What is the spiral mark on the cone of the aircraft engine?

What is the spiral mark on the cone of the aircraft engine?

Spiral - Wikimedia
Have you seen Spiral mark on the cone of aircraft engine? What is the purpose of that spiral mark?

Let's find it out!

History of Spiral Mark on the Aircraft engine

Those Spirals on aircraft engines are present for about 5 to 6 decades from now. But on older aircraft purpose of that spiral mark was something different than it used to be now. In some older aircraft, the propeller needs to spin before the fuel supply is turned on. That spiral helped ground crew of older aircraft to know the direction of rotation of engine propeller. So ground crew can spin engine fan in the proper direction and then fuel supply to the engine can be turned on. Check out engine start procedure of old aircraft engine.

Video Credits: - Christian Sturm (Youtube)

Purpose of the spiral mark on modern aircraft engine

Of course for the modern aircraft engine, There is no any need of spinning engine peropeller manually, before turning fuel supply on. The modern engines take care of this sort of things by themselves. Spiral mark on the aircraft engine cone in modern aircraft is for the safety of the ground crew. 

It is really very dangerous to work near the running engine. Aircraft engines are very powerful. One can be suck inside running engine. So, considering the safety of ground staff that spiral mark is made on the aircraft engine nose cone. By looking at aircraft engine spiral mark ground staff can identify that aircraft engine is running.

One can ask isn't aircraft engine noise enough for identifying whether aircraft engine is running or not?

Airports or places where ground staff work on aircraft are mostly very noisy. Even it is possible that several engines are running at once. So it becomes difficult for ground staff to identify which engine is running just by engine noise. So, here spiral mark on the aircraft engine cone helps ground crew.

Boeing 747 Model - Amazon

Prevents Bird strike?

On many websites on the web, it is mentioned that spiral mark helps to prevent bird strike. They said that spinning mark is like danger sign to the birds and they get out of the way of the aircraft when they see that mark and bird strike is avoided. But there is no any scientific proof for that.

According to studies by Boeing and Rolls Royce,
That spiral mark does not prevent bird strike. That spiral mark is not even visible to birds as it spins very fast! 

That mark is not always spiral!

Aircraft Engine Spinner - Wikimedia

Spiral - Wikimedia
G spiral - Flickr

Comma spinner - Wikimedia

In a case of most of turboprop engines there are marks even on the propellers!

In a case of turboprop aircraft engine, propellers rotate so fast that it becomes difficult to identify rotating propellers. So there are marks on propellers as shown below.

Marks on V22 Osprey - Wikimedia
Lockheed C130 propeller marks - Wikimedia

Thank you for reading!

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Airbus A380 Model - Amazon

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Aircraft flare: Countermeasure for Infrared homing

Aircraft flare:  Countermeasure for Infrared homing

Boeing C-17 Globemaster III Angel Smoke - Russell E. Cooley

Take a look at the cool photo taken by Russell E. Cooley. Isn't that really a great photo? First of all, that's really an original photo, It is not any kind of photoshopped photo.

That giant owl shaped smoke is produced due to flares released by Boeing C-17 Globemaster III Aircraft seen on the right upper corner of the image. That smoke is sometimes called as a smoke angel. Take a look at the following video to see how smoke angel by The Lockheed C-130 Hercules is produced. 

(Video from Airboyd Youtube)

But what is the purpose of producing such kind of smoke?
Let's find it out!

Short Answer: - That smoke is produced by flares produced by an aircraft. Flares are produced by an aircraft as a protective measure to misguide infrared homing or Heat seeking missiles, launched to destroy Aircraft.

Explanation: -

As discussed earlier that smoke is produced due to flares released by an aircraft. Flares produced by aircraft are actually countermeasure for Infrared homing or Heat seeking missiles.

Too much technical terms??
Don't worry, we will see it in a simplified manner.

What is Infrared Homing?

Infrared Seeker - Wikimedia

Infrared Homing System is a weapon (e.g. missile) guidance system. It uses Infrared waves emitted by the target to trace it. Infrared waves are emitted by hot bodies such as an aircraft engine. Heat is produced by aircraft engine due to combustion of the fuel. An infrared seeker consists of infrared sensors which detect infrared waves emitted by the hot aircraft engine. So, The infrared seekers can track aircraft based on infrared waves emitted by the hot aircraft engine. Infrared seekers are also known as 'Heat Seekers'.

The infrared Homing system is passive weapon guidance system. There is no any kind of indication to target that Infrared seeking missile is following it, unlike RADAR. As in a case of RADAR, radio waves are transmitted to the target. Radio waves reflect back from the target and received by the receiver. As Radio waves are reflecting from the target, they could indicate target about the upcoming weapon (missile).

Aircraft flare:  Countermeasure for Infrared homing

Aircraft Flares - Wikimedia

Now we are ready for the answer to our question. To protect aircraft from the upcoming Infrared seeker, Flares with the temperature higher than that of the temperature of an engine are produced. So, Flares misguide Infrared seekers and protect aircraft. And that smoke is produced due to hot flares. That Circular shape of smoke is due to vortex produced by aircraft wingtip known as 'Wingtip Vortices'.

Take a look at flares produced by aircraft

C17 Globemaster III aircraft Flares Video From Airsource Military - youtube

Lockheed C130 Aircraft Flares - Wikimedia

F-22 Aircraft Flares - Wikimedia

Boeing C17 Globemaster III Aircraft Flares - Wikimedia

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Why do Boeing 747 and Boeing 787 engine have chevron nozzle?

Why do Boeing 747 and Boeing 787 engine have chevron nozzle?

Boeing 747 Chevron Nozzle - Wikimedia

Queen of the sky Boeing 747 has GE's GEnx-2B engine & Boeing 787 Dreamliner has GE's GEnx-1B engine mounted on them.

Boeing 787 GEnx-2B engine Chevron Nozzle - Wikimedia

If you look at these engine's nozzle, you will see zigzag curves. Such type of nozzle is known as chevron nozzle. Those curves in chevron nozzle are not just for good looks. These curves have some purpose. Those curves in chevron nozzle reduce the noise produced due to an engine.

Before going into an explanation of chevron nozzle, let's see why aircraft engines produce such a huge noise. Nowadays, in most of the passenger aircraft, turbofan engines are used. Turbofan engines are simply a modification of turbojet engines. Just add a fan in front of turbojet engine and its turbofan engine.

Turbofan Engine

Turbofan engines have a high bypass ratio. It means most of the air simply passes through the engine without combustion. This air passes through the bypass duct of an engine. This increases the efficiency of an engine.

The air coming out of the combustion chamber has a higher temperature than the air passing through the engine bypass duct. This temperature difference causes a pressure difference between air flows.

Air passing through combustion chamber has higher pressure than the air coming out without combustion. When such two air flows suddenly meet each other shock waves are formed. Which causes the production of noise. (Remember that sound is just a simple pressure wave). Aerospace companies are trying very hard to reduce the amount of noise produced due to an aircraft engine.

So to reduce such type of noise Chevron nozzles are used. Chevron nozzle forces the air flow coming out of the bypass duct to concentrate on each pointed section of the nozzle. This prevents sudden mixing of two air flows. And reduce noise.

Pointed Section of Chevron Nozzle

Sometimes double chevron nozzles are used. In this case, for both the air flow, one coming out of combustion chamber & other coming out of bypass duct will have chevron nozzle. But in this case, both the nozzles will have a pointed section at an alternate location. So that air flows won't mix & produce noise. The Boeing 747 has double Chevron Nozzle.

But Chevron nozzle reduces the efficiency of an engine by the small amount.

Thanks for reading

Also read: - Why are most of the airplanes painted white?