AVIATION HUMAN FACTORS LECTURE 4 Acceleration and G-Force.

AVIATION HUMAN FACTORSLECTURE 4Acceleration and G-Force

What is Acceleration

ACCELERATION is a change in VELOCITY per unit of TIME.

It is produced when either speed or direction changes. (moving car/aircraft, falling objects)

Types of Acceleration

There are three types of acceleration. These types are Linear, Angular & Radial Acceleration.

Linear Acceleration — change of speed in a straight line. This type of acceleration occurs during take-off, landing, or in level flight.

Angular Acceleration — change in both speed and direction, which happens in spins and climbing turns.

Radial Acceleration —change in direction such as when a pilot performs a sharp turn, dive

Acceleration in Aviation

When we pilot an aircraft, all that we have learned about gravity and have become comfortable with sudden changes.

Flight—in its purest definition—is overcoming gravity to ascend through the air.

Just as when we where learning to walk, a primary goal of every flight should be to avoid painful, gravity-induced incidents with the ground.

These encounters are called aircraft accidents and mishaps, and they can be destructive, even fatal.

Introduction Human beings are adapted to live and survive within the ever-present, accelerative force of gravity.

While on earth, this is a constant, and we live and function with it from the day we are born until the day we die.

As an baby learning to walk, we learn very quickly that misstep will ultimately lead to a painful gravity-induced incident with the ground that we call “a fall.”

What Goes Up Must Come Down

The force of gravity on earth causes a constant acceleration of 9.8m/s²

That means if you drop something it goes faster and faster, increasing its speed downwards by 9.8 m/s in each passing second.

Acceleration is described in units of the force called “G.”

A pilot in a vertical turn may experience forces of acceleration equivalent to many times the force of gravity.

This is especially true in military fighter jets and high-performance, aerobatic aircraft where the acceleration forces may be as high as 9 Gs.

G-force

During positive Gs, the weight of the body is increased in direct proportion to the magnitude of the force.

For example:On the ground, pilot weight =

200poundUnder 3 Gs condition, pilot weight =

600pound

Typical examples of G-Force

Activities G-Force

•Weightless environment to train astronauts

0 g

•Standing on the Earth at sea level 1 g

•High-g roller coasters 3.5–6.3 g•Formula One car, maximum under heavy braking

5 g

•Aerobatic plane or fighter jet, maximum turn.

9-12 g

•Missile 100 g

Types of G-Forces

Three types of G-forces acted on the body include:

Gx – Transverse G (chest to back) Gy - Lateral G (side to side) Gz – Vertical G (head to foot)

**Gz is the most dangerous

Gx-Force

Gx—is described as force acting on the body from chest to back (+Gx) or from back to chest (–Gx) +Gx (positive) is experienced, for

example, during the take-off. This is the force that pushes the pilot back into the seat as the aircraft accelerates.

–Gx (negative) is encountered during landing This force pushes the pilot forward into the shoulder strap.

Naval pilots flying from aircraft carriers feel the extremes of Gx force. During take-off, the

aircraft accelerates to 160 mph in just under two seconds. During landing, the aircraft will

decelerate to a complete stop in just a few feet.

Gy-Force

Gy—occur when pilot expose to acceleration from side to side. from right to left: +Gy, from left to right: -Gy.

Gy is encountered during aileron rolls, rudder roll, vertical roll and uncontrolled aircraft.

Aerobatic pilots routinely encounter this type of G force and can still safely and precisely maneuver their aircraft.

Gz-Force

Gz - is a gravitational force that is applied to the vertical axis of the body.

+Gz (positive) - it is experienced from head to foot. This happens when a pilot pulls into an inside loop. pulls out of a dive or

–Gz (negative) - it is experienced from foot to head, and it is experienced when a pilot pushes over into a dive.

Positive Acceleration (+Gz)

Negative Acceleration (-Gz)

Physiological Effects of High G Forces

Circulatory System & Mental Function is greatly affected by changes in G-Forces. The heart and cardiovascular system unable to

keep blood flowing to the brain and maintain consciousness.

Other effects are motion sickness & disorientation.

Effects of High Gz Forces

In aircraft, g-forces are often +Gz (positive) which force blood towards the feet and away from the head;

This causes problems with the eyes and brain in particular.

As g-force is progressively increased the pilot may experience: GREY-OUT, where the loss of color vision. BLACK-OUT, a loss of vision while consciousness is

maintained. G-LOC a loss of consciousness ("LOC" stands for

"Loss Of Consciousness"). Death, if g-forces are not quickly reduced, death

can occur.

“Grey Out”&“Black out”

A “Grey Out”, occurs when the body experiences a Positive (+Gz) force.

Positive (+Gz) force causes blood flows from the head to the lower parts of the body

“Grey Out” makes a pilot loss of color vision. The eyes are extremely sensitive to low

blood flow & the retina will not be supplied with adequate blood.

At high +Gz force (5Gs), when no blood in brain pilot will experience “Black out” and will completely loss of vision.

“G-Loc”

G-LOC, G-force induced Loss Of Consciousness (LOC),

G-LOC term is to describe a loss of consciousness due to excessive g-forces that causes blood away from the brain.

The condition is most likely to affect pilots of high performance fighter and aerobatic aircraft.

If you GLOC you may ...

have some tingling or numbness have a pleasant dream not realize that you GLOCed! be a little confused or disoriented be aware that you have lost your hearing

Pilotwas subjected to

15 gfor 0.6 second

“Red Out” A “Red Out” occurs when the body

experiences a negative (–Gz) force. –Gz force causes a blood flow from

foot to the head. When “Red Out” happen, pilot vision

turns red. This is probably because capillaries

in the eyes burst under the increased blood pressure.

“Red Out” are potentially dangerous and can cause retinal damage.

Other Effect of G-force

Breathing difficulties Heartbeat abnormalities Motion Sickness Fatigue Arm, Leg & Neck Pain

G-forces treatment

Wearing the anti-G suites: this suite will enhance the blood flow to the brain.

Apply special breathing techniques, called as “anti-G straining maneuver”. This technique is to prevent the blood from flow away from the brain.

G-forces treatment

A well-rested, hydrated, and fit aviator will physically be able to withstand higher G forces can enhance aviator performance in the high-G environment.

When an aviator is well hydrated, there is more circulating volume in the blood stream, and it is easier for the heart to keep the brain with oxygen blood.

Effect of G-force may increase because of….

Fatigue Alcohol Dehydration Illness Medication

Summary

Any aircraft, civilian or military, can expose the pilot, crew, and passenger to forces in excess of 1 G.

During steep turns and unusual attitude recovery, civil aviation pilots can experience high G forces that may take them by surprise unless they are prepared.

Subsequently, all aviators need to understand what makes their body more resistant to the effects of G acceleration.