Why do jet engines have a spiral painted on the intake?

[clarksonisawilly]

You know that cone inside the fan? I don't know what it's called.
I have always wondered.

[BliarOut]

It tricks the conveyor belts...

[clarksonisawilly]

BliarOut said:

It tricks the conveyor belts...

?

[Eric Mc]

It's a humane device that hypnotises birds so they are unconscious when they are ingested by the engines.

[hurstg01]

BliarOut said:

It tricks the conveyor belts...

[Eric Mc]

clarksonisawilly said:

BliarOut said:

It tricks the conveyor belts...

?

You're a new boy here, aren't you

Edited by Eric Mc on Monday 12th July 13:31

[clarksonisawilly]

Eric Mc said:

clarksonisawilly said:

BliarOut said:

It tricks the conveyor belts...

?

You're a new boy here, aren't you

Edited by Eric Mc on Monday 12th July 13:31

Yeah I dont have pubes yet

[IforB]

It's simply so that you can see if the fan is turning or not.

[Eric Mc]

It's an old idea - the Germans used a similar system on their WW2 fighters.

[RichB]

Eric Mc said:

It's an old idea - the Germans used a similar system on their WW2 fighters.

Nice photograph Eric, I particularly like the realistic background, helps show off the model at its best.

[Eric Mc]

Not mine - unfortunately. I found it on the Hyperscale site.

[dilbert]

The handlers wear ear muffs. They can't hear the engines starting.
It's a visual cue, so that they can avoid getting sucked in.
I don't think it's a primary safety mechanism, but everything helps.

[clarksonisawilly]

Can you not see the fan blades very well then? They seem really big so I thought you'd see them turning or not quite clearly.

[dilbert]

clarksonisawilly said:

Can you not see the fan blades very well then? They seem really big so I thought you'd see them turning or not quite clearly.

I'm not precisely sure, but the blades in peripheral vision don't catch your attention. The spiral does.

[Semi hemi]

clarksonisawilly said:

You know that cone inside the fan? I don't know what it's called.
I have always wondered.

Because its cool man

[Eric Mc]

It's not always obvious. The apron can be a very noisy and distracting place - there's all sorts of movement and clatter going on - trucks, baggage trolleys, taxying aircraft, APU exhaust noise etc etc.

Many of the staff on the apron will be wearing ear defenders or even headphones so being aware of what's going on around you is essential. As has already been said, every little clue as to what's happening is usuful iinformation to take on board.

The rate at which the spiral is rotating will also give a clue as to whether the engine is powered up or not. The fans tend to rotate even when the engines are switched off - but that is a fairly slow and gentle motion. Once the engine starts spooling up, the fan rotation rate will obviously increase and the observer should be able to ascertain if the engine is actually running by just seeing how fast the spiral is rotating.

Edited by Eric Mc on Monday 12th July 13:57

[LeeME3]

Some engines object to trying to start when they're rotating 'the wrong way' which will happen if the aircraft tail is into wind and the wind is strong enough to blow through the engine and rotate the blades (should always be parked nose into wind but wind changes direction and parking slots are parking slots!). The spiral is a quick check she's turning the right way!

[Dogwatch]

I'd always assumed 'the lad' had been given the job of painting a circle round the cone but had just never managed to hold the brush steady...

[davidspooner]

[Tango13]

I remember many years ago some one being sucked into the front end of a TF34 at British Aerospace Hatfield feet first. A disgraceful failure of health and safety that was covered up by the management in a criminal manor!