Propellers, what can we say about props. Well quite a lot actually, as I'm sure you are all aware it's that funny shaped thing on the front right behind the spinner. It's actually a very complex shape and there are many different designs and styles. They all have one thing in common and that is they pull the aircraft through the air. For the sake of this little article I am talking about model propellers and not the full size. Let deal with the size measurements first. Typically a prop will have a size something like 9 X 6, 12 X 8, 14 X 10. The list of sizes is almost endless. Let's take a typical 10X6 prop. The first figure is the diameter of the propeller in inches and the second figure is the pitch. This too is measured in inches and what it means is for every revolution of the prop it pulls the model 6" through the air. However this is a theoretical figure, there is a degree of slip and friction as the prop moves. The design shape also has a bearing on the prop to. Some props for example are designed to be quiet in operation.
A rotating propeller creates a complex spiraling airflow down the fuselage and over the tail surfaces. This airflow brings the rudder and elevator control surfaces to life and give them some degree of authority, which is a great help when the model is on the ground or flying at a low airspeed. However unless the model has full span ailerons the airflow will have no effect on them. As well as airflow a propeller also creates a gyroscopic action and this often used to great effect during aerobatics.
If you look closely at a propeller you will see it has an aerofoil shape to it, similar to the shape of a wing and it's this shape that provides the thrust that when the prop is rotating. One of the most important things you can do with your propeller is to balance it. This will make the motor run smoother, produce less vibration in the airframe, less wear on the motor bearings, and it can increase the rpm slightly because it is running smoother. You will find several balancers on the market of varying designs. The one I use a a Great-planes design that is simply held between the thumb and forefinger. The prop swings on the points and the heavy blade falls to the bottom.
A prop can be balanced in one of two ways. Either by sanding the back of the heavy blade or by adding paint or lacquer to the light blade. Both methods work very well.
Damaged props should be discarded at all costs and never used. They are dangerous and could cause serious harm to anyone that happens to be in the way when they fail. Always stand behind a rotating prop, never in front or inline with it. Never ever make any adjustments to a model without first removing the prop if you intend to connect the battery.
The above are just a few simple things that may not have occurred to you about propellers.
Martin.
A rotating propeller creates a complex spiraling airflow down the fuselage and over the tail surfaces. This airflow brings the rudder and elevator control surfaces to life and give them some degree of authority, which is a great help when the model is on the ground or flying at a low airspeed. However unless the model has full span ailerons the airflow will have no effect on them. As well as airflow a propeller also creates a gyroscopic action and this often used to great effect during aerobatics.
If you look closely at a propeller you will see it has an aerofoil shape to it, similar to the shape of a wing and it's this shape that provides the thrust that when the prop is rotating. One of the most important things you can do with your propeller is to balance it. This will make the motor run smoother, produce less vibration in the airframe, less wear on the motor bearings, and it can increase the rpm slightly because it is running smoother. You will find several balancers on the market of varying designs. The one I use a a Great-planes design that is simply held between the thumb and forefinger. The prop swings on the points and the heavy blade falls to the bottom.
A prop can be balanced in one of two ways. Either by sanding the back of the heavy blade or by adding paint or lacquer to the light blade. Both methods work very well.
Damaged props should be discarded at all costs and never used. They are dangerous and could cause serious harm to anyone that happens to be in the way when they fail. Always stand behind a rotating prop, never in front or inline with it. Never ever make any adjustments to a model without first removing the prop if you intend to connect the battery.
The above are just a few simple things that may not have occurred to you about propellers.
Martin.
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