Interesting Technical Article on Propellor Design

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djschwartz

Well-Known Member
There is a very interesting article on a new paradigm for propellor design in the latest online edition of EAA Experimenter. It includes at least a small amount of real flight test data to back up the new design theory.

EAA - EAA Experimenter - ELIPPSE Propeller

gschuld

Well-Known Member
I agree, very interesting. Funny, I started a thread this past December about the same article. I believe the original article was in an earlier Contact magazine edition a while back. No biggie, I'd be happy to hear more opinions on the subject:nervous:.

In case anyone wants to read what was discussed so far:
https://www.homebuiltairplanes.com/forums/design-structures-cutting-edge-technology/4911-paul-lipps-designed-elippse-propellers.html

The most obvious functional difference with Paul Lippse designed props is his props appear to concentrate most of its forward thrust from the spinner to about half way out. More "conventional" props appear to concentrate their drive on the middle to outer half of the blades and are fairly inefficient at the spinner end. I wonder how much of this had to do with the idea that it was far more likely years ago that the front of the cowl on older planes were kind of blunt. So perhaps developing a prop that had strong drive at the spinner end would have been less effective considering the kind of shapes it was driving into:ermm:. I see the logical concept of concentrating the driving area of the propeller in the mid to outer end of the blades as it is typically in the free air around the cowling/fuselage.

I have a feeling that the "Elippse" propellers are at their best when driving a plane with a very streamlined fuselage, especially the cowl. Paul's Lancair and the reno racers that have done so well on his props all have VERY efficient cowling shapes. So having the (presumed)main driving force from the spinner to half span will best be used to pull the plane forward, as opposed to blasting a blunt faced cowl on a older plane.

Clearly by his success so far, his theory is sound. On slippery, high power to weight ratio go fast planes he might just have a winner. I'm just not sure how useful they would be on more typical GA planes:lick:. Paul has been designing a few props for testing on the RV crowd. I believe there is at least one RV-(6 maybe?) buzzing around collecting performance numbers. Paul shows up on the Vansairforce.com forum to answer question at times. There are a few threads about his props being discussed over there.

They sure look menacing:devious::devious: .... Kind of weapon-like!

George

K-Rigg

Well-Known Member
can you purchase his props? I cant find where you can.

pwood66889

Well-Known Member
"The most obvious functional difference with Paul Lippse designed props is his props appear to concentrate most of its forward thrust from the spinner to about half way out. More "conventional" props appear to concentrate their drive on the middle to outer half of the blades and are fairly inefficient at the spinner end."

You probably have something there. The logic follows Jack Norris; props go faster at the tip, so need less chord. Also, the lift drops off to zero any way, and all a wide tip makes is more noise.

And you're correct in that we've ploughed this ground before.

Percy in NM, USA

gschuld

Well-Known Member
K-Rigg,

Paul Lippse does not really sell props per say. He works for Lightspeed Engineering with Klaus Savier(world record setting Vari EZ owner) The Company- LSE Performance Team

My understanding is that he has up to recently custom designs props on an individual basis. He wants to gather info on the exact plane he is designing a prop for. So he loans you a prop, assuming it is reasonably suitable for the plane in question, assembles the performance data, then calculates what he thinks will be the best based on his computer programs. He has had Catto Props custom make his props at first and I believe he is working with another prop manufacturer to produce a series of "Elippse blades" for both fixed and adjustable pitch props for the Lycoming 4-6 banger crowd.

I believe yoou mentioned that you want to power your KR with a corvair. Corvairs turn the opposite direction than the GA standard (but so did the great WWII Merlins), and I'm fairly sure that he has no "wrong way" props to loan out. I believe the Pat Panzera(Contact Magazine and Corvair conversion fanatic) has had several conversations with Paul about designing a prop for corvair powered KRs. He has forwarded Paul with all Mark Langford's performance numbers to get a basic idea of what it will be like. But as of yet, no one has be prepared to get such a custom prop made. These are expensive props. Maple cores with MANY layers of carbon fiber jacketed over it. Well over a grand for a 2 blade standard Catto, And I imagine he would charge more for a Lippse designed prop as they woul dcertainly be more difficult to built. I have no idea what Paul Lippse would carge for the design work. Most out there in the KR world just go with off the shelf wooden Sterbas two blanded props or something similar for a few hundred bucks and call it a day. On a real cleaned up(low drag) KR with a healthy power/weight ratio, I wouldn't be suprised if a custom Lippse/Catto prop would be worth an extra 10mph on the top end and a few percent more GPH.

People blow an extra 3 grand doing the big bore 3100 corvair for an extra 10mph, an extra grand for the --possibility-- of getting the same speed improvement with the standard 2700 motor (with the better gas mileage) might not be a bad deal:lick:.

George

djschwartz

Well-Known Member
In the EAA Experimenter article he says he had his props built by Craig Catto

Catto Home

MalcolmW

Well-Known Member
Hello, I'm kind of late to this discussion, but I thought I'd toss in my two cents...

Are propellers are stuck in their design? If one looks at the blades on power-generating windmills, the configuration shows a pronounced taper and narrowing away from the shaft, very similar to Lipps design. This is done to make the windmill as efficient as possible, with the least amount of noise. Yet, the aviation industry has not taken advantage of the research and results in this area.

MalcolmW

Hugh Lorimer

Well-Known Member
The two bladed props I have designed and made were for microlights but I found them to be better (and quieter) than three bladed commercial ones from the manufacturer, since a prop blade is a mechanical device and has, as all devices have, a mechanical efficiency. so it follows that a one bladed counterballanced prop must be the best solution? but the practical problems operating same such as having a big enough blade to absorb the engine torque, assymetric bearing loads and if a pusher layout? the interference from wingwash etc and make it impractical. Attached is a wee article I penned for a magazine some time ago.

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Topaz

Super Moderator
Staff member
Log Member
Hello, I'm kind of late to this discussion, but I thought I'd toss in my two cents...

Are propellers are stuck in their design? If one looks at the blades on power-generating windmills, the configuration shows a pronounced taper and narrowing away from the shaft, very similar to Lipps design. This is done to make the windmill as efficient as possible, with the least amount of noise. Yet, the aviation industry has not taken advantage of the research and results in this area.

MalcolmW
I think it's a fair bet to say that "modern" propellers can be improved upon. However, my personal feeling is that that improvement will require the same sort of careful computer work that's being done on high-bypass-ratio turbofans (with the multi-sweep blades they're starting to use) or the current research on un-ducted-fans.

The flow field through a prop is very complicated, and from what I've seen of it, the methods used in pretty much all the general aviation community are essentially developments of either empirical "trial and error" techniques or extremely simplified theory, and that little real "modern" analysis towards improving propellers has been done in this class of aircraft, excepting possibly in some racing aircraft.

Part of that may be the small gains that can be accomplished. Even the "standard" metal props are pushing into the 80%+ efficiency range at their design points. That's not a lot left to gain for all the work required, considering how non-critical getting absolute "top" performance out of the average general aviation airplane really is. Is that work worthwhile? Yeah, IMHO it is, but I very much doubt that there's any financial gain to be made for anyone by doing that work, which is why I believe that it hasn't been done.

MalcolmW

Well-Known Member
Hello, Topaz;

I must confess that I know very little about aeronautical engineering. However, I believe that the manufacturers of large power generating windmills (companies such as GE) have done their homework on blade design. The common shape of these windmill blades is striking, which suggests that they all came to the same conclusion about the most efficient shape.

Lipps' design has a similar shape to these huge blades used on the windmills, and, they all seem to use three blades. Maybe the windmill manufacturers know something that propeller makers (for GA) don't?

Yes, I can believe you when you say that the flow field through a prop is complicated, and would require some serious modeling. This would be right up the alley of a company like GE, etc.

I do know that aircraft props make a lot of noise, and to generate noise takes energy, which could (perhaps) otherwise be directed into thrust. I'm really out of my depth here, but intuitively, I believe there is research done which could benefit prop design for small aircraft.

MalcolmW

Topaz

Super Moderator
Staff member
Log Member
Hello, Topaz;

I must confess that I know very little about aeronautical engineering. However, I believe that the manufacturers of large power generating windmills (companies such as GE) have done their homework on blade design. The common shape of these windmill blades is striking, which suggests that they all came to the same conclusion about the most efficient shape....intuitively, I believe there is research done which could benefit prop design for small aircraft.

MalcolmW
Absolutely. Of course, wind-turbine blades are operating in much different conditions than an airplane propeller, so the design data isn't absolutely applicable. But you're right, for that application, those guys have put in exactly the kind of research that would benefit airplane propellers.

The problem is that there really isn't any money to be made in improving the efficiency of a light-GA class airplane prop. Not enough to offset the research costs, anyway. I remember Orion mentioning that a full CFD analysis of a simple flying-wing airplane would cost in the region of $20,000-$40,000. Imagine what it would cost to model and research something as complex as a propeller? That's a lot of props to sell to cover that cost.

I agree with you - it's absolutely worthwhile research, and we'd probably see some definite gains in performance as a result. So far, however, nobody has been willing to make that investment, since they're unlikely to see much, if any, monetary return.

rtfm

Well-Known Member
Hi,
But, ahem, it seems that Lippse has done just this... :ermm:

Duncan

Topaz

Super Moderator
Staff member
Log Member
Hi,
But, ahem, it seems that Lippse has done just this... :ermm:

Duncan
Has he? I'm not familiar with his work, but simply coming up with a "better idea" is not research, nor are annectotal reports of improved performance actual evidence of real improvement where other possible factors have been eliminated. Maybe Lippse has come up with a genuine improvement, but without proper testing or theory development - which I've yet to hear someone talk about here - he really can't claim any more advancement than "tinkering", IMHO.

Lots of people have created various improvements upon the propeller. P-Tip, scimitar blades, etc. None have been backed by proper research or analysis that I've ever heard. Somebody just has a "good idea" that may or may not consitute an improvement, but doesn't have any real, tested, generalized theory that allows the results to other designs without empirical testing to optimize the design.

Please understand that I'm not criticizing Lippse - again, I don't know much about his work - but from what little I've heard, there's little more than annecdotal evidence that he's accomplished a genuine breakthrough.

That's not enough for me personally. I've simply seen too many "miracle improvements" turn out to be just someone's poor application testing to be less skeptical about this sort of thing than I am.

I completely understand that others may feel differently about this, and I'm not saying that you - or Lippse - are wrong.

gschuld

Well-Known Member
Topaz,

You may very well be right regarding propeller companies not doing full blown start from scratch multi million dollar studies on the basic theory of prop design for GA aircraft. But honestly, a good part of the reason I am so attracted to the homebuilt airplane community is the fairly unrestricted, uncontrolled, and unregulated nature of the experimentals. I amsimply amazed that in the over regulated world we live in that the FAA can be so loose handed with us overall. Individuals have a chance to compete head on with the big guys in the industry, and design a plane(or plane part) may with as little or as much theoretical backing behind his(her) conscience and skills will allow. Really the only thing regulating a person's design, besides an occasional FAA instector if your scratch building, is the designer/builder's confidence and level of respect for the finality of death considering that someone will need to flight test it.

Mike Arnold designed/built two awesome planes. One set a world record, the other has been killing the field in the formula 1 class in Reno with a plane that he designed and build all by himself, and carrying a concourse level (Cory Bird's Symmetry style) paint job just to rub it in. He is a film maker, with most of his experience from carefully studying aircraft design books(especially Hoerner), taking a single class on aircraft design, and getting a bit of composites experience with a sailplane builder before getting started himself. He has a way bigger set of balls in that regard than I do. But that's the kind of stuff that really intrigues me.
I have a feeling that there are some truely brilliant minds out there that are perfectly capable of really pushing the envelope, like Burt Rutan, but shy away from being formally in the aircraft business on account of liability concerns alone. I rather enjoy the people that simply buck conventional and accepted thinking and go their own way to produce something that is unique. If it proves to really be an improvement, fantactic!
Paul Lippse is a very innovative and passionate guy. He is also a well educated engineer and makes his living in the aircraft industry. It's simply too early to know for sure whether his props are a real breakthrough of not. I'm going to hazard a guess and say that his props are showing good promise on the high power to weight ratio planes that have very low drag airframes, especialy in the cowl area to utilize the thrust his props put out at the root and mid chord. Personally, I don't give a hoot if he logged in 1000 hours at the Area 51 cutting edge (and alien:rollresearch enter. If his stuff turns out to work in practice, even if it may be limited to certain applications, good for him. I'm just happy to see people that are simply going out there and doing it.

George

MalcolmW

Well-Known Member
Topaz;

not to belabor the point, but I do believe the research on windmill blade design has been done. Unfortunately, I just don't understand this branch of engineering. Could you take a look at this site and see if it makes sense to you?

Airfoils for Windmills

Thanks!

Malcolmw

orion

R.I.P.
There's been a lot of work done in connection with windmill design, including the derivation of optimized shapes for that particular application. Even large organizations such as Boeing have been involved so the data certainly exists. But it is important to keep in mind that the purpose of a windmill blade is sufficiently different from that of an airplane propeller that any design work done and/or data developed for the purpose of power generation would most likely have no application to aircraft. But much of it is a very interesting read.

I do find it interesting though that despite decades of optimized airfoil development, most propeller manufacturers, even the high end ones, tend to go to the standard section families for development of new products, despite the fact that many of those shapes date back many decades.

Mr. Lipps has done interesting work and the results speak for themselves however, in the same breath it must be pointed out that much of the work seems to be really applied only to the airplanes discussed in the articles and thus it may be argued that they might be point designs really optimized for the racing or high performance application. To the best of my knowledge there is no published data that describes how his work could be applied to a wider spectrum of airframes, nor is there any real evidence that it would work for general application. That's of course not to say that it wouldn't but personally I'd like a bit more information than is presented in the articles. Personally, despite a few areas I might have questions about, I think the article makes sense and does reflect the thinking of several prop designers I've worked with over the years who have developed some pretty bizarre looking shapes that in testing, beat out just about anything else on the market.

So in short, it would be interesting to see standardized data from an actual test cell, and how that data compared with more conventional geometry.

Topaz

Super Moderator
Staff member
Log Member
... it would be interesting to see standardized data from an actual test cell, and how that data compared with more conventional geometry.
That's what I'd like to see myself. Until we do, there's no way to separate the performance improvements of the propeller from those of the airframe. Because these guys aren't familiar with real research practices, you see them do things like use a different spinner with their prop versus the 'standard' prop, or a standard prop that isn't optimized (by standard methods) for that particular airplane, so naturally their highly-optimized prop does quite a bit better.

I really do hope that Lippse or someone else develops a genuine improvement and can demonstrate it in independant testing. I really do. I've simply seen too many claimed "improvements" turn out to be poor testing to be less than skeptical about this stuff. And whatever improvements such people might develop are pretty much useless without developing analysis routines that allow them to design improved propellers for arbitrary aircraft.

The only people in my awareness who have done really detailed propeller research in the last twenty years are GE, Pratt & Whitney, and Rolls-Royce, for their UDF programs. It's interesting that the blade shapes that they've released publically are generally similar - forward-swept at the root, wider chord near the mid-span (non-linear taper), and then aft-swept towards the tip. All are using quite thin airfoils. Obviously these UDF concepts are optimized for much higher cruise speeds than we would use, but I think the trends are there to be seen.

Topaz

Super Moderator
Staff member
Log Member
Topaz;

not to belabor the point, but I do believe the research on windmill blade design has been done. Unfortunately, I just don't understand this branch of engineering. Could you take a look at this site and see if it makes sense to you?...
I think you might have missed that I agree that the windmill folk have done some really good research on blade optimization. There's millions of dollars to be made in that industry, and pretty intense competition. Both are usually great drivers for research. :gig:

As Orion explained above, however, that research is not directly applicable to propeller design. While they look like big propellers, wind turbines operate under very different conditions than our props: different Reynold's numbers, disk loadings, rotation to inflow rates, tip Mach numbers, etc.

I'm hardly a propeller expert. I know some of the overall theory and a bit about the relevant issues in prop design, but like so many other areas in aviation, that's where my knowledge ends. I took a look through that web page and it's interesting stuff. It also highlights the differences between props and wind turbines. For example, they limited tip Mach number to 0.3, whereas our props run up into tip speed values of 0.7-0.8 Mach. They're also designing the blades to deliberately stall under certain conditions, something that propeller manufacturers strive to avoid at all costs. Much of the airfoil design work on that web page was tailored to that specific requirement.

P-Hudson

Member
Hi All,

I think the basic theory that Mr. Lippse is using is the minimum induced loss theory of propeller design and a modified blade element approach for station by station optimization combined with a simulation of aircraft performance. (But I'm just guessing!) See Martin Hepperle's paper at A Procedure for Propeller Design by Inverse Methods) I've used this to design some model airplane propellers.

When this approach is used the blade planform varies quite a bit depending on the relationship between forward speed and RPM for a given power. A slower plane with high RPM has more aera near the root. A fast plane with lower RPM has more area outboard. Play around with Martin's JAVA prop and you'll see what I mean.

-Peter-