Posted for "Justin Hawkins"
<JustinH@lancair.com>:
All flight controls must be 100% balanced. Once body worked and
painted, all flight
controls (except flaps) must be removed and balanced
following procedures found in the builder's
manual.
Flutter
Flutter is a self-feeding and potentially destructive vibration where
aerodynamic forces on an
object couple with a structure's natural
<http://en.wikipedia.org/wiki/Natural_frequency> mode of
vibration
<http://en.wikipedia.org/wiki/Vibration> to produce rapid periodic
motion
<http://en.wikipedia.org/wiki/Periodic_motion> . Flutter can
occur in any object within a strong fluid flow, under the
conditions
that a positive feedback
<http://en.wikipedia.org/wiki/Positive_feedback> occurs between
the
structure's natural vibration
<http://en.wikipedia.org/wiki/Vibration#Types_of_vibration> and
the
aerodynamic forces. That is, that the vibrational movement of the object
increases an aerodynamic load which in turn drives the
object to move
further. If the energy during the period of aerodynamic excitation is
larger than the natural damping of the system,
the level of vibration
will increase, resulting in self-exciting oscillation
<http://en.wikipedia.org/wiki/Self-exciting_oscillation>
. The vibration
levels can thus build up and are only limited when the aerodynamic or
mechanical damping of the object match the
energy input, this often
results in large amplitudes and can lead to rapid failure. Because of
this, structures exposed to
aerodynamic forces - including wings,
aerofoils, but also chimneys and bridges - are designed carefully within
known parameters to
avoid flutter. It is however not always a
destructive force; recent progress has been made in small scale (table
top) wind
generators for underserved communities in developing
countries, designed specifically to take advantage of this
effect.[1]
<http://en.wikipedia.org/wiki/Aeroelastic_flutter#cite_note-0> [2]
<http://en.wikipedia.org/wiki/Aeroelastic_flutter#cite_note-1>
In complex structures where both the aerodynamics and the mechanical
properties of the structure are not fully understood
flutter can only be
discounted through detailed testing. Even changing the mass distribution
of an aircraft or the stiffness
<http://en.wikipedia.org/wiki/Stiffness>
of one component can induce flutter in an apparently unrelated
aerodynamic component.
At its mildest this can appear as a "buzz
<http://en.wikipedia.org/wiki/Buzz> " in the aircraft structure, but at
its most
violent it can develop uncontrollably with great speed and
cause serious damage to or the destruction of the
aircraft.[3]
<http://en.wikipedia.org/wiki/Aeroelastic_flutter#cite_note-2>
from
http://en.wikipedia.org/wiki/Aeroelastic_flutter#Flutter
Justin
Hawkins
Lancair Airframe & Technical Support
Lancair Int. Inc.
250 SE Timber
AVE
Redmond, OR 97756
justinh@lancair.com <mailto:justinh@lancair.com>
541-923-2244
ext 121
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