ising the right wing, by
depressing the right aileron, correspondingly lowers the left
wing by raising the left aileron. They exercise lateral control
of a machine.

BLIMP--A non-rigid dirigible balloon. The dirigible holds its
shape due to the fact that its gas is pumped into the envelop to
a pressure greater than the atmosphere. It can move through the
air at forty miles an hour, but high speed will cause it to
buckle in the nose.

BUMP--A rising or falling column of air which may be met while
flying. A machine will be bumped up or bumped down on a bumpy
day. A hot day over flat country, at noon, will generally be
exceedingly bumpy.

CRASH--Any airplane accident. It may be a complete wreck or the
plane may only be slightly injured by a careless landing.
Crashes are often classified by the extent of damage. A class A
crash, for instance, is a complete washout. A class D crash is
an undercarriage and propeller broken.

DOPE--A varnish-like liquid applied to the linen or cotton wing
fabrics. It is made chiefly of acetone, and shrinks the fabric
around the wooden wing structure until it becomes as tight as a
drum. The highly polished surface lessens friction of the plane
through the air.

DRIFT--Head resistance encountered by the machine moving through
the air. This must be overcome by the power of the engine. The
term is also used in aerial navigation in its ordinary sense,
and a machine flying a long stretch over water may drift off the
course, due to winds of which the pilot has no knowledge.

DUD--A condition of being without life or energy. An engine may be
dud; a day may be dud for flying. A shell which will not explode
is a dud. A pilot may be a dud, without skill. It is almost a
synonym for washout.

FLATTEN Out--To come out of a gliding angle into a horizontal
glide a few feet from the ground before making a landing. The
machine loses flying speed on a flat glide, and settles to the
ground.

FLYING SPEED--Speed of a plane fast enough to create lift with its
wing surfaces. This varies with the type of plane from
forty-five miles an hour as a minimum to the faster scout
machines which require seventy miles an hour to carry them
through the air. When a machine loses flying speed, due to
stalling, it is in a dangerous situation, and flying speed must
be r