Principles of Flight

Preparatory Assignment: Read AFH ch.3-4, PHAK

Introduce basic flying maneuvers: Straight-and-level flight, Level turns, Straight climbs & Climbing turns, Straight Descents & Descending turns.

Preflight Briefing: Review the study assignment and verify an adequate understanding in the areas to be covered. If there is a lack of basic understanding, reschedule the flight and review the knowledge deficiencies. Review the lesson Completion Standards and Special Emphasis Areas.

Four Forces of Flight

The four forces acting on an aircraft in straight-and-level, unaccelerated flight are thrust, drag, lift, and weight. They are defined as follows:

  • Thrust—the forward force produced by the powerplant, propeller, or rotor. It opposes or overcomes the force of drag. As a general rule, it acts parallel to the longitudinal axis.
  • Drag—a rearward, retarding force caused by disruption of airflow by the wing, rotor, fuselage, and other protruding objects. Drag opposes thrust, and acts rearward parallel to the relative wind.
  • Weight—the combined load of the aircraft itself, the crew, the fuel, and the cargo or baggage. Weight pulls the aircraft downward because of the force of gravity. It opposes lift, and acts vertically downward through the aircraft’s center of gravity (CG).
  • Lift—opposes the downward force of weight, is produced by the dynamic effect of the air acting on the airfoil, and acts perpendicular to the flightpath through the center of lift.

In steady, unaccelerated flight, the lifting force is equal to the weight, and the thrust is equal to drag. There can be no unbalanced forces in steady, straight flight based upon Newton’s Third Law, which states that for every action or force there is an equal, but opposite, reaction or force. This is true whether flying level or when climbing or descending at a constant rate. In other words, all upward forces will equal all downward forces, and all forward forces will equal rearward forces when the aircraft is not accelerating.

PHAK: Aerodynamics of Flight

Angle of Attack, Wing Stalls, and Load Factor


The angle of attack is the angle between the chord line of an airfoil and the relative wind. The relative wind is the air coming against the airplane when it is moving. Load factor is the force exerted against an airplane. More specifically, load factor includes the centrifugal force added to weight in a turn. A stall is a loss of lift over the wings of an airplane, brought about by exceeding the critical angle of attack.

Load Factor and Bank Angle

PictureWhy does the load factor increase with greater bank angle? Load factor changes, depending on the forces acting on the airplane. For example, to get an airplane to turn, the pilot changes the position of the ailerons, which makes the airplane bank. When this bank angle is changed, the lift vector of the wings redirects from up, to sideways and up, in the direction of the turn: this is called the horizontal component of lift. The steeper the bank angle (in level coordinated flight), the more horizontal component, and thus the greater force pulling the airplane sideways.




Basically it’s because of centrifugal force, which is based on Newton’s first law of motion, (inertia): an object in ‘straight-line’ motion remains in motion in a straight line, unless acted on by another force. With more bank angle, there is more force acting ‘sideways’ on the airplane. Not only is the airplane holding the weight of the airplane (staying at the same altitude), but the bank is pulling the weight sideways.


Load Factor and Weight

PictureWhy does the load factor increase with weight?

Shopping cart Inertia Analogy
Imagine an shopping cart. Someone pushes it down the grocery store isle. At the end of the isle, you want to push the moving cart to get it to change direction. Easy, right? Now fill the cart full of groceries and do the same experiment. It will take more pushing force to get the cart to turn because you are changing not only the direction of the cart, but all the groceries inside the cart. ‘Force equals mass times acceleration’ is the ‘inertia formula’: with more mass, more force is required to change the movement of the mass.

PictureStall Speed
Why does stall speed increase as load factor and weight increases?

Why does stall speed increase as load factor increases?



Flight: Technical subject areas:

Principles of flight

Airplane flight controls

Preflight preparation

Preflight procedures

Takeoffs and landings



Lead off climbs/descents by 10% of your VSI—1000fpm = start retarding throttle and pitching level 100 feet before desired altitude

After landing, parking & securing

Special Emphasis Areas:

Positive aircraft control

Positive exchange of flight controls

Visual scanning/collision avoidance


Post-Flight Debriefing:

Identify tasks that were completed to standards or above.

Identify and discuss tasks that were not completed to standards.

Record and grade completed tasks in the training record.

Record training in the student’s logbook (reference Areas of Operation above)

Give an assignment for the next flight session.


Next Assignment: Prepare for completing this lesson by reviewing tasks that were not performed to standards. If all tasks were performed to standards, assign the next lesson’s required material.