REFLECTOR:Aileron Rigging 12.18.03

Sun Jan 29 20:01:06 CST 2006

In a message dated 12/18/2003 9:02:08 PM Eastern Standard Time, 
ALVentures at cox.net writes:
When I rigged my ailerons, I found it difficult to obtain the equal 2.5" up 
and 2.5" down that is called for in the manuals - for my 173 Elite RG

Rigging of the ailerons was a bit of a headache, at least for me, on my SE 
RG.  Referring to the manual helped – and hindered; there is the version in the 
manual that I got with the plane, and an improved version in the new manual; 
neither of which matched reality.  Perhaps my experience will be helpful to 
someone who hasn’t been there yet. 

My experience was aggravated by having push-pull cables with insufficient 
travel, so the first thing is to be certain that your cables have at least 3” of 
travel; and a little more is better. The ratio of the length of the bellcrank 
to the length of the aileron from the hinge to the back edge is very close to 
1.6; meaning that in order to get the total of 5” specified, you’d really 
like to have a minimum cable travel of 3 1/8”.  But Velocity specs the cable at 3”
, and that can work because you can gain a bit by the angles between cable 
and the bellcrank.   

As stated in the new manual the important first step is the get the rigging 
at the keel bellcrank setup to get full 3” travel, and equal in both directions 
from center.  It also says not to change the predrilled holes in the keel 
plate for the cable clamp.  In my case, these were mutually exclusive.  The cable 
clamp on the CP side was too close to the bellcrank, so that even with the 
rod end threaded fully on (shortest length) it only allowed about 1 ¼ travel to 
that side.  So I had to re-drill and move the clamp further over.  On the 
other side the angle of the cable clamp was such that it caused binding of the 
cable at the extremes of travel, so that needed to be reworked.  My experience 
may be unique, but don’t be surprised if you have to move the clamps.  It is 
unlikely that you can get full/equal travel in both directions with the rod ends 
threaded to the midpoint as suggested.

As has been previously pointed out; the position of the cable clamps (and 
configuration of the keel plate) do not result is a 90 degree approach angle 
between the cable and the keel bellcrank.  This actually results in slightly 
larger movement of the aileron, but makes the down travel of the aileron a bit 
greater than the up travel.  This we don’t like; so we compensate the other way at 
the aileron bellcrank.

The “old” manual says to rig the aileron bellcrank at the wingroot 10 
degrees forward from vertical with ailerons neutral; and adds that the objective is 
to get a 90 degree angle (approach angle) between the push-pull cable and the 
bellcrank.  Of course the angle from “vertical” will depend on the point at 
which you bring the cable through the firewall; which was not specified; so 
this isn’t very meaningful.  The new manual suggests bringing the cable through 
at about the center of the spar, at rigging for a 90 degree approach angle at 
neutral aileron. This is more definitive.

You can compensate for the approach angle at the keel by using an approach 
angle at the aileron greater than 90 degrees to get slightly more up travel than 
down travel in the aileron. However, insuring that you have 2 ½” down is 
important to good control, and without compromising on this, the amount of 
additional up travel that you can reasonable achieve, I found to be about ¼”, which 
is not likely to noticeably effect affect adverse yaw.

I found that an approach angle of about 100 degrees at neutral aileron was 
about the best I could get and still get full down travel.  You may get a little 
more than that (positioning the cable clamp forward) but you are limited by 
the forward travel ability of the bell crank.  The first photo shows the 100 
degree position.  Another way to rig to get a good result is to set the aileron 
at about 1” down travel with the cable approach angle of 90 degrees.

Ronnie suggested
 The other way is to attach the aileron cable at the wing so that the 
approach angle is more than 90 degrees.  Mine are attached at about 120 degrees, 
which results in more up travel than down travel.  My Velocity handles fine at low 
speeds, with just aileron control, similar to my Cessna 172.  If I need a 
sharper turn, I'll kick in more rudder, just like in my 172.  But normally, no 
rudder is needed, all the way down to the runway.  (But I also installed VG's 
before my first flight, these also improve low speed aileron control).

Apparently he was measureing a different angle (I’ll guess the outside 
included angle of the bellcrank from horizontal – giving 30 degrees forward from 
vertical) since 120 degrees approach angle (angle between cable and bellcrank, as 
shown in second photo) at neutral aileron would not allow sufficient forward 
travel to get full up aileron.  I’d also guess that the VG’s are the major 
factor in decreasing adverse yaw at low speeds, but have no flight experience to 
back that up.

You can see that I brought the cables through the firewall more toward the 
top of the spar to clear over the coolant connections to the wing-root radiator; 
obviously a need specific to my case. (Other non-standard features you will 
see there are a wing root extended inward to accommodate my narrower custom 
cowl; radiator air exit fairing, and an aileron fence. Tuft-testing by the guys 
in the local “EZ squadron” indicated the need for that fence, and Rodney Brim 
has confirmed it’s benefit.)

The third photo is full down aileron position.  Rigging in this fashion (vs 
the 90 degree at neutral) may reduce stick loads just slightly because you get 
maximum leverage at a down elevator position where the loads would be highest.

Disclaimer: None of this is to suggest that you should do anything different 
than the manual suggests (well; except where you have to).  It is just my 
approach, factoring in engineering judgment, analysis (did I hear over-analysis:), 
and information gained from the experience of others; and has not been 
reviewed by Velocity.

Now; back to those cowl fasteners . . .

Al
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