[NSRCA-discussion] Rudder pull-pull

Tue May 13 03:42:46 AKDT 2008

 I have done it on a World Model Super Sports Senior. The plane weighs 8 lbs
and the bell crank was made by World Models. 

 Five years and it still works perfect with no wear, no slop.

  _____  

From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of
vicenterc at comcast.net
Sent: Tuesday, May 13, 2008 7:35 AM
To: General pattern discussion
Subject: Re: [NSRCA-discussion] Rudder pull-pull

Have someone done the rudder bell crank system in a pattern plane?

--
Vicente "Vince" Bortone

-------------- Original message -------------- 
From: "Lance Van Nostrand" <patterndude at tx.rr.com> 

Jim,

I've done this on heavier IMAC style planes but never thought it could be
done light enough for pattern.  If you have thoughts on this, I am
interested.

Thanks,

--Lance

----- Original Message ----- 

From: J N Hiller <mailto:jnhiller at earthlink.net>  

To: General pattern discussion <mailto:nsrca-discussion at lists.nsrca.org>  

Sent: Sunday, May 11, 2008 8:58 PM

Subject: Re: [NSRCA-discussion] Rudder pull-pull

Lance I use a bell crank to get equal length arms and control horns. This
allows continued use of full servo travel and removes the cable tension from
the servo shaft and mounting grommets. The servo is connected with a short
link with ball end fittings. It works well especially on elevators.

Jim Hiller

-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of Lance Van
Nostrand
Sent: Sunday, May 11, 2008 5:38 PM
To: General pattern discussion
Subject: Re: [NSRCA-discussion] Rudder pull-pull

You all are so fast on this stuff that by the time I read the post the
thread is old.

Ackerman exists if the rudder has control horns (as opposed to a wheel,
which is very hard to build into a rudder).  The only ideal way to have
constant tension is to use a symmetrical servo arm that is offset from its
pivot (servo screw) the same amount as the rudder control horn attachment
point.  This will work every time and is simple, however with a 1" thick
rudder post and two 3/4" control horns you will need a 2.5" servo arm (1.25"
each side of center) and the servo throw will only be equal to your rudder
throw (maybe about 30 degrees) which gives you poor mechanical advantage and
poor use of your servo.  If you use a shorter servo arm and more servo throw
the cables will go slack.  The round servo wheel is a compromise by
offsetting this slack tendency and letting you get more servo throw.  It's
not a perf ect match but it can be very close.

Anyone that can do the math on this and present a complete answer can get a
recommendation to advance from a shade tree aerodynamicist to an apprentice.

--Lance

----- Original Message ----- 

From: John <mailto:jpavlick at idseng.com>  Pavlick 

To: General pattern discussion <mailto:nsrca-discussion at lists.nsrca.org>  

Sent: Friday, May 09, 2008 9:02 AM

Subject: Re: [NSRCA-discussion] Rudder pull-pull

Chris,

 The only benefit that I know of is that you don't have to deal with the
Ackerman angle like you do with arms / horns. The cable is always the same
distance from the hinge center no matter what the angle is.

John Pavlick
http://www.idseng.com <http://www.idseng.com/> 

----- Original Message ----- 

From: chris moon <mailto:cjm767driver at hotmail.com>  

To: nsrca-discussion at lists.nsrca.org 

Sent: Friday, May 09, 2008 9:13 AM

Subject: [NSRCA-discussion] Rudder pull-pull

Can someone explain the benefits (real or otherwise) of the pull-pull 
wheel type rudder servo arm vs. a regular servo arm? Is there some real 
benefit, or is it bling?
Thanks

Chris

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