The Gee-Wiz Factor: Airplanes Don't Have Eyes

Series Introduction

Over the past four years of flight instruction, I have witnessed many students struggle mightily, at least at some point in their training, with understanding how to control the flying machine they are trying to master. Having also flown with many seasoned pilots, I have found no shortage of backwards, inefficient, puke-inducing, and sometimes downright dangerous, control behaviors. At the core of this problem lies a mixture of some simple physics and applied aerodynamics known as the mechanics of flight.

From my first week in the right seat until now, I have wrestled with how to teach the mechanics of flight to my students. What rules of thumb should I use? What information is fact versus fiction? What level of depth is too much and what is not enough? Why teach aerodynamics if we don't apply the information? The answers and implications to these questions are, in my opinion, monumental. 

What we teach and reinforce in the cockpit, lays the groundwork for what will hopefully be many decades of flying whether for personal enjoyment or professional application. As flight instructors, we have an immense responsibility for the future safety of our students. Some of this responsibility shifts to the newly-minted private pilot to continue self-study and maintain proficiency however, the majority of it still lies in the first lessons we provide as educators.

It is my opinion that we should teach the facts of the mechanics of flight for all they are worth. They should be recognized as complex topics requiring careful study. They should not be ignored or simplified to the point of irrelevance. 

Unfortunately, the facts governing the mechanics of flight can seem unreachable, complex and unintuitive; on top of that they are often buried in the stilted and awkward language of academic writing. Take a glance into books with titles like Fundamentals of Aerodynamics and Aircraft Performance and Control and you will be met with dense paragraphs of mathematical minutia and few, if any, helpful diagrams or pictures. Theory is presented instead of application. Anyone interested in this meeting of the practical with the theoretical must understand both worlds well enough to play a "Where's Waldo?" in the textbooks.

Back in the old days of flying, the flying community knew a whole lot less about many factors governing flying than we know today. This included weather, aerodynamics, weight and balance, radio communications, etc. What I like about the old literature from those days is that when facts were well understood, pilots were expected to read, understand, and apply that knowledge to good effect. My favorite example of this is the Pilots' Powerplant Manual published by the Civil Aeronautics Administration in 1940. This book has more useful information in it about engines than what most A&P mechanic students are coming out of school with these days. If a pilot of that era were to have ingested and comprehended that book, they would have been a one-man army of engine comprehension. That is the kind of guy I would want up front in a DC-3 over some patch of inhospitable terrain at night and in the clouds with an engine issue.

Sadly, even though our collective knowledge of aerodynamics, performance, and control accelerated exponentially through the 20th century in the engineering world, the pilot community has remained in the dark on what is actually happening when we as humans interact with flying machines. There is a little-known, yet beautiful world of understanding that exists between the flying and aerospace engineering communities and is within easy mental reach of anyone smart enough to solo an airplane or pass a college aerodynamics class. 

The purpose of this series of articles is to share the amazing insight a pilot can have about how their airplane flies and will find this information can entirely change the way they control their airplane. Some of the information may or may not have practical use, but that's the cool thing about something free -- you can take or leave it at no charge! That's why I have entitled the series; The Gee-Wiz Factor.

Airplanes Don't Have Eyes

Imagine with me for a moment what it must be like to be born blind. With no ability to sense light, the beauty and detail we are all familiar with would be only a mere concept. Small objects could certainly be felt and maybe some sort of mental "picture" could be built. However, descriptions of larger structures and landscapes would likely have very little meaning. How close would your idea of the horizon, the sky, and land be to reality? I can imagine that if someone born this way were to gain sight, the larger world would be of entirely different proportion than they might have expected. Houses may seem smaller than anticipated, and skyscrapers enormously larger than expected.

The world the blind do live in however, is richly full of touch and sensation. Without a sense of sight to get in the way, these people must have an incredibly refined sense of force and pressure. The slightest air draft, brush of a book's page, or change in seat pressure when going around turns in a car is likely much more noticed and analyzed. 

If you will permit me, let's personify our airplane and imagine what it must be like to experience flight from it's blind perspective. Resting on the ramp, the tarmac presses up into our airplane's wheels as the force of gravity maintains it's ever-present pull upon every molecule of our plane. This pressure on the tires bulges them slightly, transmits this force to the axles, and up through the landing gear which bends slightly to provide the necessary resistance. This bend of the gear slightly twists against the fuselage mounts and stretches the bolts holding the two together. From here, the loads transmit into the aluminum structure and spread like a drop of food coloring in a glass of hot water to the entire airplane. Some parts experience enormous compressions, stretches, twists, and bends. Others feel only a slight reaction. You can be assured though that every part feels something. Our airplane is at rest and only it feels its own aches and pains. The cloud drifting overhead, the sun setting in the distance and even which direction is "up", are all unknown to our airplane.

All of a sudden, a door opens and in a moment extra forces have been added. Pressures run in an instant, down through the seats, across the floor, around in circles within the bulkheads, and down through the gear and tires to the tarmac which now bows ever slightly more into the earth beneath. Our airplane lets out a slight metallic groan; maybe it's only a maintenance technician checking the tach time. Suddenly, electricity flows from the battery, through some circuitry, and into the starter. The engine gallantly resists but is no match for the starter as the prop starts to swing. The conditions are just right in the engine which fires right off. Waves of vibration jump from the engine case, through the rubber mounts, to the engine mount, and finally into the airframe. Every single part of the airplane is now in rhythmic vibratory motion; every rivet and fastener is under constant assault to let go. Our airplane sighs and mutters to itself, "Here we go again."

The throttle cable feels a shove, and transmits the push to the engine which responds with more rapid rotation of the prop. Gooey wax particles on the surface of our airplane feel an increase in collisions and the slipping of tiny air molecules passing over that had just gotten kicked in the pants by the prop. The wax passes off these forces to the paint beneath, which passes it off to the primer, which passes it off to the aluminum below which then shares it with the rest of the structure. By kicking these air molecules backwards, the prop gets an equal and opposite reaction forward which strains against the crankshaft, which passes it off to the case of the engine. The same path taken by the engine's vibration is also taken by this forward tug and over a short time every molecule in the airplane is made aware of the need to move forward. Suddenly, the wings start to feel the collisions of billions of air molecules over and under their outer skins and transmit the message to the landing gear far beneath which no longer have to wage the constant fight against gravity. The rush of air over the entire plane surges faster and faster. More and more reaction is felt through the skin, which transmits to the rest of the structure, which after a while is exactly balancing out the forward tug from the propeller. Our airplane has no idea how fast it is going, which way is up, or how high it is above the ground. All it knows is that the tug-of-war on it's bone structure has stabilized and it only has to worry about the constant ache of vibration.

This is all that mechanical devices like airplanes understand; forces and their accompanying stresses. These are the only commands an airplane's bones and flesh can reply to. A force is enacted, internal stress is created, and in the absence of an opposing force, the airplane surges through acceleration in the direction of that force. Sadly, we as visual humans, have little natural capability to grasp this dark world devoid of everything except mechanical forces. Someday, I would love to put on a magical pair of glasses which would let me see into this mysterious world of actions and reactions. Yet, for the moment, diagrams and drawings in textbooks must suffice. 

In the meantime, start thinking of the airplane's controls as force controllers. The elevator doesn't merely raise and lower the nose like a grocery store grapple game stick moves the grapple from one position to another, it adds and subtracts from the forces at play upon the airplane. If this tug-of-war of forces is dominated by the force you have introduced, changes will happen. More about this battle next time.