June 21, 2013
By Dan Namowitz
A student pilot and a flight instructor are reviewing after a session of flight-test prep for the student’s private pilot checkride. The focus is on the slow flight and stall maneuvers to be demonstrated on the flight test, and the honing of the student’s understanding of the all-important angle-of-attack concept.
In a mock oral exam, the CFI asks, “What is a key difference between the straight-ahead power-on stalls we performed today, and the power-on stalls we performed in turning flight?”
The checkride applicant replies, “Maintaining the bank angle of 20 degrees was a challenge during the turning stall entries. The necessary control pressures kept changing. Not just bank, but the pitch and rudder inputs, too!”
What was going on?
Find the explanation in Chapter 4 of the Airplane Flying Handbook; it’s cited as a reference for the maneuver in the Private Pilot Practical Test Standards.
During the approach to a power-on turning stall, the pilot must control both an overbanking tendency, and a tendency toward lower pitch while maintaining “the pitch attitude that will induce a stall,” as required for the PTS task.
With the aircraft established in a nose-high turning attitude, “the angle of bank has a tendency to increase,” explains the chapter. “This occurs because with the airspeed decreasing, the airplane begins flying in a smaller and smaller arc. Since the outer wing is moving in a larger radius and traveling faster than the inner wing, it has more lift and causes an overbanking tendency.”
As for pitch: “At the same time, because of the decreasing airspeed and lift on both wings, the pitch attitude tends to lower.”
The busy pilot must control another effect as well: “In addition, since the airspeed is decreasing while the power setting remains constant, the effect of torque becomes more prominent, causing the airplane to yaw.”
All that explains why constantly changing control pressures are needed to perform a maneuver that uses a single, specified bank angle “not to exceed 20 degrees, ±10 degrees.”
And here’s a follow-up tip for a smooth turning stall entry and recovery: When the stall occurs, remember during your recovery to ease off on those aggressive control pressures; they won’t be needed for control when induced drag decreases with the lower angle of attack, and flight control responsiveness returns!
Dan Namowitz is an aviation writer and flight instructor. He has been a pilot since 1985 and an instructor since 1990.
Safety and Education,
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