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Fixed Pitch Prop That Performs Like a Constant Speed Prop

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tralika

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This video shows the result of a test of the Duc fixed pitch propeller that performs like a constant speed prop. The blades of the prop are not adjustable in flight making it LSA compliant. However the design of the blades make the plane fly faster in cruise flight with lower engine RPM. The prop blades and hub are all carbon fiber and are ground adjustable.

https://www.youtube.com/watch?v=LaXsQl9Lz4U

http://www.duc-helices.com/index.php
 

tspear

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I did not make it through the video. I assume Duc is doing something that I believe Catto talked about as a working project; no idea if in production yet. Having a blade which adjusts the twist based on the RPM. The faster the blade spins, the greater the twist automatically making the blade more course.

Tim
 

cluttonfred

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It's just a video of Jan Eggenfeller (Viking Engines) talking about the Duc prop's performance on his engine. I have seen scimitar props that allow the blades to bend forward a little to reduce pitch in climb but I was not aware that Duc made such a prop.
 

bmcj

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I did not make it through the video. I assume Duc is doing something that I believe Catto talked about as a working project; no idea if in production yet. Having a blade which adjusts the twist based on the RPM. The faster the blade spins, the greater the twist automatically making the blade more course.

Tim
In the video, he said that Duc claims the prop does not twist, but regulates via an aerodynamic effect. I’m not sure what that might be, but I suspect that language differences got in the way and that they were actually saying that the blade doesn’t twist in the sense of a controllable prop (at the hub), but the blades probably twist via airodynamic forces.
 

Victor Bravo

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The availability of carbon, and the manufacturing techniques they are using now, make this easier to do.

I am guessing that it is not so much an aerodynamic phenomenon, but that they are harnessing the centrifugal/centripetal force (which is trying to pull the blades outward, or "straighteninig" the scimitar curve) to twist the blade while it is being pulled. So the faster it turns, the more outward pull... and the amount of that pull is transferred to torsional force by means of the layup schedule and fiber mix. That torsional force is used to twist the outer half of the blade to a more coarse pitch, and vice versa.

I first heard about this general principle being used in the design of sailplane wings (AS-W20 glider), where the layup schedule resulted in the wings twisting nose-up as the wings flexed upward. This had the effect of raising the wings more, storing energy, and as the wing unloaded it twisted nose-down creating forward thrust. The net result was that when flying the '20, when you hit a gust the wings flexed upward, puliing the aircraft a little higher, and then when you flew out of the gust the wings came back down and added a little thrust. Just like birds fly. There was an article or news blurb many many moons ago in Soaring Magazine about this, they called it "The Katzmayr Effect".

Any of you guys remember that? BobK, BMCJ?
 
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pictsidhe

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The availability of carbon, and the manufacturing techniques they are using now, make this easier to do.

I am guessing that it is not so much an aerodynamic phenomenon, but that they are harnessing the centrifugal/centripetal force (which is trying to pull the blades outward, or "straighteninig" the scimitar curve) to twist the blade while it is being pulled. So the faster it turns, the more outward pull... and the amount of that pull is transferred to torsional force by means of the layup schedule and fiber mix. That torsional force is used to twist the outer half of the blade to a more coarse pitch, and vice versa.

I first heard about this general principle being used in the design of sailplane wings (AS-W20 glider), where the layup schedule resulted in the wings twisting nose-up as the wings flexed upward. This had the effect of raising the wings more, storing energy, and as the wing unloaded it twisted nose-down creating forward thrust. The net result was that when flying the '20, when you hit a gust the wings flexed upward, puliing the aircraft a little higher, and then when you flew out of the gust the wings came back down and added a little thrust. Just like birds fly. There was an article or news blurb many many moons ago in Soaring Magazine about this, they called it "The Katzmayer Effect".

Any of you guys remember that? BobK, BMCJ?
sounds like a recipe for flutter and a bumpy ride
 

Aerowerx

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...I am guessing that it is not so much an aerodynamic phenomenon, but that they are harnessing the centrifugal/centripetal force (which is trying to pull the blades outward, or "straighteninig" the scimitar curve) to twist the blade while it is being pulled.....
I thought that "aeroelastic" was a bad thing.
 

Victor Bravo

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Actually, the AS-W20 glider that I mentioned has the smoothest and most comfortable "ride"of any modern sailplane in existence. I can vouch personally for this, under what would otherwise have been very uncomfortable turbulence in the SW USA deserts and mountains.

The glider in question did not have any tendency to flutter anywhere within its approved speed limits, and then some (I only heard rumors about that...).

As far as why and how the composite layup schedule, materials, etc. was able to perform that way, and what kind of engineering it takes to make use of aeroelastic flexibility without the structure becoming divergent or damaged...... I'll have to let Autoreply and some of our other high brain function members explain it. That stuff is for people with way way higher IQ than me. I was actually afraid to ask Dr. Waibel about this when I met him, because I might not understand the answer and die of embarrassment in front of one of my heroes!

Katzmayr Effect article:
http://home.planet.nl/~kpt9/Katzmayr_effect.htm
 

Hot Wings

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flyboy2160

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...

I am guessing that it is not so much an aerodynamic phenomenon, but that they are harnessing the centrifugal/centripetal force (which is trying to pull the blades outward, or "straighteninig" the scimitar curve) to twist the blade while it is being pulled. So the faster it turns, the more outward pull... and the amount of that pull is transferred to torsional force by means of the layup schedule and fiber mix. That torsional force is used to twist the outer half of the blade to a more coarse pitch, and vice versa....
I can't see that. It would mean that the prop would have the same "pitch" on the ground at a given rpm as it did in the air at speed at that same rpm. I can see the classic case of the air load to cause the twist.
 

Victor Bravo

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Not air loads. Centrifugal loads. So if you are on the ground, engine not running, and you grab the tip of a scimitar propeller and pull it outwards away from the prop hub, the blade wants to twist as you are pulling the scimitar curve into a straight line.
 

tspear

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Not air loads. Centrifugal loads. So if you are on the ground, engine not running, and you grab the tip of a scimitar propeller and pull it outwards away from the prop hub, the blade wants to twist as you are pulling the scimitar curve into a straight line.
If I followed the description correctly. The basic idea is when doing static thrust at takeoff, or in a climb, you want a finer pitch; when in cruise or descent, you want a course pitch. The concept being in static thrust at takeoff and in climb the engine has insufficient power to turn the prop at full speed. So having lower centrifugal loads the prop will have a finer pitch. once in cruise, the engine will pick up speed as the plane increases speed, in which case the centrifugal load increases causing the prop to become more course...

Tim
 
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