Aerodynamics: The Spin

Today on LTFB, we’re featuring an excerpt from The Pilot’s Manual: Ground School (PM-2C) on spins.

A spin is a condition of stalled flight in which the airplane follows a spiral descent path. As well as the airplane being in a stalled condition, and yawing, one wing is producing more lift than the other, which results in a roll. The dropping wing is more deeply stalled than the other, and the greater drag from this wing results in further yaw, further roll, and autorotation develops. Upward pitching of the nose will also occur. You can induce a spin on purpose by yawing an airplane that is stalled, or just on the point of stalling.

In a spin, the airplane is in motion about all three axes. In other words, lots of things are happening in a spin! The airplane is:

  • stalled;
  • rolling;
  • yawing;
  • pitching;
  • slipping; and
  • rapidly losing altitude at a low airspeed (close to the stall speed).

In a spin the wings will not produce much lift, since they are stalled. The airplane will accelerate downward until it reaches a vertical rate of descent where the greatly increased drag, now acting upward, counteracts the weight. The altitude loss will be rapid as the airplane spins downward around the vertical spin axis but, because of the high angle of attack and the stalled condition, the airspeed in the spin will be quite low and fluctuating.

Characteristics of a developed spin include a low airspeed (which does not increase until recovery action is initiated), and a high rate of descent.
Spin Recovery
To recover from a spin, you must ensure power is off, oppose the yaw, and unstall the wings. First note yaw direction and apply full opposite rudder, and then move the control column forward to unstall the wings by decreasing the angle of attack. Once the airplane has stopped spinning, ease the airplane out of the dive and resume normal flight.

Misuse of Ailerons
Trying to raise a dropped wing with opposite aileron may have the reverse effect when the airplane is near the stall. If, as the aileron goes down, the stall angle of attack is exceeded, the wing may drop quickly instead of rising, resulting in a spin. The application of aileron after a spin has developed may aggravate the spin. Discuss the spin characteristics of your particular airplane with your flight instructor.

The Spiral Dive
A maneuver that must not be confused with a spin is the spiral dive, which can be thought of as a steep turn that has gone wrong. In a spiral dive the nose attitude is low, and the rate of descent is high, but neither wing is stalled and the airspeed is high and rapidly increasing. A spiral dive is really just a steep descending turn. However, because the pilot may be disoriented it is often mistaken for a spin. The high and increasing airspeed indicates that the airplane is in a spiral dive rather than a spin (when the airspeed would fluctuate at a low value).

Recovery from a spiral dive is simple. Roll wings level and pull gently out of the dive. Beware of overstressing the airplane by pulling too quickly out of the dive—remember the controls will be very effective because of the high airspeed.

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