## Introduction

By General

This guide is designed to help a student helicopter pilot prepare for the oral portion of their check ride. The guide is set up on the following manner for each section: question, brief statement, expanded explanation, and reference(s).

## What are the four aerodynamic forces?

By Aerodynamics

The four aerodynamic forces are thrust, drag, lift, and weight.

## How is lift created?

By Aerodynamics

Lift is created through the combination of Bernoulli’s principle and Newton’s 3rd law.

## What is the lift formula or equation?

By Aerodynamics

The lift formula or equation is CL ½ p V2 S.

## What is induced flow?

By Aerodynamics

Induced flow is the downward vertical movement of air through the rotor system due to the production of lift, often referred to as downwash.

## What is relative wind?

By Aerodynamics

Relative wind is the angle of airflow as it impacts an airfoil.

## What is rotational relative wind?

By Aerodynamics

Rotational relative wind is the relative wind produced by the rotation of the rotor blades.

## What is resultant relative wind?

By Aerodynamics

Resultant relative wind is angle airflow at the rotor blades considering rotational relative wind and induced flow.

## What is dissymmetry of lift?

By Aerodynamics

Dissymmetry of lift is the unequal rotor thrust, or lift, produced by the rotor disc due to forward flight or wind.

## What is flapping?

By Aerodynamics

Flapping is the vertical movement of a blade up or down to increase or decrease lift in order to compensate for dissymmetry of lift.