Rudder Pedal Flaw Enhances Groundloop Potential

[6320012s 12]

When I was learning tailwheel, I had several groundloop experiences first traced to a faulty tailwheel lock, a blown tire, and finally a quartering tailwind. In each case, I tried to counter the initiation of the groundloop with increasingly hard rudder, and in each case, as I increased rudder pressure, the swing intensified instead of correcting. Being kind of slow, and the fact that the ground loops happened pretty fast, it took until the third time to understand that the brake pedal design was partly, if not largely to blame. The flaw of the design is that as one pedal is pushed, the opposite brake pedal is potentially pushed into the opposite foot, causing braking in the opposite direction from the control input. As aerodynamic control decreases, the potential for cross control from the inadvertent braking is increased. To eliminate this potential, the cylinder must be mounted to the floor instead of the cross tube, and the cross tubes have to be raised about 1/2 inch with spacers. The pictures show how the brake pedal moves out of the way of the opposing foot when hard rudder input is given. An additional benefit is that as slight brake input is automatic with full rudder input. To get the correct pedal position, some "experimental" wooden dowel was used. The next generation of the pedal will be built for proper pedal position. With this setup, I have been able to consistently land on pavement without any problem..... and I always check the tail wheel lock!!

[akflyer 1427]

I can't remember, but I thought John had done some work on the geometry to get better mechanical advantage so you could get good pressure to the calipers. I know on the stock pedals, you could not get enough pressure to really have "good" brakes, and if you started a ground loop, there was not enough braking power to bring it back or hold it. Most people cant hold the plane from creeping during a full power ground run up.

My brothers Pacer has horrible geometry on the pedals and will do the same thing yours does. When you put in full rudder it will move the opposite toe brake pedal out a good inch to inch and a half. It is not wonder that previous owners put it on its back a few times!

I will see if I can get Mike to post up some pictures of his pedals, or when I get home I can put pics up of mine. They really do work VERY well, and they keep you from inadvertantly getting onto the brakes!