Tuesday, February 25, 2014

Rudder & Brake Pedal Assembly Completed & Modification Of Master Cylinders

Work on the rudder pedals and brake assembly was completed today along with a modification to the master cylinders (more on that later).  After deburring the WD-1209 brake pedals and WD-1211 torque tubes the torque tubes were lubricated with Lubriplate Aero white lithium grease, inserted into the rudder pedals and the brake pedals were bolted in place along with the F-1290 pedal blocks. One of the reasons Lubriplate was chosen is it is a light duty grease with corrosion inhibitors.
Greasing the F-1211 torque tubes with Lubriplate Aero white lithium grease prior to insertion into the WD-1206 rudder pedal assembly.
Assembling the WD-1209 brake pedal and F-1290 pedal block onto the F-1211 torque tube.

After tightening the pedal blocks most of the pedals had tight spots caused by a slight interference of the F-1290 pedal blocks with the weldments and dragging on the rudder pedal assembly. The inner edges touching the weldments were relieved with a box cutter. The dragging was solved by using a piece of Emory cloth laid over the tubing and rotating the F-1290 pedal block back and forth over the Emory cloth thus sanding off a small portion (mostly on the outer edges) of the pedal blocks.
Emory cloth in place over the rudder tube to sand down the inner edge of the F-1290 pedal block.

After tweaking the F-1290 pedal blocks all the brake pedals moved freely which paved the way for installing the master cylinders.
All the brake pedals and torque tubes installed and ready for instillation of the four master cylinders.

Modifying the master cylinders …. The master cylinders used on the RV-12 are the same type used on other RV models. There have been a few reports of dragging brakes on RV’s (not on the RV-12 as far as I know of) which utilize a hinge assembly on the pedals as opposed to the tubes used on the RV-12. The most common solution was to use a long bolt so the two pivot points on the pedals would rotate on one single shaft. This worked well, but a few had the drag return after much use and discovered the master cylinders were not returning all the way. The solution was to install compression springs on the shafts of the master cylinders to insure a positive return. Although the RV-12 uses tubes as pivot points, suppose the possibility exists for the master cylinders to not return fully after age as some experienced with other RV models.

Decided to make a preemptive strike so the DOG Aviation procurement department rounded up the necessary hardware locally to modify the master cylinders to insure a positive return. The parts consist of a compression spring and two nylon flanged bushings for each master cylinder. Actually all that is needed is the spring but the flanged bushings are insurance that the springs won’t scratch the shafts of the master cylinders.
The upper master cylinder modified with compression spring and two flanged bushings. The individual parts are shown on the bottom.
Installing one of the modified master cylinders onto the torque tube’s mounting eyelet.
Completed rudder and brake pedal assembly with modified brake master cylinders.

The springs used for the modification are 3 1/16" long and 11/16" wide, the flanged bushings (available from Hillman) are 1" diameter with a 3/8" hole and the center “ledge” the spring slides over is 9/16" wide. The springs are probably a little stronger than necessary … but they do make for a positive return. May search around a little and see if a spring with less tension of the same dimensions can be procured.

At this point the building instructions would have the builder install the assembly into the fuselage and fabricate the brake lines … but other builders say when installing portions of the finishing kit, the pedal assembly needed to be removed. So will move on and install this later along with the brake lines … which may be custom Teflon lines with a stainless wire outer covering.