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ELIPPSE propeller for RVs

E

elippse

Well Known Member
Many of you on this forum have expressed an interest in getting information on ELIPPSE-designed propellers. Well, wait no longer. Larry Morgan of Vari-Prop has produced a three-blade ground-adjustable or constant-speed propeller with ELIPPSE-designed blades for use on the RV-series from 150HP to 200 HP. The CS version uses an electro-hydraulic pitch-changing mechanism, so it is not necessary to have a drilled crankshaft. It will be on display at the Golden West fly-in at Yuba County airport at the end of June, 29, 30, and July 01, as well as at Oshkosh. The Vari-Prop web-site is still under construction, so for more information about this propeller, contact Larry Morgan at 503 804 5508, or [email protected]. For those of you in the Portland, OR area, you can see Larry at his hangar next door to Van's Aircraft.
 
WOW - This is going to be big

I know this going to yield a major jump in speed based on the Reno biplane class results.

Bob Axsom
 
More Information Please

Paul,

I just spoke with Larry Morgan via telephone.

Could you please share your thoughts about using the Vari-Prop hub with ELIPPSE blades on a parallel valve O-360 with a high compression ratio and electronic ignition?

I'm reasonably informed about prop vibration surveys, the varying dampening qualities of wood, carbon, aluminum, etc. So, while I welcome any input you may have, it's not my intention to burden you with a request for a treatise. :p

Thank you.
 
Where to find at Oshkosh

Larry says that they will be in Hanger C at booth 3109 (Contact Magazine booth).
 
Don't jump ahead, Roberto! Larry will do lots of before and after testing to see if there is a measurable performance increase to brag about. I'm hoping that the Reno experience is a harbinger of things to come, but let's wait and see. And Monte, I'm not at all familiar with this hub, but from what Larry tells me, it has seen lots of activity on airboats. Some of you are familiar with the somewhat different shape of my designs, and how the prop has a concave planform taper as it approaches the tip, where it goes to a point. It does not have most of the lift, not thrust, in the outer portions as in most props, but instead, as with an elliptical wing, it has an elliptical lift distribution which goes to zero at the tip, thus minimizing span-wise flow and tip vortex. Since the lift is distributed all along the blade as opposed to being mainly outboard, this should bring about rather benign bending forces at the hub. Another benefit of this taper is that the mass outboard is considerably reduced, thus greatly reducing centrifugal loading on the hub. Outboard mass reduction also helps when considering the inertial load when the prop is accelerated and decelerated on each power pulse; think of the whip at the tip of a fishing pole when casting. This minimizes the in-plane stresses where the blade emerges from the hub. I think that this is what is taking place on those blades which are having cracking problems from the big power pulses on these IO-360s. All told, I am hoping that this will not take its place among the many tales of recent CS and ground-adjustable hubs that seem to have these cracking problems. I'm not sure what this thing is about EIs being hard on CS props. LSE ignition has very precise timing on all cylinders, whereas a magneto has somewhat random small variations in timing around a mean. It could be that this very timing precision is able to excite the various resonances in some blades, whereas the magneto would throw off the periodicity somewhat, and so not produce as high an excitation amplitude. But that is really saying that the prop has resonances that are on the borderline of being properly damped. So far neither Tom on his biplane props nor I on my FP three-blade prop have seen any cracking in the hub region. Klaus is always tapping my prop with a coin in the region where the transition takes place from blade to hub. With my higher pitch angles there, in the 65-70 degree region, the transition angle is not as great as it is on the many props that have root pitch angles of about 45-50 degrees, so there is less twist to the laminate in going from the blade to the hub and so less chance of de-lamination. 'Hope this addressed some of your concerns! I hope there are many of you attending Reno this year. If you are, be sure to get a pit pass and come see the real world of Experimental Aviation, where it's taking place and not just being talked about. One of my prop designs will be on a Sport plane, two on F1s, and at least four on biplanes. Along with that, one of the racers will have my super-secret compact augmented cooling-exhaust system. As with my blade designs, when you see this you will have a hard time believing it can work! Just be aware, we have applied for a patent on it! And maybe by Oshkosh, Klaus will be able to show our new dual-redundant EFI. Two sets of drivers, two pressure-controlled pumps that require no return line to the tank. He has been flying this on his plane for three years now, as well as having raced it at Reno twice, and has wowed lots of pilots with its ease of starting on his hand-propped EZ, as well as how well it maintains A-F with change in altitude. As with the ignition, it's got lots of cool outputs that tell you pump pressure, MAP, and, both pulse and analog fuel flow. Every effort is being made to have a safe product. The control laws are in hardware, there is no software, so except for some minor circuit changes that may arise, there will be no software upgrades to implement from time-to-time.
 
Augmented exhaust

Did anyone get a peek at the augmented exhaust that Paul refers too. Paul, willing to share any details? Also interested in Klaus's FI system.

At Reno and saw some of the props! Watched some of the rebuild work going on on the worlds fastest biplane. Anybody know how he turned out this year?
 
The Elippse propeller proves a winner once more

http://www.eaa.org/experimenter/articles/2010-09_phantom.asp

Copy / Paste from the above link:

"Monday, September 13 ? An excited voice on the other end of the phone said, ?Paul, it?s Tom. I qualified at over 260 mph.? That?s when I, too, started jumping up and down! Here?s this man, this pilot, Tom Aberle, telling me that his biplane Phantom, which back in 2003 qualified at 220 mph, had now bettered that by 40 mph. Unbelievable!"
 
elippse said:
Don't jump ahead, Roberto! Larry will do lots of before and after testing to see if there is a measurable performance increase to brag about. I'm hoping that the Reno experience is a harbinger of things to come, but let's wait and see.

And Monte, I'm not at all familiar with this hub, but from what Larry tells me, it has seen lots of activity on airboats. Some of you are familiar with the somewhat different shape of my designs, and how the prop has a concave planform taper as it approaches the tip, where it goes to a point. It does not have most of the lift, not thrust, in the outer portions as in most props, but instead, as with an elliptical wing, it has an elliptical lift distribution which goes to zero at the tip, thus minimizing span-wise flow and tip vortex. Since the lift is distributed all along the blade as opposed to being mainly outboard, this should bring about rather benign bending forces at the hub.

Another benefit of this taper is that the mass outboard is considerably reduced, thus greatly reducing centrifugal loading on the hub. Outboard mass reduction also helps when considering the inertial load when the prop is accelerated and decelerated on each power pulse; think of the whip at the tip of a fishing pole when casting. This minimizes the in-plane stresses where the blade emerges from the hub. I think that this is what is taking place on those blades which are having cracking problems from the big power pulses on these IO-360s.

All told, I am hoping that this will not take its place among the many tales of recent CS and ground-adjustable hubs that seem to have these cracking problems. I'm not sure what this thing is about EIs being hard on CS props. LSE ignition has very precise timing on all cylinders, whereas a magneto has somewhat random small variations in timing around a mean. It could be that this very timing precision is able to excite the various resonances in some blades, whereas the magneto would throw off the periodicity somewhat, and so not produce as high an excitation amplitude. But that is really saying that the prop has resonances that are on the borderline of being properly damped.

So far neither Tom on his biplane props nor I on my FP three-blade prop have seen any cracking in the hub region. Klaus is always tapping my prop with a coin in the region where the transition takes place from blade to hub. With my higher pitch angles there, in the 65-70 degree region, the transition angle is not as great as it is on the many props that have root pitch angles of about 45-50 degrees, so there is less twist to the laminate in going from the blade to the hub and so less chance of de-lamination. 'Hope this addressed some of your concerns!

I hope there are many of you attending Reno this year. If you are, be sure to get a pit pass and come see the real world of Experimental Aviation, where it's taking place and not just being talked about. One of my prop designs will be on a Sport plane, two on F1s, and at least four on biplanes. Along with that, one of the racers will have my super-secret compact augmented cooling-exhaust system.

As with my blade designs, when you see this you will have a hard time believing it can work! Just be aware, we have applied for a patent on it! And maybe by Oshkosh, Klaus will be able to show our new dual-redundant EFI. Two sets of drivers, two pressure-controlled pumps that require no return line to the tank. He has been flying this on his plane for three years now, as well as having raced it at Reno twice, and has wowed lots of pilots with its ease of starting on his hand-propped EZ, as well as how well it maintains A-F with change in altitude.

As with the ignition, it's got lots of cool outputs that tell you pump pressure, MAP, and, both pulse and analog fuel flow. Every effort is being made to have a safe product. The control laws are in hardware, there is no software, so except for some minor circuit changes that may arise, there will be no software upgrades to implement from time-to-time.
Click to expand...

I am ready for this prop that needs no hydraulic connections.

Where do I find this prop?
 
I suppose that if you want one you should call Paul L or Craig Catto. Paul L has stated in the past that Catto builds to his design.
Detractors aside, I see no serious downside to trying an Ellipse prop, and at least one RV-6 150 HP has flown with one, so what's the rumble?
I have a Catto 2 blade on mine, but I'm not flying yet. If an Ellipse prop is going to be used on another RV, then someone is going to have to buck up and have it built. It's not like Paul has an obligation to build a generic RV prop any more than other custom prop builders.
 
When you call Craig

When you call Craig Catto, be sure to ask how his prop did on a Pitts when compared to Paul's, just this year.
 
The prop I designed for Tony Higa's biplane gave about 4.2mph less at 70 rpm more than his old metal prop. I told Tony that I was disappointed and something went wrong either in the design process or in the making of the prop. I gave him a check at Reno for the full price of the prop and its spinner, but asked him to hold on to it until he gets some drag reduction changes made and then to use this prop for data gathering for another design, at which time he'll return the prop to me so that I can do some measurements to see if it agrees with the design templates at every inch. Was that what you were referring to, Howard?
 
I don't know

elippse said:
The prop I designed for Tony Higa's biplane gave about 4.2mph less at 70 rpm more than his old metal prop. I told Tony that I was disappointed and something went wrong either in the design process or in the making of the prop. I gave him a check at Reno for the full price of the prop and its spinner, but asked him to hold on to it until he gets some drag reduction changes made and then to use this prop for data gathering for another design, at which time he'll return the prop to me so that I can do some measurements to see if it agrees with the design templates at every inch. Was that what you were referring to, Howard?
Click to expand...
Paul, I was suggesting that anyone contacting Craig for an Ellipse prop should raise the subject rather than my trying to repeat a fragment of a conversation accurately. I try not to be a pointless detractor nor a gossip. I was not there, at Reno. The conversation that I had was about other things. I admire your honesty in posting this and your "customer orientation", too. As you know, I admire your very impressive wins, but I'm a critic in the sense that you seem, to the uneducated such as me, to be experimenting rather than following proven principles. That's OK as long as it is understood. It worked for Edison. Serendipity has its virtues. You, Craig Catto, Lonnie Prince and many others have produced props with a number of innovative designs. Sometimes they work better, sometimes they don't. That's why we are called experimenters as a group.
 
Prop at LOE

Here's the prop on the ground at LOE.

Prop.jpg
 
hevansrv7a said:
As you know, I admire your very impressive wins, but I'm a critic in the sense that you seem, to the uneducated such as me, to be experimenting rather than following proven principles.
Click to expand...

Why would you assume that, Howard? What have I done, that you, in your self-professed, uneducated experience with propeller design, makes you feel qualified to make such a detracting statement! And please don't have the temerity to speak for the other "uneducated"; that is strictly your own personal opinion!
What are these proven principles that I'm not following that makes my designs such a hit-or-miss proposition. I've designed three different propellers for Phantom, each of them based upon a new level of performance and rpm, and each has hit its design goals.
My designs are derived from a strictly scientific process. When I first got into propeller design from a highly-predictable electronics background, I was appalled at the statements that were made by the large number of propeller-makers who told me something along the line of your statement, that it was basically a hit-or-miss kind of thing and sometimes it worked and other times didn't.
There are two unknowns in my designs, and it is not with the propeller itself. One has to do with the actual HP a client's engine has, and the other has to do with his airplane's parasite drag coefficient. When I can test his plane beforehand with a propeller of my design, I can obtain a very good estimate of both of these parameters from the reduction of the data.
This was borne out with the data reduction of Jim Smith's RV-6 with my original two-blade. I estimated that his engine, which I assumed was 160 HP, produced only 150 HP at sea-level, which turned out to be the actual rating. I also estimated that his parasite drag area was 2.15-2.20, which turned out to be close to the CAFE RV-6A estimate of 2.32 which I found out later when told about the test that was written-up in Sport Aviation.
When I am asked to design a propeller for a plane based upon the client's estimate of power and speed, then things become somewhat iffy. Then I have to rely on a drag estimate based upon typical drag estimates for a plane of that type of construction and overall planform. I will do that only with the caveat beforehand that the plane may not be able to accomplish the performance estimates with these unknowns.
This was the situation with Tony's Pitts, and I informed him when he asked me to design the prop for him that the prop was based on an estimate of his parasite drag and his biplane's Munk factor and it may not give him the desired performance, but he said to go ahead, as we can use this prop to arrive at a final solution. But my dis-satisfaction with the outcome expresses my displeasure with my own performance-estimate shortcomings.
And now, Howard, it is up to you to list all of these proven principals which you wrote of and show how and in what way I am deviating from them!
 
Oops, pushed a button?

Paul, I speak for nobody else. I simply observe that hit and miss or cut and try is what it is. I am as qualified as any objective observer and I claim no special skills. I infer a lack of principles. I do not refer to any and I'm sorry if my words were taken that way.

Let's not fight. Keep up your good work. If you want to subject your proven principles to public review then by all means, do so. Others, more qualified than I, can then judge if the principles are being consistently applied. Indeed, if you designed three props for Phantom, which one used which proven principles? Was the 2010 model as good or better than the 2009 model? Why? If one prop looks like a stretched diamond with fairly sharp corners and another looks like it has concave edges and narrow, pointy tips like a leaf then which used what ideas? If the principles are still evolving, then that's OK.

You refer back to your electronics background. Once, in ancient times, I was on the fringes of software development including security. It was a given that open review of the principles and the implementations was the only way to have robust designs. Proprietary, secret stuff was always seen as more vulnerable, as counter-intuitive as that may seem. That may be a valid analogy. Or not.

elippse said:
Why would you assume that, Howard? What have I done, that you, in your self-professed, uneducated experience with propeller design, makes you feel qualified to make such a detracting statement! And please don't have the temerity to speak for the other "uneducated"; that is strictly your own personal opinion!
What are these proven principles that I'm not following that makes my designs such a hit-or-miss proposition. I've designed three different propellers for Phantom, each of them based upon a new level of performance and rpm, and each has hit its design goals.
My designs are derived from a strictly scientific process. When I first got into propeller design from a highly-predictable electronics background, I was appalled at the statements that were made by the large number of propeller-makers who told me something along the line of your statement, that it was basically a hit-or-miss kind of thing and sometimes it worked and other times didn't.
There are two unknowns in my designs, and it is not with the propeller itself. One has to do with the actual HP a client's engine has, and the other has to do with his airplane's parasite drag coefficient. When I can test his plane beforehand with a propeller of my design, I can obtain a very good estimate of both of these parameters from the reduction of the data.
This was borne out with the data reduction of Jim Smith's RV-6 with my original two-blade. I estimated that his engine, which I assumed was 160 HP, produced only 150 HP at sea-level, which turned out to be the actual rating. I also estimated that his parasite drag area was 2.15-2.20, which turned out to be close to the CAFE RV-6A estimate of 2.32 which I found out later when told about the test that was written-up in Sport Aviation.
When I am asked to design a propeller for a plane based upon the client's estimate of power and speed, then things become somewhat iffy. Then I have to rely on a drag estimate based upon typical drag estimates for a plane of that type of construction and overall planform. I will do that only with the caveat beforehand that the plane may not be able to accomplish the performance estimates with these unknowns.
This was the situation with Tony's Pitts, and I informed him when he asked me to design the prop for him that the prop was based on an estimate of his parasite drag and his biplane's Munk factor and it may not give him the desired performance, but he said to go ahead, as we can use this prop to arrive at a final solution. But my dis-satisfaction with the outcome expresses my displeasure with my own performance-estimate shortcomings.
And now, Howard, it is up to you to list all of these proven principals which you wrote of and show how and in what way I am deviating from them!
Click to expand...
 
hevansrv7a said:
If you want to subject your proven principles to public review then by all means, do so. Others, more qualified than I, can then judge if the principles are being consistently applied. .
Click to expand...

'Sorry, Howard, but the onus is on you to do the explanation, not me, since you were the one who brought up the idea that I wasn't following what you term "proven principles" and that instead I was just "experimenting" around.
I don't have to prove to anyone what I do since my products stand in mute witness to themselves by their performance. But you are the challenger, just as you were when you wrote, provocatively, that my propeller designs were not "good all-around" propellers. I challenged you at that time to show how and in what way that description should apply to my design, but as in this posting, you demurred and avoided to show how that could apply, mainly because you can't. Howard, you should plainly avoid writing about the nature of things that you don't understand if you can't back up your statements with supporting data! The ball is in your court!
 
elippse said:
'Sorry, Howard, but the onus is on you to do the explanation, not me, since you were the one who brought up the idea that I wasn't following what you term "proven principles" and that instead I was just "experimenting" around.
I don't have to prove to anyone what I do since my products stand in mute witness to themselves by their performance. But you are the challenger, just as you were when you wrote, provocatively, that my propeller designs were not "good all-around" propellers. I challenged you at that time to show how and in what way that description should apply to my design, but as in this posting, you demurred and avoided to show how that could apply, mainly because you can't. Howard, you should plainly avoid writing about the nature of things that you don't understand if you can't back up your statements with supporting data! The ball is in your court!
Click to expand...

Paul,

I've followed your propellor posts pretty thoroughly over the years and still don't have a comprehensive understanding of your prop's performance. I'm not saying or even implying that it is intentional, but I've never seen a series of posts from you that I could point to as an apples to apples comparison of your prop vs another prop. For instance, you may show an "X" mph speed increase when switching from another prop to your design, but may leave out the RPM, MP, ambient conditions, airframe consistancy, rate of climb, or something else between the trials. One thing you have mentioned is a reduction in acceleration and climb, which are important considerations.

I'd love to see a trial where all of these factors are recorded and posted comparing your design against a known good prop by Catto, Aymar Demuth, etc. Until then, I'm left with a less than complete comparison and without the ability to determine whether your design is better or worse than others.
 
Kyle Boatright said:
Paul,
I'd love to see a trial where all of these factors are recorded and posted comparing your design against a known good prop by Catto, Aymar Demuth, etc.QUOTE]

Jim Smith ran several tests of his three-blade vs his previous Aymar-Demuth. Here are the results he obtained using two-way GPS-measured TAS:

Aymar Demuth 68-72, average of two flights, 1440 lb-
4000', 4141'dalt, 2861 rpm, 193.4 mph
6000', 6279'dalt, 2844 rpm, 189.6 mph
8000', 8275'dalt, 2798 rpm, 185 mph
10,000', 10513' dalt, 2745 rpm, 180.9 mph
ROC, 2000'-10,000' 884 fpm, static rpm 2350, 95 mph IAS, 1440 lb.

Elippse three-blade 64-74, average of two flights, 1440 lb-
4000', 4440' dalt, 2740 rpm, 193 mph
6000', 6440' dalt, 2738 rpm, 192.3 mph
8000', 8407' dalt, 2700 rpm, 187 mph
10,000', 10,400' dalt, 2655 rpm, 184.4 mph
ROC, 2000'-10,000', 916 fpm, static rpm 2125, 95 mph IAS, 1440 lb.

He also did a comparison against a test prop that was supplied to him by a prop maker, and it ran an average of 9 mph less at an average 30 rpm more on the same four altitudes. Its average ROC from 2000' to 10,000' was 774 fpm and static rpm was 2337. I won't reveal the prop-maker since the results were not very good.

To do an efficiency comparison, since the density altitudes were reasonably close, divide the speed of the first by the second, cube the result; this gives the approximate HP ratio for the speed ratio. Since HP is pretty much linearly proportional to rpm over a certain range, multiply the HP ratio by the rpm of the second and divide by the rpm of the first. The result is the efficiency of the first vs the second. For instance, at 8000', (187/185)^3=1.033. 1.033 X 2798 / 2700=1.070, or 7.0% more efficient.
4000', +3.8%; 6000', +8.4%; 10,000', +9.5%.

With his new wingtips, he is now seeing an average of 193 mph TAS with two aboard, near gross weight, a little above 10,000' dalt, both on his return from Sloshkosh and on his LOE trip. These tips have really reduced his induced drag at higher density altitudes and weights, and also resulted in the plane flying less nose-high than before. This is about an 8-9 mph increase over his previous tests at 10,400' dalt. Keep in mind that he only has 150 HP. Extrapolating to 160 HP gives 197.2, 180 HP gives 205 mph, and 200 HP gives 212.4! Actually these numbers would be even slightly higher because at the higher airspeeds the induced drag is slightly less.
Click to expand...
 
Versus CAFE's 6A?

I don't see any numbers here to suggest that at the projected 180 HP level Paul's example does any better than the CAFE test subject which used a Warnke 70 x 74 prop. Am I missing something?
 
Yes;
This aircraft may not have been equal to the CAFE aircraft, so that point is moot.
The something you are missing is that this is a comparison of propellers on a single aircraft without other mods. This is literally the "apples - to- apples comparison" that everyone demands.
 
Yes, but..

SHIPCHIEF said:
Yes;
This aircraft may not have been equal to the CAFE aircraft, so that point is moot.
The something you are missing is that this is a comparison of propellers on a single aircraft without other mods. This is literally the "apples - to- apples comparison" that everyone demands.
Click to expand...

Paul went out of his way in earlier posts to say that the aircraft in question has the same drag (2.32 pounds FP equiv.?) as the CAFE airplane. As a generality, I agree that no two planes are the same.

I agree so much that it's why I developed my own methods for determining the drag curve in flight instead of the tape measure and calculator method which did not work so well on the other airplane that Paul referred to above. My methods are documented in the links below. Anyone can test them and evaluate their validity.

Two props on the same plane - good. Assuming the prop that's being compared is good - not so much. Not all apples are good. I believe someone mentioned a Catto? Van's official specs on the 6A says 199 mph on 180 HP at GW. It's pretty well accepted that many of our planes equal or beat Van's numbers and it's one of the reasons that Van is highly regarded for his conservative, honest numbers.
 
My vague recollection is that I gained 3-4 MPH when I went to a Catto three blade from my Aymar Demuth two blade. I can't claim that it was a perfect comparison but if close, that suggests maybe a 1 MPH improvement of the ellipse prop over my Catto prop. That is within the margin of error of my measurements.
 
elippse said:
Kyle Boatright said:
Paul,
I'd love to see a trial where all of these factors are recorded and posted comparing your design against a known good prop by Catto, Aymar Demuth, etc.QUOTE]

Jim Smith ran several tests of his three-blade vs his previous Aymar-Demuth. Here are the results he obtained using two-way GPS-measured TAS:

<snip>
Click to expand...


Paul, do you have manifold pressure data to add to the other data?

Thanks,
Click to expand...
 
What if..

What if the CAFE 6A went exactly as fast at 8407 DA as the airplane in Paul's example (187 mph)?

Then, assuming a 150 BHP engine, the prop is 81.5% efficient or less for that speed and altitude.

You can use the 6A spreadsheet on my info page (link below) to work this or other combos. Here is the part that is not on the spreadsheet:

For a nominal 150 BHP engine and using 2700 rpm and ambient density at 8407', the BHP available is 116.45. If you add 1" of MAP for the ram effect that some of us get, then the BHP available is 121.46. I used the lower BHP figure. If you use the higher figure, the prop is thus less efficient. This method of guesstimating HP is, I think, the same one Paul uses, based on a previous discussion in this forum.
 
hevansrv7a said:
What if the CAFE 6A went exactly as fast at 8407 DA as the airplane in Paul's example (187 mph)?

Then, assuming a 150 BHP engine, the prop is 81.5% efficient or less for that speed and altitude.
Click to expand...

You're working too many variables. We don't know that airplane's drag matched the one in the CAFE test, AND we don't know how many HP the engine was generating - RPM was off the chart and no MP was published.

We can say that Paul's prop was more efficient at the top end than the other prop, but that may be the only conclusive result of the test.

For another data point (again, not well enough supported by specifics to make it a fair comparison), my 160 HP RV-6 with an Aymar/Demuth prop beats all of those numbers under those conditions and with the RPM at 2700 or less. I do think my airplane is a little slicker than most.
 
Data Variables - all you need

Kyle Boatright said:
You're working too many variables. We don't know that airplane's drag matched the one in the CAFE test, AND we don't know how many HP the engine was generating - RPM was off the chart and no MP was published.

We can say that Paul's prop was more efficient at the top end than the other prop, but that may be the only conclusive result of the test.

For another data point (again, not well enough supported by specifics to make it a fair comparison), my 160 HP RV-6 with an Aymar/Demuth prop beats all of those numbers under those conditions and with the RPM at 2700 or less. I do think my airplane is a little slicker than most.
Click to expand...

Oops, my mistake. Paul actually said that the RV-6 he was working with was even lower drag than the 6A:

"This was borne out with the data reduction of Jim Smith's RV-6 with my original two-blade. I estimated that his engine, which I assumed was 160 HP, produced only 150 HP at sea-level, which turned out to be the actual rating. I also estimated that his parasite drag area was 2.15-2.20, which turned out to be close to the CAFE RV-6A estimate of 2.32 which I found out later when told about the test that was written-up in Sport Aviation."

He gave the RPM as 2700 which is 100% of rated. Quote follows (my emphasis):
"Elippse three-blade 64-74, average of two flights, 1440 lb-
4000', 4440' dalt, 2740 rpm, 193 mph
6000', 6440' dalt, 2738 rpm, 192.3 mph
8000', 8407' dalt, 2700 rpm, 187 mph
10,000', 10,400' dalt, 2655 rpm, 184.4 mph
ROC, 2000'-10,000', 916 fpm, static rpm 2125, 95 mph IAS, 1440 lb."

Also, you don't need the MAP if you know it was WOT. That's why I used ambient pressure at that density altitude. If I understood the earlier thread, this is also how Paul figures BHP or is at least compatible with it. With a factory airplane, there is some MAP loss, but with RV's it is common to have MAP equal or higher than ambient.

This correction would lower the prop efficiency from the estimate that I calculated, assuming that Paul is right with his estimate. That's because if the airplane has lower drag then the THP is lower thus the efficiency is lower. And to top it off, the CAFE test was at 1650 pounds, not 1440, further lowering the efficiency calculated result.
 
BTW, you might be interested in this little tid-bit from Jack Norris' propeller book. On PI-28-BkII, he writes "Now, if we try loading a constant angle of attack, ao and CL, prop blade, elliptically vs. radius, like a wing, with far higher dynamic pressure, q, outboard, we get very narrow chords outboard, a wild shape curving to excessive chords inboard..." "But if we superimpose this elliptical lift distribution on the half teardrop radial lift distribution of an ideal B-G-T prop, we can see that moving the blade loading more inward, we would logically lose less off the tip, better than the B-G-T ideal!!!" "With a wild looking prop, we can beat the Classic Betz Ideal!"
 
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