Attitude Flying

What is Attitude Flying?

By moving the controls, the pilot changes how the aircraft is oriented relative to the earth. That orientation is called attitude. Most of the time, the airplane will be in what pilots have traditionally called a straight and level attitude.

(click on each photo to enlarge)

StLvlAttHere we are looking out over the nose of a Cessna 172. The things to note about this picture are:

      • The glare-shield – the grey-black thing along the lower left

      • The front of the nose cowling – the green arc beyond the compass, just below the fields and town and mountain

      • The horizon – where earth and sky meet, just above the mountain

These are the elements the pilot uses to see his attitude. What we see in this picture is a straight and level attitude.

Why do we need attitude?

Can’t we just look at the instruments? See if our airspeed and altitude are OK?

Sure – but those instruments tell us about now, not about what is going to happen. Do you remember the complication that arose in the last chapter (time)? And the talk of equilibrium?

That’s the reason pilots need to be aware of their attitude. Because the airplane in the above picture is in equilibrium. It is not accelerating. So the picture 30 seconds from now will be essentially the same. By holding the airplane in this attitude the pilot is maintaining equilibrium. Looking out the window, you would think the airplane was on rails.

How do we fly attitude?

It is not a perfect world. Even on a smooth day, every airplane (if left to its own devices) will drift slowly from the straight and level attitude. It is the pilot’s job to keep it there. So if a wing drops (and in the above picture the left wing may be slightly low) the pilot picks up the wing. It is not that the pilot doesn’t let the picture change (that would take super powers). It’s that he doesn’t let the picture stay changed. He puts it right back where he wants it.

Because . . . well, what if in the above picture the left wing is slightly low? What is going to happen?

Remember how an airplane turns? The pilot tilts the lift vector. If the left wing is low, the lift vector is no longer straight up and down. It is pointing slightly left. So the wing is generating a force that tugs the airplane’s flight path to the left.

In the picture the airplane’s left wing is only slightly low. So the turning force is small and the pilot would have a hard time noticing the turn, because it is happening so slowly. But – a minute from now the airplane will no longer be pointing at that little hill just to the left of those two mini-mountains. That bracket (or whatever it is) to the right of the compass will be over the town just beyond the highway.

The pilot doesn’t want that to happen. So he picks up the wing. You could say this pilot is triumphing over time. He is eliminating the complication of time by keeping the airplane in equilibrium. If the airplane is out of equilibrium (accelerating) it will be because the pilot wants to change something.

The bottom line here is that the pilot knows the attitude that will keep the airplane in equilibrium.

An imaginary flight

The pilot opens the throttle. The airplane rolls down the runway, going faster and faster. The pilot keeps the airplane on the centreline by steering with his feet on the rudder pedals. As the air rushes over the wings, the airplane wants to fly. It is getting light on its wheels and is starting to feel a bit squirrelly. The pilot pulls on the stick or yoke and watches as the nose rises. The airplane lifts off. It is flying.

So what does the pilot do now?

He wants the airplane to climb straight ahead, so he keeps the wings level and puts the nose on the horizon: the climb attitude.

ClimbAtt

Can you see how the green nose cowl is almost touching the horizon? The wings are level (parallel to the horizon) but the nose is higher than in the straight and level picture.

Why this attitude? Because with full power this is the pitch attitude which will result in the best climb. The airplane will slowly accelerate until the four forces balance. Then it will be in equilibrium in a climb. The airspeed will be 90 mph. The climb rate will be 700 feet per minute.

Time goes by. Three minutes later, the airplane is at 2000 feet, where the pilot wants to level off. What does he do?

He lowers the nose to the cruise attitude.

CruiseAttSee the difference? Now you can see the road leading to the left end of the mountain. The pilot holds the airplane in the cruise attitude.

The engine is still at full throttle. The extra thrust that had been pulling the airplane uphill is now accelerating the airplane. As the speed increases the pilot will have to push forward on the wheel or stick to keep the nose from rising back to the climb attitude. The pilot wants the airspeed to increase. He is shooting for a cruise airspeed of 110-120 mph – let’s say 115 mph. When the speed gets there he reduces the power to cruise power – let’s say 2400 rpm. With his eyes still outside, holding the airplane in the cruise attitude, he pulls back on the throttle until he hears a change in the engine note. His eyes dart down to the tachometer, then back outside. In his head he reads the tachometer: 2450 rpm. Close enough. Now he trims nose-down so he doesn’t have to hold forward pressure on the wheel. The airplane is once again in equilibrium, in cruise.

Why doesn’t the pilot look inside and watch the tachometer as he pulls the throttle back? Because if he takes his eyes off the horizon the nose will pop up back to climb attitude or higher. The whole level-off operation will get sloppy or fail altogether. The airplane’s stability will be fighting the pilot’s actions and intent. The pilot knows and understands that – the airplane’s stability is a good thing. But he knows that to get quickly and accurately from climb to cruise he has to take charge. In his head he has both what a cruise attitude looks like and a power setting and cruise airspeed (2400 rpm and 110-120 mph). He has done this before. So he holds the airplane in cruise attitude, and waits. Time passes. The airplane accelerates to cruise airspeed. The pilot selects cruise power, and trims. Done!

Once again, the complication (time and acceleration) has been overcome by the pilot, using attitude flying.

Notice that the pilot has a couple of things in his head he uses as targets: attitude, and power and speed numbers. Remember P + P = PP? These things in his head are the data he retains from his experience. They are the numbers for his airplane. And the attitude part of the data is pretty much the same for any airplane. So the experienced pilot can get out of his DC-3 (where his control movements use his hands and arms) and into his nifty Pitts S-2 (where his control movements use his fingertips) and transition without effort.

Notice, too, that he does not memorize control forces. Not only are these different from airplane to airplane, but they change with airspeed and trim. So they provide no feedback. The feedback is attitude.

A digression on skill

A good pilot is by definition a closed loop pilot. What do we mean by that?

To be accurate any control system must have accurate feedback. For example, your furnace has a thermostat. It senses the temperature and turns the furnace on and off. Then it gets as complicated as you want, because the system can always be smarter, and the pilot can always have more skill. Continuing the example, let’s say you are a software engineer trying to duplicate the function of the old reliable thermostat based on a bi-metallic spring and a mercury switch. You quickly realize you can’t turn the furnace on at the target room temperature, because that’s when you want to turn it off. So you have to leave a small gap, mimicking the mechanical thermostat’s natural hysteresis. Perhaps you want to know the outside temperature so you can calculate how fast the temperature is going to rise inside when you turn the furnace on. Perhaps you want to calculate how fast the temperature is rising. But these are details. The bottom line is this: your system (which turns the furnace off and on) has to know what effect that is having on the temperature of the room. And perhaps your new whiz-bang digital system can even anticipate how long it has to run the furnace for the desired change in temperature – seeing into the future, if you like.

The experienced pilot does something like that. If he wants to turn left 10 degrees, he rolls into a fifteen degree left bank, saying to himself, roll two three roll, and then he rolls the aircraft back level. He knows that in a standard-rate turn, the airplane changes heading at three degrees per second.

The inexperienced pilot might apply left aileron and look at his directional gyro, waiting until it moves ten degrees before he applies right aileron. The airplane might well roll into a thirty-degree bank, and will almost certainly turn left more than ten degrees. Why? Because the pilot doesn’t know where to look for the feedback he needs. He is open-loop.

The closed-loop pilot gets his control feedback from attitude. He doesn’t even glance at the directional gyro until the turn is complete.

Back to the imaginary flight

Now the pilot wants to start an approach, so he can land the airplane. This will require another transition: from cruise to approach. The target numbers for approach are 75-80 mph, 1500-1700 rpm, and a descent rate of about 500 feet per minute. The pilot plans a crisp transition like he used to get from climb to cruise. He thinks, first slow down, then go down.

Looking outside (and not letting the nose drop) he pulls on Carb Heat and reduces power by ear. The airspeed is dropping, and as it does so it will take more and more back pressure to hold cruise attitude. When the speed gets back to 80 mph, the pilot lets the nose drop just a little, so the speed doesn’t drop any further, and trims for the new speed. The airplane is now in the approach attitude.

ApprAtt

This is the pitch attitude that will hold the approach speed of 75-80 mph.

The pilot stays on the runway centreline by making small turns. He is looking for the heading that will track the axis of the runway. That may be the runway heading, but if there is a crosswind, it will be a heading slightly into the wind. In a strong crosswind the airplane will look like it is going sideways over the ground. (It is, but it is going straight through the air.)

If a gust or turbulence changes the attitude, the pilot puts it right back where he wants it. This is the secret of smooth and precise flying. The airplane looks like it is on rails.

If a wing drops, the pilot brings it back to level before the aircraft turns, changing its heading.

If the nose drops, the pilot pulls it back up to the pitch attitude he knows will hold his airspeed. He makes the correction before the speed increases.

Approach and Landing

Let’s have a look at an approach and landing. In the first photo the pilot is intercepting the final approach course.  He is rolling level from the turn onto final.

IMG_2039You can see the short runway he is aiming for, and the larger, longer parallel runway off to the right.

IMG_2040Almost level. Intercepting the runway extended centreline.

IMG_2041Slightly to the left of centreline. Looking good. Look how the pitch attitude is steady – just slightly below the cruise attitude.

IMG_2042Wings almost level. Same pitch attitude. The runway looks the same – just larger. Here we are at about 50 feet above the runway.

IMG_2043Just before the flare. This is a good pilot. Notice that the pitch attitude still hasn’t changed. He has resisted the urge to start flaring early. Notice also the windsock off to the right. There is a slight crosswind from the left. (Click on the photo to enlarge)

The main wheels are over the threshold. He is set up to touch down on the numbers.

IMG_2044Starting the flare. We are at about 10 feet above the runway. The throttle comes to idle, if it is not there already. The pilot slowly raises the nose, slowing the descent.

But he doesn’t want to touch down. Not yet. He is still flying, using up the airplane’s remaining energy, trying to fly the main wheels down to an inch or so over the runway.

IMG_2045Notice the higher attitude. As the airspeed decays, the pilot keeps raising the nose just enough to keep the wheels from touching. See how the aircraft is tracking straight down the runway. The axis of the airplane is aligned with the axis of the runway. We would be safe if we touched down now. The nose is high enough so the nose wheel won’t touch. But this pilot wants a good landing. So he doesn’t quit flying.

IMG_2046See how the pitch attitude is just a little higher? And there is slight left bank – he looks like he is going to touch the left main wheel first.

IMG_2047The nose is higher yet. He hasn’t let it touch. The stall warning is starting to squeak gently.

IMG_2048Touchdown! A nice one. That’s how it’s done!

But he’s not done yet.  The pilot is still working at:

  • steering with his feet on the rudders so the aircraft tracks down the centreline
  • holding some aileron into the wind (if there is a crosswind) so the airplane doesn’t roll away from the wind (bad)
  • gently lowering the nosewheel
  • gently braking as necessary

Bob Hoover (rest in peace) was a wonderful pilot. He did amazing things safely at airshows, and people would say, “Bob – how do you do it?” In his Texas twang he would answer, “I fly it as far into the crash as possible.”

That’s my motto now, too. Don’t quit. Keep flying the airplane until you’re down to a walking pace. And if there’s a lot of wind blowing, don’t quit then, either.

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