Replacing the Fan Blade
An unbalanced fan sounds terrible and yet many modellers don’t realise just how easy it is to get a fan to sound like a turbine. Most model aviation clubs are close to residential dwellings and so noise must be reduced. Many clubs have adopted strict noise policies in order to keep the surrounding neighbourhood happy. The reason we balance an EDF is similar to the reason we balancing a propeller or a car wheel. it reduces sound, increases efficiency and minimises the wear and tear on the sensitive components in your model aircraft.
There are many ways to balance an EDF fan and in this article, we’ll cover two reasonably easy, yet effective methods.
EDFs spin at a very high RPM and can cause serious damage to persons or property if the fan blades were to come away. If we take appropriate safety steps our chances of injury are almost nonexistent.
- Always use a test stand for fuselage
- Always use safety glasses
- Never hold a spinning EDF for any reason
- Never stand behind or in front of an EDF
- Always ensure that the area is free of free clutter and loose items. Paper can easily be drawn into an EDF with devastating results.
- Never attempt to repair an EDF fan whilst still connected to power
- Never use a chipped or cracked fan
- Never remove structural material from a fans blades
You need the following bits and pieces to complete the task.
- Complete EDF unit with motor
- EDF test cradle or plane fuselage
- Spare collets
- Good quality ESC
- Screw drivers
- Sharp Hobby Knife
- 400 Grit Sandpaper
- Fiberglass reinforced tape
- Isopropanol (rubbing alcohol)
Below are the steps you must follow, in order to get a basic balance.
- Start by disassembling the fan and collet assembly from the motor shaft. Place those parts to one side and grab a small square of sandpaper.
- Hold the motor and shroud so that the motor is at the top and is in an upwards position. This ensures that grit will not fall into the motor and damage the bearings.
- Start by rubbing the motor shaft in all directions so that the smooth surface is gone and you can clearly see the abrasive marks. This will provide a better grip for the collet at a later stage. You may spool the motor up with the sandpaper to make the scoring process faster.
- Next we check that the motor shaft is running true. Using the ESC, rotate the motor slowly and check the shaft is running true before proceeding. You are just going to sight the shaft. You might be surprised at just how good you’re eyes are at detecting the eccentricity
- It is impossible to balance your fan unless the motor shaft is running true. Place the collet back onto the motor and rotate the motor slowly again checking for imbalance. You don’t require any special tools, just your eyes, as you’ll be able to see if its running true without any eccentricity (orbit). If you detect an orbit, rotate the collet 15deg and try again until you find a sweet spot where there is no orbit. Change the collet if required and repeat.
- Place the fan on the collet and tighten the nut to bring the assembly back together again. Install the EDF into your fuselage or test platform and ensure that everything is ready for testing.
- Mark the collet and fan so that you know the starting point as this will make your testing so much easier. Spooling up the fan and listen to the sound produced. Loosen the nut and move the fan 15deg and repeat. You are looking for the best sound with the least vibration.
- Once you’ve found the spot with the least vibration add the nose cone, mark with a white marker or sharpie and begin moving in 15 deg steps. You will eventually find the spot with the least vibration.
Below you can find a video on how to replace the fan blade on your roprey models: