Chapter 1
Basic Concepts
It would be convenient to say that takeoffs and landings are affected by three thingsâaircraft flight characteristics, atmospheric conditions, and pilot flight characteristicsâand go on from there. But it is not that simple. The variations from these three sources are so tightly intertwined in so many of our flights that a better starting point is a review of some of the more important basic concepts, and particularly how we perceive and try to control angle of attack.
It is very straightforward to think of elevator movement as causing a wing to pitch about its lateral axis, or of aileron displacement as causing it to roll about its longitudinal axis, or of rudder displacement as causing it to yaw about its vertical axis. But lateral, longitudinal, verticalâyou can see that since weâre accustomed to operating with at least one foot on the ground, our control movements tend to be ground referenced.
Stick or control wheel back and the nose rises above the horizon. Stick or wheel to the right and the right wing goes down toward the ground and the left one rises. Right rudder, say, and the nose swings or yaws to the right with reference to some point on the distant horizon. In many situations, for instance in a straight-ahead climb or descent, or in correcting a displacement of the airplane in level flight, these reactions serve us well enough.
But we also fly round the bend, and next are thinking about using the controls to make the airplane go where we want it to go. And weâre off to the races. Sometimes we get into trouble less than halfway around the bend. Because, in rough air, we are called upon to exercise simultaneously pitch, roll, and yaw control. In our turns we need to think in terms of how our three controls enable us to rotate the airplane about its own pitch, roll, and yaw axes rather than about ground-referenced axes.
Meanwhile, in our turns and sometimes even in straight flight, we tend to forget that the first prerequisite to keeping an airplane flying is our ability to keep the angle at which the wing pushes through the air within very narrow limits. Too large an angle and the wing quits flying: the airplane becomes just so much weight with no means of support, and we get into gravityâs 32-feet-per-second acceleration routine, which is vertically ground referenced.
The Wright Brothers were not only the first, but the first to know all about angle of attack. With their pusher Flyer, they had a place out front where they could attach a string, which was free to align itself with the relative wind. They soon learned that in a proper climb or glide, the string would tilt, tail end up, aligning itself at a certain angle to the longitudinal axis of their machine. If they attempted to climb too steeply or glide too slowly, the stringâs angle would increase and theyâd be in trouble because with the relative wind at that angle the wing would lose its ability to provide lift.
Later, when they departed from the straight and narrow and started exploring the turn phenomenon, they discovered that in a turn if they let (with elevator) the stringâs angle get higher than was proper in a climb or glide, they were in the same trouble as in straight flight, even though in the turn they might be flying faster than in a climb.
Today, these many years later, we have no string to tell us when weâre flying too close to stalling angle of attack. So let us enter the labyrinth of how we do our best to keep our angle of attack within its small viable limits, using airspeed, attitude, power, control feel, and any other straw that flies by to give us a hint. And often agreement is not unanimous about how we even use or should use our three controls.
Elevator Versus Throttle
As you know, in recent years there has been a lot of discussion about what controls airspeed and what controls altitude. By FAA ukase we are required to think, or at least to say on our writtens, that the elevator controls altitude and the throttle controls airspeed.
I think this is a horribly dangerous concept when the chips are down because it can cause pilots to pull back on the stick to go up, or, after an engine failure, to stay up. It is instinctive for people to think in terms of pulling back on the stick to climb or maintain altitude because it is so logical.
The best example I know of this universal impulse came a few years back. My friend, little Helen Langewiesche, had been given a spin demonstration before soloing a glider. One evening after dinner with Helen and her test-pilot/author father, Wolfgang, I asked her what she would do with the stick if ever she found herself nose-down and starting to autorotate. Her answer: âWhy, dummy, Iâd pull the stick back all the way because if you donât get the nose pointed up instead of down, youâre going to fly into the ground.â Stick and Rudder, over on the other side of the fireplace, became rigid. I paled. In the ensuing silence Helen added, âOh, well, yes, first it is necessary to lower the nose to get some speed, and then you can get headed away from the ground.â In short, she knew better, but her initial statement revealed a universal instinct that has to be trained out of people.
A proper concept of airspeed and altitude control is important in thinking about takeoffs and landings because these are low-altitude operations, and virtually all stall/spin/mush accidents begin close to pattern altitude. And those who, ground shy, instinctively pull the stick back to gain or maintain altitude, go down.
The Stick Does Both
Yes, the stick controls altitude. When youâre cruising along level, if you pull the stick back a bit, the altitude increases. No doubt about it. This is imprinted in the pilotâs mind hundreds of times on even a relatively short flight. But in the process of increasing altitude, pulling back on the stick also decreases airspeed. On the other side of the coin, while flying along level in cruising flight, if you put some forward pressure on the stick, the altitude decreases. But note also that the airspeed increases. So, the stick controls both altitude and airspeed.
This is true for the simple reason that there is no such thing as a single-engine airplane. Every airplane has a second or additional engine: gravity. Along with its attitude and all-important angle-of-attack control functions, the stick is also the âthrottleâ for this additional engine.
Prove it to Yourself
Someday, with your airplane in landing configuration with full flaps, get the power set so that the airplane will fly at a constant altitude at normal approach speed. It will probably take about 50-percent power to accomplish this. Now gradually close the throttle while lowering the nose to the first mark below level on the artificial horizon and note the over-the-nose attitude. It will be about 10° nose-down. Youâll find the airspeed in this power-off glide to be virtually the same as in level flight with 50-percent power. Your friendly gravity engine, which has never had an engine failure, can provide you with 50 percent of the power of your regular engine anytime you need it if you simply put the airplane in a 10° nose-down attitude. (Lift is always perpendicular to the relative wind and in a glide it has a thrust vector, provided by gravity.) And if youâre ever in a bind for a rapid acceleration, be mindful that the nose doesnât have to go a lot lower than 10° for gravity to provide thrust equal to that of your regular engine. And this is done with the elevator control.
As well as providing a downhill thrust vector, gravity also provides an uphill drag factor or an increase in drag. Think in these terms for the moment to get a full grasp of the gravity effect. Go back to level flight, landing configuration, with 50-percent power set up. Now raise the nose almost to the first mark above level in the artificial horizon, which will be about your normal climb attitude with full power in takeoff configuration. You may find that even with full power, you canât quite maintain your level-flight speed. Gravity is pulling you back as much as the increase in power is pushing you forward, so there is no acceleration. Obviously gravity power, which is always there, can be a blessing or a curse. Gravity power: stick forward, more power; stick back, reverse thrust. The dividing line is whether, with wings level, the nose is above the horizon or below the horizon.
The Job of the Throttle
What about the official concept, namely that the regular throttle controls airspeed? On takeoff, it is certainly convincing: as the throttle is advanced, the airplane starts moving along the runway and the airspeed starts moving right on up.
At this point the throttle is controlling airspeed. No doubt about it. But bear in mind that in the takeoff run, youâre âflyingâ what is really only a ground-based vehicle. The rules of aerodynamics become applicable only at the moment of lift-off. An airplaneâs wing lives and breathes airspeed and flies only when it is moving faster than its applicable stall speed.
Actually, the best working postulate appears to be that the throttle controls altitude, not airspeed. In a climbout with full power, the thing that produces altitude is rate of climb. The highest possible rate of climb is available when the airspeed, controlled by the elevator, reaches the speed at which there is the least drag, or in other words, the aircraftâs maximum rate of climb speed.
Now reduce power a little and lower the nose as necessary to hold the best climb speed. The rate of climb, or production of altitude, declines. Reduce power still moreâthe nose has to be lowered still more to hold the maximum rate of climb speed, and the rate of climb decreases further. So what the throttle produces is not airspeed but rate of climb, and it thus provides altitude control on the basis of whatever power is available in excess of what it takes to fly level at minimum airspeed. In a full-power climb at maximum rate of climb speed, thereâs no way to increase airspeed with throttle because thereâs no additional power available. As a normally aspirated airplane goes up, this power decreases and the nose has to be carried lower to hold the maximum rate of climb speed and consequently gain the maximum of altitude from the climb power available.
The Throttle Does Both
The most convincing demonstrationâat least according to themâby the throttleâairspeed advocates needs close examination. In trimmed cruising flight, they go from cruise power to full throttle and maximum RPM and invite attention to the increase in airspeed. What they fail to mention is that as the speed increases, they have to apply increasing forward pressure on the stick, or add nose-down trim, so that the increased power will convert to airspeed rather than rate of climb. Otherwise, the airplane would...