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HomeAircraftHelicopterHIROBOOther › Need Evo 50 Tail Vibration Help
04-23-2009 07:48 PM  9 years agoPost 1
janked

rrApprentice

Spokane, WA

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I have an Evo 50 with a really bad up and down tail vibration. I have been flying for 5 years and this is my 5th Heli.

Evo 50, never crashed, OS50 Hyper, Hatori JK SB50, N/Idle1/Idle2 headspeeds 1650/1750/1950.

I run a carbon fiber Tail Rotor control rod. The TR rod shakes so badly in Idle 1&2 that it looks like a sine wave. It appears to be a high frequency vibration with a more up and down nature rather than side to side. This shake is accompanied by a loud pulsating/buzzing sound from the tail. This came out of the blue with no event to blame it on. I am stumped.

Here is what I have tried so far: (Part of this was just PM stuff)

-changed both engine bearings
-balanced fan/clutch
-dial indicated fan/clutch/start shaft to less that 1 thousandth
-replaced featering shaft (was slightly bent)
-replaced main shaft
-replaced tail output shaft
-replaced TR hub (I use the 90 size TR hub and grips)
-checked/lubed all thrust bearings
-replaced main shaft, start shaft and TR output shaft bearings
-balanced entire tail assembly (was spot on)
-replaced TR blades
-checked belt
-flybar is straight, paddles are right on
-I do run a TJ Pro governor, I turned it off with no change. I also played around with the engine tuning. No effect.

I have not replaced the head yoke yet.

Any suggestions?

David

"You can observe a lot just by watching." Yogi Berra

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04-23-2009 10:28 PM  9 years agoPost 2
mustang1349

rrApprentice

nash Texas

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is this a newer evo or a sceadu v1 converted to the evo. my converted sceadu did the same thing. never could figuar it out. what kinda of shape is the damper rubber in when i flew craptors they would act up wheN the damper went bad.

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04-24-2009 12:07 AM  9 years agoPost 3
Leif

rrElite Veteran

USA

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If you are bending spindles just from flying, then something is probably wrong in the head.

Things to check:

1. Loose frame screws for the servo frame?
(causes frame vibrations)
2. Collective servo, gears OK?
(Bad servo causes tracking problems)
3. Seesaw, might be cracked?
(had a devil of a time finding this one, caused random tracking issues)
4. Aluminum center hub OK?
(These can bend or get off-center if the J-bolt isn't tight)
5. Worn dampers?
(You could try some after-market ones as a test)
6. Damaged thrust bearings?
(Will cause tracking problems)

Typically these types of vibrations are due to the head and NOT the tail (unless you dorked the tail on the ground).

Leif

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04-24-2009 01:10 AM  9 years agoPost 4
rudyy

rrElite Veteran

E. Amherst, NY

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I would check the aluminium hub since that has not been replaced.

Rudy

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04-24-2009 01:54 AM  9 years agoPost 5
rudyy

rrElite Veteran

E. Amherst, NY

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Also, have you checked your main and tail gears? Are they stripped?

Do you have a 2nd backup Evo50 that you can completely swap the tail to isolate the problem?

Rudy

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04-24-2009 03:27 PM  9 years agoPost 6
janked

rrApprentice

Spokane, WA

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Leif

I did replace the dampers already. I had the carbon xtreme and now I have the infinivation. The thrust bearings in the head and the tail were fine. I greased them as part of my PM as well. I'll check the rest tonight.

rudyy
I will check the hub as well. Gears look fine. I could swap the TR assembly from my 90.

Is it the head or the tail?

Thanks guys. I'll post back when I know more.

David

"You can observe a lot just by watching." Yogi Berra

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04-24-2009 06:49 PM  9 years agoPost 7
Leif

rrElite Veteran

USA

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It's most likely the head, especially since you already replaced the tail shaft and tail hub.

Head problems often show up as up/down tail vibrations.

The center hub and spindle are the two most common sources of vibration (due to bending/damage).

A cracked seesaw is another possibility. While this is typically a "crash damage" concern, stress from previous incidents can take a while to show up as visible cracks. Since the plastic is black, cracks in the seesaw are really hard to detect and tend to show up only under cyclic load.

To check the mainshaft/center hub, I found the following process to be helpful:

1. Remove the blades.
2. Pop the lower swashplate links.
3. Loosen and remove the lower J-Bolt.
4. Pull the mainshaft out
5. Remove the gearset from the frame
6. Put the mainshaft back in without the gears.

Now you have a near-zero friction holder for the mainshaft. By spinning the mainshaft you can check (from the top) for any runout by eye. If you do find a problem, you're already half-way through the disassembly process for doing the fix.

Leif

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04-27-2009 03:22 AM  9 years agoPost 8
janked

rrApprentice

Spokane, WA

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I just ordered a new center hub and spindle. I can't see any obvious run out problem, but I don't know what else to try and this makes sense as the next logical step.

The vibe seems to be a very high frequency vibe, thus my assumptions about the tail being the culprit. I will post back when I test fly it with the new parts installed.

Thanks for the suggestions everyone.

David

"You can observe a lot just by watching." Yogi Berra

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04-27-2009 04:14 AM  9 years agoPost 9
Jafa

rrElite Veteran

Sydney, Australia

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Like you I would have expected it to be a tail problem given the high frequency

Does the belt have a U spot where it has been sitting in one place around the pully? That can cause a thump every time it goes through the tail

I take it the main blade tracking is spot on

A new head yoke would be worth trying


Protos | Logo 400 & 500 | Sceadu Evo | Freya Evo | Trex600N | Avant FX

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04-27-2009 10:06 AM  9 years agoPost 10
Paul Woodcock

rrElite Veteran

Dubai - United Arab Emirates

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Hi guys

Check the tail box bearings. The one closer to the tail blades does a lot of work.

Also check the axial play (end float) on the tail shaft. If you shim it too much, you pre load the bearings. You want a little play on the shaft. The play should be equal to 2x the play on a bearing. ie the play between the inner race and outer race.

Took me a long time to find this on one of my EX2's.

Regards
Paul

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04-27-2009 10:20 AM  9 years agoPost 11
hootowl

rrProfessor

Garnet Valley, Pa.

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Don't forget the belt. You never know. Try a different one.

Also try changing the tightness of your main blades.

Wolves don't lose sleep over the opinions of sheep

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04-27-2009 09:55 PM  9 years agoPost 12
Andy from Sandy

rrElite Veteran

Bedfordshire, UK

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As you have changed absolutely everything mechanical could it be either the gyro or tail rotor servo playing up some how?

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05-02-2009 05:57 AM  9 years agoPost 13
rudyy

rrElite Veteran

E. Amherst, NY

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Any update?

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05-03-2009 02:22 PM  9 years agoPost 14
John Benario

rrVeteran

Las Vegas

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Vertical shakes in the tail are main rotor related. In all the posts nowhere is it mentioned that the main blades or flybar have been balanced. Balance the flybar and main blades and check again.

John Benario

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05-03-2009 03:38 PM  9 years agoPost 15
Dr.Ben

rrMaster

Richmond, VA, USA

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I was searching for that detail as well.

The curious thing is that the model developed the shake with no apparent mishap. I presumed the same blades have been on the model the whole time, but there's no point in going nuts chasing a head shake like this unless/until the most obvious items are first addressed.

Balance means spanwise CG, chordwise CG, AND total mass, not just "they weigh the same".

Were the main blades balanced on this model in said fashion?

Ben Minor

Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA

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05-03-2009 06:00 PM  9 years agoPost 16
janked

rrApprentice

Spokane, WA

My Posts: All  Forum  Topic

Not much of an update yet because I just received my main rotor yoke in the mail. I will post back when I have tried that.

The bearings in the tail were also replaced when I did the TR output shaft replacement.

The main blades are the same ones that I have been using for quite some time. I have a K & S blade balancer and I can only check spanwise CG and weight against each other. Both of those have been done. The heli was very smooth with these blades for a very long time before this started.

Dr. Ben What is your method for balancing the chordwise CG on the main blades? I don't have a Koll Rotor Pro.

I did not balance the head/flybar without the blades, but I was very careful on the flybar install and like I mentioned earlier, everything was OK before with no changes to the head or flybar. It is a good point to bring up and I may look at that when I install the new yoke.

I really appreciate all the help up to now.

David

"You can observe a lot just by watching." Yogi Berra

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05-04-2009 12:46 AM  9 years agoPost 17
Dr.Ben

rrMaster

Richmond, VA, USA

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Doing chordwise is a bit of a PITA w/o a RotorPro because you have to teeter the blades on a razor's edge at 90D angles, mark the crossover point, and then work from there. If the mass and spanwise balance are good, then it's unlikely a chordwise issue is the culprit, especially since the blades have been smooth. The only way they would change is if you used tape, and it moved or if lead migrated in the blades. I chase chorwise CG issues when a set of blades causes problems with intermittent tracking errors or flutter.

Ben Minor

Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA

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05-04-2009 11:28 AM  9 years agoPost 18
Andy from Sandy

rrElite Veteran

Bedfordshire, UK

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if lead migrated in the blades
I have seen this happen!

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05-04-2009 03:37 PM  9 years agoPost 19
janked

rrApprentice

Spokane, WA

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Thanks. I will check the blades again and report back.

David

"You can observe a lot just by watching." Yogi Berra

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05-05-2009 04:26 AM  9 years agoPost 20
janked

rrApprentice

Spokane, WA

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UPDATE

Blades balanced fine. CG was good also.

Installed new head yoke.

Flew it with no improvement @ 1950 headspeed.

So, I started messing around with the governor. Tried it disconnected again, no change. (My curves are very close to the governor settings). Then I started tweeking the headspeed down from 1950. At 1870, most, if not all, of the tail vibe seemed to smooth out. I used to run 1950 all the time without problems, but whatever resonance is being introduced is very significant at from 1880 to 1950. (I could settle for the lower headspeed, not my favorite idea, but how much vibration is going on that might kill my electronics that I'm not seeing at 1870?)

I can't help but to lean towards the engine again, but it dial indicated and balanced out well.

Any more thoughts?

David

"You can observe a lot just by watching." Yogi Berra

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