GRAVITATIONALGRAVITATIONALFORCESFORCES

“G”

The measure of gravity acting on a object.

The normal force which acts on all bodies is equal to 1 G.

During freefall, an object will fall at 32.2 fps2 terminal velocity is reached

ACCELERATIONChange in velocity in either magnitude or direction

The most common accelerative force is gravity

DECELERATION

Any reduction in the velocity of a moving body

INERTIAL FORCE

The resistance to a change in the state of rest or motion

A body at rest tends to stay at rest, a body in motion tends to stay in motion

TRI-AXIAL REFERENCE SYSTEM

FACTORS AFFECTINGACCELERATIVE FORCES

IntensityDurationRate of onsetBody area and siteImpact direction

PHYSIOLOGICAL EFFECTS OF LOW MAGNITUDE

ACCELERATION

+Gz ForcesHead to Foot

FACTORS MODIFYING +GZ

DECREMENTAL FACTORSAny factor that reduces overall efficiency of the

body, especially the circulatory system

Blood volume decrease

- varicose veins

- hemorrhage Blood pressure decrease

- hypotension

- fatigue/illness

- alcohol abuse

INCREMENTAL FACTORS

Any factor that increases overall efficiency of the body, especially the circulatory system

Hypertension Fear & excitement Tensing of muscles Short stocky build L-1 Maneuver

L-1 MANEUVER

Procedure:Remain uprightTense musclesExhale against a closed glottis at 2 to 3 second intervals

Note: Increases G-load tolerance by 4

Disadvantages:Physically Exhausting

-Gz Forces

Foot to Head

+/- Gx FORCES

Mild transverse accelerations / decelerations during landing and taking off

TRANSVERSE “G” TOLERANCE

+Gx 15 G’s 5 seconds

-Gx 12 G’s 5 seconds

+/- Gy FORCES

Human body has minimal tolerance to right or left accelerations

Most aircraft do not apply accelerative forces in the lateral direction

PHYSIOLOGICAL EFFECTS OF HIGH MAGNITUDE ACCELERATION AND

DECELERATION

EFFECTS

Minor discomfort IncapacitatingMinor injuryIrreversible injuryLethal

SOURCES

Aircraft crashes Ejection seats

G’s

(Seconds)

AIRCREWMEMBER SURVIVABILITY DURING THE CRASH SEQUENCE

CRASH SURVIVABILITY CRITERIA

Amount of decelerative forces transmitted to the body

Occupiable living space

Human Tolerance Limits toWhole Body Impact

+9 Gs

+80 Gs

-40 Gs

-9 Gs

+20 Gs

- Gy

-Gx+Gy

+Gx

+Gz

-Gz-16 Gs (0.1 second

duration)

AIRCRAFT DESIGN FEATURES

(CREEP)! Container Restraint system Environment Energy absorption Post crash protection

QUESTIONS?