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Elippse prop

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I spoke with Craig Catto of Catto props to find out if an Elippse prop for pushers is available from his company. I am building a Cozy Mark 4. His response - No, he does not yet have the design for Elippse prop. he gave me the phone number to Paul Lipps, designer of Elippse props Here is the link to the Paul's article in the EAA Experimenter:

http://www.eaa.org/experimenter/articles/2009-02_elippse.asp

 

According to paul, it should not take a long time to design this prop for pusher planes. He asked me to send him the specs for the Cozy mark 4. If this prop provides the same improvement in efficiency for pushers, It will be very desirable to have one.

 

jas sidhu

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Do you know if some designs for Vari / Long were already produced and tested ?

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Woow this is one sexy prop.

 

Is it available for pushers? Has anybody tried it on a Long EZ ? O-235

 

Thx

Ronny

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there was one for sale at the fly-in down in June Arizona so there must be some out there

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... If this prop provides the same improvement in efficiency for pushers, It will be very desirable to have one.

With all due respect to Paul Lipps, with whom I've corresponded a number of times and who is a very smart and talented man, there is no published objective data indicating that the Ellippse propeller design performs any better than any other well designed propeller. There are only claims - no head to head comparisons where everything else is held equal. It's possible that they're more efficient, but I'm extremely skeptical, since Paul's propeller theory goes against all other propeller designer's understanding of how propellers work and should be designed. Plus, the whole lack of data thing...

 

IIRC, a builder on the COZY mailing list contacted Paul regarding designing a prop for the MKIV, and in his opinion, the cost was prohibitive so he did not go ahead with it. But I could be mistaken.

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I tend to agree with Marc: it's sounds really interesting, but without data it's not worth the electrons we're posting with. And engineering "data" are more than numbers: it's good procedures, objective measurements, repeatable results, etc.

 

I'm all for innovation and hope it works out, but then again I'm the type that'll listen to a sales pitch and suddenly start to realise it's a little far-fetched/too good to be true... then listen some more and realize there must be a catch ... listen some more and the BS alarm starts going off ... and keep listening to wild claims and nodding my head long after I've decided not to spend money on it simply because I know that there's going to be an absolutely spectacular train-wreck of a gotcha and want to hear it first hand.

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... I know that there's going to be an absolutely spectacular train-wreck of a gotcha ...

Let's be clear here - I never said that there was a train-wreck coming. The Elippse propeller seems to be a good propeller, work well, and has reasonably high efficiency. There's nothing wrong with it, other than looking a bit weird, and while it has some characteristics that seem to suit it more toward racing than being an all-around prop, it works.

 

All I was trying to point out was that there's just no data indicating that it's any better than any other reasonably high efficiency propeller. Might be a tiny bit better, might be a little worse - there's a lot of art in propeller design (and performance measurement) - but nothing indicates that there's a whole lot of difference.

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Let's be clear here ...

... Yes, I didn't mean to imply anything negative for this particular idea... like I said I hope it works out.

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... Yes, I didn't mean to imply anything negative for this particular idea... like I said I hope it works out.

i sat with 40 people and 4 used them at much improvement from the props they had been using...but what do they know !

them's pilot types cant be trusted:p

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The jury is still out on this prop for sure, but anything that looks that far from what has become conventional wisdom and works as good as the conventional, would seem to indicate that there might be some science behind it. I notice that even Marc didn't give any scientific or engineering reason why it doesn't perform as advertised, just that it hasn't been empirically proven by head to head comparison. I wonder Marc, why you say it would seem to be more suited to racing?

 

Mike

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... I notice that even Marc didn't give any scientific or engineering reason why it doesn't perform as advertised, just that it hasn't been empirically proven by head to head comparison. I wonder Marc, why you say it would seem to be more suited to racing?

I didn't say it didn't perform as advertised - I said that it wasn't proven to be any better than any other well designed, high efficiency propeller. There's a large difference - please don't misrepresent my statements.

 

If I remember Paul's statements in his articles correctly, he indicated that his props were not good low speed performers, and didn't have the same type of speed RANGE that other props might have. Therefore, I interpreted this to mean that it would be good for racing but not necessarily as good an all-around prop. Could be wrong here, and that may not have been what Paul was implying.

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Although not scientific in method, it is worth noting that the top biplane racers at Reno are using this prop design with another adopting it for next year......... When discussing this with the top biplane team at Reno this year, they suggested that it was their winning edge.

 

I'm sure time will tell with Paul's design.

 

Cheers,

 

Bruce.

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All I know about this prop and it's designer is from the Experimenter article, where he goes into a layman's level explanation of his theories. I find it interesting that no one has explained why his claims can't be true from that perspective.

 

In the article he claims 82-84% efficiency in a 110 mph i.a.s. climb at 2370 RPM, sea level density altitude, which according to him, is better than most props in cruise. In other words, even though his prop is optimized for cruise, it is also better than other props in climb conditions. All sounds to good to be true, I'll be watching to see where it goes.

 

Mike

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Mike I don't think anyone is suggesting that Paul Lipps explanation is incorrect, just that the data hasn't been viewed or comparitive data reviewed (Elippse prop and conventional prop tested on the same aircaft under the same conditions).

 

One thing that may make a difference with the Elippse prop design on a pusher is that it (if I understand correctly) generates more thrust closer to the hub than a conventional prop does. Our aft mounted prop's do not see the clean air that tractor configured aircraft do. The airflows into our prop's, especially near the hub, will not be as clean as for a tractor aircraft (with our conventional cowls).

 

Just my two bob's worth....

 

Bruce.

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Although not scientific in method, it is worth noting that the top biplane racers at Reno are using this prop design with another adopting it for next year......... When discussing this with the top biplane team at Reno this year, they suggested that it was their winning edge.

I spoke to Craig Catto regarding Paul's props, and the prop used on the biplane at Reno, which Craig built. He suggested that the prop that Paul's Elippse prop replaced was a particularly poor example of a propeller, so putting anything decent on that plane would have provided a substantial increase in performance.

 

Again, until someone does a scientific test of this (or the bicambered, or any other "new" propeller), and until you know what you're comparing the new propeller against, you don't know whether you've got something better than the best that already exists, or whether you've just designed another good propeller.

 

I never said that his claims "can't" be true - what I said was that his design philosophy disagrees with classical Theodorsen/Goldstein/Betz propeller theory, in that Paul believes that you're looking for an elliptical lift distribution on the propeller, whereas classical theory says you're not. Since major propeller manufacturers, including those that use heavy duty CFD codes to understand the flow fields around propellers still use the classical theory, and don't have props with the shape that Paul has, I'm inclined to be skeptical that there's any particular advantage to his methodology. As they say, extraordinary claims require extraordinary proof, and there's been NO scientific proof. It's possible that just having Craig Catto manufacture his propellers is the advantage, given Craig's quality.

 

And being better than "most" props means little, since "most" props aren't all that great.

 

Jeez, I'm not trying to tear the guy down - if he's actually come up with something better, that's great - I hope it catches on. But the evidence he's presented so far is thin at best, and the claims are unsubstantiated from a scientific standpoint.

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