Sound and Vibration
Introduction
Air crewmembers operate in an environment that expos them to hazardous vibration levels on a daily basis. Vibrations effect aircrew member’s coordination, vision and can degrade performance in other flight-related activities.
Proper management of the effects of vibrations can enhance cockpit performance, promote a safe flying environment and ensure successful execution of the mission. We cannot eliminate vibration during flight, but we can minimize its effects by practicing good prevention techniques and using a little common n.
After completing this lesson…
You will be able to:You will be able to discuss:
Define vibration
Define resonant frequency Define damping
Identify sources of vibration The short-term effects of vibration The long-term effects of vibration Discuss preventive measures to reduce the danger pod by vibration
Background
What is Vibration?
In simple terms, vibration is
nothing more than shaking.
More exactly, vibration is the
motion of an object, relative to a
reference position (usually the
object at rest), involving a ries of
oscillations that cau the object to
displace and accelerate. How is Vibration Measured?
Frequency: the number of
oscillations of any object measured
in cycles per cond (cps). The
standard unit of frequency is the
hertz (Hz): 1 cps equals 1 Hz.
actvAmplitude: the maximum
儿童节手抄报内容
displacement about a position at
rest.
Duration: the amount of time
expod to vibration.
Vibration and Aviation
How does vibration affect aircrew members?
Vibration can be harmful becau of the
stress of shaking on tissues. Contact with a
vibrating aircraft transfers vibration energy
to a person's body through the aircraft ats,
the flight controls or the floor. Vibrations of
different frequencies can affect the
crewmember’s whole body or only a激扬青春梦
new year resolutionparticular organ.
What is resonant frequency?
Each organ in the body has a natural
frequency at which it vibrates. When
external vibrations are transferred to the
body at or near the natural frequency of an
organ, the vibrations are amplified in that
organ. The amplified increa the stress on
the organ.
Why doesn’t vibration riously injure aviators every time they fly?
Becau the connective tissue and muscles in the body dampen vibrations. Damping is the loss of mechanical energy in a vibrating system.
The connective tissues that bind the major organs together (and muscle tissue as well) react to vibrations like shock absorbers, reducing and slowing the vibrations to less harmful intensities.
Aircraft Vibration Sources
Vibrations are produced within the aircraft and the environment in which it
operates.
Rotary Wing Aircraft:Fixed Wing Aircraft:
Aircraft Sources Main rotor 4-11 Hz
Engine 110 Hz
Tail rotor 30-60 Hz
Airframe during low
altitude high-speed flight
1-10Hz
Propellers 20+ Hz
Outside Sources
anthony hamilton
Weather (turbulence):
crewmembers may over-
control during turbulence.
Incread air speed
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Internal and external
loading
Warning: Vibration tends to be
most inten during transition
from hover to crui flight and
crui to hover.
Weather (turbulence):
crewmembers may over-
control during turbulence.
Incread air speed
Internal and external
loading
Nap of the earth (NOE)
flying
Effects of Vibration
Reduced muscle control. Vibration caus the body's muscle groups to make
reflex contractions. When the human body is in motion, pressure receptors located in tendons and muscles constantly measure angular position of the muscle in order to maintain posture and balance. The receptors respond to vibration, causing
muscle contractions. This reduces muscular control.
Reduced coordination.Vibration degrades aircrew members’ ability to perform
simple tasks during flight. Manual coordination and control "touch" is degraded at 4-8 Hz. A pilot can induce oscillations when he or she over-controls during
turbulence and/or transition from a hover to flight.
Degraded vision. Vision could be degraded due to vibration in the aircraft—
shaking instruments may be difficult to read. Furthermore, helmet mount or night
vision devices may vibrate at 4-12 Hz, adding to visual disturbances.
Distorted speech. Speech can be distorted during oscillations of 4-12 Hz. Above
12 Hz speech becomes increasingly difficult to interpret.
Short-Term Effects of Vibration:
Hyperventilation is caud when the diaphragm is vibrated at its resonant
frequency of 4-8 Hz. Hyperventilation is due to an "artificial respiration" caud
by involuntary, rapid vibration of the diaphragm.
Incread pul rate and blood pressure. The body interprets vibrations during flying as exerci. Therefore, the muscular effort of bracing against vibration
increas pul rate and blood pressure.
Naua. Vibration with a frequency of less than 1 Hz (like the slow rolling of a
ship) can produce naua in susceptible people to motion sickness.
Balance: Vibration affects the organs of balance in the middle ear: the
micircular canals and the otolith organs. The micircular canals respond to the changes in angular and linear motions (pitch, roll or yaw). The otolith organs are
stimulated by gravity and linear motions (vibrations and oscillations). Vibrations
are nd by the organs and caus disorientation.
Pain is usually due to vibration exacerbating preexisting injuries, such as stress
fractures or other traumas. Vibration aggravates tho conditions.
Long-Term Effects of Vibration:
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Exposure to vibration over a period of time may cau injury to aviators:
Raynaud's Dia (white finger) occurs in the hands after prolonged exposure to vibration from power tools, jackhammers or other equipment that vibrates at high frequencies. It is caud by chronic trauma to the arterioles and nerve endings in
the extremities. Vibration caus microtrauma, which reduces blood flow to the
effected portion of the extremity.
Backache/back pain in aircrew members may result at an earlier age than
normal. The lumbar spine, in particular, is subjected to higher pressures during
fixit
aircraft operation becau it bears the incread weight of the torso during
resonant oscillations. Bone, like other organs, requires good blood flow. When the spine is subjected to high levels of vibration, blood flow is reduced. The reduction in blood flow results in premature degeneration of bone structures within the
spine.
Kidney damage. Signs of overexposure to vibration include hematuria, (blood in
the urine) and albuminuria (albumen in the urine).
Lung damage may result after prolonged exposure to vibration at resonant
frequencies.
Reducing the Effects of Vibration?
Vibration cannot be eliminated, but its effects on human performance and physiological functions can be lesned:
Pre-flight
Proper aircraft maintenance,
such as blade tracking, can reduce
vibration.
Stretcher Loading When loading
patients on MEDEVAC aircraft,
remember that patients on the floor
will experience more vibration than
汉高祖刘邦墓patients in the upper racks.
Maintaining excellent physical
condition. Fat multiplies vibration,
while muscle dampens vibration.
Strong muscles dampen oscillations
encountered in flight. An
overweight aircrew member is
During flight
Maintain good posture during
flight. Sitting up straight in the at
enhances blood flow throughout
the body.
U of restraint systems. Restraint
systems (at harness and belts)
provide protection against high-
magnitude vibration from extreme
turbulence.
Body supports, such as lumbar
inrts and at cushions, reduce
discomfort and can dampen
vibration. However, during a crash
evolutionaryquence they may increa the
more susceptible to decrements in performance from the physiological effects of vibration. Good physical condition also lesns the effects of fatigue, helping you to function during extended combat operations with minimum rest.
Keep hydrated. Drink plenty of fluids, even if you do not feel thirsty. Dehydration coupled with vibration can worn fatigue and increa the time needed for recovery. likelihood of injury due to their compression characteristics. Limiting exposure time. Make short flights with frequent breaks, rather than one long flight, if mission permits.
Let the aircraft do the work; do not grip the controls tightly. Vibration can be transmitted through control linkages during turbulence.
