9) For each engine type certificated for use on supersonic aircraft, the following additional test requirements apply:
(i) To change the thrust setting, the power control lever must be moved from the initial position to the final position in not more than 1 second except for movements into the fuel burning thrust augmenter augmentation position if additional time to confirm ignition is necessary.
During the runs at any rated augmented thrust, the hydraulic fluid temperature must be maintained at the limiting temperature except where the test periods are not long enough to allow stabilization.
(iii) During the simulated supersonic runs, the fuel temperature and induction air temperature may not be less than the limiting temperature.
The endurance test must be conducted with the fuel burning thrust augmenter installed, with the primary and secondary exhaust nozzles installed, and with the variable area exhaust nozzles according to the methods specified in complying with Section 33.5(b).
(v) During the runs at thrust settings for maximum continuous thrust and percentages thereot, the engine must be operated with the inlet air distortion at the limit for those thrust settings.
Engines other than certain rotorcraft engines.
For each engine, except a rotorcraft engine for which a rating is desired under paragraph (c), (d), or (e) of this section, the applicant must conduct the following runs:
(1) Takeoff and idling. One hour of alternate 5- minute periods at rated takeoff power and thrust and at idling power and thrust. The developed powers and thrusts at takeoff and idling conditions and their corresponding rotor speed and gas temperature conditions must be established by the power control in accordance with the schedule established by the manufacturer. The applicant Chap 3 Par 58 85
may, during any one period, manually control the rotor speed, power, and thrust while taking data to check performance. For engines with augmented takeoff power ratings that involve increases in turbine inlet temperature, rotor speed, or shait power, this period of running at takeoff must be at the augmented rating.
engines that do not materially increase operating severity, the amount of running conducted at the augmented rating is determined by the Administrator. In changing the power setting after each period, the power control lever must be moved in the manner prescribed in
(2) Rated maximum continuous and takeoff power and thrust. Thirty minutes at -
(i) Rated maximum continuous power and thrust during fifteen of the twenty-five 6-hour endurance test cycles;
(ii) Rated takeoff power and thrust during ten of the twenty-five 6-hour endurance test cycles.
(3) Rated maximum continuous power and thrust. One hour and 30 minutes at rated maximum continuous power and thrust.
Incremental cruise power and thrust. Two hours and 30 minutes at the successive power lever positions corresponding to at least 15 approximately equal speed and time increments between maximum continuous engine rotational speed and ground or minimum idle rotational speed. For engines operating at constant speed, the thrust and power may be varied in place of speed. If there is significant peak vibration anywhere between ground idle and maximum continuous conditions, the number of increments chosen may be changed to increase the amount of running made while subject to the peak vibrations up to not more than 50 percent of the total time spent in incremental running.
minutes of accelerations and decelerations, consisting of 6 cycles from idling power and thrust to rated takeoff power and thrust and maintained at the takeoff power lever position for approximately 4-1/2 minutes. position for 30 seconds and at the idling power lever subparagraph othe In complying with this subparagraph, the power-control lever must be moved from one extreme position to the other in not more than 1 second, except that, if different regimes of control scheduling of the power-control lever motion in going from one extreme position to the other, a longer period of time is acceptable, but not more than 2 seconds.
(6) Starts. One hundred starts must be made, of which 25 starts must be preceded by at least a 2-hour engine shutdown. There must be at least 10 false engine starts, pausing for the applicant's specified minimum fuel drainage time, before attempting a normal start. There Chap 3 86 Par 58
must be at least 10 normal restarts with not longer than 15 minutes since engine shutdown. The remaining starts may be made after completing the 150 hours of endurance testing.
(C) Rotorcraft engines for which a 30-minute OEI power rating is desired. For each rotorcraft engine for which a 30-minute OEI power rating is desired the applicant must conduct the following series of tests:
(1) Takeoff and idling. One hour of alternate 5- minute periods at rated takeoff power and at idling power.
The developed powers at takeoff and idling conditions and their corresponding rotor speed and gas temperature conditions must be as established by the power control in accordance with the schedule established by the manufacturer. During any one period the rotor speed and power may be controlled manually while taking data to check performance. For engines with augmented takeoff power ratings that involve increases in turbine inlet temperature, rotor speed, or shaft power, this period of running at rated takeoff power must be at the augmented power rating. In changing the power setting after each period, the power-control lever must be moved in the manner prescribed in subparagraph (c)(5) of this paragraph.
Rated 30-minute OEI power. Thirty minutes at rated 30-minute OEI power.
(3) Rated maximum continuous power. Two hours at rated maximum continuous power.
(4) Incremental cruise power. Two hours at the successive power-lever positions corresponding with not less than 12 approximately equal speed and time increments between maximum continuous engine rotational speed and ground or minimum idle rotational speed. For engines operating at constant speed, power may be varied in place of speed. If there are significant peak vibrations anywhere between ground idle and maximum continuous conditions, the number of increments chosen must be changed to increase the amount of running conducted while being subjected to the peak vibrations up to not more than 50 percent of the total time spent in incremental running.
Acceleration and deceleration runs. Thirty minutes of accelerations and decelerations, consisting of 6 cycles from idling power to rated takeoff power and maintained at the takeoff power lever position for 30 seconds and at the idling power-lever position for approximately 4-1/2 minutes. In complying with this subparagraph, the power-control lever must be moved from one extreme position to the other in nor more than 1 second, except that, if different regimes of control operations are incorporated necessitating scheduling of the power-control lever motion in going from one extreme Chap 3 Par 58 87
position to the other, a longer period of time is acceptable, but not more than 2 seconds.
(6) Starts. One hundred starts, of which 25 starts must be preceded by at least a 2-hour engine shutdown.
There must be at least 10 false engine starts, pausing for the applicant's specified minimum fuel drainage time, before attempting a normal start. There must be at least 10 normal restarts with not longer than 15 minutes since engine shutdown. The remaining starts may be made after completing the 150 hours of endurance testing.
Rotorcraft engines for which a continuous OEI rating is desired. For each rotorcraft engine for which a continuous OEI power rating is desired, the applicant must conduct the following series of tests:
(1) Takeoff and idling. One hour of alternate 5- minute periods at rated takeoff power and at idling power.
The developed powers at takeoff and at idling conditions and their corresponding rotor speed and gas temperature conditions must be as established by the power control in accordance with the schedule established by the manufacturer. During any one period the rotor speed and power may be controlled manually while taking data to check performance. For engines with augmented takeoff power ratings that involve increases in turbine inlet temperature, rotor speed, or shaft power, this period of running at rated takeoff power must be at the augmented power rating. In changing the power setting after each period, the power control lever must be moved in the prescribed in paragraph (c)(5) of this section.
Rated maximum continuous and takeoff power.
Thirty minutes at-
(i) Rated maximum continuous power during fifteen of the twenty-five 6-hour endurance test cycies; and Rated takeoff power during ten of the twentyfive 6-hour endurance test cycles.
(3) Rated continuous OEI power. One hour at rated continuous OEI power.
(4) Rated maximum continuous power. One hour at rated maximum continuous power.
Incremental cruise power. Two hours at the successive power lever positions corresponding with not less than approximately 12 equal speed and time increments between maximum continuous engine rotational speed and ground or minimum idle rotational speed. For engines operating at constant speed, power may be varied in place of speed. If there are significant peak vibrations anywhere between ground idle and maximum continuous conditions, the number of increments chosen must be changed to increase the amount of running conducted while being subjected to the peak vibrations up to not more than 50 percent of the total time spent in'incremental running.
Chap 3 88 Par 58