I Downloaded from https://www.everyspec.com MIL-STD-81OD 19 July 1983 I-3.2.5 _Gate”izorv 5 - Jet aircraft and tactical missile a. The vib$ation environment for equipment installed in jet aircraft and tactical miaailes (except engine-mounted) stems from four principal mechaniama. These vibrationa e are random and, except where the elaatio response.of primary aircraft structure is the source, broadband. These sources are”aa follows: .:’. , (1) Engine no:ae impinging on aircraft structures. (2) Turbulent aerodynamic flow along external aircraft structures., (3) Pressure pulse impingement due to repetitive firing guns. of .
(4) Airframe structural.motions due to maneuvers, aerodynamic buffet, landing, taxi, etc. . .. The guidance provided in this section conaidera sources (1) and (2). Method 519 covers source (3). General airframe motions (4) cannot be adequately covered by general criteria. They are the result of responses of flexibie atructurea to various tranaient eventa. Two examplea of-such responses are rebound of wings and D~lOnS when heavy atores are ejected. and aeoarate flow ~~~ . . or shed vortex excitation of flight surfacea during ‘sustainedma”rieuvera.The vibration spectra are characteristic of the partfc~lar airframe involved and must be evaluated through measured data.
Airframe structural motions”are usually important for the outer regions of flexible structures (i.e. outer 1/2 of wings, empennage, pylons, etc). They are usually not important for ~~ fuselage-mountedequipment. ., ~~ Jet-noise-induced vibration ie usually dominant in vehicles which operate-at lower dynamic presaurea, i.e. limited t’osubsonic speeds at lower altitudes and transonic speeds at high altitudes. Aerodynamically induced vibration usually predominates in vehicles which operate at transonic speeds at lower altitudes or supersonic speeds at any altitude.
When equipment is used in more than one application, the vibration criteria should be enveloped and test criteria baeed on a worst-case composite. Only functional tests are performed for tactical missiles. I a. Yes t levels. In the.absence of.satisfactory measurements of field environments, functional test levels approximating jet-noise-induced and flOw-induced vibration may be derived from table 514.3-III and Figures 514.3-26 - and 514.3-27. ,. I 19 July 1983 METHOD 514.3 514.3-34