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12-06-2019 01:49 PM  5 months ago
Topic Vote0Post 1
motorrc

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canton ohio usa

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vibration issue
I have a nitro 30 helicopter that vibrates wildly when the main rotors ramp up, flies fine with no visible vibration, then after touchdown and the main rotor deaccelerates the wild vibration recurs. I have:
1) checked to be sure main blades are in balance
2) tried varying the tension on the blade grips-no effect
3) made sure the main shaft and feathering shaft are straight
4) Made sure fuel line in not swinging back and forth setting up a resonance

Any thoughts on what might be going on would be greatly appreciated.
if it doesn't fit, make it fit but don't force it.
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12-06-2019 03:10 PM  5 months ago
BeltFedBrowning

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Do you fly off of concrete or asphalt? Resonance can do this
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12-06-2019 03:15 PM  5 months ago
motorrc

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I fly off concrete. Can you explain that a little more?if it doesn't fit, make it fit but don't force it.
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12-06-2019 03:44 PM  5 months ago
BeltFedBrowning

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Kansas City

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I'm not the one to fully explain the condition, you might need an aerospace engineer for that. It occurs during spool-up or spool-down on hard smooth surfaces and the left to right and front to back vibrating of the landing skids look like the heli is about to shake itself apart. I always fly off grass and this cures problems with resonance.
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12-06-2019 05:59 PM  5 months ago
nismoflip

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Union City, CA, USA

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you're exciting modes and the stiff concrete is less compliant than, say, taking off from softer grass (basically what beltfedbrowning said). there's probably a couple more things you can check and you might have to ask the nitro guys since i only fly electric. have you dial indicated the clutch? have a tail boom support brace? have you tried adding the rubber grommets to your skids?
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12-06-2019 06:19 PM  5 months ago
motorrc

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canton ohio usa

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Ok, I'll try grass when the ice box outside goes away. Actually, the frozen grass is probably as hard as concrete now! I have not dial checked the clutch-does anyone know how much run out is acceptable? I can't remember if rubber grommets are on the skids or not-if not, I'll install some and see what happens. I do remember there is a tight fitting tail boom brace. Its interesting that one of the helis does this and the other does not, yet they are both the same in every respect I can think of.if it doesn't fit, make it fit but don't force it.
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12-06-2019 06:29 PM  5 months ago
heli4fun

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Check your dampeners,hold both grips (while heli is on the ground) and see if you can see saw the grips/blades,if they do you know what to do...(don't forget to grease the spindle and dampeners and you might as well regrease your thrust bearings too).If it flew vibration free before with no crashes,than it's a maintenance problem (dampeners)also go around the whole heli frame and ensure all bolts/screws are tightened,when I used to fly nitro while waiting for my turn to fly i would go around and tighten bolts /screws and wouldn't you know it,i found numerous bolts/screws loose maybe due to the nitro fuel and vibration of the nitro engine ( don't forget the landing skids bolts too,if loose they can cause a vibration on the heli).
I had a friend a month ago with a very nice Synergy N5,and one day for no reason it started to vibrate,he changed out the dampeners came back the next day and all was fine.
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12-06-2019 06:55 PM  5 months ago
motorrc

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I'll check the dampers.if it doesn't fit, make it fit but don't force it.
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12-06-2019 10:12 PM  5 months ago
Rojoalfa

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Punta de Mata, Monagas-Venezuela

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/
/

Main Rotor is not balanced.
Check flybar and paddles distance from center...

/
Saludos cordiales,
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12-06-2019 10:23 PM  5 months ago
heli4fun

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motorrc I have a nitro 30 helicopter that vibrates wildly when the main rotors ramp up, flies fine with no visible vibration, then after touchdown and the main rotor deaccelerates the wild vibration recurs. I have:
1) checked to be sure main blades are in balance
He did "CHECK" the balance of the main blades already!
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12-06-2019 10:27 PM  5 months ago
chopper37

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+1 on the cement try the grass
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12-06-2019 10:43 PM  5 months ago
heli4fun

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motorrc Its interesting that one of the helis does this and the other does not, yet they are both the same in every respect I can think of.
I'm going to assume that since you have two identical helis as you said..
"Same in every respect" but yet your other heli spools up and spools down on "Concrete" with no problem,that it's not the concrete surface.
I'm also going to assume that this problematic heli also (at one time or another) used to spool up and spool down on "Concrete" with no problem.
So...with that being said,why would the concrete all of a sudden be a factor now????
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12-06-2019 11:16 PM  5 months ago
Rojoalfa

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Punta de Mata, Monagas-Venezuela

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heli4fun He did "CHECK" the balance of the main blades already!
That is correct.
But, he did not check the main rotor balance...

It is a most to do that.

/
Saludos cordiales,
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12-06-2019 11:33 PM  5 months ago
heli4fun

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This is ..."Laughable"!!
Okay so,i looked up the meaning main rotor (just for sh1ts and giggles) on Google-
https://en.wikipedia.org/wiki/Helicopter_rotor

So,it distinctly defines it as "Rotor Blades" is it not the same as Main blades?
They both create lift regardless of the terminology you use between the two.
If it is not the same,please inform me as to what the difference is between
main blades and rotor blades,particulary for rc heli use.

So,according to this that he initially posted:
I have a nitro 30 helicopter that vibrates wildly when the main rotors ramp up, flies fine with no visible vibration, then after touchdown and the main rotor deaccelerates the wild vibration recurs. I have:
1) checked to be sure main blades are in balance

I'm going to assume since reading the Google definition,that...

Main rotor (as you define it) are the same as "Main Blades" on our rc heli's.
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12-07-2019 12:14 AM  5 months ago
motorrc

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canton ohio usa

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The flybar is the same distance out from the center point on both sides. Also paddles are the same distance out from the center. Its true I did not weigh the paddles, I just assumed they were the same. If the weight were different, would that cause this?

I have had the heli that does not gyrate on concrete for years, I just rebuilt the gyrating one several weeks ago and so it has been gyrating as long as I have had it.(The gyrating one had been crashed and I bought it as a basket case)
if it doesn't fit, make it fit but don't force it.
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12-07-2019 01:34 AM  5 months ago
heli4fun

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TRUMP, USA

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motorrc I have had the heli that does not gyrate on concrete for years, I just rebuilt the gyrating one several weeks ago and so it has been gyrating as long as I have had it.(The gyrating one had been crashed and I bought it as a basket case)
Good to know,now we're back to square one.
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12-07-2019 05:00 AM  5 months ago
ticedoff8

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Morgan Hill, CA. USA

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When you land, as it spools down, do you lower the collective (main blade pitch) to less than 0°?
This is bad.

If you spool up or spool down a heli with the collective below 0° pitch, the heli is going to get real wild real quick (bucking bronco).

Most noobe on nitro will have a throttle curve set such that the engine is at idle with the collective stick at full down. Then the throttle curve ramps up to a setting that spins the blades fast enough to take off.
They might also have a pitch curve that has -3° (or lower) with the collective stick full down.
They think that when the sh!t hits the fan, they can slam the collective full down and somehow save the heli.

The problem isn't so much with the spool-up. But it could happen then too.
The problem is mainly when they spool down. The head is still turning fast and now it has a negative pitch while it is "stuck" to the ground.
+ > ÷
Believe 1/2 of what you see and none of what you hear.
Fake News will be the downfall of our Republic!
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12-08-2019 12:46 AM  5 months ago
Rojoalfa

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Punta de Mata, Monagas-Venezuela

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/
/

Very funny...

Main Rotor is one thing and main blades is other thing.

The main rotor...

Main blades...

So, it is difficult to get confused.

Every one of this need to be balanced... Together or separate as you wish...

/
Saludos cordiales,
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12-08-2019 01:07 AM  5 months ago
BeltFedBrowning

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Kansas City

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I remember the days when I would balance blades, balance the rotor head, then bolt it together and balance the assembly, then number the blades to the main grip. I haven't bothered to do that in a looong time.
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12-08-2019 03:17 AM  5 months ago
RM3

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Killeen, Texas - USA

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There is nothing wrong with your Heli. Some wobble is normal during spool up and down especially if you try to speed up the rotor in a hurry. The more spring you have within the skids the more prominent the effects are as well. Leave your pitch curve alone... you need neg 5-7 deg for autos. If it doesn’t vibrate in forward flight, hover nor inverted then there is nothing wrong with static nor dynamic balance of the main rotor system and its main bladesshowing a preference will only get you into trouble, 90% of everything is crap...
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