[SPAM] Re: [SPAM] Re: Rudder counterbalance ?

Earl Haury ehaury at houston.rr.com
Sat Apr 30 18:22:33 AKDT 2005


My son flies CL FAI Combat and has had a variety of wire (size / material / 
strands) analyzed for break strength, shock absorption, stretch, etc. The 
combat guys want wire with min diameter / max strength that will "give" a 
bit to absorb a hit (not unlike that designed to take a fish strike as 
fishing line), the "give" part is bad for R/C pull-pull linkage 
applications. The variety of wire variables are numerous and the data 
scant - hard to determine which wire to use without testing the stuff. 
"Good" wire can be expensive ($1/ft/1000ft).  High quality Kevlar cord is 
probably a better choice (Kevcord from Aerospace Composites or the cord 
offered by Matt Kababjian).

Earl
----- Original Message ----- 
From: "Grow Pattern" <pattern4u at comcast.net>
To: <discussion at nsrca.org>
Sent: Saturday, April 30, 2005 4:12 PM
Subject: Re: [SPAM] Re: [SPAM] Re: Rudder counterbalance ?


> Ed,
>       The bounce is coming from the springy tension in the wires. The 
> rudder can be moved before the servo arm moves. Troy told me that he and 
> TF use 2 strand CL wire to stop the "spring/stretch" effect on their 
> rudders.
>
> I figure if I can get to do it on the bench, then don't fly it like that. 
> If yours does not do it with the rudder hanging free, i.e. the tail-wheel 
> is off the ground, then you could be OK. Did you weigh the OTOP rudder?
>
> Eric.
>
>
> ----- Original Message ----- 
> From: "Ed Alt" <ed_alt at hotmail.com>
> To: <discussion at nsrca.org>
> Sent: Saturday, April 30, 2005 5:24 AM
> Subject: [SPAM] Re: [SPAM] Re: Rudder counterbalance ?
>
>
>> meant to say stored energy in the flexed hinges, not 'fixed' hinges
>>
>> ----- Original Message ----- 
>> From: "Ed Alt" <ed_alt at hotmail.com>
>> To: <discussion at nsrca.org>
>> Sent: Saturday, April 30, 2005 5:21 AM
>> Subject: [SPAM] Re: Rudder counterbalance ?
>>
>>
>>> Eric
>>> Just curious about more details on the hinging on the Impact. Having 
>>> just completed an OTOP, I wonder if the Impact has a similar 
>>> arrangement.  If I would have gone with the stock setup, it would have 
>>> meant that 4 small Robart hines would be hanging suspended in air over 
>>> 1/4" either side of the hinge line.  This seemed unacceptable, as I 
>>> figured it would just break the hinges in short order from all the 
>>> flexing of the unsupported plastic.  All I did was to add balsa filler 
>>> blocks for each hinge location.  It required cutting off the nub on the 
>>> bottom of the rudder to let me slide the blocks in, but that was easy to 
>>> do and reset the piece later.  Rock solid so far (7 flights) with an 
>>> 8411 converted to SA and this rudder is realtively heavy as well.  I 
>>> don't have the weight figure, but can get it from a friends unfinished 
>>> OTOP if it helps to unravel the mystery.
>>>
>>> I guess the point of asking about this is that there may be a combined 
>>> effect of the relatively high mass of the ruuder and the flex of the 
>>> hinges if something similar was in play with your original setup.  I 
>>> understand the way the oscillations could start/sustain with just too 
>>> much mass for the setup to contend with.  However any flex could make it 
>>> even easier to commence, as the servo's attempt to arrest rudder 
>>> movement would be hampered and secondary movements from the stored 
>>> energy in the fixed hinges would have to be dealt with milliseconds 
>>> later.
>>>
>>> Ed
>>>
>>> ----- Original Message ----- 
>>> From: "Grow Pattern" <pattern4u at comcast.net>
>>> To: <discussion at nsrca.org>
>>> Sent: Saturday, April 30, 2005 12:43 AM
>>> Subject: Re: Rudder counterbalance ?
>>>
>>>
>>>> Jim,
>>>>        I had already converted the IMPACT supplied rudder over to a 
>>>> regular Mylar hinge set up because of the side-play in the hinge-pin 
>>>> design supplied.
>>>>
>>>> It oscillated with the stick pin hinges at the first switch-on. I 
>>>> "pulled" the composite the rudder off and fitted it with a new 
>>>> stern-post and beveled the LE, on the rudder. Then I tried all of the 
>>>> servos previously listed.
>>>>
>>>> I then cut off the IMPACT rudder and fitted the new (red) one as you 
>>>> can see on RCU.
>>>>
>>>> As powerful as our new digital servos are I don't think that they 
>>>> "brake" the return swing as well as they initiate the first 
>>>> movement/response.
>>>>
>>>> It is noticeable that the bigger planes use multiple servos with the 
>>>> thinking that more power is needed. It is more stopping power that, 
>>>> IMHO, the we really need.
>>>>
>>>> I had an 8611 that bounced when used to drive a big old VISION rudder. 
>>>> After fitting a damper from an RC car it performs flawlessly.
>>>>
>>>> Regards,
>>>>
>>>> Eric.
>>>>
>>>>
>>>>
>>>>
>>>> ----- Original Message ----- 
>>>> From: "J.Oddino" <joddino at socal.rr.com>
>>>> To: <discussion at nsrca.org>
>>>> Sent: Friday, April 29, 2005 3:26 PM
>>>> Subject: Re: Rudder counterbalance ?
>>>>
>>>>
>>>>> Eric,
>>>>> What you were experiencing was oscillation of a servomechanism and 
>>>>> that
>>>>> could contribute to flutter and flutter could be what is breaking the
>>>>> Impacts but I've never heard anyone say they heard the rudder flutter 
>>>>> before
>>>>> the fuse exploded.  I don't think we understand the root cause yet.
>>>>> Right now I'm interested in the servo/rudder oscillation.  I'm 
>>>>> wondering if
>>>>> the real solution is completely due to the light weight rudder or/and 
>>>>> to an
>>>>> improved hinging system, or did both have the same hinge installation? 
>>>>> Can
>>>>> you hang weight on your present rudder and make it oscillate?  It sure 
>>>>> would
>>>>> be nice to cure this problem for all time because I've seen it on many
>>>>> planes.  I've never heard of it breaking fuselages before though.
>>>>> Thanks for all of your experimentation.  In the end it is more 
>>>>> important
>>>>> than understanding the theory.
>>>>> Jim O
>>>>> ----- Original Message ----- 
>>>>> From: "Grow Pattern" <pattern4u at comcast.net>
>>>>> To: <discussion at nsrca.org>
>>>>> Sent: Thursday, April 28, 2005 8:55 PM
>>>>> Subject: Re: Rudder counterbalance ?
>>>>>
>>>>>
>>>>>> Peter,
>>>>>>             I nearly got to go to bed.! ...Just ran 
>>>>>> downstairs...Tripped
>>>>>> over #2 Son who is back from carrier duty - he said we dropped a lot 
>>>>>> of
>>>>>> "stuff " out there. Planes all came back without ordnance,! No lost
>>>>>> planes....A  bit worried about the local girls however.. it must be 
>>>>>> that
>>>>>> uniform thing :-)
>>>>>>
>>>>>> Where was I?...Both supplied IMPACT rudders weigh 3.1 oz each without
>>>>> hinges
>>>>>> or horns
>>>>>>
>>>>>> Replacement rudders weigh 1.3 oz before covering.
>>>>>>
>>>>>> I tried the supplied rudder and five different servos including an 
>>>>>> 8611
>>>>> and
>>>>>> they all bounced back and forth badly and were potentially 
>>>>>> destructively.
>>>>>>
>>>>>> I then cut it off (the old rudder) and fitted a foam balsa 
>>>>>> replacement.
>>>>>> Tests showed no bounce with any of the servos. [8611, 8411, 8417, 
>>>>>> 8417
>>>>> with
>>>>>> 8411 gears and the heli 8311 (nylon gears except for output shaft.]
>>>>>>
>>>>>> I did managed to stop the bounce another way. I also tried using a 
>>>>>> single
>>>>>> wire as opposed to multi-strand. It did work but once in a while I 
>>>>>> saw bad
>>>>>> "hunting" as it located the center.
>>>>>>
>>>>>> These Impacts have polyurethane foam liners about 1.5-mm thick with a 
>>>>>> skin
>>>>>> of glass inside that. They are pretty stiff to begin with.
>>>>>>
>>>>>> I did notice that a vertical former at the rear of the canopy area 
>>>>>> made a
>>>>>> huge difference in stiffness. Also switching to a four bolt wing 
>>>>>> retention
>>>>>> system made the center more rigid.
>>>>>>
>>>>>> I have abused my IMPACT #1 and hope that all the mods keep doing 
>>>>>> their
>>>>> job.
>>>>>> I still think that the rudder is simply just too heavy and the
>>>>>> spring/stretch in the pull-pull wire combines to oscillate the rudder 
>>>>>> just
>>>>>> like PIO.
>>>>>>
>>>>>> Regards,
>>>>>>
>>>>>> Eric.
>>>>>>
>>>>>> ----- Original Message ----- 
>>>>>> From: "Peter Pennisi" <pentagon.systems at bigpond.com>
>>>>>> To: <discussion at nsrca.org>
>>>>>> Sent: Thursday, April 28, 2005 6:19 PM
>>>>>> Subject: RE: Rudder counterbalance ?
>>>>>>
>>>>>>
>>>>>> >
>>>>>> > I am aware of the braces and internal formers. There have been 
>>>>>> > recent
>>>>>> > cases
>>>>>> > of failures with all the supporting structures in place.
>>>>>> >
>>>>>> >
>>>>>> > Eric,
>>>>>> >
>>>>>> > How much do your new rudders weigh typically?
>>>>>> >
>>>>>> >
>>>>>> > Regards,
>>>>>> >
>>>>>> >
>>>>>> > Peter
>>>>>> >
>>>>>> >
>>>>>> > Peter Pennisi
>>>>>> > Pentagon Systems QLD Pty Ltd
>>>>>> > P.O Box 4280
>>>>>> > Eight Mile Plains
>>>>>> > QLD 4113
>>>>>> > Australia
>>>>>> > Phone:    61+0738414234
>>>>>> > Fax:        61+0738414264
>>>>>> > Mobile:   0408007206
>>>>>> > Email: pentagon.systems at bigpond.com
>>>>>> >
>>>>>> > -----Original Message-----
>>>>>> > From: discussion-request at nsrca.org 
>>>>>> > [mailto:discussion-request at nsrca.org]
>>>>>> > On
>>>>>> > Behalf Of Atwood, Mark
>>>>>> > Sent: Friday, 29 April 2005 4:56 AM
>>>>>> > To: discussion at nsrca.org
>>>>>> > Subject: RE: Rudder counterbalance ?
>>>>>> >
>>>>>> > Well...I can certainly speak to needing this in the Rev Pro...which 
>>>>>> > I'm
>>>>>> > guessing isn't a whole lot different than the Impact in 
>>>>>> > construction.
>>>>>> > The fuselage buckled and snapped in half in flight (and yes...it 
>>>>>> > still
>>>>>> > managed to fly to the ground with relatively little damage).  Added 
>>>>>> > the
>>>>>> > light (4gm) "Ladder" crutch plate behind the wing and no problems 
>>>>>> > at
>>>>>> > all.
>>>>>> >
>>>>>> > I have a photo of the brace if someone is interested...contact me
>>>>>> > offline.
>>>>>> >
>>>>>> > -Mark
>>>>>> >
>>>>>> > -----Original Message-----
>>>>>> > From: discussion-request at nsrca.org 
>>>>>> > [mailto:discussion-request at nsrca.org]
>>>>>> > On Behalf Of Wayne Galligan
>>>>>> > Sent: Thursday, April 28, 2005 2:26 PM
>>>>>> > To: discussion at nsrca.org
>>>>>> > Subject: Re: Rudder counterbalance ?
>>>>>> >
>>>>>> > I have had conversations with a few people that own these airframes
>>>>>> > (Impact)and they along with a few others have strengthened the fuse 
>>>>>> > in
>>>>>> > two
>>>>>> > ways.  A ladder  type frame in the fuse from the wing t.e back to 
>>>>>> > the
>>>>>> > stab
>>>>>> > area and another put a stiffener(former) at the front of the wing 
>>>>>> > area
>>>>>> > to
>>>>>> > decrease the possibility of compression of the fuse in this area. 
>>>>>> > It is
>>>>>> > believed that compression of the fuse in this area contributes to a 
>>>>>> > wave
>>>>>> > progression all the way back to the tail section.  The tail section
>>>>>> > being
>>>>>> > the smallest and weakest area gets whipped and eventually the fuse
>>>>>> > breaks or
>>>>>> > contributes to tail feather flutters.
>>>>>> >
>>>>>> > From what I've heard....  FWIW
>>>>>> >
>>>>>> > WG
>>>>>> >
>>>>>> >
>>>>>> > ----- Original Message ----- 
>>>>>> > From: "Peter Pennisi" <pentagon.systems at bigpond.com>
>>>>>> > To: <discussion at nsrca.org>
>>>>>> > Sent: Thursday, April 28, 2005 4:29 AM
>>>>>> > Subject: Rudder counterbalance ?
>>>>>> >
>>>>>> >
>>>>>> >>
>>>>>> >>
>>>>>> >> Hi all,
>>>>>> >>
>>>>>> >>
>>>>>> >> Most of you would be aware that a number of Composite ARF "IMPACT"
>>>>>> > have
>>>>>> >> failed from suspected rudder flutter.
>>>>>> >>
>>>>>> >>
>>>>>> >> I raise a couple of questions to this forum;
>>>>>> >>
>>>>>> >>
>>>>>> >> I know that the purposes of counterbalances are to reduce the 
>>>>>> >> loads on
>>>>>> >> servos and linkages in our application but what are the side 
>>>>>> >> effects.
>>>>>> >>
>>>>>> >> Can a rudder counterbalance create undesired torsional stresses on 
>>>>>> >> the
>>>>>> >> fuselage?
>>>>>> >>
>>>>>> >> Can a poorly configured and tensioned pull-pull linkage to the 
>>>>>> >> rudder
>>>>>> > be
>>>>>> >> more susceptible to flutter if the rudder has a counterbalance?
>>>>>> >>
>>>>>> >> What other types of forces are at play with counterbalances?
>>>>>> >>
>>>>>> >> I am just trying to find a reason for the relatively high failure
>>>>>> > rates
>>>>>> >> against this design.
>>>>>> >>
>>>>>> >> It is the same old thing- why are some people having problems and
>>>>>> > others
>>>>>> >> don't. (Similar story to 4-stroke exhaust headers)
>>>>>> >>
>>>>>> >> I will be test flying my model soon so I am obviously concerned.
>>>>>> >>
>>>>>> >> Regards,
>>>>>> >>
>>>>>> >> Peter
>>>>>> >>
>>>>>> >>
>>>>>> >>
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