“Dynamic Analysis and Balancing of an Aircraft Gas Turbine,”
Since these jets have rear-mounted engines, excessive engine vibrations may be transmitted
to the fuselage. The fuselage, in turn, may have its own acoustic modes which, under certain
circumstances, may be excited by engine response. While the integrity of the engine has never been
an issue, there have been occasions when an engine had to be removed for re-balancing due to
excessive sound pressure levels generated·in the cabin. On larger classes of business aircraft, the
apparent passenger noise problem is avoided by having the gallery area next to the engine mounts.
However, in the smaller business jets, the executive seating is often in proximity to the engine
mounts. When the plane reaches cruising altitude, the accompanying sound pressure level may
interfere with normal conversation. Excessive noise levels in the past have led to downtime caused
by engine replacement and even loss of sales.
Extensive instrumentation was placed on the engine to determine vibration characteristics
in the test cell and also several aircraft were instrumented so that vibration levels could be
determined during flight at various altitudes and power levels.