Spinning and Recovery
Spins are uncontrolled rotations of a fully stalled airplane. In aviation’s early years, when spins were first encountered, spinning airplanes descended more or less straight down. The motion was mainly yawing and quite stable. Stability and control engineers were concerned only with recovery from spins into unstalled flight.
The coming of jet airplanes saw mass distribution changes that caused spins to be oscillatory. Emphasis shifted somewhat to the entry phase of spins and design features that made spin entry less likely during flight operations. This chapter traces the changing nature of airplane spinning from the early days and the corresponding engineering responses.
9.1 Spinning Before 1916
The spinning experience in the early days of aviation is described by B. Melvill Jones (1943):
In the early days of flying – before 1916 – the spin generally ended fatally, because what later proved to be the most effective means of checking it was in some respects contrary to the natural reaction of the pilot to the realization that he was diving towards the earth. About 1916 it was discovered that an effective way of checking the type of spin which was common in those days was to thrust the control stick forward and apply rudder in the sense opposed to the rotation. For some time after this knowledge had become general, relatively few fatalities due to spinning occurred, provided that there was enough air-room for the spin to be checked and the resulting steep dive converted into horizontal flight; the spin then became an ordinary manoeuvre.
Jones goes on to tell of the first flat spins, which occurred around 1919. Previously, spins had been steep in pitch attitude, with corresponding low stalled angles of attack of 25 to 35 degrees. On the other hand, the new flat spins had low pitch attitudes and high angles of attack, 45 degrees or higher, and high rotation rates. The flat spins were more dangerous than the early variety. An interesting speculation is that the invention of the parachute increased the number of survivors who could give reports of spins that had become uncontrollable, thus accounting for a seeming increase in the number of flat spins.