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Old Jun 26, 2003, 05:18 PM
Heli Headcase
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Cliffside Park, NJ
Joined May 2003
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Sub-Rotor balancing on Corona

Ok..so I'm up to the part where I am suppose to balance my sub rotor blades on my corona. Using the "book" method as decribed in the manual they say the heavier blade is suppose to move down and the lighter move up a little..makes sense to me. BUT..my blades seem to be magically balanced already b/c either one moves when I place them horizontally..even after I spin them. I made sure everything is level. Is this possible?? Or am I doing something wrong. Has anyone skipped this step b/c they had a similar magical self balancing sub rotor?? lol..
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Old Jun 26, 2003, 06:33 PM
jjc
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It sounds like like the subrotor is in balance for you. But to make sure, put a piece of tape on either end and see if it drops down.
John
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Old Jun 26, 2003, 06:48 PM
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United States, NY, Mechanicville
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I wonder if there is some binding going on somewhere... You may want to loosen the bearing collars at the top and bottom of the crutch and let them align themselves, then try again.

Normally, the shaft will spin very freely when the linkage is disconnected, etc.

Also, the idea of using a piece of tape is a great idea. If you can add 3 or 4 inches of electrical tape to one blade, and it still acts "balanced", then you know something else is going on.

If you still have trouble, posting a picture might help a lot (if you can).
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Old Jun 26, 2003, 11:12 PM
Heli Headcase
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Cliffside Park, NJ
Joined May 2003
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Ok I readjusted how the crutch was situated, loosened the bearing collars on the top and bottom, and what do you know...one blade hung slightly lower than the other one. So I added black electric tape to the lighter side until both blades would remain horizontal. When I tip one end to rotate it stops with only a VERY VERY slight to no jerk in the opposite direction. Does this sound ok to you guys? And by the way..what is that "patch of black stick-on plastic trim" the manual refers to to apply on the sub rotor blade? Does this come with the kit? I didnt see anything like this so I just used electric tape. Thanks again for the help guys!
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Old Jun 26, 2003, 11:43 PM
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San Diego, CA.
Joined Jan 2001
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Yeah, the kit comes with a little strip of black (and white) tape, and believe it or not, it's "stick-on"! Wow, what will they think of next. Everything sounds right to me, go for it. although I'm a newbie myself in the heli department
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Old Jun 27, 2003, 01:00 AM
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Orion-
I am with tenover (not literally). If you can see that it is not stopping with a jerk, or prematurely, you should be all set. Now you have a good reference for how free it should move, and how fine the balancing can get.

!! Good Job!!
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Old Jun 27, 2003, 05:11 PM
Heli Headcase
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Cliffside Park, NJ
Joined May 2003
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hey guys..sorry to be a bother again on this..but i'm balancing the main rotor blades now. at first one blade was slightly higher..I added trim tape and took some off until they were horizontal. ..so far so good...but then when i tap one blade to spin it a little...the blades seem to make there way back to almost the horizontal position. now I know this is not right...or at least i think its not...when they stop spinning they should remain still...and not move to the horizontal again..correct?? god this part is a pain! hehe..is there another way to do this? it seems so primitive..anyway thanks for the help !
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Old Jun 27, 2003, 05:25 PM
Gravity Tester
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Central Michigan
Joined May 2003
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After hours of fooling around with the balancing as described by the manual, I gave up and went for dynamic balancing. I assembled it all and spun it up to check for vibration. If there was none, I planned to just let it go as is. If there was a little, I planned to experiment by adding tape until the vibration was minimized. As it turned out, the vibration was excessive and seemed like no amount of tape anywhere was eliminating the vibration.

After reading the the archives here, I came across a method where the blades are weighed and their CG's marked. Tape is added to the root of the lighter blade until the CG is close to the same position as the opposite blade and then tape was added to to the CG of the lighter blade until the weight was the same.

After reassembly, no more vibration. Amazing...
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Old Jun 27, 2003, 05:34 PM
Heli Headcase
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Cliffside Park, NJ
Joined May 2003
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did you perform this technique yourself or did a hobby shop do it for you? did you need special equipment?
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Old Jun 27, 2003, 07:25 PM
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Central Michigan
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I did it all by my lonesome. The only "special" equipment was a small digital scale to weigh the blades.

I used a small wood dowel to balance the blades on to find the CG.

In my case, the blades were off .5 grams from each other and the CG was off by .1". It took one full wrap of electrical tape at the root and one full wrap at the CG on the light blade to make it come out right.
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Old Jun 27, 2003, 09:29 PM
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Orion-
If the blades are balanced, they will return to the horizontal position. I have no idea why. Maybe it's because water drains Clockwise on this side of the Equator?

Knimrod described an excellent plan for ya..
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Old Jun 27, 2003, 09:46 PM
Gravity Tester
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Central Michigan
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One thing I noticed through my trials and tribulations with the LMH method was that if the rotors are not exactly on the same centerline, the head will always want to move to the same position. Especially if the CG of the rotor assembly is below the shaft. If it is above the shaft (which I think is recommended by LMH) then the sensitivity is better but this method relies on some friction in the shaft rotation to keep it from rotating the 180 degrees to where the CG will be below the shaft again.

I spent a fraction of the time with the method I described versus the LMH method to get it to work. What really hurt me was the fairly large differnce in blade weights (.5 grams). It may not seem like much but when you start weighing the lengths of tape needed to make up for the difference, it amounts to quite a bit of tape. After researching the issue, I assume my case was the exception rather than the rule. Having said that, the next time I do it, it's going to be the new method.
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