28-05-2012, 10:56 AM
HELICOPTER VIBRATION REDUCTION TECHNIQUES
HELICOPTER VIBRATION REDUCTION TECHNIQUES.pdf (Size: 777.41 KB / Downloads: 146)
INTRODUCTION
Helicopters play an essential role in
today’s aviation with unique abilities
to hover and take off/land vertically
These capabilities enable helicopters to
carry out many distinctive tasks in both
civilian and military operations.
Despite these attractive abilities,
helicopter trips are usually unpleasant
for passengers and crew because of
high vibration level in the cabin.
This vibration is also responsible for
degradation in structural integrity
as well as
reduction in component fatigue life
decrease the effectiveness of onboard
avionics or computer systems that
are critical for aircraft primary
control, navigation, and weapon
systems
Consequently, significant efforts have
been dedicated over the last several
decades for developing strategies to
reduce helicopter vibration
Overview of Helicopter Vibration
Helicopter vibration generally originates from
many sources; for example,
transmission,
engine, and
tail rotor
but most of the vibration comes primarily from
the main rotor system, even with a perfectly
tracked rotor.
the severe vibration level is primarily
due to
impulsive loads induced by interactions
between rotor blades
and strong tip vortices dominating the
rotor wake (Fig. 1.2)
This condition is usually referred to as
Blade Vortex Interaction (BVI)
HELICOPTER VIBRATION REDUCTION METHODS
Passive Helicopter Vibration Reduction
Most of the passive strategies produce moderate
vibration reduction in certain flight conditions, and
only at some locations in the fuselage (such as, pilot
seats or avionics compartments)
The major advantage of the passive concepts is that
they require no external power to operate
However, they generally involve a significant weight
penalty and are fixed in design, implying no ability to
adjust to any possible change in operating conditions
(such as changes in rotor RPM or aircraft forward
speed).