THE FAA in their Advisory Circular AC61.67C paragraph 107 describe spins as “A spin in a small airplane or glider is a controlled (recoverable) or uncontrolled (possibly unrecoverable) maneuver in which the airplane or glider descends in a helical path while flying at an AOA greater than the critical AOA. Spins result from aggravated stalls in either a slip or a skid ( see this interesting video http://www.avweb.com/avwebflash/exclusivevids/ExclusiveVideo_AviationSafety_Cirrus_StallAccident_Dissected_201722-1.html ).
If a stall does not occur, a spin cannot occur. In a stall, one wing will often drop before the other and the nose will yaw in the direction of the low wing.”
CLEAR as mud, right? I won’t go into all the aerodynamics involved in a spin as there are numerous books and articles (including the FAA publication The Airplane Flying Handbook) that are readily available for the detail oriented. Suffice it to say that in order to have a spin, you must have a stall with yaw. The yaw causes one wing to produce more lift than the other which causes a rotation around the COG with the wing producing the least lift on the low side.
THERE are four distinct phases of flight associated with a spin;
The entry, the pilot stalls the plane while in uncoordinated flight.
Incipient, the rotation starts.
Developed, the aircraft’s rotation rate, airspeed, and vertical speed are stabilized.
Recovery, when the pilot inputs the recommended control inputs from the POH.
NASA has published a generic spin recovery procedure if there is not specific guidance in the POH. The procedure is;
Power, reduce power to idle.
Ailerons, neutralize the ailerons.
Rudder, full rudder opposite the rotation and held.
Elevator, add forward pressure to the elevator control through neutral.
Now, recover from the resulting dive.
OK, so much for the theory, from now on I will refer specifically to the Citabria and the procedures we will be using when we fly it.
The entry into a spin in the Citabria is nothing more than a power off stall and at the moment of stall, add full rudder in the direction in which you want to spin.
As the airplane stalls, the wing on the side of full rudder input starts to drop in a leisurely manner, and as it drops through about 60 degrees, the nose falls and a rapid rotation begins.
After approximately 1 full turn, the rotation and nose down attitude stabilizes with the airspeed indicator reading near stall. This is where most people doing their first spin become disoriented. The spinning earth fills the windscreen and the mind just goes blank. It takes 2 or 3 different spins before everything starts to make sense and the eyes can follow landmarks on the ground.
Recovery consists of ensuring the throttle is to idle, ailerons are neutral (stick in the center). Add full rudder opposite the direction of rotation and relax the back pressure on the elevator control through neutral (stick forward). The spin will stop within ¼ turn and you will find yourself in what seems like a vertical dive.
Start the recovery from the resulting dive as soon as possible to restrict the airspeed build up by adding aft stick shooting for around 3 G’s in the recovery. Continue the recovery right into a climb attitude and as the speed falls back towards the climb speed add power to climb to recover the lost altitude.
INADVERTENT spins are scary and dangerous things. A NASA study in the 1970’s showed that a Piper Arrow took approximately 1200 feet to recover from a spin while a FAA Small Airplane Directorate study done later found that of 1700 stall/spin accidents dating from 1973, 93% started at or below pattern altitude. Generally, pattern altitude minus 1200’ is below ground level. As you would expect, most of these were fatal.
INTENTIONAL spins are scary things initially, but are not dangerous and quickly become routine (and even fun) when done with proper instruction at the proper altitude. The forces acting on the airplane during a spin are negligible with the most active forces coming during recovery from the dive.
SPIN training is an eye opening experience and when done in the proper spirit and mind set can be fun and exciting. It may even save your life someday.
Someone smarter than I once said, "When confronted with a crisis, you will not rise to the occasion; You will sink to the level of your training".