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Old Oct 11, 2012, 06:50 AM
buyer of the farm
United States, FL, DeLand
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Originally Posted by C₄H₁₀ View Post
Phil's test data collection is solid gold. Anyone who says it's anything else is either blindly ignorant or is fooling themselves. The difference between his collected data and the multitude of calculators out there is... REAL-WORLD TEST DATA. It's actual empirical information taken straight from his test stand regarding a staggering number of motors and props, each at a wide range of voltage inputs.
100% agree with a small nit-pick. There are a couple of calculators that are built on REAL-WORLD TEST DATA. You gotta capitalize that because it's the gold standard. Diameter and pitch tell a fraction of the story for a prop and we find thread after thread talking like that's all you need to know. The test data shows it's maybe half the story.

Drive Calculator and MotoCalc are two calculators that get their results from extensive databases of real world test data. Drive Calculator is absolutely free and one of the major contributors to its database is none other than Dr Kiwi. Knowing his concern for accuracy and seeing his evil mad scientist laboratory of motor torture, I know he wouldn't contribute to a worthless program. That is why I downloaded and used Drive Calculator when designing the power system to my Slow Stick. It was dead on. I would not have had the confidence to order components unused in any Slow Stick on record without having spent ten minutes on Drive Calculator to get the recommendations.

Okay, here's part of Dr Kiwi's evil laboratory of Doom and Pepsi-Cola. You can see that he doesn't have more than $20 invested in this thing (times 20 maybe) and that any modeler can duplicate his results on the cheap.


Remember this is only a small part of the laboratory and he has $5 or $9 (times 50) more stuff lying around outside the photo.
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Old Oct 11, 2012, 08:29 AM
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Originally Posted by Rockin Robbins View Post
I just proved that within your restricted idea of what's appropriate for a Slow Stick there are 131 propellers to choose from. How do you get from there to 5 to 9? Where do you obtain your 25%. You're a mile off, by the way, and I have the research to prove it.
There are not 131 propellers available for the Slow Stick. Props in diameter 9" to 13" are the only prop options for a slow stick. There are at best 10 different combinations. That's why I said "5 or 9 different propellers". Please share your research.

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Originally Posted by C₄H₁₀ View Post
I'm still unclear by exactly what you mean by "using 5 or 9 propellers". Is this supposed to be a range of between 5 and 9 different props?

... And save 25% of what?



Testing one's own props is a good idea. The only bad ideas here are the testing criteria you've laid out. Thrust per amp? That's like choosing a new car based solely on its power-to-weight ratio without considering any other factors (fuel efficiency, safety ratings, options, price, type of vehicle etc.).

If I chose every prop based on its ratio of static thrust to current consumption, I'd end up with a lot of planes that flat-out don't fly. You mention considering pitchspeed as a sort of offhanded remark while attaching vitrually no significance to it.



Phil's test data collection is solid gold. Anyone who says it's anything else is either blindly ignorant or is fooling themselves. The difference between his collected data and the multitude of calculators out there is... REAL-WORLD TEST DATA. It's actual empirical information taken straight from his test stand regarding a staggering number of motors and props, each at a wide range of voltage inputs.

I do not know who Phil or Dr Kiwi are. You say "real world" - real world is testing it yourself, not number checking a website. I am all in on the calculator, I just said for the OP (who looks like a newer modeler) that he has his best chance by testing with a watt meter and a thrust stand. He already has his motor, which I implied in all of my posts. Picking the correct prop is not that hard. First, any prop in the ball park will work. These are model planes, not real planes that carry people. Plus, he could buy all of the 10 propellers possible for the Slow Stick and test each of them so he could save some battery while flying.

Nothing beats in person testing, since most brushless motors are likely not available on any calculator. Hobby King has hundreds of high quality motors that just became released. How could this calculator have all of them stored? What about margin of error? Whatever little gain you get in your calculator will probably be gone when you figure in each motor's character.

I wish you would stop arguing and see my good information.
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Old Oct 11, 2012, 09:15 AM
buyer of the farm
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Originally Posted by Eli Lipschitz View Post
There are not 131 propellers available for the Slow Stick. Props in diameter 9" to 13" are the only prop options for a slow stick. There are at best 10 different combinations. That's why I said "5 or 9 different propellers". Please share your research.
You asked for it! I don't make statements I can't back up. You'll learn that the hard way. Remember, I promised 131 different propellers by brand name and model number between 9" diameter and 13" diameter. This is direct output, copied from the option box of Drive Calculator. This is not the COMPLETE list of possible props, it's just the list that Drive Calculator makes available because these props were the only ones that test results were submitted for. New test results are submitted almost daily to the database. Roll-em!


There ya goes! Now count them and tell me if there are more than "5 or 9." Then reflect that this is not the complete list of all props available in these sizes. You were not only wrong, you were off the scale out of line, wrong by 15 times your claim. The advantages in running Drive Calculator and having the results of all these test just shreds your contention that the better course is to buy your own test equipment and test a handful of props. Your position is rendered ridiculous and silly.

Why, there are six 9x6 props available, each with a different amp draw, RPM, thrust and efficiency. You can't even trust the dimensions of the prop to tell you anything about its expected performance. I can put a 12" prop with equal or higher pitch on my Slow Stick that will draw fewer amps than my 11x4.7. That's how unpredictable prop performance is.

Now, do you want to have a similar conversation about motors, speed controllers and batteries?
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Old Oct 11, 2012, 10:51 AM
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Originally Posted by Rockin Robbins View Post
by brand name and model number


Do you thihnk NASA uses calculators or real life tests?

I suggest everyone to have a thrust stand and watt meter. That is all I have really been speaking about. I'm not sure why that is provocative to you.

A slow stick will have at most 10 possible prop combinations. You do not need to test APC, wood, or any other kind of wacky propeller because it will only take a slow-flyer/park--flyer propeller from GWS. I can assure you, nothing will be more accurate than measuring the watts and thrust yourself. The point of the calculator is to simulate this. Why would you go with a simulation if it is so easy to do the real thing yourself?
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Old Oct 11, 2012, 12:38 PM
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I think there may be more than 5 or 9 or 10 options for a Slow Stick. I have seen them fly with EDFs and props as small as as 4x2.5. I have personally used props from 5x3 - 15x10.

A better estimate for the number of possible prop sizes might be 5x9x10.
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Old Oct 11, 2012, 02:07 PM
buyer of the farm
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Originally Posted by Ron H View Post
I think there may be more than 5 or 9 or 10 options for a Slow Stick. I have seen them fly with EDFs and props as small as as 4x2.5. I have personally used props from 5x3 - 15x10.

A better estimate for the number of possible prop sizes might be 5x9x10.
Yeah, I was taking it easy on the guy by seriously understating the number of choices actually available. I put myself in a straightjacket and still buried his position and that's really a shame. You would think that someone taking that position would be genuinely curious about the other possibilities he hadn't thought about, like I was when C4H10 brought up the carbon and kevlar props with more efficiency than my beloved APC slow flier prop. Hit ME over the head with something new and I'm all over it! I love discovering new stuff.
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Old Oct 11, 2012, 03:09 PM
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Looks like Eli/Chuck finally took the 40. Good riddance....

Now, RR, I don't believe I ever covered the topic of the efficiency of high-performance molded props. I'm hungry and food is a long walk away so I'll keep it brief, but it comes down to stiffness as much as anything. If any prop can hit the efficiency levels of APCs or Graupners, it's doing pretty well. Those props are commonly replaced in the high-performance world with small (4.7"-5" diameter) folders made by Georgi Mirov or some such supplier for two main reasons: 1) The stiffness of the carbon blade allows for less depitching at high RPMs, allowing more performance, and 2) The folding design protects the prop on landing. It's not so much a matter of absolute aerodynamic efficiency as simply how well the prop can cope with the extremely high power levels. If someone flew a parkflyer with a GM carbon folder, it most likely wouldn't be any different than an APC or Graupner in terms of performance... But on a 220mph F5D plane, you could have the most efficient nylon prop ever made and it could still be outperformed by a crappy composite screw.

The other aspect would be the really big (17"+) folders used in hotliner applications. We can assume that they have relatively good aerodynamic performance just because of the people who make them, but I honestly don't know where they fall on the absolute scale. Those props are also commonly run with twisted yokes to affect the average pitch of the blade, which generally isn't good for efficiency but is still done for a variety of reasons. Since a majority of these props are developed for and used in high-level competition, I suspect that there's not much room for improvement.

I think there was a thread in High Performance that actually addressed the topic of relative prop efficiencies in that arena, and those guys are miles ahead of most of us when it comes to air-screwing technology.
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Old Oct 11, 2012, 03:25 PM
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those guys are miles ahead of most of us when it comes to air-screwing technology.
Shouldn't that be miles above?
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Old Oct 11, 2012, 03:36 PM
buyer of the farm
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Originally Posted by C₄H₁₀ View Post
Looks like Eli/Chuck finally took the 40. Good riddance....
Well, I'm sorry I didn't take your first advice. I didn't want to get the guy banned...

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Originally Posted by C₄H₁₀ View Post
Now, RR, I don't believe I ever covered the topic of the efficiency of high-performance molded props. I'm hungry and food is a long walk away so I'll keep it brief, but it comes down to stiffness as much as anything. If any prop can hit the efficiency levels of APCs or Graupners, it's doing pretty well. Those props are commonly replaced in the high-performance world with small (4.7"-5" diameter) folders made by Georgi Mirov or some such supplier for two main reasons: 1) The stiffness of the carbon blade allows for less depitching at high RPMs, allowing more performance, and 2) The folding design protects the prop on landing. It's not so much a matter of absolute aerodynamic efficiency as simply how well the prop can cope with the extremely high power levels. If someone flew a parkflyer with a GM carbon folder, it most likely wouldn't be any different than an APC or Graupner in terms of performance... But on a 220mph F5D plane, you could have the most efficient nylon prop ever made and it could still be outperformed by a crappy composite screw.

The other aspect would be the really big (17"+) folders used in hotliner applications. We can assume that they have relatively good aerodynamic performance just because of the people who make them, but I honestly don't know where they fall on the absolute scale. Those props are also commonly run with twisted yokes to affect the average pitch of the blade, which generally isn't good for efficiency but is still done for a variety of reasons. Since a majority of these props are developed for and used in high-level competition, I suspect that there's not much room for improvement.

I think there was a thread in High Performance that actually addressed the topic of relative prop efficiencies in that arena, and those guys are miles ahead of most of us when it comes to air-screwing technology.
Makes perfect sense. So these guys are in that region where money ceases to be much of a factor in wanting to go fast. Yup I can understand why they are miles ahead of us. They're doing stuff we can't even think about and maybe didn't want to.

Glad they're out there pushing the boundaries of what's possible and there will be some fallout of cool stuff coming our way from their work.

One thing that really surprised me about the Brandt, J.B. and Selig, M.S., "Propeller Performance Data at Low Reynolds Numbers," 49th AIAA Aerospace Sciences Meeting, AIAA Paper 2011-1255, Orlando, FL, January 2011. Study was the finding that the flexible GWS props operated at much lower efficiency because of blade flutter. You know, blade flutter might actually act differently than a merely flattened blade. It could actually increase load on the motor and INCREASE amp draw while it just creates drag and turbulence instead of thrust.
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