Kind of like a mirror... Anyway, got my Cal built back up and took it out to the field yesterday with formme2u and noticed a pretty good wobble when speeding up and slowing down the head. Found a bent main shaft. No problem, had a new one and changed it out in no time. It did get better, but I still have a very noticable wobble when hitting a certain RPM (about mid stick) that's pretty nerve racking to say the least. It hover's just fine, with no noticable vibrations, and the head is balanced. It's just an annoyance that could turn into disaster with too much wind, so I am just curious if anyone else has any ideas on what it might be.

Thanks in advance!!!
Rick

Good things come to those who wait, and PRACTICE!

If it wobbles in the air, the head speed is way too low. Increase the RPM to 1800 or greater.

If it simply wobbles somewhere as you are spooling it up, most likely it's because you didn't "straighten out" the MR blades before they started spinning, or they are loose enough that once you start up the head, they lose their position and until centrifugal force takes over and puts them where they should be, your head is woefully unbalanced.

Try tightening up your grip bolts a bit so that when you hold the heli in its side and shake it, the blades will retain their position.

Then make sure the blades are as straight out as you can get them before you start spooling up the head.

Dave

In flight, she's sweet. fromme2u thought the same thing on the ground, and we tightened up the blades a bit and made sure they were centered before start up and it still did the same thing. Once you get past that "sweet spot", it is fine. Right before it gets light on the skids, it's fine. Hovering is smooth, side to side, forward and back, no problem. Did a couple climb outs and they were fine. After landing, and running the head down, she wiggled bad at an RPM not known. It was short and sweet, but it was still kind of disturbing. It's worse on shut down than start up though. I only got one flight in yesterday due to weather, but I would like to figure this out before I take it back out if possible. I had my head speed checked last time I was out there and it was about 1700 (I think) in normal. I have idol up setup, but have yet to try it.

Rick

Good things come to those who wait, and PRACTICE!

Yeah, I'm not sure what it is. It starts the "Skid Dance" at about half stick, right before lift off and just after landing. I told him to get it in the air fast or bring the throttle back quick so it wouldn't self destruct on the deck. I know what the loose blade thing looks like because I've had it on mine. We checked his blades and tightened them up and got them to the same tightness that mine are at. He's got a brand new main mast and spindle shaft. We also balanced his blades. Only thing I could think of is maybe an unbalance clutch, clutch bell or maybe an unbalanced main gear. If we get to go out next weekend and we don't get it figured out, I will get some video of it and post it up.

Chad

US Navy Chiefs...Since 1893
118 Years of Dedicated Service.

Those small items wouldn't cause a big wobble. The clutch bell and fan being out of balance would give you foaming fuel, not a huge wobble. The main gear isn't spinning fast enough, and the mass is small enough that it also wouldn't make a noticeable wobble. I had a magnet on my main gear to run a bicycle speedometer as a tach, and the main gear was unbalanced for awhile. It wasn't noticeable.

Maybe the aluminum main rotor hub is bent. If this heli was rebuilt from a crash, it would be wise to check the main frames and servo mounts if they weren't replaced. Maybe a hairline crack somewhere, but I wouldn't hold out much hope that the problem lies there.

Getting into long shot territory now. Dampers in the head, maybe. Make sure the head was put back together correctly. Thrust bearings properly installed, if any shims were between the grips and the dampers, maybe one goe left out, or ended up on the wrong side with the other shim.

I presume the tail rotor is OK, nothing bent or unbalanced, and the belt properly installed.

Might just be some ground resonance due to the blades still not being aligned correctly. Are the skid struts particularly limber?

Dave

hey i feel ya boss, i have a cal 30 that does the same thing. right before liftoff there she goes doin the chicken dance. it is either spool up and lift off or shut or down. i have been told before that if the motor is to lean on the bottom end that it can have a wobble. i am not sure. i did not have this problem one week ago. but then i reset the motor to factory settings because i could not get a good tune and was not sure where i was anymore. anyway, as soon as i went back to factory settings her headspeed shot way up and then started the dance right before liftoff. i am still trying ot figure it out. but i think when i get the motor tuned right it will go away. just my .02.

Who keeps moving the ground closer to my heli?

We looked at it again today. I put on a set of carbon blades and it did the same thing. I am pretty sure it just doesn't like that rpm. Somewhere around 1550 and 1600. It's fine in the grass and I have learned to just get the head speed up enough to get it airborn and not deal with it on takeoff. Landing is another story. Just put it on the deck and slam the collective back. We took some video of it and Fromme2u might get it posted.

Other than that, she flies great!!! Did my first piro's today. And tried a quick nose-in hover about 3 mistakes high. Not quite ready for that though. It was pretty ugly, but (thanks to G3) I saved it with no problem. Next week I am going to do some FF. Wish me luck!!

Rick

Good things come to those who wait, and PRACTICE!

Ice

1- Check the stabaliser bar, for correct measurement equally propotioanl placement of the paddles as well as the centerline from the MR shaft.

2- Check the weights in the paddles make sure they are seated correctly. You can do a quick check and see if the weights are the issue by tapping them out and hoverin without weights.

3-If this is a used cal30 I would check the feathering shaft and the bolts that are holding down the thrust bearings and make sure they are equally tight and screwed in.

4- I had a previous problem where some dirt and oil got into the clutch linning which caused the clutch to slip and catch and inducing such a wobble, a wobble that would destroy my entire mr shaft mechanics if I continued hovering. Check the clutch linning for any dirt clean it if you can otherwise replace it.

The rpm you should be hovering is above 1700 to avoid and bad vibs like said.

Zero bubble....

Ok, I got a small video of it My Gallery down at the bottom of the page. Or you can just click

Cal Vibe Video

Shesha, where you been?

Anyway, We have checked the stab for measurement and balance. Have not tried the weights yet. will try that next time we fly. It is not a used bird. Brand new out of the box with only one crash. New spindle and main shaft. New balanced wooden blades with CG correct both ways (length wise and chord wise). It's hovering like its on rails, just on spool up and spool down it does the "Funky Chicken". Like Rick said, we took my blades off and put them on his bird and it did the exact same thing. In the grass it spools up fine with just a touch of the vibe but not nearly as much as it does on the pavement. I slowed the video down by 50% so you can see what it is doing. So bear with the sound as it is slow, too. It actually sounds pretty cool. Anyway, that is what we have tried and anymore suggestions are greatly appreciated.

Chad

US Navy Chiefs...Since 1893
118 Years of Dedicated Service.

Okay here is my 2 cents:

1- Your head speed seems to be okay.

2- Since you crossed the 1700 rpm threshold, the clutch bell is engaged into the clutch linning so there is no issue on that subject.

The only 4 things I can see from the problem you are facing,

1- Is flybar weights.

2- The MR blades maybe not be balanced correctly.

3- And the rubber bushings in the MR yoke / hub are worn out. Check the thrust bearings while you are at it.

4- That engine looks on the rish side, try leaning it out more, it sounds and looks to me as if it is 4 stroking before settling down.

Zero bubble....

Nothing wrong with your heli. You've changed to wider skids, and they are "sprung" differently than the stock skids. The problem is more severe on hard surfaces than on grass or other "softer" surfaces.

What you are seeing is ground resonance as the head spools up and down. It's more noticeable on hard surfaces as the hard surface has no "give" or damping qualities. Surfaces such as grass will change the resonance point a bit.

Notice that as soon as the skids are free of the ground, the heli settles down immediately. The two cures for ground resonance are to A)get airborne immediately, B)drop the MR RPM below the resonant point.

It would be my guess that if you kept the heli at that wobble RPM much longer, you'd end up with a heli that pretty much would do the funky chicken and spew parts everywhere.

By changing the skids, you've changed the dynamics of the heli's suspension. There's not a lot you can do to correct this problem if you use the same skids that you have on unless you can either stiffen the skids even more, or change their "springiness", or change the amount of stiffness in the heli to skid interface.

Other than the ground resonant feature, the heli flies and performs smoothly. Flybar weights are not the problem, a bent spindle or MR shaft is not the problem, nor has it anything to do with the clutch engagement or the motor tuning.

Dave

Would skid stops help any?

Chad

US Navy Chiefs...Since 1893
118 Years of Dedicated Service.

I guess you learn something new everyday

Zero bubble....

Good video, very helpful!
Possibly...just possibly...I think I saw the tail shake before the mainframe.
Could it be a tail/tail belt issue?

The Whirlybug Bit Me!

Skid stops would probably make things worse on pavement, as they would make it "stick" even more than it already does to the pavement.

A tail and/or tail belt issue would show up in the air and on the ground. The problem goes away as soon as the skids are off the ground -- ground resonance.

Dave

Cool Dave, and everybody else, I knew a video would help out. Thanks for all your help. Rick will be greatful, too, I'm sure.

Chad

US Navy Chiefs...Since 1893
118 Years of Dedicated Service.

I know someone who has a caliber 30 that does the same thing on hard surfaces. I think its just the nature of the caliber.

Thanks for all the replies and advice. I also believe it's just the nature of the beast. I am going to try to get the heli perfectly centered on the gear, as I think it might be off a little. Will do that this week and fly it Sunday. Will let you know how it goes.

Rick

Good things come to those who wait, and PRACTICE!

Tracking

Check the tracking. I had the same problem and had checked everything then finally found that the tracking was off. I chanced the tracking and the problem went away. It sounds like your heli is doing the exact same thing that mine was.

Checked it and the tracking is dead on. He has the Mavrikk Super Gear on it and we are thinking since we haven't centered it up on the frame, one side might have more bounce than the other and causing a difference in freq between sides causing the Chicken Dance. With the super gear, the stock holes don't match the Caliber frame. You have to drill 2 holes in between the stock holes to center it up. He hasn't done that yet and we will be knocking that out soon. Just need a day where both our military schedules meet. He has the gear, I have the drill press.

Chad

US Navy Chiefs...Since 1893
118 Years of Dedicated Service.