Balancing tails and mains as a whole? - RC Groups
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Jul 27, 2017, 05:28 PM
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Discussion

Balancing tails and mains as a whole?


How would i go about balancing main and tail rotors.

its all very well getting the blades balanced but then your attaching them to something thats probably not exactly balanced either..


Tails shouldnt be too difficult as a tail hub has a whole at both ends so you can get it on a prop balancer or hi point balancer.

but what about main rotot... you cant push a shaft all they way through and out the other side...
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Jul 27, 2017, 06:40 PM
banging head on wall
skyeblu's Avatar
https://www.dubro.com/products/tru-spin-prop-balancer . What I use for balancing main as a unit . There are videos around showing balancing main shaft and complete head assembly minus blades .
Du - Bro Balancer (2 min 20 sec)
Last edited by skyeblu; Jul 27, 2017 at 06:49 PM.
Jul 27, 2017, 06:46 PM
Bro, it is Christmas season!
You can use a spare main shaft and support it using two main shaft bearings on two stable supports. Remove the head including the main rotors and install it on the spare main shaft then you should be able to balance them that way. Of course you have to make sure that both blades have identical center of gravity.
Jul 27, 2017, 08:52 PM
Registered User
I do it by removing the lower jesusbolt only! Head still in heli tilt heli and balance as needed of course you need to make sure your main shaft bearings are good first
Jul 28, 2017, 05:18 AM
Registered User
All great info!!!!! Ill give it a show by removing the main gear. i think just removing the jesus bolt would still allow some resistance,

Im wanting to get a trupoint/hi point balancer as im pretty sure the fan/clutch on my 600 nitro needs balanced it was never done when the previous owner built it.
Jul 28, 2017, 07:57 PM
Team Compass/KBDD Team Pilot
Ah Clem's Avatar
Back in the old days, it was a good practice to use a high point or similar balancer to account for imbalanced or asymmetrical head components with Kavan, Kobe Kiko, and other, older machines.

With a good quality, modern helicopter (Compass, Align, MSH, SAB, Velos, Mikado, etc.), this is not necessary.

It is important that the blades weigh the same, and have matching span-wise and chord-wise CG's.

It is also important that nothing is bent (spindle, head block,blade grip, blade grip arm, etc.).
Last edited by Ah Clem; Jul 28, 2017 at 08:03 PM.
Jul 28, 2017, 08:17 PM
Registered User

dynamic balancing


I read about an app on the Copterx thread to make your cellphone a sensor for balancing. It looked pretty cool.

I didn't pay attention enough to download or remember the name of the app because I use Audacity.com (freeware--an acoustic program) to show me the rpm (convert from Hertz) and amplitude of an imbalance.
https://www.rcgroups.com/forums/show...ctral-analysis

I use this method on main rotor with no blades, tail rotor no blades, then add blades.
Jul 29, 2017, 03:43 PM
Registered User
Quote:
Originally Posted by daveapplemotors
I read about an app on the Copterx thread to make your cellphone a sensor for balancing. It looked pretty cool.

I didn't pay attention enough to download or remember the name of the app because I use Audacity.com (freeware--an acoustic program) to show me the rpm (convert from Hertz) and amplitude of an imbalance.
https://www.rcgroups.com/forums/show...ctral-analysis

I use this method on main rotor with no blades, tail rotor no blades, then add blades.
i have a kbar which has vibration analisis but its a bit of a guessing game unless you really know what your doing. by doing it the way im intending to do it you knkow that the head is balanced and if vibration is an issue its somewhere else.
Jul 29, 2017, 04:36 PM
Registered User

vibration analysis


With some calculation you can pinpoint where your vibes come from. Mainrotor spinning at 4500 rpm and tail rotor at 4 X that or 18,000 rpm . I look for spikes in the Audacity's display at 75 and 300 Hz. Miinimize each. The larger the spike the more correction you need to apply. The only guesswork is in which blade to start with.

I have rattled apart a couple of tail rotor assemblies @ 18,000 rpm before I could get them balanced. That's why I started balancing at a much slower speed. Get it good at 20-35 Hz then 75 shouldn't be too much different. Some guys run over 5,000 rotor rpm and tails 20,000,

Do some math and see the spikes that the motor creates. Or run the motor free with no gears. But math is still good to do.

Gyros work better with smaller vibrations. The whole heli works better balanced. Kinda like waxing your skis.
Jul 30, 2017, 05:17 PM
Registered User
well i removed the main gear and it looks like the main rotor is pretty closely balanced couldnt get it to stick in any 1 position and the blades always fall pretty much level or just off by a tad either direction.
Aug 01, 2017, 05:51 AM
Registered User
+1 for the dubro balancer. I just balance the whole assembly. You can balance just about anything with it if you get creative in setting it up. I never do the tail. you are adding your weight to the cog?
I also use a gram scale which makes sure you get it balanced within 1 or 2 tries. 20 bucks or less, .1g is more than sufficient.
When you get it perfect they sit level, no movement whatsoever, all day if you leave it.
find the cog with a pencil or spare main shaft, haven't ever had one off from a matched set of quality blades
static balance = identical weight
dynamic balance = identical weight && matching cog
tail vib is pretty common - highest frequency vibs from a spectrum analyzer or vib analysis
bearings most likely to cause vib? I'd say generally the main / tail shaft bearings.
The bigger stuff is real hard on bearings that have seen a crash

don't overlook the grip bearings, seen notchy ones cause some absolutely baffling symptoms due to the fbl trying to fight them

heard of motors being a source of vibs but ive only seen magnets come loose, they came apart before i had time to worry about vibs.

i've totally gotten away without checking them on a balancer. just within .1g + matched cog flies just fine in my experience

this one is purely anecdotal but I had a set of cf tail blades on my 250 that simply would not fly right, i could never figure out why, i just guessed one was weaker than the other and tossed them.
Last edited by zzyzx; Aug 01, 2017 at 06:29 AM.
Aug 01, 2017, 06:54 AM
Registered User
Quote:
Originally Posted by zzyzx
+1 for the dubro balancer. I just balance the whole assembly. You can balance just about anything with it if you get creative in setting it up. I never do the tail. you are adding your weight to the cog?
I also use a gram scale which makes sure you get it balanced within 1 or 2 tries. 20 bucks or less, .1g is more than sufficient.
When you get it perfect they sit level, no movement whatsoever, all day if you leave it.
find the cog with a pencil or spare main shaft, haven't ever had one off from a matched set of quality blades
static balance = identical weight
dynamic balance = identical weight && matching cog
tail vib is pretty common - highest frequency vibs from a spectrum analyzer or vib analysis
bearings most likely to cause vib? I'd say generally the main / tail shaft bearings.
The bigger stuff is real hard on bearings that have seen a crash

don't overlook the grip bearings, seen notchy ones cause some absolutely baffling symptoms due to the fbl trying to fight them

heard of motors being a source of vibs but ive only seen magnets come loose, they came apart before i had time to worry about vibs.

i've totally gotten away without checking them on a balancer. just within .1g + matched cog flies just fine in my experience

this one is purely anecdotal but I had a set of cf tail blades on my 250 that simply would not fly right, i could never figure out why, i just guessed one was weaker than the other and tossed them.
My blades are fairly decent although the mains are a bit beat up but still balance. Ive never found a set of blades that had exactly the same COG even align blades were off by a small amount.

ive got RJX blades on the 450 mains and tails. They balanced on my blade balancer right out of the box but the cog is not likley to be the same.

Main bearings are new as is the main shaft. feathering shaft , raidal and thrust bearings. I need to look at the kbar vibe anylisis but last i looked im sure there was some stuff down low. with a couple spikes in the tail, hwoever teh pics were well bellow the yellow line.
Aug 15, 2017, 11:40 PM
Professional heli wrecker
Luvmyhelis's Avatar
Pick up a cheap Dubro balancer. I use it on just about everything. Even name brand helis have seen some serious issues, all of them! Balance the head while seated on the main shaft, then the tail just the same. Add the grips and do it all over again. I use a very thin rubber band to hold the grips in the correct position so each side is perfectly equal. Blade balancing is an art. First weigh both blades, use the heavier one to find cog. In the old days we used a Koll balancer for doing this more easily, but, the company is gone. There are lots of how to vids on YouTube. Then weight balance the lighter blade so it matches the cog of the heavier one and then add weight to the center until they are identical. Pretty much bullet proof and the proper way to do it. Out of hundreds of sets of blades I have balanced over the years, Only three actually matched up to my standard of what is right.
Aug 16, 2017, 10:26 AM
Registered User
Quote:
Originally Posted by Luvmyhelis
Pick up a cheap Dubro balancer. I use it on just about everything. Even name brand helis have seen some serious issues, all of them! Balance the head while seated on the main shaft, then the tail just the same. Add the grips and do it all over again. I use a very thin rubber band to hold the grips in the correct position so each side is perfectly equal. Blade balancing is an art. First weigh both blades, use the heavier one to find cog. In the old days we used a Koll balancer for doing this more easily, but, the company is gone. There are lots of how to vids on YouTube. Then weight balance the lighter blade so it matches the cog of the heavier one and then add weight to the center until they are identical. Pretty much bullet proof and the proper way to do it. Out of hundreds of sets of blades I have balanced over the years, Only three actually matched up to my standard of what is right.
Pretty much looking to do this for the reasons you stated. I get issues after i putting blades on, the vibes arnt bad but i know i can get it better. For instance with blades of i could be as low as 300 in kbar but once the blades go on it kicks up past 1300 and im seeing a few spikes (although not big spikes)

Even with blade COG matched and then balanced there must still be something in the head thats throughing it off. I confirmed that by adding tape to a blade and seeing if there was improvement which got it slightly better.

its going tohave to wait though as my heli had a bad crash after the tail let go so alot is needing replaced.
Aug 17, 2017, 03:49 PM
Registered User
What tools do you need to remove the main blades on a genius 500


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