Wing loading is defined as the total
weight, including the aircraft itself, that an
aircraft is carrying divided by the
area of
lift producing
surface (
wing(s)).
Aircraft are usually
designed for
optimum characteristics within a certain wing loading range. When operated at or near
maximum wing loading an aircraft may behave
sluggishly, require excessive
fuel, and have a high
descent rate(= reduced
climb rate).
Flex wing aircraft such as
hang gliders and
paragliders can be difficult to control when flown at less than
minimum wing loading, since the wing or
airframe needs a certain
load to
flex into the proper shape. Certain
cardinal speeds of gliding aircraft depend on wing loading, such as
stall speed (
Vs),
best glide, etc. Pilots can carry
ballast to set the wing loading for desired characteristics.
Water is commonly used as ballast because it may be safely
discarded during
flight to adjust for varying conditions.
Sailplanes often have
tanks for water ballast within their wings, where a powered
plane would carry
fuel. Hang glider pilots carry ballast in their
harnesses, so water is of less use;
lead, either
shot or
scuba diving weights (or
rocks!) are often used. Hopefully, these are not dropped
on purpose.