Airspeed indicator

From Wikipedia, the free encyclopedia

Airspeed Indicator in a light single engine aircraft

The airspeed indicator or airspeed gauge is an instrument used in an aircraft to display the craft's airspeed, typically in knots, to the pilot.

Markings

A high sensitivity "540 degree" airspeed indicator used in a glider. The pointer swings past zero (top), but the colored arcs do not overlap. The needle shows an indicated airspeed of 60 knots.

Light aircraft

Airspeed indicator markings use a set of standardized colored bands and lines on the face of the instrument. The white range is the normal range of operating speeds for the aircraft with the flaps extended as for landing or takeoff. The green range is the normal range of operating speeds for the aircraft without flaps extended. The yellow range is the range in which the aircraft may be operated in smooth air, and then only with caution to avoid abrupt control movement.

A redline mark indicates V_NE, or velocity (never exceed). This is the maximum demonstrated safe airspeed that the aircraft must not exceed under any circumstances. The red line is preceded by a yellow band which is the caution area, which runs from V_NO (maximum structural cruise speed) to V_NE. A green band runs from V_S1 to V_NO. V_S1 is the stall speed with flaps and landing gear retracted. A white band runs from V_SO to V_FE. V_SO is the minimum steady flight speed with flaps extended, and V_FE is the highest speed at which flaps can be extended. Airspeed indicators in multi-engine aircraft show a short radial red line near to the bottom of green arc for V_mc, the minimum indicated airspeed at which the aircraft can be controlled with the critical engine inoperative and a blue line for V_YSE, the speed for best rate of climb with the critical engine inoperative.

Airspeed indicator markings for a light multiengine airplane.

Large aircraft

The airspeed indicator is especially important for monitoring V-Speeds while operating an aircraft. However, in large aircraft, V-speeds can vary considerably depending on airfield elevation, temperature and aircraft weight. For this reason the coloured ranges found on the ASIs of light aircraft are not used - instead the instrument has a number of moveable pointers known as bugs which may be preset by the pilot to indicate appropriate V-speeds for the current conditions.

Jet aircraft do not have V_NO and V_NE like piston-engined aircraft, but instead have a maximum operating IAS, V_MO and maximum Mach number, M_MO. To observe both limits, the pilot of a jet airplane needs both an airspeed indicator and a Machmeter, each with appropriate red lines. In some general aviation jet airplanes, the Machmeter is combined into a single instrument that contains a pair of concentric indicators, one for the indicated airspeed and the other for indicated Mach number.

An alternative single instrument is the "maximum allowable airspeed indicator." It has a movable pointer that indicates the never-exceed speed, which changes with altitude to avoid the onset of transonic shock waves on the wing. The pointer is usually red-and-white striped, and thus known as a "barber pole". As the aircraft climbs to high altitude, such that M_MO rather than V_MO becomes the limiting speed, the barber pole moves to lower IAS values.

Modern aircraft employing glass cockpit instrument systems employ two airspeed indicators: an electronic indicator on the primary flight data panel and a traditional mechanical instrument for use if the electronic panels fail. The airspeed is typically presented in the form of a "tape strip" that moves up and down, with the current airspeed in the middle. The same color scheme is used as on a mechanical airspeed indicator to represent the V speeds.In modern aircraft it even have another electronic indicator airspeed.

Operation

Airspeed indicator connections

Along with the altimeter and vertical speed indicator, the airspeed indicator is a member of the pitot-static system of aviation instruments, so named because they operate by measuring pressure in the pitot and static circuits.

Airspeed indicators work by measuring the difference between static pressure, captured through one or more static ports; and stagnation pressure due to "ram air", captured through a pitot tube. This difference in pressure due to ram air is called impact pressure.

Internal mechanism of an airspeed indicator

The static ports are located on the exterior of the aircraft, at a location chosen to detect the prevailing atmospheric pressure as accurately as possible, that is, with minimum disturbance from the presence of the aircraft. Some aircraft have static ports on both sides of the fuselage or empennage, in order to more accurately measure static pressure during slips and skids. Aerodynamic slips and skids cause either or both static ports and pitot tube(s) to present themselves to the relative wind in other than basic forward motion. Thus, alternative placement on some aircraft.

Icing is a problem for pitot tubes when the air temperature is below freezing and visible moisture is present in the atmosphere, as when flying through cloud or precipitation. Electrically heated pitot tubes are used to prevent ice forming over the tube.

The airspeed indicator and altimeter will be rendered inoperative by blockage in the static system. To avoid this problem, most aircraft intended for use in instrument meteorological conditions are equipped with an alternate source of static pressure. In unpressurised aircraft, the alternate static source is usually achieved by opening the static pressure system to the air in the cabin. This is less accurate, but is still workable. In pressurised aircraft, the alternate static source is a second set of static ports on the skin of the aircraft, but at a different location to the primary source.

Use

The airspeed indicator is used by the pilot during all phases of flight, from take-off, climb, cruise, descent and landing in order to maintain airspeeds specific to the aircraft type and operating conditions as specified in the Operating Manual.

During instrument flight, the airspeed indicator is used in addition to the Artificial horizon as an instrument of reference for pitch control during climbs, descents and turns.

The airspeed indicator is also used in dead reckoning, where time, speed, and bearing are used for navigation in the absence of aids such as NDBs, VORs or GPS.

Alternatives: Lift Reserve Indicator

Lift Reserve Indicator as installed

The "Lift Reserve Indicator", or LRI, has been proposed as an alternative or backup to the Airspeed Indicator (ASI) during critical stages of flight. This is an elegant device but is rarely found in light aircraft or even transport jets. The conventional Airspeed Indicator is less sensitive and less accurate as airspeed diminishes, thus providing less reliable information to the pilot as the aircraft slows towards the stall. The actual stall speed of an aircraft also varies with flight conditions, particularly changes in gross weight and wing loading during maneuvers. The ASI does not show the pilot directly how the stall is being approached during these maneuvers, whereas the LRI does.

The LRI shows the pilot directly the Potential of Wing Lift (POWL) above the stall at all times and at any airspeed, so it is more descriptive and easier for the pilot to use. The LRI uses dynamic differential pressure and angle of attack to operate. It is very fast acting and extremely accurate at slow airspeeds, thus providing more reliable information to the pilot as airspeed diminishes and become critical.

The LRI uses a three zone, red-white-green display. During flight, the green zone is well above the stall where flight controls are firm, angle of attack is low, and the unused POWL is high. The white zone is near the stall where flight controls soften, angle of attack is high, and the unused POWL is diminished. The top of the red zone defines the beginning of the stall. The severity of stall increases as the needle travels deeper into the red. During the takeoff, the LRI uses dymanic pressure to operate and will not lift the needle above the red zone until enough airspeed energy is available to fly.

The pilot adjusts the instrument to indicate the edge of the red-white zone during minimum airspeed practice at altitude, indicating the aircraft has zero POWL beyond that point. Since the wing will stall at the same angle of attack at any airspeed, once properly adjusted the LRI will indicate the red-white edge anytime the stall is approached. This includes landing stalls, climbing stalls, and accelerated stalls. After adjustment, the black line in the center of the white indicates maximum angle of climb and maximum angle of descent with enough reserve lift for the landing flare. With practice, the pilot can use the LRI to determine the exact moment for liftoff with minimum ground roll and maximum angle of climb combined.

The LRI has been well received by STOL pilots and pilots of experimental or home-built aircraft. The LRI is very useful for short field landings, short field takeoffs, and slow speed maneuvers such as steep turns, steep climbs, and steep descents, and also allows pilots of fast or "slippery" aircraft to land with little or no float very reliably. Since the LRI is so useful at the critical lower end of the flight envelope, most pilots will use the LRI as a complement to the ASI, using the LRI for slow speed work and the ASI for cruising and navigational work.

Types of airspeed measurements

Memory aid: "ICE-T" (iced tea), or Indicated->Calibrated->Equivalent->True

At increased Density Altitude, for the same given indicated airspeed the aircraft's true airspeed (TAS) will be higher, but the same indicated airspeed limits (IAS) apply. Likewise, most efficient cruise speed, total drag, available lift, stall speed, and other aerodynamic information depend on calibrated, not true airspeed. Most aircraft exhibit a small difference between the airspeed actually shown on the instrument (indicated airspeed, or IAS) and the speed the instrument should theoretically show (calibrated airspeed or CAS). This difference, called position error, is mainly due to inaccurate sensing of static pressure. It is usually not possible to find a position for the static ports which, at all angles of attack, accurately senses the atmospheric pressure at the altitude at which the aircraft is flying.

Bernoulli's principle states that total pressure is constant along a streamline. Pitot pressure is equal to total pressure so pitot pressure is constant all around the aircraft and does not suffer position error. (However, pitot pressure can suffer alignment error if the pitot tube is not aligned directly into the oncoming airflow.)

The position of static ports must be selected carefully by an aircraft designer because position error must be small at all speeds within the operating range of the aircraft. A calibration chart specific to the type of aircraft is usually provided.

At high speeds and altitudes, calibrated airspeed must be further corrected for compressibility error to give equivalent airspeed (EAS). Compressibility error arises because the impact pressure will cause the air to compress in the pitot tube. The calibration equation (see calibrated airspeed) accounts for compressibility, but only at standard sea level pressure. At other altitudes compressibility error correction may be obtained from a chart. In practice compressibility error is negligible below about 3,000 m / 10,000 feet and 100 m/s / 200 knots CAS.

The true airspeed can be calculated as a function of equivalent airspeed and local air density, (or temperature and pressure altitude which determine density). Some airspeed indicators incorporate a slide rule mechanism to perform this calculation. Otherwise, it can be performed with a calculator such as the E6B handheld circular slide rule. For a quick approximation of TAS add 2% per 300m / 1000 feet of altitude to IAS (or CAS). e.g. IAS = 52 m/s /100 Knots. At 3000 m / 10,000' Above Sea Level, TAS is 62 m/s / 120 Knots.

See also

• Airspeed
• Flight instruments
• Machmeter
• Position error
• V speeds

Sources

• (2004) Airplane Flying Handbook. U.S. Government Printing Office, Washington D.C.: U.S. Federal Aviation Administration. FAA-8083-3A.
• (2005-11-25) Instrument Flying Handbook. U.S. Government Printing Office, Washington D.C.: U.S. Federal Aviation Administration. FAA-H-8083-15.
• (2003) Pilot's Handbook of Aeronautical Knowledge. U.S. Government Printing Office, Washington D.C.: U.S. Federal Aviation Administration. FAA AC 61-23C.

Installing and flying the Lift Reserve Indicator, article and photos by Sam Buchanan http://home.hiwaay.net/~sbuc/journal/liftreserve.htm

This article incorporates text from Airplane Flying Handbook, a public domain work of the United States Government.
This article incorporates text from Instrument Flying Handbook, a public domain work of the United States Government.
This article incorporates text from Pilot's Handbook of Aeronautical Knowledge, a public domain work of the United States Government.

Stick shaker

From Wikipedia, the free encyclopedia

A stick shaker is a mechanical device to rapidly and noisily vibrate the control yoke (the "stick") of an aircraft to warn the pilot of an imminent stall. It is connected to the control column of most business jets, airliners and military aircraft.

The stick shaker is a component of the aircraft's Stall Protection System, which is composed of wing-mounted angle of attack sensors that are connected to an avionics computer. The computer receives input from the AOA sensors and a variety of other flight systems. When the data indicates an imminent stall condition, the computer actuates both the stick shaker and an auditory alert.

The shaker itself is composed of an electric motor connected to a deliberately unbalanced flywheel. When actuated, the shaker induces a forceful, noisy and entirely unmistakable shaking of the control yoke. This shaking of the control yoke matches the frequency and amplitude of the stick shaking that occurs due to airflow separation in conventional aircraft as they approach the stall. The stick shaking is intended to act as a backup to the auditory stall alert, in cases where the flight crew may be distracted.

In larger aircraft (especially in T-tailed jets that might be vulnerable to deep stall), some Stall Protection Systems also include a stick pusher system to automatically push forward on the elevator control, thus reducing the aircraft's angle of attack and preventing the stall.

Both systems have to be tested and armed before takeoff and remain on during flight.

References

Patent for Boeing Stall Protection System (with description)
http://www.patentstorm.us/patents/5803408-claims.html

Retrieved from "http://en.wikipedia.org/wiki/Stick_shaker"

Stall (flight)

From Wikipedia, the free encyclopedia

In aerodynamics, a stall is a sudden reduction in the lift forces generated by an airfoil. This occurs when the critical angle of attack of the airfoil is exceeded, typically about 14 to 16 degrees.

Because stalls are most commonly discussed in connection with aviation, this article discusses stalls mainly as they relate to aircraft. In simple terms, a stall in an aircraft is an event that causes the wing to lose lift suddenly.

Note that an aerodynamic stall does not mean that an aircraft's engines have stopped or that the aircraft has stopped moving.

Overview

Aircraft are supported in the air by an aerodynamic force called lift, which is generated by the wings of the aircraft as air flows past the wings as a result of the forward movement of the aircraft. The wings of the aircraft generate lift because of a pressure reduction above the wings. The lower pressure above the wing combined with the higher pressure under the wing constitutes lift.^[1] An immediate increase in lift can be obtained by increasing the angle between the wing chord and the relative airflow. (The angle is called the angle of attack, or AOA, and is often symbolized with the Greek letter alpha.)

But increasing the AOA also increases drag. Without a sufficient increase in engine power, the aircraft slows, and wing-lift decreases. Above a particular angle, the "critical angle of attack", the airflow behind the wings becomes turbulent, the wing-lift largely disappears, and the wing stalls—that is, it suddenly ceases to provide enough lift to support the aircraft.^[2] In addition, the turbulence dramatically increases drag, which further slows the aircraft as it moves through the air, further reducing wing-lift. Rapidly the aircraft begins to accelerate downward.

In many aircraft recovering from a stall is simple. Since the stall is caused by an excessive angle of attack, simply pointing the nose of the aircraft downward will arrest the stall by reducing the angle between the wings and the flow of air (this is for a fixed wing aircraft rather than a helicopter). Some aircraft have a natural tendency to pitch downward (sometimes dramatically) when the wings stall; others must be directed downward by the pilot. As soon as the angle of attack drops below the critical angle, the aerodynamic stall of the wings will cease: the wings will start to produce lift and far less drag. However, the aircraft may still be flying too slowly to generate enough lift to prevent the aircraft from continuing to descend: complete stall recovery includes regaining this necessary speed.

In some circumstances stalls can result in more complicated problems, such as a 'spin' or a 'deep stall'.

A stall is caused by the pilot attempting to fly the aircraft too slowly, or to pull up too quickly from a dive, or to turn too steeply. Each of these causes the nose to be lifted until the wing's critical angle of attack is exceeded. Increasing engine power counteracts the increased drag caused by the stall and also increases air speed, and this helps in recovery from a stall. The critical action in recovering from a stall is reduction in the angle of attack, i.e., lowering the nose.

Altitude (height above the ground) is lost by the aircraft during the stall itself but considerably more height can be lost during the recovery. If the aircraft is already at a high altitude this is not a problem. If the aircraft is very close to the ground, however, a stall may cause the aircraft to lose so much altitude that it hits the ground before recovery from the stall is possible. For this reason, pilots are especially careful to avoid stalls during take-off and landing procedures, when the aircraft is very close to the ground.

Stalls in aircraft usually do not occur without warning. In addition to sensors which alert the pilot when the aircraft is about to stall, experienced pilots can sense an incipient stall by noting changes in the behavior of the aircraft. Since the conditions that produce stalls are very well understood, pilots can easily avoid stalls, and many pilots never experience stalls outside of their pilot training. Standard pilot training includes training in the proper ways to avoid, recognize, and recover from stalls.

A few types of aircraft with a T-shaped tail or rear-mounted engines can enter a deep stall or superstall. This is a type of stall that produces turbulence behind the wings that can interfere with the operation of engines or the tail of the aircraft. Recovery from a deep stall can be impossible, resulting in a crash. Some aircraft with such characteristics are fitted with special control devices to prevent the aircraft from ever approaching a position that can cause a deep stall. An example of such a device is a stick pusher, which forces the nose of the aircraft down whenever it approaches a stall, regardless of any actions taken by the pilot.

The remainder of this article describes stalls in more technical terms.

Formal definition

A stall is a condition in aerodynamics and aviation where the angle between the wing's chord line and the relative incoming wind (the angle of attack) increases beyond a certain point such that the lift begins to decrease. The angle at which this occurs is called the critical angle of attack. This critical angle is dependent upon the profile of the wing, its planform, and its aspect ratio but is typically in the range of 8 to 20 degrees relative to the incoming wind for most subsonic airfoils. The critical angle of attack is the angle of attack on the lift coefficient versus angle-of-attack curve at which the maximum lift coefficient occurs, and it usually represents the boundary between the wing's linear and nonlinear airflow regimes. Flow separation begins to occur at this point, decreasing lift, increasing drag, and changing the wing's center of pressure. A fixed-wing aircraft during a stall may experience buffeting or a change in attitude (normally nose down in General aviation aircraft). Most aircraft are designed to have a gradual stall with characteristics that will warn the pilot and give the pilot time to react. For example an aircraft that does not buffet before the stall may have an audible alarm or a stick shaker installed to simulate the feel of a buffet by vibrating the stick fore and aft. The "buffet margin" is, for a given set of conditions, the amount of ‘g’, which can be imposed for a given level of buffet. The critical angle of attack in steady straight and level flight can only be attained at low airspeed. Attempts to increase the angle of attack at higher airspeeds can cause a high speed stall or may merely cause the aircraft to climb.

Any yaw of the aircraft as it enters the stall regime can result in autorotation, which is also sometimes referred to as a 'spin'. Because air no longer flows smoothly over the wings during a stall, aileron control of roll becomes less effective, whilst simultaneously the tendency for the ailerons to generate adverse yaw increases. This increases the lift from the advancing wing and accentuates the probability of the aircraft to enter into a spin.

Depending on the aircraft's design, a stall can expose extremely adverse properties of balance and control; particularly in a prototype.

An example of the relationship between angle of attack and lift of a wing. The exact relationship depends on the wing section profile/planform & its aspect ratio.

Graph

The graph shows that the greatest amount of lift is produced as the critical angle of attack is reached (which in early 20th century aviation was called the "burble point"). This angle is 17.5 degrees in this case but changes from airfoil to airfoil. The graph shows that as the angle of attack is exceeded beyond the critical angle, the lift produced by the wing decreases significantly. The airfoil is now stalled.

This graph shows the stall angle, yet in practice most pilots discuss stalling in terms of airspeed. This is because in general terms the angle of attack can be related to airspeed - a lower speed requires a greater angle of attack to produce the necessary lift and vice versa. Thus as speed falls, AoA can increase, until the critical angle is reached. The airspeed at which this angle is reached is the (1g, unaccelerated) stalling speed of the aircraft in that particular configuration. Deploying flaps/slats decreases the stall speed to allow the aircraft to land at a lower speed.

Aerodynamic description of a stall

Stalling an aeroplane

An aeroplane can be made to stall in any pitch attitude or bank angle or at any airspeed but is commonly practiced by reducing the speed to the unaccelerated stall speed, at a safe altitude. Unaccelerated (1g) stall speed varies on different aeroplanes and is represented by colour codes on the air speed indicator. As the plane flies at this speed the angle of attack must be increased to prevent any loss of altitude or gain in airspeed (which corresponds to the stall angle described above). The pilot will notice the flight controls have become less responsive and may also notice some buffeting, a result of the turbulent air separated from the wing hitting the tail of the airplane.

In most light aircraft, as the stall is reached the aircraft will start to descend (because the wing is no longer producing enough lift to support the aeroplane's weight) and the nose will pitch down. Recovery from this stalled state usually involves the pilot decreasing the angle of attack and increasing the air speed, until smooth air flow over the wing is resumed. Normal flight can be resumed once recovery from the stall is complete. The manoeuvre is normally quite safe and if correctly handled leads to only a small loss in altitude. It is taught and practised in order to help pilots recognize, avoid, and recover from stalling the aeroplane.

The most common stall-spin scenarios occur on takeoff (departure stall) and during landing (base to final turn) because of insufficient airspeed during these manoeuvres. Stalls also occur during a go-around manoeuvre if the pilot does not properly respond to the out-of-trim situation resulting from the transition from low power setting to high power setting at low speed. Stall speed is increased when the upper wing surfaces are contaminated with ice or frost creating a rougher surface.

A special form of asymmetric stall in which the aircraft also rotates about its yaw axis is called a spin. A spin will occur if an aircraft is stalled and there is an asymmetric yawing moment applied to it. This yawing moment can be aerodynamic (sideslip angle, rudder, adverse yaw from the ailerons), thrust related (p-factor, one engine inoperative on a multi-engine non-centreline thrust aircraft), or from any number of possible sources of yaw.

Stalls can occur at higher speeds if the wings already have a high angle of attack. Attempting to increase the angle of attack at 1g by moving the control column back simply causes the aircraft to rise. However the aircraft may experience higher g, for example when it is pulling out of a dive. In this case, the wings will already be generating more lift to provide the necessary upwards acceleration and so there will be higher angle of attack. Increasing the g still further, by pulling back on the control column, can cause the stalling angle to be exceeded even at a high speed. High speed stalls produce the same buffeting characteristics as 1g stalls and can also initiate a spin if there is also any yawing.

Symptoms of an approaching stall

One symptom of an approaching stall is slow and sloppy controls. As the speed of the aeroplane decreases approaching the stall, there is less air moving over the wing and therefore less air will be deflected by the control surfaces (ailerons, elevator and rudder) at this slower speed. Some buffeting may also be felt from the turbulent flow above the wings as the stall is reached. However during a turn this buffeting will not be felt and immediate action must be taken to recover from the stall. The stall warning will sound, if fitted, in most aircraft 5 to 10 knots above the stall speed.

Stalling characteristics

Different aircraft types have different stalling characteristics. A benign stall is one where the nose drops gently and the wings remain level throughout. Slightly more demanding is a stall where one wing stalls slightly before the other, causing that wing to drop sharply, with the possibility of entering a spin. A dangerous stall is one where the nose rises, pushing the wing deeper into the stalled state and potentially leading to an unrecoverable deep stall. This can occur in some T-tailed aircraft where the turbulent airflow from the stalled wing can blanket the control surfaces at the tail.

“Stall speed”

Airspeed Indicator

Stalls depend more on angle of attack rather than airspeed. However, since, for every weight of every aircraft, there is an airspeed at which the wing's angle of attack will exceed the critical angle of attack, airspeed in a given configuration is often used as an indirect indicator of approaching stall conditions.

There are multiple V speeds which are used to indicate when a stall will occur:

• V_S: the computed stalling speed with flaps retracted at design speed. Often has the same value as V_S1.
• V_S0: the stalling speed or the minimum steady flight speed in landing configuration (full flaps, landing gear down, spoiler retracted).
• V_S1: the stalling speed or the minimum steady flight speed in a specific configuration (usually a "clean" configuration with flaps, landing gear and spoilers all retracted).
• V_SR: reference stall speed.
• V_SR0: reference stall speed in the landing configuration.
• V_SR1: reference stall speed in a specific configuration.
• V_SW: speed at which onset of natural or artificial stall warning occurs.

On an airspeed indicator, the bottom of the white arc indicates V_S0 at maximum weight, while the bottom of the green arc indicates V_S1 at maximum weight. While an aircraft's V_S speed is computed by design, its V_S0 and V_S1 speeds must be demonstrated empirically by flight testing.

Accelerated stall

Illustration of an accelerated stall, occurring during a co-ordinated turn.

An accelerated stall is a stall that occurs at a higher airspeed than the design stall speed – which always refers to straight and level, unaccelerated flight – because of the fact that the aircraft is maneuvering (i.e. accelerating).^[3] A notable example of air accident caused by a low-altitude accelerated stall is the 1994 Fairchild Air Force Base crash.

Deep stall

Illustration of a deep stall

A deep stall (also called a superstall) is a dangerous type of stall that affects certain aircraft designs, notably those with a T-tail configuration. In these designs, the turbulent wake of a stalled main wing "blankets" the horizontal stabilizer, rendering the elevators ineffective and preventing the aircraft from recovering from the stall.

Although effects similar to deep stall had long been known to occur on many aircraft designs, the name first came into widespread use after a deep stall caused the prototype BAC 1-11 to crash, killing its crew. This led to changes to the aircraft, including the installation of a stick shaker (see below) in order to clearly warn the pilot of the problem before it occurred. Stick shakers are now a part of all commercial airliners. Nevertheless, the problem continues to haunt new designs; in the 1980s a prototype of the latest model of the Canadair Challenger business jet entered deep stall during testing, killing one of the test pilots who was unable to leave the plane in time. Also, paragliders are sometimes known to enter a deep stall condition.

Deep stall is possible with some sailplanes, as their most common designs are T-tail configurations.^{[citation needed]} The IS-29 glider is one of the gliders that are vulnerable to deep stalls when the CG and the overall weight are between certain limits^{[citation needed]}.

In the early 1980s, a Schweizer SGS 1-36 sailplane was modified for NASA's controlled deep-stall flight program.^[4]

A different type of stall affecting the F-16 fighter is also known as a deep stall because of its similar difficulty in recovery, but for a different reason. The aircraft is designed to be inherently unstable, which when kept under control by its "fly-by-wire" system allows for higher maneuverability. However, this design, coupled with the intent of the control computer to keep the fighter level, prevents the aircraft from pitching nose-down in a stall, which would allow the pilot to recover given sufficient altitude. This is known as a deep stall because the elevators are rendered useless by the flight computer even though, unlike a T-tail, air does contact the elevators, and even with the computer disabled it is difficult to recover from (the pilot must "rock" the aircraft with elevator input until it pitches nose-down, which can take several seconds).

Stall warning and safety devices

Aeroplanes can be equipped with devices to prevent or postpone a stall or to make it less (or in some cases more) severe, or to make recovery easier.

• An aerodynamic twist can be introduced to the wing with the leading edge near the wing tip twisted downward. This is called washout and causes the wing root to stall before the wing tip. This makes the stall gentle and progressive. Since the stall is delayed at the wing tips, where the ailerons are, roll control is maintained when the stall begins.
• A stall strip is a small sharp-edged device which, when attached to the leading edge of a wing, encourages the stall to start there in preference to any other location on the wing. If attached close to the wing root it makes the stall gentle and progressive; if attached near the wing tip it encourages the aircraft to drop a wing when stalling.
• Vortex generators, tiny strips of metal or plastic placed on top of the wing near the leading edge that protrude past the boundary layer into the free stream. As the name implies they energize the boundary layer by mixing free stream airflow with boundary layer flow thereby creating vortices, this increases the inertia of the boundary layer. By increasing the inertia of the boundary layer airflow separation and the resulting stall may be delayed.
• An anti-stall strake is a wing extension at the root leading edge which generates a vortex on the wing upper surface to postpone the stall.
• A stick pusher is a mechanical device which prevents the pilot from stalling an aeroplane. It pushes the elevator control forwards as the stall is approached, causing a reduction in the angle of attack. Generically, a stick pusher is known as a stall identification device or stall identification system.^[5]
• A stick shaker is a mechanical device which shakes the pilot's controls to warn of the onset of stall.
• A stall warning is an electronic or mechanical device which sounds an audible warning as the stall speed is approached. The majority of aircraft contain some form of this device that warns the pilot of an impending stall. The simplest such device is a stall warning horn, which consists of either a pressure sensor or a movable metal tab that actuates a switch, and produces an audible warning in response.
• An AOA Indicator or A.K.A Lift Reserve Indicator is a pressure differential instrument that integrates airspeed and angle of attack into one instantaneous, continuous readout. An AOA indicator provides a visual display of the amount of available lift throughout its slow speed envelope regardless of the many variables which act upon an aircraft. This indicator is immediately responsive to changes in speed, angle of attack and wind conditions and automatically compensates for aircraft weight, altitude, and temperature.
• An angle of attack limiter or an "alpha" limiter is a flight computer that automatically prevents pilot input from causing the plane to rise over the stall angle. Some alpha limiters can be disabled by the pilot.

If a forward canard is used for pitch control, rather than an aft tail, the canard is designed to meet the airflow at a slightly greater angle of attack than the wing. Therefore, when the aircraft pitch increases abnormally, the canard will usually stall first, causing the nose to drop and so preventing the wing from reaching its critical AOA. Thus the wing virtually never stalls.

If an aft tail is used, the wing is designed to stall before the tail. In this case, the wing can be flown at higher lift coefficient (closer to stall) to produce more overall lift.

Many aircraft have an angle of attack indicator among the pilot's instruments which lets the pilot know precisely how close to the stall point the aircraft is.

Spoilers

In most circumstances, a stall is an undesirable event. Spoilers, however, are devices that are intentionally deployed to create a carefully controlled stall over part of an aircraft's wing, in order to reduce the lift it generates, and allow it to descend without gaining speed. Spoilers are also deployed asymmetrically (i.e. on one wing only) to enhance roll control. Spoilers can also be used on aborted take-offs and after main wheel contact on landing to increase the aircraft's weight on its wheels for better braking action.

To look at it in a more simple way spoilers are effectively lift dumpers. A roll to the left could be aided by the left wing spoiler erecting.

Popular misconceptions

Since most aircraft have one or more engines, some confusion exists within the general public and most news media between an aerodynamic stall and the so-called "stall" of an aircraft engine. The misunderstanding results from the common use of the word "stall" with respect to automotive engines. An aerodynamic stall is an abrupt loss of lift due to excessive angle of attack, as explained in this article. An engine "stall" is an abrupt loss of power from an engine and a resulting loss of thrust; the proper aviation term for this situation is engine failure. In all correctly described aviation contexts, stall means aerodynamic stall. Nevertheless, many reports in the media and eye-witness accounts by lay people (and even the law enforcement officers responding to the scene of an accident) quoted in these sources will still often incorrectly use the word "stall" when referring to what should properly be called an engine failure.

The above confusion is wide-spread in the general public because of the very common misuse of the term stall in the media. This misunderstanding also results in another less common popular misconception, namely, that aircraft that have suffered an engine failure will just fall from the sky. This is because an aerodynamic stall will usually result in a significant loss of altitude during the recovery from the stall. If one assumes that stalls have something to do with the engines then one can see how this misconception can arise. However, and to the contrary, all fixed-wing aircraft rely on their wings to generate lift, and can therefore safely glide, sometimes for great distances (depending on their altitude at the time of engine failure), without any thrust from the aircraft engine(s).

References

• Chapter 4, "Slow Flight, Stalls, and Spins," in the Airplane Flying Handbook. (FAA H-8083-3A)
• Clancy, L.J. (1975), Aerodynamics, Pitman Publishing Limited, London. ISBN 0 273 01120 0
• Alpha Systems AOA Website for information on AOA and Lift Reserve Indicators [1]

Notes

1. ^ Clancy, L.J., Aerodynamics, section 5.3
2. ^ Clancy, L.J., Aerodynamics, section 5.28
3. ^ Brandon, John. "Airspeed and the properties of air". Recreational Aviation Australia Inc. Retrieved on 2008-08-09.
4. ^ Schweizer-1-36 index: Schweizer SGS 1-36 Photo Gallery Contact Sheet
5. ^ US Federal Aviation Administration, Advisory Circular 25-7A Flight Test Guide for Certification of Transport Category Airplanes, paragraph 228

See also

• Airfoil
• Wing twist
• Angle of attack
• Air safety
• Coefficient of lift
• Compressor stall
• Spin (flight)
• Spoiler (aeronautics)
• Dynamic stall

• All text is available under the terms of the GNU Free Documentation License. (See Copyrights for details.)
  

Spin (flight)

From Wikipedia, the free encyclopedia

In aviation, a spin is an aggravated stall resulting in rotation about the center of gravity wherein the aircraft follows a downward corkscrew path. Spins can be entered unintentionally or intentionally, from any flight attitude and from practically any airspeed--all that is required is sufficient yaw at the moment an aircraft stalls. An incipient spin is typically driven by inputs made and held by the pilot, whereas a fully developed spin is a self-sustaining maneuver. In either case, however, a specific and often counterintuitive set of actions may be needed to effect recovery. If the aircraft exceeds published limitations regarding spins, or is loaded improperly, or if the pilot uses incorrect technique to recover, the spin can lead to a fatal crash.

In a spin, one wing is sufficiently stalled and generates significant drag but little or no lift, and the other is either not stalled or not stalled as fully as the other, and generates significant lift. This causes the aircraft to autorotate due to the non-symmetric lift and drag. Spins are characterized by high angle of attack, low airspeed, and high rate of descent.

Spins differ from spiral dives which are characterized by low angle of attack and high airspeed. A spiral dive is not a type of stall because the wing is not stalled and the airplane will respond to the pilot's inputs to the flight controls.

How a spin occurs

Aerodynamic spin diagram

Certificated, light, single-engine aircraft must meet specific criteria regarding stall and spin behavior. Even so, it is generally true that such an airplane will only depart into a spin if the pilot simultaneously yaws and stalls the airplane (intentionally or unintentionally). Under these circumstances, one wing tends to stall more deeply than the other. The wing that stalls first will drop, increasing its angle of attack and deepening the stall. The other wing will rise, decreasing its angle of attack, and the aircraft will yaw towards the more deeply-stalled wing. The difference in lift between the two wings causes the aircraft to roll, and the difference in drag causes the aircraft to yaw.

One common scenario that can lead to an unintentional spin is an uncoordinated turn towards the runway during the landing sequence. A pilot who is overshooting the turn to final approach may be tempted to apply rudder to increase the rate of turn. The result is twofold: the nose of the airplane drops below the horizon and the bank angle increases. Reacting to these unintended changes, the pilot may then begin to pull the elevator control aft (thus increasing the angle of attack) while applying opposite aileron to decrease bank angle. Taken to its extreme, this can result in an uncoordinated turn with sufficient angle of attack to cause the aircraft to stall. This is called a cross-control stall, and is very dangerous if it happens at low altitude where the pilot has little time to recover. In order to avoid this scenario, pilots are always taught the importance of making coordinated turns.

A famous example of an unexpected spin was the death of Major Thomas McGuire. He attempted to fight a Nakajima Ki-43 Hayabusa piloted by Akira Sugimoto at low altitudes over Negros island in WWII. He flew a Lockheed P-38 Lightning. Instead of the "zoom and dive" tactics usually employed by P-38 pilots, he attempted to dogfight the nimble Japanese fighter without releasing his auxiliary fuel tanks. The plane was heavier than normal, and sudden drop of airspeed combined with a tight aileron and rudder turn made the plane stall and spin, from which he did not have altitude to recover. McGuire's plane crashed in the jungle and exploded.

Spins can also be entered intentionally for training, flight testing, or aerobatics.

Phases

A spin has four phases in aircraft that are capable of recovering from a spin. In aircraft that cannot recover from a spin, there are only three phases—the developed phase continues until the aircraft hits the ground.

Entry

The pilot provides the necessary elements for the spin, either accidentally or intentionally.

Incipient

The aircraft stalls and rotation starts.

Developed

The aircraft's rotation rate, airspeed, and vertical speed are stabilized.

Recovery

The angle of attack of the wings decreases below the critical angle of attack and autorotation slows. The nose steepens, after which autorotation stops.

Modes

The US National Aeronautics and Space Administration (NASA) has defined four different modes of spinning. These four modes are defined by the angle of attack of the airflow on the wing.^[1]

NASA Spin Mode Classification

Spin mode	Angle-of-attack range, degrees
Flat	65 to 90
Moderately flat	45 to 65
Moderately steep	30 to 45
Steep	20 to 30

During the 1970s NASA used its spin tunnel at the Langley Research Center to investigate the spinning characteristics of single-engine general aviation airplane designs. A 1/11-scale model was used with nine different tail designs.^[2]

Some tail designs that caused inappropriate spin characteristics had two stable spin modes – one steep or moderately steep; and another that was either moderately flat or flat. Recovery from the flatter of the two modes was usually less reliable or impossible. The further aft that the center of gravity was located the flatter the spin and the less reliable the recovery.^[3] For all tests the center of gravity of the model was at either 14.5% of Mean Aerodynamic Chord (MAC) or 25.5% of MAC.^[4]

Single-engine airplane types must be demonstrated to recover from a spin of at least one turn.^[5] NASA recommends various tail configurations and other strategies to eliminate the flatter of the two spin modes and make recovery from the steeper mode more reliable.^[6]

History

In aviation's early days, spins were poorly understood and often fatal. Proper recovery procedures were unknown, and a pilot's instinct to pull back on the stick served only to make a spin worse. Because of this, the spin earned a reputation as an unpredictable danger that might snatch an aviator's life at any time, and against which there was no defense.

The spin was initially explored by individual pilots performing ad-hoc experiments (often accidentally) and by aerodynamicists. In August 1912, Lieutenant Wilfred Parke RN became the first aviator to recover from an accidental spin when his Avro biplane entered a spin at 700 feet AGL in the traffic pattern at Larkhill. Parke attempted to recover from the spin by increasing engine speed, pulling back on the stick, and turning into the spin, with no effect. The aircraft descended 450 feet, and horrified observers braced themselves for a fatal crash.

Parke was disabled by centrifugal forces but was still considering a means of escape. In an effort to neutralize the forces pinning him against the right side of the cockpit, he applied full right rudder, and the aircraft leveled out fifty feet^[7] above the ground. With the aircraft now under control, Parke climbed, made another approach, and landed safely.

In spite of the discovery of "Parke's technique," pilots were not taught spin-recovery procedures until the beginning of World War I.

The first documented case of an intentional spin and recovery is that of Harry Hawker. In the summer of 1914, Hawker recovered from an intentional spin over Brooklands, England, by centralizing the controls.

In 1917, Frederick Lindemann, conducted a series of experiments that led to the first understanding of the aerodynamics of the spin.

Entry and recovery

Some aircraft cannot be recovered from a spin using only their own flight control surfaces, and must not be allowed to enter a spin under any circumstances. If an aircraft has not been certified for spin recovery, it should be assumed that spins are not recoverable and are unsafe in that aircraft. Important safety equipment, such as stall/spin recovery parachutes, which generally are not installed on production aircraft, are used during testing and certification of aircraft for spins and spin recovery.

Spin-entry procedures vary with the type and model of aircraft being flown, but there are general procedures applicable to most aircraft. These include reducing power to idle and simultaneously raising the nose in order to induce an upright stall. Then, as the aircraft approaches stall, apply full rudder in the desired spin direction while holding full back-elevator pressure for an upright spin. Sometimes a roll input is applied in the direction opposite of the rudder (i.e., a cross-control).

If the aircraft manufacturer provides a specific procedure for spin recovery, that procedure must be used. Otherwise, to recover from an upright spin, the following generic procedure may be used: Power is first reduced to idle and the ailerons are neutralized. Then, full opposite rudder (that is, against the yaw) is added and held to counteract the spin rotation, and the elevator control is moved briskly forward to reduce the angle of attack below the critical angle. Depending on the airplane and the type of spin, the elevator action could be a minimal input before rotation ceases, or in other cases, the elevator control may have to be moved to its full forward position to effect recovery from the upright spin. Once the rotation has stopped, the rudder must be neutralized and the airplane returned to level flight. This procedure is sometimes called PARE, for Power idle, Ailerons neutral, Rudder opposite the spin and held, and Elevator through neutral. The mnemonic "PARE" simply reinforces the tried-and-true NASA Standard spin recovery actions -- the very same actions first prescribed by NACA in 1936, verified by NASA during an intensive, decade-long spin test program overlapping the 1970's and '80's, and repeatedly recommended by the FAA and implemented by the majority of test pilots during certification spin-testing of light airplanes.

Inverted spinning and erect or upright spinning are dynamically very similar, and require essentially the same recovery process but use opposite elevator control. It must be noted that in an upright spin both roll and yaw are in the same direction, but that an inverted spin is composed of opposing roll and yaw. It is crucial that the yaw be countered to effect recovery. The visual field in a typical spin (as opposed to a flat spin) is heavily dominated by the perception of roll over yaw, which can lead to an incorrect and dangerous conclusion that a given inverted spin is actually an erect spin in the reverse direction.

In some aircraft that spin readily upright and inverted—such as Pitts- and Christen Eagle-type high-performance aerobatic aircraft—an alternative spin-recovery technique may effect recovery as well, namely: Power off, Hands off the stick/yoke, Rudder full opposite to the spin (or more simply "push the rudder pedal that is hardest to push") and held (aka the Mueller/Beggs technique). An advantage of the Mueller/Beggs technique is that no knowledge of whether the spin is erect or inverted is required during what can be a very stressful and disorientating time. Even though this method does work in a specific subset of spin-approved airplanes, the NASA Standard/PARE procedure will also be effective, but care must be taken to ensure the spin does not simply cross from positive to negative or vice versa. The converse, however, may not be true at all—many cases exist where Beggs/Mueller fails to recover the airplane from the spin, but NASA Standard/PARE will terminate the spin. Before spinning any aircraft the flight manual should be consulted to establish if the particular type has any specific spin recovery techniques that differ from standard practice.

Although entry techniques are similar, modern military fighter aircraft often tend to require yet another variation on spin recovery techniques. While power is still typically reduced to idle thrust and pitch control neutralized, opposite rudder is almost never used. Adverse yaw created by the rolling surfaces (ailerons, differential horizontal tails, etc.) of such aircraft is often more effective in arresting the spin rotation than the rudder(s), which usually become blanked by the wing and fuselage due to the geometric arrangement of fighters. Hence, the preferred recover technique has a pilot applying full roll control in the direction of the rotation (i.e., a right-hand spin requires a right stick input), generally remembered as "stick into the spin." Likewise, this control application is reversed for inverted spins.

Center of gravity

The characteristics of an airplane with respect to spinning are significantly influenced by the position of the center of gravity. In general terms, the further forward the center of gravity the less readily the airplane will spin, and the more readily it will recover from a spin. Conversely, the further aft the center of gravity the more readily the airplane will spin, and the less readily it will recover from a spin. In any airplane the forward and aft limits on center of gravity are carefully defined. In some airplanes that are approved for intentional spinning the aft limit at which spins may be attempted is not as far aft as the aft limit for general flying. Intentional spinning should not be attempted casually, and the most important pre-flight precaution is to determine that the airplane's center of gravity will be within the range approved for intentional spinning.

Unrecoverable spins

If the center of gravity of the airplane is behind the aft limit approved for spinning, any spin may prove to be unrecoverable except by using some special spin-recovery device such as a spin-recovery parachute specially installed in the tail of the airplane; or by jettisoning lead pellets specially installed as ballast at the tail of the airplane.

In the past, some airplanes displayed an unrecoverable spin in which the nose was higher, relative to the horizon, than in conventional spins. This is sometimes called a flat spin, although whether a flat spin is indeed unrecoverable depends on aircraft type and loading. The plane spins on its belly along the transverse axis. The empennage will feel very light and loose. Depending on the aircraft, rudder and aileron inputs and changing engine power settings may have little effect. There is a small number of accounts of heroic pilots recovering from flat spins by loosening their restraint harnesses and leaning forward in an attempt to favourably alter the position of the center of gravity. Unfortunately, the great majority of pilots who have experienced an unrecoverable spin have not lived to talk about it if they could not bail out of/eject from the aircraft. Generally speaking, such characteristics are confined to high-performance aircraft, primarily fighters.

Some World War II airplanes were notoriously prone to flat spins when loaded erroneously, such as the Bell P-39 Airacobra. The P-39 was a unique design with the engine behind the pilot's seat and a large cannon in the front. Without ammunition or a counterbalance load in the nose compartment, the P-39's center of gravity was too far aft to recover from a spin. Soviet pilots did numerous tests of the P-39 and were able to demonstrate its dangerous spinning characteristics. Bell then issued a recommendation to bail out if the airplane entered a spin. North American P-51 Mustangs with auxiliary fuel tanks not originally designed for the P-51 suffered from the same problem. Similarly, the Vought F4U Corsair was reputed to have appalling stall and spin recovery characteristics, even in the "clean" (no stores) configuration.

Modern fighter aircraft are not immune to the phenomena of unrecoverable spin characteristics. Although highly resistant to entering into a spin, once caught in one the Grumman F-14 Tomcat can exhibit a fast, flat spin from which it is nearly impossible to recover. This was instrumental to the plot of the movie Top Gun where a flat spin results in the death of Nick "Goose" Bradshaw (portrayed by Anthony Edwards). Another example of a nonrecoverable flat spin occurred in 1963, with Chuck Yeager at the controls of the NF-104A rocket-jet hybrid: after setting an altitude record, Yeager lost control and entered a flat spin, then ejected and survived. (The plane did not.)

The mathematics of the flat spin are that if the center of lift force is ahead of the center of gravity on longitudinal axis, the real number components of the eigenvalues of the stability matrix exceed zero and the poles of the stability matrix migrate to the positive half of the complex number plane. This will indicate positive feedback on attempts at control: the plane will resist any attempts at recovery and stabilizing the plane. Some modern fighter aircraft, like the F-16 Fighting Falcon and the Saab Gripen have, for greater maneuverability, been intentionally designed to be unstable and are controlled by a computer to stabilize the plane.

In purpose-built aerobatic aircraft, spins may be intentionally flattened through the application of power and aileron within a normal spin. Rotation rates experienced are dramatic and can exceed 400 degrees per second in an attitude that may even have the nose above the horizon. Such maneuvers must be performed with the center of gravity in the normal range and with appropriate training, and consideration should be given to the extreme gyroscopic forces generated by the propellor and exerted on the crankshaft.

Aircraft design

For safety, all certificated, single-engine fixed-wing aircraft, including certificated gliders, must meet published criteria regarding stall and spin behavior. These designs typically have a wing with greater angle of attack at the wing root than at the wing tip, so that the wing root stalls first, while the ailerons may remain somewhat effective until the stall migrates outward toward the wing tip. One method of tailoring such stall behavior is known as washout. Some designers of recreational aircraft seek to develop an aircraft that is characteristically incapable of spinning, even in an uncoordinated stall.

Some airplanes have been designed with fixed leading edge slots. Where the slots are located ahead of the ailerons they provide strong resistance to spinning and may even leave the airplane incapable of spinning.

The flight control systems of some gliders and recreational aircraft are designed so that when the pilot moves the elevator control close to its fully aft position, as in slow speed flight and flight at high angle of attack, the trailing edges of both ailerons are automatically raised slightly so that the angle of attack is reduced at the outboard regions of both wings. This necessitates an increase in angle of attack at the inboard (center) regions of the wing, and promotes stalling of the inboard regions well before the wing tips.

The US certification standard for civil airplanes up to 12,500 lb maximum takeoff weight is Part 23 of the Federal Aviation Regulations, applicable to airplanes in the normal, utility and acrobatic categories. Part 23, §23.221 requires that single-engine airplanes must demonstrate recovery from either a one-turn spin if intentional spins will be prohibited, or six-turn spins if intentional spins will be approved. Even large, passenger-carrying single-engine airplanes like the Cessna Caravan must be subjected to one-turn spins by a test pilot, and repeatedly demonstrated to recover within no more than one additional turn. With a small number of airplane types the FAA has made a finding of equivalent level of safety (ELOS) so that demonstration of a one-turn spin is not necessary. For example, this has been done with the Columbia 300/350 and the Cirrus SR20/22. Successful demonstration of the one-turn spin does not allow an airplane type to be approved for intentional spinning. If an airplane is to be approved for intentional spinning it must be repeatedly subjected to a spin of six turns, and then demonstrated to recover within one and a half additional turns. Spin testing is a potentially hazardous exercise and the test aircraft must be equipped with some spin-recovery device such as a tail parachute or jettisonable ballast, or some method of rapidly moving the center of gravity forward.

Agricultural airplanes are typically certificated in the normal category at a moderate weight. For single-engine airplanes this requires successful demonstration of the one-turn spin. However, with the agriculture hopper full these airplanes are not intended to be spun, and recovery is unlikely. For this reason, at weights above the maximum for the normal category, these airplanes are not subjected to spin testing and, as a consequence, can only be type certificated in the restricted category. As an example of an agricultural airplane see the Cessna AG series.

Spin Kit

To make some sailplanes spin easily for training purposes or demonstrations a spin kit is available from the manufacturer.

Many training aircraft may appear to be resistant to entering a spin even though some are intentionally designed and certified for spins. A well known example of this is the Piper Tomahawk, which is certified for spins, though the Piper Tomahawk's spin characteristics remain controversial. Aircraft that are not certified for spins may be difficult or impossible to recover once the spin exceeds the one-turn certification standard.

Although it has been removed from most flight test syllabuses, there are some countries that still require flight training on spin recovery. In the U.S. spin training is required only for flight instructor candidates. A spin occurs only after a stall, so the FAA emphasizes training pilots in stall recognition, prevention, and recovery as a means to reduce accidents due to unintentional stalls and/or spins.

A spin is often intimidating to the uninitiated, however many pilots trained in spin entry and recovery find that safely spinning is an interesting experience. In a spin the occupants of the airplane will only feel reduced gravity during the entry phase, and then will experience normal gravity, except that the extreme nose-down attitude will press the occupants forward against their restraint harnesses. The rapid rotation, combined with the nose-down attitude, can also be disorienting.

The recovery procedure from a spin requires using rudder to stop the rotation, then elevator to reduce angle of attack to stop the stall, then pulling out of the dive without exceeding the maximum permitted airspeed (VNE) or maximum G loading. The maximum G loading for a light airplane in the normal category is usually 3.8G. For a light airplane in the acrobatic category it is usually at least 6G.

References

• Airplane Flying Handbook, ch. 4: Slow Flight, Stalls, and Spins

• NASA Technical Note TN D-6575 Summary of Spin Technology as Related to Light General-Aviation Airplanes. Retrieved 2008-06-13

• NASA Technical Paper 1009 Spin-tunnel Investigation of the Spinning Characteristics of Typical Single-engine General Aviation Airplane Designs. Retrieved 2008-06-13

Notes

1. ^ NASA Technical Paper 1009. p.11
2. ^ NASA Technical Paper 1009. p.8
3. ^ NASA Technical Note TN D-6575. p.15
4. ^ NASA Technical Paper 1009. p.9
5. ^ US Federal Aviation Regulations, Part 23, §23.221
6. ^ NASA Technical Paper 1009. p.14
7. ^ History of Aerobatics - Jet Fighter School 2 by Richard G. Sheffield

External links

• Stalls and spins
• 60-turn spin in a Cessna 152
• Video of a spin in a Cessna 152
• Videos of Accelerated, Flat, Inverted, Crossover, and Knife Edge spins
• Narrated, in-flight videos of all spin modes taken from an Extra 300 aerobatic aircraft

• All text is available under the terms of the GNU Free Documentation License. (See Copyrights for details.)