Air defense of many countries, notably India use different types of aircraft for their air combat operations. These types could include twin engine or single engine fighters, have twin/single fins and could have radically different design and operational philosophies. On the other handudLRU's and missile/gun platforms may become common as standardization and indeginization and single sourcing is attempted. These could be mounted at various locations of an aircraft fuselage, wing etc. As aircraft age, retrofitting and upgrades are now extremely cost effective.udThese upgrades especially of radar, avionics etc. need to be accommodated at various locations. Weapon systems also change over time and new advanced technology installed onudthese aircraft. While these are generally qualified to various standards like MIL-810E, the qualification by these standards is based on a number of assumptions. Sources of vibration identified are engine noise impinging on aircraft structures, turbulence, shock pressure pulse in gun firing, maneuvers, buffeting etc. Typical MIL 810E acknowledges that vibration spectra are characteristic of the particular airframe and evaluated through measured data. It notesudthat outer regions of flexible structure are especially where the data is required. MIL-810E also provides a zonal test condition at various zones: Wing, fuselage, equipment mounted on engines etc. and accounting for whether the aircraft is propeller driven or by turbine engine,udthe spectra changes. Typical for helicopter the rotor frequencies drive the zoning that needs to be considered.
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