Rigging Checks and adjustments

Rigging Checks

Mechanical Difficulty:

This is a job which an owner/pilot can do without any additional supervision or sign off, because you are only CHECKING the control travel, not making adjustments to the primary flight controls.

Checking the rigging on a Grumman is a very simple job if you have the factory templates shown in the Maintenance Manual. They are available for rent from FletchAir on a weekly basis.

Many rigging checks can be made without the factory templates, with slightly more effort. Each year at the AYA Convention, the rigging templates and the Rigging Check volunteers are available to help owners check for discrepancies in their rigging of their planes.

The goal of rigging checks (and adjustments as needed) is to bring the plane into compliance with its Type Certificate Data Sheet specs, and to improve the handling and performance of the plane. In the hundreds of planes checked at the AYA conventions since 1998 at the first Cody Convention when I spearheaded the effort to start the riging checks, I have yet to see ONE PLANE that had correct rigging on all surfaces. All that I have personally checked had at least 2 measurements out of spec. Too little or too much control displacement, but always at least 2 out of spec!

Significant performance changes can be obtained by removing the errors and getting theplane correctly rigged. At conventions its been sort of a tradition to help correct the plane that "wins" the worst rigged plane award. There have been stabilizers without enough UP travel that caused the pilot to always land at 90 mph, planes with bent outboard aileron bearing brackets that had made it impossible to fly "hands off" since the plane was purchased by its current owner, and an amazing array of other rigging errors that induced all sorts of strange handling characteristics that the owners just put up with. Then there were those rigged so poorly that they had significant performance deficits. Some people have spent many thousands of dollars for "speed mods", and found more performance in FREE rigging adjustments than in all their combined speed mod improvements.

Rigging Adjustments

Mechanical Difficulty: -

Any adjustments to the flight controls requires appropriate certificates and a log book sign off. You will need an Airframe mechanic to supervise and sign off the following work.

After rigging checks determine that there are control travels outside the specified limits, the next step is to attempt to correct the errors. On the elevator and rudder, the adjustments are under the plastic tail cone. They consist of 4 stop bolts with jam nuts on them to prevent unwanted movement of the stops. Loosen the jam nut on the stop in question (7/16" offset box end wrench is the best tool), and then turn the stop bolt IN for more travel and OUT for less. Re-check with template or protractor to confirm the adjustment, and when correct, re-snug the jam nut. Most of the Type Certificate Data Sheet specs give a range of travel that is acceptable. Adjusting to the maximum travel will give the most control authority, and may provide the last bit of control that you need some day.

The Elevator trim can not be "adjusted" for total travel, but it can be adjusted to center the travel such that the UP and DN limits are correct. The most common cause of elevator trim miss-rigging is lack of maintenance. The trim wheel in the console between the front seats drives the indicator, and it also drives a pair of bevel gears that convert the motion of the wheel into rotation of the trim drive, a long aluminum tube just above the floor in the tail cone. Failure to clean the old dried grease and grit from the gears, from the bearings that support the trim drive tube, and from the threads and actuator nut in the plastic tail cone can lead to excess torque required to move the trim. This can cause the bevel gears to slip, and cause the trim position indicator to no longer be sync'd with the actual position of the trim. The fix is to clean all the trim drive parts and re-lubricate them, and then set the indicator to match the elevator trim by disengaging the bevel gears and re-meshing them. Its also important to check the backlash in the gears and adjust the depth of their engagement, so that the trim won't easily return to its mis-adjusted state.

Flaps are rigged by adjusting 2 pairs of Heim joints, one pair for each side. The first step is to inspect for the correct AMOUNT of total travel.

Aileron rigging is subject to several possible faults.

<To be continued>