Tuesday, 25 May 2010

g-force and its effects!

Fighter pilots experience a certain "g-force" while maneuvering the aircraft at large speeds. The pilot could either be involved in aerobatics or trying to make quick twists and turns in a dogfight. While he is on to this, he is being subjected to a g-force.

To start, let us define what a g-force is.
A g-force is the force that acts on a body due to accelerations. It is measured in terms of g(or relative to g, if you like it), which is the acceleration due to gravity on Earth, normally assigned a value of 9.8 meters per second per second, although it varies very slightly according to location and altitude. To put it simply, it is the force that you experience when you accelerate. Now isn't this a common experience? When you are in an elevator, you tend to be pushed down toward the elevator floor at the instant the elevator starts its ascent. On the other hand, you feel lifted up the elevator floor slightly when the elevator just starts its descent. In this case, you are experiencing a g-force.

You have also experienced g-force in other situations. Like, for instance, when you sneeze, you experience a 3g acceleration at the time of sneezing. A typical cough lets you experience a 3.5g acceleration. Roller coaster rides are designed to give you the thrill of going through accelerations any where up to 3g. Remember, you pay for the accelerations at an amusement park. Our body is an accelerometer. We react to accelerations. This is the reason you find the rides in an amusement park thrilling. If the roller coaster ride was on a straight line track that uniformly traveled at 40 km per hour, trust me, you would not feel a thing.

Now that its established, accompanied by personal experiences, that our body reacts to accelerations, its imperative that we study the effects of g-force. Humans can tolerate even 100g's provided it happens in a split second. The moment the human body is made to go through acceleration of even 10g for a period of time, it can prove to be fatal.

Now, let's get down to the effects :
> The force pushes down on the lungs, which leads to emptying of the air. This gives you a sensation of lack of air and you experience fatigue. The person finds it difficult to breathe.
> The force pulls the blood down toward the feet. This resists the pumping action of the heart which means, the blood doesn't make it to the brain. Due to the diminished flow of the blood to the eyes, your vision turns gray. On continual experience to g-forces, you will have tunnel vision after which, things will lose color, turn white and then, a complete blackout. You lose consciousness at this point; and its called GLOC - Gravity Induced Loss Of Consciousness.

The most suitable remedy is the G-suit. As aforementioned, the blood is pulled down toward the feet, resisting the pumping action of the heart; so the blood doesn't flow to the brain. Keeping this vital element in mind, the principle of the G-suit is designed in order to pump the blood back up the body to avoid the various effects such as greyout, tunnel vision, blackout, GLOC. Modern g-suits use compressed air to pump the blood back up the body.

Until now, we spoke about the effects of positive g's, which is the direction assigned to the g-force acting vertically downward along the body. The above mentioned effects are caused due to positive g's. Imperatively, negative g's leads to a force that acts vertically upward along the body. It would be relatively easy to take a guess at what the effect of negative g is. Suppose you are flying straight, parallel to the ground. You want to make a steep dive by pushing the nose of the plane downward. The primary experience you will have is that your weights lessens. You feel lighter. Just the opposite is true for positive g's. You gain weight while experiencing positive g's. The harder you push the nose down, the more weightless you feel. As I told you about the guesswork being relatively simple, negative g's result in all of the blood being pumped straight up to the head. As the negative g's increase in magnitude, the blood vessels in your eyes will rupture. This is known as redout.

There are someways you could avoid a redout. It is clearly given in this particular link - http://www.voodoo-world.cz/falcon/agf.html . I will take a few lines from it and paste it here, but for complete information, you could go through the link.

There is a simple way to avoid negative Gs that also gives you much better maneuverability. Instead of pushing forward on the stick to dive /which creates negative Gs/ , roll your aircraft 180 deg. And pull back on the stick. If you roll so that your cockpit is facing toward the ground and then pull back on the stick, you will still be diving toward the ground but will be experiencing positive Gs instead. Your tolerance is much greater to positive Gs.

That's all folks!
Happy flying!

References :

No comments: