[NSRCA-discussion] Elevator setup with anhedral stabs

Fri Sep 21 10:06:44 AKDT 2007

In regards to control horn positions etc.  The anhedral stab I am setting up
is a replacement for a standard stab with servos in each half.  I used the
same control horns, rods and servos.  Right servo stayed on right side etc.
Even with trying to keep everything the same, end points needed to be
adjusted on one servo to match throw to the other one.  Some slight change
in control horn positioning, control rod angle etc caused a difference.
Control horns are Chip Hyde, so not adjustable. (I would only use that type
with twin servos that can be adjusted individually.  With DEPS type systems
an adjustable control horn makes much more sense.)

Stuart

-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of J N Hiller
Sent: Friday, September 21, 2007 1:44 PM
To: NSRCA Mailing List
Subject: Re: [NSRCA-discussion] Elevator setup with anhedral stabs

Stuart, I see your problem and have no direct reference solution. Unlike the
direct comparison using alignment sticks on a straight stab every thing I
can think of involves an indirect reference and potential for error.

Jim, I have eliminated the half turn adjustment and duel servo balancing
problems by using a full pull-pull cable system from a single servo driven
bell-crank. The elevator travel can be balanced extremely close and is the
tightest system I have ever installed.
Yes bending the control horn repositions the clevis pin, which changes the
pushrod to hinge line angle adding or decreasing differential travel. We did
this before computer radios and I still do it to correct a miss-located
control horn. Dean Pappas covered this issue quite well in his trimming
series of articles in Flying Models.
I designed my Option-120 in CAD including component and control system
installation. During this process I have done exactly as you suggest to
layout differential deflection angles. If you will send me some actual
installation information I will layout some examples showing the resulting
differential travel.
I started drawing F4-U's when I was about 10 years old and still like to
draw. I have CAD drawings of motors, servos, clevises etc. that can be
easily imported into assembly drawings.

Jim Hiller

-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of Woodward, Jim
Sent: Friday, September 21, 2007 6:45 AM
To: NSRCA Mailing List
Subject: Re: [NSRCA-discussion] Elevator setup with anhedral stabs

HI Stuart,

I saw your RCU post.  I use 12" long triangle stock pointers clamped
onto the elevators to see if they are tracking or not.  I like your idea
of using the 1/8" CF rods though too.

The anhedral stab is not as easy to line up.  You might be left to
positioning the fuselage on a table with the tail in the air and solidly
hold down the plane (maybe some masking tape to make sure the fuse isn't
going to move once you put it in place on some hard resting points, off
the foam tires too).

Position your pointers on the elevators and move them to full stop, then
take a straight down measurement to the table.  Between a measurement
and the "eye-ball" I bet you will be VERY close - certainly within the
1/2 turn of adjustability on a clevis for up/down adjustment.  You can
more than likely get within the 1/2 turn precision just with your
eyeball if the plane is solidly position on the table.

Speaking of the 1/2 turn of precision a clevis offers, sometimes I
really just want to see the tracking perfect within the normal flying
rate of 10'ish degrees of throw.  If it is good through the 10 degrees
up and down, I'm not so critical of what happens at 18 degrees of throw.
If the geometry of the servos and pushrod, control surface horn, or any
other little gremlin is not equal to the other side, you can't really
get perfectly matched up and down throw through the whole travel.  What
really sucks is if you have DEPS system in stalled, and say the up
travel is equal, but the down travel is not equal on one 1/2.  It can
happen.

What would be interesting to see is a blown-up diagram of this.
Supposing the surface is hinged perfectly, the control horn moves in an
arc equal to its length.  What if you bend the control horn aft thus
moving the clevis attach point slightly aft, lengthen the clevis to keep
the neutral point the same, then see if it "changes" how much the
surface moves up and down in one direction.  Since the control horn
moves in an arc, this would (could??) mean that more of the motion is
going vertical relative to the other side.

Thanks,
Jim W.

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

From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Stuart
Chale
Sent: Friday, September 21, 2007 9:24 AM
To: 'NSRCA Mailing List'
Subject: Re: [NSRCA-discussion] Elevator setup with anhedral stabs

I tried this question on RCU and didn't get any great answers so I
thought I
would try here.

Does anyone have a good method for comparing the throw of both elevator
halves on anhedral stabs?  With a regular stab I use a 15 inch piece of
1/8
carbon fiber rod on each elevator meeting behind the rudder and compare
their track with movement of the elevator stick.  This is much more
accurate
to me, than clip on throw meters or ruler measurements.  With anhedral
stabs
the two rods will separate as you give up elevator and come together and
cross with down elevator.  I guess you can measure the height of the end
of
the rod from the table at different positions but does anyone have a
better
method?

Thanks,
Stuart

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