Propeller preparation before use
The driving system plays a primary role in the model aviation. The thrust force produced by the driving system is required to be as precise as possible for an effective and efficient flight. An electrical motor drives the propeller in a revolution motion; providing the propulsion thrust for the flight.
The propeller looks simple, yet it requires precision to produce and to assemble to the model. In this article, the scope is only on a nylon propeller for electric model with direct drive (without gearbox) through a propeller adapter. However, some of this technique is also applicable to other systems which implement a prop adapter.
This technique is optional and some modelers prefer to just use the propeller without any pre-preparation. Most of the propellers provided from the manufacturer are already able to fit in the prop adapter just fine, but some have the hub center holes which are required to be enlarged.
There are many ways to enlarge the existing center holes of the propeller. The most precise process is to use a bench drill press, but a proper clamp has to be used for securing the propeller in place during the drilling process. There is also risk involves a propeller damage during the clamping process. Secure it too tightly; it might damage the leading or trailing edge of the propeller blade or damaging the hub. Secure it too loose; the propeller might fly- off, hurting the people in the area (this should be prevented at all costs).
All these risks also present when you decide to use an electric hand drill. The less precise and safest way is to use manual hand reamer tool. You could just slowly rotate the reamer tool manually by hand; the tapered cone should self-feed to the centre axis of the hole. With this manual tapered hand reamer, you are free from the mentioned risks.
The deeper the reamer feed into the hole, the larger the hole is formed. Be cautious not to oversize the hole. Try to test fit the propeller to the prop adapter after a few revolution of the reaming process and repeat the process until the propeller is just-fit into the prop adapter.
Another preparation process involves in balancing the propeller. The production process from the manufacturers is already precise, but there are always tolerances in the manufacturing process. Again, this is optional. A more balanced propeller would help to minimize vibration during the flight. Vibration could be small, but even a small and continuous prolong vibration will caused uneven wear on the ball-bearing of the motor; reducing the performance and the lifetime. Besides the wear and tear issue, vibration is the notorious enemy for aerial photography/videography/cinematography. The vibration results in a jelly-like video. This issue is overcome by implementing steady gimbals for the camera.
In this article, only the 2 blade-propeller is discussed. A prop balancer tool is used to show whether the propeller is balanced or not. The propeller is secured on its center by cone nuts on a shaft. For a smaller prop center hole, the cone nuts are configured in such way that the cone’s peak is facing each other. For a larger prop center hole, the one of the cone nuts is swapped for its face orientation. When the shaft is mounted on the tool, the magnets on each end will automatically hold the shaft at its centre axis.
If the propeller is unbalanced, it should be heavy on one side and one of the blades will rest on the ground.
To balance the propeller, a strip of tapes is used. Try to mount the tape closer to the center as it will reduce the disturbance near the edge of the blade. Adjust the mount position and the amount of the tapes until the propeller is balanced and automatically rest on the centre.
If you have finished with the adjustment, you may finalize it. Try not to mount around the leading and trailing edge of the blade to minimize the change in the blade’s airfoil. You may mount the tapes on both the front and back sides.
The propeller is now ready for use.
D.L. ENGINEERING - The Sky is Home
You might want to check out the FliteTest Video series on balancing propeller :