Unit 2 BASICS OF FLIGHT MECHANICS Physical properties and structure of the atmosphere, temperature, pressure and altitude relationships Newton’s law of motions applied to aeronautics – Aircraft Axis system- Motions of Aircraft with respect to the axis system – evolution of lift, drag and moment. Nomenclature of aerofoil, classification of Airfoils-NACA aerofoil, Mach number, maneuvers.

Physical properties and structure of the atmosphere, temperature, pressure and altitude relationships

Atmospheric Circulation Moving things around on present day Earth

Wind is a moving air or flow of gases on a large scale WINDS Wind is a moving air or flow of gases on a large scale

Definition of wind The horizontal movement of air along the earth surface is called wind. The vertical movement of air is known as air current. Wind and air current together comprise a system of circulation in the atmosphere.

Causes of winds Pressure gradient-pressure force Rotation of the earth-coriolis force Friction of the earth-velocity of the wind -

Types of winds Permanent or planetary winds or prevailing wind Trade/Westerlies/polar wind Periodic winds or local wind Sea/land/moonson

Atmospheric circulation Powered by sunlight – uneven solar heating About 51% of incoming energy is absorbed by Earth’s land and water Energy absorption varies depending on the angle of approach, the sea state and the presence of ice or other covering

Atmosphere The gaseous envelopes surrounding the earths surface. Pressure and temperature play an extremely important role in the performances of airplanes. The critical elements is air density which decreases as pressure falls and temperature rises.

The aerodynamic qualities of the airframe depends upon air density . If the air density decreases, then aerodynamic qualities decreases. High temperature and low pressure cause a decreases in air density. The atmosphere consists of mixture of gases that surround the earth and held to it by the force of gravity.

For this reason, the atmosphere is denser near the earths surfaces and the air density decreases as height is gained. Since both engine and aerodynamic performance depends on air density they also decrease with altitude.

The mixture of gases that we call air consists mainly on nitrogen and oxygen and water vapor.

Composition of the atmosphere 78% nitrogen and 21% oxygen Other elements make up < 1% Air is never completely dry and water can be up to 4% of its volume.

Atmospheric Structure

Troposphere Close to earth surfaces Up to 10 km Turbulent condition of air Temperature decreases

Stratosphere It extends from troposphere to about 50km Highest velocity but no gusty flow Temperature remains constant up to about 25km and then temp Increases

Mesosphere It extends from Stratosphere to about 80km Temperature decrease Pressure and density of air very low

Mt. Everest (8,850 m)

Structure of the Atmosphere Troposphere is densest and is where our weather occurs Substances in the stratosphere persist for long periods because there are few removal processes In troposphere, temperature decreases with altitude In stratosphere, temperature increases with altitude due to interactions with particles and radiation from the sun The ozone layer is within the stratosphere

PHYSICAL PROPERTIES- Pressure If the aircraft sense the actual outside air pressure which corresponds to a certain standard altitude, then that altitude is called pressure altitude.

PHYSICAL PROPERTIES- Density If the aircraft sense the actual outside air density, which corresponds to a certain standard altitude, then that altitude is called density altitude.

PHYSICAL PROPERTIES- Temperature If the aircraft sense the actual outside air temperature, which corresponds to a certain standard altitude, then that altitude is called temperature altitude.