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07-20-2006 03:37 AM  14 years ago
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DPSElias

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Dunstable, Ma USA

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Tail vibration
When I spool my Hawk up my tail seems to vibrate, is this normal? If not what can I do to correct this? Any help or information can and will help.
Thanks
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07-20-2006 03:59 AM  14 years ago
cassat

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Alberta,Canada

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Thoughts
In my opinion, the Hawks seem to like a fairly high headspeed on the main rotor. You did not say wether you have the Hawk Pro orolder Hawk Sport.
Is it vibrating or is the tail wagging back n forth? IF so, your gain on the gyro may be set too high.

Cassat
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07-20-2006 04:11 AM  14 years ago
catzazz

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Vancouver Island, BC, Canada

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Check the tail blades grips, This is a sign that 1 or both are to tight and not moving freely to allow them to center, This can also happen with main blades too.
Also your gain may be too high, Try a lower gain.

Cheers, Mark M,
http://www.pdqflyers.com
Fly like you borrowed it!! Land like you stole it!! visit www.virc.ca
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07-20-2006 05:18 AM  14 years ago
rcrebel

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Michigan

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Are you talking about when you first spool up to take-off after setting the heli on the ground? If so, that is normal and happens until the blade spindle/feathering shaft "centers" itself in the rotor head.

Happy flying!
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07-20-2006 11:36 AM  14 years ago
DPSElias

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Dunstable, Ma USA

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This is a new Hawk Pro, that a friend of mine is helping with the final setup.
The grips seem loose enough, is it bad to have them too loose? Well the problem is more like a tip vibration, looking at the vertical fin you can see it shacking.

Spool up to half throttle heli stays on the ground and you see the vertical fin shack.

A friend is the only one that has had flight time, I need to get to a field to fly....need to find a good one first.
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07-20-2006 01:20 PM  14 years ago
SteveH

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Texas

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About tail vibrations, if the tail shakes left and right, it's probably gyro related, and most likely too much gain.

If the tail shakes up and down, it's probably main rotor related, and could be a tracking problem. A bent main shaft will also shake the tail.

If the tail vibrates...most visible in the tail fin vibrating, it's probably the tail rotor itself. Look for the tail rotor out of ballance, assembled incorrectly, the blades too tight or too loose. Also, a bent tail rotor shaft, or bad bearings can do this.
The government cannot give you anything without first taking it from someone else.
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07-20-2006 02:08 PM  14 years ago
Jb4w

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Massachusetts

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More Information
I am the friend that is helping get the heli up and running and noticed the tail shake that is up and down and not side to side, which would be gyro related. In addition, he failed to mention that he had a minor boom strike, where I wasn't present, and hit the tail fin on the ground. He has informed me that the tail rotor (TR) did not hit the ground, however I informed him that the plastic tail fins easily deflect and that he ought to take the TR apart and check for bent parts. I also at first contemplated the TR blade grips being too tight but after loosening them found that the up and down shake was still present. I bet on bent or imbalanced parts........
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07-20-2006 03:18 PM  14 years ago
DPSElias

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Dunstable, Ma USA

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That is correct I did have a boom strike, but the vibration was noticable before the strike.
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07-20-2006 05:05 PM  14 years ago
DPSElias

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Dunstable, Ma USA

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My intent was to find out if a vibration is characteristic to the Hawk and its torque tube setup?
If not looks like I have some investigating to do.
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07-20-2006 05:18 PM  14 years ago
SteveH

rrProfessor

Texas

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The vibration is not characteristic, and if it is up and down like you say, I would concentrate on the main rotor. It is dissimular lift as the rotor goes around that shakes the tail up and down. A tracking error can cause it, out of ballance blades can cause it, a bent main shaft can cause it, a bent feathering shaft can cause it, and a bent flybar can cause it. Those are the things that I can think of off the top of my head, but I'm sure there are others.The government cannot give you anything without first taking it from someone else.
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07-20-2006 06:42 PM  14 years ago
DPSElias

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Dunstable, Ma USA

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Thanks steve, My friend balanced my blades and tracked them so I know thats not it....but I will check everything in the head out, is it possible for this to have been bent out of the box?
thanks
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07-20-2006 06:44 PM  14 years ago
SteveH

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Texas

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I suppose anything is possible, but after a boom strike, it could be anything. Double check the feathering shaft and main shaft...they almost always get bent with a boom strike.The government cannot give you anything without first taking it from someone else.
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07-20-2006 07:41 PM  14 years ago
DPSElias

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Dunstable, Ma USA

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This wasn't a boom strike from falling out of the air, it was from the gyro not being reversed to correct the tail right, so when I spooled up and it got lite on the skids and due to uneven pavement it the fin scraped the ground, I powered down as soon as I saw it rotating. made only about one revolution.

Don't know if that helps in diagnose the problem.
Is there an easy way to tell if the feathering or main shaft is bent without dismantling the whole head?
thanks again.

Sorry for all the questions but I am trying to learn and understand what goes on with certain things....I am a nitro car guy and can diagnose those all day long but I haven't enough time on a heli.
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07-20-2006 09:45 PM  14 years ago
SteveH

rrProfessor

Texas

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You can test the feathering shaft by removing the blades and bolts. Then with a nut driver, rotate one nut on the end of the feathering shaft and observe the blade grips. If the shaft is bent substantially, the blade grip will wobble. Do it from each side and watch the other blade grip. The main shaft must be removed to check it, and when you do, pay special attention to the end where it is stepped down to 8 mm, because with a light hit, it will bend on that end first.The government cannot give you anything without first taking it from someone else.
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07-20-2006 10:40 PM  14 years ago
BC Don

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Calgary, AB Canada

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Doesn't take too much to take the main shaft out. Once you do, get a glass plate and slowly roll the main shaft on it. I have a piece of glass plate that I use. I put the main shaft on it, hold it up to the light so I can see if there is light between the glass and the shaft and let gravity roll it by tilting the plate back and forth. If the shaft is bend you'll see more light at one point when it rolls than at another. If the shaft is bent where it contacts the glass plate you'll hear a "bumpty-bumpty-bumpty" as it rolls along. If bent on the thinner part then you'll have to look for the amount of light.

Also, it is normal when you are first spooling up for the tail to vibrate as the head alignes itself. BUT, you should be able to take off and land and when you land it should be fine. So, if you are talking about spool up then what you see is normal and will happen with all helis. Make sure your main grips are tight enough on the blades but still loose enough that they will move in the grips.
Got Money? Send it to me, I'm a Heli Addict.
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07-21-2006 12:25 PM  14 years ago
DPSElias

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Dunstable, Ma USA

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I am no heli expert but when I bent my main shaft in my CP it was highly noticable. Plus when the heli is in flight the only thing that vibrates is the boom tip nothing else.

So the main and feathering shaft does not even have to come in contact with anything to do any damage? The heli never came off the ground. Are these heli that easily damaged?

I did spin the head and everything looks dead nuts, the flybar is straight, and there is no apparent wobble in the feather shaft. I also looked at the tail shaft but the set screw is way to tight and can't break it free for a further inspection.

Thanks again for all your help.
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07-21-2006 12:43 PM  14 years ago
avator

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New Jersey

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I don't remember what the hawk uses for a tail drive system, I wonder if it uses a drive shaft, if the shaft bearings are out of the bearing mounts and the shaft is flopping around in the tail boom causing the vibration. If it's a belt drive, then, it's a moot point.
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07-21-2006 01:06 PM  14 years ago
DPSElias

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Dunstable, Ma USA

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yes the hawk uses a shaft driven tail. I will make sure the bearing are seated when I re-assemble.

Does the Hawk Pro use the set screws to hold the pins for the beveled gears in place still? Because when I took my tail apart the pin was falling out of the gear on the main shaft.
Thanks for your time sorry for the annoying newb questions.
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07-29-2006 01:28 AM  14 years ago
CWOAV8R

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Naples, FL USA

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Just a long shot but...
I bought my son a Hawk which he built on his own... I helped him set the curves and test hovered it yesterday.

I was a little surprised that it was tracked perfectly off the bench but it had a small vertical shake in the tail and was quite prominent aft of the boom supports. I know the tail rotor drive shaft is straight so I went for the T/R blades. They were balanced fine so I went back to lateral balance on the main rotor system. (which should NOT have contributed to the vertical) Added a little tape to one side at a time and it just developed a lateral that it didn't have before. I even tried flying the blades slightly out of track and it just got worse both directions.

As I was cleaning up the helicopter and wiping down the blades I noticed that the heat shrink was a little loose in a couple of places on both blades. Out with the heat gun... vibration is gone.

Stupid me... I checked over everything with a fine tooth comb but the blades came out of storage at the last minute and I just failed to notice some very small loose spots in the blade covering. They were brand new blades I recieved a few months ago and I just assumed...

Smoothest Hawk I ever seen!!! Flies better than mine!

Might be worth checking if you havn't already...

Let us know how it goes.

Ed
I tried flying upside down once... but I couldn't take the blood rushing to my head.
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07-30-2006 07:56 AM  14 years ago
RotorRage

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Lake Charles, La.

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I had the same problem today. All i had to do was loosen my tail blades. I found the srews in the main bearing block were loose too but i'm not sure if that had anything to do with it. Just on more thing to check.A friend will bail you out of jail. A real friend sits with you in the cell saying"That was awe
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