CHAPTER 5. INTERNAL COMPONENTS VIBRATION
5.1. General. In addition to vibration resulting from excitations of natural frequencies (resonances), if applicable, consider the effect of rotor unbalance on internal components (see chapter 3).
5.2. The Blades, Vanes, Rotor Disks, Spacers, and Rotor Shafts.
a. Blades, vanes, rotor disks, spacers, and rotor shafts shown to comply with § 33.83, Vibration test, also satisfy the § 33.63 requirement that engine components must not be subjected to excessive stresses because of vibration. The blades, vanes, rotor disks, spacers, and rotor shafts not tested in compliance with § 33.83 should be addressed under § 33.63. In addition, the design aspects or operating conditions that affect vibration and that were not assumed for compliance with § 33.83 should be addressed under § 33.63. For example, you should consider the ranges of geometric tolerances, tip clearances, and other factors affecting natural frequencies and amplitude response, if these were not examined in compliance with § 33.83. To demonstrate that the stresses are not excessive, we recommend that you use the criteria of § 33.83(d).
Otherwise, you should justify different criteria.
b. You should address the effects on vibration that are anticipated or determined to occur in operating conditions like icing, rain, and hail, and for which repeated or continuous engine operation is expected. These conditions might affect, for example, blade vibratory amplitude responses or flutter margins. Repeated exposure to high cycle fatigue stresses in excess of endurance limits for even short periods of time could lead to cumulative fatigue damage and subsequent component failure. If these vibratory stresses exceed the levels demonstrated during § 33.83 compliance, § 33.63 requires that you show they are not excessive.
5.3. The Fan Case. You should show by analysis, test, or experience that the fan case and fan rotors are not sensitive to rotor-case interactions, and no conditions exist that may cause this phenomenon to develop. Fan rotor-case interaction is a dynamic phenomenon that must be avoided since it is potentially hazardous. This interaction could rapidly produce destructive and unavoidable vibration, rendering the vibration monitors ineffective for any timely action or response.
5.4. Other Components. You should assess any other internal components sensitive to engine vibration not referenced in paragraphs 5.2 and 5.3 and show that they are not subjected to excessive stresses. The compliance methods may be based on test or analysis and may use data or observation collected during certification testing in compliance with other part 33 regulations (see Table 1).
CHAPTER 6. CONDUCT OF TESTING
6.1. Configuration.
a. The engine and its components, including mountings, attachments, and vibration isolators, that are tested for compliance with § 33.63 must be representative of their type design.
For testing purposes for every component and engine system, you should create the vibratory environment that adequately represents the engine. You should also configure any test to account for the engine installation features or interfaces that might affect engine vibration. Examples of installation features are the cowling; the engine mounts; and airframe elements, such as inlet and exhaust structures, for which the weight, center of gravity, or stiffness would affect engine vibration. When the installation features are not entirely known, you should provide in the installation instructions required by § 33.5 the methods to evaluate their effects on engine vibration.
b. Certain components, such as fluid-filled lines and hoses, should be configured to assess the effects on vibration of pressures, temperatures, or any other functional parameters.
6.2. Instrum entation.
a. You must ensure that sufficient instrumentation is present to monitor engine vibration throughout the test. The instrumentation must be capable of, and located, so that it properly identifies the critical vibratory environment for those components subjected to test. For example, the vibration monitor units must be placed based on their sensitivity response to rotor unbalance.
The comparison of vibratory signatures of the nominal versus unbalanced rotors may constitute an indicator for the sensitivity response of the vibration monitor units. You should consider placing accelerometers or vibration sensors on or near the fan case, compressor case, combustor case, exhaust frame, and accessory gearbox to determine their vibratory environment.
b. Additional instrumentation may be required to identify the vibratory environment for specific components and accessories.
6.3. Test Sequence and Success Criteria.
a. Prior to testing, you must identify the pass/fail criteria, such as engine or component performance, vibration levels, and acceptable post-test inspection criteria. The pass/fail criteria must include the capability to detect the engine vibration with an acceptable level of accuracy.
b. You should plan the test sequence to ensure that significant vibration is found and addressed in subsequent testing. For example, the vibration signature test must precede the stairstep and dwell tests to ensure that all peak and significant vibration emerging during the vibration signature test are considered during the stair-step and dwell tests.
6.4. Post Test Inspection. You should perform all necessary post-test evaluations and inspections with the goal of detecting any component structural or functional failures. Because high cycle fatigue damage may not be detected by a simple visual inspection, remove the 12
vibration sensitive components and thoroughly inspect them. Your test plan should identify the inspection methods, including visual, non-destructive inspections, or functional tests. You should explain any damage, distress, or wear beyond the limits set for post-test inspection and provide an analysis of the impact that it presents.