N5C vibration. Help!

[flyboynellor]

Hello all,
Trying to isolate vibration in the frame. My N5C is used and in great shape. I recently installed a CGY750 and having a low frequency vibration in the frame. The whole frame shakes violently. When I run the HS at 1850 rpm or less I get a bad shaking in the frame. Like the gains are too high. When I reduce the gain on the ele and aile down to 35 its better but not gone. I have changed the gain from 90 down to 35 and no real difference. When I run the HS up to 1950 and greater its smooth as silk. I run my gain in idle up to ele 45 aile 55 rudder 60. This is per Matt B. post on HeliFreak (N5 with cgy750 tip). My feathering spindle is perfect and main shaft also perfect. I'm running the 606 Rail blades and CY 92mm tail blades. I'm running a OS 55 HZ with HS needle at 1 and 1/4 out from closed. Midrange needle at 1 turn out. Engine runs great lots of smoke and great throttle response. Engine doesn't run hot . I do run my main blades on the tight side on the bolts. This is my first FBL setup and I have to say its difficult to setup and the manual for the 750 isn't the easiest to understand. My FB helis weren't near as difficult to setup. I do have a FB head for the N5C. Maybe thats next. LOL. I would appreciate any help resolving my problem. Thanks in advance for the help.

[flyboynellor]

**update** Just got back from a test flight. I loosened up the main blade bolts and got rid of half of the vibration. Moving in the right direction. Changed the gain up and down with no further reduction in vibration. The fuel in the tank is bubbling and not foaming if that helps any. Thanks again.

Bob

[Tommy Wagner]

Is the tank foaming at idle, the 1850 and at a higher RPM


Tommy

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[flyboynellor]

No foaming at idle. No foaming at 1850 but bubbling if you know what I mean. Big bubbles not smooth. At 1950 dead smooth. Not a ripple.

[Tommy Wagner]

If it is smooth at a higher RPM l would think that the motor mite need a finer tuning that head speed mite be on both needles causing the motor to run a little rich maybe try leaning the mid a click or two


Tommy

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[flyboynellor]

I've been doing that. I don't want to lean too much. I'm already at 1 1/4 HS and 1 mid needle. I get good top end punch and great transition from idle to mid. Thanks

[Ross Lawton]

I've had and seen similiar issue on a various machines in the past, some have been engine related and some have been mechanical.

Couple of things which might be worth checking if you have not already:

1. Engine - What is the condition of the rear bearing? If it has had some use it may need replacing as it could be causing the engine to run rough and causing excess vibration.

2. Head Assembly - The heads usually come pre-assembled, check to make sure the bearings are installed correctly and that they are in good condition. Also check the dampers and if necesary lightly grease them with a little silicone based grease to allow the spindle to float.

Running at low head speeds with new dampers can cause a head wobble untill they have a few flights on them and they have bedded in.

Hope this helps and let us know how you get on.

Cheers!
Ross

[flyboynellor]

Thanks Ross,

I was told that the rear bearing was changed recently. The only question mark would be main shaft and main bearings. I guess I could change and see what happens.

[flyboynellor]

Well. I changed out the main shaft and main bearings and no difference. Still getting shaking at 1850 HS. I have changed the gain on the aileron and elevator from 80 down to 30 with only minimal reduction in shaking. When I run the HS up to 1950 and greater the shaking goes away. I'm about ready to ditch the CGY 750 and reinstall the FB head. Too much headache. Please help.

Thanks
Bob

[Kevin Feil]

Bob,

are your boom supports tight? check to make sure the Ca hasn't come loose in the rod ends.. I have had this happen.  Please don't get to discouraged!! I know it's a pain in the Arss but it can be resolved!! Stick with it Bro. Has the heli seen a Crash?? Give us just a little bit more info..

Kevin

[Will Campbell=Crashr30]

You noted at the beginning that it smooths out at 1950. That sounds right. The reason is that the head is very rigid due to the dampers.
Makes for great 3d but at a lower head speed you will get this shake. It is common in any heli with very stiff dampers. Now the other thing
Is what servos are in the machine?  In the 750 there is an option for head response. 2 is the default value for head response. Do not change it to 1
As it will get worse. Move the number to 3 and it may help. Very fast servos will respond to every little input from the 750 .  The closer the value is
To 1 then the faster the servos respond and then you will see this shake as well. I too tried to run 1850 and had the same thing. Do not worry your
Machine is fine. Just turn the head speed up a bit and/or play with the head response value.

[flyboynellor]

Thanks Kevin,
Just checked the boom supports and they are tight. I bought the heli used from a guy on Run Ryder. flyboy907. He stated NEVER crashed and only 30 flights. Judging by the condition of the heli when I received it I believe it to be true. But you never really know. He said he put one new rear bearing in the engine. The only thing left to do would be to change out both engine bearings and the start shaft bearings. If that doesn't resolve the shaking I have no clue. He indicated he used the CGY 750 for a brief time. I don't really want to change out the engine bearings but I have to take it one step at a time. Thanks again for all your help.

Bob

[flyboynellor]

Thanks crashr30,
My cyclic servos are Futaba BLS 252. Would you recommend not changing out the engine bearings? I was also thinking of making my normal mode HS 1950. That would solve the problem. I did notice a slight shake at 1950 once in a while but I would say 95% reduction of the shake. My current governor settings are Normal=1850 Stunt 1=1950 Stunt 2= 2000. Thanks for your help.

[Will Campbell=Crashr30]

Your real good in the servo department.  Make sure that the spindle is well lubed.  I use a synthetic wheel bearing grease you can get at any auto store.  Regular wheel bearing grease is fine as well.  That helps a bit as well.  On the engine bearings, unless you see alot of rust on the bearing or the engine feels rough or sounds loud(like a grinding sound) when running I would not change the bearing.  Try raising the head response to 3 and see if it takes out that last little bit of shake.  You will not notice the heli slow down in response or anything like that.  It is more like raising or lowering the sensity of the gyro if you will. (Kind of a broad description).  And yes I would keep the headspeed at minimum of 1950.  I would put stunt 2 at 2100 but 2000 will be OK.  2100 does not over stress the machine so do not worry about that if that is your thought.  Hope this helps. 

[flyboynellor]

Thanks crashr30,
What part of the 750 menu is the head response? I looked for it and didn't find it.

Bob