What is usually at the level of L4?

Semi-monocoque fuselages get their principal strength from the

The pressure produced by a column of fluid is determined by the density of the fluid and its

The vertical flight of a helicopter is controlled by

Archimedes’ principle states that

The main supporting members of a wing are

The elevators of a conventional airplane are used to provide rotation about the

If the pressure of a dry gas is reduced by one third, the volume will

An airplane wing is designed to produce lift resulting from relatively

An observer sees the flash of a gun three seconds before he hears the sound of the gun firing.  Approximately how far is the observer from the gun?   (speed of sound = 1100 ft/sec)