Chapter 13 - Section 7

Installing Master Brake Cylinders


I put this section on hold for a long time before returning - I don't quite remember why. I think I wanted to wait until the rudder is in place with its cables connected to the front, before taking this section on...


For me, there are two parts in this section - 1) mounting the master brake cylinder to the rudder pedals and 2) link the rudder cables to the rudder pedals. As I mentioned prior, my rudder pedal design uses the Velocity's hanging pedal concept - with some deviations.


Mounting the Rudder Cables

One of those deviations is how I attach my rudder cable to the pedals. The Velocity pedals have two outer most arms (besides the 4 foot pedals) for attaching the rudder cables (shown left) . Initially, I built the two outer arms as well. Eventually, I realized I did not need those outermost arms if I find a way to tie the rudder cables directly to the foot pedal arms (recall my foot pedal arms have 5 large holes down each arm). Solution was not too far out of reach...













My rudder cable attachments consist of a cotter pin, 2 small lathe parts (a plug and a bushing), a washer (which turned into a thicker bushing/washer later on), and a cable thimble. I was happy how these parts turned out - I made them with my mini-lathe.










I took advantage of the holes in the rudder pedal arms for anchoring the cable attachment (and later on, the master cylinder). Here's how they are arranged when attaching to my rudder arms instead of the outer arms. The 'plug' goes through the lowest hole in the pedal arm while the other parts stack through its post. 









Here's another view of the mounting hardware attached to my rudder pedals.











Normally, the pedal is positioned all the way against the side wall to the right. I moved it out so that I could take the picture and show its connections. I also plan on mounting a turnbuckle in line with the cable so that I can keep the cable taut. This way, I can eliminate the outer most arms and reduce a bit of weight in the process... I was pretty happy with the result.



[Hindsight] Jamie got a chance to see my design and gave me a B grade. He thinks I should combine the turnbuckle as part of the cable attachment assembly. I know he will show me how...(to be continued).  




Combining Turnbuckle To Rudder Cable Attachment

OK, Jamie gave me some ideas and I followed his recommendation. I used a similar rudder cable mounting concept (as above) but added the turnbuckle directly to the 'plug post' at the rudder pedal arm (left). The cable thimble is moved to the trailing end of the turnbuckle. This way, I can get the cable in close proximity, then tighten it by turning the turnbuckle. Notice my cotter pin is a bit too long (in the picture) - they will be replaced with more appropriate length ones.








With the re-design, I did not like the mounting post as part of the 'plug' (above) because I have to turn it down to 3/8" in diameter to accommodate the attachment hole of the turnbuckle. Its kind of skinny and I felt it had a remote possibility of breaking off - though the pull force on the rudder is minimal. But then, losing rudder control in the air is not a trivial problem...









I decided to use a through bolt (AN3) in place of the post. This way, the bolt has to be completely sheared off before losing my rudder cable connection. If you look close, you can see the through hole & bolt I added through the plug. Note the rudder arm is ~12.9o aft from vertical per plan.









Don't forget the quick disconnect behind the firewall. Note I added shrink sleeving to all my cable terminations, just to keep the dirt out.











Mounting the Master Cylinder

I used a similar concept (above) to engage the master cylinder. However, our pedal design requires us to engage the rudder cable first before the brake cylinders. Since my hanging pedals are of different design than plan, I have to figure a way to do the same as well. Calculations for the amount of pedal travel (to activate my rudders and master cylinders) are discussed in Chapter 16 - Section 6 Rudder Stops and Brakes).


Here are the parts I made for activating the master cylinder yet provide free travel for the rudder cable. I have seen somewhat of a similar concept in the past, but cannot re-locate it anymore. Therefore, whoever it is - thanks for the idea!


My master cylinder mounting hardware includes:

- a 5/8" square bar with 2 through slots at one end and a threaded hole at the other end. The long slot is for the foot pedal to slip through. The short slot is for guiding a steel pin. The threaded hole (at the other end) is for connecting the bar to the master cylinder;

- a round bushing & guide pin that fit inside the third hole (from top) of the foot pedal - providing a 2.42 mechanical advantage (Matco recommends 2.5 ma);

- an anchoring bracket for the end of the master cylinder. I made the bracket out of an aluminum U channel.


As shown in the assembly (left), the foot pedal is pulled back ~17.5o from vertical at neutral position. This is being pulled back by the turnbuckle from the rudder cable pedal. As the foot pedal is pushed forward (engaging the rudder) for 17.5o (which equates to the ~4.2" rudder swing per plan), my foot pedal will be at vertical position. During this time, the steel pin will merely travel along the slot of the square rod. 


Once the pedal reaches the vertical position, the steel pin will reach the end of its travel along the (short) slot and will push against the square bar, which in turn pushes against the master cylinder, thus starting the brake engagement. The threaded hole at the end of the square bar provides fine length adjustment for brake engagement position. The long slot, which is designed to accommodate the foot pedal body, will provide enough travel for the full travel of the brake cylinder (~1.5"). Per Cozy archive and my prior testing, the master cylinder should need less than 1/2" of travel for hard braking...My current setting provides ~.75" of travel.


Determining Slot Clearance Horizontal Outer Tube

With the hanging rudders, a slot is cut on the outer tube to allow for the swing of the pedal arm that is attached to the inner tube. The challenge here is that if the slot is too long, it will weaken the outer tube, thus the infamous 'twisting' of the rudder tubing. On the other hand, if the slot is too short, it will limit the pedal arm movements in the event more brake travel is needed. 


Based on my calculations in Chapter 16 - Section 6, my pedal swing is -17.5o to +17.5o. To verify my calculations with the actual part, I lay the entire rudder pedal set upside down on the work bench nicely. I made two (2) wood templates with angles drawn - radiating from the center of the outer tube as shown. Now I can move the pedal arms back and forth - while I can lengthen the slot (or narrow down the pedal arm) a bit at a time. When I was done, I have ~1/8" clearance on each side of the pedal arm - which equate to additional rudder swing if needed or possible.







Here's another view of the slot length and clearance...


The 1/8" clearance turned out OK. It allowed me to lengthen or shorten the turnbuckle and/or the master cylinder contact point. Thus, providing fine adjustments for activation points for both the rudders and brake cylinders.  












Master Cylinder Attach Hard Points

Since my master cylinders are mounted on both sides of NG-30, their hard point locations are somewhat obvious. The only unknown is its height position.


I decided to build up a foam/glass 'faceplate' and glassed it against F-5 as shown. Note that the initial 'faceplate' was a bit wide (vertically) such that I can test out the optimal position of the attach points. In addition, I made a 45o support for the face plate.











Once I figured out the optimal location (minimum push force) of the attach point, I trimmed the faceplate size to minimum. In addition, I just did not like the looks of the 45o glass support for the face plate (above picture) and decided to replace it with an angle bracket as shown.









After glassing the angle support, the master cylinders are re-mounted. The only thing I need to add is the reservoirs.










I disassembled the unit, took it to an aircraft welding shop and tig welded the rudder pedal arms onto the hanging tubes - being very careful with its alignment and positions. With all the jigging and welding, it took about 30 minutes. I took it home, cleaned off the weld marks with Scott Bright and painted it silver. With the turnbuckle taut, I can bring the foot pedal quite a ways back - for the shorter pilots...


Between the turnbuckle and the threaded post of the master cylinder, I got a relative range for positioning the rudder pedals.