777 fan blades

[TCX_757]

I was wondering are the fan blades of most 777's mainly made of some sort of titanium alloy? And if so, what properties of titanium alloy make it suitable for use within the engine?

Thanks for replys in advance.

[spannersatKL]

Would have thought that the ability to enable half frozen chickens bounce off at 500 MPH would be one good property?

[Fargoo]

wide-chord jet engine fan blades - Rolls-Royce (http://civil.rolls-royce.com/wide-chord-jet-engine-fan-blades/)

GE - Aviation: GE90 Fan Blade Receives Best of Show Honors at Composites Competition (http://www.geae.com/aboutgeae/presscenter/ge90/ge90_20051012.html)

So , some are titanium and some are composite!

[BigJoeRice]

all are bleedin' expensive!

[NutLoose]

The Rolls Royce engines are mounted to the 777 via the Boeing Slushy maker ;)

[N1 Vibes]

TCX_757 and Fargoo,

just a small technicality on the GE90 'composite' blades. They do have 2 major titanium components in their structure, the leading edge strip to chop up the birdies and an upside down L-shaped/boomerang feature at the trailing edge/tip, not visible as it is indisde the carbon weave, this is to absorb the shock/impact of hitting the bird, and prevents the trailing edge of the blade exploding into a mess of carbon string. So GE couldn't get away totally with making a 100% composite blade.

Interesting note - the Museum of Modern Art in NYC has one blade on display as a 'work of art'.

http://farm1.static.flickr.com/64/213778140_d4ef9ce8fd.jpg?v=1155452574

Regards,

N1 Vibes

[glob]

Does the word PNUMONIC ring a bell.:ok:

[Mike_s]

So they dont deform under massive centrifugal forces. If one fan blade breaks off, it cannot smash others off with it.

Basically titanium alloys are used for the strength and toughness

Also it is good at resisting corrosion

[CY333]

Dont forget light and have a wide range of tempreture operation.
Also are highly resistand to creep caused by the centr. forces.

[PT6ER]

Methinks creep is associated with Cf loading and temperatures in the higher region of bloody hot.

If you ever get to see a slow mo of a blade off test, you will see that the liberated blade does actually take one or more of the less inclined to leave ones. The big deal is the out of balance force caused by the loss of blade mass whilst the hub continues to spin.

I believe GE had to add spoolies to the inlet attachment flange bolts so they didnt liberate the inlet when the blade went south - these crush and absorb the energy of the deforming fan case. Fails the test if that leaves without an invite :)

[TURIN]

If you ever get to see a slow mo of a blade off test, you will see that the liberated blade does actually take one or more of the less inclined to leave ones. The big deal is the out of balance force caused by the loss of blade mass whilst the hub continues to spin.

Here's a good compilation of Blade Off (http://uk.youtube.com/watch?v=Ek6adm4iV4Y) tests. :ok::ouch:

[Mr Grimsdale]

Back in the 90s I did a PhD researching the high temperature mechanical properties of titanium aluminide (4722XD), principally for LP turbine blades and stators in gas turbines.

You certainly wouldn't want to use regular titanium alloys in any of the hot parts of a gas turbine (they've been used in exhaust components for years but it's relatively cool) due to their poor creep performance and oxidation properties.

I've lost track of developments but I know back in the mid/late 90s GE were intending to use titanium aluminide in the front fan assembly of the GE90.

The advantage of titanium aluminide is that it is an intermetallic, i.e. it combines the properties of a traditional alloy with some of the properties of, in this case, a ceramic. The material comes in several different compositions, some of which were quite frankly shocking...

In one incident I was setting up a test rig and attaching a thermocouple to a specimen when the sample broke at room temperature with only a very low load on it. Not a problem except the test machine nearly caved my skull in when the swing arm came crashing down.

Other batches of titanium aluminide were a lot more consistent, the variety I focussed on 4722XD (Ti-47Al TiB2) offered good creep resistance at the typical LP temperatures of 750C under the multiaxial stress conditions found in the blade root fixing.

The key thing with titanium aluminide, and any material in the engine, is to let the temperatures rise slowly and equalise themselves. You want to minimise the temperature gradients otherwise blades end up making unscheduled appearances. I'm not sure what the state of the art materials are these days but back in the 90s you'd have found single crystal blades made from CMSX4 in the HP turbine and various nickel based alloys from the Nimonic family used elsewhere. These materials have great creep resistance but are very heavy. From memory steel has a density of about 7800 kg m-3, Nimonics have a density of about 8200 kg m-3 and titanium alloys have a density of around 4500 kg m-3.

I've written all this from memory as I finished my PhD 10 years ago yesterday so apologies if some of it seems a little vague. If anyone is interested I'll have a look through my hard drive, log books, under the bed and see if I can find out anything else.