In Stick and Rudder, the author warns pilots against the unreliability of judging airspeed and hence “buoyancy” — his term for how far the airplane is from aerodynamic stall — by throttle position, engine noise, and nose attitude.
Perhaps the most deceptive of these factors is g load. When an airplane, flying at a certain speed, goes into a turn and loads itself down with g load it assumes larger Angle of Attack and this gets closer to the stall. That has been described earlier in this book. But it isn’t the whole story. At the larger Angle of Attack, the wings have more drag, and thus the airplane will slow up, unless the throttle is opened wider. The airplane assumes a still higher Angle of Attack and gets still closer to the stall! Few pilots realize how strong and dangerous this effect is.
Langewiesche, Wolfgang. “The Flying Instinct.” In Stick and Rudder: An Explanation of the Art of Flying, 58. New York: McGraw-Hill, Inc., 1944.
He then gives a surprising example.
The average small airplane, fully loaded and with its throttle set at cruising, is actually unable to hold indefinitely any turn banked much more than 45 degrees! The effect just described will slow it down gradually, as it circles, so that the pilot’s stick comes farther and farther back; until finally, after perhaps twenty turns have been completed, it will stall: stall, mark you, out of level flight with cruising throttle!
Why doesn’t nosing over to leave the steep turns for straight-and-level attitude with open throttle produce sufficient airspeed to avoid the stall?