Fan & Propeller shapes: Sickle and Curved

**kach22i** · Jul13-07, 10:10 AM

Air or Water:
I'm looking for information on fan and propeller shapes (ducted and non-ducted) which might lead to more quiet if not more efficient shapes.

Noise is lost energy just as heat is lost energy in a mechanical system, right?

I have a thread which contains many bits of information for the context of this request. It also has many pictures which if you cannot see tell me and I'll repost all the links here.

I'm no engineer, pretty pictures tell me a lot. However if you have recommended text books, graphs, charts or other information you feel you can share, please add it to this thread.

Reference Thread:
http://www.hoverclubofamerica.org/fo...opic=1244&st=0

Sample Picture and second link:
http://www.hoverclubofamerica.org/fo...opic=1232&st=0

Cheers, George/kach22i

**DaveC426913** · Jul13-07, 02:06 PM

And cavitation. Big problem in propellors. That's why they're curved.

**FredGarvin** · Jul13-07, 04:51 PM

Do realize that fan shape is an extremely active area of research. We are always looking for ways to tweak our fan blade designs to achieve exactly what you are asking about. 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.

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

You can also see the tips here on Honda's blatant copy of our engine:
http://world.honda.com/HondaJet/Back...images/top.jpg

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

**berkeman** · Jul13-07, 04:56 PM

Originally Posted by FredGarvin

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.

Beautiful picture, Fred. But I want to hear the story behind this picture in the same directory....

http://www.turbokart.com/images/DSC01746.JPG

.

**kach22i** · Jul14-07, 03:57 PM

Originally Posted by FredGarvin

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.

Turbofan Video-1:
http://s184.photobucket.com/albums/x...t=Imgp1438.flv

Turbofan Video-2:
http://s184.photobucket.com/albums/x...t=Imgp1448.flv

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?

http://s184.photobucket.com/albums/x295/kach22i/

The Horten brothers and their WWII flying wings had some odd pusher propellers, I'll try to find my books and post those pictures too.

**FredGarvin** · Jul14-07, 10:28 PM

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?

Anyways, there are certain things that fan design need to accomplish:
- High thrust
- Low weight
- Low Noise
- Structural integrity

It's difficult to say exactly what each fan designer had in mind with each specific piece of geometry. As I mentioned before. the tip area, especially on a large diameter fan, is going to have a lot of supersonic shock issues. That means noise. So pretty much any design is an effort to increase the efficiency and decrease the noise at the tips.

**kach22i** · Jul18-07, 11:50 AM

Originally Posted by FredGarvin

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?

Yes, the double rotor did a mock rescue of a downed flyer.

My 34 picture album of the Willow Run airshow, mostly B-25 nose art.

http://s184.photobucket.com/albums/x...%20Run%202007/

Back to the topic; does anyone know if NASA has any current or very recent projects dealing with curved blades? I know they did a super quiet prop. It was hollow and had air pumped through it. The escaping air controled the vortex's which make sound. The air did not escape out the tips, rather it vented on the backside of the prop surface via the hub.

**kach22i** · Jul18-07, 02:24 PM

From page 12 of the Random Picture thread in the O.T. section of HCA.

http://www2.nlr.nl/public/facilities/AVET-...PropBlades.html

Daniel T. Valentine, Ph.D.
http://people.clarkson.edu/~space/VALPG1.html

Photo from the Naval Institute Proceedings web site;
this propeller was the first highly-skewed propeller
installed on a U. S. Merchant ship. The Project was
supported by MARAD. It was designed by Valentine
(when working at DTRDC under Dr. Wm. B. Morgan).

From page 13.........................of HCA thread.
http://www.hoverclubofamerica.org/fo...pic=779&st=180

http://frontier.cincinnati.com/blogs/art/2..._01_default.asp

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.

http://www.geae.com/aboutgeae/presscenter/...0_20041116.html

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.

http://www.hoverclubofamerica.org/forum/in...=779&st=180

NASA
Novel Engineering and Fabrication Techniques Tested in Low-Noise-Research Fan Blades
http://www.grc.nasa.gov/WWW/RT2001/7...unningham.html

Trailing Edge Blowing blade with top skin removed. Air enters at the retainer (bottom right) and exits through turning vanes at the trailing edge

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.

**berkeman** · Jul18-07, 02:26 PM

Wow! That NASA fan blade design is wild.

**kach22i** · Jul18-07, 02:31 PM

Originally Posted by berkeman

Wow! That NASA fan blade design is wild.

It reminds me of a Aerial Tennis Birdie (badminton).

http://www.everbe.com/Products/Sport...20rackets.html
http://www.everbe.com/Products/Sport...on%20birdy.jpg

**kach22i** · Jul19-07, 01:09 PM

Why do helicopter rotor blades have weights in them?

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

Why?

Helicopter blades have weights in them?
http://www.cavalrypilot.com/fm1-514/Ch3.htm

**FredGarvin** · Jul20-07, 07:31 AM

Originally Posted by kach22i

Why do helicopter rotor blades have weights in them?

For track and balance purposes. The blades need to be rotating in the same plane or as close to the same plane as possible. If you don't you get control and vibration issues. Since there is no real fine tune adjustment per blade on a rotor head, blade weights adjust the tracking.

Originally Posted by kach22i

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

I can't be for sure, but I can not say that I have ever seen them anywhere else.

**kach22i** · Jul21-07, 11:32 PM

I thought this paper may be of interest to some.

Senior Thesis Project
University of Virginia Department of Mechanical and Aerospace Engineering
Raymond Scott Ciszek
March 25, 2002
http://members.aol.com/sciszek/propfan.htm

**AlephZero** · Jul22-07, 04:46 PM

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?

If you mean the snubbers (the cantilevers sticking out of each blade at about 2/3 of the blade height) their function is to control vibration, not noise reduction.

When the engine is running, the blades twist and the snubbers press against each other to act like a solid ring. That has a big effect on the lowest vibration frequency of the blades, and eliminates some aerodynamic stability problems (a.k.a. flutter). The disadvantage is they partly block the airflow through the fan.

Modern fan designs have longer blade chords and "hollow" blades (actually, lightweight composite structures inside the blade) to control these vibration issues without using snubbers between the blades.

**kach22i** · Jul23-07, 10:53 AM

Originally Posted by AlephZero

snubbers

Thank you, I was not familiar with that term.

EDIT:
AlephZero are you calling the vane riblets "snubbers"?

Will the turbofan's blades will be pulled foreward and well into the larger part of the duct opening under full speed? You see the level changes there (right?), one is sloping a little.

This cannot be good for tip blade vortex generation, right?

http://s184.photobucket.com/albums/x...rent=FAN-1.jpg

http://s184.photobucket.com/albums/x...rent=FAN-2.jpg

**normofthenort** · Apr13-08, 02:44 PM

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?