View Full Version : Fanblades

13th Feb 2008, 20:04
What do the wavy fanblades like these
http://www.airliners.net/photo/Jet-Airways/Boeing-777-35R-ER/1326732/M/ (http://www.airliners.net/photo/Jet-Airways/Boeing-777-35R-ER/1326732/M/)

do better than the normal straight ones?

I guess its increased airflow or something to to do with increase rate of intake? either way they look cool!

The African Dude
13th Feb 2008, 20:13
I think the chord length of the fan increases about halfway out from the centre. Judging from the pictures it doesn't look like it comes back in again. Therefore I'd guess it increases the chord length at the outermost radius of rotation, and thus the corresponding "lift" of the blade (according to the formula for lift coefficient) is increased. So I'd guess it's a power augmentation thing :confused:

E.Z. Flyer
13th Feb 2008, 22:02
I think they have to flex in a thermo dynamic fashion as a function of their lift and in order to slow down so they cool off without warping or becoming brittle. That or they're just so powerful at speed they eat air.

14th Feb 2008, 00:10
The greater chord towards the tip unloads (aerodynamically) the blade there, where it is going faster so reducing Mach/Shock problems.. thus increasing efficiency.
Only advanced structural design analyses have made this sort of thing possible, as you really want more material at the root for structural reasons...

All guesswork of course from basic principles.

What are those engines?

14th Feb 2008, 11:49
GE90-115B (the only engine you can have on a 777-200LR/300ER). I think the chord doesn't change from the root to the tip that much - it's more that the blades are "twisted" so you are looking at them more edge-on at the center. The wavy shape reminds me of modern helicopter rotor blades that have that swept, shovel shape at the end which I believe makes them quieter. So my guess is it has to do with the way the shock waves from each blade interact with each other, i.e. it makes them quieter.

I often wander up to the intake of one of these and marvel at their awesomeness.:8 They are very popular with flight crews for photo ops too.

14th Feb 2008, 22:35
Attention FTEs

Can anyone comment on how close fan/bipass compressor blades get to the stall. Their designers would want them to be close to stalling at max n over root theta - that is max RPM over the square root of the relative temperature.

Is that formuala still valid for fan blades?

N1 Vibes
15th Feb 2008, 05:23
Somebody from RR once told me an increased thrust and SFC benefit for the same blade length/fan diameter.