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Stalls, Slips, Skids, and Incipient Spins

Sideslip

During their training and subsequent fight reviews, many aviators seem to get little exposure to and practice with stalls from turns—although turning stalls are among the maneuvers specifically required by the FAA Practical Test Standards.

For example, Objective 5 of Task C (POWER-ON STALLS) in the Private Pilot PTS notes that: "[The applicant must...] maintain a specified heading, ±10°, in straight flight; maintain a specified angle of bank not to exceed 20°, ±10°, in turning flight, while inducing the stall." (The standards are tighter in the Commercial Pilot PTS.)

Confusion (and anxiety) about turning stalls increases when the discussion moves along to slipping and skidding stalls. (You can find a good description of slips beginning on p. 8-10 of the Airplane Flying Handbook; the detailed discussion of stalls begins on p. 4-3. To learn more about the aerodynamics of slips, skids, and stalls, see Chapter 3, “Aerodynamics of Flight,” in the Pilot’s Handbook of Aeronautical Knowledge.)

The Airplane Flying Handbook offers general descriptions of the effects of slips and skids during stalls. For example:

An airplane will stall during a coordinated steep turn exactly as it does from straight flight, except that the pitching and rolling actions tend to be more sudden. If the airplane is slipping toward the inside of the turn at the time the stall occurs, it tends to roll rapidly toward the outside of the turn as the nose pitches down because the outside wing stalls before the inside wing. If the airplane is skidding toward the outside of the turn, it will have a tendency to roll to the inside of the turn because the inside wing stalls first. If the coordination of the turn at the time of the stall is accurate, the airplane’s nose will pitch away from the pilot just as it does in a straight flight stall, since both wings stall simultaneously (p. 4-10).

Many pilots have been startled by those effects during their training because the airplane was not coordinated when a stall occurred. And, as the Airplane Flying Handbook notes:

In a cross-control stall, the airplane often stalls with little warning. The nose may pitch down, the inside wing may suddenly drop, and the airplane may continue to roll to an inverted position. This is usually the beginning of a spin (p. 4-11).

If the airplane is yawing (i.e., if the airplane is rotating about its vertical axis—the nose is slewing ahead of or lagging behind the airplane's flight path), the effects described above are exaggerated and can surprise a pilot who hasn't been exposed to slipping and skidding stalls. Now, the Airplane Flying Handbook does note that stalls from slips are often less exciting than those from skids:

Unlike skids, however, if an airplane in a slip is made to stall, it displays very little of the yawing tendency that causes a skidding stall to develop into a spin. The airplane in a slip may do little more than tend to roll into a wings level attitude. In fact, in some airplanes stall characteristics may even be improved (p. 8-11).

But that reassurance often does little to reduce the heart rate of a pilot who suddenly experiences an uncommanded roll during a stall—even if the initial change in bank is back toward wings-level flight.

Video Demonstrations

It's often difficult to transfer the academic discussion excerpted above to practical experience in an airplane. Sudden rolls and rapid changes in pitch feel especially dramatic when you're in the pilot's seat. To help pilots see the effects of slips and skids on stalls, I experimented with several types of stalls during a series of flights in my Extra 300L.

You can find several videos about stalls, incipient spins, and spins at my YouTube channel, BruceAirFlying. For example, the following video shows incipient spins from skidding and slipping turns.

As the lawyers say, for you pilots out there, none of the videos is intended as instruction. They're just guides to help you understand stalls, slips, skids, and spins. If you want to explore stalls and spins in an airplane, get competent instruction in an appropriate aircraft.

The links below take you to more videos that focus on stalls and spins. All of the videos are in one of my SkyDrive folders.

The videos are in Windows Media Player format, which is available as a free download for both Windows and Mac OS systems.

Area near 61BThe following list describes the videos that I recorded during several flights in December 2006 from the Boulder City, NV (KBVU) airport near Las Vegas (the winter home for my Extra 300L). If you're curious about the area where I flew while capturing the videos, follow this link to a chart at Skyvector.com.

The videos show the typical effects of stalls in the conditions described for each demonstration and in the Airplane Flying Handbook. It's important to acknowledge that the Extra 300L is a high-performance aerobatic airplane. It has a spritely roll rate, plenty of power available for quick recoveries, inverted fuel and oil systems, etc. But when flown properly, it has benign stall characteristics (as the last video of an inverted stall demonstrates).

To learn more about how experience flying (or watching) an airplane like an Extra 300L relates to aviating in "normal" airplanes, I recommend reading "Low Impact Aerobatics" by Bruce Landsberg of the Air Safety Institute and "Transfer of Skills" from APS Emergency Maneuver Training.

Stalls at 61BEach airplane has its quirks, and pilot technique varies. The effects you experience in a particular make and model during stalls depend on many factors, such as the area and effectiveness of the flight controls, rigging, CG, pilot inputs, power settings, and so on.

Even a tame Cessna 172 can snap into a rapid roll when provoked, either through clumsy pilot technique in a stall or, for example, during an encounter with wake turbulence, as one of my colleagues discovered during an otherwise routine approach to Boeing Field (KBFI).

Nevertheless, airplanes share general flight characteristics, and the videos below demonstrate the effects of several situations that often come up in discussions of stalls and spins.

But now...on to the videos:

Learn More About Stalls and Spins

Airplane Flying HandbookYou can find excellent information, much of it free, from many sources on the Web. Here are some links that I recommend to my students and colleagues:

Authoritative Stall/Spin Information

Stowell coverThe best single source for information about stalls and spins in GA aircraft is Rich Stowell’s book, The Light Airplane Pilot’s Guide to Stall/Spin Awareness.

Stowell covers the history of stall/spin research and training, analyzes the perennial debate about the value of stall/spin training, and, most importantly, offers practical, sound advice about how anticipate and react to stall/spin phenomena in a variety of aircraft. It should be on the reading list of every pilot and flight instructor.