Rudder counterbalance ?

[Richard Strickland]

Hi Peter,

I really haven't followed the threads much except for Jason's and a little
bit from others--but everyone seems to think the rear former is a must.
Were the failures on IC or E ?  I suspect the rudder hinging design and not
getting the rudder as close to the rudder post as possible may be part of
the problem as there about a half inch of exposed hinge pin already in the
design that could flex a bit and get things oscillating.  The post has to be
recessed a bit and the interior fin sides chamfered  so the rudder gets as
close to a 'seal' as possible.  I'm not nutty about that part of the design
as you really don't have a real seal.  I'd suggest making sure your hinges
are glued very well and  the rudder is snuggled up against the post and
recessed a bit.  Also,  pull-pull systems stretch a bit when new, so check
the tension even before the first flight as they will relax a little between
building and first flight--certainly after the first few flights.  If you
use another linkage system other than the double flat plate--make sure it's
solid as there isn't a lot of meat for a pin type that can control that much
surface.  Right now I'm sitting at about 11-3 all up 'E' with a very heavy
rec. battery.  With a couple changes(and some judicious grinding), I think
It'll make weight OK.

BTW, I've got pull-pull on rud.-elev. on mine and they have lost a bit of
tension since I installed them a couple weeks ago.  THAT was a lot of fun.
Finally got the battery system worked out and doing the batt. tray
tonite--with any luck, this weekend should be some nervous fun.

Good luck with yours,

Richard

----- 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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