An Airplane's Flight Mechanism | Fallacies And Truth Revealed | How the plane lifts off the ground

in science •  5 months ago

Ever wondered why you can’t feel air blow whenever you are behind a standing fan or a vent?

This is something that you may experience everyday of your life. In the office, hospital, even at home but may not care to ask "why?"

Lets leave our homes now and go to the sky!

AIRPLANE'S FLIGHT

Four forces acts on a moving aeroplane(British). Two horizontal opposite forces namely, Thrust(forward force) and drag(backward force). The other two are vertical opposite forces namely, lift(upward force) and gravity(downward force). The drag and gravity are two opposing forces that must be overcome for the plane to fly and move linearly.

If you are an upcoming physicist or engineer, maybe you felt that the engines in airplanes have special features that makes them fly, which is absent in other vehicles. NO, that’s wrong. The plane's flight is based on a principle similar to that of a rotating fan.

The Wright Brothers. (Public domain, No attribution) from Wikimedia Commons

Before progressing, much credit must be given to the Wright brothers, Orville and Wilbur, who were the two American aviation pioneers, creating and flying the first successful plane in the world, one of the greatest inventions of all time.

The Job of the Engine

Author:US federal aviation administration (public domain). From Wikimedia Commons

As earlier stated, it is wrong to think that the engine of a plane, is what makes it fly. Its job, just as in cars, lorries and other vehicles is to move it forward at high speed. If you have always thought that, the engine is the key to flying a plane, then when next you want to travel with one, try removing the wings and see what happens when you take off. And please don’t tell anyone I am the one who asked you to perform this experiment. In short, the engine controls the thrust.

This is one of the mistakes people make, especially when they are new to this field.

Another wrong understanding of the plane’s flight, even among aeronautic engineers goes thus:

The True Aspect: For most airplanes, their wings are made to have a curved upper surface and a flat lower surface which is usually termed "aerofoil"(British). When, the plane moves at high speed, air molecules hits the front of the aerofoil, and separates into two parts. One part moves over the curved surface of the wing, while the other part moves underneath, along the flat surface.

aerofoil with airflow. Author: Jhbdel(talk). (Licensed under Creative Commons Attribution-ShareAlike 3.0.) from Wikipedia

The False Aspect: Many explanations give that; since the length of the curved surface is greater than that of the flat surface, air molecules above the surface, have to move at a greater speed than that of the molecules underneath, in order for both to meet with each other at the end of the foil. And according to Bernoulli’s Principle, the pressure of the wind above the wing is lesser than that of the lower wind, since it is faster. As a result of this difference in air pressure around the wings, the plane tends to move upwards.

The fact that there is pressure difference around the wing is true, but the reason for this difference and its effect from the above explanation is wrong.

Why?

• Nothing or no one can prove that, the air molecules which separate at the front of the front aerofoil will meet with as exact pairs at the back end of the foil. Fact, the molecules are meant to meet up other molecules in their path, before reaching the tail.
Also, the above theory which explains that the air moving over the top, moves at a greater speed because it has longer distance to cover, goes against Newton’s law of physics, which states that:

In an inertial frame of reference , an object either remains at rest or continues to move at a constant velocity, unless acted upon by a force. Wikipedia - Newton's laws of motion

Illustration

An electric fan blows air across a big room or a small room at the same speed. It is the force of the fan that matters, not the distance. Air doesn’t know it has further to go and so decides to speed up. There is no force of distance. source

In a nutshell, what affects the speed of the wind, is the speed, with which the plane moves linearly and not the distance which the wind has to flow along. See conservation of linear momentum.

• Consider this condition. If the pressure difference was the true key to a plane's flight, then why can acrobatic planes fly upside down? If such planes were flown upside down, the higher air pressure is now above and the lower air pressure is beneath. According to the wrong explanation, this clearly means that, a ‘downlift' will be produced, which would push the plane downwards with a force greater than that of gravity, thereby causing it to crash.

The Right explanation of Pressure Difference | DOWNWASH |

Already pointed out, one thing about the above fallacy which is true is the fact that, the air pressure over the wing is lesser than the air pressure underneath it. But, What's the true reason?

The top surface of the wing is curved, therefore has a longer length than the bottom. This means that the air molecules above the wing are stretched out into a bigger volume, which results to reduction in its pressure.

Recall,

P = F/A....... Pressure

The force acting on the two separated winds is the same, but the area of the top surface is larger than that of the bottom surface. And since pressure is inversely proportional to area, then the pressure of the top wind reduces.

This causes a great increase in the velocity of the upper wind. But this doesn’t mean that the separated air molecules will meet as exact pairs, at the end of the foil. It only means that the upper wind has attained more speed which is greater than that of the aeroplane as well as the wind underneath. And when both winds meet at the tail, they would together, be speeding downwards and create a lifting force that makes the plane fly. See Newton’s third law of Motion.

Let's go back to the first question at the top.

“Ever wondered why you can’t feel air blow behind a standing fan or a vent?”
Why do ceiling fans suck or move air only in one direction?

The three blade ceiling fan at Nizampet. (Creative Commons Attribution-Share Alike 3.0 Unported) from Wikimedia Commons

The reason is because, the rotors are made to either be slightly curved or tilted at an angle, so that, as they rotate, they hit the air molecules at what is known as angle of attack.

Angle of attack. Author: Civil air patrol.(public domain), from Wikipedia

This is exactly what happens when a helicopter wants to take off - but with a greater force. It is known as DOWNWASH. As the rotor moves the air downwards at high speed, an equal but opposite force(lift) is produced, which moves the chopper upwards. See Newtons third law of Motion.

The wing of the airplane, performs this same function, even if its motion is linear and not circular. Since the wings are inclined, the air that moves along it are pushed downwards, at its tail, this as well causes downwash.

Even if the wings were to be symmetrical, and there was no pressure difference, and attainment of extra speed, downwash will still be created, so long the wing is tilted - but it will be lower than that of the former. This type of wing could be used in planes that carry less load and vice versa. The reason why the curved wing is used in planes which carry great load, is because it accelerates the downwash, causing the lifting force to be greater than the gravity. This makes flying safer.

CONCLUSION

The angle of attack is one of the most important phenomenon in flying a plane, whether it uses wings or rotating fans. It is what affects the direction of the downwash. The pilot can change the angle of attack, so that the downwash could turn to a horizontal backwash - usually done when landing. As the plane tilts to a point, airflow along the aerofoil is horizontal, and the plane moves downwards.
For planes to produce high downwash enough to lift it, it has to move linearly for some time, to attain momentum. This is why planes, first have to move on the runway at high speed before ascending.
Conclusively, an aeroplane/airplane, flies with its wings and rotors, both of them, having an angle of attack.

REFERENCES

ALL ARGUMENTS, QUESTIONS AND ADDITIONS SHOULD BE PLACED IN THE COMMENT SECTION BELOW. Thank You

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I AM SYNICK
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I too thought the lift was created by the air speed difference. Now that I think about it the downwash explaination makes so much more sense.
Thanks!

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Yea, i also thought so too, until I researched deeper.

Not everything written online is true. Therefore, you must always seek proof.

I am SyNick

I never knew the mechanism that enabled a plane fly. I've always wondered how a big bird like an aeroplane fly with a lot of weight. It's nice I came across this article, I now have a prior knowledge on how things works.

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At least, we got to understand, a little science, of the things we do or experience. It helps eradicate ignorance and create solutions to flaws.

I am SyNick

I have seen this explanation elsewhere before. It seems to make more sense than the faster and slower air explanation.

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Surely make more sense.

Air doesn't know when it needs to be fast, certainly, not because of high distance to cover. The velocity of anything, changes only if an external force acts on it.

SyNick

I was thinking about it some time ago but it did not come to my mind to read about then ... thanks, it's easy to understand, well-written post. Cheers!

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You're welcome.

It even occurred to me recently that i should do a research on this topic, because, just as you did, i thought and wondered.

SyNick

If you have always thought that, the engine is the key to flying a plane, then when next you want to travel with one, try removing the wings and see what happens when you take off.

LOL, it wouldn't even take off.

I like the quality of your article and the analysis you made is top notch. Kudos!

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True statement, it wouldn't even take off. They'd be wasting time, trying to fly it.

But they shouldn't say I asked them to do so. Lol

Anyway, thanks for the appreciation.

SyNick

This could'be been merely explanatory and therefore boring, but you added the antagonist (the fallacy) and suddenly the whole topic became much more interesting! I find that juxtaposing ideas this way makes any topic fascinating. The moon landing, for example, can be transformed from a boring science topic to a much more interesting one just by adding the (wrong) hypothesis that it's all a hoax!

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That's true, you got that absolutely right. Not everyone is interested in the knowledged but everyone uses the product of that knowledge. For example, as an engineer you may not be interested in the full working mechanism of your body, but you wanna live healthy.
I guess, relating science and socialism is the bomb.

Thank you very much.

SyNick

A really awesome explanation! But does it explain why acrobatic planes are able to fly upside down? I'm a little confused wouldn't they still produce downlift??

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You're welcome
There is no special thing about acrobatic planes. Acrobatic planes and jets usually a built having symmetrical wings because they don't carry much load, like cargo planes.

On how they fly, their pilots a well trained, and know how to maneuver the plane in such a way that the angle of attack is maintained. This is usually done by slightly tilting the nose of the plane upwards, this helps the plane continue its creation of down lift.

An assignment: watch a video of an acrobatic plane flying. You'll see that from the nose they are directed upwards. What I simply mean is, they seldomly fly horizontally when upside-down.

SyNick

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Very smart! Thanks for the explanation :)

I learnt this in school a long time ago. However, your explanation about the change in pressure due to surface area, rather than speed of airflow, makes more sense. It's surprising how widespread the misconception about speed of airflow creating lift is. Thank you very much for enlightening me.

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You're welcome @huangriver, I also may have continued too in the misconception until I learnt the truth. I felt everyone should also get it too.