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Mikado Modellhubschrauber . GrandRC . CanoMod

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Avant Aurora - EFX - FX > Help with the shakes?
 
 
Doug L
Veteran
Location: Minnesota

Aurora
YS 91 SR
Hatori SB19
Radix 690 blades
90mm Vpaddles
Almost 3 gallons through the heli.



Main and Tail blades are CG'd and balanced. It's smooth at low headspeeds (1700), but starts to oscillate as the headspeed climbs. Lots of fuel foaming. The gears are very smooth with no backlash or tight spots. Cheesy video taken with a camera, but if it helps.:

http://www.youtube.com/watch?v=H8tfT2SH8CU

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06-25-2008 02:08 PM
HOMEPAGE  
 
 
Uppie
Senior Heliman
Location: Murrieta, CA

What headspeed are you running? After you fly it at full power for a bit do you still have the shakes? How do you have your dampners set up..ie. med/hard or hard/med? We have noticed this at lower headspeeds at the beginning of a flight when the motor is still rich and not running efficient. Generally around the 1800 rpm range once the motor cleans up and we get to 1900 no shakes.
06-25-2008 03:43 PM
 
 
rappyfly
Senior Heliman
Location: Toronto, ONT

Try some mild 3D flight and and end with hover to observe if the wobble still persist.

The wobble is related to the damper with dampering tube inside the head block. I had this while back and the cause was the dampering tube is not sitted in the center of the spindle shaft. I also lube the O-ring so it will settle in the damper cup better.

No problem afterward.

D
06-25-2008 03:47 PM
 
 
Dood
Elite Veteran
Location: America's Dairyland

Fuel Foaming

a head wobble doesn't explain the fuel foaming though. foaming comes from high frequency vibrations such as from the tail or the engine.
too hard to see foaming in the video.

(\__/)
(='.'=) The Dood abides.
(")_(")
06-25-2008 03:57 PM
HOMEPAGE  
 
 
Critterracing
Heliman
Location: totowa nj good old USA

very unstable.

CritterRacing R/C Heli Club.
06-25-2008 04:15 PM
HOMEPAGE  
 
 
creightoncarr
Veteran
Location: Missouri City, Texas - USA

Quote 
The wobble is related to the damper with dampering tube inside the head block. I had this while back and the cause was the dampering tube is not sitted in the center of the spindle shaft. I also lube the O-ring so it settle in the damper cup better.

Yeah, I had some wobble that was caused by this as well. The wobble was much more pronounced at lower headspeeds, probably because of the very stiff dampening. I measured the gap between the head block and the blade grips and one side was ~2.5mm while the other was ~2mm. The difference was actually noticeable just by eyeballing it. I disassembled the head and re-centered the tube on the spindle and the lubed up the dampeners so that when I tightened everything up it woudl properly center itself. That solved the problem for me.
06-25-2008 04:19 PM
 
 
Doug L
Veteran
Location: Minnesota

Thanks for the replies!

The oscilation starts at higher headspeeds 1850-1900. It's not noticable under loads, and if anything gets better inverted. It's the same type of shake you'd get with a stiff head at low headspeeds. The dampers are installed with the hard towards the center, and medium out.

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06-25-2008 04:27 PM
HOMEPAGE  
 
 
Doug L
Veteran
Location: Minnesota

creightoncarr, This is my next step. I was going to tear it down last night, but didn't have the c clip tool with me to pull the spindle.

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06-25-2008 04:29 PM
HOMEPAGE  
 
 
rappyfly
Senior Heliman
Location: Toronto, ONT

Mine was at 1850 and 1950 rpm as well. The wobble would persist at first flight after the fix, but I just flew it and I had no problem since.
06-25-2008 04:37 PM
 
 
Doug L
Veteran
Location: Minnesota

I thought it might just go away, but I'm at 3 gallons now and feel like I'm hurting the rest of the helicopter to continue to fly it like this.

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06-25-2008 04:47 PM
HOMEPAGE  
 
 
Chopper
Key Veteran
Location: Stow,Oh- oops, I mean St Louis, nope Stow again

Doug. Put some lube on the dampers anyway, but I suspect that if your problems get worse with higher head speeds, you have a gyro/tail issue or a radio/vibration issue. If your fuel is foaming...then you have something going on with the primary power line, the engine (usually) or the drive train to the tail. This same problem could be giving your tail/gyro some oscillation. You could also be shaking a servo pot loose at higher rpm causing a servo to move and give the oscillations.

Lube the dampers for the head, but track down the vibration. I suspect your fins are buzzing too?????

Paul Soha is a Futaba Team Pilot , Aurora Team Pilot, Wildcat Team Pilot, SAB blades
06-25-2008 07:25 PM
 
 
Chopper
Key Veteran
Location: Stow,Oh- oops, I mean St Louis, nope Stow again

Hey Doug. Are your ball links nice and lose? I'm looking at the video and I don't see a lot of fuel foaming. I don't see the fins buzing either, but the way the heli is all over the place, it gives me the impression that the ball links are too tight.

You should be able to twist the rods and they should roll smoothly on the balls. If not, they are too tight.

Paul Soha is a Futaba Team Pilot , Aurora Team Pilot, Wildcat Team Pilot, SAB blades
06-29-2008 05:53 AM
 
 
brentm
Heliman
Location: issaquah, wa

hey doug,
I had the same problem on mine - 1700rpm fine, any higher and bad vibration. Turned out to be that the bolts holding the landing skids to the bottom frame weren't tight enough. Have you checked them?
06-29-2008 08:02 AM
 
 
zx7rider
Senior Heliman
Location: Manalapan,NJ

I just had a slow wobble at the skids also with new avant FX/Prog Head. Turned out to be the spindle not being centered in Yoke. It was a real tight fit with tubing so I used a vise to center the spindle and reattached grips. Problem solved.

What goes up, Has to come down. Usually in 1 piece.
06-29-2008 09:47 AM
 
 
Doug L
Veteran
Location: Minnesota

Hey Guys,

Thanks for the replies and suggestions!

The other day I pulled the head apart and found the tubing on the spindle pressed in part way over one of the dampers. After a few attempts at getting the tubing to center and not be squished into the dampers I cut about 1/8" off the tubing and reinstalled. The wobble is pretty much gone and if it happens now it's at lower headspeeds the way most stiff heads act. What I saw as fuel foaming earlier was just pressurizing the tank at the beginning of a run. After I get down to 3/4 tank the fuel is very smooth, and I think any issues with the shakes now is engine related. I'm running a fuel magnet with the YS, but still seem to go lean at 1/4 tank. The helicopter flies very nice in forward flight and autos forever.

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06-29-2008 05:39 PM
HOMEPAGE  
 
 
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Avant Aurora - EFX - FX > Help with the shakes?
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