Propeller size

How to choose the propeller for rc plane

 

Prop banner

 

 

 

 

 

 

 

 

 

When come up with this question there are also more questions involved in the thread. Propeller size is the output of a good harmony among Airplane weight, Engine size, Type of plane we fly. For example if we want to fly trainer plane the weight to power ratio of at least one to one should be fine.  To understand these explanation you can try to hold the plane head up in the air while accelerate the engine to full throttle.  If the plane can sustain itself in the air without dropping down it should be safe for this reason.

 

Engine testing

Engine testing

Now I believe you understand the relationship between engine power and airplane weight. But before making further explanation I would like to make prior understanding that it is necessary to use electric motor in the explaining of how to choose a right propeller. Today most beginners learn to fly with electric plane since it has less trouble to set up and fly in comparison to nitro engine plane. A good motor manufacturer usually provides informative manual and specification you need to set up the electrical system. Over a decade of my flying was spent on so many motor that were good and bad.  To this extent and for sample reason I will use one of a reliable Motor with reasonable price for explanation.

 

 

Choosing propeller

 

From the picture please be careful to go over each column one by one.

 

Starting from B which is the total weight of the plane we have plus extra thrust we need. For Electric rc plane the battery weight must be included.  Nitro plane is differed, do not add engine fuel to total weight. The reason why we need to add extra thrust in here is when flying some type of plane such as an aerobatic plane it generally needs more power to weight ratio.  At least 1.5 x  to 2.0 x of power to weight ratio is needed to make the maneuver done smoothly. According to the table if the plane weights 1,800 g you may want to choose the motor that gives 3,100 g thrust.

 

Now you can go over to column A. At this point you will find a suitable propeller for the motor in your plane. It is not over yet please also see that there are some more dependable factor involved in your setting. There is one column that displays MAX current. You can use the current value there to determine the ESC (Electronic speed control) for your electric plane. With the propeller you choose is 10 x 5 then you need the speed control that can withstand more than 47A. The ideal ESC should be 50 or 60A – it is a good idea to add in some safety factor to the nominal value.

 

In Column C you will find the motor model that match all your requirement. Please also pay attention to the Cell Count column as it is important to note that Four Cell Li-Po battery is what you need to use in the plane.  One more suggestion is that do not depend much on column D since it is a rough information to all aspect of this motor.

 

To whom who may wonder why I do not directly matching motor to the propeller. 

 

Yes this will be a time saver like knowing Motor’s K V then you can sort out the propeller size right away. Sorry to say that it dose not always works thing thoroughly.  Motor with same K V but differs in Watt are common from all manufacturer. Moreover propeller is just one thing among many electrical devices in rc plane, and each of them all have its limitation. Choosing correct propeller means coordinating these devices together to reach the ultimate performance of the plane.  Hence I would prefer to gather all data or value that is needed to determine the system – not for just propeller.

 

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