How does an airplane fly?
An airplane flies because its wings generate lift by creating pressure differences and by deflecting air downward.
Explain Bernoulli’s Principle
According to Bernoulli’s Principle, as the velocity of airflow increases, its pressure decreases. Air flows faster over the curved upper surface of the wing, creating lower pressure above the wing compared to the higher pressure beneath it. This pressure difference contributes to lift.
What is downwash?
Downwash is the downward deflection of airflow behind the wing. The wing accelerates air downward, and by Newton’s Third Law, the reaction force acts upward on the wing, contributing to lift.
What are the four forces of an aircraft?
Lift: aerodynamic force acting upward
Weight: gravitational force acting downward
Thrust: force that propels the aircraft forward
Drag: aerodynamic resistance opposing motion
What is lift?
Lift is the aerodynamic force perpendicular to the relative airflow that opposes weight. It is produced by pressure differences between the upper and lower wing surfaces and by the downward deflection of air caused by the wing.
What is a Boundary Layer? What is its velocity relative to the freestream air?
The boundary layer is the thin layer of air that adheres to the surface of the wing due to friction.
Within the boundary layer, air velocity increases from zero at the wing surface to nearly 100 percent of freestream velocity at the outer edge.
What is the chord line?
The chord line is an imaginary straight line connecting the leading edge and trailing edge of an airfoil. It is used as a reference when describing airfoil geometry and aerodynamic forces.
What is the definition of Center of Pressure (CP)?
The center of pressure is the point along the chord line where the total aerodynamic force acts.
As angle of attack increases, the center of pressure moves forward; as angle of attack decreases, it moves aft. This movement affects aircraft balance, stability, and structural loading.
What are airfoils and how do they produce lift?
An airfoil is a shape designed to produce lift when moving through air. It is shaped to take advantage of airflow velocity and pressure changes.
Can symmetrical airfoils produce lift?
Yes. Symmetrical airfoils can produce lift when they are flown at a positive angle of attack. Lift is generated by airflow deflection and pressure changes, not solely by wing curvature.
What is downwash and why is it important?
Downwash is the downward flow of air behind the wing caused by lift generation.
It is important because it represents the downward momentum imparted to the air. By Newton’s Third Law, this results in an upward force on the wing.
What are wingtip vortices?
Wingtip vortices are rotating airflows created when high-pressure air from beneath the wing flows around the wingtip toward the low-pressure area above the wing.
They create downwash, increase drag, and reduce effective lift near the wingtip.
How do winglets reduce drag?
Winglets reduce the flow of high-pressure air around the wingtip, weakening wingtip vortices. This reduces induced drag and improves aerodynamic efficiency.
How does aircraft performance change as altitude increases?
As altitude increases, air density decreases.
Lower air density results in:
Reduced engine power
Reduced thrust
Reduced lift
Decreased overall aircraft performance
Why is density altitude important?
Density altitude represents the altitude in the standard atmosphere at which the aircraft performs.
Higher density altitude means thinner air, causing degraded aircraft performance.
What factors increase density altitude?
High altitude, high temperature, low pressure, and high humidity.
Why does humid air reduce aircraft performance?
Water vapor is lighter than dry air, which reduces air density and increases density altitude.
Why is the standard atmosphere used?
It provides a common reference for instrument calibration and aircraft performance comparisons.
