1、I NOT MEASUREMENT 1 SENSITIVE 1 ADS-27A-SP 02 MAY 2006 CAGE Code 81996 AERONAUTICAL DESIGN STANDARD STANDARD PRACTICE REQUIREMENTS FOR ROTORCRAFT VIBRATION SPECIFICATIONS, MODELING AND TESTING AMSC N /A DISTRIBUTION STATEMENT A. Approved for public release, distribution is unlimited. Provided by IHS
2、Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-REQUIREMENTS FOR ROTORCRAFT VIBRATION SPECIFICATIONS, MODELING AND TESTING UNITED STATES ARMY AVIATION AND MISSILE COMMAND AVIATION ENGINEERING DIRECTORATE REDSTONE ARSENAL, ALABAMA fixed system dynamic loads and vibr
3、ations may result. 5.4.2 Rotating Element One/Revolution Vibration Level Specifications. The IP vibration levels of all the rotating components shall be controlled by design and manufacturing techniques to levels that are below levels that will degrade occupant effectiveness and shall not cause any
4、damage to, nor reduce the performance of, the airframe, engines, electronics, or weaponry. The levels and frequencies are necessarily configuration specific. In addition, within the stabilized operating rotor speed range, shafting imbalance shall produce discrete frequency vibration levels of no mor
5、e than 0.5 ips at the shafting mounts and tail rotor imbalance shall produce no more than 0.3 ips at the tail rotor/airframe interface. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-5.4.3 Design Configurations 5.4.3.1 One/Rev Drawing Details During
6、 design, the limits for the primary causes of imbalance (airfoil profile variations, eccentricities, wall thickness variations, bond squeeze out, shaft straightness, pilot centering, etc.), shall be specifically noted on the drawings. Inspection records shall show that these variables are controlled
7、. 5.4.3.2 Imbalance Capability The drive shafts, rotors, and their supports shall carry the imbalance forces which would result from the worst case build up of manufacturing and maintenance tolerances at the limit rotor speed (power on or off). Additionally, these components shall carry any addition
8、al imbalance which would result from any damage consistent with the ballistic survivability or blade strike requirements for the system. The capability of the drive shafts and/or rotor supports to carry imbalance forces shall be evaluated either by operational fatigue or endurance tests or by a cons
9、ervative stress analysis. These capabilities shall be expressed as design conditions in the systems specification; for example, “the main rotor and the tail rotor support systems are capable of withstanding the imbalance resulting from the loss of 0.5% of the weight of a single blade at its the outb
10、oard end“. This 0.5% value is only an example, the actual limits shall be agreed to. For drive shafts, the imbalance limits shall be expressed in inch-ounces or equivalent metric units and then related to the imbalance force reacted by the support structure and the estimated vibration levels, in inc
11、hes/sec, of the support structure. 5.4.3.3 Shaft Critical Speeds Shaft critical speeds and fixed system support frequencies shall be located to avoid resonant frequency operation by at least 15% between the limit rotor speed (power on or off) and the minimum operating speed of the rotor. This margin
12、 shall be demonstrated by analysis, laboratory tests and vehicle ground tests (to the maximum rotor speed attainable). Resonance is defined as any condition where a natural frequency coincides with an exciting frequency in either the rotating shaft or the support structure. Excitations may be caused
13、 by imbalance, misalignment, coupling deflections or torsional oscillations. If the resonance is proven heavily damped or the strain energy of the mode is proven Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-to be primarily in the non-rotating syst
14、em, and the resulting stresses are acceptable, then this requirement may be relaxed. 5.4.3.4 Fuselage, Wing, and Pylon Frequency Placement Fuselage, wing, and rotor pylon (of all rotors) frequency placements, in all directions, and with any allowable fuel and stores loading shall be at least 10% awa
15、y from continuous rotor operating rpms. This is necessary to prevent field track and balance problems. 5.4.4 Engine Vibration Specifications The vibration levels at the engine manufacturer specified accelerometer locations on the engine and the combined steady and oscillatory loads at each engine mo
16、unting point shall not exceed the frequency dependent limits established by engine vibration analysis and tests for the appropriate Region (i.e., Regions I, I1 and I11 for a helicopter) as defined by the engine manufacturers. 5.5 Modeling 5.5.1 Rotor and Airframe Compatibility. A rotor airframe comp
17、atibility modeling plan shall be developed and submitted to the Government for approval. The plan shall layout the overall strategy to be used to meet the specified rotorcraft vibration environment. As a minimum the plan shall call for the development and maintenance of a state-of-the-art rotor/airf
18、rame analytical model which shall be verified and updated based on data from the following tests as they are accomplished during the development process: a. Wind tunnel test or flight test of similar dynamic configurations. b. An airframe shake test as described in 5.6.1 - 5.6.1.2, to beconducted on
19、 an early full scale airframe. c. Rotor blade and hub properties test as described in 5.6.2 - 5.6.2.2. 5.5.2 Engine and Airframe Compatibility An engine structural dynamic model shall be derived based on structural dynamic analysis and test sufficient for calculating the engine bending frequencies w
20、ith the engine installed on the airframe. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-The analytical engine compatibility modeling shall be conducted in three stages: a. The engine on the mounts, shall be attached to a rigid structure. b. The eng
21、ine on the engine mounts, shall be attached to a compliant structure represented by a spring in each direction for which loads are reacted. A parametric variation of springs, with all spring rates equal for a given case, shall be conducted and the variation of each mode with spring rate determined.
22、The spring rates shall then be individually set to the values calculated for the fuselage interface compliance. c. The engine installation model shall then be integrated with the rotorcraft dynamic model and the engine rigid body and flexible body modes defined. The engine frequency response transfe
23、r functions shall be developed for each of the vertical, lateral, fore-and-aft, pitch, roll, and yaw degree of freedom directions. If possible, the excitations shall be applied at the locations and in the directions corresponding to those of the required shake tests. The forced response at each sign
24、ificant rotor harmonic to each significant type of hub excitation shall then be calculated and the expected values of these excitations used to predict the resulting in-flight engine vibrations. 5.5.3 Stores and Airframe Compatibility 5.5.3.1 A finite element model of the rotorcraft and any weapons
25、or stores to be carried shall be derived. 5.5.3.2 Shake tests of the stores shall be conducted to validate and improve the analytical model. 5.5.3.3 Shake tests (5.6.1 - 5.6.1.2) of the airframe with selected store configurations shall be used to validate and improve the analytical model. 5.5.3.4 Th
26、e validated analytical model shall be used to examine the matrix of stores and stores dispensing sequences. Critical configurations shall be determined both for store configuration effects on the rotorcraft, and for store configuration effects on store response and performance. 5.5.3.5 The modeling
27、results, in coordination with structural loads and fatigue considerations, shall be used to define the matrix of stores and stores dispensing sequences to be flown for Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-system loads, vibration, and accur
28、acy surveys. 5.6 Vibration Tests 5.6.1 Airframe Shake Tests. A full scale airframe shake test is required as early as possible in the rotorcraft development process to determine the natural frequencies and other modal properties of the airframe and rotor support system, to determine the major forced
29、 response mode shapes of the rotorcraft, to determine the transfer functions from force inputs at the rotor hub to the response at locations critical for vibration, and to evaluate the effectiveness of any fixed system vibration control devices and tune these as needed. Weapons firing effects shall
30、also be determined as needed. Tests shall be performed with the developmental rotorcraft in conjunction with ground and flight test. This is required to help solve any vibration, firing loads, or stability problems which might be encountered during FSED. The tests shall be repeated with the final pr
31、oduction configuration to document the fielded rotorcrafts dynamic properties. This information is needed to investigate any field service problems which may arise, and for future modifications to the rotorcraft. 5.6.1.1 Aircraft Configurations. The rotorcraft configurations tested shall include: a.
32、 The basic rotorcraft with no ordnance or cargo added, or the configuration to be used during initial flight tests b. The primary mission configuration c. The configuration(s) to be used for the flight vibration survey (5.6.4 ) d. Any other configurations, including external stores installations, wh
33、ich prior analysis and test have predicted to be critical for vibration or aeromechanical stability. In general, the rotorcraft shall be tested with all doors and panels in their normal positions and all equipment installed. If a piece of equipment is not available during the test, a dynamically sim
34、ilar model of the item may be installed instead. The effects of various fuel loadings, and cargo loadings, if appropriate, shall be investigated. Crewmembers and passengers/troops shall be simulated as appropriate. The vibration test shall be conducted with the rotorcraft completely suspended from t
35、he rotor hub(s) to simulate flight. To validate the inputs to the aeromechanical stability analyses, the shake Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-tests shall be conducted with the critical gross weight on the landing gear, with the rotor
36、craft completely suspended and at intermediate conditions as needed. If the configuration can be conclusively shown to be immune to ground resonance instabilities, the full weight on the landing gear tests may be omitted. 5.6.1.2 Test Procedures and Instrumentation. Consideration shall be given to t
37、he following: a. The instrumentation, excitation system, and data analysis system shall be sufficient to accurately and efficiently obtain the required data. b. The rotorcraft suspension system shall simulate free flight as closely as possible, and the effects of the suspension system shall be accou
38、nted for in the analytical vibration model of the rotorcraft. c. Care shall be taken to insure that the effects of any instrumentation cables, power cables, hydraulic lines, etc. on the rotorcrafts structural dynamics are minimized. d. The locations, directions, magnitudes, frequencies, and phases o
39、f all excitations shall be accurately measured. Any shakers used shall be mounted in a manner that minimizes the amount by which their installation changes the structural dynamics of the rotorcraft. e. The mass of the rotors shall be simulated in the manner which, based on analysis, best represents
40、the operating condition. f. Tests to determine the linear range of the structure and define any nonlinearities are required early in the test program. Any nonlinearities found may require that test procedures be modified to insure that the results of the shake test will be satisfactory for their int
41、ended use. 5.6.2 Rotor Blade and Hub Properties Determination. The rotor blade and hub physical properties used in the system dynamic analytical models shall be verified by tests performed on flight-worthy (or equivalent) test articles prior to first flight. For all these tests, the actual test boun
42、dary conditions shall be determined, and the analyses shall include the effects of these non-ideal boundary conditions. These measured properties, corrected as appropriate for the boundary conditions, shall be used to update the analytical models. The Provided by IHSNot for ResaleNo reproduction or
43、networking permitted without license from IHS-,-,-updated models shall be used to justify the safety of flight release for the rotorcraft. 5.6.2.1 Blade and Hub Properties. For any newly designed blade, the following tests shall be conducted: a. One blade shall be sectioned into at least 20 sections
44、. Each section shall be weighed to determine the running mass at that section, and the chordwise C.G. of each section shall be measured. b. Blade contour, twist, and platform measurements shall be made for at least 20 blade stations on at least four rotor blades to determine manufacturing variations
45、 in contour. c. Deflection tests shall be conducted on at least four rotor blades to determine flapwise, chordwise, and torsional stiffness distributions. d. Non-rotating modal properties shall be experimentally determined. Flapwise modes 1 through 3, chordwise modes 1 and 2, and torsion mode 1 shal
46、l be measured on at least four rotor blades. 5.6.2.2 Control Couplings. Static kinematic pitch-lag, pitch- flap, and flap-lag couplings and control system stiffness shall be measured. Swashplate-pylon couplings and swashplate-mast bending couplings shall be measured as appropriate. 5.6.2.3 Rotor Fre
47、quency Tests. Prior to first flight, ground run rotor speed sweeps shall be conducted with instrumented main and tail rotors to determine the rotating natural frequencies. This data shall be used to validate the analytical predictions. Means of exciting all relevant modes shall be incorporated as ne
48、eded. Misrigging to achieve extreme rotor speeds is not required. 5.6.3 Component Shake Table Testing. 5.6.3.1 Vibration Qualification Test. The vibration qualification test of equipment mounted on or in rotorcraft shall consist of the following sequence of steps: a. All functions of the equipment s
49、hall be exercised and each function shall meet the equipment performance specifications. b. The equipment shall be mounted in a manner that simulates the expected rotorcraft installation boundary conditions. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-c. A resonant search shall be performed in three orthogonal
