wide Chord Fan Blades

[Beech19]

Busy going through "Ace the Tech" and i'm not buying it's discription of WCF blades.

What are the advantages to Wide Chord Fan blades?
I Know the that they are stronger, and therefore handle FOD better, and also being thicker, they are less suseptable to vibration. But why would having a lower aspect ratio (Not mentioned in ACE) be such an advantage? I'm no aerodynamic expert, but i thought that the issue of aspect ratio was important to us when it comes to Induced drag, but surely this is not an issue here, after all, it's ducted!!
Would WCF's be capable of higher speeds? Or would it not need to as a wider chord would produce the required airflow at a lower speed.

I'm a bit lost:confused:

thanks

[lomapaseo]

Busy going through "Ace the Tech" and i'm not buying it's discription of WCF blades.

What are the advantages to Wide Chord Fan blades?
I Know the that they are stronger, and therefore handle FOD better, and also being thicker, they are less suseptable to vibration. But why would having a lower aspect ratio (Not mentioned in ACE) be such an advantage? I'm no aerodynamic expert, but i thought that the issue of aspect ratio was important to us when it comes to Induced drag, but surely this is not an issue here, after all, it's ducted!!
Would WCF's be capable of higher speeds? Or would it not need to as a wider chord would produce the required airflow at a lower speed.

I'm a bit lost:confused:

thanks


I'll add a bit or two here and expect a few others to chime in as well

Yes, by virtue of the their design function (aerodynamic) they are a bit thicker at the LE and enjoy a more robust resistance to FOD.

They are of course quite a bit more expensive to replace.

Vibration can get you in a multitude of ways (first order bending, coupled modes, flutter, torsion etc.) I'm sure that RR would gave a few bad words to say about one of these modes with their WCF. On the other hand both GE and P&W have even more words to say about their narrow chord blades in their early machines.

With that said. it's an easier all around job to handle WCF blades for the ultra High-bypass engines. then it would be for the narrow chords.

[N1 Vibes]

Beech19

in response to your last question. Imagine rowing a boat with a blade as thin as a matchstick, how many more strokes, or speed of stroke, you need to move the boat at a given speed. Then put a biger blade on the oar and you need less strokes, or slower stroke speed to make the same boat speed.

Also, for rotor speeds there is another factor. The JT9 fan blade at take off has the equivalent to a 42 ton truck hanging on the end of it due to centrifugal force. Now make a blade that weighs more than 2x the weight, it has to run slower to keep within current blade root technology and strength.

My 2 penneth,

N1 Vibes

[idg]

If you compare a WCF with an early example you will see that many of the early engines have fan 'snubbers' at approx. the mid point of the blade. These were there to support the blades and to keep the separation between blades correct.

A WCF does not need these because of it's inherent strength and is therefore much 'cleaner' aerodynamically than it's early counterpart.