1.2: Aerodynamic Forces

Question 1

The four aerodynamic forces acting on an airplane during flight are? ***

Answer 1

1. Lift, the upward-acting force
2. Weight, the downward-acting force
3. Thrust, the forward-acting force
4. Drag, the rearward-acting force

Question 2

When the airplane is in steady, unaccelerated flight, the basic aerodynamic forces are in equilibrium when: ***

Answer 2

Lift = Weight
Thrust = Drag

Question 3

What is lift?

Answer 3

Lift is the force created by an airfoil when it is moved through the air.

Question 4

What are the principle airfoils of an airplane?

Answer 4

1. Wings
2. Propeller
3. Horizontal tail surfaces.

Question 5

What is Bernoulli’s Principle?

Answer 5

“the internal pressure of a fluid (liquid or gas) decreases at points where the speed of the fluid increases.”

In other words, high-speed flow is associated with low pressure, and low-speed flow is associated with high pressure.

Question 6

How does Bernoulli’s principle applies to an airplane wing? ***

Answer 6

an airplane wing because the wing is designed and constructed with a curve or camber. When air flows along the upper wing surface, it accelerates, causing a lower pressure area above the wing than below the wing. This generates a lift force over the upper curved surface of the wing.

Question 7

What is weight?

Answer 7

Weight is the force caused by gravity accelerating the mass of the airplane toward the Earth and is expressed in pounds.

Question 8

What is the airplane’s center of gravity (CG)?

Answer 8

The airplane’s center of gravity (CG) is the imaginary but determinable point on the airplane at which all weight is considered to be concentrated. It is the point of balance.

Question 9

Where is the CG located on an airplane?

Answer 9

The CG is located along the longitudinal centerline of the airplane (the imaginary line from the nose to the tail) and somewhere near, but forward of, the center of lift of the wing.

Question 10

What impacts the CG of an airplane?

Answer 10

The location of the CG depends on the location and weight of the load (including cargo, fuel, passengers, etc.) placed in the airplane.

Question 11

What is thrust?

Answer 11

Thrust results from the propeller, acting as an airfoil, producing the forward force that drives the airplane through the air.

Question 12

What is drag?

Answer 12

Drag is the rearward-acting force resulting from the forward movement of the airplane through the air.

Question 13

Total drag may be classified into what types?

Answer 13

1. Induced drag

2. Parasite drag

Question 14

What is induced drag?

Answer 14

Induced drag is the undesirable but unavoidable by-product of lift.

Question 15

What is parasite drag?

Answer 15

Parasite drag is the resistance of the air as the airplane passes through it.

Question 16

The four forces that act on an airplane are said to be ________ when in unaccelerated, level flight.

Answer 16

in equilibrium

Question 17

The four forces acting on an airplane in flight are

A. lift, weight, thrust, and drag.
B. lift, weight, gravity, and thrust.
C. lift, gravity, power, and friction.

Answer 17

lift, weight, thrust, and drag.

Question 18

When are the four forces that act on an airplane in equilibrium?

A. During unaccelerated level flight.
B. When the aircraft is accelerating.
C. When the aircraft is at rest on the ground.

Answer 18

During unaccelerated level flight.

Question 19

What is the relationship of lift, drag, thrust, and weight when the airplane is in straight-and-level flight?
A. Lift equals weight and thrust equals drag.
B. Lift, drag, and weight equal thrust.
C. Lift and weight equal thrust and drag.

Answer 19

Lift equals weight and thrust equal drag.

Question 20

Which statement relates to Bernoulli’s principle?

A. For every action, there is an equal and opposite reaction.
B. An additional upward force is generated as the lower surface of the wing deflects air downward.
C. Air traveling faster over the curved upper surface of an airfoil causes lower pressure on the top surface.

Answer 20

Air traveling faster over the curved upper surface of an airfoil causes lower pressure on the top surface.