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HelicopterGasser Model RC HelicoptersOther › Predator vibration up and down on the tail
06-06-2010 09:45 PM  7 years agoPost 1
theriddick45

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United States

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I got a predator with a 231 mod new just out of the breaking 3 1/2 gallons. I am experience a tail vibration up and down. I change the torque tube, I took apart the tail case check all the bearings and gears, front tail check no problems, main gear one way bearing good, bell is new and the bearing as well, starter shaft new with bearing case and the bearings new, new cluth shoe. I'm running 6.92 gear ratio, head is FBL RJX just about 6 gallons thru, main blades are 720 and 690 both FAI/F3C. HS on normal 1590 idle 1 1740 idle 2 1910 vibrations are seening at lower head speed and idle 1 when the HS is at 1910 no vibs. Oil ratio is 3.6 oz toa gallon.

Any help with this up and down vibration will be appreciated.

Suzi Janis 800e & 700e 3blade both w/Ikon

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06-06-2010 10:44 PM  7 years agoPost 2
Gearhead

rrMaster

Vt

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is it a Vibration on the tail or is it more that the Tail is Bobbing up/down ??,,
on the Maiden of one of my new Ravens I had the Tail Bobbing up/down a good inch or so, I found the Tail Blades needed balancing, once the Tail Blades were balanced the problem was gone for good,,

hope I have helped !!

Jim
Buzz Buzz Buzz

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06-06-2010 11:07 PM  7 years agoPost 3
theriddick45

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United States

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Tail blades grips and blades are balance I check that on a prop balancer and they are good I really have check everthing and are very frustrated.

Suzi Janis 800e & 700e 3blade both w/Ikon

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06-07-2010 01:48 PM  7 years agoPost 4
AceBird

rrElite Veteran

Utica, NY USA

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HS on normal 1590 idle 1 1740 idle 2 1910 vibrations are seening at lower head speed and idle 1 when the HS is at 1910 no vibs.
I don't have any experience with FBL but this sounds like tuning the electronics. There must be some paramater that can be tuned in the FBL software that is related to headspeed. 1590 to 1910 is quite a swing. I am not sure why you want that but you must have your reasons. Remember dynamic balance is affected by RPM. Typically all you are capable of is static balance which is a step you must take but it ain't the end all.

Ace
What could be more fun?

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06-07-2010 02:01 PM  7 years agoPost 5
theriddick45

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United States

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AceBird.

I don't use the FBL electronic no stab system on my heli just the tail gyro.

I fly more on the 1740 and 1810 but due to the resent vibration I tried 1910 and 1950 and at that point there was no vibs wierd I use FAI/F3C blades which gives you the balance you need without the flybar.

I have not had a crash resently either

Any other suggestions please!!

Suzi Janis 800e & 700e 3blade both w/Ikon

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06-07-2010 03:21 PM  7 years agoPost 6
AceBird

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Utica, NY USA

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I use FAI/F3C blades which gives you the balance you need without the flybar.
I didn't realize that was possible. There has to be a downside to removing the flybar or else why would they exist?

Ace
What could be more fun?

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06-07-2010 06:14 PM  7 years agoPost 7
theriddick45

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United States

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Most people don't realize this I most say I'm not agains the electronics but they way I see it the unit will correct and keep the Heli in one poSsition just like the tail gyro those. But if you use 3D type blades without the FBL electronics you will strougle alot keeping the Heli in a good hover and flight pattern I had tried it before.

I do have a FBL HEAD from RJX and I like it so far and everything was working fine specialy on the breaking process for this new motor. I am taking everything out the head main gear and tail case I am going to change all the gears and shaft I'm doing it now as we speak but if anyone knowssome tips and tricks please let me know ASAP.

Suzi Janis 800e & 700e 3blade both w/Ikon

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06-07-2010 08:05 PM  7 years agoPost 8
Rojoalfa

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Punta de Mata, Monagas-Venezuela

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Less RPM...with heavier blades...

/
/

Good point!... flybarless without electronic!... wow..!

Cool McCool ! "Danger is my business"...

With flybar at low RPM, I suggest to install weights at flybar... beging with a little and so on...

With no flybar...opps... less RPM... try heavier blades...

more RPM... more resonance... My dear "Cool McCool", install the electronics for this FBL head...

/

Saludos cordiales,

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06-08-2010 02:01 AM  7 years agoPost 9
theriddick45

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United States

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Rojoalfa.

In time I will but for now is flying with no problems except this up and down on the tail other than that is fine.

I changed tail gear and front transmition but still and I have to clarify that being without the electronics have nothing to do.

I got my trex 600 the same way with the outrage head and is flying aweasome. So getting the FBL electronics now is not a good idea i guess since i have to fine the ghost first but thanks for the suggestion. Any other ideas are welcome.

Suzi Janis 800e & 700e 3blade both w/Ikon

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06-11-2010 12:39 PM  7 years agoPost 10
theriddick45

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United States

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Figure out!!!

Figure out it was the turque tube reading on all forums I read that the torque tube needs a 1mm or so of a gap inside the boom. I mark the boom when it was all the way in on the front transmition then back up 1mm with the turque tube in the I installed the rotor tail transmition and to make it better and not have the same problem I back up the transmition 1/2mm. Now there is a very small movement in idle 2 but normal and idle 1 is pretty good.

Thank you all!!!

Suzi Janis 800e & 700e 3blade both w/Ikon

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06-11-2010 04:55 PM  7 years agoPost 11
oldfart

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Vancouver, Canada

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A VIBRATION will cause your tail fin to BUZZ (you will see the tips vibrate is a blurry fashion).

If your heli cycles (wags) in a for/aft manner, that is more of a "high frequency rocking", with no tail fin buzz, then that is usually caused by running a head speed that is to low for the damping (mechanical and electrical in your case).

I believe the mechanical damping of the RJX BBL head is designed for 3D flying. This would mean it uses a rather hard mechanical damping system. As you drop down in rotor speed, it will tend to rock in teh fore/aft axis.

This can be amplified (made worse) by the electronic damping settings in your FBL controller, if the gains that relate to damping are set too high...much like an overly high gain on the tail gyro will cause the tail to wag. Some of the lower cost FBL units cannot be set for proper damping at low rotor speeds. So they are OK for 3D but not for flying at lower rotor speeds as one may want for scale or FAI hover flight.

You may find the Century FBL head better for a wider variety of rotor speeds.

Phil

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06-12-2010 03:47 AM  7 years agoPost 12
theriddick45

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United States

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oldfart.

That's a good point never cross my mind. I will research more on the FBL system since I'm still flying without the electronic/stab system. Now that I got this info I will make sure I get one with this option.

I think the Sk360 will be ok but let see, the other day I got a PM from a guy that is going to put one on his gasser and i think he will let me know the outcome.

Thanks for the info!!!

Suzi Janis 800e & 700e 3blade both w/Ikon

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06-15-2010 06:48 PM  7 years agoPost 13
oldfart

rrProfessor

Vancouver, Canada

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I just solved a similar vibration on one this past weekend.

The fellow explained that he had just made some repairs from a crash and had replaced the feathering spindle. Of course having been so informed we chased all manner of other components. Finally I figured he must have erred somehow in his head assembly so I took it apart. Here I found he had mistakenly installed the old bent spindle instead of the new one !!!

After replacing the spindle - all was well and his smile was back on his face.

Moral of the story. Sometimes we may think we did something when we didn't. So it is always a good practice to go over any rebuild with a fine tooth comb, so to speak.

As for being forgetful, we had been using my LiPo powered starter during all of this and I left the field forgetting my starter!! Thank god he recovered it for me....must be one of those 20+ grey hairs on my head that was responsible for that.

Phil

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06-16-2010 05:50 AM  7 years agoPost 14
lejon

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Las Vegas, Nevada

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Also I started to develop a vibration that was noticeable in the skids and the tail. I chased everything and could not find anything. I went back over it one more time and noticed that there was what had appeared to be the standard looseness in the tail blade holders. I looked a little closer and noticed that the tail hub was actually moving on the output shaft. I replaced the hub and fortunately it was the hub and not the shaft that had worn. Put it all back and went for a test. No vibration.

It is my understanding that the blade grips will wobble slightly and when spinning the centrifugal force holds them out straight. This was wobble of the hub on the shaft.

Might be worth checking out.

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