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Heads and Rotor Blades Heads and Rotor Blades Discussion


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Old 03-24-2019, 09:17 PM   #1 (permalink)
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Default Head balancing

I'm using the Align 3-blade head on my 600 size AS350. I just replaced the main shaft with a longer one to get the correct scale height of the rotor over the doghouse. Because of that, I am now using a Vario swash driver instead of the stock one.
I am now wondering whether I should dremel off the lugs on the central hub that the orginal Align swash driver was mounted to, to improve the balance of the rotor head. The size of that lug is about 5x5x10mm^3; even if it was steel (which it is not, besides probably some inserts for the threads - not sure) its weight would be about 2 grams. The lug is about 1cm from the center of the main shaft. The static imbalance would be equivalent to having one 600mm long blade (COG 35cm from the axis of rotation) being about 60 milligrams (0.06 grams) heavier than the others.

This difference seems tiny, but I would really like to get some input here.
Thanks!!!
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Old 03-24-2019, 11:57 PM   #2 (permalink)
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Hi:


A picture of the offending lug would really help with this. Take care.


Don
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Old 03-25-2019, 06:56 AM   #3 (permalink)
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Hi Don,


Here you go.
It was a little late last night to sneak out to the garage to take pictures...


Thanks!
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Old 03-25-2019, 05:46 PM   #4 (permalink)
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Having the lug on the same side as the counterweight of the swash driver doesn't help, either. For what it might get you, the lug on the bottom of the main rotor hub could easily be removed without any ill effects. If you spool it up before removal, have a look at the skids or horizontal and vertical fins to see how they are moving. These surfaces can give you tell tale signs of something out of balance. A gyro, like a Skookum or iKON2 can give you vibration logs that can tell you if there is anything amiss.


At times, annoying vibrations and buzzing parts can drive you around the bend but if you look at where they might be originating, you can look for items running at the same frequency as the graphs will show you. If the graph shows a vibration at 1600 (typical head speed), then you know it is something spinning at the same rpm as the main rotor. If it is 10,000, you can just about nail it down to the motor but each individual helicopter will have different readouts for those frequencies.


So let's say you have a large deflection at 1600 rpm, remove the lug and then see what change to the chart it made. If you saw that it lowered the level some (or a lot), you will be on your way to reducing the vibrations a bit at a time overall in the helicopter. In many cases, the counterweight (or lack there of) can be as much to blame as a slight imbalance of the blades. I have some helicopters that have vibration levels so low as to be non-existent. Hope this helps.

Don
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Old 03-25-2019, 06:19 PM   #5 (permalink)
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Hi Don,


I use an original BeastX (not the Plus), and don't have vibration logging.

I guess I will just remove the lug, assuming that the Vario swash driver by itself is reasonably balanced. Do you think that's a fair assumption?
I always hate burning bridges by cutting things off, though I will almost certainly never go back to the original configuration.


Thanks!
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Old 03-25-2019, 07:25 PM   #6 (permalink)
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I would hope it would be close. Having an adjustable swash driver gives you are very quick method of setting up the phasing of the blades. No need to hook it up to a computer to make minor corrections. Even if a multi-blade head is perfectly set so that the blades track at 90 degrees ahead of their rotational position, a helicopter may not track perfectly straight. It may drift slightly to the right or left, depending on the individual helicopter. The slight correction to the left or right (sometimes less than a degree or two) will bring the helicopters' flight path inline with the control sticks. It is rare but it does happen and I am fairly certain that I have some phase correction in my MH-6. Hope this helps.


Don
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Old 03-25-2019, 07:36 PM   #7 (permalink)
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Alright, I guess that's my task for the weekend then.


Thanks for your help!
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Old 03-27-2019, 06:08 PM   #8 (permalink)
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Well, the lug is gone. Even if it did not contribute any significant vibrations - which I will never know due to lack of vibration logging - it certainly looks better.
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