RunRyder - Vibrations??

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Main Discussion > Vibrations??

helicopter34
Veteran
Location: New Jersey, exit 82

Do blades usually have the problem of having different pitches? The rotor head is the only part of my heli that I haven't thoroughly taken apart and put back together because I got it used, so I am not that familiar in the interrior assembly, but is differing pitch ever really a problem. Even a minute amount of difference would seem to make it wobble like a top. Is a pitch gauge accurate enough to detect a difference in pitch.

01-29-2002 Over year old.

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d-n-jensen
Veteran
Location: Bellevue WA

blade pitch

The pitch guage is only used on the bench to set reference points +10 full stick, 0 center stick, -10 full negative stick, with +5 and -5 at the hover points (this is a typical 3d setup). Once it flies you track (adjust the links) the blades to get them tracking just right. Some wood blades can have different strengths so they can flex differently. Most fiberglass and carbon blades do not have this problem (notice I said most). It's a you get what you pay for kind of thing. If the blades are out of track it will beat your heli to death sooner of later. The more out of track the sooner.

hope this helps

01-29-2002 Over year old.

helicopter34
Veteran
Location: New Jersey, exit 82

How to you put them back in track

How to you put them back in track??

01-29-2002 Over year old.

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helicopter34
Veteran
Location: New Jersey, exit 82

Vibrations

I thought I did a very good job at balancing my blades. Althouhg I do not have a blade balancer, I used a knife in a vice and then found the center of gravity. I marked that center of gravity also on the other blade and put tape on the outside until it balanced on the knife exactly on the line. Then I srewed both blades into a piece of metal (from an erector set) and balanced them on the knife and put tape on the lighter blade directly on the center of gravity.

Well I fired it up and watched the rotor spin as the heli sat on the ground and noticed a reasonable amount of vibration in the heli. It was apparently at the same frequency as the blades spinning so it must be directly related to the blades. My question is do you think the blades are not fully balanced, or one of the blades is offset of the other causing one to always have more pitch than the other and makes it wobble like a top.

Should I strip down the rotor head and realign the blade grips? Is there any special method for doing this.

Is a certain amount of vibration normal during takeoff? Could it be offset by a boom strike.

01-29-2002 Over year old.

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Mike99
Veteran
Location: Canal Winchester, OH

Depends on what speed you were watching the vibration. If you were just spooling up, a nominal amount of vibration is normal. You have to get the blades "spun out" or extended with the centrifugal force of the head RPM. A balance problem could be anything, besides the blades, it could be the head, or the clutch, or something like a bent spindle (rod between the blades in the head). Once the head gets up to speed (light on the skids) look across the disk and see if one blade is higher than the other, then stop the head and correct it by changing the linkage length. Usually severe shaking is not caused by blades out of track, but something caused by a crash of some sort.,

Mike99

01-29-2002 Over year old.

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JCadwell
Key Veteran
Location: Richland WA/ Morro Bay, CA

You could have bent a mainshaft. Not sure how bad your boomstrike was, but you could also have bent your linkages to the mainblades, causing them to be WAY out of track? Were you running it up on pavement, or a hard surface? How fast did you get the blades spinning... Were you just seeing the funky chicken on pavement?

01-29-2002 Over year old.

helicopter34
Veteran
Location: New Jersey, exit 82

Nah, its not the main, I replaced that because of wear around the washout. The linkages don't seemed to be bent really. It wasn't that bad of a boom strike. I was running up on grass and I could see the tail bouncing up and down, I was hardley running it fast at all. I thought it might be that they needed to straiten out, so I loosened them a little and then tried a little higher rpm. The frequency just got higher and only a little bit less. I have seen videos of people starting up and then their ships are hardley shaking at all. I noticed that my flybar paddles have a tiny bit of give in them when you try to rotate them. I thought it was from the washout, so I replaced it, and there was still a little bit of the give left. I noticed on a hiribo that I have seen that there wasn't any give at all. Could this be part of my problem? This vibration has a very low frequency so I think it must be for something large, if it was a clutch or something or the engine, it would be a higher pitch vibration. Maybe the spindle is a little bent.

01-29-2002 Over year old.

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maybeim
Senior Heliman
Location: Stockton, California

balance, balance

Hello helicopter34,

If you built your blades and used the "knife" method as you say, balancing is probably off.

The best method is an accurate scale and a "koll balancer" .Dead on accuracy can be acheived. If you are going to build your own blades. I recommened these two building tools. The cost for the "koll" is about $80.00 U.S. supplied by Minature Aircraft and the more accurate and readout digits the scale has, the more they cost, around $100 to $ infinity dollars, I'm guessing here.

This invesment pays off quickly in the savings over buying "carbon blades" especially if you are starting out.Only costing 25$ instead of 125$ per set, everytime you re-kit your heli. Which, by the way, is what I like to call an "opportunity to upgrade"

Are the blades warped? twisted along the length?. If so, they will never track 'right on' and are only good for starting a nice fire.

Not having pulled the head apart, leaves the spindle that connects the two main blade holders, suspect. Just like the main shaft it has to be true.
The way to check trueness, is by rolling the shaft on a piece of flat glass. This will quickly tell you if it is bent.

Also the dampners that support the spindle could be worn or broken and could cause vibrations buy not holding the spindle correctly. Also check bearings. If it has thrust bearings make sure they are installed correctly.

The tail does setup a higher vibration if not balanced properly and should not be over looked in the building process. Once again the "koll" and "scale" will bring it right on. Then dynamic balance using a "prop" balancer. Same with the head with main blades mounted, use the "prop" balancer, once the blades have been 'perfected'eek:

Look at the main gear and start shaft also, check the bearings.

Of course this is just a little info and by no means complete and I take no responsibiltiy if your heli gets 're-kitted' On the other hand if it runs like a swiss watch when you are done, I take full reponsibility

It's a great hobby, just keep working at it and enjoying it, lot's of rewarding feelings coming your way.

Paul A.

01-29-2002 Over year old.

JCadwell
Key Veteran
Location: Richland WA/ Morro Bay, CA

The koll rotor pro looks like a great tool, and is available at

http://www.ronlund.com/Merchant2/me...Balancing+Tools

However, if this thing is really as crazy as you say it is, you could have bigger issues. See what else is wrong.

BTW I have balanced a set of woodies using the knife edge method, then balancing the whole head on two drinking glasses, and I never had any problems getting them close enough to fly. It took a while, and required lots of patience...

01-29-2002 Over year old.

helicopter34
Veteran
Location: New Jersey, exit 82

Vibrations

I loosened up the tail rotors, they were a little stiff and I think they were causing a little vibration by being locked in offset. I ran the heli today and noticed the same thing. The tail wags up and down until it gets to a little higher rpm and around rpm to fly, the tail doesnt really wag at all, just a little vibration in the heli. Is this normal? I do not want to try to fly until I get everything perfect becuase I definitely dont want to crash.

01-30-2002 Over year old.

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