In the last article, we discussed how the structure of an airplane behaves and responds to outside forces. These forces included the upward pressure from the pavement on the landing gear and airflow over the fuselage and flying surfaces. We looked more at what the forces did to the airplane internally, instead of how the airplane interacted externally with the forces themselves. Today, let's look at the airplane's interaction with the air through which it travels.
Imagine if you will, what it must be like to be a bird in flight. These flying creatures seem to have an innate understanding of how to maneuver in the air from the moment they first leave the nest. They know what they can and can't get away with when using the air to provide their path. Our winged friends know a whole lot more about aerial maneuvering than even the best of pilots.
Consider though, a poor bird caught out of the roost at night and in the clouds. The poor fellow has no idea where or how high he is or which way he’s pointed. He decides to just keep flying until morning and then hope to see well enough to land safely. In the meantime, all he can do is flap his wings. About the only sense our poor friend can rely on is the rushing of air straight over his beak and back to his tail feathers. Sadly, this is no guarantee that he is flying straight and level and slowly, something in his bird brain senses that he is descending. This is not a concrete sense like his vision could have given him on a clear day--it’s just an inkling. He lowers his tail feathers, and he feels the air shift from hitting him on the beak down to hitting him on the neck. The air flows past him at an angle now instead of from beak to caboose. Our friend has just changed his Angle of Attack (AoA). Unfortunately, this is the only thing he can know for sure.
Now, let's wish our poor feathered friend the best and for the sake of a happy ending we’ll say he made it till morning and broke out of the clouds to find his nest nearby. What we need to take from this story though, is the pure and isolated idea that any heavier-than-air flying machine is governed and limited by its AoA. Try to put away every single property that you might want to see or control. This includes pitch, bank, airspeed, and so on. No matter which direction you are going, whether straight and level, turning, straight up, or slightly down, you will have some AoA. You can be pointed in any direction and have any AoA. In short, only think about the wind and the wing.
Now we must consider how we control this relationship and the inherent realities and limits behind it. Know that the stick in your hand is purely an aerodynamic control. It is not an up and down control. It definitely is not an airspeed or an altitude control. The stick in your hand controls AoA and that's it. If you need more AoA pull the stick back; if you need less, push it forward. You should have a good idea from your early training that pulling on the stick has its limits. Pull it back so far and you keep getting more AoA. Pull it back too far and the wing now meets the wind at too steep of an angle to get useful lift out of the wing. Remember this can and has happened to many aviators in all sorts of attitudes, not just with the nose being up. Most aviators have never performed anything other than benign straight-ahead stalls at shallow pitch attitudes. It is ingrained in us from early on to not let the nose get too high. The nose gets high and we start to get timid of pulling on the stick in a serious way. Sadly, all of this creates a fallacious link between pitch and AoA. Then, when you start doing aerobatics, or heaven-forbid end up in an inverted unusual attitude emergency all our faulty intuition falls out the window vent. The timidity to pull that came from a nose-up attitude is unconsciously lost. We then haul back on the stick hoping for a miracle. The wing stalls, and what we may have bet our lives on isn't there to save us.
Imagine now you and your airplane replacing our poor bird in our previous example. All you have in the panel is an AoA gauge, nothing else. This, of course, would be a horrible and deadly situation to be in but just imagine for now it's a harmless lab experiment. You are flying along and you pull back hard on the stick for a good thirty seconds. The AoA gauge goes up while you hold it back. Did you pitch straight up? Did you do a loop or a turn? Did you nose up and then pitch forward again? Is up even up anymore? There is no way to know. All you know is that for thirty seconds, the wind met the wing at a steeper angle than it had before you pulled back. Now you push forward on the stick and hold it. The needle on the AoA drops to zero. The air rushes right over the nose of your plane--straight from spinner to tail, leading edge to trailing edge. You push even harder forward, the needle plummets below zero. The air now rushes at the upper camber of the wing and parts the trailing edge heading for beacon light on top of the rudder. Have you done an inside loop? Plummeted straight toward Mother Earth? Pointed straight up? There really is no way to tell.
The moral of this story is that the wing can never meet the wind at more than the critical angle of attack. You could be completely upside down and turning but if the AoA isn't critical yet, you will have control relative to the air. In essence, the air can still be used to bend and shape your flight path. What we need then is a consistent way to know when we are near or at the stall.
The avionics guy's answer to this problem might be an AoA gauge. These are nice to have but are incredibly expensive and rare in GA so they are off the table as a blanket option. Some might say you could rely on an airspeed indicator for this. Sadly, airspeed indicators are pretty lousy at universal stall prediction. Do you know the stalling speed of your airplane inverted at sixty degrees of bank? Good luck calculating that one. We need something else and sadly money can't just purchase it new out-of-the-box.
Let's shift our thinking to the loose nut who is death-gripping the stick. You would be amazed how many pilots get busy and don't even realize they are pulling the stick back dangerously far. Their brain is on autopilot and just trying to keep the attitude "right". This pilot is only thinking about his relationship to the horizon, not the air he is journeying through. Believe me, it happens and more frequently than we might like to admit. In a car, it's incredibly easy to stay on the road, you just keep your eyes forward and turn the wheel as the curves come and go. Try to think about the air as a road, not the land beneath you or the horizon ahead of you. This invisible road can only have turns so tight, and the grades only so steep.
Thankfully, there is an answer to our problem. We need to get our brain into the feedback loop with our arm and hand as they are pulling on the stick. In short, you need something telling you how far back you can pull the stick without stalling out. This is what replaces the needs for instruments or numbers in our head. Start trying to feel for cues in your arm and hand muscles as you are pulling; learn to recognize when you are asking for more from the wing. Know what your arm feels like along your side or on your leg when you've got it back at or near the stall. You may or may not get buffeting cues depending on the airplane. Know what they feel like at 50 knots and 100 knots; in other words, mushiness in the controls is not a guarantee you are near stall. Practicing with many different attitudes and airspeeds will let you build this universal awareness of how much is enough and how much is too much.
One of my favorite ways to practice is to go up and do high-speed turning stalls. Climb to a healthy altitude, bank steeply, and then pull as hard and as quickly as you dare to enter a turn. It's kind of like the Price is Right for Pilots. The person who pulls the most without going over, wins. Keep in mind this is all about how far back you have the stick. You don't need to measure it with a ruler or find the magical amount of pull to induce a stall. That's the wrong way to approach this. You just need to know how much you've been pulling on the stick and if it's back or not. Then, when you are in the pattern and trying too hard to crank it around the base to final turn, a little voice will travel up your arm to your noggin and say, "Woe is you if you pull back anymore".
Now for a few side-notes. It amazes me how basic and limited the Private Pilot standards are for stalls. Advanced stalls, the ones that will get you in serious trouble, only have to be demonstrated to the student once. They don't have to practice them and most don't want to! The average new private ticket holder probably only has twenty or thirty stalls to their name. That's hardly an introduction, let alone mastery. Go out and do twenty or thirty stalls in one flight. Your confidence, awareness, and familiarity will vastly improve. Keep track in your logbook and set a lofty goal of say a thousand stalls. Track them like you track your flying time; you will want more. Also, if you don't have a g-meter stay below maneuvering speed. If you do have one put the airframe to the test and venture out beyond the false security of one-g and maneuvering speed. You will be amazed what these flying machines can really do. The same principle applies to AoA gauges; they let you know right away how much you've used and how much is left. You'll be pleasantly surprised at how aggressive you can get and yet stay within limits. Finally, keep in mind that not every airplane can be flown by feel like we are used to in GA. Here again, consciously knowing you are bringing the stick back can be a help in addition to AoA gauges and stick shakers.
Clear skies and tailwinds,
David
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