glidepath73
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Could This Be The Future Of Prop Power?

Tue Dec 01, 2009 12:03 pm

Hi guys!

A friend of mine showed me this faszinating stuff :

http://www.dyson.com/technology/airmultiplier.asp

How is this working? Could it be adapted for maybe a one person aircraft?
Could this power even bigger aircraft's in the future?

Greets,
Patrick
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Starlionblue
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RE: Could This Be The Future Of Prop Power?

Tue Dec 01, 2009 3:29 pm

I read about this. As I recall you get far less air flow per power input than with an actual prop driving air directly. It works by pumping air out through holes spread around the ring, which takes surrounding air with it. Obviously, there IS a fan in the contraption. You just can't see it. Something has to push the air.

So no, I don't think this is a good idea for aircraft. The only reasons it is neat for fans is because a child (or a drunk adult) can stick his hand in it without damage, and also because the airflow is nice and smooth instead of "flap-flap-flap-flap". And oh yes, it looks pretty cool.

Here's a better article: http://gizmodo.com/5379890/dyson-air...ew-making-a-300-fan-takes-cojones. As the author notes: $300 for a fan is far, far from an upsell when I can get 95% of the experience for $10 at Walmart
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FredT
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RE: Could This Be The Future Of Prop Power?

Tue Dec 01, 2009 6:51 pm

Brought to you by the same people who brought you the magnetic fuel atomizer. If I had a Harley, I could use their sales pitch to wash it. Luckily, I'm a Suzuki rider so I don't have to.  Wink

The technology has been used on aircraft e g to provide airflow through oil coolers when on the ground. It is then called an ejector.

Check this article for more information than you want.
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glidepath73
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RE: Could This Be The Future Of Prop Power?

Wed Dec 02, 2009 11:37 am

Thanks guys,

looks cool, but under the line its to weak. I wonder what would happen when this diffusor would be combined with a jet engine...  spin 
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speedygonzales
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RE: Could This Be The Future Of Prop Power?

Wed Dec 02, 2009 3:27 pm

I've been wondering if anyone would be crazy enough to build an aircraft with a Voith-Schneider propeller.
http://en.wikipedia.org/wiki/Voith_Schneider_Propeller
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rwessel
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RE: Could This Be The Future Of Prop Power?

Wed Dec 02, 2009 6:52 pm



Quoting SpeedyGonzales (Reply 4):
I've been wondering if anyone would be crazy enough to build an aircraft with a Voith-Schneider propeller.

Helicopters?

That kind of omni-directional thruster is somewhat pointless on a conventional aircraft, since you never really want the thrust to go sideways. It would also be much harder to implement to just lateral thrust because the working fluid is so much less dense for an aircraft. Nor is efficiency all that high a priority in the usual applications for these sorts of things.
 
wingscrubber
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RE: Could This Be The Future Of Prop Power?

Wed Dec 02, 2009 7:04 pm

That Dyson thing looks like a convoluted ducted fan to me, the only similar aerospace applications would be things like 'blown flaps' for lift augmentation, not so good for pure thrust.

As for prop-power, for me, the prevalance of turbo-prop engines growing ever-more blades is going one direction (i.e. C-130J, Airbus A-400, Antonov An-70), while turbofans becoming higher and higher bypass is going the other. I would love to meet the two concepts in the middle and see what power and efficiency you might get if you took a pair of PT-6s, get rid of the reduction gearbox and attach a multi-bladed fan to them both, face them against each other fan-to-fan, slap a duct over the fans and some fairings over the engines then see what kind of thrust you can get out of it. With a smaller-diameter ducted fan you wouldn't have to worry about blade tips going supersonic, noise would be reduced, and some careful venturi-sculpting may afford some extra thrust. I do realize though that putting a Caproni-style barrel over a perfectly good engine and prop won't really do anything.
Also, problem with this idea is you'd end up with a rather long engine pod which wouldn't fit a typical airframe, might hang nicely underneath a wing though, or protrude like a bee's stinger from the tail of a Rutan-esque vari-eze.

Anyway here's a quick diagram I made of what I'm thinking about... just daydreaming.
http://i32.photobucket.com/albums/d37/Peeto999/TwinPT6.jpg
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wingscrubber
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RE: Could This Be The Future Of Prop Power?

Wed Dec 02, 2009 7:07 pm



Quoting Rwessel (Reply 5):
Helicopters?

Good idea - maybe for tail rotors? Sort of like NOTAR...
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DocLightning
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RE: Could This Be The Future Of Prop Power?

Wed Dec 02, 2009 11:05 pm



Quoting SpeedyGonzales (Reply 4):
I've been wondering if anyone would be crazy enough to build an aircraft with a Voith-Schneider propeller.
http://en.wikipedia.org/wiki/Voith_S...eller



Quoting Rwessel (Reply 5):

Helicopters?

That kind of omni-directional thruster is somewhat pointless on a conventional aircraft, since you never really want the thrust to go sideways. It would also be much harder to implement to just lateral thrust because the working fluid is so much less dense for an aircraft. Nor is efficiency all that high a priority in the usual applications for these sorts of things.

Wouldn't work for a helicopter because you'd still need a downward component to the thrust. In a helicopter, most of the thrust is always pointed down, but it can be tilted slightly in any direction to provide lateral thrust. Adding one of these would simply add another motor without any benefit.

However, it could work very well for lighter-than-air craft.
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Starlionblue
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RE: Could This Be The Future Of Prop Power?

Wed Dec 02, 2009 11:29 pm



Quoting DocLightning (Reply 8):
However, it could work very well for lighter-than-air craft.

Sure, but what's the point? Isn't an ordinary prop way more efficient?
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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DocLightning
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RE: Could This Be The Future Of Prop Power?

Thu Dec 03, 2009 12:16 am



Quoting Starlionblue (Reply 9):

Sure, but what's the point? Isn't an ordinary prop way more efficient?

Not in water, apparently. At least, not for craft that need high maneuverability.

However, all the variables for air are different. So nobody can answer that question until the analysis is done.
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rwessel
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RE: Could This Be The Future Of Prop Power?

Thu Dec 03, 2009 12:55 am



Quoting DocLightning (Reply 8):
Wouldn't work for a helicopter because you'd still need a downward component to the thrust. In a helicopter, most of the thrust is always pointed down, but it can be tilted slightly in any direction to provide lateral thrust. Adding one of these would simply add another motor without any benefit.

My tongue-in-cheek comments was to imply that the main rotor of a helicopter already does most of what this type of thruster does, and in a somewhat similar manner (notably the periodic adjustment of the AoAs of the individual blades).

Quoting DocLightning (Reply 10):
Not in water, apparently. At least, not for craft that need high maneuverability.

However, all the variables for air are different. So nobody can answer that question until the analysis is done.

I believe that the main advantages are quick response and ruggedness. Rudders and (rotating) podded engines are both vulnerable to all sorts of damage. This sort of thruster has very quick response times (compared to spinning a pod or maneuvering with a rudder), and is very easy to make almost invulnerable by putting a small cage around it. You can also mount it closer to the center of the tug than a podded engine or rudder, further enhancing its protection.

But I don't believe they're particularly efficient in the sense of "converts shaft energy to useful thrust."

While a lighter than air application might make sense, there's the question of whether or not airships need that kind of maneuverability. These tend to be fairly slow lumbering beasts, and I’m not sure they really need to change – perhaps if LTA cargo becomes a big deal you’d want more maneuverability to help load/unload cargo in high winds, but airships and gusts don’t mix all that well. And rotating pods or airfoils in the prop slipstreams seem a much simpler solution given the necessary size of propellers. Or if that's too crude, some ductwork, a handful of valves, and a blower motor for fine control.

This sort of thruster is also going to be quite large and heavy compared to a propeller. Substantial parts of the blades are constantly at a position where they cannot contribute to thrust, thus you'd need more blade area, not to mention a big rotating structure on which to mount them. The blades themselves will likely need heavier structure too – much of the stress on a propeller is along the blade’s axis (which is by far the easiest way tot sustain load) – in this kind of structure the equivalent of that force instead adds to the bending of the blade caused by thrust production. Of course the other mechanism (rotating pods, moving airfoils) contribute weight too.
 
bond007
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RE: Could This Be The Future Of Prop Power?

Thu Dec 03, 2009 3:16 am



Quoting DocLightning (Reply 10):
Not in water, apparently. At least, not for craft that need high maneuverability.

However, all the variables for air are different. So nobody can answer that question until the analysis is done.

I can be almost 100% sure that the analysis has been done, and it didn't take long, and the result was that it isn't a more efficient propulsion system for aircraft than we have today.

I'll be the first to admit I'm wrong, but I think I'm pretty safe on that!!

Jimbo
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tdscanuck
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RE: Could This Be The Future Of Prop Power?

Thu Dec 03, 2009 3:43 am



Quoting Rwessel (Reply 11):
But I don't believe they're particularly efficient in the sense of "converts shaft energy to useful thrust."

They should actually be pretty comparable on efficiency, possibly even better than a conventional prop due to the high aspect ratio, since they're using the same basic principle (airfoil lift). However:

Quoting Rwessel (Reply 11):
This sort of thruster is also going to be quite large and heavy compared to a propeller.

The power density will be low, because of all the issues you noted. On a boat, you don't really care, but power density is a huge requirement for aircraft.

Tom.
 
rwessel
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RE: Could This Be The Future Of Prop Power?

Thu Dec 03, 2009 5:21 am



Quoting Tdscanuck (Reply 13):
They should actually be pretty comparable on efficiency, possibly even better than a conventional prop due to the high aspect ratio, since they're using the same basic principle (airfoil lift). However:

True, although most conventional propellers, at least for lower speed operations, have pretty high aspect ratios too.

I think the main efficiency issue I see is that the individual blades spend a lot of time being dragged through the water (or air) at very awkward angles where they'll still be generating plenty of parasitic drag, but little useful lift. And while I'm having trouble visualizing some of the flows (to darn much stuff rotating!) I think this gets worse as speed increase.
 
astuteman
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RE: Could This Be The Future Of Prop Power?

Thu Dec 03, 2009 6:13 am



Quoting DocLightning (Reply 10):
Quoting Starlionblue (Reply 9):

Sure, but what's the point? Isn't an ordinary prop way more efficient?

Not in water, apparently. At least, not for craft that need high maneuverability.

However, all the variables for air are different. So nobody can answer that question until the analysis is done.

The "analysis", as you call it, was done decades ago.

Voith-Schneider propellers aren't the most efficient way of flinging water around.
But for a tug in a confined waterway, are easily the best way of providing the ultimate in manouevrability, as well as being more resistant to touching the bottom...

It also eliminates the need for a rudder..  Smile

Rgds
 
prebennorholm
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RE: Could This Be The Future Of Prop Power?

Sat Dec 05, 2009 2:33 am

Quoting Tdscanuck (Reply 13):
They should actually be pretty comparable on efficiency, possibly even better than a conventional prop due to the high aspect ratio...

No way. The blades only work in their optimal way at their 6 and 12 o'clock positions (considering forward thrust). At their 3 and 9 o'clock positions they only produce drag, and at any other positions they produce a combination of drag and thrust in unwanted directions.

The unwanted thrust direction on the, say, 2 o'clock blade is fully cancelled by the opposite unwanted direction by the 8 o'clock blade, so you don't feel it. You just make a terrible tubulence in the water (or air) to no avail.

Quoting Tdscanuck (Reply 13):
...since they're using the same basic principle (airfoil lift).

When at 6 and 12 o'clock positions the blades produce thrust with opposite angle of attack. That calls for a symmetrical airfoil (or waterfoil) section which is way less efficient than the sections used on aircraft and ship propellers.

This propulsion system is great for ships like tugs or small ferries which must be able to maneuver easily and fast, go forward, backward, sideways, and rotate. But they pay a high price in propulsion efficiency.

Also the mechanism to constantly reverse the angle of attack for every half rotation would be very heavy, and at air propeller speed it would be very maintenance intensive due to wear. Just imagine a constant speed propeller which had to change from forward cruise pitch to brake pitch setting and back again for every revolution. That's what is needed to make it work.

[Edited 2009-12-04 18:48:13 by prebennorholm]
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rwessel
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RE: Could This Be The Future Of Prop Power?

Sat Dec 05, 2009 4:52 am



Quoting Prebennorholm (Reply 16):
The blades only work in their optimal way at their 6 and 12 o'clock positions (considering forward thrust). At their 3 and 9 o'clock positions they only produce drag, and at any other positions they produce a combination of drag and thrust in unwanted directions.

I don't think they have to produce much off-axis lift. You'd just have to rotate the blades to the zero lift position once they're far off the perpendicular positions that the angle-of-attack limits made thrust on the desired axis impossible.

That still leaves drag, of course, and does reduce the potential power output for a given sized propulsor (although an "emergency" mode that accepted some off axis lift would be possible, with the attendant decrease in efficiency).

I'm not sure you could do that with a simple mechanism, though.
 
andthensome
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RE: Could This Be The Future Of Prop Power?

Sun Dec 06, 2009 11:22 pm

I spent more time on a device like this than I want to admit.......
The small prototype I built along with all the notes and calcs are in storage since the moment I found out that not only individuals but even the USAF (back in the 70s) obtained patents on similar devices........ and failed MISERABLY!!!!!!
A quick search on the US Patent Office (www.uspto.gov) and the European Patent Office (www.epo.org) with apporpriate keywords and their combination (coanda effect, engine, air amplifier, etc.) will show you what I mean.
I have a love-hate relationship with coanda-effect devices and I still have one crazy idea in my head (actually I have it since 2002...) but I keep it in the back of my head for now............ one day............ perhaps............
 
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Francoflier
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RE: Could This Be The Future Of Prop Power?

Mon Dec 07, 2009 2:45 am



Quoting Wingscrubber (Reply 6):
Anyway here's a quick diagram I made of what I'm thinking about... just daydreaming.

I think having two engines in such a configuration would make it much more complex and inefficient than having a bigger engine with two props and a gear box to make them turn in opposite direction.

And then would than not 'just' be a contra-rotating turbofan?
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prebennorholm
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RE: Could This Be The Future Of Prop Power?

Tue Dec 08, 2009 1:07 am



Quoting Rwessel (Reply 17):
I don't think they have to produce much off-axis lift. You'd just have to rotate the blades to the zero lift position once they're far off the perpendicular positions that the angle-of-attack limits made thrust on the desired axis impossible.

That very right. I was afraid that few readers would understand my reply #16 - that I couldn't express myself clearly enough, but you surely understood.

There could be made a angle-of-attack variation profile allowing "zero lift" outside, say, 11 to 1 o'clock and 5 to 7 o'clock blade positions. (I assume that current maritime applications work on a simple sinus curved angle-of-attack variation profile, and that rotating the variation profile mechanism 360 degrees gives thrust in any direction).

Such a "complicated" (non-sinus curved) variation profile will, however, only be optimized for one fixed relation between rpm and airspeed on a plane.

If we want it optimized for climb and cruise, and for cruise at different plane weights, and at different cruise altitudes (air density), then it calls for variable, complicated non-sinus curved angle-of-attack variation profile (huh!)

No, it ain't easy.

But on the other hand, current day variable pitch constant speed propellers aren't perfect either. At least not until someone invents a propeller blade with variable twist.
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DocLightning
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RE: Could This Be The Future Of Prop Power?

Tue Dec 08, 2009 1:48 am



Quoting Prebennorholm (Reply 16):

This propulsion system is great for ships like tugs or small ferries which must be able to maneuver easily and fast, go forward, backward, sideways, and rotate. But they pay a high price in propulsion efficiency.

And yet it is more efficient than Z-drives, which are basically pod-mounted conventional propellers on a swiveling pod.

But that's a ship in water, where considerations of weight are different. And water behaves differently from air.
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