Gravitational Forces
Aircraft Change; Humans Don’t
Terminal Learning Objective
 ACTION: Manage the effects of gravitational forces
 CONDITION: While performing as an aircrew
member
 STANDARD: IAW TC 3-04.93 and Fundamentals of
Aerospace Medicine
Administrative Information
 Risk Assessment: Low
 Environmental Considerations: None
 Safety Considerations: None
 Evaluation: 50 Question exam at the end of
Aeromedical Training at USASAM
ELO A
 Action: Define gravitational force terms
 Condition: Given a list
 Standards: IAW TC 3-04.93 and Fundamentals of
Aerospace Medicine
The Law of Gravity
“G”
 The measure of the magnitude of an accelerative
force with respect to gravity
 Equal to 32.2 ft/sec²
 Until terminal velocity is reached
Acceleration
 Rate of change of
velocity with respect
to time
 Gravity is the most
common accelerative
force
Deceleration
 Reduction in the velocity of a moving body with
respect to time
 (Negative Acceleration)
 0 – 632 MPH in 5.4 seconds
 632 – 0 MPH in 1.4 seconds
Inertial Force
 The resistance to change in the state of rest or
motion
 Newton’s First Law of Motion:
A body at rest tends to stay at rest, a body in
motion tends to stay in motion, until acted upon
by an outside force
 Newton’s Third Law of Motion:
For every action there is an equal and opposite
reaction
Inertial Force
Tri-axial Reference System
QUESTIONS?
Check on Learning
 What is the definition of Inertia?
The resistance to change in the state of rest or
motion
 What does Newton’s First Law state?
A body at rest tends to stay at rest, a body in
motion tends to stay in motion, until acted upon
by an outside force
ELO B
 Action: Recognize the factors of acceleration with
their appropriate effects
 Condition: Given a list
 Standards: IAW TC 3-04.93 and Fundamentals of
Aerospace Medicine
Factors Affecting Accelerative Forces
 Body area and site
 Intensity
 Rate of onset
 Duration
 Impact direction
Factors Affecting Accelerative Forces
 Body Area and Site
The greater the size of
the body area affected,
the less severe the
effects
 Intensity
The greater the intensity, the more severe the
effects of accelerative forces
Closely related to duration
Factors Affecting Accelerative Forces
 Rate of Onset
The faster the rate of acceleration, the more
severe the effects
Factors Affecting Accelerative Forces
 Duration
The longer the force is
applied, the more
severe the effects
Factors Affecting Accelerative Forces
 Impact Direction
Force in the Gy axis
will not be tolerated
as well as a force
applied to another
axis because of
aircraft structural and
human physiological
limitations
QUESTIONS?
Check on Learning
 If the rate of onset of acceleration increases, the
severity of the effect on the body will…
Increase
 If body area or size increases, the severity of
acceleration on that body will…
Decrease
ELO C
 Action: Identify the effects of low-magnitude
acceleration
 Condition: Given a list
 Standards: IAW TC 3-04.93 and Fundamentals of
Aerospace Medicine
Low Magnitude Accelerations
 G’s that range from 1 – 10 G’s and lasting for
several seconds
Positive (+Gz)
Arterial Blood Pressures @ 1G
77mm Hg
100mm Hg
204mm Hg
Sustained Positive Acceleration (+Gz)
Factors Modifying G Tolerance
 Decremental Factors
 Incremental Factors
Factors Decreasing G Tolerance
 Blood volume decrease
 Blood pressure decrease
Dehydration
Fatigue/illness
Hemorrhage
Acute alcohol abuse
Varicose veins
Factors Increasing G Tolerance
 Asymptomatic hypertension
 Fear & excitement
 Tensing of muscles
 Short stocky build
Negative (-Gz)
Negative (-Gz)
Sustained Negative Acceleration (-Gz)
(+/-) Gx Forces
 Mild transverse accelerations/decelerations during
landing and taking off
(+/-) Gx Tolerance
 +Gx
20 G’s
5 seconds
 -Gx
20 G’s
5 seconds
Gy Forces
 Human body has minimal
tolerance to left or right
accelerations
 Most aircraft do not tolerate
accelerative forces in the
lateral direction
QUESTIONS?
Check on Learning
 What is the definition of low-magnitude
acceleration?
G’s that range from 1 – 10 G’s and lasting for
several seconds
 True or False: Fear/excitement transiently increases
G-tolerance by increasing blood pressure
True
ELO D
 Action: Identify the physiological effects of high-
magnitude acceleration/deceleration
 Condition: Given a list
 Standards: IAW TC 3-04.93 and Fundamentals of
Aerospace Medicine
High Magnitude Accelerations
 G-forces exceeding 10 G’s and lasting less
than a second
Sources
 Aircraft Crashes
 Ejection Seats
 Parachutes
Effects
 Minor discomfort
 Minor injury
 Incapacitating
 Irreversible injury
 Lethal
QUESTIONS?
Check on Learning
 What is the definition of high-magnitude
acceleration?
G-forces exceeding 10 G’s and lasting less than
a second
ELO E
 Action: Recognize aircrew member survivability
criteria
 Condition: Given a list
 Standards: IAW TC 3-04.93 and Fundamentals of
Aerospace Medicine
Crash Survivability Criteria
 Amount of decelerative (crash) force transmitted to
the crewmember
Limits to Whole Body Impact
Crash Survivability Criteria
 Amount of decelerative (crash) force transmitted to
the crewmember
 Occupiable living space
Occupiable Living Space
Occupiable Living Space
Crash Survivability Criteria
 Amount of decelerative (crash) force transmitted to
the crewmember
 Occupiable living space
 Aircraft design features (CREEP)
Aircraft Design Features (C.R.E.E.P.)
 Container
 Restraint System
 Environment
 Energy Absorption
 Post Crash Factors
QUESTIONS?
Check on Learning
 Intensity is closely related to which other factor of
acceleration?
Duration
 What factors increases +Gz tolerance?
Asymptomatic hypertension, fear/excitement,
tensing of muscles, short stocky build
Check On Learning
 What are the aircraft occupant survivability criteria?
Amount of crash forces transmitted, occupiable
living space, aircraft design features
 What acronym describes aircraft design features
that enhance crash survivability?
CREEP
Summary
 Gravitational terms and definitions
 Acceleration factors and effects
 Managing the effects of G-forces
 Low and high magnitude accelerations
 Aircrew member survivability criteria
Conclusion