Fan & Propeller shapes: Sickle and Curved

For example, the forward swept tip is now the standard.
http://www.turbokart.com/images/ge90_huge.jpg

I'll see if I can dig up any more sources.

In regards to noise, the tip geometry is pretty much king. That's where you are sure to go supersonic and that is where the noise is generated.

I didn't get a chance to get down to Willow Run this time. I was bummed out. Did the MING have one of their CH-47s there?

GE Aircraft Engine's Jet Engine Fan Blade (2001) that the museum acquired just before reopening in fall 2004. That's the composite fiber resin, polyurethane and titanium blade at left.

It's Great Design Too: World's Biggest Jet Engine Fan Blade at The Museum of Modern Art
November 16, 2004 -- EVENDALE, Ohio - Today's three-dimensional aerodynamic designs create not only extremely efficient jet engines--but also, beautiful works of design.

The Museum of Modern Art in New York City has acquired the world's largest jet engine fan blade, produced by General Electric Company (GE), into its Architecture and Design collection. The GE fan blade will be on view when the museum reopens on November 20.

Nearly four feet long and with a unique curved design, this fan blade is on the GE90-115B, the world's largest and most powerful jet engine. Unprecedented in size, the GE90 front fan blade is also the only composite fan blade in commercial aviation. The composite material results in the blade's distinctive black color.

The GE90 engine powers Boeing 777 aircraft around the globe.

The GE90 blade blends form and function. Using three-dimensional aerodynamic computer design tools, GE engineers modeled these huge blades to pull massive amounts of air into the engine while operating at low noise levels. The artistic, curved design serves a key function--to enable the fan blades to withstand supersonic airwaves generated during flight.

The blades' composite material gives the GE90 engine a rare combination of unprecedented power and low noise. Here's how: The front fan turns more slowly than the front fan of jet engines of similar thrust, and thus it is quieter. But the blades have to be huge to pull enough air into the engine to produce the super-high thrust. Traditional titanium blades would have resulted in far too much engine weight.

The GE90 blade's carbon fiber polymeric material and a titanium leading edge for extra protection were a lightweight and durable solution.

Each fan blade weighs between 30 and 50 pounds. Every GE90-115B engine contains 22 of these fan blades, which add approximately 2,000 pounds to the engine's thrust capability, while providing better fuel burn.

GE Transportation - Aircraft Engines, a part of General Electric Company (NYSE: GE), is one of the world's leading manufacturers of jet engines for civil and military aircraft. GE Transportation is headquartered in Cincinnati, Ohio.

A major source of fan noise in commercial turbofan engines is the interaction of the wake from the fan blades with the stationary vanes (stators) directly behind them. The Trailing Edge Blowing (TEB) project team at the NASA Glenn Research Center designed and fabricated new fan blades to study the effects of fan trailing edge blowing as a potential noise-reduction concept. The intent is to fill the rotor wake by supplying air to the rotor blade trailing edge at the proper conditions to minimize the wake deficit, and thus generate less noise. The TEB hardware is designed for the Active Noise Control Fan (ANCF) test rig in Glenn's Aeroacoustic Propulsion Laboratory.

Wow! That NASA fan blade design is wild.

Why do helicopter rotor blades have weights in them?

Do other types of fans or propellers have end tip or leading edge weights?

These details look very odd to me, taken at a local airshow last week at Willow Run (FedEx jet). Do these steps and bevels or cants help reduce noise?

snubbers

Here's a related question: Both (air) fan blades and ships' propellor blades often have one side that's curved (convex) and another side that's either straight or concave. But the orientation is OPPOSITE on fan blades and propellors! I.e., props seem to lead with their curved (convex) edge, as the leading edge, while fan blades seem to lead with the other side and use the curved (convex) edge as a trailing edge!

How can the optimum blade shape for these two common fluids be OPPOSITE from each other? Seems weird to me.

BTW, I'm old enough to remember when fan blades looked like prop blades. I don't think the shape of props has changes hugely in those decades, but the shape of fan blades has. Now some of them seem to have concave leading edges with swept-forward "points" at the outside! If that were a universally efficient way of slicing through the air at an angle to generate lift, I'd expect modern airplanes to have wings with concave LEs with swept-forward wing tips. But I haven't seen anything like that -- at least not yet!

What gives?