Rudder Pedal Geometry

In our last episode, I was moving the rudder pedals forward to address the potential over-center problem that Mark at Avipro brought to our attention. Back when Richard was building, the consensus was to locate the rudder pedals for ergonomics. Subsequent experience led to a new recommendation to locate the rudder pedals exactly as depicted on the plans. To meet those requirements, I ended up moving the pedals forward just about as far as they could go.

New Rudder Pedal Location

Here's the new location, and you can also see the old hole.

After moving the rudder pedals, I noticed right away that the brake cylinders would be touching the forward-most tubes when the pedals were at max deflection. I wanted to measure the rudder deflection so that I could see if the pedals would stop before reaching that point. To measure the rudder deflection off of a theoretical fuselage centerline, I needed to measure the angle formed by the fuselage sides so that I could subtract it from the desired total deflection.

Figuring out the angles

Measuring the angle of the fuselage sides so that I can create a template for measuring rudder deflection

Final Answer

Here's the final answer- 40 degrees on the template; 10 for the fuselage side and 30 for the deflection.

After all of that hassle, the final answer was that the rudder was at exactly the right deflection when the horn hit the stop (with no bolts in the tubes). Also, the brake cylinders do not contact the tubes at max deflection, but they are close!
Rudder Stops

Perfect deflection with no added bolts. For some reason I thought that I was supposed to have bolts in there- I guess not!

While I was thinking about it, I wanted to measure the rudder horn to see if it was the original design, or the temporarily different design. At one point there was a change in the rudder horn, then a few years later it changed back to the original design again. I believe that we have the interim horn size. Eric says that this change was simply one of control sensitivity, and that his is also the shorter interim length. The shorter length here means less pedal movement for the same amount of rudder deflection. I’m not planning to change the horn back to the original length, since I didn’t think that the rudder was too sensitive on Eric’s airplane, and since the change is optional.
Measuring the Rudder Horn

Measuring the Rudder Horn

With all of that head scratching done, I took a break to get a few things done at home. I came back later in the afternoon to start work on the steel tabs for the skylight structure. I wanted the option of using nutplates in the tabs, so I sized them with that goal in mind. (Mysterious note from the future: I subsequently decided not to use nutplates on most of the tabs, just because the skylight screws are going to be very rarely removed, and because access is easy with another person comfortably seated in the cabin)
Planning the tab size

Planning the tab size

Pile o tabs

Here's a pile of all of the rough cut tabs.

Since I moved the rudder pedals forward, I found the cables to be too short. My remedy was to make new steel attach straps. I used the materials and specifications from the Beartracks and Avipro assembly manual. As you can see in the picture below, I used a washer to draw the radius for the end.
Rudder Pedal Straps

Blanks for the new rudder cable straps

4 strap blanks

Here are the 4 straps- two for each side.

The next step is to drill the holes and install the straps.

Posted on
Hours Logged This Session: 4.8
Total Hours: 1883.75

Leave a Reply