Four Forces of Flight

Throughout learning about aviation there is a lot of talk about forces. For an aircraft, a force is considered anything that can influence a change in speed or direction of an object. Physics heavily involves studying the sciences behind force. When dealing with aviation, it is important to look at the four forces that effect how an aircraft flies.

Four Forces of an Aircraft

Drag - A force such as drag is created by air resisting (or a force opposite of where the direction is intended to flow). Imagine running down a track with a small parachute attached to your back. You would notice that it is more difficult to run with the parachute pulling you back versus running with no parachute. The parachute in this example is what is considered drag. As a plane is flying in the air there is drag force (or resistance) that must be overcame in order to achieve required thrust to achieve lift. An aircraft's drag can be affected by an aircraft's shape, texture, velocity, as well as other factors.

Thrust - This is the force that provides movement of an aircraft. Thrust is produced by propulsion systems or engines. When enough thrust is applied, drag is overcome, and lift is closer to being achieved. Similar to the example of running down the track, using your legs to run faster and faster can be thought of as a form of thrust.

Weight - A combination of factors affect the weight of an aircraft and can include cargo, passengers, fuel, parts of the aircraft, material of the aircraft, and such items. Weight is always directed towards the center of Earth due to the planet's gravitational pull. Every object on Earth has weight applied to it, including you. As you are standing still the Earth's gravity pulls you towards the planet's center - in other words this is gravitational acceleration. Take your mass and multiply it by the rate of acceleration (gravitational acceleration = 9.8 m/s2) and you can calculate your weight. This can be done for any object within reason and uses the formula F=m*a. Just like yourself, an aircraft's weight is focused around its center of gravity. In order to achieve lift, an aircraft must overcome its weight.

Lift - When an aircraft takes off and is flying, it is said to have achieved lift. Lift results when an aircraft overcomes its weight. An aircraft's lift depends on its aerodynamics (or movement of air along an object) which takes into account factors including the size and design of the aircraft. When designed and built correctly, an aircraft uses an airfoil design in the wings to allow air to flow around them and for lift to occur.

Principal Axes of an Aircraft

Controlling the four forces determine how a plane flies and they also play a part in how the aircraft is controlled. As an aircraft flies there are three principal axes that a plane moves around and is controlled along.

The Three Axes

The longitudinal axis runs lengthwise down the aircraft. It is the axis where the roll from left to right of the plane occurs.

The lateral axis of an aircraft goes from wingtip to wingtip and is where the pitch occurs. Think of being on a seesaw and moving up and down. That up and down movement is your pitch and it occurs along a lateral axis which is at the fulcrum (center triangle of a seesaw).

Along the vertical axis yaw occurs. Yaw is the side to side movement of an aircraft's nose. You can observe yaw movement along a vertical axis if you were to put your hand flat on a table top and rotate it from side to side with your palm staying on the table.

With movement along the principle axes, an aircraft can control its direction while flying. There are control surfaces on the wing, horizontal stabilizer and vertical stabilizer.

Roll Pitch Yaw

Parts of an Airplane

As we have learned, there are different axes that an aircraft is controlled along. An aircraft is controlled along these axes by its various parts.

Parts of an Aircraft

Ailerons - These are located towards the end of an aircraft's wings. They control the roll of an aircraft along its longitudinal axis. When turning and controlling the aircraft in rough weather, the ailerons play an important part in flying an aircraft in specific directions.

Flaps - In order for aircrafts to produce lift a pilot uses flaps to change the amount of drag as well as the angle of attack. Using the flaps can change the way air flows around a wing and can help produce required lift to initially get an aircraft off the ground. Once in the air, a pilot can change the angle of the flaps to reduce drag and produce more efficient flight.

Wing - One of the most important and most noticeable parts of an aircraft is its wings. Most aircrafts cannot fly, or produce lift, without wings. The wings provide an airfoil which allows air to flow around the wing producing lift.

Vertical Stabilizer - Located on the tail of an aircraft is the vertical stabilizer which controls the nose of the plane and prevents it from losing control of side-to-side movement along the yaw axis. On the vertical stabilizer is the rudder, which is typically controlled by pedals at the pilot's feet. The rudder controls movement along the yaw axis. The rudder is used by the pilot to control the side-to-side movement of the aircraft nose. It is important to remember the rudder is used to control the steadiness of flight but not to control the turning of a plane. That is done with the ailerons.

Horizontal Stabilizer - Similar to the vertical stabilizer, the horizontal stabilizer is typically located on the tail of an aircraft and controls the pitch along the lateral axis. On the horizontal stabilizer are elevators. The elevators are moving parts that determine the pitch of an aircraft as well as influence the angle of attack, and can be controlled using the yoke (The controller of an aircraft similar to the steering wheel of a vehicle) by pushing it in or out.

Engine - Thrust is produced from the engines of an aircraft. When thrust is applied the aircraft, it can move about on the ground as well as in the air. In order for lift to be achieved, a certain amount of thrust if required for different aircrafts so that airflow can occur around the airfoil of the wings.

EngineTypes - Over time aircrafts have been given a variety of engines that provide the required thrust.

Propeller Engine - Since the first controlled, heavier-than-air flight, numerous aircrafts have used an internal combustion engine (similar to engines used in cars) to its drive pistons which rotate a propeller. The propeller is made up of blades held together by a hub. Each blade is similar to a wing in that they have an airfoil design. As the blades rotate they pull in air, towards and around the aircraft, producing thrust.

Jet Engine / Turbofan- Developed during WWII, jet engines revolutionized aviation. A jet engine is an internal combustion engine that uses a turbine to compress air which it then mixes with fuel. Once the air and fuel mixture is compressed inside the engine it is ignited then exhausted. This exhaust is very fast and can provide a large amount of thrust. The turbofan is a form of jet engine that is commonly seen today on commercial airlines and even fighter jets.

Turboprop - A turboprop engine is a combination of propeller and jet engine technologies. The jet part of a turboprop uses a turbine to draw in and compress air which is then mixed with fuel and ignites. However, in this case most of the energy from the exhaust is used to power the turbine which is connected to a propeller. The thrust of the engine is provided by the rotation of the propeller.

Spoilers - Lift is vital for an aircraft to fly, but not as much of it is required when descending and landing. Spoilers are located within the wings and are used to reduce the amount of lift an aircraft has. An aircraft will apply the spoilers when descending and coming in for the landing so that it can produce an angle to safely touch down without producing lift that could prevent a safe landing. Not only does a spoiler reduce the amount of lift but also reduces the speed of an aircraft so that when landing the aircraft isn't going too fast.

Gears - In order for an aircraft to move along the ground as well as safely land, an aircraft requires gears. Gears consist of wheels, shocks, and brakes. Very similar to a car's wheels, the gears support the weight and movement of an aircraft when it isn't flying. Once take-off occurs, many planes can tuck their gear inside of the fuselage, which reduces drag and increases aerodynamics of an aircraft.

Fuselage - The fuselage of an aircraft is the main body. It holds the cargo and passengers and holds all of the parts (wings, cockpit, stabilizers, gears, etc...) of an aircraft together.

Cockpit - This is the area at the front of an airplane where pilots sit and control all the parts of an aircraft. The cockpit is full of instruments and devices that allow pilots to precisely control an aircraft when on the ground and while in flight. Pilots train very hard and for a long period of time to learn about all the different parts and instruments of not only the cockpit but also the entire aircraft.

 

Weather Elements and Flight

Understanding the parts of an airplane and how they work together to produce flight is very important, but they are not the only things to take into consideration. Weather is very vital to how an aircraft flies. It must must be monitored closely to prevent accidents. Monitoring weather includes watching the different cloud types and air masses which can provide evidence of weather hazards including thunderstorms, snow, fog, and other inclement weather conditions. Another factor to remember is that flying conditions can be different not only due to weather but also due to the different levels of atmosphere. Aerodynamic designs are altered based upon the layer of atmosphere an aircraft flies through.  The Rockets 2.0 STEM Application provides a full review of weather and its impact on flight.