Aerodynamic Principals Flashcards
What does aerodynamics deal with?
The motion of air and the forces acting on bodies moving relative to the air.
What are the four forces of flight?
Lift
Weight
Thrust
Drag
What is lift?
The force created by the effect of airflow as it passes over and under a wing. The ariplain is typically supported in flight by lift.
What is weight?
The downward pull of gravity.
What is thrust?
The forward force which propells the airplane through the air. It varies with the amount of engine power being used.
What is drag?
It’s a backward or retarding force which limits the speed of the airplane.
What is unaccelerated flight?
The plane is maintaining a constant speed–neither accelerating or decelerating.
What are vectors?
The arrows that show the forces acting on an airplane. Magnitude is indicated by the arrow’s length and direction is indicated by the arrow’s orientation.
What is a resultant?
When two or more forces act on an object at the same time.
In straight and level flight, describe the state of the four forces?
They are in equalibrium. Lift is equal to Weight and Thrust is equal to Drag.
What is the resultant of two oposite forces that are equal in magnitude?
The resultant is zero.
What is the direction of the resultant when Horizontal and Vertical forces are applied?
The resultant is diagonal.
What is Newton’s first law of motion?
A body at rest tends to remain at rest, and a body in motion tends to remain moving at the same speed in the same direction.
What is Newton’s second law of motion?
When a body is acted upon by a constant force, its resulting acceleration is inversely proportional to the mas of the body and is directly porportional to the applied force. (Force= mass X acceleration)
What is Newton’s third law of motion?
For every action there is an equal but opposite reaction.
What is Bernoulli’s principle?
As the velocity of a fluid (such as air) increases, it’s pressure decreases.
What is an airfoil?
Any surface (such as a wing) that provides aerodynamic force when it interacts with a moving stream of air.
How does the shape of a wing cause air to circulate over it?
Air accelerates as it passes over the wing and decellerates as it passes under the wing.
What is upwash?
The deflection of the oncoming airstream upward and over the wing.
What is the leading edge?
The part of the airfoil which meets the airflow first.
What is the trailing edge?
The portion of the airfoil where the airflow over the upper surface rejoins the lower surface airflow.
What is downwash?
The downward deflection of the airstream as it passes over and under the wing and past the trailing edge.
What is the angle of attack?
The angle formed by the wing chord line and relative wind.
What is a chord line?
An imaginary straight line drawn through the airfoil from the leading edge to the trailing edge.
What is relative wind?
The airflow which is parallel to and opposite the flight path of the airplane.
What is a wing’s camber?
The characteristic curve of the airfoil’s upper and lower surfaces. It impacts the difference in velocity between the airflow on the top and on the bottom of the wing.
Is flight path and attitude always the same thing?
No. A plane can be flying straight and level but still be descending due to less power. In this case the flight path would be forward and down and the relative wind would be upward and back.
How does Bernoulli’s theorem relate to wing lift?
The increase in speed on the top of an airfoil produces a pressure drop on the top of the wing and the decreased in airspeed below the wing causes an increase in pressure below the wing. Together these pressures result in lift.
How does Newton’s third law relate to downwash?
The opposite reaction to downwash results in an upward force on the wing.
What is coefficient of Lift?
A way to measure lift as it relates to angle of attack. Maximum lift occurs at a different angle of attack for every airfoil depending on design.
When does a stall occurr?
When the critical angle of attack is exceeded. This is regardless of airspeed, flight attitude, or weight.
How does coefficient of Lift relate to maximum lift and the angle of attack?
As the angle of attack increases, so does the coefficient of lift until you reach maximum lift. Once maximum lift is exceeded, lift rapidly decreases and there is a stall and the moment of the stall is the critical angle of attack.
What is the critical angle of attack?
The angle of pitch that causes and airplane to stall.
What is the definition of a stall?
A separation of airflow from the wing’s upper surface.
How do you recover from a stall?
Decrease the angle of attack.
What are signs that a stall is beginning?
Mushy flight controls
A Stall Warning Horn
Slight buffetting of the airplane
What are the four things to be considered with wing design?
Wing planform
Camber
Aspect Ratio
Total Wing Area
What does Cl stand for?
Coefficient of Lift
What does Clmax stand for?
Maximum Lift
What is the boundary layer?
A thin layer of air next to the surface of an airfoil which shows a reduction in speed due to the air’s viscocity or stickiness.
What are the two ways to describe a boundary layer?
Laminar
Turbulent
What is a laminar airflow?
It begins near the leading edge and consists of smooth layers of air sliding over eachother. It eventually transitions to a thicker turbulent flow with higher velocities.
Which has higher velocity, laminar or turbulent airflow?
Turbulent
Is pressure higher or lower closest to the leading edge?
Pressure is highest closest to the leading edge and decreases with distance.
