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Home✈️Aircraft🚁HelicopterGasser Model RC HelicoptersOther › Help with Balancing
01-12-2006 03:25 AM  13 years ago
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CaliberCrasher

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Milwuakee, WI

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Help with Balancing
When I spool up the gasser on the AP mount and then spool down i get a harmonic and the heli starts to shake quite bad. I have to hit the gas and then let it spool down to avoid a lot of unhealthy shaking.

I did a search and did not find any real great tips on balancing the head. I have a high-point balancer and am just now planning to give it a shot.

Does anyone have some links or resources that would be useful to make sure I get the most from my efforts and use the smartest methods to balance the head? If the head balances with the blades on, do i need to balance the blades separately or is that good enough then? They are Rotortech carbon symetricals so i doubt there is an issue there. I have checked the runout, replaced the main shaft and the spindle.

Thanks!

Caliber
Not everything that counts can be counted. And, not everything that can be counted counts.
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01-12-2006 03:45 AM  13 years ago
SteveH

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Texas

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Caliber,

A shake on run up is usually caused by the blades moving in the blade grips at different amounts and changing the lead-lag, not by ballance. It is amplified on the AP mount because of the height and it's relative flexability.

If you were to run up the head speed to lift off, and then let the rotor speed decay slowly to stop, tighten the blade grip bolts to the point that the blades could not move, then it would not shake on the next run up. However, you don't want to do that, and probably could not tighten them to the point they could not move anyway.

To minimize the shake, make shure the blades are reasonably tight in the grips, the blades are straight as you can get them in the grips, and do the run up slowly so as not to change their position in the grips from acceleration.
The government cannot give you anything without first taking it from someone else.
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01-12-2006 04:30 AM  13 years ago
rbort

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Franklin, MA - USA

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Its from the mount
The autonomous MIT helis that I fly have the same problem. They used a raised gear to make room for a computer below the heli, and there is a shake on spoolup. They made the gear taller to allow for more room, and the taller the gear the worse the shake.

Personally when I fly I spool up pretty quick to get by the shakes as once I get to takeoff rpms all is smooth. On landing I touch down and hit throttle hold, then just feed in collective all the way gradually to slow down the rotor quick.

Its not in the heli. If you took the camera mount off you will see there is no shake...

-=>Raja.
MA 1005 Hanson 280, 4264 flts
Spectra 27 3DMax, 3392 flts
Whiplash V1-2 Hanson 300, 1808 flts
Whiplash V2 Hanson 300, 705 flts
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01-12-2006 04:52 AM  13 years ago
xcellgasman101

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WOODWARD, OKLA....

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Another way to get by this is to fly the heli alone before you put the mount under it,, that way everything is lined up and ready to go.. that is how I do it,, Hope this helps.. XGMJohn Crotts
www.soonerhelicamproductions.com
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01-12-2006 05:13 AM  13 years ago
Toadster25

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Iowa

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I've noticed that on my Fury when I set it on my camera mount but it wasn't bad enough to worry about. It didn't do it all the time either. I thought it might have something to do with the wind blowing and the blade going with the wind would have no resistace and the one going into the wind would have alot. I'm probably wrong but that is what I thought might have caused it.
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01-12-2006 06:27 AM  13 years ago
Disciple4123

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USA

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My experiences with this kind of ground resonance is that laterally springy mounts make it worse, taller mounts make it worse, and running 810 blades makes it worse than when I do AP with the 30 sized heli or with 700 blades on the gasser. The blade weight being a greater percentage of total heli weight gives it more throw in the shake. I am an advocate of 810 blades though for other reasons.

I usually engage the governor early on and bring the heeadspeed up fairly quick, then if it shakes too much, I bring it off the ground as it is nearing final headspeed. Not a perfect situation, but it gets me by. Shaking used to be more of a bother than after getting used to it.

Reccomendations to manually straigten blades, and tighten grips equally are also helpful to prevent this.
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01-12-2006 01:36 PM  13 years ago
CaliberCrasher

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Milwuakee, WI

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HOW ABOUT SPOOL DOWN??
My shaking is on spooling DOWN. Is that normal too? I don't notice this when the heli is off the mount, but i have had my share of problems with tail wag, etc which is now solved for the most part. I do have a vibration problem where I can see the tail boom virating vertically in flight. So, it is good to know that some vibration and weird harmonic activity occurs for everyone on the mount for spool up as I had never heard this brought up on the forum before.

Is it normal to have this on spool down, always around the same rpm? The head button is moving back and forth as much as two inches and then I panic and hit the gas, it comes back to center and I slowly release the gas to get by this rpm. Sometimes it works to do what Raja said and quickly run by that rpm by using throttle hold and collective.

I am sure I need to fix my vibration and some tips there would be great. I am very glad to know that the mount can cause the greater issue I have and that it might be normal. I have a Broadcast 180 by the way.

I almost convinced myself that I had bad Rotortechs because one blade would lag the other after I flew and while and brought her back in without the mount. I am convinced that was just me not ramping it down smooth enough because when i do I can put a long straight edge along the center of the blades and they look good without getting too scientific about it.

Do I need to balance the head,and is this shaking normal on spool down? I have not had a problem on spool up actually as I just power through it, the GV1 goes to hover speed before liftoff and it is fine.

Thanks,

Caliber
Not everything that counts can be counted. And, not everything that can be counted counts.
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01-12-2006 02:28 PM  13 years ago
rbort

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Franklin, MA - USA

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Two things
I don't like the "tailboom shaking up and down in a hover" bit, is this happening without the camera mount? Is so look into this. Its coming from the main rotor.

Second, when you are coming to land, try to hover about 6 inches off the ground, hit throttle hold, and gradually increase collective to keep it in the air until it can't no more. Will it land good this way or still shake? Probably not since its off the ground...

-=>Raja.
MA 1005 Hanson 280, 4264 flts
Spectra 27 3DMax, 3392 flts
Whiplash V1-2 Hanson 300, 1808 flts
Whiplash V2 Hanson 300, 705 flts
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01-12-2006 04:19 PM  13 years ago
SteveH

rrProfessor

Texas

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Caliber,

I doubt your Rotortechs are bad, but it's easy enough to check. Take them off the heli and hang them on a shaft off the side of the work bench. That will check the for and aft CG, and they should hang exactly the same angle...straight down. You can also hang a weight like a plumb bob at the same time to check CG.

By all means, check the ballance of the head. It can happen that the head with blades is a little out of ballance even though the blades are ballanced.

I believe, however, your shake on spool down is caused by the same thing as the one on spool up, unequal change in lead/lag of the blades. You can minimise the problem by running your blades tight in the holders, but what ever tightness you run, make shure they are equal tightness.
The government cannot give you anything without first taking it from someone else.
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01-13-2006 01:20 AM  13 years ago
CaliberCrasher

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Milwuakee, WI

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Raja and Steve...

Raja, i am not sure what you mean as far as will it shake when I hit throttle hold? I would be afraid to try that with the mount on. Without the mount there is no problem with the rotor head issue at vaious RPM's when I had the GV1 off to test my throttle curves. I would imagine that this would give the same answer? I don't know if I trust myself to do the test at this point. You should see what I did to my Caliber 30 this weekend! They don't call me CaliberCrasher for nothin YAHOO was I having fun when it happened though...

Steve: I am going to try tightening the blades when they are straight out and see what happens. I just checked and one was tighter than the other. If that doesn't do it, I'll balance the head. I like the trick to test the blade balance easily too as I can never figure out the darn blade balancer.

I'll let y'all know what I find out.

Thanks much for everything

Caliber
Not everything that counts can be counted. And, not everything that can be counted counts.
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01-13-2006 01:37 AM  13 years ago
rbort

rrProfessor

Franklin, MA - USA

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Do this
After you finish flying the machine with the camera mount, bring it down to a 6 inch hover. While hovering there (don't touch down), hit throttle hold at 6 inches high, and, add some collective continously to full collective as it drops in for the landing. Basically auto it from 6 inches. I don't think you can crash doing that, even is your screen name is caliber crasher! The idea is to slow down the rotor in the air so when you touch down you are at full collective and the rotor speed is decaying fast and it will have no time to shake during spooldown. Just another way of landing and avoiding the shake.

Get yourself a Koll Rotor Pro balancer, they are the best in my opinion. Minair makes them. About $85, but well worth it. You can balance your blades well with that. However, I will tell you now, most carbon blades and pretty close and take only a little tape to make perfect. You are NOT going to stop these shakes by balancing the blades that last 2% of imperfection. It helps sure, but, its not the root cause.

Let us know how you make out!

-=>Raja.
MA 1005 Hanson 280, 4264 flts
Spectra 27 3DMax, 3392 flts
Whiplash V1-2 Hanson 300, 1808 flts
Whiplash V2 Hanson 300, 705 flts
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01-13-2006 02:44 PM  13 years ago
AceBird

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Utica, NY USA

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QUOTE…..

its not the root cause.

END QUOTE………….


What is the route cause? My guess would be head bushings. When you add mass to the helicopter you change its resonant frequency. My next guess would be to go with softer bushings or not tighten them so much. An AP rig should have bigger blades and turn slower so the resonant frequency would go down.

I am not quite seeing the picture on this static balancing of the head. The blades are not going to be in the same relationship at 1300 RPM as they are at 300 RPM. IMO what is more important is that the head runs true. You can check this by removing the blades and installing the bolt back in the blade grips. Then wedge something between the grip and the bolt so it pushes the bolt out (don’t bend the bolt). Clamp the frame to something that doesn’t move and then rotate the head by turning the gear backwards to indicate the two bolts. You really don’t need an indicator. All you need is something you can fix in space when you touch one bolt that you can reference to the other. If you need to know the actual measurement then you can use feeler gages (shims) between the one that is closest in. What ever feeler gage it takes to fill the gap is your TIR.

How far out is it?

Ace
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01-15-2006 01:11 AM  13 years ago
CaliberCrasher

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Milwuakee, WI

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AceBird:

I am not sure if this is what you were looking for me to do, but I measured the head from the grip bolts to the head button to use this as a guage as to if things were the same distance. I used digital calipers and it was within .003 mm of the same distance. So, i think the shims are all OK. I have flybar weights on the heli so i played with those a bit and could not really get things dialed in much better by moving either one in from the full outside position. I thought about taking the head off and using the high point and I read Rays handbook method. I don't know how I could fix the head with toothpics the way he says without taking the flybar control assembly all apart to get the ball links off. That looks like a pain. I checked the paddles and they are the same distance out as well and angled correctly. It was warm today so i had to adjust the carb and that seemed to help. i flew her today and the tail wag is all but gone and the vibrations seem much better controlled at 1750 rpms rather than 1850. I do suspect that when i put the mount back on I will have the same shaking problem. I am not sure where to go with this to get the last 5% ironed out.

On a fun note, i burned a gallon of fuel and even did a mini-auto after flaming out during an overzealous climbout while tweeking the high needle too much. i came down all crooked but had just enough headspeed to pull her upright. The blades were about 3 inches off the ground at one point - YIKES. Hey, that is how we learn. Burn fuel and buy parts! I have a 10X on the way to me as we speak that i am pretty excited about too.

Thanks for all the help!

Caliber
Not everything that counts can be counted. And, not everything that can be counted counts.
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01-16-2006 02:40 PM  13 years ago
AceBird

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Utica, NY USA

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QUOTE>>>>>>>>>>

I used digital calipers and it was within .003 mm of the same distance.

END QUOTE>>>>>>>>>


WOW! How in the world did you measure to that accuracy with calipers? Are you sure you don’t mean inches? Even that would be pretty good.
Let’s say it is inches. Now you know how everyone is all hopped up on dialing in their clutch to within .002 inch TIR; that’s .001 off center and that is a miniscule amount of unbalance compared to the .003 on the rotor blades and you’re not done yet. By just measuring the distance from the CL of the shaft to the CL of the bolt you haven’t taken in any run out of the shaft itself. You could check the run out of the shaft alone but that wouldn’t pick up the three thou you already have on the grip bolts. It is best to measure run out as a whole assembly rotating about the actual bearings that are in the heli.

Ace
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01-16-2006 06:27 PM  13 years ago
CaliberCrasher

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Milwuakee, WI

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Inches not MM
Yep, I measured inches and not in mm. I have a buddy that is into real high-end CNC machines from Germany and so he has a dial indicator that cost two-grand alone. I checked the engine shaft and the clutch and he got the runout well within the .003 inches, actually about half that. I never thought to check the shaft with the head on. It would be hard to hold the heli that stable I would think given the plastic landing gear struts, etc. It is worth a try to see how close it is. The digital calipers i used were from a local home improvement shop and my measurements assume that the headbutton is perfectly round and that I was on the exact far end of each bolt for the measurement on both sides. Nonetheless, i can say that it is not way off - and that a mm is almost always smaller than an inch - and that which I use matters

Thanks for the help!
Not everything that counts can be counted. And, not everything that can be counted counts.
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01-17-2006 01:01 PM  13 years ago
AceBird

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Utica, NY USA

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QUOTE

It would be hard to hold the heli that stable I would think given the plastic landing gear struts,

END QUOTE


It would be better to remove the skids and clamp the frame down to something solid or slip a couple of bars between the skids and the frame so you could clamp it solid. You also need a bench mark that is solid to measure to either by calipers or feeler gages.

The head button could be .010 inch off because it is screwed on and I don't believe it is piloted in any way to the head. When and if you indicate the bolts you may be surprised to see how much wobble there is up there. Don't forget to take all the slop out of the grip holes that the bolt goes through. When the blades are turning that bolt will be pulled to the outside and that is what you want to measure. If you have sloppy holes in your grips you could be way off center.

Ace
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