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Century Hawk - 50NX - Raven - Predator > Can trainer undercarriage cause Vibration?
 
 
jim 73strat
Heliman
Location: Perth Western Australia

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I have been getting vibration/wobble in my century hawk. I am using wooden blades and have done my best to balance them.
I suspect the Trainer undercarrige as I removed it today and had a very short flight ( I am just learning to hover and it was a bit windy so I was keen to get back on the ground ASAP) But it did seem to Stop the problem.
I am getting some high quality blades tomorrow and will contnue my testing.
I wonder if anyone could advise me? Cheers

(The hele has never been crashed or had a hard landing so everything else should be fine)

WA
09-23-2009 11:12 AM
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HarveyR
Heliman
Location: France - North

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I don't think that the trainer undercarriage will cause the vibrations but it can amplify any existing vibration.

Have you tried changing head speed a little?

If the wooden blades are correctly balanced, there should not be a problem with them. However, because of side effects (different head speed, different wait/CoG, ...), maybe with the new blades you're getting the problem might disappear.

Can you see any wagging (nose/tail left/right) or see any nodding (nose/tail up/down) or bobbing (body leaning left/righ)?

Any other symptoms than the undercarriage vibrating?
09-23-2009 11:21 AM
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jim 73strat
Heliman
Location: Perth Western Australia

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Yes I think you are correct in saying it is amplifying some small vibration. I have tried different head speeds and the slower the head speed the less it does it but it never really dissapears.
Yes it does wag the tail from side to side, but only small vibrations.

WA
09-23-2009 11:35 AM
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HarveyR
Heliman
Location: France - North

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I guess your tracking is good and that the flybar paddles are nicely aligned and symetrical (with no horizontal play in the flybar).

You could just randomly test the following to see if it has any good effect :

- put some tape (1 or 2 cm) on one main blade and then the other. You can also try this on the tail blade
- try changing tracking of one blade in both directions for 1 turn for example
- try moving the flybar weights full in and full out
- try running a little richer/leaner (without changing head speed)

this might sound a little "random" but it doesn't take long and can give some good directions.

Don't know what the weather's like in Perth, but here (France) it's changing quite fast these days? Has the weather changed a lot since it was flying well?
09-23-2009 01:45 PM
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FBoss
Key Veteran
Location: Aurora Indiana USA

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I agree, not the cause but may amplify the vibration, TGear. On the fly bar weights. Put them where they need to be in order to balance the head, no place else. Engine tune can cause vibration, along with many other things. Use the 5 sec. rule for general tune (finger on bottom back plate for 5 sec after engine is warmed up) Too cool is a vibration problem, too hot is a motor burn up problem.
One other thing, It took me too long to learn, you are much better off with the heli over your head when learning to hover. Cost me more than a few $$ trying to hover 2' off the deck. Make sure you know where your throttle hold swich is! When its going in for sure you want to be in T. Hold.

The good ole times are now ,Hawk, Raven, Raven NX, Logo 10
09-23-2009 02:09 PM
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jim 73strat
Heliman
Location: Perth Western Australia

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Cool will check all that. what is the advantage of throttle hold when going in?

WA
09-23-2009 02:44 PM
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HarveyR
Heliman
Location: France - North

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FBoss, about the flybar weights, maybe I wasn't clear. They sure must be kept symetrical (equal distance from head block), but they can both be moved out or in. This changes the overall inertia of the rotating head and can impact vibrations modes, thus avoid the head entering vibration at all. Of course, at the same time this makes the heli more or less responsive, I'm not saying this is the solution, it can just give some indications to what the problem could be and how to solve it.

I don't quite get the "throttle hold when flying in" either? If you mean that when you've lost control and going to crash it's a good idea to hit throttle hold, I agree. Crashing with throttle hold sure can save some parts (clutch, engine, gears, tail, head components, ...).

Personnaly, I took the "low hovering" option (up to let's say 50 cm) when learning and it turned out well (my first crash came much later, well learning circuits). I find it hard to fly at 2 or 3 meters high without been able to hold the heli in place.
09-23-2009 02:56 PM
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FBoss
Key Veteran
Location: Aurora Indiana USA

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I see where you are comin' from and agree.
Yes I meant hit Thold when all is lost but would also add, I crash ah....more than my fair share and in a good percentage of them I realised I should have kept on flyin' kept on tryin' to save it before it went in. So I guess thats rather contradictory but in the end you are better off in THold when the dirt starts flyin'!
As far as the "what height to start at" to each his own I guess. I did alot of stupid stuff at 1 meter, stuff that at 6-8 meters I would have flown outa.

The good ole times are now ,Hawk, Raven, Raven NX, Logo 10
09-23-2009 03:33 PM
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JuanRodriguez
Elite Veteran
Location: Rochester, New York

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jim 73strat,

I respectfully dissagree with the others..... In my experience, training gear attached to your skids CAN cause your heli to "vibrate"...... or "oscillate" would probably be a better term....

While helping a beginner a few yrs ago getting a Nexus set up, his "home made" training gear induced a most definite "vibration" in the heli...... Once the gear was removed, the heli was smooth as a baby's behind.....

You kind of answered your own question on your first post when you said the following , after removing your training gear.....

Quote 
But it did seem to Stop the problem.

Again, opinions may vary and I'm not here to start one of those infamous RR pi**ing contests...... just relaying to you my experience and pointing out to you that you resolved your issue by removing the training gear......

That being said, I would suggest that you shorten the length of your training gear...... that might also resolve the issue and give you that "crutch" until you feel comfortable getting rid of it altogether....
09-23-2009 08:57 PM
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BeltFedBrowning
Veteran
Location: Albany, MO USA

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I also have have found that training gear can make an otherwise smooth heli vibrate and oscillate. Keep the woodies on for training!!!
09-23-2009 09:22 PM
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imnxtc
Veteran
Location: Dawson

My Posts This: Topic  Forum
I agree with Juan, they act like a tuning fork and will induce a resonance vibration at different head speeds.

As for your mention of a "wobble". This can also be brought about when operating at a rotor speed that is too low for the damping in the rotor head, and will occur if the heli is set-up for too low a speed (even with the best blades installed).

In fact the stiffer the blade, the higher the head speed will be required to prevent this. But staying above 1600 should keep you away from it with the Hawks damping.
09-23-2009 09:23 PM
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MikeInMobile
Key Veteran
Location: Mobile, Alabama

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Sounds like the head/blade assembly is out of balance! I usually use a high point balancer on the entire head, including blades. This will make sure that the head is in balance. The undercarriage (training skids) will NOT cause ony additional vibration, but WILL make any vibration evident and visible. I always use training gear on a new machine, or a michine that I have just repaired, to see if there is any vibration in the machine. This lets me get everything right!
09-23-2009 09:58 PM
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FBoss
Key Veteran
Location: Aurora Indiana USA

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Juan, no P match here buddy we all have our own opinions and experiences. The more the better

The good ole times are now ,Hawk, Raven, Raven NX, Logo 10
09-24-2009 01:06 AM
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jim 73strat
Heliman
Location: Perth Western Australia

My Posts This: Topic  Forum
Put some new carbon fibre blades on still doing exactly the same thing, also changed head speed but no better. Will do a vid and post it so you guys can have a look.

WA
09-25-2009 10:31 AM
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FBoss
Key Veteran
Location: Aurora Indiana USA

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Have you removed the T gear? Still a problem? some thing is bent

The good ole times are now ,Hawk, Raven, Raven NX, Logo 10
09-25-2009 11:05 AM
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HarveyR
Heliman
Location: France - North

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I'm curious to see the video...
09-25-2009 11:27 AM
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jim 73strat
Heliman
Location: Perth Western Australia

My Posts This: Topic  Forum
ha when this wind dies down i will remove the traning gear and have fly and see what happens. There should be nothing bent as its never had any hard landings/crashes. But you never know. I am fitter & machinist by day so its annoying that I can't sort it!!! I thought I was good at building things accurately....

WA
09-26-2009 07:05 AM
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nivlek
rrProfessor
Location: Norfolk England

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The training u/c causes more vibration hovering over hard surfaces like concrete than over grass .

At the end of the day , it gets dark .
09-26-2009 08:58 AM
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MartyH
Elite Veteran
Location: Cincinnati

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It can definately cause vibrations and can exacerbate existing resonances.

Marty,
Raptor 90 3D, Freya and more
10-08-2009 07:37 PM
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Dilbeck
Key Veteran
Location: Springdale Arkansas

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As Imnxtc and MartyH described, Training gear will and does cause vibration/wobble, And it will happen at different head speeds. To test this, move the heli up rather quickly and then settle back into a hover. It will be gone but only momentarly. The training gear are hanging out there on a pole/wire and will vibrate the most when they are longer out. If you slide the balls closer to the landing skids it will stop.

If it doesn't fly sell it!
10-08-2009 11:44 PM
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Century Hawk - 50NX - Raven - Predator > Can trainer undercarriage cause Vibration?
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