TABLE 523. l-II. Relative frequency of вЧзнЮп tvpea.

MISSION TYPE

A/C TYPE

r. OF SORTIES

1. Patrol Mission I

Fighter A Fighter В

50 30

2. Patrol Mission II

Fighter a Fighter В

20 20

! 3. Strike Escort Mission!

Fighter A Fighter В

; 4. Strike Mission

Fighter В

TABLE 523.l-III. Mission phase analysis (fPthter B. strike mission).

NEraOD 523.1

With a conposlte freq\iency distribution of tenperature levels at hand, a conposlte mission tenperature profile may be constructed by arranging the conposlte tenperature level durations in segments ordered to simulate a typical mission or a few missions. Such a staiKlard conposlte mission tenperature profile is showr. in figure 523.1-3. ien the t*Bpepat-ts e profiles of the various nussions are dissimilar, segments may be separated into groiips of similar characteristics and the conposlte profile constructed to include a mission or mission phase requirements for each of the groups. Total duration at each tenperature level nust still reflect the distribution fxjnction calculated.

The standard conposlte mission tenperature profile nust now be adjisted for climatic tenperature variations since the standard atmosphere, based on the standard day , represents only an abstract climatic condition. Tenperatures both higher and lower than *standar4i day values агв comnonly met due to seasonal or geographical changes in mission operations. Preparation of tenperature verevis altitude information to cover all likely climatic mission situations vnuld become too involved for practical consideration. Therefore, judgment of the relative frequency of expected ocGurrence of tenperaturss within this range, is normally resorted to. Tenperature extremes (frequency of occurrence 5% or less) nay be omitted. A climatic atlas is helpful at this step.

Climatic tenperature estimates may be incorporated into the test by selecting a representative groi of fixed tenperature offsets which add to or subtract from the standao conposlte misSion tenperatise ртОхИе. By having these offsets represent equiprcbable tenperature intervals, a full climate set cf these temperature profiles can sinulate the wtiole tenperature system Mhich the store could experienee, A sanple conposlte mission tenperature profile climatic set is shown in figure 523.1-4. Note that the profiles are clustered arotmd the standard value to reflect the higher frequency of operations in nore tenperature climates. For practical test operation, eacai test cycle (one composite mission) will trace a composite tenperatis profile, starting and ending at a resting tenperature. The resting period between consecutive test cycles should be sufficient to allow internal store tenperature to stabilize, thve simulating the ground time occurring between service missions. A climatic set of test cycles will consist of a sequence of test cycles (usually 6 to 15) in which the composite mission tenperature pattern is offset stepwise upward and downward from zero offset. Figure 523.1-5 illustrates a typical offset sequence for an 8-cycle climatic set. To provide uniformity eind consistency from one test tc the next, it is ispcrtant that several full climate sets be conpleted before the expected Mean-Time-to-Fal lure of the store is reached. A test mininun of five sets is reconmended.

1-3.4.2 Vibration profile. A composite mission vibration profile may be generated by determining the dynamic pressures during each stable segment of aircraft flight (see 1-2.5). A rough profile can now be constructed. The periods of changing tenperature will usually also be periods of changing q since both are dependent on aircraft altitude and velocity. However, since vibration in the laboratory nay be

4. >-

С

С

60 90

Elapsed Mlaaion Tlae, Mlnutea

FIGURE 523.1-3. Tgirature profile for COBpoaltC laalOD-

0 Э0 60 90 ISC

El>p 4 NistlOB Tie*. Шпигм PIOURI 523.1-4. CI \ma<t\t. net of teaperature profiles for OMPCllf MlBalQD.

changed almost instantaneously (not with lag, like tenperature) and is. more easily controlled at fixed levels, the q profile is teually laid out as a series of steps. Figure 523.1-6 shows a typical composite mission dynamic pressure profile matching the corresponding figure 523.1-7 tenperature profile. Data from instrumented flights are used to determine the spectral envelope for various mission phases and the translation from q to vibration level.

The sinplified vibration profile shoves intensity only. The spectrum envelope a.nd the spatial distribution (including directivity) of the vibration are additional variables that, Mhen uncontrolled, can cause error in the sinulation process. Experimental adjustment should be done in the test cheunber so as to achieve a reasonable correlation between accelerometer vibration records from captive-flights and from the Store under test.

1-4 SPECIAL (X)MSIDERATIOMS. None. 1-5 References

a. Meeker, D.B. and A.Q. FierSol, Accelerated Reliability Testing under Vibracoijatic Environmeiits, Reliability Design for Vibracoustic Environments, ASME A,MD-Vol ©, New York, NY 1974.

b. Dantowitz. A., G. Hirschberger. and D. Pravidlo, Analysis of Aeronautical Equipment Environmental Failures. Air Force Flight Dynamics Laboratory, TR-71-32. Kfay 1971.

c. Jfeeker, D.B. and S9.D. Everett, U.S. Navy Experience. sn theffects

of Carrier-Aircraft. BivirQnment on Guided Missiles. AGARD conference proceedings No. CP270, M y 1979.

MIL-rn>-810E U JiI.Y 1989

50 H

-10-1

-30 i

I I i I

I

----1

v..-

[Л\ li!

(orrin

I

i iMMt OffMt и* i

-1-1-Г-

ISO ?bO 300

Elapsed Time, Minutes

-Г 360

FICORE 523.1-5 rii-tic alan ehpwina offset aeouenoe.

о

с

0 30 60 90 120

Elapsed nietion Tlae, Stinutss PICUM 523.1-6 grmr* arijaasure. 0. profile for гпЯТЮЯПе llaiiOD.

ilOD 523.1

ICrnOD 523.1 VIBBu-ACOUSTIC, TEmFERATuRE SECTKMI II

II-l APPARATUS

II-l.l GEhERAL.. The facility uLt ineluie a large accvstical ncise test chasber capable of approximately a 155 dB intensity level and associated air-conditioning equipment to provide controlled, fixed air teiif>eratijr s and rapid tenperature changes (4% per minute) in the range -40% to -fSS. Mechanical or hydraulic shakers capable of stressing the store(s) tjnder test may also be required. Adequate inetrunentation for controlling, sonitoririg, calibrating arid recording the enviro-iment variables will be needed.

II-l.2 Test chamber. Chanber shape and dimensions shall provide for diffusion and uniform distribution of the acoustic field, and support reverberation of acoustic frequencies of 150 Hz and above. Ports nuet be provided for introdijction of the acoustic energy, for pressure stabilization (exit of modulator air), for entry and exit of tenperature-conditioned air and for access by nultiple electrical cables and waveguides, light beams, anechoic ducting, etc. as applicable. Some stores may require specialized test apparatus auch as artificial targets, r-f anechoic shrouds, or visible gages mich must be incorporated without cororalslng the cosijlned environments.

II-1.3 Vibration,.equipment. A suitable acoustic energy field shall be provided by an acoustic power source controlled to reproduce the acoustic mission profile. Typical paratus consists of a constant-pressing conpressed air aource auch as a reclprcctirig cospresscr with pressure regulator feeding an air modulator that is acoustically coupled to the chanber through an exponential horn. The air modulator la excited electrically by an anpl If led audio algnal. Considerable acoustic power is needed to reach required levels, often 10 to 30 KW; multiple modulator-hom units nay be necessary to reach desired intensities.

To provide low-frequency vibration below about 100 Hz, electrodvnamic or hydraulic shakers nay be used to augment the acoustic field. Such ahakera may also be used to provide limited mechanical shock Inpulsea. To maintain access to the stores by the conditioned air and acoustic energy, sijapended stores can be vibrated at low levels using a rod and collar arrangement to conduct the vibration from the shaker(s). Procedure VI of method 514.3 will f\sieh sorai guidelinea for this prooeduf. A possible aprangement is dlatiranned in figure 523.1-7

КЕТЮО 523.1

II-l.4 Tenperature ecruipment. Tenperature conditioning of the store(s) under test must be acconplished without adversely affecting the acoustic environment. One process for acconplishing this is to duct high velocity conditioned air across the stores by means of thin flexible shrouds that are acoustically transparent. They can be supported by light metal fraaeworks.

Thin silicone rubber and rip-stop nylon sheetings have been fotBid to be suitable shroud materials. To provide the rapid temperature changes required, one method xjses insulated tanks or hot and cold fluids hich are pvnped through heat exchangers as required to tenperature-condition the blower-driven air. By increasing the blower speed or by narrowing the circumferential gap between the surface of the test item and the shroud usually between 2 and 4 cm), the boundary air velocity can be raised to provide the needed rapid heat transfer to or from the store to simulate the captive flight conditions. A possible arrangement is diagramned in figure 523.1-7.

II-l.5 Electrical stress equipmBnt. Basic electrical stresses always present in electrical or electronic circuits are produced by power on/off transients and resulting localized thermal shocks, and also by hot spots acconpanying the full power condition. A switching system is nornal ly used to form tv-pical patterns of store operation during the conposlte mission test cycle. The use of equipment to modify th© power source to the store(s), to simulate likely variations (voltage, frequency, transients, ripple, noise, etc.) met during mission operations, is optional.

II-l.6 Instrumentation and control

II-1.6.1 Functional moni tor ing of the store. The operating stores should be adequately monitored to indicate failures when they occur. Some form of nanual or automatic test performed at intervals (at least once for each composite mission cycle) can be used. Failxnre criteria, based on equipment Specifications and functional requirements, must be clearly defined. Functional monitoring must be accomplished without adversely affecting the environmental simulation. Fimctions which can only be maasiA*ed outsid© the environmental 4han*>er should be checked at intervals which are short compared to the equipments mean-time-to-fai lure.

II-l.6.2 Vibration monitorinit

II-1.8.2.1 Acoustic stimulus. The acoustic signal зогп се is norraliy a pre-recorded tape or the shaped output of a noise generator. Filters are used as required to control spectral distribution. Intensity level is monitored by calibrated microphones. Microphone placement should conform with II-2, step 6, method 515.3 unless other placement can be Justified by measurement and analysis.

II-l.e.2.2 Mechanical stiniul;. The shaker input signal is nornal ly a pre-recorded tape or the shaped output of a noise generator. Filters are used as required to control spectral distribution. Intensity level is monitored by calibrated accelerometers mounted on or in the store(s) which measure the vibration response (see II-1.6.2.3). The shaker frequency range is limited (typically <200 Hz) so that feedback control is unnecessary.

этп1(лг> COT 1

II-l.6.2.3 Vibration response. Calibrated accelerometers mounted in and on the store(s), when used with appropriate analysis equipment, provide the needed response monitoring for both acoustic and ffieehanical stimuli. AccelerouSEter positions in and on the store, at least during setup, should be as close as possible to those used to obtain captive-flight data. Accelerometer placement should aim to provide coverage for possible directional variation (e.g., longitudinal, lateral and vertical axes) and for possible extension or radial variation (e.g.. fore, mid. aft, external. Internal). Poveer Spectral Density (PSD) measurement or display (g*/Hz tmlts) plus intensity readings (grms units) furnish the needed information for conparlng test chanber and captive-flight vibration parameters (see (II-2.4).

11-1.6.3 Temperature jnonitorinjt. Tenperature sensors on the surface of the store(8) provide the best location for monitoring and feedback control. (Figure 523.1-7).

II-l.6.4 Hvgiiditv monitorinit. Although hunidity is not a controlled variable for procedure I, the ducted airstresin inay be oontinuouBly aenitored for moisture content, either by dssspoint or relative hjnidity ser.sing. It should be noted that raoistsjse can collect on a stores surface when it has reached and holds a cold tenperature that is below the dewpoint of warmer air following in the mission cycle. TTilS is a normal and expected condition.

II-i.6.5 Electrical..input {nonitoring. All electrical inputs to the storevs) should be monitored whether or not they are modified tc represent expected mission irregularities.

II-2 PREPARATIOW FOR-TEST

11-2.1 Test plan. A test plan shall be prepared to docxmient teats vising this method. The fol lowing areas should be addressed in the test plan:

a. Scope and purpose. Test procedures differ with different test goals (see table 523.1-1). A design qualification test might require demonstration of a specific Mean-Time-to-Fai lure (MTTF), a quantitative value. A Test, Analyze, and Fix (TAAF) during development would be qualitative in nature since its primary purpose is the

identification of failure modes to be expected in service.

b. Test time. The items to be tested must be clearly identified. Their service designation, source, and exact configuration should be recorded. Dra ing ntnbers or other specific docxjmentation should be referenced.

c. Perfornance parameters. List those to be used in the test,

d. Failure criteria. These must be clearly stated and be based on the performance monitoring system to be vised.

e. Fai Ixjre analysis. Indicate how failures are to be analyzed, classified and reported. For example, failures can be classified by cause Csxjspected stress), siibsystem or unit involved, effect on Store operation, or responsibility (i.e., bad conponent or material, poor workmanship, inadeqijate inspection, deficient design, etc.).

f. Mission profile. Infornation nust be Supplied that will allow the mission profile to be properly cheu?ted for the p>articular test item. The needed information may be provided through the referencing of relevant documents or by inclusion in the test plan. The information should include:

(1) The particuloo* enviroriroents that are to be controlled. Tenperature and acovstic energy environments are always used. Shaker vibration and/or shock stresses are optional additions.

(2) Data on all operational missions using the test item in the aircraft captive-cariry mode. Needed information includes types of aircraft used, length of missions, aircraft flight paths and patterns, air-craft velocities in different operational modes, theater of expected глзе and percent-of-time estimates for the vario\je categories.

(3) Climatic and atnospheric data. WbrId-wide seasonal altitude-versus-tenperature tables or charts are needed.

g. Measured store responses to snvirorjnsnts used in determining test stresses.

h. Test data. List specific performance and environmental {parameters to be recorded before, during, or after a test cycle and whether recordings should be continuous or made at stated intervals. Explain how data are to be handled and specify recording methods. If analysis is required, methods should be referenced. All raw test data should be sorted, labeled and stored fcr possible later use in analyses or for graphic illustration (see II-4.).

i. Test reDorting. State how results eu?e to be reported and whether conclusions and recomnendations are to be included.

j. Test procedures. Critical operations should be pointed out and requirements for step-by-step procedures stated (see I1-3).

II-2.2 Safety program plan. A safety program plan shall be prepared **iich shall incorporate all safety policies, practices and regulations applicable to the preparation and conduct of the test. Safety policies and directives of the facility condxx:ting the test, contractual safety requirements where applicable, safety precautions applying to the stores under test, and special hazards involved ssith the test apparatus sb.all be treated. The plan sh.all require that operating procedures prepared for this test method shall be even-sequenced and contain suitable warnings