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How To Balance Your RC Helicopter Blades

January 12th, 2008 · 8 Comments ·

With almost every new or used RC helicopter, whether it’s an RTF (Ready To Fly), ARTF (Almost Ready To Fly) or a kit you build from scratch, the main rotor blades should be balanced before your first flight.

Some RTF and ARTF models claim the blades have already been macthed and balanced at the factory and they don’t require further balancing and many of the higher end carbon fiber rotor blades also claim to be balanced and ready to fly right out of the box.

Maybe it’s just bad luck on my part, but I’ve never come across a pair of perfectly balanced main rotor blades and always check them out and balance them before I fly with them.

The reasoning is simple. If your blades are out of balance, it will cause vibration in your helicopter which can lead to many problems including difficulty hovering or flying, loosened screws or radio frequency interference.

Also, heading hold gyros work better when vibrations are miniimized because they gradually accumulate yaw error with every little motion. Reducing vibrations will minimize gyro drift which causes the RC heli to slowly drift on it’s axis.

Furthermore, having perfectly balanced blades will also give the RC helicopter more power and better performance because less energy is wasted shaking the heli.

There are many ways to balance your rotor blades, but here I’ll show you the method I use. It’s not the only way, it may not be the best way, but it’s consistent and works well for me and many others.

It also minimizes the amount of tape used and for the most part, avoids disrupting the airflow where the blades generate the most lift (at their tips) by placing most of the tape near the center of graivty (CG), bolt holes and not near the blade tips.

Be sure to use blade balancing tape to blance your blades, or if you don’t have that available, you can use electircal tape. Regular transparent (scotch) tape is not heavy enough whereas electrical tape weighs about 0.1 gram per 2.5cm (1 inch) and works well as a substitute if you don’t have balancing tape available.

Also, before we start, I just wanted to mention that I won’t be using any special balancing tools in this example. If you have them, please feel free to use them if you’d like.

Part 1: Matching The Center Of Gravity

1. The eaisest way to do this is to balance the rotor blade on a round shaft or sharp point of some kind until the blade balances evenly from left to right. This is the center of gravity (CG).

In the picture below I’m balancing the blade on a spare main shaft, though you can also use a wooden dowel a uniformly round marker, blade balancer or anything else that’s round or has a sharp edge that you can use for balancing.


(balancing main rotor blade on a spare main shaft)

2. Mark the CG with a felt tip, permanent marker or a small pice of tracking tape. If using a permanent marker, it can easily be removed later with nail polish remover, hairspray or acetone.


(CG of blade marked with a small piece of red tracking tape)

3. Repeat steps 1 and 2 for the other rotor blade.

4. Stack the rotor blades one on top of each other, facing different directions and put a bolt through the main hole. Check to see if the marks line up. If they do, then the CG is matched and you can proceed to Part 2.


(blades with matched CG)

5. If they don’t line up, determine which blade has the CG farthest away from the bolt hole. You want to move the CG of this blade closer to the bolt hole (to match the CG of the other blade) by applying a small piece of blancing or electrical tape to the underside of the blade on the bolt hole end.


(example of tape applied near both hole to match the CG)

6. After applying the tape, check the CG again by repeating steps 1, 2 and 3 and continue to apply tape to the same rotor blade until the CG’s match up perfectly.

Part 2: Matching The Weight

1. If you’d like, you can skip this first step, but I like to weight each blade prior to balancing them. It’s not really necessary, but it will give you a good idea of how closely matched they are and how much balancing you’ll need to do.


(weighing blade #1)


(weighing blade #2)

The Radix blades I’m using are factory balanced, but they never come perfect. Since they’re only 1/10th of a gram off, you could do without balancing them if you wanted and use them right out of the box, though for a smoother setup, I’d recommend getting them bananced properly.

2. Put a bolt through both blades bolt holes attaching them as a unit (facing opposite directions) and line them up so they are straight. You can do this against a flat wall or counter to check for uniformity. If you own a blade balancing aperatus, you can use it here in lieu of steps 2 and 3.

3. Balance either end of the bolt on a block of wood, book, or other object that it high enough to life the blade off the table and let them move freely.


(blades slightly off balance)

4. If the blades to not balance (ie. they are not perfectly horizontal), put a small piece of tape on the the lighter blade at the center of gravity.


(tape applied to lighter blade at CG to match weight of heavier blade)

5. Continue to add or remove tape on the lighter blade at the CG point until the blades balance evenly. If you’ve used multiple pieces of tape, you might want to measure how long it is and cut a single piece or two of tape to the correct length.


(tape wrapped around blade)

6. Repeat step 3 to to ensure that the blades are properly balanced.


(blades are now horizontal = balanced)

Part 3: Optimizing Tape Usage (Optional)

If only one rotor blade has tape on it or if you used less than 3-5 inches of tape in steps 1 and 2, then you can skip this step. But if one blade has a lot of tape near the bolt hole and the other has a lot of tape on the CG, then you’ll probably want to perform this step. Frankly, if your blades have require that much tape to get them balanced, you might want to consider returning or exchanging them.

1. On the blade with tape near the bolt hole, remove all the the tape and set it aside.

2. On the blade with tape at the CG, remove the tape and discard half of it. Reapply the other half of the tape to the blade but at a point halfway between the CG and the tip.

3. Go back to Part 1 and 2 and rebalance the baldes. Continue to repeat the steps until the blades have the same CG and balance evenly.

Hopefully that helps a little when it comes to balancing the main rotor blades on your RC helicopter – if you have any questions, please feel free to ask by leaving a comment and I’ll get back to you.

PS: After you’ve balanced your blades, don’t forget to make sure that they’re tracking properly.

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Tags: RC Helicopter How To Articles

8 responses so far ↓

  • Markus // Jun 28, 2008 at 3:37 am

    WOW. What a perfect guide of balancing the blades. I will give you a link from my site.

  • Johan Opperman // Sep 17, 2008 at 6:03 am

    I tried to use this method.
    However, once i balanced the blades in one orientation and then turn them, as one unit attound so the top is now facing down, then the blades go out of balance.

    Could you please tell me why or what am I Missing?

    Kind regards
    Johan Opperman (BiJC)

  • admin // Sep 18, 2008 at 2:25 am

    Hi Johan,

    Without seeing your setup, it’s hard to know what the problem is, but it could simply that whatever you’re balancing the blades on isn’t level and is affecting their balance.

    If they are perfectly level and the center of gravities are matched, it shouldn’t matter which way they’re facing.

  • Technex // Jan 7, 2009 at 2:37 pm

    Hi,

    Great manual on how to balance blades.

    I just have a question if I may. Why can’t you just use the scales to balance the blades? I mean if you add tape to the COG until they both match each other to 0.01 of a gram (perfectly).

    Thanks!

  • admin // Jan 10, 2009 at 2:41 am

    Hey, good question.

    Technically, you could just weight each blade and add tape to the CG, but you’ll get more accurate results by balancing them as described for a number of reasons. The weight just doesn’t need to add up, but it needs to mach up span wise as well and that’s something that proper balancing will address.

    When they’re spinning as fast as they do, if they’re off even a little bit it can lead to unnecessary vibrations and all the problems that go along with that.

  • Scott // Mar 28, 2009 at 5:26 pm

    Hello…

    Good info and I used it to double check what I was doing to get my blades balanced up. Good new is that they’re almost perfectly balanced and the CG is within 1/16 of the exact same place on each blade. Bad news is that my heli (Belt CP) still bounces around on both power up and power down.

    It was fine before I killed the previous set of blades in an unfortunate encounter with a plastic storage crate. When the strike happened I was at 0% power but had only been there for a couple seconds and blades were moving pretty quick.

    Is is possible I’ve screwed something up somewhere besides just the main rotors that’s causing this bounce on power up/down? No broken or cracked plastic anywhere that I can see.

    Thanks,

    Scott

  • abby // Apr 14, 2009 at 7:35 pm

    perfect information, it seems that you are very professional in RC Helicopter , so you must be a big RC Helicopter lover , here I have good place that want to recommend to you , that is : tradestead
    there are different kinds of beautiful RC Helicopter that I am sure you will like it soon!

  • my RC helicopters // Apr 30, 2009 at 12:34 am

    good stuff
    i usually just use 2 cups and some tape and a 3 sided ruler, that seems to work.

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