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HomeAircraftHelicopterCentury Radikal G20-30 N640 Hawk Predator › Radical G30 Tail Bounce
03-11-2013 12:53 AM  5 years agoPost 1
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rrApprentice

Moses Lake, Wa.

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Was helping a friend today with his G30. Having a problem with a tail bounce up - down . We have replaced the carbon side frame on the tail , because the right side started to show signs of bearing slop . Replaced the the stock plastic blade grips with century's Alum grips . Running Curtis Youngblood 105mm tail blades .

Just can't figure out the tail bounce up-down . The side to side holds good .

This G30 is running the WooKong-S system . Head speed is 1740 rpm , JR8717 on the Cyclic . With the WooKong in GPS-ATTI mode in a hover the heli is rock solid , just the tail bounces up-down slightly .
Any Ideas on what to check for would help?

Thanks
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Whiplash Gasser -Raptor X50F - Raptor 90se

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03-11-2013 02:22 AM  5 years agoPost 2
RM3

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Killeen, Texas - USA

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One place would be to give a detailed look over is the head...

I once had an issue with tail bounce on a G20, I checked everything...turned out that it was one of the blade grip bolts had worn a bigger hole into the grip bolt hole...another thing to check would be to see how tight each of the blade grips is....rule of thumb I use is that the grip needs to be just tight enough to hold the blade when held sideways...

showing a preference will only get you into trouble, 90% of everything is crap...

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03-11-2013 06:16 PM  5 years agoPost 3
madog

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Mountain View, CA USA

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The speed of the bounce will help narrow down where it is from. Fast would be tail related.

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03-11-2013 09:07 PM  5 years agoPost 4
Gearhead

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Vt

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now that I have thought about this I did have this problem once on my 50, it was the NHP tail blades, and the tail bobbed up and down

Jim
Buzz Buzz Buzz

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03-11-2013 09:34 PM  5 years agoPost 5
Triggr Happy

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Ontario, Canada

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If it is a slow wobble up and down while hovering, it is likely a head speed issue, bump it up another 50-100rpm and it should go away.

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03-11-2013 10:04 PM  5 years agoPost 6
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rrApprentice

Moses Lake, Wa.

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Thanks all for the suggestions .
I'm going to take the tail hub off , and check the balance of the hub with the grips and blades on a High Point balancer this afternoon .

If the bounce is still there , I will raise the head speed up and try that .

This Heli is new , and has about 2 gal. thru it so far. I know the main blades are alittle on the snug side . But not that tight . I run my 90 size all the time with about the same tension on the blade grips . With no issues . The tail blades tension is just enough to hold under there own weight .

Again thanks for the help and suggestions

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Whiplash Gasser -Raptor X50F - Raptor 90se

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03-12-2013 02:11 AM  5 years agoPost 7
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rrApprentice

Moses Lake, Wa.

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Triggr Happy , Your suggestion did the trick . Raised the head speed up to 1850 . Then raised to 1900 rpm were it was the happiest . The bounce went away .

Also checked the balance on the tail rotor , wasn't bad just a little off . rebalanced , all is good .

Thanks again for all the imput from everyone .

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03-12-2013 09:17 PM  5 years agoPost 8
Triggr Happy

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Ontario, Canada

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I would think you should not see the bounce / wobble at 1850, normally the wobble indicates too slow a head speed. You would normally see it on a heli around the 1500-1650 range.

If you have to go that high an rpm to make the wobble go away, I would check the condition of the dampers. Grab the head by the grips and hold the heli down, see if the grips wiggle around on the hub at all (to check for worn dampers). If the shims are not installed properly then you can easily destroy a set of dampers in 2-3 flights.

If the dampers are ok, try harder ones, if you dont already have hard ones.

I would also check main blade balancing.

What type of main blades are you using?

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03-12-2013 09:25 PM  5 years agoPost 9
fla heli boy

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cape coral, florida

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agree. Back in the early 90's, a high HS was 1650-1700. We didn't get the wobbles until WELL below that.

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03-13-2013 01:29 AM  5 years agoPost 10
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Moses Lake, Wa.

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Triggr Happy ,

The head dampers are new , My freind got them from a vendor at IRCHA this last year for him to try . The stock dampers that came with the heli were shot after about 2 tank of fuel .

Not sure of the Vendor right now , But I know he got 3-4 different sets that was given to him . I installed the next to stiffest dampers on the heli . It has never been flown hard at all . just hovering to get the DJI set up . And to break the engine in .

The main blades are Rotor Tech F3C-720's Scott Gray .From Century Helicopter . The CG on the blades are perfect . Along with the balance is spot on .

Just not sure on this bird , I have checked everything more than twice . And rechecked again . The drive train is as smooth as butter . Nothing binds , or moves with any kind of notchy binding manner .

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03-13-2013 03:37 AM  5 years agoPost 11
Billme

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MS

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How did you tighten the head? Jesus bolt first, and then the split bolts?
I do the split bolts first, then the jesus bolt, seems to center the head better...might as well try it
Make sure the slits are all lined up perfect with each other on the insert for the 10 mm shaft..
I have increase the split deeper on the insert to allow better centering near the Jesus bolt too when the split bolts are tighten...

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03-13-2013 07:27 PM  5 years agoPost 12
Triggr Happy

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Ontario, Canada

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The stock dampers that came with the heli were shot after about 2 tank of fuel .
If the shims are not installed properly then you can easily destroy a set of dampers in 2-3 flights.
Just because they are new does not mean they are any good. Hence why I mentioned the shims. I have never used anything but stock century dampers on any machines since I started flying them about 7 years ago.

If the shims are not right, your dampers will be toast in no time.

I use the Rotor Tech 720 FAI blades on my predator 90, mainly for doing really cool auto's

I occasionally get a little wobble as well with those blades, but only for a narrow rpm range when the head slows down in an auto.

Maybe later on try a set of Rotor Tech 710's, they still auto well and give a bit better cyclic rates.

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