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OCKPIT CLASSROOM

HISTORY OF SPINS I n reading about the history of aerobatics, and especially the history of spins, in Acrobats In The Sky by John W. Underwood (1972) it is apparent that what was called the "spiral dive" in the early 1900's was one of the dark mysteries of aviation. In September 1911, Avro (British) test pilot Fred Raynham attempted to fly through a patch of fog and got into what was then known as a "spiral dive". In 1911 the term "tailspin" had not yet appeared in the glossary of aeronautics. According to early spin history, others had the same horrifying experience, invariably fatal, but Raynham somehow managed to recover control. "What caused this strange mystery, no one knew; some supposed it was simply an act of God," (Underwood 1972). According to early historical accounts of spinning following Raynham's near crash, another Englishman found himself in the same terrifying predicament. "Lt. Wilfred Parke of the Royal Navy had initiated a power-off spiral descent for a landing in his biplane (Avro) which fell into a spin to the left. Lt. Parke's first impulse was to get the nose up. Instinctively he added power, hauled back on the wheel and applied full left rudder, the latter action being the accepted method in dealing with the incipient side-slip. It was all to no avail; if anything the spinning accelerated. But Parke kept his head while centrifugal force was pressing him toward the right side of the cabin. Once he realized that it was the spinning, not the diving, that had to be checked, Parke applied right rudder and the spinning stopped allowing Parke to recover just 50 feet from the ground," (Underwood 1972). Since Parke's spin recovery, which had been witnessed by several observers, it was important to record this episode for the benefit of fellow airmen while the details were still fresh. According to Underwood, the report published by FLIGHT in August 1912 promulgated the first rule for spin recovery: APPLY

By Harold Holmes

"tailspin". Lincoln Beachey, who had built the famous Little Looper was supposed to have invented the term "tailspin" around the year 1915. There seems to be some confusion in the records whether Beachey actually performed the spin. In the early days of flying, the tailspin was a common and dangerous problem. Then it was described as "an uncontrolled, rotating dive earthward by the airplane and the motion resembles a corkscrew being drilled into a bottle. Now called simply a SPIN, it results when the aircraft is severely and fully stalled but it actually begins when one wing stalls ahead of the other one with the aircraft then falling off in the direction of the first wing. (This could happen, for instance, in a poorly coordinated steep turn.) The second wing,

RUDDER OPPOSITE TO THE DIRECTION OF ROTATION. This sounds familiar, doesn't it? Entitled Parke's

Dive, it evoked widespread interest and prompted the Royal Aero Club to suggest further experimentation. Another term which cropped up during the early days of flying was the term 48 FEBRUARY 1985

DIAGRAM 1

having more lift, ends up chasing the other one. As the plane descends, fully stalled, it rotates around its center of gravity, usually in a nose down attitude." This is an early description of a spin (Aerospace Encyclopedia). Spin instruction and spin recovery techniques were just beginning to be introduced in the United States in 1917. Some of the early pioneers (Underwood) were Gilbert G. "Gil" Budwig, a civilian flight instructor at Chanute Field, Illinois, Harold T. "Slim" Lewis, Eddie Hubbard, Mike Brown, Eddie Stinson, Lloyd Bertaud and E. Hamilton Lee. Stunt flying was prohibited in the U.S. Air Service up to 1917, however, in September 1917 Hubbard, Brown and Budwig were assigned to teach a new course called "Basic Battle Acrobacy and Trick Flying." Each American training center class was given a week's training in stalls, spins, loops, barrel rolls and chandelles (Underwood 1972). The "acrobatics" were performed in WWI Jennies. Shortly after the outbreak of World War I, the subject of spinning began to come up during hangar flying sessions. At this time in history, a spin was considered an extremely dangerous maneuver, however, a spinning airplane made a poor target in a dogfight. "A newly graduated LT. E. V. Rickenbacker, who loathed the thought of spinning, decided that there would be an advantage to be able to do it. He had much influence in getting spins introduced into the military flight training programs," (Underwood 1972). It is interesting to note that WWI aerobatic terminology had a strong French accent; "the Vrille' was a spin and a Virage' was a tight turn. The 'reinversement' came to be known as the 'split-S'. The 'barrel roll' of 1918 was a 'snap-roll'; today it is a form of aileron roll," (Underwood 1972). During WWI, an alarming number of fatalities were being caused by inverted spins in certain aircraft, notably the RAF Camel. Pilots who, according to early records, had survived the inverted spin experience only through trial and error techniques. After the end of WWI came a new concern for aviation safety. For instance, an investigation of 13 Camel accidents revealed that 10 had involved inverted spinning. Many different theories for the causes of these accidents were presented by investigators. One belief was that once in an inverted spin, it could not be checked. A program of testing was initiated late in an inverted spin, it could not be checked. A program of testing was initiated late in 1919 to determine the truth about inverted flight. The puzzle was soon to be solved. Lt. Joyce, an American, and T.F.N. Gerrard, a British Naval pilot with much Camel time, had discovered, through

DIAGRAM 2

desperate manipulation of the controls, that pulling the stick back instead of pushing it forward, as in a normal spin recovery, was the only inverted spin recovery technique. A report entitled The Maneuvers of Inverted Flight, published by the Aeronautical Research Committee, disspelled many misconceptions regarding inverted flight following the flight testing program. Spin research has been conducted on a continuous basis since the early 1900s and even today, the stall/spin has been cited as a causal factor in 30% of all fatal general aviation accidents according to NASA. A NASA report also indicates that the aircraft designer does not currently have a reliable means of determining stall/spin characteristics prior to prototype flight tests. This information, I would think, would be especially important for the amateur builder of a sport airplane. In recognition of this problem, NASA is continuing its efforts in the conduct of an extensive stall/spin research program at Langley Research Center. Some of the conclusions of NASA researchers is vital safety information for all pilots. One important finding by NASA, important for pilot training pro-

grams is that for recoverable spins, normal recovery controls (rudder against the spin followed by down elevator) provided the fastest recoveries (NASA Report, 79-1786). Out of a total of 529 spins performed using a low-wing research airplane, they studied spin characteristics ranging from slow and steep to fast and flat, and in 16 cases the spin recovery parachute was required to recover the airplane. Their findings in general indicated that deflecting ailerons with the spin (rolling into the spin) steepened the spin (reduced the angle of attack); deflecting ailerons against the spin (rolling out of the spin) flattened the spin — increasing the angle of attack. Eric Muller, following hours of spin tests, made some similar observations in his article The Spin — Myth and Reality. He mentions that using ailerons against the spin rotation makes the aircraft spin faster. Muller, in addition, points out that moving the stick forward also results in an increase in the rotation rate. Eric also states that the earliest method of getting out of a spin when disoriented is to close the throttle, remove the hands off the stick and kick full opposite rudder (see Diagram 2). SPORT AVIATION 49

site the direction in which the plane is spinning. This slows rotation. Then, with rudder pedals neutralized, the stall itself must be broken by forward pressure on the elevator controls. With the plane still in a dive, final recovery to straight-andlevel flight must be gradual until all of the controls become effective again. Power must be off during recovery," (Bennet 1968). Gene Beggs (EAA 80005) stated in

his article Aerobatics With Beggs

SPORT AVIATION 1984, that "the most important spin emergency spin recovery method is: 1. Cut the throttle 2. Take your hand off the stick 3. Kick full opposite rudder until the spin stops 4. Neutralize rudder and pull out of the dive" The FAA Flight Training handbook, AC 61 -21A (p. 157), states that any time a spin is encountered, regardless of the conditions, the normal spin recovery sequence should be used (see Diagram

1):

DIAGRAM 3

Another interesting point concerning the NASA spin tests were the spin entry combinations of normal, acceleration, roll, pitch, yaw and power. The spin in each case was identical after 1 or 2 turns regardless of entry conditions. Spin recoveries by NASA test pilots

were attempted by reversing rudder and then elevator (normal recovery controls), by simultaneously reversing rudder and elevator, by neutralizing controls, by reversing rudder alone and by reversing elevator alone. In all cases normal recovery controls provided the quickest recovery from moderately flat spins. Neutralizing controls produced the slowest recoveries. Reversing elevator alone would not recover the airplane. For most of the aircraft tested when recovery was attempted by reversing the rudder alone, the 50 FEBRUARY 1985

airplane would recover from left spins, but not from right spins. To check for slipstream effects, a 6-turn spin was performed with the propeller stopped. No changes were noted in the left or right turn recovery characteristics (NASA 1979). Spin Recovery Theories "In the majority of airplanes, the rudder is the principal control for spin recovery. Powerful control of sideslip at high angles of attack is required to effect recovery during a spin. Since the effectiveness of the vertical tail is reduced at large angles of attack, the directional control power necessary for spin recovery may produce a critical requirement of rudder power," (Aerodynamics For Naval Aviators 1965). "Recovery can be achieved fairly easily with application of full rudder oppo-

1. Retard power 2. Apply opposite rudder to slow rotation 3. Apply positive forward-elevator movement to break stall 4. Neutralize rudder as spinning stops and 5. Return to level flight In recent weeks I have had the unique opportunity to experience each of these spin recovery techniques with Woody Woods. Up until recent months, I only knew of one spin recovery technique and that was the spin recovery sequence which I learned in the Navy flight training program. Obviously, there is still some disagreement over spin recovery techniques among highly experienced pilots and various aviation agencies. Continuing spin research is still needed. Nevertheless, spin training is important and every pilot should be able to recognize when an incipient spin condition exists, and take prompt action to prevent a fully developed spin and to know the proper technique from a fully developed spin either inverted or upright. FAA says that performance on a pilot flight test is considered unsatisfactory if more than one turn of a spin occurs or if it becomes necessary to lake control of the airplane to avoid a fully developed spin. In the few articles in SPORT AVIATION Woody Woods and I will present our thoughts and experiences in spinning Cessna 172s and 152s as well as the aerodynamics of spins. If you wish to contact the author for additional information, please write Harold Holmes, 1038 Inverrary Lane, Deerfield, IL60015.