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Home > Air Travel > Gravity Matters
Gravity Matters
Flying - Air Travel
Saturday, 23 July 2016 13:22
Image - Travel 3Sixty
What makes apples fall from trees? What stops you from floating off into space? Gravity – the force that pulls or attracts a body towards the centre of the Earth.

Tightrope walkers understand this better than anyone else. Precariously navigating a rope that seems as fine as a thread, with just a balancing pole as an aid, these stunt artists are able to entertain us because they understand the simple concept of the centre of gravity (CG).

On a plane, this concept is equally important. A conventional aircraft normally has a forward CG. This is designed in such a way that should anything happen to the engines, the nose of the aircraft would dip downwards, allowing the plane to glide like a paper plane.

Most planes glide well. For example, an Airbus A330 can glide without engines for about 160 kilometres from a height of 40,000 feet! This was proven when, in 2001, an Air Transat (a Canadian airline) plane ran out of fuel due to a ruptured fuel line while flying from Toronto to Lisbon in Portugal. The pilots made history by flying the plane without power and gliding to land safely on an island in the Azores region in the Atlantic Ocean.

SEATS FOR A SMOOTH RIDE

The position of the CG is very important, both in terms of safety, as well as helping the airline in saving costs in order to be competitive. As a passenger, you would not know where the position of the CG is but a rough guide would place its safe range to be somewhere near the wings.

Seats at the front of the plane are usually quieter, which is where the first or premium class seats are usually located. Equally comfortable are seats near to the CG, as they would be least affected by turbulence. A passenger who might be prone to air sickness should choose seats as close to the wings as possible.

Think of the plane as a see-saw, where the centre is placed on a pivot, called the fulcrum. The farther away one is from the fulcrum, the more motion would be experienced where the turbulence tends to be amplified. Similar to a bus ride, the bumpier seats are the ones at the back!

Technically, the CG of the plane moves around the centre of the wings (it also changes as fuel is consumed) and not exactly at the middle of the cabin. So, any seats near or forward of the wings would provide a smoother ride than anywhere else.

WHICH IS BETTER – NOSE HEAVY OR TAIL HEAVY?

Did you know that where you sit is determined by a qualified professional called a loadmaster? This person is responsible for planning the way a plane is loaded. He or she calculates weight and plans cargo and passenger placement to keep the aircraft within the permissible limits of its centre of gravity throughout the flight.

At times, depending on the weight of the cargo carried, as well as the number of passengers on board, a plane may be either nose or tail heavy – but always within the safe range as stipulated by aviation regulations.

To pilots, a forward CG is nose heavy, which means that more force is required to raise the nose when taking off. It has more drag (opposing force) and hence, affects fuel consumption. An aft CG (slight tail heavy) plane gives better cruise speed and better controllability. For any medium-range Airbus A320 or A330 aircraft, the preferred CG position would be slightly at the rear, as the flight controls for the pilot are lighter. Prior to takeoff, the pilot will inspect the load sheet to ensure the CG is within the safe limit and at the optimum position for the particular flight.

During the landing phase, the intention is for the rear wheels to touch the ground first, followed by the nose wheels. Hence, a slight aft CG would be more desirable for the pilot. However, in a less-than-perfect landing in any other aircraft type, especially with a forward CG, the nose wheel may touch the ground earlier than usual with a thump at the front, but that is a fairly infrequent occurrence.

WEIGHT AND BALANCE

As you can imagine, the weight and distribution of passengers on board the plane is a significant factor to ensure a smooth flight. Most airlines use a standard weight of 75 kilograms for an adult passenger but there are several other factors that may alter this figure. For example, on a flight departing from Kuala Lumpur to Melbourne during winter, a loadmaster must take into consideration the weight of the average Caucasian passenger, which is usually heavier than the average Asian passenger, as well as the fact that passengers may be carrying thick winter jackets to prepare for the chilly weather upon landing. AirAsia X usually allocates 80 kilograms per Caucasian passenger. For passengers who have not pre-booked their seats, the loadmaster will distribute seating in the cabin to ensure a well-balanced cabin.

On a light flight, passengers have a tendency to move around, opting for seats other than their assigned ones. This could affect the weight and balance of the aircraft. Sometimes, when the CG is too far forward, the captain will ask the crew to move passengers from the forward cabin to the back of the plane.

NO SEAT-HOPPING!

As a passenger, you can definitely do your part to help your favourite airline maintain a smooth flight by not unnecessarily altering the position of its CG, especially when you move randomly away from your assigned seats or congregate at the back of the plane for a casual group chat!

On smaller or lighter planes, ensure your cabin bags are lightly packed and not overloaded. A small airliner operating out of the Chicago airport once had a close call. The captain reported that he needed more power and a longer distance to lift off the runway than what he had initially expected. Upon investigation, it was found that most of the passengers on board were coin collectors who were travelling to a convention with more than a ton in coins in their carry-on baggage!

Remember that you would also be charged excess baggage fees if you overload your check-in bags. Some airlines also impose a limit on each item; this is to ensure that ramp agents are not overly taxed when lifting heavy loads. Some baggage handlers have even refused to accept very heavy luggage, due to the high rate of back injuries – a hazard of the profession.

So, if you thought that only people struggle with their weight, think again; airliners do too! However, airline weight issues cannot be remedied by the latest diet fad. It takes the cooperation of a lot of people to ensure balanced weight distribution for a smooth flight.

On that note, have a safe flight. And don’t forget to travel light!

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