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Old Sep 19, 2004, 10:11 AM
user
Guest
n/a Posts
ARG! Concept-60 sr Side-2-side wobble driving me nuts! any suggestions?


Fellow Flyers,

I have a concept-60sr which likes to wobble side to side. It is
smooth in a hover, then slowly this wobble builds until the heli is
near unfly-able. The wobble is about 1 Hz.

Changing RPM will extinguish the wobble momentarily, then it comes
back. Changing engine mix doesn't seem to affect it.

Any constructive suggestions would be MOST welcome...

Old Sep 19, 2004, 04:11 PM
helinut
Guest
n/a Posts
Re: ARG! Concept-60 sr Side-2-side wobble driving me nuts! any suggestions?

Normally, a side to side wobble indicates the head speed is too low, however
if this is OK I would hazard a guess at the damper rubbers in the head. I
cant exactly remember, but the concept 60 was allways known for having soft
damping, so if the o rings have perished a bit it will be worse than ever.
Just a thought

"user" <user@here.com> wrote in message
news:8sdrk0d03gimf0er3s48i74m5fdctugjt9@4ax.com...
>
> Fellow Flyers,
>
> I have a concept-60sr which likes to wobble side to side. It is
> smooth in a hover, then slowly this wobble builds until the heli is
> near unfly-able. The wobble is about 1 Hz.
>
> Changing RPM will extinguish the wobble momentarily, then it comes
> back. Changing engine mix doesn't seem to affect it.
>
> Any constructive suggestions would be MOST welcome...
>



Old Sep 21, 2004, 08:11 PM
Beav
Guest
n/a Posts
Re: ARG! Concept-60 sr Side-2-side wobble driving me nuts! any suggestions?


"user" <user@here.com> wrote in message
news:jb4vk0t9dkm4mjdhebde11gfholp5sa4tt@4ax.com...
> Thanks for the info !
>
> What seems to cause the problem with the blades? Chordwise or
> spanwise CG?


Chordwise. they're usually a tad too tail heavy.
>
> When you say the CG is too far back, do you mean toward the tip, or
> the trailing edge?


Towrds the trailing. Some added weight to the leading edge (near the tip can
work if they're REALY bad.
>
> Can a set of blades be "fixed" with weight, or is it not practical?


It's "doable" but it's not as easy as just sticking a bit of weight on. the
usual method is to trench out a slot (a router does that spectacularly well)
and inserting and GLUEING lead rod in the slots. This needs to be done VERY
close to the leading edge too, so although is IS doable, it's a "bit of a
job" and probably not worth the time/cost. A pair or decent blades will be a
quick and easy fix.

>
> Is the "alternate" concept 60 head (that looks like a big 30-srx head)
> better?


Not better, just better at not wobbling:-) The SR head is stronger and more
"tnable" than the grown up 30 head, but I liked the feel of the first head
beter than the SR head. Some say the original head was more prone to boom
strikes too, but I never found that to be a problem.


--
Beav


Please note my E-mail address is "beavis dot original at ntlworld dot com"
(with the obvious changes)

Beavisland now lives at
www.beavisoriginal.co.uk


Old Sep 22, 2004, 12:11 AM
Steve R.
Guest
n/a Posts
Re: ARG! Concept-60 sr Side-2-side wobble driving me nuts! any suggestions?

"Beav" <beavis.original@ntloxoworld.com> wrote in message
news:10l1dsdtkb87obd@news.supernews.com...
>
> "user" <user@here.com> wrote in message
> news:jb4vk0t9dkm4mjdhebde11gfholp5sa4tt@4ax.com...
>> Thanks for the info !
>>
>> What seems to cause the problem with the blades? Chordwise or
>> spanwise CG?

>
> Chordwise. they're usually a tad too tail heavy.
>>
>> When you say the CG is too far back, do you mean toward the tip, or
>> the trailing edge?

>
> Towrds the trailing. Some added weight to the leading edge (near the tip
> can
> work if they're REALY bad.
>>
>> Can a set of blades be "fixed" with weight, or is it not practical?

>
> It's "doable" but it's not as easy as just sticking a bit of weight on.
> the
> usual method is to trench out a slot (a router does that spectacularly
> well)
> and inserting and GLUEING lead rod in the slots. This needs to be done
> VERY
> close to the leading edge too, so although is IS doable, it's a "bit of a
> job" and probably not worth the time/cost. A pair or decent blades will be
> a
> quick and easy fix.
>


Just a comment on this.

If you understand why we balance out a fixed wing airplane to be a little
nose heavy, then you should understand why a helicopter rotor blade that's a
little tail heavy (C of G too far back from the leading edge) will be
unstable in flight. The flybar and control systems on our helicopters can
compensate for a slightly tail heavy set of rotor blades but only to a
point. If the cord wise C of G is at or slightly ahead of the rotor blades
CL (center of lift), the rotor blade will be more stable, aerodynamically,
and the helicopter will be a "lot" more pleasant to fly.

FWIW!
Fly Safe,
Steve R.


Old Sep 24, 2004, 12:11 PM
user
Guest
n/a Posts
Re: ARG! Concept-60 sr Side-2-side wobble driving me nuts! any suggestions?

Fellow flyers,

Thanks for all the comments. I'm going to try again this weekend.
How important is it that the CG is the same between blades across the
short axis of the blade (I can't remember if this is chordwise or
spanwise)?











On Wed, 22 Sep 2004 04:06:42 GMT, "Steve R."
<srhodes13@houston.rr.nospam.com> wrote:

>"Beav" <beavis.original@ntloxoworld.com> wrote in message
>news:10l1dsdtkb87obd@news.supernews.com...
>>
>> "user" <user@here.com> wrote in message
>> news:jb4vk0t9dkm4mjdhebde11gfholp5sa4tt@4ax.com...
>>> Thanks for the info !
>>>
>>> What seems to cause the problem with the blades? Chordwise or
>>> spanwise CG?

>>
>> Chordwise. they're usually a tad too tail heavy.
>>>
>>> When you say the CG is too far back, do you mean toward the tip, or
>>> the trailing edge?

>>
>> Towrds the trailing. Some added weight to the leading edge (near the tip
>> can
>> work if they're REALY bad.
>>>
>>> Can a set of blades be "fixed" with weight, or is it not practical?

>>
>> It's "doable" but it's not as easy as just sticking a bit of weight on.
>> the
>> usual method is to trench out a slot (a router does that spectacularly
>> well)
>> and inserting and GLUEING lead rod in the slots. This needs to be done
>> VERY
>> close to the leading edge too, so although is IS doable, it's a "bit of a
>> job" and probably not worth the time/cost. A pair or decent blades will be
>> a
>> quick and easy fix.
>>

>
>Just a comment on this.
>
>If you understand why we balance out a fixed wing airplane to be a little
>nose heavy, then you should understand why a helicopter rotor blade that's a
>little tail heavy (C of G too far back from the leading edge) will be
>unstable in flight. The flybar and control systems on our helicopters can
>compensate for a slightly tail heavy set of rotor blades but only to a
>point. If the cord wise C of G is at or slightly ahead of the rotor blades
>CL (center of lift), the rotor blade will be more stable, aerodynamically,
>and the helicopter will be a "lot" more pleasant to fly.
>
>FWIW!
>Fly Safe,
>Steve R.
>


Old Sep 25, 2004, 12:11 PM
Beav
Guest
n/a Posts
Re: ARG! Concept-60 sr Side-2-side wobble driving me nuts! any suggestions?


"user" <user@here.com> wrote in message
news:1kr8l0pvt6oc81o97in4gv10u2s20rag6b@4ax.com...
> Fellow flyers,
>
> Thanks for all the comments. I'm going to try again this weekend.
> How important is it that the CG is the same between blades across the
> short axis of the blade (I can't remember if this is chordwise or
> spanwise)?


It's not VITALLY important that they're both the same, which is good,
because adjusting the chordwise CG is a PITA.

Spanwise balance is good enough if the blades hang level when attached to
the head and the head is OFF the heli and supported across two drinking
glasses.

I'm not getting involved in a "Dynamic vs. Static" balance argument. Suffice
to say that if the blades sit level when they're supported by the flybar,
they're balanced enough that your heli will be turbine smooth if everything
is straight.


--
Beav


Please note my E-mail address is "beavis dot original at ntlworld dot com"
(with the obvious changes)

Beavisland now lives at
www.beavisoriginal.co.uk


 


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