Whats the spiral on an engine fan for?

Profile picture for user adamdowley

Member for

16 years 3 months

Posts: 1,381

Hi all This just occured to me - what's the painted spiral on the cone at the centre of the fan for, as shown in the a.net shot? i see it on some engines, but not on others? http://www.airliners.net/open.file/0998402/L/ thanks
Original post
Profile picture for user by738

Member for

15 years 6 months

Posts: 1,012

Suppose to make it more noticeable when its spinning
Profile picture for user greekdude1

Member for

19 years 9 months

Posts: 2,956

It's designed to scare birds away to prevent bird strikes.
Profile picture for user LBA-EGNM

Member for

13 years 9 months

Posts: 328

yer im sure its to show ground staff aswell that it is still turning
Profile picture for user PMN

Member for

14 years 2 months

Posts: 5,530

It's the two reasons mentioned above. Its primary function (as I understand it at least) is to scare birds away. Birds have a higher vision 'refresh rate' than humans, so although it may just look like a tiny swirl in the middle of the fan to us, for birds it's much more noticable. And of course it allows ground crews to see when the engine is tuning in low light when it's not easy to see the fan blades. Paul
Profile picture for user Bharatheeyan

Member for

14 years 1 month

Posts: 89

To hypnotize the curious onlookers ;)
Profile picture for user adamdowley

Member for

16 years 3 months

Posts: 1,381

cheers guys!

Member for

15 years 6 months

Posts: 170

How could anyone man or bird see the spiral once the engine has been run up. Unless they have strobe vision!

Member for

14 years 11 months

Posts: 93

How could anyone man or bird see the spiral once the engine has been run up. Unless they have strobe vision!
Dude.. read all the posts again. Birds have better framing rate than humans. Hence... !
Profile picture for user adamdowley

Member for

16 years 3 months

Posts: 1,381

How could anyone man or bird see the spiral once the engine has been run up. Unless they have strobe vision!
Well, I guess if you can't see it - you know its spinning.
Profile picture for user cloud_9

Member for

14 years

Posts: 2,343

...what's the painted spiral on the cone at the centre of the fan for,...i see it on some engines, but not on others?
Interesting topic, I too have been curious to know why this is the case...and now I know - thanks for the information!
To hypnotize the curious onlookers ;)
LMAO!:D:D:D
Profile picture for user Hugh Jarse

Member for

14 years 8 months

Posts: 192

While the tips may be going round close to the speed of sound the centre is stationary. As distance from the centre increases as does the speed. It is possible to see the shape (it's not always a spiral) painted on the spinner particularly at idle. Another use of the shape is to indicate rotation to the pushback crew as some engines require a call to confirm the N1 is rotating before fuel is selected on. I don't know why some engines don't have them though. We have one aircraft that has one engine with the painted spinner and one that doesn't.
Profile picture for user andrewm

Member for

19 years 9 months

Posts: 4,213

They arn't an aircrafts equivalent of go faster stripes :eek: :eek: :eek: :eek: :eek:
Profile picture for user andrewm

Member for

19 years 9 months

Posts: 4,213

A little trick i learnt in pre-gcse HE classes - If you get the paint in its pourable form and spin the nose cone for the fan blades very quickly (like normal idle spinning or maybe just a bit less) then pour the paint from the center in a line directly to the edge of it. This will create the spiral effect :D Usually used with chocolate or carmel etc
Profile picture for user Hugh Jarse

Member for

14 years 8 months

Posts: 192

How about painting this type? Engine damage caused by a heron hit very close to V1! http://img.photobucket.com/albums/v701/hughjarse/DSCF0085.jpg
Profile picture for user adamdowley

Member for

16 years 3 months

Posts: 1,381

How about painting this type? Engine damage caused by a heron hit very close to V1! http://img.photobucket.com/albums/v701/hughjarse/DSCF0085.jpg
did the heron make that large white mess on the cone? seriously now, to raise another question, whats the pipe sticking out of the top of the engine casing in that picture for?
Profile picture for user andrewm

Member for

19 years 9 months

Posts: 4,213

pitot tube?
Profile picture for user wysiwyg

Member for

19 years 9 months

Posts: 3,538

Pitot tubes are used to measure the air pressure resultant from the forward motion of the aircraft. This probe measures the pressure of the air immediately prior to entering the fan/compressor stages and amongst other things is used to compute the EPR indication.
Profile picture for user andrewm

Member for

19 years 9 months

Posts: 4,213

So is that a yes?
Profile picture for user Bharatheeyan

Member for

14 years 1 month

Posts: 89

I think the real reason is, if you use fluoroscent lighting, you will misjudge the fan speed. The spiral will clearly show the actual rotation. That will help maintenance crews. JM2C
Profile picture for user wysiwyg

Member for

19 years 9 months

Posts: 3,538

So is that a yes?
No. Pitot probes are on the nose. :p