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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