AIRCRAFT STALL AND HOW TO PREVENT IT - When flying an airplane, a stall has nothing to do with the engine or another mechanical part. An airplane stall is an aerodynamic condition in which an aircraft exceeds its given critical angle of attack and is no longer able to produce the required lift for normal flight. This type of stall should not be confused with an engine stall, familiar to anyone who has driven an automobile. The angle of attack on an airfoil is measured by the angle between the chord line (i.e., the imaginary line from the leading edge to the trailing edge of the wing) and the relative wind. At the critical angle of attack, the airflow over the wing is disrupted enough to inhibit lift, resulting in the nose of the aircraft to fall. Characteristics of a stall include a distinctive decrease in lift, which is usually noted by a sudden (if sometimes gradual) pitch down of the nose of the aircraft. While this can feel like the plane is falling and has no lift, in reality, it's only a decrease in lift and a change in the plane's level.

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Aircraft Stall and How to Prevent It

BY SARINA HOUSTON

An airplane stall is an aerodynamic condition in which an aircraft exceeds its given critical angle of attack and is no longer able to produce the required lift for normal flight.

This type of stall should not be confused with an engine stall, familiar to anyone who has driven an automobile.

When flying an airplane, a stall has nothing to do with the engine or another mechanical part.

In piloting, a stall is only defined as the aerodynamic loss of lift that occurs when an airfoil (i.e., the wing of the airplane) exceeds its critical angle of attack.

Angle of Attack

The angle of attack on an airfoil is measured by the angle between the chord line (i.e., the imaginary line from the leading edge to the trailing edge of the wing) and the relative wind.

It is dependent on the shape of the airfoil, including its platform and aspect ratio. At a high angle of attack, the airflow over the wing is disrupted.

At the critical angle of attack, the airflow over the wing is disrupted enough to inhibit lift, resulting in the nose of the aircraft to fall.

The critical angle of attack for an airfoil never changes. However, factors such as weight, configuration (e.g., flaps and gear changes, or other conditions, like airframe icing), and load factor, can change the airspeed at which an airplane will stall.

Stall Characteristics

Characteristics of a stall include a distinctive decrease in lift, which is usually noted by a sudden (if sometimes gradual) pitch down of the nose of the aircraft.

While this can feel like the plane is falling and has no lift, in reality, it's only a decrease in lift and a change in the plane's level.

Additionally, a stall may be accompanied by a roll or yaw to one side if the aircraft is uncoordinated. If this happens and recovery procedures are not initiated right away, an aircraft may enter a spin.

Stability

In a stable airplane, the drop in the nose at the beginning of a stall often is enough to regain the proper amount of lift for the airfoil.

If this happens, the airplane is easily recoverable just by lowering its pitch attitude and increasing airspeed.

However, in an unstable airplane, a stall that is not corrected can further develop into a spin, which can be difficult or impossible to recover from.

Airspeed

Stalls commonly occur at slow airspeeds. For this reason, slow-speed flight, such as during approach and departure, are critical phases of flight, and pilots must be particularly cognizant at these times to prevent stalling the aircraft.

A stall at cruise altitude offers the pilot enough space to recover. A stall during landing with limited space doesn't offer the same envelope of security from which to recover.

While stalling may be most common at slow speeds, a stall can happen at any airspeed, regardless of the attitude.

Therefore, a pilot should not rule out the possibility of a stall based on airspeed or attitude.

For example, when pulling out of a dive, the airspeed is high, but the angle of attack can be higher than you think because the plane is still dropping in altitude even though its nose is raised. If the angle of attack exceeds about 17 percent, the plane can stall.

Tailplane Stalls

Tailplane stalls often indicate that something is happening to the aircraft wings, but the plane's horizontal stabilizer can also stall. While this tailplane stall is also dangerous, it is a much less common aerodynamic condition.

Practicing Stalls and Recovery

Stall recovery procedures are different for each aircraft, but in general, a pilot can initiate a stall recovery by increasing airflow over the wing.

This is usually accomplished by lowering the pitch attitude, leveling the wings, and increasing power or thrust.

When a wing has stalled, it is usually best to use the rudder to raise the wing, rather than the ailerons.

Pilots practice stalls and recovery as part of their training, and they must perform a stall and recovery to earn a private or commercial certificate.

However, routine flight reviews often do not involve stalls, and as a result, pilots may forget how to recognize the indications that an airplane is going into a stall.

Practicing stalls and recovery at slow speeds — and at sufficient altitude to recover, of course — helps pilots recognize the early signs of a stall condition so that they can make the proper corrections.

Sarina Houston

Commercial Pilot and Flight Instructor with Single and Multi-Engine Instrument ratings

Worked for Embry-Riddle Aeronautical University as an administrative director

Founding President of a chapter of Women in Aviation, International

Member of NAFI (National Association of Flight Instructors)

Experience

Sarina Houston is a former writer for The Balance Careers covering aviation and aerospace. Houston is an FAA-certified Commercial Pilot and Flight Instructor with Single and Multi-Engine Instrument ratings. She has been a flight instructor since 2005.

In addition to flying, Houston has experience in administrative and nonprofit management. She has worked for Embry-Riddle Aeronautical University as an administrative director, and was the founding President of a chapter of Women in Aviation, International—a nonprofit organization that provides support for women and men who choose to enter the challenging world of aviation.

She maintains professional memberships with AOPA (Aircraft Owners and Pilots Association), WAI (Women in Aviation, International), and NAFI (National Association of Flight Instructors).

Houston currently works as an independent flight instructor and a freelance aviation writer.

Education

B.S. in Aeronautical Science, Embry-Riddle Aeronautical University

M.S. in Aeronautical Science, ERAU-Worldwide, specializing in Aviation Safety and Operations

About The Balance Careers and Dotdash

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https://www.thebalancecareers.com/what-is-an-aircraft-stall-282603

PROPELLERS - The blades of the propeller are an aerofoil, which generates an aerodynamic force as they spin, the same as any other aerofoil that is moving through the air. The blades of a propeller are slightly angled. As the blade rotates, air accelerates over the front surface, causing a reduced static pressure ahead of the blade. This results in a forward thrust, which pulls the aircraft along. As the aircraft moves forward in flight, the propeller produces both rotational and forward velocity.

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Propellers

How Propeller Works & Functions Of Propeller

engineeringinsider

A propeller works in a similar way that a screw works.

The blades of the propeller are an aerofoil, which generates an aerodynamic force as they spin, the same as any other aerofoil that is moving through the air.

The blades of a propeller are slightly angled. As the blade rotates, air accelerates over the front surface, causing a reduced static pressure ahead of the blade.

This results in a forward thrust, which pulls the aircraft along.

When the aircraft is stationary, the spinning propeller blades cause purely rotational velocity.

As the aircraft moves forward in flight, the propeller produces both rotational and forward velocity.

The combined vector of these forces is called the pitch, the angle of advance.

As a result of this combined rotational and forward velocity, each propeller blade section follows a ‘corkscrew’ path through the air.

Different points along the blade will have an optimal angle to the relative airflow to operate efficiently at a given airspeed.

Propellers are designed to have the most efficient angle of attack along the entire length.

To achieve this, blades are designed with a twist, which reduces the blade angle from the centre to the tip.

Fixed-pitch propellers have only one forward velocity (airspeed) for a given rpm at which they will operate efficiently.

Some propellers are designed with the ability for pilots to adjust the pitch in flight, allowing the propeller to operate most efficiently over a wider range of airspeeds. 

https://engineeringinsider.org/propeller-working/ 

AIRPLANES FLYING UPSIDE DOWN - Airplanes, or anything that sails through the air for that matter, such as birds, kites, a boomerang or even a folded paper plane, have a physical force working in their favor that allows them to continue their flight: lift. Lift, deserves its name, as it is the force that lifts things into the air. It is closely linked to Newton’s Third Law of Motion: “To every action, there is an equal and opposite reaction.” The lift generated by an airplane depends on its wings; although their shape matters, that’s not the primary contributor to the lift that an airplane experiences. The ‘angle of attack’ of the wings is what makes an airplane cruise. The ‘angle of attack’ is the angle that an imaginary reference line on the airplane makes with the oncoming air. The higher the angle of attack, the more lift is generated beneath the airplane.

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Airplanes Flying Upside Down

How Do Fighter Jets Fly Upside Down?

Ashish  

Wings are the most important part of an airplane when it comes to flying, because they’re shaped in a way that maximizes the buoyant force offered by air.

However, if the shape of the wings is the sole reason behind the capacity of an airplane to fly, then how do stunt planes and fighter jets manage to fly upside down?

Doesn’t the orientation of the wings with respect to the airplane body get messed up when airplanes fly upside down?

In other words, when the plane’s wings face the opposite direction of their aerodynamic design, why don’t they crash?

Although it’s true that the shape of an airplane’s wings plays a significant role in its ability to fly, that’s not actually the primary reason why an airplane is able to soar through the air.

If it were, then fighter jets and other aircraft would never be able to fly upside down and perform such breathtaking maneuvers while airborne, because the shape of the wings would change with respect to the direction of the airplane’s motion. 

There is clearly another important factor at play….

1.      Lift

2.      Airplanes, or anything that sails through the air for that matter, such as birds, kites, a boomerang or even a folded paper plane, have a physical force working in their favor that allows them to continue their flight: lift.

3.      Put in simple terms, ‘lift’ deserves its name, as it is the force that lifts things into the air.

4.      More specifically, it directly opposes the weight of an object moving through a fluid (air, in this case).

5.      It is closely linked to Newton’s Third Law of Motion: “To every action, there is an equal and opposite reaction.”

6.      For an airplane moving through air, the force acting downwards on its body is its ‘Weight’ (slightly different from the ‘mass’ of the airplane, by the way).

7.      To counteract this force, lift is applied perpendicular to the plane, but in the upward direction.

8.      To better understand the forces acting on an airplane in flight, take a look at this image:

Angle of attack

The lift generated by an airplane depends on its wings; although their shape matters, that’s not the primary contributor to the lift that an airplane experiences.

Rather, the ‘angle of attack’ of the wings is what makes an airplane cruise.

The ‘angle of attack’ is the angle that an imaginary reference line on the airplane makes with the oncoming air.

The picture below will help you visualize this better:

 

The higher the angle of attack, the more lift is generated beneath the airplane.

That’s why airplane wings are tilted with the leading edge pointed up relative to the oncoming wind. This forces wind to ‘pile up’ beneath the wings.

The velocity of wind moving above the wings is greater than the velocity of the wind beneath them. Therefore, there is greater pressure beneath the wings due to Bernoulli’s principle.

You can say that the airplane (more specifically, the wing) is riding atop a ‘dense cloud of air’, which provides sufficient lift.

The same is true for airplanes flying upside down. Note that not every airplane is meant to fly upside down; you wouldn’t expect a commercial plane flying in this fashion, except in Hollywood flicks (like Flight).

However, airplanes that consistently have to fly upside down (like stunt planes or fighter aircraft), have symmetrical wings.

Therefore, they can’t rely on the shape of the wings; they only manage to fly upside down by tilting their wings in the right direction to generate sufficient lift.

All in all, it’s true that the shape of the wings does play a significant role in making an airplane fly.

However, it’s essentially the angle of attack of the wings that facilitates all those arduous and breathtaking maneuvers that stunt airplanes and fighter jets pull off so impeccably.

Ashish is a Science graduate (Bachelor of Science) from Punjabi University (India). He spends a lot of time watching movies, and an awful lot more time discussing them. He likes Harry Potter and the Avengers, and obsesses over how thoroughly Science dictates every aspect of life… in this universe, at least.

https://www.scienceabc.com/eyeopeners/how-airplane-jets-stunt-planes-fly-upside-down-lift-shape-of-wings-angle-of-attack.html