Chapter 16 - Basic Aerodynamic Theory

What is Bernoulli’s principle in regards to Streamlined Airflow?

In streamlined airflow, dynamic energy + static pressure = a constant

What happens when airflow speed increases according to Bernoulli’s principle in streamlined airflow?

When airflow speed increases, the air gains dynamic energy and it’s static pressure decreases accordingly.

What happens when airflow speed decreases according to Bernoulli’s principle in streamlined airflow?

When airflow speed decreases, the air loses dynamic energy and its static pressure increases accordingly.

When does Bernoulli’s principle become less accurate?

Bernoulli’s principle is generally accurate up to about 250 kt. At higher speeds:

• Compressibility becomes important.

• Shock waves may form.

• More advanced aerodynamic equations are needed.

What is Lift?

Lift is the component of the total aerodynamic force (TR) acting at right angles (perpendicular) to the relative airflow.

What is Drag?

Drag is the component of the total aerodynamic force (TR) acting parallel to the relative airflow and opposing the aircraft’s motion.

How does angle of attack affect total reaction (TR) and centre of pressure (CP)?

As angle of attack increases, TR increases and tilts rearward.
The CP moves forward at first, then at/near the stalling angle moves markedly rearward.
Beyond the stall, TR decreases and tilts further rearward.

Lift =

C_L¹/₂𝜌 V²S

From the lift equation, C_L =

Coefficient of Lift, for a given shape depends on Angle of Attack.

From the lift equation, ¹/₂𝜌 V² =

Dynamic Pressure, which equates to IAS.

From the lift equation, S =

Wing Area (Normally Constant)

Total Drag =

Induced Drag + Parasite Drag

Parasite Drag =

Profile Drag _{(Skin Friction + Form Drag)} + Interference Drag

What is Induced Drag?

Drag associated with the production of Lift. This drag arises from the generation of wingtip and trailing-edge vortices.

What is Parasite Drag?

Drag not associated with the production of Lift.

What is Interference Drag?

This is the drag found at joints of the plane surfaces, where convergence and mixing of airflows occur. E.g: where a wing strut connects to the fuselage.

What is Profile Drag?

Skin Friction + Form Drag