Part 20: Installing the "Upgrade Package" to our Zodiac CH 601 XL: Aileron Mass Balance

Continuing where we left off yesterday, now we install the mass balance to the ailerons. Since this was mandated by the UK LAA earlier this year for Zodiac XL owners there, we used their drawings (which was engineered and tested by the LAA), as specified in the AMD Safety Alert.

The aileron mass balance consists of an 18-inch arm (3/4" x 3/4" square alum. tube) with balance weight on one end, attached to the aileron with two new aileron ribs located on the outboard ends of both ailerons.

First we drill out the rivets in the top of the outboard end of the ailoron. (Note that we had drilled out the rivets in the top of the left aileron to install the trim servo angles).

We mark the position of the new aileron ribs (that will support the mass balance arm)...

Note that the 13 mm. block under the outboard end of the aileron shown above is for the built-in aileron twist.
Next we pilot drill:

We lift up the skin and insert the ribs, and drill them into position (through the pilot holes):

Steve lays out the balance arm (square tube) between the ribs...

...and drills it into position.

Now, Roger marks the position of the balance arm where it will go through the aileron skin:

and drills through the skin and trims the opening to fit the square tube as marked.

We then insert the assembly into the aileron:

The two new aileron ribs bolt together sandwiching the balance arm:

We rivet the aileron ribs in place and re-rivet the top aileron skin:

We use mild steel plates as the weights for the needed balance:

We clean them up and deburr them:

...and bolt them to the end of the balance arm:

The balance aileron assembly (outside of the wing):

With the balanced aileron assembly complete, we drill and cut out the opening in the rear channel of the wing where the mass balance arm will pass through (here we use a nibbler to cut out the opening):

We then position the aileron to the wing (we slide the balance arm through the above opening with the steel balance weights removed):

A view of the inside of the outboard (left) wing where the balance arm enters through the rear channel opening:

View from the side (end of the left wing):

Here Caleb checks the angle and verifies that the aileron balances with the correct amount of counterbalance on the balance arm:

View from the side (end of the right wing):

The balance weights on our mail room scale: 1 lb. and 3.8 oz. (560 grams). This was the required balance amount for the right aileron.

To obtain a perfect balance, the number of installed steel plates can be adjusted, as well as their size...

The installed balance arm with the balance weight (primed).

We also added the "skin protection plates" as prescribed by the LAA Balanced Aileron drawing.

The top "skin protection plate" over the balance weights:

Video Clip: Installing the aileron balance arm (part 1):
Video Clip: Installing the balanced ailerons (part 2):

Next, we'll install the upgrades to the spar center section.

Views: 1388


You need to be a member of Zenith Aircraft Builders and Flyers to add comments!

Join Zenith Aircraft Builders and Flyers

Comment by Jerry "Sonny" Webster on April 30, 2012 at 9:24am

How long is the balance arm?

Is the arm and the attached ribs assembled at an 87 degree angle?  If so it should be noted that the 3 mount holes in each rib will be in slightly different locations (not mirrored).  This is necessary to enable the front rib flanges to fall on the same plane as the aileron skin front web.

Comment by Sebastien Heintz on December 4, 2009 at 4:30pm
You can always regain access to the aileron balance weight by adding an access panel in the wingtip...
Comment by Jake Reyna on December 4, 2009 at 7:03am
That's why they call it Experimental. If you want to use Lead, as the Manufacturer, you can make that decision. If you want an access panel, so be it, and probably not a bad idea. As long as you adhere to Acceptable Standards, anything is possible. Not saying it is wise, just possible.

If you have your Airworthiness, you could decide not to install the balance weights, since testing showed that flutter isn't an issue, but I would do the rest of the Upgrade at minimum, eventually. Another option for those of us that don't have our Airworthiness is to install the balance weights for the inspection and then ....
Comment by John Thompson on December 3, 2009 at 8:59pm
I would think Lead would be superior to cold roll for the balance portion. Easier to trim and tailor to fit, and less bulky.
Comment by Charles (Chet) W. Chesnut on December 3, 2009 at 7:57pm
I would think the balance could be changed by installing a balance arm access hole.
Comment by Mark Hubelbank on December 3, 2009 at 7:37pm
It might be noted that unlike the fleet that really requires a balance, there appears to be no balance specification and that this is a one way trip. Once things are closed up, it can't be changed. Thus if future painting changes the balance, no adjustment is possible. I am not concerned. This design has been proved so flutter stable with no balance that a slight imbalance in the direction of being aileron heavy should be insignificant.
A minor note from the flutter theory, if one over compensates a balance so it is weight heavy, a whole new set of failure modes can be set up. I don't think these have been investigated at all and we should probably stay out of that region.

New from Zenith:

Weather Maps

Custom Instrument Panels
for your Zenith

Custom instrument panels are now available directly from Zenith Aircraft Company exclusively for Zenith builders and owners. Pre-cut panel, power distribution panel, Approach Fast Stack harnesses, Dynon and Garmin avionics, and more.

New Custom Upholstery Kits for your Zenith Aircraft:

Zenith Vinyl Upholstery Kits

New Zenith Apparel from EAA:

Zenair Floats

Flying On Your Own Wings:
A Complete Guide to Understanding Light Airplane Design, by Chris Heintz.

Builder & Pilot Supplies:

How to videos from

Developed specifically for Zenith builders (by a builder) these videos on DVD are a great help in building your own kit plane by providing practical hands-on construction information. Visit for the latest DVD titles.


Zenith transition and Sport Pilot training:

Quality Sport Planes
Cloverdale, California:

Wheels & Wings

Pro Builder Assistance

© 2018   Created by Zenith.Aero.   Powered by

Badges  |  Report an Issue  |  Terms of Service