April 1, 2013
By Rod Machado
As a flight instructor, I’ve taken a fancy to certain flight maneuvers that offer a lot of educational bang for the bank. One of these is the steep turn. From an airmanship perspective, practicing steep turns is like receiving a pregnant cat for your birthday. It’s a gift that keeps on giving.
According to the FAA, the steep turn helps improve your coordination, control smoothness, division of attention, and orientation (even if you’re not from the Orient). All true, and there are additional benefits that the FAA does not even mention. One of these is the message the airplane sends your way in the form of an immediate increase in apparent weight, as if it suddenly qualified for a Jenny Craig weight-loss scholarship.
So what does this message mean? It means the wings are not only producing the lift necessary to keep you aloft, but they’re also producing an extra amount to pull you sideways, too. Your airplane and its contents (yes, you are contents) always resist any change in motion and protest it loudly with a silent increase in load factor. This is why you feel heavier in the turn, as if your machine and fanny have suddenly become too fat to fly. Consider this message the aviation version of a Western Union stall-o-gram: You’ve just experienced an increase in load factor. Stop. This tells you something. Stop. Your wings have moved closer to their critical angle of attack. Stop. Your stall speed has increased. Stop. This is just one of the many lessons steep turns teach. Please stay seated with your seatbelts fastened, because class isn’t over.
In a 60-degree bank, the wings are supporting two airplanes’ worth of weight. As you pull aft on the yoke to extract more lift from those wings, the increase in angle of attack induces them to throw a portion of their lift rearward—the same direction in which drag acts. Lift induced to act like drag becomes drag. We call this induced drag, and it’s the primary reason your airplane decelerates when turning.
Of all the mischievous things you can do with a pair of wings, who would have thought you could make them work in opposition to engine thrust when flying at relatively low cruise airspeeds? Now you know why nothing happens quickly when you move the throttle forward in a steep turn. There’s simply more induced drag to overcome. If your machine had barrel-sized pistons under the cowl, you could accelerate in a steep turn, remaining above the increased stall speed and below the critical angle of attack. Smaller airplanes can’t accelerate as well because of their power-to-wait ratio, meaning that there’s always a long wait for anything to happen when power is applied—if anything happens at all. This is another valuable lesson that steep turns teach.
If you didn’t consume too many Pop Rocks in the early 1980s, you can still visualize what happens to the airspeed as you enter a steep turn using limited power or without using power at all. Imagine making a power-off turn to final approach from base leg with a combination crosswind/tailwind. The unanticipated higher groundspeed results in your overshooting the runway. You steepen the turn and pull aft on the yoke, only to find that the previous airspeed margin above stall has disappeared. Unless you immediately release elevator back pressure and unload those wings, you will receive another stall-o-gram—an accelerated stall-o-gram.
Steep turn practice should teach you at least four important lessons. The maneuver helps you understand how an increase in bank angle is associated with increasing angle of attack. It demonstrates how quickly any airspeed margin above stall speed can disappear as the bank angle steepens, especially during power-off approaches. In airplane engines equipped with little pistons, steep turns teach that you can’t necessarily trust the thrust to keep you well above an increased stall speed. Finally, the steep turn teaches you that the only good thing that comes from an increase in load factor is the ability to recognize the bad things that come with it. To make these bad things go away, you need only unload those wings by releasing elevator back pressure and/or by reducing your bank angle.
If you understand these fundamentals, then you’ve learned the essence of what steep turns have to teach.
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Safety and Education
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The widespread presence of angle-of-attack indicators in general aviation aircraft could reduce fatal loss-of-control accidents caused by inadvertent stalls, said the FAA.
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