## Why Are Most Airplanes Painted White?

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As Aircraft Nerds, we have the craze of looking at aircrafts. We like to observe each and every part of an aircraft and know more about an aircraft. While looking at an aircraft, have you ever wonder why  most of them are painted white?

There are both scientific as well as economic reasons for painting an aircraft white. We will take a look at all of them one by one.

### Scientific Reasons

Before we begin, here is an interesting question about colors

Suppose, there is a yellow colored flower. Then what are the colors (wavelengths of light) absorbed by that flower?

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Most of you will say yellow! But That's wrong!

Yellow colored flowers will absorb all the colors (All the wavelengths of light) except yellow. As that flower cannot absorb the color yellow, it reflects it. That's why we see that flower as yellow!

Now moving towards the color white. Objects painted white cannot absorb any color (any wavelength of light) and so they reflect all the colors (All the wavelengths of light) and we see that color as white. White is actually a mixture of all the colors.

(White color is mixture of all colors)

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When Aircraft is painted with any other color apart from white, it will absorb the light (wavelength) of that color & convert the absorbed light energy into heat energy. This will heat up the aircraft's body.

So when the aircraft is painted white, It will reflect all of the wavelengths of the light and hence will not absorb any light and that will result in it not heating up as much.

Also the color white helps an aircraft to cool down faster when aircraft is parked on the hot ground.

#### 2. Visibility Factor

When an aircraft crashes, most of the time it becomes easier to spot it if its white in color. As white  is easy to spot on the ground from the sky even during the night.

Image from: - Wikimedia

#### 3. Inspection of Aircraft Body

It is easy to find dents or cracks on white color than on any other color. Hence aircraft maintenance engineers can easily find out defects on an aircraft's body. Also, no color is lighter than white, that is, all colors are darker than white. So if there is any leakage in fuel, it forms a stain on the aircraft's body, and can be detected from the location of the stain. Also if there is corrosion occurring on any part of the aircraft's body it can be easily detected by a visual inspection.

Image from: - Wikimedia

#### 4. White Color Doesn't Fade

Image From: - Wikimedia

Any other color fades out when exposed to UV rays (Ultra Violet rays) present in sunlight. As UV rays are capable of breaking down bonds present in the paint which absorbs a specific wavelength of color. As mentioned before, white color doesn't absorb any wavelength of color. Hence, white color isn't affected as much by UV rays. While white color gets dull, it still looks better than any color that has faded out!

So in the case of a white colored aircraft recoloring is not needed.

#### 5. Logo Can Be Seen Easily On White

Image from: - Wikimedia

Again, all colors are darker than white. Any dark color can be seen easily against white. Hence it's easy to identify company name and logo printed on an aircraft.

### Economic Reasons

#### 1. Painting is Expensive

Image from: - Wikimedia

Of course, painting the entire aircraft requires an investment of money as well as time. It takes between two to seven days to paint entire aircrafts like the Boeing and the Airbus. Approx 3,600 liters of paint is required to paint the world's largest passenger aircraft, the Airbus A380. In a case of Boeing 747, the simple white polished paint will weigh approx. 25 Kg while if fully painted with any other color over white, the total color will weigh up to 250 kg. Of course, 250 kg of paint will cost more than 25 kg of paint. Also as the weight of the aircraft increases, the amount of fuel required will increase. So the cost of the required fuel will also increase. In addition efficiency of the aircraft decreases with increased weight.

#### 2. Lease Terms & Condition

Image from: - Wikimedia

Many airlines don't own some of their aircraft. Aircrafts are very expensive. Hence most of the companies take aircrafts on lease. About 56 aircraft are leased by Lufthansa airline. Some leasing companies don't allow painting the aircraft. Hence it is sometimes mandatory for the airline to use white colored palnes.

#### 3. Low Resale Value

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If the owner wants to sell his/her aircraft then painting of the entire aircraft is not needed. Just changing the company name and logo is enough. It saves the owner's money while selling the aircraft. Also if the buyer wants to paint the aircraft with any other color, it is easy to apply paint on white color than on any other color.

So these are some of the reasons for most of the aircrafts being white.

But still some companies use colored aircraft like KLM airline

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## why do helicopters have a tail rotor?

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Have you ever looked at the small fan at the tail of some helicopters? What does that small fan do? What is need of that small fan?

Let's Find it out!

That small fan at the tail of the helicopter is known as the tail rotor. The tail rotor is very important in a case of helicopters. Without a tail rotor, it will become almost impossible to control the helicopter.

Before going to tail rotors lets take a look at how helicopter gets a lift?

### How helicopters get a lift?

Image From: - Wikimedia

Helicopter consists of the main rotor at its top. That main rotor rotates and creates a difference in air pressure on top and below the blades. The high-pressure air below helicopter blade pushes helicopter up. It is same as how aircraft wing gets a lift. To know more about how an aircraft wing produces lift check out my this post

### What is the need of Tail Rotor?

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This was all about the lift to the helicopter. But with the production of the lift, in addition to that torque is produced in helicopter body. Torque is simply a force that tends to cause rotation  As we all know according to newton's third law, every action has an equal and opposite reaction. Similarly, as helicopter main rotor rotates, in reaction to that helicopter body will also start to rotate in the opposite direction to the rotor. If Helicopter rotor is rotating in the clockwise direction helicopter body will rotate in a counter-clockwise direction.

To prevent such rotation tail rotor is needed!

### What does tail rotor do?

The Tail rotor is attached vertically to the tail of the helicopter. Similar to the main rotor of the helicopter, the tail rotor also produces lift to the blades of the tail rotor due to the pressure difference. But in this case, lift is horizontal. The Tail rotor simply pushes the tail of the helicopter in the opposite direction of the torque & prevents the rotation of the helicopter.

But not all the helicopters have tail rotors. They have other components to counteract torque.

### Alternatives of Tail rotor

• Co-Axial Rotors
• Dual Rotors
• NOTAR

#### 1. Co-Axial Rotors

Image From: - Wikimedia

Such helicopters have two concentric rotors placed one above another. One rotates in Clockwise direction while the other rotates in a Counter-Clockwise direction to counteract Torque.

#### 2. Dual Rotors

Image From: - Wikimedia

Dual rotors have two rotors placed side by side. One rotates in Clockwise direction while the other rotates in a Counter-Clockwise direction to counteract Torque.

Quadcopters (Quadrotors) have four rotors. Two of them rotates in Clockwise direction while other two rotate in Counter-Clockwise direction.

#### 3. NOTAR

Image From: - Wikimedia

NOTAR Stands for NO roTAR. NOTAR system uses the fan inside the tail of the helicopter. Which pushes the high volume of air in the opposite direction of the torque.

## Dihedral & Anhedral Aircraft Wings

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In a case of low wing Aircraft, such as Boeing 747, wings are angled upward while in a case of high wing aircraft, such as Antonov An225, wings are angled downwards.

But why are wings angled?

Upward angled wings of low wing Aircraft are known as dihedral wings & Downward angled wings of high wing aircraft are known as anhedral wings.

### Need of Dihedral wings

Suppose wings of low wing aircraft are straight without any angle. So when Aircraft is cruising, Lift force will act perpendicular to the relative upcoming airflow. So if Aircraft rolls, the direction of lift force on each wing will change with aircraft. Suppose aircraft rolls to left ( Anti-Clockwise), So the direction of lift force on each wing will also tilt to the left at some angle.
So now there are two components lift force. One in vertical direction & other in a horizontal left direction. The magnitude of components of lift force will be same on each wing of the aircraft.
So Due to the horizontal component of lift force, aircraft will slip towards left. And Aircraft will become unstable.

### How do dihedral wings work?

Image from: -Wikimedia

In a case of dihedral wings, at the time of cruising direction of lift force on each wing is already tilted towards aircraft as wings are angled in the upward direction.
Now suppose again if aircraft rolls to left(Anti-Clockwise direction), lift force on each wing will tilt to the left at some angle. Here, the left wing of aircraft is lower wing & right wing is the upper wing. If we find components of lift force on each wing, the magnitude of the vertical component of lift on left wing will be higher than the magnitude of the vertical component of lift force on the right wing as the lower left wing has a higher angle of attack than the higher right wing.

Image from: - Wikimedia

This difference in lift force on aircraft wings will produce a moment in opposite direction. This prevents Aircraft from slipping & stabilizes aircraft.

### Anhedral Wings

Image from: - Wikimedia

In a case of the high wing aircraft, The Anhedral angle is given to move the center of gravity of an aircraft to the bottom. So that such aircraft have good rolling stability.

Image From: - Wikimedia

Remember Center of gravity doll (Roly-poly toy)? Even such dolls have a center of gravity at the bottom. Same principle as of this doll is the reason for the better stability of high wing aircraft.

## Vortex Generators

Courtesy: - wikimedia

Vortex generators is small device used to improve stability of the aircraft and delay its stall. But how do they do it?

Before going ahead lets take a look at basics of fluid mechanics.
To understand vortex generators it is necessary to know about boundary layers.

### What is boundary layer?

Consider an air is moving over any aerofoil. (Aerofoil is simply cross section of an Aerodynamic shape). If we take a look at microscopic level, velocity of the air just above the surface of the aerofoil will be zero. This is because of viscous & frictional forces between air and aerofoil surface. So due to viscous and frictional forces velocity of air just above aerofoil surface will be zero. Due to this stationary layer air above this layer will slow Down again due to viscous force. This forms region above surface of the aerofoil with gradually increasing velocity of air. At far distance from the surface of the aerofoil there will be a point where velocity of the air will be equal to velocity of incoming air. So the region from surface of an aerofoil where velocity of air is zero to this point is known as boundary layer.

## Need of Vortex Generators

Formation of boundary layer with high energy keeps air flow in contact with wing surface.
But at slow speed and higher angle of attack this air flow seperates from the wing surface and some times aircraft stalls.
Also some times airflow seperates from the wing before reaching to control unit such as ailerons. And pilot looses controls!
So to overcome such problems, Vortex Generators are used. As name suggests vortex generators forms vortex and energize the boundary layer.

### How Vortex Generators work?

At slow speed and higher angle of attack airflow cannot remain attached with wing due to its low energy. So here comes vortex generators. Vortex generators forms vortices. Vortices are just small tornados. Actually vortex generators brings high energy air above boundary layer near the surface of wing by forming vortices & energize boundary layer. This keeps airflow attached with wing and reduce the possibilities of aircraft stalling.

### Other use of vortex generators

Vortex generators are used under wing of Airbus A320 family aircraft to reduce noise generated by airflow over circular pressure equalisation vents for the fuel tanks. Lufthansa claims a noise reduction of up to 2 dB can thus be achieved.

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## Why do pilots reduce aircraft engine power after takeoff?

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Do you know that after taking off aircraft pilots reduce engine power? Why do they do that?

First of all while taking off pilots do not move throttle stick directly from ideal to maximum take-off power. Pilots take a small pause before moving throttle stick to maximum take-off power. Pilots do that to ensure that all of the engines have started with equal power. Aircraft like Boeing 747 have big engines. Such a big engines produce very high thrust. Consider that you moved throttle stick directly to maximum take-off power. But due to some issue engines on one side of aircraft are producing more thrust that engines on the another side of the aircraft. This unsymmetrical thrust will produce a torque on the aircraft. So aircraft will take an unnecessary turn. Which can cause aircraft to move away from the runway. To avoid such a situation pilots take a small pause before moving throttle stick directly to the maximum.

now moving towards our question,

Initially Pilot moves throttle stick to maximum take-off power.  After climbing enough altitude pilot reduces aircraft engine power. And again restore it.

Most of the time airports are in the city area with a high number of residents. So after take-off just in few minutes aircraft is in the city area. And aircraft engines produce really very loud noise. That loud noise can be irritating for residents. To reduce that noise problem, at an altitude between 1000ft (0.3048Km) to 1500ft (0.4572Km) above ground level pilots reduce engine power. And after some time pilot again restores engine power.

And again reaching cruising altitude pilot reduces engine power up to certain extent. This increases the fuel efficiency of an aircraft.

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## Commercial Airbus planes naming

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Airbus is leading Aircraft manufacturing company in Europe. From. Today we are going to see how Airbus aircraft are named.

If you look closely at Airbus aircraft names you will see names with format A3XX. Such as A320, A350, A380, etc.

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First commercial aircraft manufactured by Airbus was Airbus A300. Here A in A300 stands for Airbus. Airbus thought 300 will be the number of passengers in that aircraft. But later on, they realized that 300 passengers are a bit too much. For better performance, they reduced the number of passengers to 260 and named their aircraft A300B.

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After Airbus A300B, Airbus named their aircraft as A310, A320, A330, A340, A350, and A380. You can see the pattern. If any variants of these aircraft then those aircraft are named by just changing digits little bit. For example A318, A319 are shorter variants of Airbus A320, and A321 is a longer variant of Airbus A320.

Again same as Boeing aircraft, Airbus aircraft are named like Airbus A3XX-ABC

Here ABC is code for the engine used in Airbus Aircraft.
For example, take an aircraft A320-231.

Comparing A320-231 with A3XX-ABC

So, A is 2, B is 3 & C is 1

here 2 is series of aircraft A320-200, then 3 for IAE(International Aero Engine) and engine version 1. So name A320-231

For an Airbus A330-244

A is 2, B is 4, C is 4

Here 2 is series of aircraft A330-200, 4 for Rolls Royce engine & other 4 for Trent 775 at the 334kN thrust

### Engine code  (Courtesy: - Wikipedia)

0 General Electric (GE)

1 CFM International (GE and SNECMA)

2 Pratt & Whitney (P&W)

3 International Aero Engines (P&W, RR, MTU, Kawasaki, Mitsubishi, and IHI)

4 Rolls-Royce (R-R)

5 CFM International (GE and SNECMA) (CFM International LEAP-1A for A320 NEO Family)

6 Engine Alliance (GE and P&W)
7 Pratt & Whitney (P&W) (Pratt & Whitney PW1100G for A320 NEO)

## Commercial Boeing Planes Naming

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Boeing is one of the leading aircraft manufacturing company. Along with Boeing company, aircraft manufactured by Boeing are also very famous. As aircraft nerds, we all know Boeing aircraft 737, 747, 787, etc. But ever wondered how these planes are named. Let's reveal this mystery today. (To see How Airbus Aircraft are named Click here)

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If you take a close look at commercial Boeing aircraft naming. You will observe that most of Boeing aircraft are named like 7X7. It means names starts & ends with 7.

First Boeing aircraft to name like 7X7 was Boeing 707.  There were many myths about the Boeing 707 name. Maths lovers & engineers were saying that name 707 was because sine of swept angle of wings of  Boeing 707 was 0.707. But it wasn't true as swept angle of Boeing 707 was 35° and not 45°!
Some people believing in superstitions were saying that as number 7 is lucky that's why Boeing aircraft was named like 707. But none of these were true.

So what is truth?

Boeing has assigned sequential model numbers to its designs for decades such as Model 40, Model 80, Model 247, Model 307 Stratoliner and Model 377 Stratocruiser., etc.

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Initially, Boeing was just military aircraft manufacturing company. But William Allen decided to expand their business to commercial airplanes, and pursue the new fields of missiles and spacecraft. To support this diversification strategy, the engineering department divided the model numbers into blocks of 100 for each of the new product areas: 300s and 400s continued to represent aircraft, 500s would be used on turbine engines, 600s for rockets and missiles and 700s were set aside for jet transport aircraft.

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At first, The 707 prototype was called the 367-80, or "Dash 80." 367-80 jet powered model of Boeing was made after modifications in propeller-driven aircraft 367 which was better known as KC-97. As 367-80 was jet powered aircraft it has to be named according to decided series i.e 700s(for jet transporter) But for company's first commercial aircraft name 700 was not so catchy. Hence Boeing business team decided to name their aircraft as 707 (Pronounced as Seven Oh Seven). Following these patterns, Boeing is naming their aircraft as 7X7 till date.

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But this is not over yet!

Boeing names their aircraft as 7X7-ABC (e.g. Boeing 747-400) where ABC is any three digit number.

Now, what is the mystery of that ABC?

Actually, that ABC is Boeing's Customer code.
Example
a 747-121 would be a 747-100 sold to Pan Am