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Some Whats About Weight

One of the first rules you’re taught in boating is never to overload your vessel. It doesn’t take much in way of imagination to understand the reasons as to why. The same rule applies in aviation. The problem for aviators, however, is in being able to picture the consequences of an overloaded aircraft. Add weight to a boat, and its hull slips further into the water. There’s no such evidential tell-tale on an aircraft.

An aircraft’s performance is influenced by its weight. Make it heavier, and all sorts of negative things happen. For starters, with a heavier load, the aircraft’s take-off run will become longer. With too heavy a load, that required take-off run could exceed the length of runway you need to take off.

An aircraft’s angle of climb, and its rate of climb, will be reduced with heavier loads. Its maximum ceiling will be lower and its range will be shorter. A heavier airplane, upon landing, will not only have a higher landing speed, it will also use more runway to slow down. Extra weight can have implications on an aircraft’s airframe: more weight equates to higher load factors on the airframe. Structural stresses can occur in an overloaded aircraft during abrupt manoeuvres that would otherwise be quite safe if the aircraft were lightly loaded.

A pilot flying a heavily loaded airplane should know that the actual load on the wings could be greater than what he or she is feeling through the controls. In rough air, a heavy airplane is steadier than when it’s light. The pilot may, therefore, get the false impression that the air turbulence is not excessive. However, the reality may be very different: the wings may be nearing their breaking point. Paradoxically, the lightly loaded airplane that is getting bounced around by turbulence is giving its pilot the sense that the airplane is being overstressed when, in fact, it’s nowhere near such a point.

As with all things related to an aircraft’s operation, the pilot-in command is responsible for the safe loading of the airplane. The pilot must, therefore, ensure that the total gross weight authorized by the manufacturer is never exceeded. Knowledge of such weight limitations is critical. In the case of general aviation aircraft, it often means that some seats cannot be filled, or that the baggage compartment cannot be filled to capacity, and/or that a full load of fuel cannot be taken.

Every aircraft’s Pilot Operating Handbook will list the gross weight limitation of the entire aircraft. It should also list a separate weight limitation for the aircraft’s baggage compartment. Every pilot should pay close attention to these weight limitations: overloading the baggage area, even if the aircraft is below its gross weight, may move the centre of gravity outside of its allowable limits.

When loading an airplane, its centre of gravity must remain within the measurable area specified by the manufacturer. Therefore, whatever weight is added to the aircraft before a flight, its positioning is critical. Where it goes affects how the aircraft will handle in the air. With weight positioned correctly, the aircraft will be stable and maneuverable while in flight. Positioned incorrectly, then the airplane will become nose heavy (with too much weight positioned forward) or tail heavy (with too much weight positioned rearward).

The flight characteristics of an airplane at gross weight, with a rearward centre of gravity, differ from the same aircraft if lightly loaded. In order to keep lift and weight in equilibrium for a desired flight attitude, more lift must be produced to balance the heavy weight. Thus, a heavily rearward-loaded aircraft has to be flown at a higher angle of attack. Flown in such a way, however, means that the aircraft will stall at a higher airspeed, (i.e. sooner than expected) than it will if it’s carrying less weight.

As the flight of the airplane progresses and fuel is consumed, the weight of the airplane decreases. This changes the distribution of the aircraft’s weight, altering its centre of gravity. Pilots should take this into consideration when flying, so as to be aware of the changes in their aircraft’s handling between what it was at the start of their flight compared to what it is at its end.

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