The Propeller
The angle of attack of the blades of the propeller relative to an approaching air stream is called the pitch of the propeller blades. When the pitch is low, the angle of attack is also low. When the pitch is high, the angle of attack is also high. Changing the pitch changes the thrust characteristics of the propeller and the pull that it will generate. Most airplanes with engines of 150hp or less have fixed-pitch propellers because of the limited load capacity and speed range of smaller aircraft. Constant-speed propellers are more expensive and also the norm in larger aircraft. The pitch of the blades of a constant-speed propeller changes within certain limits. The internal mechanisms of the constant-speed propeller also change the pitch of the blade instantaneously.
In-Flight Propeller Effects
When the airplane is flying, there are several forces created by the propeller that affect the way the airplane flies. As the propeller rotates, the air flowing through it is twisted, creating a spiraling slipstream. The spiraling slipstream as it works its way out of the plane exerts a sideways force on the fuselage of the airplane and also upon the vertical tail surface.
Torque is the force that is generated in the direction opposite to the direction of rotation. American engines turn clockwise and hence, torque is a counterclockwise force from the pilot’s point of view. Generally, the torque is not felt by the pilot because of the design of the airplane.
The P-factor is an effect of the propeller that is most apparent when the airplane is at a higher angle of attack such as during lift off or during a climb. The P-factor will cause the nose to go left because of the propeller’s descending blade has a greater angle of attack than the opposite, ascending blade. This causes an unequal pull and the swinging of the nose that results consequently, is called a yaw.
The Engine
Airplanes generally use air-cooled engines which are very reliable and are lighter than liquid-cooled engines. They are also very efficient and run for extended periods of time. Increasingly, they are being designed to be quite fuel-efficient. Most of the engines have horizontal opposed cylinders similar to the engines used to power the original Volkswagen Beetle.
The ignition system
In an airplane, the engine has two complete and separate ignition systems that supply power to the spark plugs in the cylinders. The electrical energy that is needed to supply power to the spark plugs is derived from two magnetos or mags. The electrical system consists of a battery and either a generator or an alternator. The electrical system provides the energy to start the engine, run the radios, night flying lights, and other electrical equipment. The electrical failures that are possible in an electrical system have no effect upon whether the engine will work or not, which is an obvious safety mechanism.
There are two magnetos or mags in an airplane and because each one powers a totally separate and unconnected ignition system, including one of the two spark plugs in each cylinder, one entire ignition system could fail and the engine will continue to work on the other system. The ignition switch in the cockpit has 5 normal positions: off, left, right, both, and start. The start is spring-loaded and similar to a car, it will start the engine. The both position is the normal position for flight, allowing both ignition systems to work separately and independently. Left and right positions allow you to select one ignition system and disable the other system.
The primer injects raw fuel into the intake manifold to get the engine started. Some engines need a lot of priming to start especially in cold weather, whereas others need little to none.
