by Budd Davisson
If you ever want to know exactly how the little plastic pilot in an R/C pattern ship feels, go strap on an Edge 540. In truth, no 1:1 scale airplanes give the three-dimensional freedom a pattern ship has because of the power-to-weight ratio, but the Edge comes terribly close.
The Bill and Judy Zivko Edge series of airplanes are serious unlimited competitors. The very fact that National Champion Kirby Chambliss flies an Edge speaks volumes for the airplanes. The Edgeís are right at the leading edge (hence the name) of aerobatic technology.
To anyone used to flying general aviation airplanes, the Edge 540 is going to feel scary, if nothing else because it has no ìfeelîóthere are virtually no pressures at all on the control stick. These kinds of control forces have become standard for unlimited aerobatic birds. It could easily be said that you feel more pressure with your thumb on an R/C joy stick than you do on an Edge control stick. The results, however, are much more numbing. No oneís ever burst blood vessels in their eyes while flying R/C, although a few of us have felt like vomiting after stuffing a prized bird in.
When talking about control feel in a real airplane there are three factors that have to be considered. First is the breakout forceóhow hard do you have to push to get the stick started out of center? This is what determines the self-centering characteristics of the controls. Second is the stick force gradientóonce the controls are off center, how much does the force increase the further you displace it? And third is the accelerationóhow quickly does the airplane leave level flight and assume the roll or pitch rate that amount of control displacement demands?
In most airplanes the centering (break out) force is enough to let you find center and the controls get heavier the further you move them. Plus, most airplanes have a perceptible time lag between control displacement and airplane acceleration.
All of this tech talk is well and good, but it doesnít mean squat in an Edge. There are no centering forces. The only way you know the controls are in the center is the airplane isnít moving on way or the other. And the controls donít ever change pressureófull aileron feels just like a tiny bit of aileron, except your head is bouncing off the canopy because the airplane doesnít hesitate a nanosecond before ripping around
The first time I visited Bill and Judy at their plant in Guthrie, Oklahoma and they strapped me into a 540, I thought I was prepared, but I wasnít. About all my many thousands of Pitts hours did for me was ensure a safe landing. The Zivko is so light on the controls and so incredibly quick to respond that it made my lovely little Pitts feel like a dump truck. A very creaky, over-loaded dump truck.
For one thing, the Edge rolls at over 400 degrees per second. That means it takes less than .9 second to do a complete roll and, when this is coupled with zero control pressures, initially just level flight becomes a chore.
The first time I cranked it inverted and pushed into an outside loop from the bottom, I inadvertently slammed six negative Gís on myself when I was only looking for fouróthe amount of pressure it takes to push (stick force per G) was just as low outside as it was inside, which is to say, it was close to zero. Just push and it goes around.
It would take a book, or better yet, a video to adequately describe what forty-five minutes of yanking and banking in an Edge is like. Unfortunately, as hard as I try to describe it, in reality, only the plastic guy in your pattern bird can truly understand what Iím talking about.
