Whether a Cessna 152 or a Boeing 747, every aircraft must be flown within certain certified limits of weight and balance. This helps to ensure that the aircraft performs adequately, remains controllable, and is not overstressed in flight or on the ground. Weight and balance principles for airline and corporate aircraft are identical to those of smaller general aviation aircraft. Some of the terms, however, are different, and of course the numbers are a lot larger.
The Weight in “Weight and Balance” As with any aircraft, it’s important that turbine-powered airplanes not exceed certain maximum weight values. In light piston aircraft there is often only a single maximum gross weight. Larger airplanes, however, are certified with several weight limits to allow for the large amounts of fuel carried and consumed during the course of a flight. Maximum ramp weight is the most a given aircraft may weigh while parked, taxiing, or running up before takeoff. This value is slightly greater than takeoff weight, allowing for the weight of fuel burned during taxi and run-up. Maximum zero-fuel weight (MZFW) is maximum allowable aircraft weight excluding fuel. This is a structural limitation; fuel in the tanks favorably redistributes aircraft structural loads (Figure 11.1). Maximum takeoff weight (MTOW) is the most an aircraft is certified to weigh for takeoff. MTOW, itself, is a structural limitation. However, there are usually performance-limited takeoff weights for a given aircraft. These further restrict takeoff weight under certain conditions of density altitude (airport elevation and temperature), climb requirements, runway length and conditions, or aircraft systems in use (such as bleed-powered engine anti-ice).
CHAPTER 11
Weight and Balance
Maximum landing weight (MLW) is an aircraft’s greatest allowable weight for landing. There is much more stress on an aircraft’s structure during landing than on takeoff. Since most turbine aircraft fly for long distances, they burn off lots of fuel enroute. In order to get maximum utility from such aircraft, they are often certified for takeoff at greater weight than is allowed for landing. This greatly extends aircraft range by allowing takeoff with more fuel, but there’s also a downside. The problem occurs when an aircraft lifts off at MTOW and then must return unexpectedly for landing. To address this problem maximum cabin load
With a big cabin load and not much fuel the wings can be overstressed.
maximum cabin load
fuel load
fuel load
MZFW limits ensure that cabin loads do not overstress the wings in bending. Fuel may be added beyond MZFW, however, because it loads the wings outboard and thereby actually reduces wing bending moments.
FIGURE 11.1 | Maximum zero fuel weight (MZFW).
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