A ground-adjustable propeller is a simple type of aircraft variable-pitch propeller where the blade angle can be adjusted between pre-set limits of fine and coarse pitch.[1] As its name implies, a ground-adjustable propeller may be adjusted only when the aircraft is on the ground and when the engine is not running.
Ground-adjustable propellers, which are mostly used on light and very light aircraft, are much cheaper and lighter than more sophisticated and versatile in-flight-adjustable propellers. A ground-adjustable propeller allows pitch changes to be made, although not in flight, to optimise the aircraft for current payload and flying conditions.[2]
To adjust the propeller, the blades are loosened in the hub, a new angle set and then the hub tightened.[3] The process is one of compromise, and of trial & error. After a flight, if, say, climb seemed too sluggish, the pitch angle may have been set too coarse and would need to be made finer. Alternatively, if the aircraft reached take-off speed quickly but struggled to reach a comfortable cruise speed, the pitch would need to be coarsened. The person making the adjustments would be advised to do so in small increments until a satisfactory outcome were reached.
The device or the component of the aircraft that converts the rotational energy from the engine or any other part of the aircraft to propulsion is known as a propeller. A propeller is an integral part of an aircraft as the aircraft cannot fly without it.
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Through the years, many different types of aircraft propellers have been made and tried in the aviation industry by aviation welding technicians. Some were more successful than others. The following blog enlists the different types of propellers used on airplanes in the aircraft industry so you can learn the differences between them.
Propellers that have the blade angle or blade pitch converted into a propeller are called fixed-pitch propellers. It is called ‘fixed’ because once the propeller has been made, the blade angle cannot be changed. Fixed pitch propellers usually come in one piece and are made up of aluminum alloy or wood.
These propellers are designed to provide maximum efficiency for the forwarding motion of a plane. They are made to fit the specific needs of both the aircraft engine and speed. Even a slight change in the specified conditions can lower the efficiency of the engine and the propeller. In turn, these inconsistencies in the engine also affect other components like the engine mount.
Fixed-pitch propellers are used in aircraft with a slow speed, power, altitude, and range. Many single-engine aircraft have fixed-pitch propellers installed as they are simple in operation and less expensive.
Wooden fixed propellers are hardly found in modern aircraft. However, they were widely used before metal propellers were invented. These propellers were made using the layer-to-layer approach using specially made wood. Yellow birch wood, black cherry wood, sugar maple wood, and black walnut wood were commonly used to make these vintage wooden propellers.
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Metal propellers were first used for military purposes in . These were made extra strong by using credible aluminum alloy. The metal material used in the making of the propeller was treated to enhance its properties and make them resistant to immediate warping from heat and cold damage.
Metal propellers have taken over the aviation industry to the extent that now it is almost impossible to find a propeller made of anything else but metal.
The operation of ground-adjustable propellers are similar to that of the fixed-pitch propeller. The pitch and the blade angle of the propeller can only be changed when it is not turning. A clamping mechanism is responsible for holding the blades in place. You can move the blades by loosening this mechanism.
However, there is no way to move the pitch during the flight to meet the varying requirements. In fact, this is the top reason why ground-adjustable propellers are not used in modern aircraft.
These types of propellers provide high speed when the airplane dives and slows down when it climbs. This is due to the changing pressure and usage of the aircraft engine. To ensure that the propellers provide a smooth and efficient flight, the pilots try to keep the speed as constant as possible.
The working mechanism of a constant-speed propeller is called a propeller governor. A propeller governor senses the speed of the engine and changes the blade angle accordingly, irrespective of the aircraft's operating condition.
These types of propellers are used for propulsion in multi-engine aircraft. If one of the engines fails, the propellers lower the propelling drag to the minimum. Feathering propellers are equipped to turn their blades during a flight to a 90 degree angle. Propellers are usually turned to feathering mode when the aircraft engine does not produce the required power to turn the propeller.
To understand how feathering works, just understand that the blades of the propeller are rotated parallel to the line of the flight to minimize the drag on the plane. When the blades become parallel, they stop turning, and the windmill effect is minimized.
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