Advantage of Wide Chord Fans.

[Skunkworks1011]

What are the advantages of a WCF?

I can think of;

- Fewer blades ---> saved weight.
- More damage resistant.


Are these correct and are there other advantages?


Thanks!

 

[scotty7]

No snubbers between blades, therefore lower losses, is the primary reason for WCFB. The snubbers are required on thinner (higher aspect ratio) blades for mechanical purposes (flutter, birdstrike etc).

The weight one may be a red herring, because of the increased structural weight required for containment (sometimes kevlar is used, instead of steel, because of this).

 

[plasgears]

- Robust against FOD, birds, etc.
- Opportunity for hollow core at neutral axis.
- Potential lower cost, fewer blades.

Prior GE QCSEE fan dev engr.

 

[tbuelna]

Skunkworks1011, For high bypass turbofan, wide chord fan blade:

http://www.rolls-royce.com/civil_aerospace/technology/widechord.jsp

scotty7: containment of a "deviant" fan blade is a serious issue. I worked with BMW/Rolls-Royce (BRR) on the BR710/BR715 engine. I worked on the accessory gearbox design. The gearbox housing had to maintain structural integrity (ie. not crack open and dump oil everywhere) for 30 seconds during a "blade out" condition. 30 seconds was the amount of time deemed necessary for an out-of-balance engine to stop shaking and come to a halt.

To test for a "blade out" condition, the engine was run up to max RPM (like during a take-off) and a fan blade was explosively separated from the rotor. I remember seeing the high speed test film of the fan blade being blown free and impacting the kevlar containment structure of the fan shroud. The kevlar composite containment structure was at least an inch thick and seemed as solid as a rock. But when that 40 inch diameter fan blade, spinning at about 15,000 rpm, came loose and hit that containment structure, it looked as though it was made of rubber. It contained the fan blade alright, but it sure "moved around" alot doing so.

I also recall a couple of years ago that a woman and her child were killed during a take-off of an MD-90 aircraft (it has fuselage mounted engines) when a fan blade separated from the engine and penetrated the fuselage.

To make a long story short, the less a fan blade weighs, the less destruction it will cause if it decides to come loose. A wide chord composite fan blade would seem beneficial in this regard.

 

[Skunkworks1011]

Thanks for the replies!

The containment tests must be really impressive! Are there any movies available on the internet? I'm not trying to be a "wise guy", but isn't the fan normally turning a lot slower than 15,000rpm?

Also, about the swept fan blades - is the idea to get a more elliptical loading on the blade? I read in Flight Intl that the swept blades 'transition the shock wave away from the tip toward the core'.

 

[scotty7]

The fans do run a lot slower. Not sure on BR715, but RB211 series (B747 etc) is around 4000rpm. And yes, it is energetic! RB211 uses steel containment 3/4" thick. I was RR's dev eng who ran the RB211-524G containment test, so I was about 50 feet from it when it went bang. Enough energy to lift a 1 tonne car about 70 feet in the air... We have put together a video for public consumption, but not aware of a net posting.
A single WCFB will weigh more than a single narrow fan blade (but because there are fewer the shipset will probably be lighter). Therefore it is more energetic and requires heavier containment than a narrow blade. And if either gets out of the casing, I would not like to be in the way...

 

[scotty7]

OK, I lied...

http://www.msm.cam.ac.uk/phase-trans/2002/RR.html

Doesn't really show the rubber casing, but mighty impressive anyway.