Control Engineering

Link This | Email this | Blog This | Comments (1)

Who said: “Power is nothing without control?”
February 25, 2008

After an exhaustive Internet search (meaning that I searched until exhausted), I’m forced to conclude that “Power is nothing without control” originated as a marketing slogan for the Pirelli Tyre company. Despite its origin as a marketing slogan, there is good reason to recognize it as both clever and true.

Let’s start with one of the first super-inventions of the 20th Century: the airplane. Folks had been “inventing” aircraft since the 1700s, and had been dreaming about human flight for at least 2,000 years before that. Even the Egyptian Book of the Dead describes a soul “flying like a hawk” after passing its Afterworld Entrance Exams.

Would-be aviators over the centuries felt they had to come up with two things: an aerodynamic shape to generate lift, and a propulsion system providing enough power to sustain flight. They failed miserably (and often fatally) because they missed the most important ingredient: control.

As any aerodynamicist, and most people who live in windy places, can tell you: you can make almost anything fly. If you don’t believe me, skip a stone across a pond. A piece of paper will fly if the wind catches it. This morning I noticed a torn plastic bag tangled in the upper branches of a 60 foot oak tree in front of my house. It didn’t get there by blowing along the ground. Unless an enterprising squirrel carried it up there, it had to fly on its own.

Glider pilots are only too happy to point out that you don’t need a propulsion source to fly, either. They make do with good ol’ gravity — which most people associate with falling rather than flying — augmented with a strategically placed updraft or two. It ain’t power, baby, that makes it fly.

It’s control.

Aeronautical wannabes died like flies (pun intended) for thousands of years because they simply did not understand how to control a heavier-than-air craft.

What set the Wright Brothers apart was that they were the first to solve the control problem of heavier than air flight. Through years of experimenting with models and full-scale kites and gliders, they carefully studied aircraft control requirements. Over time, they learned that motion through the air could be controlled only through applications of the point transformations of pitch, yaw, and roll. These acted to generate transverse forces (lift and steering) through interaction between the aircraft’s shape and its forward motion.

As for the rudder, which early investigators imagined would steer the aircraft like a boat, it turned out to do no such thing. In fact, as Wolfgang Langewiesche (Don’t ask me to pronounce it!) says in his aviation classic Stick and Rudder, “The important thing to understand about the rudder pedals is that they are unnecessary; like your wisdom teeth, they serve no very good purpose but can cause much trouble.”

Now, I happen to like rudder pedals. There are a lot of fun things you can make an airplane do with rudder pedals that it won’t do without them. You can, for example, cross control the thing (roll to achieve bank for a left or right turn, and apply rudder for the opposite turn) to make it slide through the air sideways when coming in for a landing, like a baseball player sliding into second base. It has about the same effect, too. If you’re coming in too “hot,” cross controlling can make the plane slow down realfast!

Another one I like is the knife-edge maneuver. Roll the plane 90º so that the wing is vertical instead of horizontal. Use the rudder to keep the nose angled upward to achieve lift by laying the plane on the side of its fuselage. Lots of fun at parties!

In the interest of honesty in journalism, I have to point out that my piloting skills and the equipment I usually get my hands on aren't up to doing the air-show version of a knife edge — at low altitude. At high altitude it gives you a great view of the ground, though.

Anyway, the point is that you can do these maneuvers quite nicely in a glider because they’re all about control. If you don’t have control, however, there’s only one maneuver possible — crashing.

The same goes for ground transportation. Sixties-era muscle cars were all about power. They did fantastic feats in the stop-light Grand Prix, but take ‘em out on the back-road twisties and you realized they were overpowered land yachts. To borrow a line from Douglas Adams’ The Restaurant at the End of the Universe: “Looks like a fish. Moves like a fish. Steers like a cow.”

As we glide (like fishes?) into the 21st Century. Our technology will more and more embody the wisdom of Pirelli’s marketing phrase. It will all be about control.

New to Control Engineering? Here’s some related reading to help.

Posted by Charlie Masi on February 25, 2008 | Comments (1)