(From FAA General Aviation News, November/December 1979)
What are the chances that you will someday find yourself in the cockpit of an airplane that is spinning dizzily toward the ground, at an altitude that would allow time for a safe recovery if you knew how to carry out the correct procedure?
Pretty low. Spin accidents in general aviation have been averaging about 140 per year in recent years, according to the National Transportation Safety Board, but fewer than five percent of these spins developed high enough above the ground to allow for a normal recovery. Of course that is only part of the picture, since we have no data concerning the number of pilots who were able to pullout safely from an inadvertent spin and continue happily on their way. Chances are this number is not high either, because pilots who are able to extricate themselves safely from an unintentional spin are usually pretty savvy about avoiding it in the first place. We do know for a certainty that spins which culminate in an accident are more likely to cause fatalities than any other category of accident cause. In 1977, the latest year for which figures are complete, there were 147 spin accidents; 121 or 82% of these were fatal, with 206 fatalities. The proportions are typical for recent years. No other category of accident - even mid-air collisions - has as high a rate of fatal accidents.
As with stall awareness (see September/October issue of FAA General Aviation News), spin awareness requires a habit of constant alertness toward the conditions of flight. Inadvertent stalls and spins most often occur when the pilot is either busy with cockpit duties - as in landing or takeoff - or when his attention is drawn away from the airplane because of other interests ( crop dusting, search and rescue, forest or pipeline patrol, aerial photography, sightseeing, buzzing, etc. ) .Inflight mechanical problems or difficulties with weather also can be distractions which lead to loss of control. Spin recovery skills are little help when a pilot allows an airplane to enter a spin at an altitude too low to effect a recovery .An ounce of prevention here is worth many pounds of cure.
Pilots who wish to gain some experience in spin maneuvers are advised to begin with several hours of dual instruction from a certificated instructor, preferably one who has special experience in spin training. All pilots can benefit from a basic understanding of spin aerodynamics. A spin is often a confusing maneuver, with many unpredictable aspects that vary according to make and model, cabin loading, and other conditions, but the basic procedure for entry and recovery is fairly standard.
What is a spin? Theoretically, a spin can be described as a rapidly descending maneuver in which the airplane rotates about its vertical axis with unequally stalled wings. From the pilot's point of view the event is apt to be experienced in much more exciting terms.
All spins are preceded by a stall, but under some circumstances there may be little or no buffeting and the aircraft may appear to move directly from a yawing turn into a spin as the nose and one wing drops down.
Rotation speed builds up and the flight path becomes nearly vertical. At the completion of the first turn the nose may come back up and then pitch down again. By the end of the second turn the spin may be fully developed, as the rolling, pitching and turning motions become somewhat repeatable and stabilized from turn to turn. Airspeed is approximately stall speed, with the stall warning horn and lights signaling intermittently. Descent rate is significant, ranging from approximately 5,000 to 8,000 fpm in light single-engine planes. Stress load is minimal and not likely to cause damage even to an aircraft that is not designed for spinning ( although stress damage can occur during recovery with excessive "0" loads). The pilot may become dizzy or disoriented, especially if he stares at his spiralling wingtips.
Recovery from the spin involves arresting the rotation with rudder, breaking the stall by reducing the angle of attack on the wings and pulling out of the dive smoothly and positively without inducing excessive load factors on wings or tail assembly of the airplane.
Many aircraft will stop spinning if the pilot simply reduces power to idle and takes his hands and feet off the controls. However, unless the pilot promptly resumes control, the airplane may continue in a spiral descent.
A spiral dive, incidentally, is often confused with a spin, and it is important to be able to distinguish between the two. In a spin the aircraft remains stalled, with little or no aileron response, and a fairly stabilized airspeed and attitude. In a steep spiral the aircraft is not stalled; the bank angle may steepen; and the airspeed may build up excessively in a short time. One clue is in the airspeed indicator; in a spin it will not read much above stall speed. Recovery procedures are not alike, and if inappropriately applied could worsen the situation. Subjective impressions are not reliable.
This is the basic procedure for most light, single-engine aircraft, and it also applies to most light twins. With some twins, if normal procedures do not result in recovery, power from the engine in the down wing can be used to stop rotation, but if the wrong throttle is advanced the results could work against recovery. Airplane spin characteristics vary broadly, so defer always to the recommendations of your manufacturer.
Caution: The principles outlined above are for general understanding, and are NOT intended as guidelines for self-instruction in spin recovery practice. No one should deliberately spin an aircraft without prior dual instruction.
Note: since an aircraft spins around its center of gravity, aircraft loading affects recovery. In general, the farther forward the center of gravity (within allowed limits), the more responsive the rudder will be in stopping rotation. An excessively aft C.G. will reduce the effectivenesss of the rudder and make it more difficult (perhaps impossible) to recover. That is why many aircraft are placarded against spins with passengers in the rear seats. Even in a (side by side) two-seater, when recovery is sluggish, pushing the pilot seats as far forward as they can go may help.
The rudder is the key control surface, both in spin entry and recovery .The dominant cause of the inadvertent spin is exceeding the critical angle of attack for a given stall speed while executing a turn with excessive or insufficient rudder - an uncoordinated turn. In a sense, the lack of coordination could also be ascribed to insufficient or excessive aileron, but when the airplane approaches stall speed the ailerons may be nearly or completely unresponsive - at a stage where the rudder is still fairly effective. The spin normally goes in the direction indicated by the rudder; i.e., holding left rudder will normally give you a rotation to the left, right rudder will normally give you a rotation to the right, regardless of which wing tip is raised.
In a skidded turn (to the left, for example) it seems natural to expect that if a stall and spin develop, the rotation will be with the rudder, since the left aileron and rudder are being held. But in a slip, with opposite aileron held against the rudder, it comes as a surprise to some pilots to find that if a spin develops the wing will usually roll over against the held aileron.
It is also important to remember that in an uncoordinated maneuver such as a slip, pitot/ static instruments, notably altimeter and airspeed, are unreliable (because of the uneven distribution of air pressure over the fuselage). Unless the pilot is very attentive to the feel of the controls he may not realize he has exceeded the critical angle of attack until he hears the stall warning horn, and by that time it may be too late to avoid a stall and possible a spin.
The slip, incidentally, is a maneuver which historically developed as a means of burning off excessive altitude during an approach to land without turning or going around, in airplanes without wing flaps. Some pilots and instructors now advise against its use at low altitudes, because of the possibility that with insufficient airspeed a stall and spin could result. S-turns are considered by some as a better way of losing altitude; if they do not suffice, a go-around is likely to be a safer maneuver than a slip close to the ground, where unexpected turbulence could easily convert the slip into a deadly spin.
Remember, rudder pressure initiates the spin rotation, rudder pressure sustains it, and opposite rudder pressure is the primary means of arresting the rotation. (Some airplanes will stop rotating if the rudder pressure is simply released, some will not.) All other control inputs are likely to worsen the situation. Pushing the control wheel forward, for example, before applying appropriate rudder pressure, may prolong recovery because of increased blanketing of the rudder, or lead to an inverted spin. (Recovery from an inverted spin, which requires reversed use of rudder and elevator, would be extremely difficult and confusing for a non-aerobatic pilot.)
The length of time required for the rudder to stop the turn will depend upon the design of the tail and the angle of the attack. In a spin attitude, the horizontal stabilizer may blanket the rudder to some extent, depending on design because of the near-vertical movement of air. No matter how close he is to the ground, the pilot must resist panic impulses to pull back on the control wheel before the rotation and the stall have been overcome. Care must be taken as soon as rotation stops to neutralize the rudder, in order to prevent a possible spin in the opposite direction, or recovering inverted.
The only certain method of breaking out of the stall is reducing the wing angle of attack and recovering to level flight smoothly and positively as the airspeed builds up. If the ground is already very close, the outcome may be in doubt, to say the least, but the pilot has no alternative. Unless he reduces the angle of attack with down elevator at this point, the airplane may immediately stall and possibly spin again. He must trade off altitude for control. If an impact cannot be prevented the less control the pilot has, the poorer his chances of survival. Attempting to increase airspeed by opening the throttle prematurely is likely to pull the nose up excessively and bring about an accelerated stall. Avoiding that sinking, spinning feeling at a low altitude is a matter of constant control - and of maintaining airspeed and attitude appropriate to the maneuver being carried out. Specialized pilot training and study, however helpful, do not eradicate the tendency of an airplane to stall and spin under favorable conditions. Furthermore, an airplane which recovered easily from a spin under one set of circumstances may resist recovery strongly under other circumstances. A slight modification of the airfoil (from icing, for example, or dried mud), a small change in the configuration - even an uncalculated change in density altitude over high terrain could affect recovery time, with serious consequences.
Perhaps some day a spin-proof aircraft will be designed. Meanwhile, expect them all to be potential dervishes. Don't turn them on.
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