Trim Question--Long

[Del K. Rykert]

Boy..
    If I could only remember half of what I learn on the list. I sure buy it
Troy.

        Del

----- Original Message ----- 
From: "Troy Newman" <troy_newman at msn.com>
To: <discussion at nsrca.org>
Sent: Sunday, April 18, 2004 6:40 PM
Subject: Re: Trim Question--Long


> Dan,
>  since the plane has a counter balance.......I would say I have seen some
> funny things happen with the counter balanced rudders that so many planes
> have today.
>
> Not totally sure why its happening but probably do in some part to control
> Snatch. This happens when the control surface tab grabs the air and
reaches
> a point where it overrides the flight forces normal on the surface. What
> happens is when you reach a certain point in rudder deflection the tab
gabs
> and all of a sudden the load on the servo reverses from pulling the left
> cable to hold left rudder...to the result of the tab...trying to get more
> left rudder than commanded. The servo is then driving right to hold the
> commanded position left rudder. Not sure if I'm explaining it correctly or
> not....
>
> Where I have seen this happen most is rolling from inverted to a knife or
an
> 8th point position.  The coupling in the model is mixed perfectly for
knife
> edge flight even to the point of extreme rudder throws and knife edge
> loops....but when the model is rolling in certain orientations the
coupling
> changes. I have seen this tendency with almost all counter balanced rudder
> models I have flown. The counter balance works very well at making the
> rudder servo work less....However in these certain conditions its putting
> bigger loads on the servo in the snatch condition...
>
>
> My theory on this as rolling from inverted the rudder and specifically the
> tab is in clean air below the model....it digs in and has some more
> effective responses than we are used to. Since you are flying in a normal
> almost no rudder or no rudder situation perhaps the tab is catching in the
> clean air....How is your rudder trim? Is the rudder straight to the
> fuse....not the tab but the rudder...Look from the belly of the model
while
> inverted back at the rudder and see if its tracking straight...If it is
here
> How is the tab centered on the fin....Basically is the rudder straight,
and
> tab sanded correctly to track straight... Next rudder cable tension?
Tighter
> cables may help.....Next geometry on your pull pull system? Can you get
more
> leverage for the servo.....Sometimes crossing the cables can do this.
> Sometimes not.
>
> Solutions I have found work.....Better rudder servo. If you are not using
an
> 8411SA this is what you need...I even know of some very loyal Futaba
flyers
> that found the 8411SA to be a solution to their rudder problems. Not
bashing
> any servos here just stating the facts I have experienced. I minimized
this
> on my Smaragd with a rudder tab using the 8411SA....then I tested an 8611
on
> the rudder and the issue went away...This proved to me it was servo power
> and precision related.
>
> Better geometry on the linkage. Final thing is the knife and put the
rudder
> tab on top of the fin with some clear tape and see if it solves it. We
have
> found that it can be minimized using better servo setups...and eliminated
> with the removal of the tab. This is one really good reason to have a
> removable rudder...You can just take the rudder off...remove the tab and
> then attach it temp style with tape to the fin and fly it....
>
> Another solution to minimize the problem is CG....Change the way the model
> is flying....Maybe add some nose weight and see if the problem minimizes
And
> I don't mean a 1/2 oz....Like 4-6-8ozs and see what happens. As the guys
on
> this list gasp for air....I'll say that big CG changes can tell you a  ton
> about the way the model is flying. If you make a huge shift forward like
> 4ozs on the nose. Most models will tend to chage the little settle down
> things like you are dealing with. If the 4ozs helps a littl...then go
> another 4ozs. I hate to say move the CG back as I feel many pilots fly
their
> CG too far aft as it is......
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>
>


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