United States Army School of Aviation Medicine
Fort Rucker, Alabama
JULY 1997
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STUDENT HANDOUT
TITLE: GRAVITATIONAL FORCES
FILE NUMBER: 2/5/9/9E/UEA/UEC/UEE/34/68/4504-1
PROPONENT FOR THIS LESSON PLAN IS:
United States Army School of Aviation Medicine
ATTN: MCCS-HAF
Fort Rucker, Alabama 36362-5000
FOREIGN DISCLOSURE RESTRICTIONS: The materials contained in this lesson plan have been
reviewed by the instructor/training developer and determined to be public domain
materials. This product is releasable to military students from all requesting foreign
countries without restrictions.
GRAVITATIONAL FORCES
TERMINAL LEARNING OBJECTIVE (TLO):
ACTION: Verbalize knowledge of acceleration and crew member survivability criteria.
CONDITION: While performing as an aircrew member.
STANDARD: In Accordance With(IAW) FM 1-301 and FM 8-2.
A. ENABLING LEARNING OBJECTIVE (ELO) #1:
ACTION: Match gravitational force terms with their appropriate definition.
CONDITION: Given a list of terms and definitions.
STANDARD: IAW FM 1-301.
a. "G"- Measure of the magnitude of an accelerative force with respect to gravity.
(1) Equal to 32.2 feet per second squared.
(2) Until terminal velocity is reached.
b. Acceleration- a change of velocity in magnitude as well as a change in direction with respect to time.
c. Deceleration- (negative acceleration) a reduction in the velocity of a moving body with respect to time.
d. Inertia- the resistance to a change in the state of rest or motion.
(1) A body in motion tends to stay in motion.
(2) A body at rest tends to stay at rest.
e. F=MA- a net force(F) on a mass(M) will produce an acceleration(A) in the same direction as the force.
f. Tri-axial reference system- identifies the direction in which the body receives accelerative forces.
B. ENABLING LEARNING OBJECTIVE (ELO) #2:
ACTION: Match the factors of acceleration with their appropriate effects.
CONDITION: Given a list of factors and effects.
STANDARD: IAW FM 1-301.
a. Factors of acceleration.
(1) Intensity-- the greater the intensity, the more severe the effects of accelerative forces. (Intensity, however, is closely related to duration)
(2) Duration-- the longer the force is applied, the more severe the effects.
(a) Exposure to +15 Gz for 2 seconds will render unconsciousness.
(b) There will be 2 to 3 minutes of cognitive difficulties after normal blood pressure is returned.
(3) Rate of onset-- the faster the rate of acceleration ,the more severe the effects.
(4) Body area and site-- the greater the size of the body area affected, the less severe the effects.
(5) Impact direction--a 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.
ENABLING LEARNING OBJECTIVE (ELO) #3:
ACTION: Identify the effects of low magnitude acceleration.
CONDITION: Given a list of physiologic effects.
STANDARD: IAW FM 1-301.
a. Physiological effects of low magnitude accelerations are described as "G"s that range from 1 to 10 "G"s lasting for several seconds.
(1) +Gz--during a +Gz maneuver, body weight increases in direct proportion to the force (200 pounds will weight 600 pounds during a 3G maneuver).
(2) Circulatory effects
(a) Blood pooling in the lower extremities.
(b) As the force exceeds 2G’s, blood flow to the eye decreases causing a gradual loss of peripheral vision(grayout).
(3) +Gz tolerance limits.
(a) 1.0-2.5 Gz: Blood pooling.
(b) 2.5-4.0 Gz: Grayout.
(c) 4.0-4.5 Gz: Blackout.
(d) 4.5 and above: Unconsciousness.
b. Factors that modify +Gz tolerance.
(1) Decremental factors are any factor that reduces the overall efficiency of the body, especially the circulatory system.
(a) Blood volume decrease
(b) Varicose veins
(c) Hemorrhage, both internal and external
(2) Blood pressure decrease
(a) Due to blood loss or dehydration.
(b) Illness/not aeromedically fit.
(c) Acute alcohol abuse.
(3) Incremental factors are any factor that enhances the ability of the body to withstand G-forces.
(a) Hypertension
(b) Fear/excitement
(c) Tensing of muscles.
(d) Short stocky build.
(e) L-1 maneuver.
(4) -Gz circulatory effects
(a) Result in inadequate circulation to sustain consciousness. Blood pooling and stagnation occur in the head and neck.
(b) A rise in intracrainial pressure is counterbalanced by a rise in intracrainial cerebral spinal fluid pressure.
(5) -Gz tolerance limits
(a) 0.0 to -1.0 Blood pooling.
(b) -1.0 to -2.5 Vision affected.
(c) -2.5 to -3.0 Redout.
(d) Over -3.0 Incapacitation.
(6) Postive and negative Gx effects
(a) Air crew members experience mild transverse accelerations and deceleration’s when taking off and landing.
(b) Individuals are more tolerant of forces on the Gx axis because transverse G’s interfere very little with blood flow.
(c) Tolerance limits.
1. Greater than +7 or -7 G’s breathing may become more difficult.
2. Some individuals have withstood up to +20 and -20 G’s for several seconds without any severe effects.
(7) Positive and negative Gy effects.
(a) Aircraft are structurally designed to handle aerodynamic loads which are transmitted to aircraft occupants primarily in the Gx or Gz axis.
(b) This creates a structural design limitation which makes lateral accelerations (Gy axis) the most lethal to aircraft occupants.
D. ENABLING LEARNING OBJECTIVE (ELO) #4:
ACTION: Identify the physiological effects of high magnitude acceleration/deceleration.
CONDITION: Given a list of effects.
STANDARD: IAW FM 1-301.
a. High magnitude accelerations/deceleration’s are described as G-forces exceeding 10 G’s and lasting less than a second.
(1) Physiological effects.
(a) Minor discomfort
(b) Minor injury.
(c) Incapacitation.
(d) Irreversible injury.
(e) Lethal injury.
(2) The primary source of high magnitude accelerations and deceleration’s are aircraft crashes.
E. ENABLING LEARNING OBJECTIVE (ELO) #5:
ACTION: Select aircrew member survivability criteria.
CONDITION: Given a list of items.
STANDARD: IAW FM 1-301.
NOTE: Occupant survivability during the accident sequence is contingent on the following criteria:
(1) Amount of crash forces transmitted.
(2) Occupiable living space.
(3) Aircraft design features.
F. ENABLING LEARNING OBJECTIVE (ELO) #6:
ACTION: Select aircraft design features that enhance crash survivability.
CONDITION: Given a list of items.
STANDARD: IAW FM 1-301.
a. Aircraft design features that enhance crash survivability.
(1) Container.
(a) Acts as an effective protective shell.
(b) Crushable material to attenuate crash forces.
(2) Restraint system.
(a) Should be comfortable and snug.
(b) Should adequately restrain major body parts.
(3) Environment, make the cockpit less dangerous.
(4) Energy absorption.
(a) Landing gear
(b) Aircraft undercarriage.
b. Post crash factors.
(1) Fire
(2) Evacuation