ELIPPSE propeller for RVs

[mrreddick]

Here's the prop on the ground at LOE.

[elippse]

Originally Posted by hevansrv7a

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.

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!

[hevansrv7a]

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.

Originally Posted by elippse

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!

[elippse]

Originally Posted by hevansrv7a

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. .

'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!

[Kyle Boatright]

Originally Posted by elippse

'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!

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.

[elippse]

[quote=Kyle Boatright;473060]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.

[tcone1]

I'd love to see more about Jim Smith's wingtips.

Any thread you can point me to?

[Danny7]

one thread http://www.vansairforce.com/communit...ight=jim+smith

[hevansrv7a]

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?

[SHIPCHIEF]

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.