Rap90 vibration

[Splattt]

OK im running a converted rap 60 to 90 i've upgraded everything to the 90 specs and Im running 8.45 gear ratio on a ys91 mp2 combo 690 vblades, and 90 mm vpaddles, 105 tail blades, GV-1, 401 9253. head speed set to 1500 and 1750 idle up.


so here's the problem in normal mode the heli seems perfectly fine runs well but when u kick it up into idle up the tail starts twitching really bad...left to right aggressivly it gets so bad it start to woble the whole heli. I've checked all main shaft spindle, tail shaft all are perfect, The fan is balanced as well. all bearings are fairly new...only a dozen flights on them and I greased all bearings in my initail build. no crashes so I havent wacked out a bearing or something....

Im at my wits end trying to figure it out...it ran great on my os 70 i never had an issue with it then...untill I installed the 91... HELP!! IDEAS PLEEEAAAZZZEEE!!

Thanks
Matt

[cnsheets]

Have you tried simply turning down your gyro gain a touch?

[Splattt]

opps sorry forgot to mention that...thanks for reminding me...Im currently running the gain at 79...I've tried cranking it up doesnt make a difference...and turning it way down...doesnt help. Limit is set to 120 and atv's are at 100...I use a 8103 if that matters, w/ a 649 pcm receiver

[cnsheets]

Check for binding, Binding could be causing the tail to not be able to respond fast enough with the increase in tail rotor speed.


or

Just buy a 601!!!!!

[Splattt]

yup thats always the answer...throw more money at it!! Certianly an excuse to upgrade!! :D

I'll check out the tail to make sure it isnt binding...thanks for the ideas

[Splattt]

would a bad torque tube cause this sort of problem...I have the aluminum one and I'm running two bearings in the boom???? It's a brand new torque tube...but I have heard of people having problems with these.

[WillJames]

I don't think a bad TT would do this. Up and down vibration is usually what a bad TT causes. Sounds more like something that involves the gyro. I know this sounds obvious but is your tail rotor axle tight on the tail box output shaft? Thunder tiger axles are bad to get loose. The sad part is that if it is loose you have to remove the grips to tighten it up. OR... Get a standard vigor axle and grips and slider/links and it goes right on the output shaft. No more removing the grips to tighten the axle and you can remove the axle with grips and blades attached to balance on your highpoint by just removing two grub screws.

HTH,

[Splattt]

Good Idea...I'll give that a look as well...

THanks!!

[pookie8]

i had bad vibs from the engine causing this on my fury i balanced the fan and all is good no more twitching it wasnt bad until you cranked up the headspeed you may look there next

jeremy

[Sar]

Couple of suggestions:

Check the engine tuning.

Make sure your tailboom isn't pushed all the way into the main body of the heli, this puts pressure on the torque tube and causes weird things with the tail.

[Splattt]

THanks guys for all the tips I'll have to get back here in a week or so and let you know what the problem was...the Wife and I are moving in less than a week and I have all my heli stuff packed up. got out this afternoon and atleast got the 50 in the air for a bit but it got packed tonight as well...even G2 is packed up...Im heli-less for a week :cry:

[Buzzin Brian]

I have found that a lot of the time this stuff is found to be the engine tuneing. Look there first before you go through a bunch of stuff you don't need to. I have a friend that was trying to set up a new govenor, and it was doing some real weird stuff. Pulsing, and bad vibration. It turned out that the engine was running to rich. When that was sorted all was well. I have seen engine tuneing show up in the tail more times han I can count. Look into this. You might just be suprised.

[Splattt]

Thanks Brian...Its probably good im moving this week...I'm about to throw it out the window. Kinger(aka Mike King) wanted me to point out that its not a buzz vibration...but more like a tail kick.

[Buzzin Brian]

Still sounds like the engine. That is what they will do if the engine is running inconsisdantly. As the engine "burps" a little the head speed will actually drop off for a split second. Then the gyro lets go just a tad, and the tail kicks a little. Listen to the engine in conjunction with the littel tail "kick" and I bet the two will mesh. Lean it out a little a see what happens. If it gets worse, of course go the other way. But I bet it is running to rich. Just trying to help.

[Splattt]

Thanks...right now I'll take any suggestion I can get!!!