A propeller is really a set of rotating wings. Each blade is an airfoil that produces thrust the same way a wing produces lift. Here is how a propeller works, and the difference between fixed-pitch and constant-speed props.
Part of our How Airplanes Work guide.
A propeller is a rotating wing
Each propeller blade has an airfoil shape, like a wing. As the engine spins it, the blade meets the air at an angle of attack and produces a force, thrust, that pulls the airplane forward. The blade is twisted from root to tip because the tip travels much faster than the root, so the twist keeps the angle of attack effective along the whole blade.
Blade angle and pitch
The blade angle is the angle between the blade’s chord line and its plane of rotation. Pitch is not the same thing: it is the distance the propeller would move forward in one revolution if there were no slippage. Because blade angle largely determines pitch, pilots often use the two terms interchangeably. A lower pitch takes a smaller bite of air (good for acceleration and climb), while a higher pitch takes a bigger bite (efficient at cruise). How pitch is managed defines the two main propeller types.
Fixed-pitch vs. constant-speed propellers
Fixed-pitch propellers have one blade angle set by the manufacturer, a compromise for either climb or cruise. They are simple and common on basic trainers; you control power with the throttle alone, reading RPM.
Constant-speed propellers use a governor to automatically change blade pitch and hold a selected RPM. You set RPM with a propeller control and power with the throttle, reading manifold pressure. This lets the engine and prop operate efficiently across a wide range of conditions, and it is a feature you may train on later. On its own, a constant-speed prop does not make an airplane complex: under 14 CFR 61.1, a complex airplane has retractable landing gear, flaps, and a controllable-pitch propeller (a constant-speed prop counts, as does an engine control system such as a full authority digital engine control, or FADEC). Our complex and high-performance endorsements guide explains the training.
Left-turning tendencies
A spinning propeller creates four left-turning tendencies, and they do not all work the same way. Spiraling slipstream and P-factor (the descending blade taking a bigger bite at a high angle of attack) yaw the nose left, and both are strongest at high power and low airspeed. Torque reaction rolls the airplane left in flight; on the takeoff roll it loads the left tire, and the extra friction yaws the nose left. Gyroscopic precession turns a pitch change of the propeller disc into yaw, such as the left yaw when the tail of a tailwheel airplane comes up on takeoff. You counter the yaw with right rudder, especially on takeoff and climb. Our left-turning tendencies guide covers each one.
What you'll need
The FAA handbooks that explain how your airplane works, from PilotMall.com.
Related: how manifold pressure works with a constant-speed propeller.
Frequently asked questions
How does a propeller create thrust?
Each blade is an airfoil. As it spins, it produces a forward force the same way a wing produces lift.
What is the difference between fixed-pitch and constant-speed props?
A fixed-pitch prop has one blade angle; a constant-speed prop uses a governor to change pitch and hold a selected RPM for efficiency.
Why do I need right rudder on takeoff?
To counter the left yaw at high power and low airspeed. The spiraling slipstream strikes the left side of the tail, P-factor builds as the angle of attack increases, torque reaction loads the left tire on the takeoff roll, and in a tailwheel airplane raising the tail adds a left yaw from gyroscopic precession.